Force-velocity profiling in athletes: Reliability and agreement across methods

Reliability and Acute Changes in the Load-Velocity Profile During Countermovement Jump Exercise Following Different Velocity-Based Resistance Training Protocols in Recreational Runners

This study aimed (i) to explore the reliability of the load-velocity relationship variables (load-axis intercept [L0], velocity-axis intercept [v0], and the area under the load-velocity relationship line [Aline]) obtained during the countermovement jump exercise in successive sessions and (ii) to examine the feasibility of the load-velocity relationship variables to detect acute changes in the lower-body maximal mechanical capacities following different velocity-based training (VBT) protocols. Twenty-one recreational runners completed four randomized VBT protocols (three back squat sets with three minutes of rest) on separate occasions: (i) VBT with 60% of the one-repetition maximum (1RM) and 10% velocity loss (VBT60-10); (ii) VBT with 60% 1RM and 30% velocity loss (VBT60-30); (iii) VBT with 80% 1RM and 10% velocity loss (VBT80-10); and (iv) VBT with 80% 1RM and 30% velocity loss (VBT80-30). The load-velocity relationship was determined before and after each VBT protocol using the two-point method in the countermovement jump with a 0.5 kg load and another matching a mean velocity of 0.55 m·s-1. All load-velocity relationship variables had an acceptable reliability (CV ≤ 5.61% and ICC ≥ 0.83, except for v0 between VBT60-30 and VBT80-10). Both v0 and Aline were reduced after VBT60-30 and VBT80-30 (p ≤ 0.044 and ES ≥ -0.47) but not after VBT60-10 and VBT80-10 (p ≥ 0.066 and ES ≤ -0.37). The post-pre differences were not significantly associated between VBT protocols for any load-velocity relationship variable (r ≤ 0.327 and p ≥ 0.148). Although the load-velocity relationship is reliable and sensitive to high-repetition VBT protocols, its use to detect acute changes in the lower-body maximal mechanical capacities is characterized by a high variability in individual responses.

Is the Force-Velocity Profile for Free Jumping a Sound Basis for Individualized Jump Training Prescriptions?

INTRODUCTION

Formulating individualized optimized jump training prescriptions based on the force-velocity profile has become popular, but its effectiveness has been contested. Such training programs have opposite effects on "maximal average force" and "maximal average shortening velocity," and we set out to investigate which training-induced changes in the neuromuscular system could cause such effects.

METHODS

We used a musculoskeletal simulation model with four body segments and six muscle-tendon actuators to simulate vertical squat jumps with different loads. Independent input was muscle stimulation over time, which was optimized for maximal jump height. We determined the force-velocity profile for a reference model and investigated how it changed when we modified muscle properties and initial postures.

RESULTS

We could not reproduce the reported training effects by realistically improving muscle properties (maximal force, shortening velocity, and rate of force development) or modifying initial postures of the model. However, the profile was very sensitive to gains in jump height at low loads but not high loads, or vice versa. Reaching maximal height in force-velocity profile jumps requires skill. We argued that submaximal performance in low-load or high-load jumps caused by lack of skill could be responsible for large imbalances in profiles before training. Differential skill training promoted by the individualized optimized approach could explain quick changes toward a balanced profile.

CONCLUSIONS

If the success of individualized optimized training studies is explained by selective skill improvements, training effects are unlikely to transfer to other tasks, and individualized optimized training will not be superior to other types of training.

Predicting Multijoint Maximal Eccentric and Concentric Strength With Force-Velocity Jump Mechanics in Collegiate Athletes

PURPOSE

Maximal muscle strength is often assessed with single-joint or repetition-maximum testing. The purpose of this study was to evaluate the reliability of countermovement-jump (CMJ) velocity-load testing and assess the relationship between CMJ velocity-load kinetics and concentric-isometric-eccentric multijoint leg-extension strength tested on a robotic servomotor leg press in trained athletes.

METHODS

University athletes (N = 203; 52% female) completed 3 concentric, isometric, and eccentric maximum voluntary leg-extension contractions on the robotic leg press, followed by CMJ velocity-load testing with an additional external load of 0% (CMJBW), 30% (CMJ30), and 60% (CMJ60) of body mass. A linear model was fit for the CMJ takeoff velocity-load relationship to obtain the load intercept. Force-velocity parameters were obtained for the CMJ eccentric deceleration and concentric phases. Linear mixed-effects models were constructed to predict concentric, isometric, and eccentric leg-press force using the CMJ takeoff velocity-load relationship and CMJ kinetics.

RESULTS

Isometric leg-press strength was predicted by load intercept and sex (P < .001, R2 = .565, prediction error = 14%). Concentric leg-press strength was predicted by load intercept, CMJ60 concentric impulse, and sex (P < .001, R2 = .657, prediction error = 10%). Eccentric leg-press strength was predicted by minimum downward velocity, CMJ60 eccentric deceleration impulse, and sex (P < .001, R2 = .359, prediction error = 14%).

CONCLUSIONS

Given the relevance of muscle-strength testing for sport performance and injury prevention, assessing force-velocity mechanics with loaded CMJ testing is a reliable and viable approach to predict maximal concentric, isometric, and eccentric leg-press strength in competitive athletes.

Associations between force-velocity-power profile in sprinting and ballistic lower limb tests in adolescent elite footballers

This study investigated the relationships between performance and force-velocity (F-v) parameters obtained from a ballistic lower limb (BLL) and a 30-m sprint test in 24 adolescent elite footballers (13.2-15.1 years old). In the BLL test, normal ground reaction force and velocity were recorded by two force plates and a linear encoder, respectively, and take-off velocity (vto) at 0% of body mass was considered as performance. In the 30-m sprint test, raw velocity-time data were measured using a radar, and 5, 10 and 30 m sprint times using a timing gate system. Theoretical maximal force (F0), velocity (v0) and power (Pmax) were determined using the Samozino's method. All sprint times were significantly correlated with vto (p = 0.004 to p < 0.001; -0.57 to -0.72), but no significant correlation was found between the respective F-v parameters ;(p = 0.152 to 0.913). As both tests assess explosive performance, players who can produce a high vto will also perform best in short sprints. However, the F-v discrepancies highlight the complementarity of these tests: the BLL test minimises the coordination and technical influences that can affect sprint performance in adolescents.

