A simple method for computing sprint acceleration kinetics from running velocity data: Replication study with improved design

Acute effects of lower limb wearable resistance on horizontal deceleration and change of direction biomechanics

This study aimed to investigate the acute effects of lower limb wearable resistance on maximal horizontal deceleration biomechanics, across two different assessments. Twenty recreationally trained team sport athletes performed acceleration to deceleration assessments (ADA), and 5-0-5 change of direction (COD) tests across three load conditions (unloaded, 2% of BW, 4% of body weight (BW)), with load attached to the anterior and posterior thighs and shanks. Linear mixed effect models with participant ID as the random effect, and load condition as the fixed effect were used to study load-specific biomechanical differences in deceleration mechanics across both tests. Primary study findings indicate that for the ADA, in the 4% BW condition, participants exhibited significantly greater degrees of Avg Approach Momentum, as well as significant reductions in deceleration phase center of mass (COM) drop, and Avg Brake Step ground contact deceleration (GCD) in both the 2% BW, and 4% BW condition, compared to the unloaded condition. In the 5-0-5 tests, participants experienced significant reductions in Avg Approach Velocity, Avg deceleration (DEC), and Stopping Time in the 4% BW condition compared to the unloaded condition. Similar to the ADA test, participants also experienced significant reductions in Avg Brake Step GCD in both the 2% BW and 4% BW conditions, and significant increases in Avg Approach Momentum in the 4% BW condition, compared to the unloaded condition. Therefore, findings suggest that based on the test, and metric of interest, the addition of lower limb wearable resistance led to acute differences in maximal horizontal deceleration biomechanics. However, future investigations are warranted to further explore if the use of lower limb wearable resistance could present as an effective training tool in enhancing athlete's horizontal deceleration and change of direction performance.

Effect of Advanced Footwear Technology Spikes on Sprint Acceleration: A Multiple N-of-1 Trial

BACKGROUND

In contrast with Advanced Footwear Technology-AFT running shoes for long-distance, little is known about AFT sprint spikes on performance and acceleration parameters. However, their use has become widespread since the Tokyo 2020 Olympics, and knowledge of their effects would seem to be an essential starting point before any clinical or socio-economic considerations.

OBJECTIVES

Our objectives were to determine intra- and inter-subject sprinting performance modifications with Nike® AFT spikes (NAS) compared to standard spiked-shoes (SS).

METHODS

Healthy regional to national sprint athletes (n = 21, ≥ 750 pts World Athletics) performed 16 repetitions of 30-m sprints with either the NAS or SS condition during a single session, based on the multiple N-of-1 method, with pairwise randomisation and double-blind procedure. Time on 30-m sprints (Stalker radar), force-velocity profile (F0, V0, Vmax, Pmax, RF, DRF and FVP slope), and confounding factors (wind and shoe mass) were measured. Statistical analyses included a mixed linear regression model for group analyses, and randomisation test inversion and non-overlap-of-all-pair (NAP) methods for intra-individual analysis.

RESULTS

NAS improved 30-m time by a mean of - 0.02 s (SMD = 0.4, p = 0.014), with no interaction with any confounding factors. Significant changes were seen in velocity (Vmax : SMD = 0.9, p < 0.001; V0: SMD = 0.7, p < 0.001) and the horizontal ratio of force (RFmax: SMD = 0.5, p = 0.043), with no changes observed in force production. Whatever the footwear, one unit of positive wind (+ 1 m.s- 1 ) improved performance by - 0.03 s (p < 0.001). At an individual level, four athletes improved (NAP ≥ 0.69), and one had a statistical decrease in performance. Changes in F-V profiles were largely individual.

CONCLUSIONS

A positive effect on sprint acceleration characteristics was observed when using Nike® AFT spikes, due to an increase in velocity and the horizontal ratio of force. A major variability in inter-individual response justifies single-case experimental designs for research on the topic.

TRIAL REGISTRATION NUMBER

NCT05881148.

Running sprint force-velocity-power profile obtained with a low-cost and low frame rate acquisition video technique: reliability and concurrent validity

The Force-velocity (F-v) and Power-velocity (P-v) relationships quantify athlete's horizontal force production capacities during sprinting. Efforts are underway to enhance ecological validity for practitioners and sports coaches. This study provides detailed data comparison of a low frames per second setup (30 Hz; FPSlow) with splits from a high FPS camera to derive F-v and P-v relationships. Sixty-six sprints performed by 11 university track and field athletes (6 male, 5 female) were evaluated. Data were recorded using FPSlow, photocells, and a high-speed camera (240 Hz; MySprint). In the FPSlow setup, bias was 0.17s, and Limits of agreement was 0.09s compared to photocells. ICC was 1.00, and the coefficient of variation (CV) was 1.0% [0.8-1.1%]. Time acquisition comparison between MySprint and FPSlow setups revealed high consistency (ICC = 0.99) and low CV (2.9% [2.8-3.1%]). F-v profile variables exhibited biases from trivial to small, with ICC ranging from moderate to nearly perfect. CV ranged from 2.7% to 11.8%, and improved using the average of three sprints (CV between 1.8% and 8.6%). The 'simple method' applied to data from the low FPS video setup yielded kinetic and kinematic parameters comparable to those obtained by the validated previous method and photocells.

Hamstrings on focus: Are 72 hours sufficient for recovery after a football (soccer) match? A multidisciplinary approach based on hamstring injury risk factors and histology

This study aimed to assess acute and residual changes in sprint-related hamstring injury (HSI) risk factors after a football (soccer) match, focusing on recovery within the commonly observed 72-h timeframe between elite football matches. We used a multifactorial approach within a football context, incorporating optical and ultrastructural microscopic analysis of BFlh (biceps femoris long head) muscle fibres, along with an examination of BFlh fibre composition. Changes in sprint performance-related factors and HSI modifiable risk factors were examined until 3 days after the match (MD +3) in 20 football players. BFlh biopsy specimens were obtained before and at MD +3 in 10 players. The findings indicated that at MD +3, sprint-related performance and HSI risk factors had not fully recovered, with notable increases in localized BFlh fibre disruptions. Interestingly, match load (both external and internal) did not correlate with changes in sprint performance or HSI risk factors nor with BFlh fibre disruption. Furthermore, our study revealed a balanced distribution of ATPase-based fibre types in BFlh, with type-II fibres associated with sprint performance. Overall, the results suggest that a 72-h recovery period may not be adequate for hamstring muscles in terms of both HSI risk factors and BFlh fibre structure following a football match.

Effects of the Flying Start on Estimated Short Sprint Profiles Using Timing Gates

Short sprints are predominantly assessed using timing gates and analyzed through parameters of the mono-exponential equation, including estimated maximal sprinting speed (MSS) and relative acceleration (TAU), derived maximum acceleration (MAC), and relative propulsive maximal power (PMAX), further referred to as the No Correction model. However, the frequently recommended flying start technique introduces a bias during parameter estimation. To correct this, two additional models (Estimated TC and Estimated FD) were proposed. To estimate model precision and sensitivity to detect the change, 31 basketball players executed multiple 30 m sprints. Athlete performance was simultaneously measured by a laser gun and timing gates positioned at 5, 10, 20, and 30 m. Short sprint parameters were estimated using a laser gun, representing the criterion measure, and five different timing gate models, representing the practical measures. Only the MSS parameter demonstrated a high agreement between the laser gun and timing gate models, using the percent mean absolute difference (%MAD) estimator (%MAD < 10%). The MSS parameter also showed the highest sensitivity, using the minimum detectable change estimator (%MDC95), with an estimated %MDC95 < 17%. Interestingly, sensitivity was the highest for the No Correction model (%MDC95 < 7%). All other parameters and models demonstrated an unsatisfying level of sensitivity. Thus, sports practitioners should be cautious when using timing gates to estimate maximum acceleration indices and changes in their respective levels.

Are the ground reaction forces altered by the curve and with the increasing sprinting velocity?

In 200- and 400-m races, 58% of the total distance to cover is in the curve. In the curve, the sprinting performance is decreased in comparison to the straight. However, the reasons for this decreased performance is not well understood. Thus, the aim of this study was to identify the kinetic parameters underpinning the sprinting performance in the curve in comparison to the straight. Nineteen experienced-to-elite curve specialists performed five sprints in the straight and in the curve (radius 41.58 m): 10, 15, 20, 30, and 40 m. The left and the right vertical, anterior-posterior, medial-lateral, and resultant ground reaction forces (respectivelyF V $$ {F}_{\mathrm{V}} $$ ,F A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ ,F M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ , andF TOT $$ {F}_{\mathrm{TOT}} $$ ), the associated impulses (respectivelyIMP V $$ {IMP}_{\mathrm{V}} $$ ,IMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ ,IMP M - L $$ {IMP}_{\mathrm{M}-\mathrm{L}} $$ , andIMP TOT $$ {IMP}_{\mathrm{TOT}} $$ ) and the stance times of each side were averaged over each distance. In the curve, the time to cover the 40-m sprint was longer than in the straight (5.52 ± 0.25 vs. 5.47 ± 0.23 s, respectively). Additionally, the left and the rightF A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ andIMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ were lower than in the straight while the left and the rightF M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ increased, meaning that theF M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ was more medial. The leftF V $$ {F}_{\mathrm{V}} $$ was also lower than in the straight while the left stance times increased to keep the leftIMP V $$ {IMP}_{\mathrm{V}} $$ similar to the straight to maintain the subsequent swing time. Overall, the sprinting performance was reduced in the curve due to a reduction in the left and the rightF A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ andIMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ , that were likely attributed to the concomitant increasedF M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ to adopt a curvilinear motion.

