THE EFFECT OF FATIGUE ON LOWER LIMB MOTOR VARIABILITY DURING A CONTROLLED REPETITIVE STRETCH-SHORTEN CYCLE TASK

This study evaluated changes in lower limb joint coupling variability during single-leg hopping to exhaustion. Twenty recreationally active male and female participants performed single-leg hopping at 2.2 Hz to a target height. At 0, 20, 40, 60, 80 and 100% of the total duration of hopping, spatio-temporal characteristics and variability of the kneeankle (KA) and hip-knee (HK) joint couplings were determined. There was a significant increase in variability of the KA and HK joint couplings in the flexion-extension axes during the loading and propulsion phases as hopping progressed. However, there was maintenance of performance output characteristics throughout the task. These findings suggest that changes in joint coupling variability may be a compensatory strategy to allow continuous single-leg hopping as the effects of muscular fatigue increase

DOES THE METHOD OF MEASURING CENTRE OF MASS DISPLACEMENT AFFECT VERTICAL STIFFNESS CALCULATION IN SINGLE-LEG HOPPING?

The purpose of this study was to compare vertical stiffness values calculated from two kinetic and two kinematic estimations of the vertical displacement of the centre of mass. Twenty recreationally active male and female participants completed one 15 s single-leg hopping trial at 2.2 Hz with vertical stiffness calculated for the first 10 complete hop cycles. Vertical displacement was estimated using double integration (DI), first principle (FP), sacral marker cluster (SMC) and segmental analysis (SA) methods. Bland-Altman plots demonstrated the SA and DI methods to have a small bias (0.92 kN/m) and tight 95% limits of agreement (-1.16 to 3.08 kN/m). In contrast, the SMC and FP methods underestimated and overestimated vertical stiffness, respectively. These findings suggest the SA and DI methods can be used interchangeably to calculate vertical stiffness

ACUTE EFFECTS OF MASSAGE ON PASSIVE ANKLE STIFFNESS FOLLOWING AN EXHAUSTIVE STRET CHSHORTEN CYCLE TASK: A PILOT STUDY

This preliminary study evaluated the effect of massage on the passive stiffness of the calf muscle complex following single-leg hopping to volitional exhaustion. Four young and healthy male participants had their ankle taken through full joint excursion to determine the resistance to ankle dorsiflexion both prior to and immediately following hopping. A 10 minute rest and massage were then applied in a random order and follow up measures taken immediately Mer each intervention. Calf muscle stiffness increased in three of the four participants following hopping and two participants had a decrease following massage. This study suggests that changes in calf muscle stiffness are sensitive to both exercise and massage. It is important to determine the underlying mechanism(s) to changes in calf stiffness following exercise and whether massage offers any benefit

SEX DIFFERENCES IN LOWER LIMB MOVEMENT VARIABILITY DURING A FATIGUING REPETITIVE LOADING TASK

This study evaluated differences in lower limb joint coupling variability between recreationally-active male (n = 21) and female participants (n = 20) during single-leg hopping to exhaustion. Spatio-temporal characteristics and variability of the knee-ankle and hip-knee joint couplings were determined over the duration of hopping. As fatigue progressed joint coupling variability increased by a greater magnitude in females compared to males. Females had significantly lower variability compared to males in the knee-ankle couplings during the propulsion phase at the beginning of the trial but this effect progressively disappeared during the trial. These findings suggest that as fatigue progresses, there is a regression to a similar magnitude of joint coupling variability which may represent a common level of synchronous joint interaction between sexes

A RANDOMISED CONTROLLED TRIAL EVALUATING THE EFFECTS OF COMPRESSION GARMENTS DURING SINGLE-LEG HOPPING TO EXHAUSTION

The purpose of this investigation was to determine the effect of compression garments on spatiotemporal and leg mechanical characteristics during single-leg-hopping (2.2 Hz) to volitional exhaustion. This study demonstrated that compression garments had no significant effect on leg mechanical characteristics or performance parameters of single-leg hopping to volitional exhaustion. There was a significant increase in the duration of the loading phase and decrease in the flight phase from the start to the end during single-leg hopping task indicating that there may have been a shift in the motor control strategy used to preserve vertical leg stiffness and hopping frequency in a repeated and rapid loading task