The Impact of Rest Intervals on the Force-Velocity Relationship Obtained During the Keiser's 10-Repetition Leg Press Test

Background: The Keiser 10-rep leg press test protocol employs short inter-repetition rest intervals (2-38 s), raising concerns as to whether athletes perform optimally. Objectives: The aim of this study was to compare the results of the standard Keiser protocol with an identical protocol modified to include a significantly longer inter-repetition rest intervals and to evaluate whether these effects differed between men and women. Methods: A total of 30 athletes (age 17.1 ± 0.9 years, height 177.8 ± 8.8 cm, and body mass 71.9 ± 11.3 kg) performed three separate tests (total of ~900 repetitions) in a Keiser A420 leg press machine, separated by 4 to 8 days. Test day 1 included a 1RM test followed by a 10-repetition force-velocity test with a standard rest intervals. Test days 2 and 3 involved the same test, with either standard short rest intervals or fixed 3 min inter-repetition rest intervals. Results: Increasing inter-repetition rest intervals significantly improved V0 and Pmax for men and V0 and FVslope for women. The benefits of longer rest were notably more pronounced in men, particularly at light to moderate loads, where standard Keiser rest intervals are short (2-9 s). However, extending rest intervals beyond approximately 30 s, as applied at higher loads, provided no additional advantages. Conclusions: Longer rest intervals improved force-velocity metrics more in men than women, with the effect being most pronounced at light to moderate loads where standard protocols utilize short rest intervals (2-9 s). These findings suggest that women recover faster than men under these conditions. However, extending rest beyond 30 s at higher loads provides no additional benefits and is counterproductive at maximal loads.

Are Young Female Basketball Players Adequately Prepared for a Force-Velocity Jumping and Sprinting Assessment?

PURPOSE

The aim of this study was to explore the interday reliability of mechanical variables obtained from the horizontal and vertical force-velocity (FV) profiles in adolescent female basketball players. If found to be reliable, the associations between FV parameters (theoretical maximal force, velocity, and power), squat jump (SJ) height, 30-m sprint, and change of direction (COD) times were evaluated.

METHODS

After familiarization, SJ against incremental loads, 30-m sprint, and 505-COD tests were obtained twice in 36 adolescent female basketball players (age = 15.4 [1.2] y).

RESULTS

Reliability for vertical FV parameters was unacceptable, whereas 505-COD times and FV horizontal parameters (except for theoretical maximal power) showed a moderate to high reliability. 505-COD time was correlated with FV horizontal parameters (range: r = -.821, -.451), and a large association was observed with both SJ height (r = -.678, -.600) and 30-m sprint time (r = .813, .858).

CONCLUSIONS

Due to low levels of strength, our athletes were not adequately prepared to obtain a reliable vertical FV profile. Practitioners can expect acceptable reliability of the horizontal FV profile. Given the association between COD performance and SJ height and 30-m sprint time, we encouraged practitioners with limited equipment at their disposal to use COD and/or 30-m sprint tests.

The Battle of the Equations: A Systematic Review of Jump Height Calculations Using Force Platforms

Vertical jump height measures our ability to oppose gravity and lower body neuromuscular function in athletes and various clinical populations. Vertical jump tests are principally simple, time-efficient, and extensively used for assessing athletes and generally in sport science research. Using the force platform for jump height estimates is increasingly popular owing to technological advancements and its relative ease of use in diverse settings. However, ground reaction force data can be analyzed in multiple ways to estimate jump height, leading to distinct outcome values from the same jump. In the literature, four equations have been commonly described for estimating jump height using the force platform, where jump height can vary by up to ∼ 15 cm when these equations are used on the same jump. There are advantages and disadvantages to each of the equations according to the intended use. Considerations of (i) the jump type, (ii) the reason for testing, and (iii) the definition of jump height should ideally determine which equation to apply. The different jump height equations can lead to confusion and inappropriate comparisons of jump heights. Considering the popularity of reporting jump height results, both in the literature and in practice, there is a significant need to understand how the different mathematical approaches influence jump height. This review aims to investigate how different equations affect the assessment of jump height using force platforms across various jump types, such as countermovement jumps, squat jumps, drop jumps, and loaded jumps.

Test-retest reliability of lower limb muscle strength, jump and sprint performance tests in elite female team handball players

PURPOSE

This study aimed to assess the reliability of lower limb muscle function (knee extensor/flexor peak torque, rate of torque development (RTD), impulse, and countermovement jump (CMJ) performance) and sprint performance (acceleration capacity).

METHODS

CMJ performance was evaluated on a force plate. MVIC, RTD and impulse variables were investigated using a portable isometric dynamometer and sprint performance was assessed with dual-beam photocells in elite female athletes.

RESULTS

CMJ test variables maximal vertical jump height, peak and mean power, concentric work, and body center of mass displacement demonstrated good-to-excellent test-retest correlations between Test 1 and Test 2 (ICC ≥ 0.70, CWw-s = 3.4-11.0%). Peak MVIC torque for the knee extensors and flexors demonstrated excellent test-retest correlations (both ICC = 0.84) along with CVw-s values of 6.8 and 6.0%, respectively. Late-phase (0-100 ms, 0-200 ms) RTD for the knee flexors demonstrated excellent test-retest correlations (ICC = 0.89-0.91, CVw-s = 4.8-8.5%). Sprint times at 10- and 20-m demonstrated excellent test-retest reproducibility (ICC = 0.83 and ICC = 0.90, respectively) with CVw-s values of 1.9 and 1.5%. For 5-m sprint times, test-retest reproducibility was good (ICC = 0.71) with CVw-s of 2.8%. Sprint testing performed while dribbling a handball improved (p < 0.05) from test to retest at 5-, 10- and 20-m.

CONCLUSION

In conclusion, the force plate, the mobile isometric dynamometer, and dual-beam photocells provide reproducible tools for field-based testing of countermovement jump performance, knee extensor and flexor strength and sprint performance.

