Comparison of step-by-step kinematics of resisted, assisted and unloaded 20-m sprint runs

Impact of Hydraulic Resistance on Spatiotemporal Characteristics of Initial Six Steps When Sprinting Under Varying Loads

Background: Evaluations of the usability of hydraulic resistance for resisted sprint-training purposes remains rare. Thus, this study compared step-by-step changes in spatiotemporal characteristics during the first 10 m of sprints with varying hydraulic resistance loads. Methods: Fourteen male athletes performed 20 m sprints under minimal (10 N, considered as normal sprint), moderate (100 N), and heavy (150 N) hydraulic resistance loads. Split times at 10 m, contact time (CT), step length (SL), flight time, and step speed (SS) from the first to the sixth step were measured. A two-way repeated measures ANOVA (load × step) and a one-way ANOVA (load) with post hoc comparisons were used to assess the effects on spatiotemporal characteristics and split times, respectively. Results: Under higher loads, the 10 m times were significantly longer (η2 = 0.79). The CT, SL, and SS varied significantly from step to step within all loads (η2 = 0.45, 0.41, and 0.54, respectively). The CT, SL, and SS of the first, fourth, fifth, and sixth steps of normal sprint differed significantly from most steps under moderate and heavy load (Cohen's d = -3.09 to 5.39). In contrast, the smallest differences were observed between the second and third step of normal sprint and second to sixth steps under heavy load (Cohen's d = -0.67 to 1.32, and -0.71 to 1.38, respectively). Conclusions: At the same load settings, a hydraulic resistance device induces changes in step characteristics comparable with those of other motorized devices and is therefore a viable option for resisted sprint training. If the goal of the training is to replicate the steps of the initial sprint acceleration phase, ~150 N of hydraulic resistance would be optimal.

The Longitudinal Effects of Resisted and Assisted Sprint Training on Sprint Kinematics, Acceleration, and Maximum Velocity: A Systematic Review and Meta-analysis

BACKGROUND

Sprinting is important for both individual and team sports, and enhancing performance is often done through resisted, assisted, or combined sprint training. However, the effectiveness of these methods compared to traditional sprint training remains inconclusive. The objective of this review with meta-analysis was to review the current literature on intervention studies analyzing the effects of resisted, assisted, and combined (resisted-assisted) training on sprint kinematics and performance in terms of acceleration and maximum velocity.

METHODS

A literature search was conducted using SPORTDiscus up to and including April 19, 2023. The following eligibility criteria were applied: (1) a longitudinal study over a minimum of four weeks; (2) studies using resistance (sleds, parachutes, uphill slope, towing devices) or assistance (towing devices, downhill slope), or a combination of both; (3) a main intervention focused on resisted or assisted training, or a combination of both; (4) measurement of maximum velocity, acceleration measured in (s) with a minimum distance of 10-m, or kinematic changes such as step frequency, ground contact time, flight time, and step length; and (5) peer-reviewed studies.

RESULTS

Twenty-one studies were included in this review with meta-analysis. Kinematic changes, changes in acceleration, and changes in maximum velocity were analyzed. Only resisted sprint training was associated with a significant improvement in 10-m acceleration compared to normal (i.e. without assistance or resistance) sprinting (Z = 2.01, P = 0.04). With resisted, assisted and combined sprint training no significant changes in kinematics, 20-m times or maximum velocity were found when compared to normal sprint training. However, in the within group, effect sizes resisted sprint training had a moderate effect on 10-m times. A moderate effect on ground contact time, step frequency, 10-and 20-meter time after assisted sprint training was found, while combined sprint training had a moderate effect on maximum velocity.

CONCLUSION

Resisted sprint training seems to be effective for improving acceleration ability, with significant decreases in the 10-m times. There were no other significant findings, suggesting that normal sprinting yields the same change in 20-m times, kinematics and maximum velocity as resisted, assisted and combined sprint training. However, moderate effect sizes using these different training methods were found, which may suggest that the different training forms could be useful for improving different parts of the sprint and changing the kinematics. Combination (uphill-downhill) sprint training seems to be effective at improving maximum velocity, while assisted sprint training was the most effective training to increase step frequency, which can affect sprint performance positively. However, more studies, especially in assisted sprints, need to be conducted to determine the full effect of these training forms.

