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

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

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

Differences in plantarflexor function during a stretch-shortening cycle task due to limb preference

Most healthy humans move symmetrically at gross limb level but large kinetic and kinematic asymmetries have been observed at joint level during locomotion. The aim of this study was to assess muscle function asymmetries in healthy, active adults using an adapted force sledge apparatus which isolates the plantarflexors during a stretch-shortening cycle task. Peak force, rate of force development and stretch-shortening cycle function of preferred and non-preferred limbs were assessed in 21 healthy, active individuals using the adapted sledge and three-dimensional motion analysis. Between-limb differences and relationships were determined using paired t-tests/Wilcoxon-Signed rank test, Cohen’s dz, absolute symmetry index and Pearson’s r/Spearman’s rho. Significant differences with moderate effect size (ES) were observed in peak force (ES: 0.66), rate of peak force development (ES: 0.78), rate of force development in the first 50 ms (ES: 0.76), flight time (ES: 0.64) and stretch-shortening cycle function (0.68), with no difference in contact time or duration of eccentric loading. A small ES (0.56) was observed in rate of force development in the first 30 ms. The upper range of asymmetry observed (up to 44.9%) was larger than previously reported for healthy individuals, indicating compensations occur at proximal joints during locomotion to ensure symmetrical movement

Corrigendum: Reliability and consistency of plantarflexor stretch-shortening cycle function using an adapted force sledge apparatus

Corrigendum: Reliability and consistency of plantarflexor stretch-shortening cycle function using an adapted force sledge apparatu

Sex-related differences in plantarflexor function during repeated stretch-shortening cycle loading

Introduction: Differences between male and female muscle-tendon units have been previously observed. It is unknown if a sex-related difference exists in the plantarflexor response to repeated stretch-shortening cycles, as occurs during activities of daily living such as walking and running. Methods: An adapted force sledge was used with three dimensional motion analysis to investigate the response of the plantarflexors of 34 age and training-matched males and females during stretchshortening cycle impacts. Results: Contact times and flight times were found to be similar between groups. Statistically significant differences in absolute peak force and rates of force development were observed during loading. With normalisation to plantarflexor muscle volume, small and moderate effect sizes were observed for all force and rate of force development variables but only peak force remained statistically significant. Differences in absolute stiffness, peak negative and positive power and work were statistically significant with moderate effect size, but with normalisation only differences in peak negative power and work remained statistically significant with a moderate effect size. Conclusion: These results show females have lower force, rate of force production and force absorption capabilities, which are of relevance in injury prevention and rehabilitation, and informing personalised engineering design. Level of evidence: III b (individual case-control study)

Reliability and consistency of plantarflexor stretch-shortening cycle function using an adapted force sledge apparatus

There are various limitations to existing methods of studying plantarflexor stretch-shortening cycle (SSC) function and muscle-tendon unit (MTU) mechanics, predominantly related to measurement validity and reliability. This study utilises an innovative adaptation to a force sledge which isolates the plantarflexors and ankle for analysis. The aim of this study was to determine the sledge loading protocol to be used, most appropriate method of data analysis and measurement reliability in a group of healthy, non-injured subjects. Twenty subjects (11 males, 9 females; age: 23.5 ±2.3 years; height: 1.73 ±0.08 m; mass: 74.2 ±11.3 kg) completed 11 impacts at five different loadings rated on a scale of perceived exertion from 1 to 5, where 5 is a loading that the subject could only complete the 11 impacts using the adapted sledge. Analysis of impacts 4 to 8 or 5 to 7 using loading 2 provided consistent results that were highly reliable (single ICC >0.85, average ICC >0.95) and replicated kinematics found in hopping and running. Results support use of an adapted force sledge apparatus as an ecologically valid, reliable method of investigating plantarflexor SSC function and MTU mechanics in a dynamic controlled environment