Effects of Different Loading Types on the Validity and Magnitude of Force-Velocity Relationship Parameters

BACKGROUND

Force-velocity (F-V) relationship models gained popularity as a tool for muscle mechanical assessment. However, it is not clear whether the validity of the F-V relationship parameters (maximal theoretical force [F0], velocity [V0] and power [Pmax]) is affected using different load types: gravitational (W, rubber bands pulling the barbell downward), inertial (I, rubber bands pulling the barbell, which is equalized to the weight of the added plates upward), and combined (W + I, weight of the plates).

HYPOTHESIS

Load type would affect both the magnitude and validity of F-V relationship parameters. The highest magnitude and validity was expected for F0 using a W, for V0 using an I, and for Pmax using a W + I load.

STUDY DESIGN

Cross-sectional.

LEVEL OF EVIDENCE

Level 3.

METHODS

A total of 13 resistance-trained men (body mass, 87.7 ± 11.2 kg and body height, 183.9 ± 6.4 cm) performed bench press (BP) throws (BPTs) using 3 types of loads against 30 to 80 kg. The validity of F-V relationship parameters was explored with respect to the tests used traditionally for force (maximal voluntary contraction and 1-repetition maximum [1RM]), velocity (maximal velocity achieved during almost unloaded tasks), and power (BPT against the 50%1RM and medicine ball throws) assessment.

RESULTS

The W + I loading promoted the highest values of F0 and Pmax, while the highest magnitude of V0 was promoted by the I loading. The validity was acceptable for F0 obtained using the 3 loading conditions with respect to the BP 1RM (r range, 0.30-0.83), and V0 obtained using the I loading with respect to the stick throw (r = 0.54).

CONCLUSION

The magnitude of the F-V relationship parameters is affected by load type, but their validity with respect to standardized tests is comparable, with the exception of the higher validity of V0 when obtained using the I loading.

CLINICAL RELEVANCE

Any load type can be used for assessing F0, while I load should be selected when assessing V0.

Effect of maturity status on force-velocity relationships in a ballistic lower limb test in high-level soccer players

This study aimed to investigate the effect of maturity status on force-velocity relationships in a ballistic lower limb (BLL) test in high-level soccer adolescents and young adults. The population was 61 adolescents (13.0-17.9 years) and 23 young adults (18.0-26.2 years). Subjects completed the BLL test on a ballistic ergometer equipped with two force plates and a linear encoder. Following Samozino's method, maximal power output (Pmax), force (F0) and velocity (v0) were determined. An allometric model was applied to Pmax and F0 with body mass (BM) and fat-free mass (FFM). Significant effects of maturity status were found for absolute Pmax, F0, relative Pmax to BM and FFM, relative F0 to FFM and F0 allometrically scaled to BM and FFM (p = 0.02 to p < 0.001; η  = 0.10 to η  = 0.49). There was no significant effect for Pmax allometrically scaled to BM and FFM, F0 relative to BM and v0. Body dimensions explain group differences in Pmax whereas for F0, qualitative factors explain the differences between the groups. As maturity status and body dimensions influence Pmax, these factors should be considered when assessing explosive short efforts. This could help to better identify potential athletic talent and adapt training content.

Comparison of Different Take-off Thresholds When Assessing Vertical Jump Performance

Reliably determining vertical jump (VJ) take-off on a force plate is crucial when identifying performance-related biomechanical factors. Therefore, the purpose of this study was to compare several take-off thresholds (20 N, 10 N, 5 N, 1 N, five standard deviations above an unloaded force plate (5SD), and peak residual force (PkRes) produced when the force plate was unloaded) in terms of jump height (JH), movement time (MT), reactive strength index modified (RSImod), net impulse (netIMP), and propulsive impulse (prIMP). Twenty-one participants performed five countermovement VJs on a force plate. All thresholds were reliable with intraclass correlations ≥ 0.835 and coefficient of variation < 10%. Our results show significant differences across the different take-off thresholds for JH, MT, RSImod, netIMP, and prIMP. However, these differences were considered trivial based on effect sizes. While differences in these thresholds may not be practically meaningful, practitioners are encouraged to consider the noise in the force-time signal and select an appropriate threshold that matches PkRes within their given environment.

Feasibility of vertical force-velocity profiles to monitor changes in muscle function following different fatigue protocols

PURPOSE

This study aimed to explore the feasibility of vertical force-velocity (F-V) profiles to monitor changes in muscle function following different fatigue protocols. The between-day reliability of vertical F-V profiles and the acute effects of two fatigue protocols on the changes of lower limb muscle function were examined.

METHODS

Twelve resistance trained males completed a preliminary session to determine their back squat one-repetition maximum (1RM). Afterwards, they randomly performed two experimental sessions that only differed in the fatigue protocol applied: heavy-load traditional (HLT; five repetitions at 80% 1RM) and light-load ballistic (LLB; five repetitions at 30% 1RM) squat protocols. Participants' vertical F-V profiles (maximum theoretical force [F0], maximum theoretical velocity [v0], and maximum power output [Pmax]) were calculated before and immediately after each fatigue protocol.

RESULTS

F0, v0, and Pmax showed acceptable to good between-day reliability (coefficient of variation ≤ 4.4%; intraclass correlation coefficient ≥ 0.84). Both fatigue protocols promoted a comparable reduction in Pmax (-10.1% for HLT and -12.2% for LLB). However, the LLB squat protocol reduced more v0 (-9.7%) than F0 (-0.4%), while the HLT squat protocol reduced F0 (-8.4%) more than v0 (-4.1%).

CONCLUSIONS

The vertical F-V profile can be used to monitor changes in muscle function given its acceptable between-day reliability and its high sensitivity to detect the acute effect of force-oriented and velocity-oriented fatigue protocols on specific maximal neuromuscular capacities.