Validity of spatiotemporal and ground reaction force estimates during resisted sprinting with a motorized loading device

We aimed to examine the validity of estimating spatiotemporal and ground reaction force (GRF) parameters during resisted sprinting using a robotic loading device (1080 Sprint). Twelve male athletes (age: 20.9 ± 2.2 years; height: 174.6 ± 4.2 cm; weight: 69.4 ± 6.1 kg; means ± SDs) performed maximal resisted sprinting with three different loads using the device. The step frequency and length and step-averaged velocity, anteroposterior GRF (Fap ), and the ratio of Fap to resultant GRF (RF) were estimated using the velocity and towing force data measured using the device. Simultaneously, the corresponding values were measured using a 50-m force plate system. The proportional and fixed biases of the estimated values against those measured using the force plate system were determined using ordinary least product (OLP) regression analysis. Proportional and fixed biases were observed for most variables. However, the proportional bias was small or negligible except for the step frequency. Conversely, the fixed bias was small for step-averaged velocity (0.11 m/s) and step length (0.04 m), whereas it was large for step frequency (0.54 step/s), Fap (16N), and RF (2.22%). For all variables except step frequency, the prediction intervals in the OLP regression dramatically decreased when the corresponding values were smoothed using a two-step moving average. These results indicate that by using the velocity and force data recorded in the loading device, most of the spatiotemporal and GRF variables during resisted sprinting can be estimated with some correction of the fixed bias and data smoothing using the two-step moving average.

Validity and Reliability of the Acceleration-Speed Profile for Assessing Running Kinematics' Variables Derived From the Force-Velocity Profile in Professional Soccer Players

ABSTRACT

Alonso-Callejo, A, García-Unanue, J, Guitart-Trench, M, Majano, C, Gallardo, L, and Felipe, J. Validity and reliability of the acceleration-speed profile for assessing running kinematics' variables derived from the force-velocity profile in professional soccer players. J Strength Cond Res 38(3): 563-570, 2024-The aim of this research is to assess the validity and reliability of the acceleration-speed profile (ASP) for measuring the mechanical variables of running kinematics when compared with the force-velocity profile (FVP) obtained by reference systems. The ASP and FVP of 14 male players of an elite football club were assessed during a competitive microcycle. Three ASPs were tested according to the number and type of sessions included in its plotting (ASP1: 5 training sessions and competitive match; ASP2: 5 training sessions; ASP3: competitive match). Force-velocity profile was tested 4 days before match (MD-4) with a 30-m linear sprint using 3 previously validated devices (encoder, mobile App, and global positioning system). Level of significance was p < 0.05. Acceptable reliability (intraclass correlation coefficient > 0.5) was found between the ASP1 and the encoder for all variables (F 0 -A 0 , V 0 -S 0 , and V max ). The more reliable ASP method was the ASP1 showing a lower bias than the ASP2 and ASP3 methods for almost all variables and reference systems. For ASP1, lower mean absolute error (MAE: 0.3-0.5) and higher correlation (P-M corr: 0.57-0.92) were found on variables related to the velocity in comparison with variables related to the early acceleration phase (F 0 -A 0 ; MAE: 0.49-0.63; P-M corr: 0.13-0.41). Acceleration-speed profile, when computed with data from a complete competitive week, is a reliable method for analyzing variables derived from velocity and acceleration kinematics. From these results, practitioners could implement ASP and the applications of the FVP previously studied, such as resistance training prescription, performance assessment, and return-to-play management.

Modeling the Early and Late Acceleration Phases of the Sprint Start in Elite Long Track Speed Skaters

ABSTRACT

Zukowski, MH, Jordan, MJ, and Herzog, W. Modeling the early and late cceleration phases of the sprint start in elite long track speed skaters. J Strength Cond Res 38(2): 236-244, 2024-This study established the reliability of an exponential function to model the change in velocity during the speed skating sprint start and the validity of associated model parameters in a group of subelite and elite long track speed skaters. Long track speed skaters ( n = 38) performed maximal effort 50-m on-ice accelerations from a standing start while tethered to a horizontal robotic resistance device that sampled position and time data continuously. An exponential function was applied to the raw data to model the change in velocity throughout the acceleration phase and compute the maximal skating speed (MSS), maximal acceleration capacity (MAC), maximum relative net horizontal power ( PMax ), and an acceleration-time constant ( τ ). All constructed models provided a sufficient fit of the raw data ( R -squared > 0.95, mean bias <2%). Intraday reliability of all model parameters ranged from good to excellent (intraclass correlation coefficient >0.8 and coefficient of variation <5%). Strong negative correlations ( r : -0.72 to -0.96) were observed between MSS and PMax and the 10 and 20 m split times measured with the robotic resistance and with 100 split times obtained from 500 m races. Moderate-to-large between-group differences were observed in MSS, MAC, and PMax between the elite vs. subelite speed skaters (Cohen d effect sizes: 1.18-3.53). Our results indicate that monoexponential modeling is a valid and reliable method of monitoring initial acceleration performance in elite level long track speed skaters.

A Systematic Review and Meta-Analysis of Wearable Satellite System Technology for Linear Sprint Profiling: Technological Innovations and Practical Applications

ABSTRACT

Cormier, P, Meylan, C, Agar-Newman, D, Geneau, D, Epp-Stobbe, A, Lenetsky, S, and Klimstra, M. A systematic review and meta-analysis of wearable satellite system technology for linear sprint profiling: technological innovations and practical applications. J Strength Cond Res 38(2): 405-418, 2024-An emerging and promising practice is the use of global navigation satellite system (GNSS) technology to profile team-sports athletes in training and competition. Therefore, the purpose of this narrative systematic review with meta-analysis was to evaluate the literature regarding satellite system sensor usage for sprint modeling and to consolidate the findings to evaluate its validity and reliability. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, an electronic search of the databases, PubMed and SPORTDiscus (EBSCO), was conducted. Concurrent validity and reliability studies were considered, and 16 studies were retained for the review from the initial 1,485 studies identified. The effects on outcomes were expressed as standardized mean differences (SMDs, Cohen's d ) for each outcome (i.e., maximal sprint speed [MSS], the acceleration constant [τ], maximal theoretical velocity [ V0 ], relative force [ F0 ], and relative power [P max ]). Effect magnitudes represented the SMD between GNSS-derived and criterion-derived (i.e., radar and laser) and resulted in the following estimates: small for MSS ( d = 0.22, 95% CI 0.01 to 0.42), τ ( d = -0.18, 95% CI -0.60 to 0.23), V0 ( d = 0.14, 95% CI -0.08 to 0.36), relative F0 ( d = 0.15, 95% CI -0.25 to 0.55), and relative P max ( d = 0.21, 95% CI -0.16 to 0.58). No publication bias was identified in meta-analyzed studies and moderator analysis revealed that several factors (sampling rate and sensor manufacturer) influenced the results. Heterogeneity between studies was considered moderate to high. This highlighted the differences between studies in sensor technology differences (i.e., sampling rate, sensor fusion, and satellite network acquisition), processing techniques, criterion technology used, sprint protocols, outcome reporting, and athlete characteristics. These findings may be useful in guiding improvements in sprint modeling using GNSS technology and enable more direct comparisons in future research. Implementation of all-out linear sprint efforts with GNSS technology can be integrated into sport-specific sessions for sprint modeling when robust and consistent data processing protocols are performed, which has important implications for fatigue monitoring, program design, systematic testing, and rehabilitation in individual and team sports.

Individual In-Situ GPS-Derived Acceleration-Speed Profiling: Toward Automatization and Refinement in Male Professional Rugby Union Players

BACKGROUND

Recently a proof-of-concept was proposed to derive the soccer players' individual in-situ acceleration-speed (AS) profile from global positioning system (GPS) data collected over several sessions and games. The present study aimed to propose an automatized method of individual GPS-derived in-situ AS profiling in a professional rugby union setting.

METHOD

AS profiles of forty-nine male professional rugby union players representing 61.5 million positions, from which acceleration was derived from speed during 51 training sessions and 11 official games, were analyzed. A density-based clustering algorithm was applied to identify outlier points. Multiple AS linear relationships were modeled for each player and session, generating numerous theoretical maximal acceleration (A0), theoretical maximal running speed (S0) and AS slope (ASslope, i.e., overall orientation of the AS profile). Each average provides information on the most relevant value while the standard deviation denotes the method accuracy. In order to assess the reliability of the AS profile within the data collection period, data were compared over two 2-week phases by the inter-class correlation coefficient. A0 and S0 between positions and type of sessions (trainings and games) were compared using ANOVA and post hoc tests when the significant threshold had been reached.

RESULTS

All AS individual profiles show linear trends with high coefficient of determination (r2 > 0.81). Good reliability (Inter-class Correlation Coefficient ranging from 0.92 to 0.72) was observed between AS profiles, when determined 2 weeks apart for each player. AS profiles depend on players' positions, types of training and games. Training and games data highlight that highest A0 are obtained during games, while greatest S0 are attained during speed sessions.

CONCLUSIONS

This study provides individual in-situ GPS-derived AS profiles with automatization capability. The method calculates an error of measurement for A0 and S0, of paramount importance in order to improve their daily use. The AS profile differences between training, games and playing positions open several perspectives for performance testing, training monitoring, injury prevention and return-to-sport sequences in professional rugby union, with possible transferability to other sprint-based sports.

KEY POINTS

AS profiles computed from rugby union GPS data provide positional benchmarks during training and competition. This study provides automatic detection of atypical data and the computation of error measurement of theoretical maximal acceleration and speed components. This refinement constitutes a step forward for a daily use of ecological data by considering data collection and method reliabilities. This easy-to-implement approach may facilitate its use to the performance management process (talent identification, training monitoring and individualization, return-to-sport).

