ASSESSMENT OF LOWER LIMB ASYMMETRY: DIFFERENCES DURING ISOMETRIC AND STRETCH-SHORTENING CYCLE TASKS

Assessment of limb function asymmetry is of interest to practitioners due to its role in return to play guidelines and reported links to injury. Dynamometry is one of the most commonly used methods of assessing muscle function, but the mode of contraction used is different to the stretch-shortening cycles experienced during real-life activities. The aim of this study was to compare measures of limb function asymmetry during isometric and stretch-shortening cycle tasks and investigate agreement between the methods. Different between-limb effect sizes were observed between limbs dependent on test used, with different ranges of asymmetry observed. Agreement between methods was very poor. These results show the importance of assessing asymmetry in a condition that is as similar as possible to the task of interest

PRELIMINARY ANALYSIS OF SLEDGE REACTION FORCES DURING CYCLICAL LOADING OF THE TRICEPS SURAE

To date, no methodology exists that can measure Achilles tendon stiffness in a controlled dynamic situation while simultaneously investigating tendon and joint stiffness interactions. Stiffness refers to the ratio between force and elongation, and the aim of this preliminary study was to establish an analysis protocol for sledge reaction forces during cyclical loading of the triceps surae. Results indicated the magnitude of forces was just under 50% of body weight, which was expected. Removal of the first two trials from analysis reduced standard deviation and 95% confidence interval of plantarflexor force, contact time and contact time-flight time ratio, suggesting this protocol is suitable to ensure data gathered is repeatable and consistent. Future work using inverse dynamics and ultrasound shall provide information on Achilles tendon loading and stiffness

THE EFFECT OF INCREASED LOADING ON PLANTARFLEXOR FUNCTION DURING A STRETCH-SHORTENING CYCLE TASK

Increasing loading is one of the most common methods used to increase exercise intensity but it is important to consider the influence of the increase on subsequent force output, rate of force development and, in the case of plyometric exercise, contact time. The aim of this study was to investigate the effect of altering loading on plantarflexor force and force production during a fast stretch-shortening cycle task. Results showed load increased force production and contact time and decreased flight time and reactive strength index. These results have important implications for practitioners in determining the optimal method of increasing training intensity in order to avoid negative training effects

DO FLEXIBILITY SCREENING TESTS REFLECT JOINT RANGE OF MOTION DURING DYNAMIC TASKS?

The aim of this study was to investigate if ankle joint range of motion (ROM) during a functional screen test was related to ankle ROM and plantarflexor reactive strength index (RSI) during a dynamic task. The three measures were correlated for the dominant and non-dominant legs to identify what relationship, if any, existed between the three measures. Results showed that there was no relationship between the two measures of ROM, and ROM during the sledge task was positively related to plantarflexor RSI. This is in contrast to other work, possibly due to the isolation of the plantarflexor muscles in the sledge task. Interestingly, between-leg relationships were lower in the dynamic task, suggesting increased variability in the movement strategies used or underlying training differences

PLANTARFLEXOR FORCE PRODUCTION IN ISOMETRIC AND STRETCH-SHORTENING CYCLE TASKS

The ankle joint and its surrounding musculature are vital in sprinting, and recent work has developed a method to isolate the plantarflexor muscle group for analysis of its force-producing capabilities. The aim of this study was to compare values for plantarflexor force obtained using isometric dynamometry and an adapted force sledge in twenty healthy subjects. Results showed low relationships between isometric and dynamic strength measures, probably because the dynamic test utilises a stretch-shortening cycle. No relationship was observed between isometric strength and the sledge foot plate height during the task with a moderate relationship observed between dynamic strength and plate height. This highlights the important role the Achilles tendon plays in dynamic tasks

SOFT TISSUE MOVEMENT IN THE LOWER LIMB DURING DROP JUMPS

Understanding loading on the human body and movement energetics is essential for researchers and practitioners to optimise training and investigate potential mechanisms of injury and adaptation. Recent work has suggested soft tissue movement relative to underlying bones during impact affects not only calculated loading but also metabolic cost. The aim of this study was to quantify the movement of the centre of mass of the soft tissues of the shank during high-impact, drop jump landings from 30 and 45 cm in healthy, adult males, and quantify the work done by these tissues. Soft tissue centre of mass moved by up to 0.038 m in the vertical direction (average: 0.021 m), and the soft tissues performed 2.9-3.5 J of work (4.1-6.4 J absolute work) during the landings. These results may hence have a significant effect on calculated joint torques and movement energetics

INFLUENCE OF JUMPING MEASURES AND SQUAT 1RM ON SPRINT SPEED IN RUGBY UNION PLAYERS

This study examined the relationship of countermovement (CMJ), squat (SJ), and rebound jumps (RBJ), estimated 1RM back squat (SQ), contact time (CT) and Reactive Strength Index (RSI) for the RBJ to 30 m sprint time of sub-elite, semi-professional Rugby Union players. The results show that with the exception of SQ and CT, all variables were significantly (p .575). The best determinant of predicting 30 m sprint time was RSI. The relationships of SJ, CMJ, and RBJ jump height and RSI to 30 m sprint time suggest that these rapid movements are all common in Rugby Union players. The results show that estimated 1 RM back squat has little influence on sprint performance

RELIABILITY OF JUMP AND PERFORMANCE MEASURES IN RUGBY UNION PLAYERS

The current study examined the reliability of countermovement (CMJ), squat (SJ), and rebound jumps (RBJ) to sprint and estimated 1RM back squat (SQ) of sub-elite Rugby Union players drawn from two teams of similar competitive level. Comparisons of mean performance on all tests were made via Student t-tests. The three trial reliability of jump height for the SJ, CMJ, RBJ, contact time (CT) and Reactive Strength Index for the RBJ, T-Test agility run (TA-Test), 30 and 36.58 m (40 yd) sprint times were estimated via ICC and ReANOVA. All variables displayed Average measures ICC ≥ .900; and except for the TA-Test, the three trials did not differ from each other. The performance of the two teams was found to be similar on all tests except the 30 m and 40 yd sprint tests. All the studied performance measures could be reliably assessed with one trial, except the TA-test

MAPPING OUT THE RESPONSE SEQUENCE OF THE SPRINT START

Establishing the limits of sprint start response time (SSRT) requires the mapping of the muscular sequence of activation and mechanical response delays and was the aim of the current study. Sprint start performance of 15 sprinters was examined with kinematic, EMG, and block force data collected. A general muscle activation sequence was identified, with both deltoid muscles, the rear leg rectus femoris, and the rear leg tibialis anterior the first muscles to increase activation from the set position. With ankle dorsiflexion the initial motion during the block push, examining the period between tibialis anterior muscle onset and block force onset is critical for quantifying mechanical response delays . Estimates of this delay period were as low as 7 ms which has implications for our understanding of the minimum SSRT a sprinter can legally produce

New developments in vector coding methods for assessing coordination variability

The purpose of this study is to propose modifications to current methods for the assessment of coordination variability through vector coding techniques. Commonly, vector coding starts from calculating the vector difference between adjacent data points on an angle-angle plot. This initial stage is analogue to estimating angular velocities from displacement, but with the limitation of differentiating the three axial components in isolation. Instead, the calculation of angular velocities from 3D data should take into account movement in other planes of motion. This study suggests the use of angular velocities in vector coding in place of the difference calculations and demonstrates how using this method can be integrated with recent developments which involve the use of ellipses for calculating coordination variability of angle-angle diagrams