A Resisted Sprint Improves Rate of Force Development During a 20-m Sprint in Athletes

The effect of different resistance and assistance loads on 30-m sprint kinematics

Resisted sprint and assisted sprint are the two main types of training methods used by athletes in sprint training, so optimizing resisted sprint training and assisted sprint training process is beneficial for improving athletes' sprint performance. Kinematics is the most intuitive parameter that reflects the quality of training during running process, and it is particularly important to analyze the gait of athletes during resisted and assisted sprint process. Therefore, this paper investigates the effects of resisted and assisted sprint on the sprint kinematics of sprinters in the first 30 meters to demonstrate the targeted effects of resisted and assisted sprint training. The experimental results show that compared to the unloaded running, male collegiate sprinters increase their total step count, decrease their step length, increase their step time, increase their contact time, whereas have almost no change in the flight time when performing the 30-m resisted sprint. Male collegiate sprinters decrease their total step count, increase their step length, increase their step time, decrease their contact time and increase their flight time, when performing the 30-m assisted sprint. In addition, it is found that resisted sprint training is beneficial for improving the athletes' power and explosiveness during the acceleration phase, thereby improving acceleration ability. However, prolonged and frequent resisted sprint training may reduce the step length and step frequency of athletes. Assisted sprint training is beneficial for shortening the contact time of athletes, improving their step length and flight time, and enabling them to overspeed, thereby increasing their maximum speed ability.

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.

Reliability of a semi-tethered front crawl sprint performance test in adolescent swimmers

This study aimed to evaluate the test-retest reliability of a sprint performance test with semi-tethered front crawl swimming to indirectly assess the current potential to perform at maximal anaerobic effort in adolescent swimmers. Eight adolescent swimmers participated in this study (gender: females (n = 4) aged 13.0 ± 0.8 years, body height 1.6 ± 0.0 m, body mass 50.1 ± 4.5 kg; and males (n = 4) aged 13.3 ± 1.3 years, body height 1.7 ± 0.1 m, body mass 59.0 ± 8.2 kg. The testing protocol consisted of two trials of 25 m semi-tethered front crawl swimming with maximal effort and with 1 kg resisted isotonic load. Velocity data were recorded automatically by the 1080 Sprint device for 15 m (between 3 m and 18 m). The Fast Fourier Transform algorithm filtered raw instantaneous swimming velocity data in distance (time) function. A third-degree polynomial was used to extract the individual velocity profile, from which the following variables were chosen for test-retest reliability and the assessment of sprint performance: ttrial15, vmax, vmin, tvto max, tvat max, Dto vmax, Dat vmax, fatigue index. Parameters such as vmax, vmin, and ttrial15 were estimated from swimming velocity profiles and considered as reliable. The CV showed low variance <5%; while ICC2,1 demonstrated respectively good (ICC2,1: 0.88), very good (ICC2,1: 0.95), and excellent (ICC2,1: 0.98) rate of relative reliability; and the Bland-Altman index revealed an acceptable agreement (LoA ≤5%) between two measurements. The sprint performance test based on semi-tethered front crawl swimming confirmed that ttrial15, vmax, and vmin were reliable variables to indirectly indicate a potential to perform the maximal anaerobic effort among adolescent swimmers. The evaluation of the swimming velocity profiles allows coaches to monitor the adaptive changes of performance during the training process.

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.