Bias in estimated short sprint profiles using timing gates due to the flying start: simulation study and proposed solutions

Short sprints are most frequently evaluated and modeled using timing gates. Flying start distance is often recommended to avoid premature timing system triggering by lifting knees or swinging arms. This results in timing system initiation not being aligned with the initial force application, which yields bias in estimated short sprint parameters. This simulation study aims to explore the effects of the flying start distance on bias and sensitivity to detect changes in short sprint parameters using three models: the contemporary No Correction model and two proposed Estimated time correction (Estimated TC), and Estimated flying distance (Estimated FD) models. In conclusion, both the Estimated TC and Estimated FD models provided more precise parameter estimates, but surprisingly, the No correction model provided higher sensitivity for specific parameter changes. Besides standardizing the sprint starting technique for the short sprint performance monitoring, practitioners are recommended to utilize and track the results of all three models.

Four Sessions of Repeated-Sprint Cycling Training With or Without Severe Hypoxia Do Not Modify Overground Running Sprint Force-Velocity Profile

PURPOSE

To investigate the effect of cycling-based repeated-sprint training in hypoxia versus in normoxia on single overground running sprint performance and associated force-velocity (F-V) profile in world-class female rugby sevens players.

METHODS

Eighteen world-class female rugby sevens players were randomly assigned to repeated-sprint cycling training in normobaric hypoxia (n = 9) or normoxia (n = 9) groups. Training consisted of 4 sessions of repeated-sprint cycling training in normobaric hypoxia or in normoxia (4 × 5 × 5-s cycle sprints-25-s intersprint recovery performed in simulated altitude of ∼5000 m or in normoxia with 3-min interset rest in normoxia for both groups) in addition to rugby sevens training and strength and conditioning sessions within a 9-day intervention period before an international competition. Before and 1 day after the intervention, single 50-m overground running "all-out" sprint performance and associated F-V-related mechanical output were assessed.

RESULTS

No interaction (group × time; all P > .088), time effect (before vs 1 d after; all P > .296), or group effect (repeated-sprint cycling training in normobaric hypoxia vs in normoxia; all P > .325) was detected for 50-m overground running sprint performance and any derived F-V profiling variables.

CONCLUSIONS

Four sessions of repeated-sprint training either in hypoxia or in normoxia performed over 9 days had no influence on single 50-m overground running sprint performance and associated F-V profile. In world-class female rugby sevens players, the intervention (training camp before an international competition) might have been too short to induce measurable changes. It is also plausible that implementing a similar program in players with likely different F-V profile may result in negligible mechanical effect.

Influence of horizontal resistance loads on spatiotemporal and ground reaction force variables during maximal sprint acceleration

This study aimed to elucidate the influence of horizontal resistance loads on the spatiotemporal and ground reaction force (GRF) variables during maximal sprint acceleration. Nine male sprinters (20.2 ± 1.2 years; 175.3 ± 4.5 cm, 69.7 ± 6.1 kg) performed sprint-running with six loading conditions of one unresisted and five resisted loads of 4, 6, 8, 10, and 12 kg using a resistance training device with intelligent drag technology. During the trials, the GRFs for all steps were determined using a 50-m force plate system. The spatiotemporal and GRF variables at running velocity of every 0.5 m/s were obtained and compared across the loading conditions. The maximal running velocity under 0, 4, 6, 8, 10, and 12 kg loading conditions were 9.84 ± 0.41, 8.55 ± 0.41, 8.09 ± 0.33, 7.62 ± 0.34, 7.11 ± 0.31, and 6.71 ± 0.29 m/s, respectively. ANOVA revealed significant main effects of load on the measured variables (η2 = 0.236-0.715, p < 0.05), except for stance-averaged anteroposterior GRF and braking impulse. However, the observed differences between the loading conditions were small, with approximately 4% (1.3-7.5%) for the GRF variables and approximately 9% (1.2-22.3%) for the spatiotemporal variables. The present study indicates that horizontal resistance load in sprint acceleration has little impact on the spatiotemporal and GRF variables at a given running velocity. In contrast to a general recommendation, one should adopt a heavy load in resisted sprint aiming to improve performance in the earlier stage of maximal sprint acceleration.

Validity of Global Positioning System Technology to Measure Maximum Velocity Sprinting in Elite Sprinters

ABSTRACT

Thome, M, Thorpe, RT, Jordan, MJ, and Nimphius, S. Validity of global positioning system (GPS) technology to measure maximum velocity sprinting in elite sprinters. J Strength Cond Res 37(12): 2438-2442, 2023-The objective of this study was to assess the concurrent validity of 10-Hz wearable Global Positioning System (GPS) technology to measure maximum velocity sprinting (Vmax) relative to Doppler radar in elite sprinters. Data were collected from a single training session performed by elite 100 and 200 m sprinters (males: n = 5; 100 m best times: 10.02 ± 0.07 seconds, range: 9.94-10.10 seconds; 200 m best times: 20.29 ± 0.42 seconds, range: 19.85-20.80 seconds; females: n = 2; age: 28.0 ± 4.2 years; body mass: 65.8 ± 4.6 kg; 100 m best times: 11.18 ± 0.34 seconds; 200 m best times: 22.53 ± 0.04 seconds). Velocity and time data from 16 maximal, 60-m sprint efforts were recorded simultaneously with 10 Hz GPS and 47 Hz radar. Validity was assessed using Bland-Altman 95% limits of agreement (LOA) and intraclass correlation coefficient (ICC), each with respective 95% confidence intervals (CI). Vmax measured with 10 Hz GPS demonstrated a LOA of -0.11 m·s-1 (-0.17, -0.05) and an ICC of 0.99 (0.98, 1.0) relative to the radar device.10 Hz GPS overestimated Vmax by 0.11 m·s-1 relative to the radar but could still be considered a suitable tool for monitoring external load in elite sprinters. However, the much smaller average annual improvement in this population (∼0.1-0.2%) in comparison with the ∼1% overestimation reduces the utility of 10 Hz GPS to detect meaningful performance changes in maximum velocity.

Minimal Number of Events Required for Acceleration-Speed Profiling in Elite Women's Soccer

PURPOSE

To determine the minimum number of events (training or matches) for producing valid acceleration-speed (AS) profiles from global navigation satellite system (GNSS) data.

METHODS

Nine elite female soccer players participated in a 4-week training camp consisting of 19 events. AS profile metrics calculated from different combinations of athlete events were compared to force-velocity (FV) profile metrics from 2 × 40-m stand-alone sprint effort trials, using the same GNSS 10-Hz technology. Force-velocity profiles were calculated, from which AS profiles were obtained. AS profiles from training and matches were generated by plotting acceleration and speed points and performing a regression through the maximal points to obtain the AS metrics (theoretical maximal speed, x-intercept [in meters per second], theoretical maximal acceleration, y-intercept [in meters per second squared], and the slope per second). A linear mixed model was performed with the AS metrics as the outcome variables, the number of events as a fixed effect, and the participant identifier as a mixed effect. Dunnett post hoc multiple comparisons were used to compare the means of each number of event grouping (1-19 events) to those estimated from the dedicated sprint test.

RESULTS

Theoretical maximal speed and theoretical maximal acceleration means were no longer significantly different from the isolated sprint reference with 9 to 19 (small to trivial differences = -0.31 to -0.04 m·s-1, P = .12-.99) and 6 to 19 (small differences = -0.4 to -0.28 m·s-2, P = .06-.79) events, and the slopes were no longer different with 1 to 19 events (trivial differences = 0.06-0.03 s-1, P = .35-.99).

CONCLUSIONS

AS profiles can be estimated from a minimum of 9 days of tracking data. Future research should investigate methodology resulting in AS profiles estimated from fewer events.

The Effects of Heavy Resisted Sled Pulling on Sprint Mechanics and Spatiotemporal Parameters

ABSTRACT

Stavridis, I, Ekizos, A, Zisi, M, Agilara, G-O, Tsolakis, C, Terzis, G, and Paradisis, G. The effects of heavy resisted sled pulling on sprint mechanics and spatiotemporal parameters. J Strength Cond Res 37(12): 2346-2353, 2023-This study examines the effects of 2 resisted sled sprinting (RSS) training programs: with a load corresponding to the running velocity associated with the apex of the individual velocity-power relationship (50%vdec), with a load equal to 10% of body mass (10% BM), and of an unresisted sprint training (URS). We measured the 30-m sprint performance in intervals of 5 m examining sprint acceleration, mechanical properties (theoretical maximal horizontal power [Pmax], force [F0], velocity [v0], slope of the force-velocity relationship [SFv], maximal ratio of horizontal-to-resultant force [RFmax], rate of decrease in RF [Drf]), and spatiotemporal parameters (step frequency [SF], step length [SL], flight time [FT], and contact time [CT]). Twenty-seven sprinters were randomly assigned into the 50%vdec, 10% BM, and URS groups, performing 12 sessions over 6 consecutive weeks (2 sets of 5 sprints per session). The 50%vdec group significantly improved (p < 0.05) their performance in all 30-m intervals. Posttraining, the 50%vdec group showed significantly increased Pmax, F0, and RFmax (mean differences: 1.46 ± 1.70 W·kg-1, 0.51 ± 0.68 N·kg-1, and 0.17 ± 0.18%, respectively), compared with pretraining. The 50%vdec group achieved higher SF, whereas FT decreased postintervention. No significant changes (p > 0.05) were found in the performance and mechanical and spatiotemporal variables in the other groups. In conclusion, RSS training with a load of 50%vdec provides an effective loading stimulus to induce adaptations that improve sprint acceleration performance. The improvements are explained by greater amounts of force and power, efficient force application, and higher step frequencies.

