The effects of lower-limb wearable resistance on sprint performance in high school American football athletes: A nine-week training study

Time constraints often result in the challenge to fit desired programming into training time allotments. Wearable resistance (WR) may be an option to optimise the training content in function of constrained training time. The purpose of this study was to determine the effects of a lower-limb WR sprint running training intervention on athlete speed capabilities following a nine-week off-season, low volume training period within a sample of American football high school athletes. Nineteen athletes completed pre- and post-intervention testing of two maximal effort 30 m sprints. Horizontal force-velocity mechanical profiling variables, sprint times, and maximal velocity were calculated from sprint running velocity data collected by a radar device. The athletes completed seventeen dedicated sprint training sessions during the off-season. The intervention (WR) group completed the sessions with 1% body mass load attached to the shanks (i.e. 0.50% body mass load on each limb). The control group completed the same training sessions unloaded. Post-intervention, no statistically significant between group differences were observed (p > 0.05). However, athletes in both groups experienced increases in velocity measures following the sprint training. The greater adjusted mean theoretical maximal velocity scores (p > 0.05; ES = 0.30) found for the WR group compared to the control group at post-intervention may suggest that WR amplifies the nuances of the training protocol itself. Coaches can consider using lower-limb WR training to increase in-session workloads during periods of low volume training but more research is needed to better understand to what extent WR training might provide an added value to optimise both the training content and planning, as well as the athlete’s training response in order to improve sprint running performance

INTEGRATING RESEARCH AND PRACTICE WITH A VIEW TO ENHANCING SPORTS PERFORMANCE: EXAMPLES FROM SPRINT ACCELERATION

One of the three primary purposes of ISBS is to bridge the gap between researchers and practitioners. This paper aims to identify important concepts for incorporating coaching viewpoints into biomechanical analyses in an attempt to enhance sports performance. A continuum of possible sources of evidence was identified and, through a series of sprint acceleration-based examples, four key concepts were proposed. These were 1) the need for a clear and appropriate common goal to be defined, 2) the requirement for asking relevant questions, 3) the need to provide meaningful answers, and 4) the ability to demonstrate that a difference can be made. These concepts provide a framework to stimulate discussion amongst researchers and practitioners for how this integration of information, and ultimately levels of sporting performance, can continue to be improved

Characterising initial sprint acceleration strategies using a whole-body kinematics approach

Sprint acceleration is an important motor skill in team sports, thus consideration of techniques adopted during the initial steps of acceleration is of interest. Different technique strategies can be adopted due to multiple interacting components, but the reasons for, and performance implications of, these differences are unclear. 29 professional rugby union backs completed three maximal 30 m sprints, from which spatiotemporal variables and linear and angular kinematics during the first four steps were obtained. Leg strength qualities were also obtained from a series of strength tests for 25 participants, and 13 participants completed the sprint protocol on four separate occasions to assess the reliability of the observed technique strategies. Using hierarchical agglomerative cluster analysis, four clear participant groups were identified according to their normalised spatiotemporal variables. Whilst significant differences in several lower limb sprint kinematic and strength qualities existed between groups, there were no significant between-group differences in acceleration performance, suggesting inter-athlete technique degeneracy in the context of performance. As the intra-individual whole-body kinematic strategies were stable (mean CV = 1.9% to 6.7%), the novel approach developed and applied in this study provides an effective solution for monitoring changes in acceleration technique strategies in response to technical or physical interventions

Calculation of the centre of pressure on the athletic starting block

We aimed to evaluate the accuracy of a new method to calculate the centre of pressure (COP) on a starting block above a force platform, and to examine how this method affected lower extremity joint torques during the block clearance phase compared against a previously used method which projects the COP from the metatarsophalangeal (MP) joint. To evaluate the accuracy of the new method, one experimenter applied force at 18 known locations on a starting block (under six block position and orientation conditions), during which ground reaction force was recorded underneath using a force platform. Two sprinters then performed three block starts each, and lower extremity joint torques were calculated during block clearance using the COP obtained from the new method and from the projection of the MP joint location. The calculated COP using the new method had a mean bias of ≤0.002 m. There were some large differences (effect sizes = 0.11–4.01) in the lower extremity joint torques between the two methods which could have important implications for understanding block clearance phase kinetics. The new method for obtaining the COP on a starting block is highly accurate and affects the calculation of joint torques during the block clearance phase