The Acute Effects of Heavy Sled Towing on Acceleration Performance and Sprint Mechanical and Kinematic Characteristics

The aim of this study was to investigate the effects of heavy sled towing using a load corresponding to a 50% reduction of the individual theoretical maximal velocity (ranged 57–73% body mass) on subsequent 30 m sprint performance, velocity, mechanical variables (theoretical maximal horizontal force, theoretical maximal horizontal velocity, maximal mechanical power output, slope of the linear force–velocity relationship, maximal ratio of horizontal to total force and decrease in the ratio of horizontal to total force) and kinematics (step length and rate, contact and flight time). Twelve (n = 5 males and n = 7 females) junior running sprinters performed an exercise under two intervention conditions in random order. The experimental condition (EXP) consisted of two repetitions of 20 m resisted sprints, while in the control condition (CON), an active recovery was performed. Before (baseline) and after (post) the interventions, the 30 m sprint tests were analyzed. Participants showed faster 30 m sprint times following sled towing (p = 0.005). Running velocity was significantly higher in EXP at 5–10 m (p = 0.032), 10–15 m (p = 0.006), 15–20 m (p = 0.004), 20–25 m (p = 0.015) and 25–30 m (p = 0.014). No significant changes in sprint mechanical variables and kinematics were observed. Heavy sled towing appeared to be an effective post-activation potentiation stimulus to acutely enhance sprint acceleration performance with no effect on the athlete’s running technique.

Comparison of development of step-kinematics of assisted 60 m sprints with different pulling forces between experienced male and female sprinters

The purpose of this study was to compare step-by-step kinematics of normal and assisted 60 m sprints with different loads in experienced sprinters. Step-by-step kinematics were measured using inertial measuring units (IMU) integrated with a 3-axis gyroscope and a laser gun in 24 national level male and female sprinters during a normal 60 m sprint and sprints with a 3, 4, and 5 kg pulling force. The main findings were that using increasing assisted loads resulted in faster 60 m times, as a result of higher step velocity mainly caused by longer step lengths in both genders and by shorter contact times in women. Men had longer step lengths, longer contact times, and shorter flight times than women. However, the assisted loads had a greater effect on women than on men, as shown by their larger decrease in sprint times. These time differences in gender were the result of more and longer duration increases in maximal step velocity with increasing assisted loads for women (70-80% of distance) than men (65-70% of distance). This was mainly caused by shorter contact times, and by more increased step lengths in women compared to men. In terms of practical application, it is notable that employing this approach, when using assisted loads can help athletes to reach higher step velocities and hold this for longer, which may be a training impulse to move the speed barrier upwards.

Relationships Between Sprinting, Broad Jump, and Vertical Jump Kinetics Are Limited in Elite, Collegiate Football Athletes

ABSTRACT

Boone, JB, VanDusseldorp, TA, Feito, Y, and Mangine, GT. Relationships between sprinting, broad jump, and vertical jump kinetics are limited in elite, collegiate football athletes. J Strength Cond Res 35(5): 1306-1316, 2021-To evaluate the relationships and agreement in kinetics measured during a 10-yd sprint, a standing broad jump (SBJ), and a vertical jump (VJ), 73 collegiate football players (22.3 ± 0.8 years, 188 ± 7 cm, 113 ± 23 kg) volunteered for this cross-sectional study over a 3-year period. At the beginning of each athlete's off-season training phase and after a standard warm-up, each athlete completed 2-3 maximal trials of each test while tethered to a robotic, cable-resistance device (10-yd sprint and SBJ) or a linear position transducer (VJ alone). Force (N), velocity (m·s-1), and power (W) were measured during the first 2 steps, acceleration phase (units·step-1), and entire 10-yd sprint, and the entire SBJ and VJ. Spearman and partial correlations (controlling for stature) revealed small-to-moderate relationships (r = -0.30 to -0.34) between the second sprinting step and VJ force. Small negative relationships were also noted between sprinting and VJ force and power, but not when controlling for height. Agreement was determined by examining relationships between the differences in and averaged kinetics measured on each test. Trivial-to-small relationships (r < 0.29) were observed between sprinting (first step and 10-yd) and VJ velocity, and between VJ and SBJ velocity, although coefficient of variation (CV) ranged between 64 and 104%. All other relationships ranged from moderate-to-practically perfect with CVs exceeding 500%. Although some relationships exist between sprinting and jumping kinetics, their agreement is variable. These data suggest that coaches and athletes should not use one of these assessments in place of, or to predict performance in, the other assessments.