Reliability and validity of sprint performance using the Alex7 motorized device

Introduction

Advancements in technology have recently made it possible to implement effective training solutions across different environmental conditions. This study evaluated the reliability and validity of measures obtained from the innovative motorized device, Alex7 (Inosportas, Lithuania), and differences in speed and kinematic characteristics between resisted and assisted sprinting in young football players.

Methods

Twenty-seven male athletes (mean age: 16.5 ± 0.8 years; height: 179.5 ± 6.9 cm; body weight: 67.7 ± 8.3 kg) each performed 30-m sprints twice under three different conditions: regular, resisted, and assisted sprinting. The Alex7 device provided the assistance and resistance during sprints. Results were compared with those from Witty timing gates. Ground contact time, flight time, stride length, and pace were measured using the OptoJump system. Reliability was assessed using two-way mixed intraclass correlation coefficients (ICCs) for single measures, the standard error of the mean (SEM), and the coefficient of variation (CV). Pearson's correlation coefficient determined the associations between Alex7 and Witty timing systems. Criterion-referenced validity was based on the mean difference and CV. Systematic bias was determined by limits of agreement using Bland-Altman analysis.

Results

Running times obtained using the Alex7 equipment exhibited good to excellent test-retest reliability between sessions (ICC, 0.83-0.94) and good to excellent correlation (Pearson's r = 0.88-0.98) between the Alex7 and Witty systems in both assisted and resisted running conditions. However, the Alex7 device consistently produced longer running times than the Witty device (up to 0.16 s difference, p < 0.001). The different running conditions produced substantial variations in kinematic variables, such as stride length, ground contact time, and running speed (p < 0.001 for all), but the effects on flight time and running pace were smaller.

Discussion

The Alex7 device shows high reliability for creating resisted and assisted running conditions for young football players. However, it tends to overestimate running time, necessitating caution when assessing the time parameters.

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.

Speed Training Practices of Brazilian Olympic Sprint and Jump Coaches: Toward a Deeper Understanding of Their Choices and Insights (Part II)

This is the second article in a three-article collection regarding the plyometric, speed, and resistance training practices of Brazilian Olympic sprint and jump coaches. Here, we list and describe six out of the ten speed training methods most commonly employed by these experts to enhance the sprinting capabilities of their athletes. Maximum speed sprinting, form running, resisted sprinting, overspeed running, uphill and downhill running, and sport-specific movement methods are critically examined with reference to their potential application in different sport contexts. In an era when sprint speed is of critical importance across numerous sports, practitioners can employ the methods outlined here to design efficient training programs for their athletes.

Transition from upright to greater forward lean posture predicts faster acceleration during the run-to-sprint transition

BACKGROUND

Forward body lean and greater horizontal ground reaction force have been associated with being able to accelerate during running. However, kinematic features which may predict acceleration during the run-to-sprint transition have not been determined. The purpose of this study was to determine which kinematic changes occur in recreationally active adults and which kinematic features may predict greater acceleration during the run-to-sprint transition.

METHODS

Forty-seven healthy adults completed straight line running along a 30 m track by running in at ∼4 m.s-1. A minimum of 20 trials were completed, with 25 % triggering a light to signal the participant to accelerate as fast as possible. Step characteristics (velocity, length, duration, cadence) and kinematics (neck, trunk, hip, knee and ankle angles and excursions) were determined using a radar gun and inertial measurement units, respectively. ANOVA was used to determine the step-to-step differences and a multiple linear regression was used to determine the relationship between kinematics and acceleration.

RESULTS

There was an initial increase in trunk flexion angle during early acceleration (p < 0.001) with knee joint excursion significantly lower (p < 0.001) during loading and propulsion compared to the run-in steps. Greater acceleration was predicted using a stepwise linear regression by five variables including less neck flexion excursion and trunk flexion angle during swing of the 1st step, greater trunk flexion angle and extension excursion of the neck during propulsion of the 2nd step and greater hip flexion angle at foot strike of the 3rd step (r2 =0.804, p < 0.001).

SIGNIFICANCE

Faster acceleration was observed when participants transitioned from an upright posture to greater forward trunk lean in the early phase of acceleration. Training the run-to-sprint transition, which was shown to have the greatest increase in velocity over the first 5 m, may be encouraged as a sports specific exercise.