INVESTIGATIONS OF THE STEP LENGTH-STEP FREQUENCY RELATIONSHIP IN SPRINTING: APPLIED IMPLICATIONS FOR PERFORMANCE

The relationship between velocity, step length (SL) and step frequency (SF) has received much attention in the biomechanical literature, but there is not a consensus on which of SL and SF is most important to performance in elite sprinting. This paper presents a series of linked studies aimed at increasing the understanding of the individualised nature of the relationship. The research has revealed that elite sprinters’ velocity can be individually reliant on either SL or SF, and that the athlete’s training programme also plays an important role in determining SL and SF. Furthermore, it is thought that sprinters can manipulate the SL-SF relationship throughout a maximal sprint to maintain velocity. The influence of joint kinetics on SL and SF is not yet fully understood, but further work in this area will accelerate the understanding of the biomechanics of sprint performance

Inter- and intra-limb coordination during initial sprint acceleration

In complex movements, centre of mass translation is achieved through effective joint and segment rotations. Understanding segment organisation and coordination is therefore paramount to understanding technique. This study sought to comprehensively describe inter- and intra-limb coordination and assess step-to-step changes and between-individual variation in coordination during initial sprint acceleration. Twenty-one highly trained to world class male (100 m PB 9.89-11.15 s) and female (100 m PB:11.46-12.14 s) sprinters completed sprint trials of at least 20 m from which sagittal plane kinematics were obtained for the first four steps using inertial measurement units (200 Hz). Thigh-thigh, trunk-shank and shank-foot coordination was assessed using a modified vector coding and segment dominancy approach. Common coordination patterns emerged for all segment couplings across sexes and performance levels, suggesting strong task constraints. Between-individual variation in inter-limb thigh coordination was highest in early flight, while trunk-shank and shank-foot variation was highest in late flight, with a second peak in late stance for the trunk-shank coupling. There were clear step-to-step changes in coordination, with step 1 being distinctly different to subsequent steps. The results demonstrate that inter-limb coordination is primarily anti-phase and trailing leg dominant while ankle motion in flight and late stance appears to be primarily driven by the foot

VARIABILITY IN THE STEP CHARACTERISTICS OF INTERNATIONAL-LEVEL SPRINTERS DURING THE ACCELERATION PHASE

This study investigated within-session and across-season variability in step characteristics during maximal effort sprint accelerations of internationally competitive sprinters (n = 7) during training. Kinematic data were collected across multiple sessions over the training season. Of each adjacent four-step interval, steps 1-4 showed the highest absolute variation for step frequency, contact and flight time across the cohort, within-session. Across the season, the variability in each kinematic measure (relative to season mean) was specific to the individual, and no single technique variable fluctuated consistently with velocity. Athletes may benefit from being exposed to a variety of situational and environmental constraints that reflect the unpredictability of competition, enabling them to develop variable movement strategies whilst maintaining consistent performance levels

CONTRIBUTIONS TO BRAKING IMPULSE DURING INITIAL ACCELERATION, TRANSITION AND MAXIMAL VELOCITY IN SPRINTING

The aim of this study was to quantify the magnitude of braking impulse induced on the centre of mass by the accelerations at the foot-floor joint during steps three, nine and 19 of maximal sprinting. An induced acceleration analysis was performed to quantify the induced centre of mass accelerations. The accelerations at the foot-floor joint following touchdown generated -0.02 ± 0.01 m.s-1 (143 ± 72%), -0.04 ± 0.01 m.s-1 (80 ± 47%) and - 0.07 ± 0.01 m.s-1 (50 ± 13%) of the total relative braking impulse during steps three, nine and 19. A large portion of these foot-floor accelerations resulted from the deceleration of the foot at touchdown. The results suggest that minimising horizontal foot velocities prior to touchdown will result in reduced braking forces. Further research is required to empirically investigate this mechanism in an applied setting