The Effects of Resisted Post-Activation Sprint Performance Enhancement in Elite Female Sprinters

Considering the effectiveness of resisted sprint training, and the acute enhancement of sprinting performance through locomotor post-activation performance enhancement, the main objective of the research was to determine the acute effects of resisted activation with loads of 5, 10, and 15% body mass on sprint and flying start sprint performance in elite female sprinters using resisted drag technology system. Ten elite female sprinters (age: 23.2 ± 5.4 years, body mass: 54.2 ± 6.1 kg, height: 167.4 ± 7.3 cm, personal best for 100 m: 12.05 ± 0.56 s, and for 400 m: 53.17 ± 2.76 s) performed two unresisted 20-m sprints (from a crouched and flying start) before and after a single resisted sprint loaded with 5, 10, or 15% body mass to verify the effectiveness of the activation stimulus. Compared with pre-activation, Friedman tests showed that peak velocity increased by 1.6 ± 2.2% [effect size (ES) = 0.66], 2.3 ± 1.5% (ES = 1.33), and 0.2 ± 1% (ES = 0.09), as well as peak force by 2.8 ± 2.1% (ES = 0.49), 3.5 ± 2.3% (ES = 1), and 0.5 ± 2.4% (ES = 0.14), concomitant with a significant decreased in sprint time by −0.5 ± 1.2% (ES = −0.07), −2.5 ± 1.3% (ES = −0.64), and −1 ± 1.4% (ES = −0.36) for the 5, 10, and 15% body mass post-activation, respectively (p < 0.001; for all). Furthermore, the ANOVA showed that peak power increased by 2.9 ± 2.3% (ES = 0.61), 3.8 ± 2.2% (ES = 1.05), and 2 ± 7.1% (ES = 0.22) for the 5, 10, and 15% body mass resisted-conditioning activity, respectively, with no difference between the three conditions (p = 0.003 main effect time, no interaction). Moreover, compared with the 5 and 15% body mass trials [−1.5 ± 2% (ES = −0.44), −0.8 ± 0.8% (ES = −0.44), respectively], the ANOVA showed that flying start sprint time significantly decreased by −4.3 ± 1.1% (ES = −1.25) (p < 0.001, interaction effect) after a 10% body mass resisted-conditioning activity. The results of this study indicated that resisted sprints acutely enhance sprint performance; however, their effectiveness depends on the applied load. A single resisted sprint using 10% body mass is effective at inducing a potentiating effect on subsequent 20-m flying start sprint performance in elite female sprinters. Therefore, keeping in mind the optimal load, it is recommended to perform resisted sprints as a conditioning activation when seeking to acutely enhance 20-m flying start sprint performance in these athletes.

Effect of active resisted 30 m sprints upon step and joint kinematics and muscle activity in experienced male and female sprinters

This study compared the kinematics (step and joint) and muscle activity of unresisted and active resisted 30 m sprints with different loads (10-40% body mass) in experienced male and female sprinters. Step kinematics were measured using a laser gun and contact mat in 28 male and female participants during unresisted 30 m sprint, and sprints with 10-40% of body mass (BM) active resistance, while peak angular velocities of lower limb was measured, together with muscle activation of nine muscles. Increased resisted loads resulted in slower 30 m times, as a result of lower step velocity mainly caused by shorter step lengths and frequencies, flight times and longer contact times, with a greater effect on women than on men. These step kinematic differences, due to increasing load were accompanied with lower peak joint movements. However, gender differences were only found for peak plantar flexion with unresisted and 10% BM resisted sprints. Furthermore, increasing load decreased calf and hamstring muscles activity, while medial vastus activity increased. Based upon these findings, it was concluded that when introducing active resisted sprints, women should sprint with approximately 10% less active loads than men to have equal step and joint kinematics development over the sprint distance.