Jump and sprint force velocity profile of young soccer players differ according to playing position

Our study aimed to compare explosive performance and underlying mechanical determinants explored through F-V profiles in jumping and sprinting among young soccer players based on their playing position. Ninety elite soccer players were categorized into the following positions: goalkeepers, central defenders, wide defenders, central midfielders, wide midfielders, and forwards. Two testing sessions were conducted to measure the 30-metre sprint time (T30) using an over-ground sprint test and jump height (Hmax) through the SJ test. Results demonstrated performance variations among positions. In sprinting, forwards showed greater T30 (4.5 ± 0.14 s) compared to other positions, with goalkeepers exhibiting the lowest T30 (4.86 ± 0.18 s). Forwards also displayed higher maximal theoretical velocity (8.8 ± 0.4 m.s-1) and power output (Pmax) (19.4 ± 2.6 W.kg-1) than other positions, while goalkeepers had the lowest Pmax (16.5 ± 2 W.kg-1). In jumping, forwards (33.2 ± 3.9 cm) and wide-midfielders (33.6 ± 3.8 cm) achieved higher Hmax compared to goalkeepers (29.2 ± 5 cm) and central-midfielders (29.2 ± 3.8 cm). Wide-midfielders (28.5 ± 4.8 W.kg-1) and forwards (27.1 ± 4.3 W.kg-1) surpassed goalkeepers (23 ± 2.8 W.kg-1) and central-midfielders (25.1 ± 3.8 W.kg-1) in Pmax. Our findings reveal substantial position-related disparities in F-V profiles among elite young soccer players, in sprinting and jumping emphasizing the need for position-specific training programmes to optimize player development and on-field performance from an early age.

Longitudinal Development of Sprint Performance and Force-Velocity-Power Characteristics: Influence of Biological Maturation

ABSTRACT

Edwards, T, Weakley, J, Banyard, HG, Cripps, A, Piggott, B, Haff, GG, and Joyce, C. Longitudinal development of sprint performance and force-velocity-power characteristics: influence of biological maturation. J Strength Cond Res 37(11): 2178-2184, 2023-This study was designed to investigate the influence of biological maturation on the longitudinal development of sprint performance. Thirty-two subjects performed 2 assessments of maximal sprint performance that were separated by 18 months. Each sprint assessment was measured through a radar gun that collected instantaneous velocity with the velocity-time data used to derive sprint times and force-velocity-power characteristics. The biological maturity of each subject was assessed using a predictive equation, and subjects were grouped according to predicted years from peak height velocity (circa-PHV: -1.0 to 1.0; post-PHV: >1.0). A 2 × 2 mixed model analysis of variance was used to assess group × time interactions, and paired t -tests were used to assess the longitudinal changes for each maturity group. No significant group × time interactions were observed for any sprint time or force-velocity-power characteristic. The circa-PHV group experienced significant within-group changes in maximal theoretical velocity (6.35 vs. 5.47%; effect size [ES] = 1.26 vs. 0.52) and 5-m sprint time (-3.63% vs. -2.94%; ES = -0.64 vs. -0.52) compared with the post-PHV group. There was no significant change in the magnitude of relative theoretical maximum force in either group; however, both the circa-PHV and post-PHV groups significantly improved the orientation of force production at the start of the sprint (RFmax [4.91 vs. 4.46%; ES = 0.79 vs. 0.74, respectively]). Considering these findings, it is recommended that practitioners adopt training methods aimed to improve relative lower-limb force production, such as traditional strength training and sled pulling and pushing, to improve sprint performance and relative theoretical maximum force.

Characterising coordination strategies during initial acceleration in sprinters ranging from highly trained to world class

Identifying coordination strategies used by sprinters and features that differentiate these strategies will aid in understanding different technical approaches to initial sprint acceleration. Moreover, multiple effective coordination strategies may be available to athletes of similar ability, which typical group-based analyses may mask. This study aimed to identify sub-groups of sprinters based on thigh-thigh and shank-foot coordination during initial acceleration, and assess sprint performance across different combinations of coordination strategies. Angular kinematics were obtained from 21 sprinters, and coordination determined using vector coding methods, with step 1 and steps 2-4 separated for analysis. Performance was assessed using metrics derived from velocity-time profiles. Using hierarchical cluster analysis, three distinct coordination strategies were identified from thigh-thigh and shank-foot coordination in step 1 and two strategies in steps 2-4. Coordination strategies primarily differed around early flight thigh-thigh coordination and early stance shank-foot coordination in step 1, while timing of reversals in thigh rotation characterised differences in later steps. Higher performers tended to have greater lead thigh and foot dominance in step 1 and early swing thigh retraction in steps 2-4. The novel application of cluster analysis to coordination provides new insights into initial acceleration technique in sprinters, with potential considerations for training and performance.

Concurrent Validity and Reliability of the Sprint Force-Velocity Profile Assessed with K-AI Wearable Tech

Establishing a sprint acceleration force-velocity profile is a way to assess an athlete's sprint-specific strength and speed production capacities. It can be determined in field condition using GNSS-based (global navigation satellite system) devices. The aims of this study were to (1) assess the inter-unit and the inter-trial reliability of the force-velocity profile variables obtained with K-AI Wearable Tech devices (50 Hz), (2) assess the concurrent validity of the input variables (maximal sprint speed and acceleration time constant), and (3) assess the validity of the output variables (maximal force output, running velocity and power). Twelve subjects, including one girl, performed forty-one 30 m sprints in total, during which the running speed was measured using two GPS (global positioning system) devices placed on the upper back and a radar (Stalker® Pro II Sports Radar Gun). Concurrent validity, inter-device and inter-trial reliability analyses were carried out for the input and output variables. Very strong to poor correlation (0.99 to 0.38) was observed for the different variables between the GPS and radar devices, with typical errors ranging from small to large (all < 7.6%). Inter-unit reliability was excellent to moderate depending on the variable (ICC values between 0.65 and 0.99). Finally, for the inter-trial reliability, the coefficients of variation were low to very low (all < 5.6%) for the radar and the GPS. The K-AI Wearable Tech used in this study is a concurrently valid and reliable alternative to radar for assessing a sprint acceleration force-velocity profile.

Opposition Skill Efficiency During Professional Rugby Union Official Games Is Related to Horizontal Force-Production Capacities in Sprinting

PURPOSE

This study aimed to determine relationships between parameters of force-production capacity in sprinting and opposition skill efficiency in rugby union games according to position.

METHODS

The sprint force-velocity profile of 33 professional rugby union players divided into 2 subgroups (forwards and backs) was measured on a 30-m sprint. Skill efficiencies (in percentage) of offensive duels, tackles, and rucks were assessed using objective criteria during 12 consecutive competitive games. Pearson correlation was used to determine the relationships between parameters of horizontal force-production capacity in sprinting (maximum propulsive power, theoretical maximum force [F0], theoretical maximum velocity, maximum ratio of horizontal force [RFmax], and rate of decrease of this ratio of forces with increasing velocity) and skill efficiencies. Two multiple linear regression models were used to observe whether skill efficiencies could depend on determinants of horizontal force application in low- or high-velocity conditions. A first model including F0 and theoretical maximum velocity was used as a macroscopic analysis, while a second model including RFmax and rate of decrease of this ratio of forces with increasing velocity was used as microscopic analysis to determine the most significant determinants of skill efficiency.

RESULTS

All skill efficiencies were strongly correlated with maximum propulsive power in forwards and backs. In forwards, F0 and RFmax were the key predictors of dueling, rucking, and tackling efficiency. In backs, F0 was the main predictor of dueling and rucking efficiency, whereas RFmax was the key predictor of dueling and tackling efficiency. F0 and theoretical maximum velocity equivalently contributed to tackling performance.

CONCLUSIONS

In rugby union forward and back players, skill efficiency is correlated with maximum propulsive power and may be more explained by horizontal force-production capacity and mechanical effectiveness at lower velocities than at higher velocities.

Wheelchair Rugby Sprint Force-Velocity Modeling Using Inertial Measurement Units and Sport Specific Parameters: A Proof of Concept

BACKGROUND

Para-sports such as wheelchair rugby have seen increased use of inertial measurement units (IMU) to measure wheelchair mobility. The accessibility and accuracy of IMUs have enabled the quantification of many wheelchair metrics and the ability to further advance analyses such as force-velocity (FV) profiling. However, the FV modeling approach has not been refined to include wheelchair specific parameters.

PURPOSE

The purpose of this study was to compare wheelchair rugby sprint FV profiles, developed from a wheel-mounted IMU, using current mono-exponential modeling techniques against a dynamic resistive force model with wheelchair specific resistance coefficients.

METHODS

Eighteen athletes from a national wheelchair rugby program performed 2 × 45 m all-out sprints on an indoor hardwood court surface.

RESULTS

Velocity modelling displayed high agreeability, with an average RMSE of 0.235 ± 0.07 m/s-1 and r2 of 0.946 ± 0.02. Further, the wheelchair specific resistive force model resulted in greater force and power outcomes, better aligning with previously collected measures.

CONCLUSIONS

The present study highlights the proof of concept that a wheel-mounted IMU combined with wheelchair-specific FV modelling provided estimates of force and power that better account for the resistive forces encountered by wheelchair rugby athletes.

Comparison of acceleration-speed profiles from training and competition to individual maximal sprint efforts

This study aimed to (1) compare "in-situ" monitored acceleration-speed (ASin-situ) profile metrics from training/competition data in elite female soccer players to similar metrics from profiles developed from isolated maximal sprint efforts (ASsprint) and; (2) compare the confidence interval (CI) and a Tukey boxplot (BP) outlier removal technique on the training/competition data to derive ASin-situ profiles. Fifteen national team soccer players participated in a 4-week camp while wearing 10 Hz GNSS units. Towards the middle of the camp, 2 × 40 m isolated maximal sprints were performed. ASin-situ profiles (theoretical maximum acceleration A0 in m∙s-2 and speed S0 in m∙s-1) were computed using the CI and BP techniques with training/competition data. The sprint data were modelled separately to construct horizontal force-velocity (FV) profiles, from which ASsprint profiles were derived. Bland-Altman analysis was used to assess agreement between the CI- and BP-derived ASin-situ profiles to the ASsprint profiles, as well as regression analysis for systematic and proportional bias. Additionally, 1-way ANOVAs with Tukey posthoc compared the metrics between each method of analysis. Using the BP method, good agreement of the ASin-situ with ASsprint profile metrics A0/S0 was displayed, whereas good to moderate agreement was shown for the CI. The CI technique showed a proportional bias for A0/S0. Good to excellent intertrial reliability was demonstrated for isolated sprint metrics. Both BP and CI techniques provided comparable ASin-situ profiles to ASsprint profiles. This current research demonstrated that ASin-situ profiling is applicable in elite women's soccer and will have further application in many team sports.