Single Leg Lateral and Horizontal Loaded Jump Testing: Reliability and Correlation With Long Track Sprint Speed Skating Performance

ABSTRACT

Zukowski, MH, Jordan, MJ, and Herzog, W. Single leg lateral and horizontal loaded jump testing: reliability and correlation with long track sprint speed skating performance. J Strength Cond Res 37(11): 2251-2259, 2023-This study examined the intraday reliability of 2 novel unilateral loaded jump protocols designed for long track speed skaters. Highly trained ( n = 26), national level athletes performed single leg jumps with a horizontal robotic resistance across 3 external load conditions (10 N, 7.5% of body mass and 15% of body mass) using their dominant limb. Jumps were performed in both the horizontal (Jump Horz ) and lateral (Jump Lat ) direction to replicate the body position and line of force application observed during the running and gliding phases of on-ice acceleration. Subjects completed 2 consecutive trials of the same jump protocol to examine the intraday reliability of the peak velocity achieved for each loading condition. Peak velocity across each jump type and loading condition had good reliability (intraclass correlation coefficient >0.8, coefficient of variation <5%). Significant positive relationships ( r = 0.5-0.8, p < 0.05; n = 22) were observed between all jump conditions and on-ice sprint race split times obtained including 100, 400, and 500 m. Our results indicate that unilateral loaded jump tests are reliable in speed skating athletes and may help practitioners diagnose and monitor lower-limb maximal muscle power capacity in a sport-specific manner.

Reliability and Validity of Different Lower-Limb Strength Tests to Determine 1RM in the Keiser A300 Leg Press

ABSTRACT

Larsen, F, Loturco, I, Sigvaldsen, E, Strand, MF, Kalhovde, JM, and Haugen, T. Reliability and validity of different lower-limb strength tests to determine 1RM in the Keiser A300 leg press. J Strength Cond Res 37(10): 1963-1968, 2023-The aim of this study was to explore the reliability and validity of different lower-limb strength tests to determine the one-repetition maximum (1RM) value in the Keiser A300 leg press. Twenty-eight recreationally active subjects performed load-velocity (L-V) relationship, 1RM, isometric midthigh pull (IMTP), and maximal repetitions to failure (MRF) tests on 3 separated sessions. Predicted 1RMs for the L-V relationship were estimated from a linear regression equation, correlating movement velocity and relative loads. The number of repetitions from the MRF tests (at loads relative to bodyweight) and peak force from the IMTP tests were used in regression equations to predict 1RM. The level of significance was set to ρ ≤ 0.05. All 1RM prediction methods were highly comparable with the traditional 1RM test, as only trivial and nonsignificant differences were observed. Furthermore, the L-V relationship was the most reliable (intraclass correlation coefficient [± 95% confidence interval] = 0.99 [0.98, 0.996]; effect size = -0.01 [-0.38, 0.36], standard error of the measurement = 6.4 kg; coefficient of variation = 3.0 [2.2-3.8]% and valid (r = 0.95 [0.89, 0.98], effect size = 0.08 [-0.29, 0.45], standard error of the estimate = 20.4 kg; coefficient of variation = 7.4 [5.5-9.3]%) when compared with direct 1RM measurements. The L-V relationship test showed a significant change score relationship (r = 0.41 [0.04, 0.68]) against the direct 1RM measurements. In conclusion, the tests used in this study cannot be used interchangeably, but they represent a good alternative in training settings where 1RM testing is not feasible.

Monitoring Changes in Lower-Limb Strength and Power in Elite Athletes With the Countermovement-Jump and Keiser Leg-Press Tests

PURPOSE

To determine the utility of countermovement-jump and Keiser leg-press tests for tracking changes in elite athletes of different sports.

METHODS

Elite athletes of the Norwegian Olympic Federation (126 individuals from 18 sports) performed countermovement-jump and Keiser tests on 2 to 11 occasions between 2014 and 2021. Separate analyses were performed for male and female alpine skiing, male and female handball, male ice hockey, and males and females of other sports. Means and standard deviations of consecutive change scores were combined with short-term error of measurement (3.7%-7.0%) and smallest important changes (2.0%-3.6%, defined by standardization) to determine the proportions of athletes who experienced decisive changes in 2 senses: first, the athlete did not get substantially worse or better (>90% chance of either), and second, the athlete did get substantially worse or better (>90% chance of either).

RESULTS

Averaged over sports, Keiser peak power and relative peak power had the highest proportions of decisive changes in the first (60% and 55%) and second senses (25% and 28%). The velocity intercept of the force-velocity relationship had the lowest proportions in the first and second senses (29% and 11%), while jump height, Keiser mean power, relative mean power, the force intercept, and the slope of the force-velocity relationship had similar proportions (40%-53% and 15%-21%).

CONCLUSIONS

With the possible exception of the Keiser test velocity intercept, the proportions of observed decisive changes in elite athletes using Keiser measures and countermovement-jump height between tests appear adequate for the measures to be useful for routine monitoring.

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.

Two-point Method Applied in Field Conditions: A Feasible Approach to Assess the Load-Velocity Relationship Variables During the Bench Pull Exercise

ABSTRACT

Miras-Moreno, S, García-Ramos, A, Jukic, I, and Pérez-Castilla, A. Two-point method applied in field conditions: a feasible approach to assess the load-velocity relationship variables during the bench pull exercise. J Strength Cond Res 37(7): 1367-1374, 2023-This study explored the between-session reliability and concurrent validity of the load-velocity (L-V) relationship variables obtained from different methods during the Smith machine bench pull exercise. In a counterbalanced order, 23 resistance-trained male subjects performed 2 sessions against 6 different loads in one week and 2 sessions against the lightest and heaviest loads in another week. The L-V relationship variables (load-axis intercept [ L0 ], velocity-axis intercept [ v0 ], and area under the L-V relationship line [ Aline ]) were obtained using the mean and peak velocity by the standard multiple-point (all 6 loads were used for the L-V modeling), modified multiple-point (the data point that most reduced the coefficient of determination was omitted from the L-V modeling), and 2-point (only 2 loads were used for the L-V modeling) methods. The reliability of the L-V relationship variables was acceptable for all methods (within-subjects coefficient of variation [CV] = 2.09-9.21%). The standard multiple-point and 2-point methods provided greater reliability for all L-V relationship variables compared with the modified multiple-point method (CV ratio ≥ 1.27), while the 2-point method provided similar (CV ratio = 1.04 for Aline ) or greater (CV ratio = 1.50 for L0 and 1.62 for v0 ) reliability than the standard multiple-point method. The concurrent validity of the modified multiple-point and 2-point methods was acceptable for the L-V relationship variables (effect size ≤ 0.62; r ≥ 0.76). These results suggest that the 2-point method is not only a valid procedure but also more reliable, simpler, faster, and less prone to fatigue than multiple-point methods for assessing maximal neuromuscular capacities through the L-V relationship.

