FORCE-VELOCITY-POWER PROFILES OF ELITE SPRINTERS: INTER-AND INTRA-INDIVIDUAL DETERMINANTS OF PERFORMANCE

Elite athletes are underrepresented in scientific research and evidence from group-based studies may not be applicable to individual elite athletes. The purpose of this study was to investigate mechanical determinants of sprint performance in elite sprinters using inter- and intra-individual approaches. Six elite and six sub-elite sprinters performed maximal effort sprint acceleration trials and their force-velocity-power profiles were computed. Theoretical maximum velocity, power and the ratio of force were greater in the elite than the sub-elite athletes. Within the elite group, individuals achieved their fastest times through greater theoretical maximum horizontal force with only small differences in theoretical maximum velocity between the best and worst trials. Practitioners should consider these intra-individual data when coaching and programming for elite athletes

EFFECT OF FOOT POSITION ON THE COMPRESSION AND LATERAL FORCE PRODUCTION OF A PLAYER IN A RUGBY SCRUM

Knowledge of the force production of an individual player with different foot positions, and ultimately of the full pack, will provide coaches and trainers with valuable information in order to improve their team's ability to manipulate the scrum forces and moments as well as making the scrum more stable thereby improving safety. This study aimed to examine the differences in the scrum compression force and lateral force generated by an individual player during the sustained pushing phase of the scrum with parallel and nonparallel foot positions. Nineteen front row rugby players scrummed against an instrumented scrum machine with three different foot positions. The results showed that the parallel foot position produces a higher pushing force than either of the other two nonparallel conditions. It was also shown that the nonparallel conditions produces a greater lateral force than the parallel foot condition with the lateral force being directed towards the side of the front foot.

INTER-LIMB COORDINATION DURING SPRINT ACCELERATION

Bilateral coordination is inherent to running motions but has not been investigated during sprint acceleration. The purpose of the study was to examine inter-limb thigh coordination during the first four steps of sprint acceleration in elite and sub-elite athletes. Anti-phase coordination patterns predominated in each step, but the proportion of anti-phase motion was higher in elite athletes (85.9 ± 10.8%) than sub-elite athletes (76.8 ± 10.9%, ES 0.83). Coordination profiles suggest that sub-elite athletes exhibit longer periods of the trailing (+) pattern around the time of touchdown (swing thigh flexing, stance thigh fixed) and the leading (-) pattern in the latter part of stance (stance thigh extending, swing thigh fixed) compared with elite athletes. These results provide preliminary empirical support for the emphasis placed on the switching of the limbs by coaches

THE RELIABILITY AND USEFULNESS OF BIOMECHANICAL MEASURES OF COUNTERMOVEMENT JUMP PERFORMANCE IN ELITE ROWERS

Countermovement jump performance and associated biomechanical variables are commonly used to monitor athletes’ neuromuscular function. The purpose of this study was to quantify the reliability and usefulness of these variables in a cohort of fourteen elite male rowers, and to apply these findings in individual athlete monitoring. Seven of the nine variables demonstrated acceptable reliability (CV \u3c 5%). Peak power was classified as OK for usefulness (CV ≈ SWC; signal-to-noise ratio ≈ 1) while all others were classified as poor. Within the athlete monitoring program, many of the observed changes in countermovement jump variables exceeded the threshold for interpretation of a clear change based on the signal-to-noise ratio. This study demonstrates the importance of understanding the reliability and usefulness measurements for accurate interpretation of monitoring data

SIMILARITY OF COORDINATION PATTERNS IN A GROUP OF HIGHLY TRAINED SPRINTERS: A NOVEL APPROACH

Understanding coordination patterns aids technical understanding and potential grouping of athletes that exhibit similar movement patterns. This study assessed between-individual similarity in initial sprint acceleration coordination in highly trained to world class sprinters using a novel pairwise approach. Similarity between participants was higher for thigh-thigh coordination compared to shank-foot and trunk-shank coordination. Mean similarity increased from step 1 to step 4 in shank-foot (0.74 to 0.83) and trunk-shank (0.68 to 0.79) couplings but remained consistent in the thigh-thigh coupling (0.89 to 0.91). Researchers and practitioners should consider that coordination between sprinters converges over initial acceleration, but between any two individuals coordination similarity might increase or decrease across steps