Exploring the Low Force-High Velocity Domain of the Force-Velocity Relationship in Acyclic Lower-Limb Extensions

PURPOSE

To compare linear and curvilinear models describing the force-velocity relationship obtained in lower-limb acyclic extensions, considering experimental data on an unprecedented range of velocity conditions.

METHODS

Nine athletes performed lower-limb extensions on a leg-press ergometer, designed to provide a very broad range of force and velocity conditions. Previously inaccessible low inertial and resistive conditions were achieved by performing extensions horizontally and with assistance. Force and velocity were continuously measured over the push-off in six resistive conditions to assess individual force-velocity relationships. Goodness of fit of linear and curvilinear models (second-order polynomial function, Fenn and Marsh's, and Hill's equations) on force and velocity data were compared via the Akaike Information Criterion.

RESULTS

Expressed relative to the theoretical maximal force and velocity obtained from the linear model, force and velocity data ranged from 26.6 ± 6.6 to 96.0 ± 3.6% (16-99%) and from 8.3 ± 1.9 to 76.6 ± 7.0% (5-86%), respectively. Curvilinear and linear models showed very high fit (adjusted r2 = 0.951-0.999; SEE = 17-159N). Despite curvilinear models better fitting the data, there was a ~ 99-100% chance the linear model best described the data.

CONCLUSION

A combination between goodness of fit, degrees of freedom and common sense (e.g., rational physiologically values) indicated linear modelling is preferable for describing the force-velocity relationship during acyclic lower-limb extensions, compared to curvilinear models. Notably, linearity appears maintained in conditions approaching theoretical maximal velocity. Using horizontal and assisted lower-limb extension to more broadly explore resistive/assistive conditions could improve reliability and accuracy of the force-velocity relationship and associated parameters.

Force-velocity profiling in ice hockey skating: reliability and validity of a simple, low-cost field method

In recent years, a simple method for force-velocity (F-v) profiling, based on split times, has emerged as a potential tool to examine mechanical variables underlying running sprint performance in field conditions. In this study, the reliability and concurrent validity of F-v profiling based on split times were examined when used for ice hockey skating. It was also tested how a modification of the method, in which the start instant of the sprint is estimated based on optimisation (time shift method), affects the reliability and validity of the method. Both intra- and inter-rater reliability were markedly improved when using the time shift method (approximately 50% decrease in the standard error of measurement). Moreover, the results calculated using the time shift method highly correlated (r > 0.83 for all variables) with the results calculated from a continuously tracked movement of the athlete, which was considered here as the reference method. This study shows that a modification to the previously published simple method for F-v profiling improves intra- and inter-rater reliability of the method in ice hockey skating. The time shift method tested here can be used as a reliable tool to test a player's physical performance characteristic underlying sprint performance in ice hockey skating.

The effects of hip- vs. knee-dominant hamstring exercise on biceps femoris morphology, strength, and sprint performance: a randomized intervention trial protocol

BACKGROUND

The hamstrings are an important muscle group that contribute to horizontal force during sprint acceleration and are also the most injured muscle group in running-based sports. Given the significant time loss associated with hamstrings injury and impaired sprinting performance following return to sport, identifying exercises that drive adaptations that are both protective of strain injury and beneficial to sprint performance is important for the strength and conditioning professional. This paper describes the study protocol investigating the effects of a 6-week training program using either the hip-dominant Romanian deadlift (RDL) or the knee-dominant Nordic hamstring exercise (NHE) on hamstring strain injury risk factors and sprint performance.

METHODS

A permuted block randomized (1:1 allocation) intervention trial will be conducted involving young, physically-active men and women. A target sample size of 32 will be recruited and enrolled participants will undergo baseline testing involving extended-field-of-view ultrasound imaging and shear wave elastography of the biceps femoris long head muscle, maximal hamstrings strength testing in both the RDL and NHE, and on-field sprint performance and biomechanics. Participants will complete the 6-week training intervention using either the RDL or NHE, according to group allocation. Baseline testing will be repeated at the end of the 6-week intervention followed by 2 weeks of detraining and a final testing session. The primary outcome will be regional changes in fascicle length with secondary outcomes including pennation angle, muscle cross sectional area, hamstring strength, and maximal sprint performance and biomechanics. An exploratory aim will determine changes in shear wave velocity.

DISCUSSION

Despite extensive research showing the benefits of the NHE on reducing hamstring strain injury risk, alternative exercises, such as the RDL, may offer similar or potentially even greater benefits. The findings of this study will aim to inform future researchers and practitioners investigating alternatives to the NHE, such as the RDL, in terms of their effectiveness in reducing rates of hamstring strain injury in larger scale prospective intervention studies.

TRIAL REGISTRATION

The trial is prospectively registered on ClinicalTrials.gov (NCT05455346; July 15, 2022).

Reliability of individual acceleration-speed profile in-situ in elite youth soccer players

The aims of this study were to describe differences in the acceleration-speed (A-S) profile in-situ and to assess the week-to-week reliability of the A-S profile in-situ over a given training cycle of elite youth soccer players, in relation to the number of sessions included and analyse the effect of the inclusion or not of a specific sprint session. In this retrospective study, 18 male elite U19 football players (179.4 ± 7.1 cm; 69.0 ± 9.5 kg) participated. GPS data collected from three consecutive typical training weeks were used to calculate different combinations of A-S profile in-situ variables (theoretical maximal acceleration [A₀], theoretical maximal speed [S₀] and the slope of the acceleration-speed [AS_slope]). The number (and content) of sessions affected mainly S₀ while A₀ remained similar with or without a sprint session. The reliability of the A-S profile in-situ is more related to the spread of points rather than a specific number of sessions (and thus points) and was improved when a high percentage of maximum speed (i.e. ≥ 95%) was reached. The present study showed low week-to-week variability for A₀, S₀ and AS_slope. However, practitioners need to make sure that the values cover a sufficient range of raw data [20-95% of maximum speed] to build a clear and consistent linear regression, and in turn extrapolate meaningful A-S profile values.

The Effect of a Heavy Resisted Sled-Pull Mesocycle on Sprint Performance in Junior Australian Football Players

ABSTRACT

Edwards, T, Piggott, B, Banyard, HG, Haff, GG, and Joyce, C. The effect of a heavy resisted sled-pull mesocycle on sprint performance in junior Australian football players. J Strength Cond Res 37(2): 388-393, 2023-This study assessed the effect of heavy resisted sled-pull training on sprint times and force, velocity, and power characteristics in junior Australian football players. Twenty-six athletes completed a 6-week resisted sled-pull training intervention which included 10 training sessions and 1-week taper. Instantaneous velocity during 2 maximal 30 m sprints was recorded 1 week before and 1 week after the intervention with a radar gun. Velocity-time data were used to derive sprint performance and force, velocity, and power characteristics. A paired t -test assessed the within-group differences between preintervention and postintervention testing. Statistical significance was accepted at p ≤ 0.05. Hedges' g effect sizes (ESs) were used to determine the magnitude of change in dependent variables. Maximum velocity (ES = 1.33) and sprint times at all distances (ES range 0.80-1.41) significantly improved after heavy resisted sled-pull training. This was reflected in sprint force, velocity, and power characteristics with significant improvements in relative theoretical force (ES = 0.63), theoretical velocity (ES = 0.99), relative maximum power (ES = 1.04), and ratio of horizontal to vertical force (ES = 0.99). Despite the multifactorial nature of training and competing physical demands associated with preseason training, these findings imply that a short, resisted sled-pull training mesocycle may improve sprint performance and underlying force, velocity, and power characteristics in junior athletes.

Concurrent Validity and Reliability of Different Technologies for Sprint-Derived Horizontal Force-Velocity-Power Profiling

ABSTRACT

Cormier, P, Tsai, M-C, Meylan, C, Agar-Newman, D, Epp-Stobbe, A, Kalthoff, Z, and Klimstra, M. Concurrent validity and reliability of different technologies for sprint-derived horizontal force-velocity-power profiling. J Strength Cond Res XX(X): 000-000, 2022-This study evaluated the validity and reliability of common systems to assess sprint-derived horizontal force-velocity-power (FVPH) profile metrics. Two double constellation athlete monitoring systems (STATSports Apex, Catapult Vector S7) and one timing gate system were compared with a radar gun for the computation of FVPH metrics. Intersystem validity was assessed using intraclass correlation coefficients (ICC), Pearson's correlation coefficients (R2), and Bland-Altman plots with absolute and percent agreement. Intrasystem reliability was assessed with agreement bias and ICC. STATSports demonstrated moderate agreement for F0, Pmax, τ, and Drf (8.62, 6.46, -9.81, and 9.96%, respectively) and good agreement for V0 and MSS (-2.18 and -1.62%). Catapult displayed good agreement across all metrics (F0, V0, Pmax, MSS, τ, and Drf: -0.96, -0.89, -1.85, -0.84, 0.38, and -0.27%, respectively). Timing gates demonstrated good agreement with V0 and MSS (-2.62 and -1.71%) and poor agreement with F0, Pmax, τ, and Drf (19.17, 16.64, -20.49, and 20.18%, respectively). Intrasystem reliability demonstrated good agreement (<2% bias) with very large to near-perfect ICC (0.84-0.99) for Catapult and STATSports systems. Overall, GPS/GNSS 10 Hz technology is reliable across devices and can provide moderate-to-good accuracy of FVPH metrics in single maximal effort sprints. However, Catapult provided better agreement for more FVPH metrics than STATSports, which may be related to differences in proprietary algorithms. Also, modeling timing gate data using current FVPH profiling techniques results in poor bias that requires greater investigation. GPS/GNSS data can be used for FVPH profiling, which could inform performance and rehabilitation processes.