The Force-Velocity Profile for Jumping: What It Is and What It Is Not

INTRODUCTION

Force-velocity profiling has been proposed in the literature as a method to identify the overall mechanical characteristics of lower extremities. A force-velocity profile is obtained by plotting for jumps at different loads the effective work as a function of the average push-off velocity, fitting a straight line to the results, and extrapolating this line to find the theoretical maximum isometric force and unloaded shortening velocity. Here we investigated whether the force-velocity profile and its characteristics can be related to the intrinsic force-velocity relationship.

METHODS

We used simulation models of various complexity, ranging from a simple mass actuated by a linearly damped force to a planar musculoskeletal model comprising four segments and six muscle-tendon complexes. The intrinsic force-velocity relationship of each model was obtained by maximizing the effective work during isokinetic extension at different velocities.

RESULTS

Several observations were made. First, at the same average velocity, less effective work can be done during jumping than during isokinetic lower extremity extension at this velocity. Second, the intrinsic relationship is curved; fitting a straight line and extrapolating it seem arbitrary. Third, the maximal isometric force and the maximal velocity corresponding to the profile are not independent. Fourth, they both vary with inertial properties of the system.

CONCLUSIONS

For these reasons, we concluded that the force-velocity profile is specific for the task and is just what it is: the relationship between effective work and an arbitrary estimate of average velocity; it does not represent the intrinsic force-velocity relationship of the lower extremities.

Force-Velocity Profiling in Club-Based Field Hockey Players: Analyzing the Relationships between Mechanical Characteristics, Sex, and Positional Demands

The purpose of this study was to investigate differences between sex and positional demands in club-based field hockey players by analyzing vertical force-velocity characteristics. Thirty-three club-based field hockey athletes (16 males - age: 24.8 ± 7.3yrs, body mass: 76.8 ± 8.2kg, height: 1.79 ± 0.05m; 17 females - age: 22.3 ± 4.2yrs, body mass: 65.2 ± 7.6kg, height: 1.66 ± 0.05m) were classified into two key positional groups (attacker or defender) based on dominant field position during gameplay. Force-velocity (F-v) profiles were established by performing countermovement jumps (CMJ) using a three-point loading protocol ranging from body mass (i.e., zero external mass, 0%) to loads corresponding to 25% and 50% of their own body mass. Across all loads, between-trial reliability of F-v and CMJ variables was determined by intraclass correlation coefficients (ICCs) and coefficient of variation (CV) and deemed to be acceptable (ICC: 0.87-0.95, CV% 2.8-8.2). Analysis by sex identified male athletes had significantly greater differences in all F-v variables (12.81-40.58%, p ≤ 0.001, ES = 1.10-3.19), a more enhanced F-v profile (i.e., greater theoretical maximal force, velocity, and power values), plus overall stronger correlations between relative maximal power (P_MAX) and jump height (r = 0.67, p ≤ 0.06) when compared to female athletes (-0.71≤ r ≥ 0.60, p = 0.08). Male attackers demonstrated a more 'velocity-oriented' F-v profile compared to defenders due to significant mean differences in theoretical maximal velocity (v₀) (6.64%, p ≤ 0.05, ES: 1.11), however differences in absolute and relative theoretical force (F₀) (15.43%, p ≤ 0.01, ES = 1.39) led to female attackers displaying a more 'force-oriented' profile in comparison to defenders. The observed mechanical differences identify the underpinning characteristics of position specific expression of P_MAX should be reflected in training programmes. Therefore, our findings suggest F-v profiling is acceptable to differentiate between sex and positional demands in club-based field hockey players. Furthermore, it is recommended field hockey players explore a range of loads and exercises across the F-v continuum through on-field and gym-based field hockey strength and conditioning practices to account for sex and positional mechanical differences.

The effects of being told you are in the intervention group on training results: a pilot study

Little is known about the placebo effects when comparing training interventions. Consequently, we investigated whether subjects being told they are in the intervention group get better training results compared to subjects being told they are in a control group. Forty athletes (male: n = 31, female: n = 9) completed a 10-week training intervention (age: 22 ± 4 years, height: 183 ± 10 cm, and body mass: 84 ± 15 kg). After randomization, the participants were either told that the training program they got was individualized based on their force-velocity profile (Placebo), or that they were in the control group (Control). However, both groups were doing the same workouts. Measurements included countermovement jump (CMJ), 20-m sprint, one-repetition maximum (1RM) back-squat, a leg-press test, ultrasonography of muscle-thickness (m. rectus femoris), and a questionnaire (Stanford Expectations of Treatment Scale) (Younger et al. in Clin Trials 9(6):767-776, 2012). Placebo increased 1RM squat more than Control (5.7 ± 6.4% vs 0.9 ± 6.9%, [0.26 vs 0.02 Effect Size], Bayes Factor: 5.1 [BF₁₀], p = 0.025). Placebo had slightly higher adherence compared to control (82 ± 18% vs 72 ± 13%, BF₁₀: 2.0, p = 0.08). Importantly, the difference in the 1RM squat was significant after controlling for adherence (p = 0.013). No significant differences were observed in the other measurements. The results suggest that the placebo effect may be meaningful in sports and exercise training interventions. It is possible that ineffective training interventions will go unquestioned in the absence of placebo-controlled trials.