Resisted Sled Sprint Kinematics: The Acute Effect of Load and Sporting Population

In this study, we assessed the acute kinematic effects of different sled load conditions (unloaded and at 10%, 20%, 30% decrement from maximum velocity (Vdec)) in different sporting populations. It is well-known that an athlete’s kinematics change with increasing sled load. However, to our knowledge, the relationship between the different loads in resisted sled sprinting (RSS) and kinematic characteristics is unknown. Thirty-three athletes (sprinters n = 10; team sport athletes n = 23) performed a familiarization session (day 1), and 12 sprints at different loads (day 2) over a distance of 40 m. Sprint time and average velocity were measured. Sagittal-plane high-speed video data was recorded for early acceleration and maximum velocity phase and joint angles computed. Loading introduced significant changes to hip, knee, ankle, and trunk angle for touch-down and toe-off for the acceleration and maximum velocity phase (p < 0.05). Knee, hip, and ankle angles became more flexed with increasing load for all groups and trunk lean increased linearly with increasing loading conditions. The results of this study provide coaches with important information that may influence how RSS is employed as a training tool to improve sprint performance for acceleration and maximal velocity running and that prescription may not change based on sporting population, as there were only minimal differences observed between groups. The trunk lean increase was related to the heavy loads and appeared to prevent athletes to reach mechanics that were truly reflective of maximum velocity sprinting. Lighter loads seem to be more adequate to not provoke changes in maxV kinematics. However, heavy loading extended the distance over which it is possible to train acceleration.

Step-to-Step Kinematic Validation between an Inertial Measurement Unit (IMU) 3D System, a Combined Laser+IMU System and Force Plates during a 50 M Sprint in a Cohort of Sprinters

The purpose was to compare step-by-step kinematics measured using force plates (criterion), an IMU only and a combined laser IMU system in well-trained sprinters. Fourteen male experienced sprinters performed a 50-m sprint. Step-by-step kinematics were measured by 50 force plates and compared with an IMU-3D motion capture system and a combined laser+IMU system attached to each foot. Results showed that step kinematics (step velocity, length, contact and flight times) were different when measured with the IMU-3D system, compared with force plates, while the laser+IMU system, showed in general the same kinematics as measured with force plates without a systematic bias. Based upon the findings it can be concluded that the laser+IMU system is as accurate in measuring step-by-step kinematics as the force plate system. At the moment, the IMU-3D system is only accurate in measuring stride patterns (temporal parameters); it is not accurate enough to measure step lengths (spatial) and velocities due to the inaccuracies in step length, especially at high velocities. It is suggested that this laser+IMU system is valid and accurate, which can be used easily in training and competition to obtain step-by step kinematics and give direct feedback of this information during training and competition.

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.

Effect of Volume on Eccentric Overload-Induced Postactivation Potentiation of Jumps

PURPOSE

To investigate the postactivation potentiation (PAP) effects of different eccentric overload (EOL) exercise volumes on countermovement-jump (CMJ) and standing-long-jump (LJ) performance.

METHODS

In total, 13 male university soccer players participated in a crossover design study following a familiarization period. Control (no PAP) CMJ and LJ performances were recorded, and 3 experimental protocols were performed in a randomized order: 1, 2, or 3 sets of 6 repetitions of flywheel EOL half-squats (inertia = 0.029 kg·m2). Performance of CMJ and LJ was measured 3 and 6 minutes after all experimental conditions. The time course and magnitude of the PAP were compared between conditions.

RESULTS

Meaningful positive PAP effects were reported for CMJ after 2 (Bayes factor [BF10] = 3.15, moderate) and 3 (BF10 = 3.25, moderate) sets but not after 1 set (BF10 = 2.10, anecdotal). Meaningful positive PAP effects were reported for LJ after 2 (BF10 = 3.05, moderate) and 3 (BF10 = 3.44, moderate) sets but not after 1 set (BF10 = 0.53, anecdotal). The 2- and 3-set protocols resulted in meaningful positive PAP effects on both CMJ and LJ after 6 minutes but not after 3 minutes.

CONCLUSION

This study reported beneficial effects of multiset EOL exercise over a single set. A minimum of 2 sets of flywheel EOL half-squats are required to induce PAP effects on CMJ and LJ performance of male university soccer players. Rest intervals of around 6 minutes (>3 min) are required to maximize the PAP effects via multiple sets of EOL exercise. However, further research is needed to clarify the optimal EOL protocol configurations for PAP response.