Microdosing Sprint Distribution as an Alternative to Achieve Better Sprint Performance in Field Hockey Players

Introduction: The implementation of optimal sprint training volume is a relevant component of team sport performance. This study aimed to compare the efficiency and effectiveness of two different configurations of within-season training load distribution on sprint performance over 6 weeks. Methods: Twenty male professional FH players participated in the study. Players were conveniently assigned to two groups: the experimental group (MG; n = 11; applying the microdosing training methodology) and the control group (TG; n = 9; traditional training, with players being selected by the national team). Sprint performance was evaluated through 20 m sprint time (T20) m and horizontal force−velocity profile (HFVP) tests before (Pre) and after (Post) intervention. Both measurements were separated by a period of 6 weeks. The specific sprint training program was performed for each group (for vs. two weekly sessions for MG and TG, respectively) attempting to influence the full spectrum of the F-V relationship. Results: Conditional demands analysis (matches and training sessions) showed no significant differences between the groups during the intervention period (p > 0.05). No significant between-group differences were found at Pre or Post for any sprint-related performance (p > 0.05). Nevertheless, intra-group analysis revealed significant differences in F0, Pmax, RFmean at 10 m and every achieved time for distances ranging from 5 to 25 m for MG (p < 0.05). Such changes in mechanical capabilities and sprint performance were characterized by an increase in stride length and a decrease in stride frequency during the maximal velocity phase (p < 0.05). Conclusion: Implementing strategies such as microdosed training load distribution appears to be an effective and efficient alternative for sprint training in team sports such as hockey.

Center of mass velocity comparison using a whole body magnetic inertial measurement unit system and force platforms in well trained sprinters in straight-line and curve sprinting

BACKGROUND

Sprint performance can be characterized through the centre of mass (COM) velocity over time. In-field computation of the COM is key in sprint training.

RESEARCH QUESTION

To compare the stance-averaged COM velocity computation from a Magneto-Inertial Measurement Units (MIMU) to a reference system: force platforms (FP), over the early acceleration phase in both straight and curve sprinting.

METHODS

Nineteen experienced-to-elite track sprinters performed 1 maximal sprint on both the straight and the curve (radius = 41.58 m) in a randomized order. Utilizing a MIMU-based system (Xsens MVN Link) and compared to FP (Kistler), COM velocity was computed with both systems. Averaged stance-by-stance COM velocity over straight-line and curve sprinting following the vertical axis (respectively V_zMIMU and V_zFP) and the norm of the two axes lying on the horizontal plane: x and y, approximately anteroposterior and mediolateral (respectively V_xyMIMU and V_xyFP) over the starting-blocks (SB) and initial acceleration (IA - composed out of the first four stances following the SB) were compared using mean bias, 95 % limits of agreements and Pearson's correlation coefficients.

RESULTS

148 stances were analyzed. V_xyMIMU mean bias was comprised between 0.26 % and 2.03 % (expressed in % with respect to the FP) for SB, 5.63 % and 7.29 % over IA respectively on the straight and the curve. Pearson's correlation coefficients ranged between 0.943 and 0.990 for V_xy, 0.423 and 0.938 for V_z. On the other hand, V_zMIMU mean bias ranged between 2.33 % and 4.69 % for SB, between 1.44 % and 19.95 % over IA respectively on the straight and the curve SIGNIFICANCE: The present findings suggest that the MIMU-based system tested slightly underestimated V_xyMIMU, though within narrow limits which supports its utilization. On the other hand, V_zMIMU computation in sprint running is not fully mature yet. Therefore, this MIMU-based system represents an interesting device for in-fieldV_xyMIMU computation either for straight-line and curve sprinting.

The effect of a combined sprint training intervention on sprint force-velocity characteristics in junior Australian football players

Background

Sprint performance in junior Australian football (AF) players has been shown to be a differentiating quality in ability level therefore developing sprint characteristics via sprint-specific training methods is an important aspect of their physical development. Assisted sprint training is one training method used to enhance sprint performance yet limited information exists on its effect on sprint force-velocity characteristics. Therefore, the main aim of this study was to determine the influence of a combined sprint training intervention using assisted and maximal sprint training methods on mechanical characteristics and sprint performance in junior Australian football players.

Methods

Upon completing familiarization and pre-testing, twenty-two male junior Australian football (AF) players (age 14.4 ± 0.3 years, body mass 58.5 ± 10.0 kg, and height 1.74 ± 0.08 m) were divided into a combined sprint training (CST) group (n = 14), and a maximal sprint training (MST) group (n = 8) based on initial sprint performance over 20-meters. Sprint performance was assessed during maximal 20-meter sprint efforts via a radar gun (36 Hz), with velocity-time data used to derive force-velocity characteristics and split times. All subjects then completed a 7-week in-season training intervention consisting of maximal sprinting (MST & CST groups) and assisted sprinting (CST only), along with their usual football specific exercises.

Results

Moderate to large pre-post within group effects (-0.65 ≤ ES ≥ 0.82. p ≤ 0.01) in the CST group for relative theoretical maximal force (F₀) and power (P_max) were reflected in improved sprint performance from 0-20 m, thereby creating a more force-oriented F-v profile. The MST group displayed statistically significant pre-post differences in sprint performance between 10-20 m only (ES = 0.18, p = 0.04). Moderate to high relative reliability was achieved across all sprint variables (ICC = 0.65-0.91), except for the force-velocity slope (S_FV) and decrement in ratio of forces (D_RF) which reported poor reliability (ICC = 0.41-0.44), while the CST group exceeded the pre-post minimal detectable change (MDC) in most sprint variables suggesting a 'true change' in performance across the intervention.

Conclusion

It is concluded that implementing a short-term, combined sprint training intervention consisting of assisted and maximal sprint training methods may enhance sprint mechanical characteristics and sprint performance to 20-meters in junior AF players.

Relevance of force-velocity and change of direction assessments for the ranking position in elite junior tennis players

Purpose

This study aimed to correlate sprint mechanical parameters (SMP) of a linear sprint (LS) and a tennis specific modified 505 (Tm505) change of direction (CoD) test obtained with a motorized resistance device (MRD) to the current tennis ranking position (RP).

Methods

107 male and 86 female elite junior tennis players nationally ranked in the German Tennis Federation between 10 and 18 years participated in the study. According to their age at peak height velocity (PHV), players were divided into pre-PHV, circa-PHV, and post-PHV groups. SMP were derived from instantaneous time-velocity data of two 20 m all-out LS measured with 333 Hz. Further, mean values from two Tm505 trials with constant 3 kg loading over acceleration-deceleration (1a) and reacceleration (1b) phases were measured with an MRD. SMP of LS and CoD measurements were partially correlated with the current RP in the overall national ranking by controlling for biological maturation.

Results

Low to moderate correlations (r_s  = -0.1 to -0.3) were found between SMP and the RP in all male and female age groups. Correlations of the CoD measurements were overall more pronounced, particularly in girls (r_s  = -0.44). All linear SMP, like maximal theoretical force (F₀; N/kg), and maximal theoretical velocity (v₀; m/s), maximal power (P_max; W/kg), improved over maturation for both genders with P_max being most important for sprint performance. Further, P_max was shown to correlate with the girls ranking position (r_s  = -0.31). During the Tm505, matured players achieved significantly faster overall total and CoD times. Positioning of CoM before CoD enlarged over maturation and was found to correlate to the RP in both sexes. In addition, nearly all SMP significantly correlated to the primary performance outcomes in the Tm505 test in both genders (r = -0.3 to -0.6).

Conclusion

CoD performance has a moderate and higher impact on tennis performance compared to LS. CoD performance as well as P_max achieved a higher relevance for the ranking position predominantly in girls compared to boys. Hence, particularly P_max as well as the transfer to on-court CoD motor skills should be a central training goal in elite junior tennis players besides technical skills and should depend on maturation status and gender.

Exploratory Analysis of Sprint Force-Velocity Characteristics, Kinematics and Performance across a Periodized Training Year: A Case Study of Two National Level Sprint Athletes

Objective: This case study aimed to explore changes to sprint force-velocity characteristics across a periodized training year (45 weeks) and the influence on sprint kinematics and performance in national level 100-meter athletes. Force-velocity characteristics have been shown to differentiate between performance levels in sprint athletes, yet limited information exists describing how characteristics change across a season and impact sprint performance, therefore warranting further research. Methods: Two male national level 100-meter athletes (Athlete 1: 22 years, 1.83 m, 81.1 kg, 100 m time: 10.47 s; Athlete 2: 19 years, 1.82 cm, 75.3 kg, 100 m time: 10.81 s) completed 12 and 11 force-velocity assessments, respectively, using electronic timing gates. Sprint mechanical characteristics were derived from 30-meter maximal sprint efforts using split times (i.e., 0-10 m, 0-20 m, 0-30 m) whereas step kinematics were established from 100-meter competition performance using video analysis. Results: Between the preparation (PREP) and competition (COMP) phase, Athlete 1 showed significantly large within-athlete effects for relative maximal power (P_MAX), theoretical maximal velocity (v₀), maximum ratio of force (RF_MAX), maximal velocity (V_MAX), and split time from 0 to 20 m and 0 to 30 m (-1.70 ≤ ES ≥ 1.92, p ≤ 0.05). Athlete 2 reported significant differences with large effects for relative maximal force (F₀) and RF_MAX only (ES: ≤ -1.46, p ≤ 0.04). In the PREP phase, both athletes reported almost perfect correlations between F₀, P_MAX and 0-20 m (r = -0.99, p ≤ 0.01), however in the COMP phase, the relationships between mechanical characteristics and split times were more individual. Competition performance in the 100-meter sprint (10.64 ± 0.24 s) showed a greater reliance on step length (r ≥ -0.72, p ≤ 0.001) than step frequency to achieve faster performances. The minimal detectable change (%) across mechanical variables ranged from 1.3 to 10.0% while spatio-temporal variables were much lower, from 0.94 to 1.48%, with Athlete 1 showing a higher 'true change' in performance across the season compared to Athlete 2. Conclusions: The estimated sprint force-velocity data collected across a training year may provide insight to practitioners about the underpinning mechanical characteristics which affect sprint performance during specific phases of training, plus how a periodized training design may enhance sprint force-velocity characteristics and performance outcomes.