Measurement Agreement Between Samozino's Method and Force Plate Force-Velocity Profiles During Barbell and Hexbar Countermovement Jumps

ABSTRACT

Hicks, DS, Drummond, C, and Williams, KJ. Measurement agreement between Samozino's method and force plate force-velocity profiles during barbell and hexbar countermovement jumps. J Strength Cond Res 36(12): 3290-3300, 2022-This study aimed to measure agreement between using Samozino's method and force plates to determine mean force, velocity, and power during unloaded and loaded barbell and hexbar countermovement jumps. Twenty-one subjects performed countermovement jumps against incremental loads using both loading conditions. Ground reaction force was recorded using a dual-force plate system (1,000 Hz) and used as the criterion method to compare with Samozino's method. Reliability and validity was determined by intraclass correlation coefficients (ICCs), coefficient of variation (CV), limits of agreement plots, and least products regression analysis. Samozino's method provided acceptable levels of reliability for mean force, velocity, and power (ICC > 0.90, CV% < 5.5) across both loading conditions. Limits of agreement analysis showed the mean bias was 2.7, 15.4, and 7.2% during barbell countermovement jumps and 1.8, 12.4, and 5.0% during hexbar countermovement jumps for mean force, velocity, and power, respectively. Based on these findings, Samozino's method not only is reliable when measuring mean force, velocity, and power during loaded and unloaded barbell and hexbar countermovement jumps but also identifies limitations regarding concurrent validity compared with the gold standard. Across loading conditions, Samozino's method overestimated mean force (0.5-4.5%) and underestimated mean velocity (11.81-16.78%) and mean power (2.26-7.85%) compared with the force plates. Because of fixed and proportional bias between criterion and predictor, the results do not support the use of Samozino's method to measure mean force, velocity, and power. Therefore, it is not recommended for practitioners to use Samozino's method to estimate mechanical variables during loaded and unloaded countermovement jump actions using a barbell and hexbar.

Isokinetic Leg-Press Power-Force-Velocity Profiles Are Reliable in Male and Female Elite Athletes but Not Interchangeable With Vertical Jump Profiles

PURPOSE

To evaluate the test-retest reliability of isokinetic leg-press power-force-velocity profile (P-F-v) parameters in male and female elite athletes. In addition, we determined the concurrent validity of leg-press against squat-jump (SJ) P-F-v parameters in task-experienced athletes.

METHODS

For test-retest reliability, 22 female and 23 male elite athletes (22.3 [4.1] y) with different sporting backgrounds conducted 3 isokinetic leg-press test sessions over 3 consecutive weeks. The testing consisted of bilateral leg extensions at isokinetic velocities of 0.1, 0.3, 0.7, and 1.2 m·s-1. For concurrent validity, 13 ski jumpers (20.3 [3.3] y) were recruited to perform the isokinetic leg-press and SJ P-F-v profile tests using 5 predefined loading conditions of 0%, +20%, +40%, +60%, and +80% of body mass.

RESULTS

Relative and absolute reliability were acceptable for female (intraclass correlation coefficient ≥.87 and coefficient of variation ≤6.5%) and male (intraclass correlation coefficient ≥.89 and coefficient of variation ≤5.7%) elite athletes. In contrast, concurrent validity was insufficient, with correlations ranging from -.26 to .69 between isokinetic and SJ P-F-v parameters.

CONCLUSION

Irrespective of sex, isokinetic leg-press P-F-v profiles provide reliable parameters. However, leg-press P-F-v profiles do not serve as a valid substitute for SJ P-F-v profiles. P-F-v parameter magnitudes are likely dependent on the constraints of the tested movement and testing device.

A novel equation that incorporates the linear and hyperbolic nature of the force-velocity relationship in lower and upper limb exercises

The purpose of this study is to provide a force-velocity (F-V) equation that combines a linear and a hyperbolic region, and to compare its derived results to those obtained from linear equations. A total of 10 cross-training athletes and 14 recreationally resistance-trained young men were assessed in the unilateral leg press (LP) and bilateral bench press (BP) exercises, respectively. F-V data were recorded using a force plate and a linear encoder. Estimated maximum isometric force (F₀), maximum muscle power (P_max), and maximum unloaded velocity (V₀) were calculated using a hybrid (linear and hyperbolic) equation and three different linear equations: one derived from the hybrid equation (linear_hyb), one applied to data from 0 to 100% of F₀ (linear_0-100), and one applied to data from 45 to 100% of F₀ (linear_45-100). The hybrid equation presented the best fit to the recorded data (R² = 0.996 and 0.998). Compared to the results derived from the hybrid equation in the LP, significant differences were observed in F₀ derived from linear_0-100; V₀ derived from linear_hyb, linear_0-100 and linear_45-100; and P_max derived from linear_hyb and linear_45-100 (all p < 0.05). For the BP, compared to the hybrid equation, significant differences were found in F₀ derived from linear_0-100; and V₀ and P_max derived from linear_hyb, linear_0-100 and linear_45-100 (all p < 0.05). An F-V equation combining a linear and a hyperbolic region showed to fit adequately recorded F-V data from ~ 20 to 100% of F₀, and overcame the limitations shown by linear equations while providing relevant results.

Strength and Power Testing of Athletes: Associations of Common Assessments Over Time

PURPOSE

This study examined the associations among common assessments for measuring strength and power in the lower body of high-performing athletes, including both cross-sectional and longitudinal data.

METHODS

A total of 100 participants, including both male (n = 83) and female (n = 17) athletes (21 [4] y, 182 [9] cm, 78 [12] kg), were recruited for the study using a multicenter approach. The participants underwent physical testing 4 times. The first 2 sessions (1 and 2) were separated by ∼1 week, followed by a period of 2 to 6 months, whereas the last 2 sessions (3 and 4) were also separated by ∼1 week. The test protocol consisted of squat jumps, countermovement jumps, jump and reach, 30-m sprint, 1-repetition-maximum squat, sprint cycling, and a leg-press test.

RESULTS

There were generally acceptable correlations among all performance measures. Variables from the countermovement jumps and leg-press power correlated strongly with all performance assessments (r = .52-.79), while variables from sprint running and squat-jump power displayed more incoherent correlations (r = .21-.82). For changes over time, the correlations were mostly strong, albeit systematically weaker than for cross-sectional measures.

CONCLUSIONS

The associations observed among the performance assessments seem to be consistent for both cross-sectional data and longitudinal change scores. The weaker correlations for change scores are most likely mainly caused by lower between-subjects variations in the change scores than for the cross-sectional data. The present study provides novel information, helping researchers and practitioners to better interpret the relationships across common performance assessment methods.