WITHIN-SUBJECT REPEATABILITY AND BETWEEN-SUBJECT VARIABILITY IN POSTURE DURING CALIBRATION OF AN INERTIAL MEASUREMENT UNIT SYSTEM

Inertial measurement units (IMUs) are a valuable tool for field based sports research, but within- and between-subject comparisons may be affected by variation in the 0° position established by a standing calibration position. This study assessed within-subject repeatability and between-subject variability in IMU sensor orientations during calibration. Calibration posture was reliable within-subjects given standardised instructions (typical error \u3c 1.9°). Sensor angles relative to a global vertical axis had large between-subject ranges for upper spine (21–35°), lower spine (1–23°) and pelvis (11–35°), while lower limb segment angles had much lower variability (0-6°). Thus, a standing calibration posture is repeatable within participants given suitable instructions, however variability in standing posture may need to be accounted for before making between-subject comparisons, particularly with regard to spine and pelvis segments

1st Conference of the South African Society of Biomechanics

Abstracts for the Conference of the South African Society of Biomechanic

A COMPARISON OF TRUNK AND SHANK ANGLES BETWEEN ELITE AND SUB-ELITE SPRINTERS DURING SPRINT ACCELERATION

Acceleration is a movement that requires skilful positioning of the body to apply force in the desired direction. The sagittal plane orientation of the trunk and shank are features that coaches use to visually assess sprint acceleration technique. This study examined differences in trunk and shank angles between elite and sub-elite sprinters during early acceleration using inertial sensors. Elite sprinters exhibited more vertical trunk positions throughout all four steps compared to sub-elite with moderate to very large differences at discrete events (d = 0.79 - 2.16). Shank angles were more vertical at touchdown in sub-elite compared to elite sprinters (d = -0.70 - -0.39), but similar at toe-off. These results suggest that less horizontal trunk lean during acceleration is a feature of higher level sprinters, coaches should be conscious of this when giving technical feedback

A LARGE-SCALE NUMERICAL ANALYSIS OF UNIMODAL AND BIMODAL FEATURES IN FORCE PLATE DATA MEASURED DURING VERTICAL COUNTERMOVEMENT JUMPING

This study presents a novel algorithm for automatically analyzing modality patterns in countermovement jump (CMJ) force-time curves. Bimodal peaks (Fz1, Fz3) are identified using a minimum threshold (Ttrough_drop) for their relative drop to the intermediate trough value (Fz2). In a large sample of athletes (n = 214), 75% of jumps were technically bimodal (Ttrough_drop \u3e 0%) but this decreased to 17% (Ttrough_drop \u3e 5%) and 0% (Ttrough_drop \u3e 20%) using alternative definitions. This suggests that conflicting findings in other studies may be explained by a lack of standardized criteria for classifying modality. The drop from Fz1 to Fz2 in bimodal jumps was also largely correlated (r = 0.75) to the force at zero velocity and braking acceleration (r = 0.63). These findings highlight the potential value of extracting new quantitative features related to curve modality for CMJ research and interpretation

CAN FIELD-BASED TWO-DIMENSIONAL MEASURES BE USED TO ASSESS THREEDIMENSIONAL LUMBAR INJURY RISK FACTORS IN CRICKET FAST BOWLERS?

Bayne et al. (201 6) recently established a direct link between lumbar injury incidence and increased 30 measures of thorax lateral flexion, pelvis rotation and hip extension during the cricket fast bowling action. However, the majority of bowlers are not able to avail themselves to 30 biomechanical analysis. Therefore, we set out to ascertain whether it is appropriate to use 20 measures to assess 3D lumbar injury risk factors in fast bowlers. Nineteen fast-medium bowlers were simultaneously recorded by 30 motion capture and 20 video. Results showed that 2D thorax lateral flexion and pelvis rotation at ball release correlate particularly well with the 3D equivalents. The information presented may be practically applied by coaches to improve field-based lumbar injury risk screening processes