Effects of Fatigue Induced by Repeated Sprints on Sprint Biomechanics in Football Players: Should We Look at the Group or the Individual?

The aim of this study was to analyse the influence of fatigue on sprint biomechanics. Fifty-one football players performed twelve maximal 30 m sprints with 20 s recovery between each sprint. Sprint kinetics were computed from running speed data and a high-frequency camera (240 Hz) was used to study kinematic data. A cluster analysis (K-mean clustering) was conducted to classify individual kinematic adaptations. A large decrease in maximal power output and less efficiency in horizontally orienting the ground reaction force were observed in fatigued participants. In addition, individual changes in kinematic components were observed, and, according to the cluster analysis, five clusters were identified. Changes in trunk, knee, and hip angles led to an overall theoretical increase in hamstring strain for some players (Cluster 5, 20/51) but to an overall decrease for some others (Cluster 1, 11/51). This study showed that the repeated sprint ability (RSA) protocol had an impact on both kinetics and kinematics. Moreover, fatigue affected the kinematics in a different way for each player, and these individual changes were associated with either higher or lower hamstring length and thus strain.

Sprint Acceleration Mechanical Outputs Derived from Position- or Velocity-Time Data: A Multi-System Comparison Study

To directly compare five commonly used on-field systems (motorized linear encoder, laser, radar, global positioning system, and timing gates) during sprint acceleration to (i) measure velocity−time data, (ii) compute the main associated force−velocity variables, and (iii) assess their respective inter-trial reliability. Eighteen participants performed three 40 m sprints, during which five systems were used to simultaneously and separately record the body center of the mass horizontal position or velocity over time. Horizontal force−velocity mechanical outputs for the two best trials were computed following an inverse dynamic model and based on an exponential fitting of the position- or velocity-time data. Between the five systems, the maximal running velocity was close (7.99 to 8.04 m.s−1), while the time constant showed larger differences (1.18 to 1.29 s). Concurrent validity results overall showed a relative systematic error of 0.86 to 2.28% for maximum and theoretically maximal velocity variables and 4.78 to 12.9% for early acceleration variables. The inter-trial reliability showed low coefficients of variation (all <5.74%), and was very close between all of the systems. All of the systems tested here can be considered relevant to measure the maximal velocity and compute the force−velocity mechanical outputs. Practitioners are advised to interpret the data obtained with either of these systems in light of these results.

Hip Torque Is a Mechanistic Link Between Sprint Acceleration and Maximum Velocity Performance: A Theoretical Perspective

Sprinting performance is critical for a variety of sports and competitive activities. Prior research has demonstrated correlations between the limits of initial acceleration and maximum velocity for athletes of different sprinting abilities. Our perspective is that hip torque is a mechanistic link between these performance limits. A theoretical framework is presented here that provides estimates of sprint acceleration capability based on thigh angular acceleration and hip torque during the swing phase while running at maximum velocity. Performance limits were calculated using basic anthropometric values (body mass and leg length) and maximum velocity kinematic values (contact time, thigh range of motion, and stride frequency) from previously published sprint data. The proposed framework provides a mechanistic link between maximum acceleration and maximum velocity, and also explains why time constant values (τ, ratio of the velocity limit to acceleration limit) for sprint performance curves are generally close to one-second even for athletes with vastly different sprinting abilities. This perspective suggests that specific training protocols targeted to improve thigh angular acceleration and hip torque capability will benefit both acceleration and maximum velocity phases of a sprint.

Concurrent Validity and Reliability of Sprinting Force-Velocity Profile Assessed With GPS Devices in Elite Athletes

PURPOSE

The aims of this study were to (1) assess the concurrent validity of global positioning systems (GPSs) against a radar device to measure sprinting force-velocity (F-v) profiles and (2) evaluate the interunit reliability of 10-Hz GPS devices (Vector S7, Catapult Innovations).

METHODS

Sixteen male elite U18 rugby union players (178.3 [7.6] cm; 78.3 [13.2] kg) participated. Two 50-m sprints interspersed with at least 5 minutes of recovery were completed to obtain input (maximal sprint speed and acceleration time constant τ) and output (theoretical maximal horizontal force, sprinting speed, and horizontal power) F-v profile variables. Sprint running speed was concurrently measured with a radar and 2 GPS units placed on the upper back of each player. Concurrent validity and interunit reliability analyses were performed.

RESULTS

Moderate to nearly perfect correlations were observed between radar and GPS-derived F-v variables, with small to large typical errors. Trivial to small coefficients of variation were found regarding the GPS interunit reliability.

CONCLUSION

The GPS devices tested in this study represent a valid and reliable alternative to a radar device when assessing sprint acceleration F-v profiles in team-sport players.

Contribution of segmental kinetic energy to forward propulsion of the centre of mass: Analysis of sprint acceleration

This study aimed to measure the contribution of each body segment to the production of total body kinetic energy (KE) during a 40-m sprint. Nine recreational sprinters performed two 40-m sprints wearing a MVN Biomech suit (Xsens). Data recorded were used to calculate total body KE, and the KE of each segment. The KE of each segment was then expressed as a percentage of the total body KE. We divided the sprint into three phases: 1 - start to maximal power (P_max), 2 - P_max to maximal velocity (V_max), and 3 - V_max to the end of the 40 m. Total body KE increased from the start to the end of the 40-m sprint (from 331.3 ± 68.4 J in phase 1 to 2378.8 ± 233.0 J in phase 3; p ≤ 0.001). The contribution of the head-trunk increased (from 39.5 ± 2.4% to 46.3 ± 1.1%; p ≤ 0.05). Contribution of the upper and lower limbs decreased over the three phases (respectively from 15.7 ± 2.5% to 10.6 ± 0.6% and from 44.8 ± 2.1% to 43.1 ± 1.5%; p ≤ 0.05). This study revealed the important contribution of the trunk to forward propulsion throughout the entire acceleration phase.

A Comparison of Sprint Mechanical Parameters Measured With Timing Gates and a Laser Gun

The aim of the study was to compare sprint mechanical parameters measured with timing gates and a laser gun. Thirty-four female team handball players (age: 17.0 ± 2.3 years, height: 1.70 ± 0.07 m, body mass: 66.7 ± 9.7 kg) performed three 30 m sprints in which the times were measured at 5, 10, 20 and 30 m with timing gates (accuracy 0.01 s) together with the distance over time by a laser gun. The main findings were that with a correction of +0.21 s (timing gates) the times and sprint mechanical properties calculated with the spreadsheet of Morin between timing gates and laser gun were not different. But when peak velocity was derived directly from the laser gun (MusclelabTM system) this was significantly higher than maximal velocity (vmax), and lower than the theoretical maximal velocity (v0) calculated with the spreadsheet. It was concluded that a correction of +0.21 s should be used to get correct mechanical properties when measuring with timing gates compared with laser gun measurements on an indoor court.

Level of Agreement, Reliability, and Minimal Detectable Change of the MusclelabTM Laser Speed Device on Force-Velocity-Power Sprint Profiles in Division II Collegiate Athletes

This study examined the level of agreement (Pearson product-moment correlation [rP]), within- and between-day reliability (intraclass correlation coefficient [ICC]), and minimal detectable change of the MusclelabTM Laser Speed (MLS) device on sprint time and force−velocity−power profiles in Division II Collegiate athletes. Twenty-two athletes (soccer = 17, basketball = 2, volleyball = 3; 20.1 ± 1.5 y; 1.71 ± 0.11 m; 70.7 ± 12.5 kg) performed three 30-m (m) sprints on two separate occasions (seven days apart). Six time splits (5, 10, 15, 20, 25, and 30 m), horizontal force (HZT F0; N∙kg−1), peak velocity (VMAX; m∙s−1), horizontal power (HZT P0; W∙kg−1), and force−velocity slope (SFV; N·s·m−1·kg−1) were measured. Sprint data for the MLS were compared to the previously validated MySprint (MySp) app to assess for level of agreement. The MLS reported good to excellent reliability for within- and between-day trials (ICC = 0.69−0.98, ICC = 0.77−0.98, respectively). Despite a low level of agreement with HZT F0 (rP = 0.44), the MLS had moderate to excellent agreement across nine variables (rp = 0.68−0.98). Bland−Altman plots displayed significant proportional bias for VMAX (mean difference = 0.31 m∙s−1, MLS < MySp). Overall, the MLS is in agreement with the MySp app and is a reliable device for assessing sprint times, VMAX, HZT P0, and SFV. Proportional bias should be considered for VMAX when comparing the MLS to the MySp app.