Effectiveness of individualized training based on force-velocity profiling on physical function in older men

The study aimed to investigate the effectiveness of an individualized power training program based on force–velocity (FV) profiling on physical function, muscle morphology, and neuromuscular adaptations in older men. Forty‐nine healthy men (68 ± 5 years) completed a 10‐week training period to enhance muscular power. They were randomized to either a generic power training group (GPT) or an individualized power training group (IPT). Unlike generic training, individualized training was based on low‐ or high‐resistance exercises, from an initial force–velocity profile. Lower‐limb FV profile was measured in a pneumatic leg‐press, and physical function was assessed as timed up‐and‐go time (TUG), sit‐to‐stand power, grip strength, and stair‐climbing time (loaded [20kg] and unloaded). Vastus lateralis morphology was measured with ultrasonography. Rate of force development (RFD) and rate of myoelectric activity (RMA) were measured during an isometric knee extension. The GPT group improved loaded stair‐climbing time (6.3 ± 3.8 vs. 2.3% ± 7.3%, p = 0.04) more than IPT. Both groups improved stair‐climbing time, sit to stand, and leg press power, grip strength, muscle thickness, pennation angle, fascicle length, and RMA from baseline (p < 0.05). Only GPT increased loaded stair‐climbing time and RFD (p < 0.05). An individualized power training program based on FV profiling did not improve physical function to a greater degree than generic power training. A generic power training approach combining both heavy and low loads might be advantageous through eliciting both force‐ and velocity‐related neuromuscular adaptions with a concomitant increase in muscular power and physical function in older men.

Sex influence on muscle synergies in a ballistic force-velocity test during the delayed recovery phase after a graded endurance run

The acute and delayed phases of the functional recovery pattern after running exercise have been studied mainly in men. However, it seems that women are less fatigable and/or recover faster than men, at least when tested in isometric condition. After a 20 km graded running race, the influence of sex on the delayed phase of recovery at 2-4 days was studied using a horizontal ballistic force-velocity test. Nine female and height male recreational runners performed maximal concentric push-offs at four load levels a week before the race (PRE), 2 and 4 days (D2 and D4) later. Ground reaction forces and surface electromyographic (EMG) activity from 8 major lower limb muscles were recorded. For each session, the mechanical force-velocity-power profile (i.e. theoretical maximal values of force ( F ¯ 0), velocity ( V ¯ 0), and power ( P ¯ max)) was computed. Mean EMG activity of each recorded muscle and muscle synergies (three for both men and women) were extracted. Independently of the testing sessions, men and women differed regarding the solicitation of the bi-articular thigh muscles (medial hamstring muscles and rectus femoris). At mid-push-off, female made use of more evenly distributed lower limb muscle activities than men. No fatigue effect was found for both sexes when looking at the mean ground reaction forces. However, the force-velocity profile varied by sex throughout the recovery: only men showed a decrease of both V ¯ 0 (p < 0.05) and P ¯ max (p < 0.01) at D2 compared to PRE. Vastus medialis activity was reduced for both men and women up to D4, but only male synergies were impacted at D2: the center of activity of the first and second synergies was reached later. This study suggests that women could recover earlier in a dynamic multi-joint task and that sex-specific organization of muscle synergies may have contributed to their different recovery times after such a race.

Strength and Power Testing of Athletes: A Multicenter Study of Test-Retest Reliability

PURPOSE

This study examined the test-retest reliability of common assessments for measuring strength and power of the lower body in high-performing athletes.

METHODS

A total of 100 participants, including both male (n = 83) and female (n = 17) athletes (21 [4] y, 182 [9] cm, and 78 [12] kg), were recruited for this study, using a multicenter approach. The participants underwent physical testing 4 times. The first 2 sessions (1 and 2) were separated by ∼1 week, followed by a period of 2 to 6 months, whereas the last 2 sessions (3 and 4) were again separated by ∼1 week. The test protocol consisted of squat jumps, countermovement jumps, jump and reach, 30-m sprint, 1-repetition-maximum squat, sprint cycling, and a leg-press test.

RESULTS

The typical error (%) ranged from 1.3% to 8.5% for all assessments. The change in means ranged from -1.5% to 2.5% for all assessments, whereas the interclass correlation coefficient ranged from .85 to .97. The smallest worthwhile change (0.2 of baseline SD) ranged from 1.2% to 5.0%. The ratio between the typical error (%) and the smallest worthwhile change (%) ranged from 0.5 to 1.2. When observing the reliability across testing centers, considerable differences in reliability were observed (typical error [%] ratio: 0.44-1.44).

CONCLUSIONS

Most of the included assessments can be used with confidence by researchers and coaches to measure strength and power in athletes. Our results highlight the importance of controlling testing reliability at each testing center and not relying on data from others, despite having applied the same protocol.

Power–Force–Velocity Profiling as a Function of Used Loads and Task Experience

Purpose: To evaluate cohort-specific reliability and concurrent validity of 3 different vertical power–force–velocity (P–F–v) profiles to determine force, velocity, maximal power, and the slope of the force–velocity relationship using squat jumps. Methods: Fifteen male sport students and 15 elite ski jumping athletes (male = 11; female = 4) conducted 2 block-randomized test–retest sessions with 5-point-method or 2-point-method loading conditions. A third P–F–v profile was established by excluding the data point most declining the coefficient of determination (r2) of the 5-point method. Results: Acceptable absolute and relative reliability were found across methods in ski jumping athletes (intraclass correlation coefficient [ICC] ≥ .79, coefficient of variation [CV] ≤ 6.2%). However, force values were significantly lower in the retest (≤2.1%, d ≤ 0.75). In contrast, no systematic differences (P ≥ .461), but unacceptable absolute and relative reliability, were found in sport students (ICC ≥ .63, CV ≤ 14.8%). The P–F–v parameters of the different collecting and evaluating approaches yielded high to excellent correlations (ski jumping athletes: r ≥ .64; sport students: r ≥ .61), but maximal power (≤4.6%) and velocity (<6.2%,) values of sport students revealed significant differences. Conclusion: The similarity of P–F–v testing and basic ski jumping training daily exercises seems to be more significant to obtain reliable force–velocity parameters than the methodological approach. Accordingly, P–F–v profiles seem to be reliable with the proposed methods only in highly task-experienced athletes but not in less task-experienced cohorts like sport students.

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.

Validity of a simple sit-to-stand method for assessing force-velocity profile in older adults

BACKGROUND

Lower limb muscle strength is an important determinant of physical function in older adults. However, its measure in clinical settings is limited because of the requirement for large-scale and costly equipment. A new simple protocol based on sit-to-stand test (STS) is developed to measure force velocity (F-v) and power velocity (P-v) profile in the community-dwelling older adults.