Validity of Velocity Measurements of a Motorized Resistance Device During Change of Direction

The aim of this study was to determine validity of velocity measurements of a motorized resistance device (MRD) during change of direction (CoD). Eight male (age: 22.1 ± 4.2 yrs; weight: 83.3 ± 17.1 kg; height: 181.6 ± 12.6 cm) and three female participants (age: 21.7 ± 1.5 yrs; mass: 69.7 ± 2.4 kg; height: 167.0 ± 3.6 cm) completed the modified 505 CoD test (m505) with turning off the left and right foot while exposed to external loads (3, 6, and 9 kg) provided by the MRD. Three-dimensional kinematic data were measured (200 Hz) for all tests using a full-body marker set with an additional marker placed on the pulley used to attach the carabiner (CAR) at the end of the line from the MRD to the participant. Average velocity of overall center of mass (COMvel), pelvis (COMpelvis_vel), and pulley (CARvel) was then calculated and compared to the velocity measured by MRD (MRDvel) in 0.5 s intervals 1.5 s before and after CoD. Average velocities from these intervals were then compared using correlational, Bland-Altman analysis, coefficient of variation (CV), and statistical parametric mapping (SPM). Mostly, excellent correlations were observed and ranged from 0.93 to 1.00, 0.53 to 1.00 and 0.93 to 1.00 for the 3, 6, and 9 kg load conditions, respectively. CV values ranged from 0.3 to 3.2%, 0.8 to 4.3%, and 1.5 to 7.7% for the CARvel, COMpelvis_vel, and COMvel comparisons, respectively. The biases for CARvel comparisons ranged from -0.027 to 0.05 m/s, -0.246 to 0.128 m/s and -0.486 to 0.082 m/s across all load conditions and time intervals for the CARvel, COMpelvis_vel, and COMvel comparisons, respectively. SPM analysis indicated significant differences between MRDvel and COMvel and COMpelvis_vel over short time periods during the CoD, but no difference between MRDvel and CARvel. The velocity measurements obtained by a MRD during a m505 test are valid as low biases, low CV's, and high correlations are observed for the MRDvel to CARvel comparison. As single points of measurement (i.e., laser) has been proven useful to assess other athletic tasks (i.e., sprint running), the single point CARvel comparison is an appropriate comparison for validating MRDvel measurements during the m505 test.

Is the Concept, Method, or Measurement to Blame for Testing Error? An Illustration Using the Force-Velocity-Power Profile

When poor reliability of “output” variables is reported, it can be difficult to discern whether blame lies with the measurement (ie, the inputs) or the overarching concept. This commentary addresses this issue, using the force-velocity-power (FvP) profile in jumping to illustrate the interplay between concept, method, and measurement reliability. While FvP testing has risen in popularity and accessibility, some studies have challenged the reliability and subsequent utility of the concept itself without clearly considering the potential for imprecise procedures to impact reliability measures. To this end, simulations based on virtual athletes confirmed that push-off distance and jump-height variability should be <4% to 5% to guarantee well-fitted force–velocity relationships and acceptable typical error (<10%) in FvP outputs, which was in line with previous experimental findings. Thus, while arguably acceptable in isolation, the 5% to 10% variability in push-off distance or jump height reported in the critiquing studies suggests that their methods were not reliable enough (lack of familiarization, inaccurate procedures, or submaximal efforts) to infer underpinning force-production capacities. Instead of challenging only the concept of FvP relationship testing, an alternative conclusion should have considered the context in which the results were observed: If procedures’ and/or tasks’ execution is too variable, FvP outputs will be unreliable. As for some other neuromuscular or physiological testing, the FvP relationship, which magnifies measurement errors, is unreliable when the input measurements or testing procedures are inaccurate independently from the method or concept used. Field “simple” methods require the same methodological rigor as “lab” methods to obtain reliable output data.

Reliability and Minimal Detectable Change of Sprint Times and Force-Velocity-Power Characteristics

ABSTRACT

Edwards, T, Banyard, HG, Piggott, B, Haff, GG, and Joyce, C. The reliability and minimal detectable change of sprint times and force-velocity-power characteristics. J Strength Cond Res 36(1): 268-272, 2022-Research has not yet provided critical information for practitioners to determine the minimal detectable change (MDC) in sprint times or force-velocity-power characteristics. Therefore, the aim of this study was to establish the interday reliability and MDC of sprint times and sprint force-velocity-power characteristics in junior Australian football (AF) players. Seventeen players were assessed using a radar device that recorded instantaneous velocity during 3 maximal 30-m sprint accelerations performed on 2 nonconsecutive days. Sprint force, velocity, and power characteristics were derived through inverse dynamics applied to the raw velocity-time data. Relative and absolute reliability was determined by calculating the intraclass correlation coefficient (ICC), coefficient of variation (CV), and MDC. Data analysis was assessed for (a) the first trial, (b) the best trial (the fastest 30-m split time), (c) the average of the first 2 trials, and (d) the average of all 3 trials from each testing session. The main findings were (a) absolute theoretical maximum force (F0), theoretical maximal velocity (V0), absolute and relative maximum power (Pmax), maximum ratio of force (RFmax), maximum velocity (Vmax), and all sprint distance times (5-30 m) displayed acceptable reliability (CV < 10% and ICC >0.75) and 2) the average of 2 and 3 trials was the best method of establishing reliable sprint times and force-velocity-power characteristics between sessions. This study provides important information for practitioners to determine the MDC in sprint times and force-velocity-power characteristics that allow coaches to identify true changes in performance.

Association and Predictive Ability of Jump Performance with Sprint Profile of Collegiate Track and Field Athletes

This study examined the relationship between broad jump (BJ), countermovement jump (CMJ) and light load countermovement jump (LL-CMJ) performance and sprint performance and Sprint Profile measures in athletes. Additionally, this study aimed to determine the predictive ability of jump measures on Sprint Profile components. Twenty-five athletes performed BJ, CMJ, LL-CMJ, 30-metre acceleration and 30-metre maximal speed fly-by sprints. Results revealed moderate to very large correlations between BJ, CMJ and LL-CMJ performance with acceleration sprint completion times (r = -0.423 to -0.807; p < 0.05), fly-by sprint completion times (r = -0.452 to -0.838; p < 0.05) and maximal sprint speed (r = 0.424 to 0.794; p < 0.05). Additionally, associations were observed with multiple jumping measures and components of the Sprint Profile (r = 0.431 to 0.777; p < 0.05) during acceleration sprints. Furthermore, the BJ distance was the best predictor of Sprint Profile components during acceleration sprints (R2 = 0.57-0.76; p < 0.01) and maximal speed fly-by sprints (R2 = 0.775; p < 0.001). The forces and the manner of force application during the BJ to propel the athlete forwards and upwards are similar to those necessary to exhibit superior sprint performance. This may be due to the rapid generation of forces and orientation of force application during both movements.

Optimal mechanical force-velocity profile for sprint acceleration performance

The aim was to determine the respective influences of sprinting maximal power output ( P H max ) and mechanical Force-velocity (F-v) profile (ie, ratio between horizontal force production capacities at low and high velocities) on sprint acceleration performance. A macroscopic biomechanical model using an inverse dynamics approach applied to the athlete's center of mass during running acceleration was developed to express the time to cover a given distance as a mathematical function of P H max and F-v profile. Simulations showed that sprint acceleration performance depends mainly on P H max , but also on the F-v profile, with the existence of an individual optimal F-v profile corresponding, for a given P H max , to the best balance between force production capacities at low and high velocities. This individual optimal profile depends on P H max and sprint distance: the lower the sprint distance, the more the optimal F-v profile is oriented to force capabilities and vice versa. When applying this model to the data of 231 athletes from very different sports, differences between optimal and actual F-v profile were observed and depend more on the variability in the optimal F-v profile between sprint distances than on the interindividual variability in F-v profiles. For a given sprint distance, acceleration performance (<30 m) mainly depends on P H max and slightly on the difference between optimal and actual F-v profile, the weight of each variable changing with sprint distance. Sprint acceleration performance is determined by both maximization of the horizontal power output capabilities and the optimization of the mechanical F-v profile of sprint propulsion.

Acute impact of Nordic hamstring exercise on sprint performance after 24, 48 and 72 hours

The Nordic Hamstring Exercise (NHE) improves the strength of the hamstring muscles, as well as prevents and rehabilitates the injuries of said muscles. However, the eccentric demand of NHE may influence the athlete's performance, making compliance with these programmes difficult. The aim is to analyse the acute impact on sprint performance after the passing of 24, 48, and 72 hours respectively since an NHE-based session (4 sets of 10 repetitions) had taken place. Participants were randomly divided into an experimental group (EG) (n = 12 male participants) who carried out an NHE session and a measurement of their 30 m sprint performance in each of the three subsequent days, and a control group (CG) (n = 12 male participants) who did not take part in the NHE session. The results show a significant reduction of maximum power within 24 hours (t = 3.57, d = 0.22, P < .0273) as well of the production of high speed horizontal force up to after 48 hours (t = 4.82, d = 0.22, P < .0001) in the EG. These results may suggest separating weekly NHE sessions from competition or demanding training in which sprint performance should not be affected by at least 72 hours.

Uphill sprinting load- and force-velocity profiling: Assessment and potential applications

This study aimed to quantify the validity and reliability of load-velocity (LV) relationship of hill sprinting using a range of different hill gradients and to describe the effect of hill gradient on sprint performance. Twenty-four collegiate-level athletes performed a series of maximal sprints on either flat terrain or hills of gradients 5.2, 8.8 and 17.6%. Velocity-time curves were recorded using a radar device. LV relationships were established using the maximal velocity achieved in each sprinting condition, whilst force-velocity-power (FVP) profiles were established using only the flat terrain sprint. LV profiles were shown to be valid (R² = 0.99) and reliable (TE < 4.4%). For every 1-degree increase in slope, subjects' velocity decreased by 1.7 ± 0.1% on average. All the slopes used represented low resistance relative to the entire LV spectrum (<25% velocity loss). Subjects who exhibited greater horizontal force output at higher velocities on flat terrain were most affected by the gradient of the hill. Hills of gradients up to 17.6% do not provide sufficient resistance to optimize power development. However, such hills could be used to develop late-stage technical ability, due to the prolonged horizontally oriented body position that occurs as subjects attempt to overcome the acceleration due to gravity.