OBJECTIVE

The objective of this study was to assess the validity of this new methodology for measuring F-v and P-v profile compared to the gold standard isokinetic BIODEX.

PARTICIPANTS

46 older people aged 65-85 years (M = 73.7; SD = 7.7).

METHODS

F-v and P-v profiles were assessed in participants on their dominant leg. The concurrent validity of STS was tested using Spearman's rank correlation coefficient and Passing Bablok: maximal power output Pmax, optimal velocity and force Vopt and Fopt, maximal force at null velocity F0, maximal unloaded velocity V0 and coefficient of F-v (S_FV) and P-v equation (a_poly, b_poly).

RESULTS

No proportional difference for F0 and b_poly and a low significant correlation for Pmax (r = 0.314), S_fv (r = 0.229), a_poly (r = 0.335) and b_poly (r = 0.226) whereas the other parameters were non correlated significantly.

CONCLUSION

STS method is moderately reliable on force and power parameters whereas further improvements are needing for velocity parameters. However, its feasibility, portability and lower cost compared to other methods makes it very affordable in clinical context and will allow easy investigation of aging population.

Should we individualize training based on force-velocity profiling to improve physical performance in athletes?

The present study aimed to examine the effectiveness of an individualized training program based on force-velocity (FV) profiling on jumping, sprinting, strength, and power in athletes. Forty national level team sport athletes (20 ± 4years, 83 ± 13 kg) from ice-hockey, handball, and soccer completed a 10-week training intervention. A theoretical optimal squat jump (SJ)-FV-profile was calculated from SJ with five different loads (0, 20, 40, 60, and 80 kg). Based on their initial FV-profile, athletes were randomized to train toward, away, or irrespective (balanced training) of their initial theoretical optimal FV-profile. The training content was matched between groups in terms of set x repetitions but varied in relative loading to target the different aspects of the FV-profile. The athletes performed 10 and 30 m sprints, SJ and countermovement jump (CMJ), 1 repetition maximum (1RM) squat, and a leg-press power test before and after the intervention. There were no significant group differences for any of the performance measures. Trivial to small changes in 1RM squat (2.9%, 4.6%, and 6.5%), 10 m sprint time (1.0%, -0.9%, and -1.7%), 30 m sprint time (0.9%, -0.6%, and -0.4%), CMJ height (4.3%, 3.1%, and 5.7%), SJ height (4.8%, 3.7%, and 5.7%), and leg-press power (6.7%, 4.2%, and 2.9%) were observed in the groups training toward, away, or irrespective of their initial theoretical optimal FV-profile, respectively. Changes toward the optimal SJ-FV-profile were negatively correlated with changes in SJ height (r = -0.49, p < 0.001). Changes in SJ-power were positively related to changes in SJ-height (r = 0.88, p < 0.001) and CMJ-height (r = 0.32, p = 0.044), but unrelated to changes in 10 m (r = -0.02, p = 0.921) and 30 m sprint time (r = -0.01, p = 0.974). The results from this study do not support the efficacy of individualized training based on SJ-FV profiling.

Validity of Force-Velocity Profiling Assessed With a Pneumatic Leg Press Device

PURPOSE

The aim of this study was to examine the concurrent validity of force-velocity (FV) variables assessed across 5 Keiser leg press devices.

METHODS

A linear encoder and 2 independent force plates (MuscleLab devices) were mounted on each of the 5 leg press devices. A total of 997 leg press executions, covering a wide range of forces and velocities, were performed by 14 participants (29 [7] y, 181 [5] cm, 82 [8] kg) across the 5 devices. Average and peak force, velocity, and power values were collected simultaneously from the Keiser and MuscleLab devices for each repetition. Individual FV profiles were fitted to each participant from peak and average force and velocity measurements. Theoretical maximal force, velocity, and power were deduced from the FV relationship.

RESULTS

Average and peak force and velocity had a coefficient of variation of 1.5% to 8.6%, near-perfect correlations (.994-.999), and a systematic bias of 0.7% to 7.1% when compared with reference measurements. Average and peak power showed larger coefficient of variations (11.6% and 17.2%), despite excellent correlations (.977 and .952), and trivial to small biases (3.9% and 8.4%). Extrapolated FV variables showed near-perfect correlations (.983-.997) with trivial to small biases (1.4%-11.2%) and a coefficient of variation of 1.4% to 5.9%.

CONCLUSIONS

The Keiser leg press device can obtain valid measurements over a wide range of forces and velocities across different devices. To accurately measure power, theoretical maximal power calculated from the FV profile is recommended over average and peak power values from single repetitions, due to the lower random error observed for theoretical maximal power.

Reliability of Sprint Force-Velocity-Power Profiles Obtained with KiSprint System

This study aimed to assess the within- and between-session reliability of the KiSprint system for determining force-velocity-power (FVP) profiling during sprint running. Thirty (23 males, 7 females; 18.7 ± 2.6 years;) young high-level sprinters performed maximal effort sprints in two sessions separated by one week. Split times (5, 10, 20 and 30 m), which were recorded with a laser distance meter (a component of the KiSprint system), were used to determine the horizontal FVP profile using the Samozino's field-based method. This method assesses the FVP relationships through estimates of the step-averaged ground reaction forces in sagittal plane during sprint acceleration using only anthropometric and spatiotemporal (split times) data. We also calculated the maximal theoretical power, force and velocity capabilities and the slope of the FV relationship, the maximal ratio of horizontal-to-resultant force (RF), and the decrease in the RF (D_RF). Overall, the results showed moderate or good to excellent within- and between-session reliability for all variables (ICC > 0.75; CV < 10 %), with the exception of FV slope and D_RF that showed low relative reliability (ICC = 0.47-0.48 within session, 0.31-0.33 between-session) and unacceptable between-session absolute reliability values (CV = 10.9-11.1 %). Future studies are needed to optimize the protocol in order to maximize the reliability of the FVP variables, especially when practitioners are interested in the FV slope and D_RF. In summary, our results question the utility of the sprint-based FVP profiling for individualized training prescription, since the reliability of the FV slope and D RF variables is highly questionable.