Control of the lower limb during a fatiguing dynamic task

Human locomotion often requires the performance of submaximal, repeated and rhythmical efforts over an extended period of time. The ability to maintain consistent performance for extended periods is likely due to multiple adaptive mechanisms and may be affected by the progression of fatigue. However, it remains unclear whether changes in movement strategies are due to fatigue, changes in task performance or the repetitive nature of the task. Further, it is unknown if there are differences in movement strategies between the sexes during extended and fatiguing locomotive tasks. The aims of this thesis were to investigate the influence of fatigue and the effect of sex on neuromechanical characteristics during a repetitive and rapid lower limb loading task while performance output was maintained. To address these aims, a series of experimental investigations were completed. The findings of these studies demonstrated a relationship between increased muscle activity and variability between adjoining lower limb segments as fatigue progressed. Further, men and women demonstrated differential changes as the level of fatigue increased. Women demonstrated a greater increase in joint coupling variability than men, which may have been associated with the greater relative dependence on the knee extensor muscle as the task progressed. These results extend the understanding of how there is an optimisation of variability in the neuromechanical system during the performance of repetitive tasks to fatigue in a healthy recreationally active population. Importantly, these results provide insight into what compensatory strategy may be utilised when motor performance was stereotypical

Does the method of measuring centre of mass displacement affect vertical stiffness calculation in single-leg hopping?

The purpose of this study was to compare vertical stiffness values calculated from two kinetic and two kinematic estimations of the vertical displacement of the centre of mass. Twenty recreationally active male and female participants completed one 15 s single-leg hopping trial at 2.2 Hz with vertical stiffness calculated for the first 10 complete hop cycles. Vertical displacement was estimated using double integration (DI), first principle (FP), sacral marker cluster (SMC) and segmental analysis (SA) methods. Bland-Altman plots demonstrated the SA and DI methods to have a small bias (0.92 kN/m) and tight 95% limits of agreement (-1.16 to 3.08 kN/m). In contrast, the SMC and FP methods underestimated and overestimated vertical stiffness, respectively. These findings suggest the SA and DI methods can be used interchangeably to calculate vertical stiffness

The effect of fatigue on lower limb motor variability during a controlled repetitive stretch-shorten cycle task

This study evaluated changes in lower limb joint coupling variability during single-leg hopping to exhaustion. Twenty recreationally active male and female participants performed single-leg hopping at 2.2 Hz to a target height. At 0, 20, 40, 60, 80 and 100% of the total duration of hopping, spatio-temporal characteristics and variability of the knee ankle (KA) and hip-knee (HK) joint couplings were determined. There was a significant increase in variability of the KA and HK joint couplings in the flexion-extension axes during the loading and propulsion phases as hopping progressed. However, there was maintenance of performance output characteristics throughout the task. These findings suggest that changes in joint coupling variability may be a compensatory strategy to allow continuous single-leg hopping as the effects of muscular fatigue increase

Adaptation of ankle-knee interaction during repeated submaximal loading to exhaustion

Background: Neuromotor patterns which are different between tasks may be sensitive to subtle adaptations, especially if there are physiological changes such as fatigue or familiarisation. It is plausible that there may be a modulation of a neuromotor pattern during continuous tasks. Purpose: This study evaluated the ankle-knee joint interaction during repetitive submaximal effort loading to exhaustion. Methods: Seventeen volunteer, healthy and recreationally active participants (mean (SD)) 22.7 (2.5) years of age, 173.5 (6.7) cm in height, 72.7 (10.6) kg in body mass) provided written and informed consent for inclusion in this study which was approved by the University of Western Sydney Human Research Ethics Committee (H1074). Each participant completed a trial of on-the-spot single-leg hopping on the dominant leg to exhaustion in synchrony with an audible metronome (2.2 Hz) to a target hop height using tactile feedback. Synchronous recording (First Principles v1.2.4) and processing (Visual 3D) of force plate (low-pass Butterworth filter with 50 Hz cut-off), kinematics (4th order Butterworth filter with 8 Hz cut-off) (lower limb, pelvis and trunk) and surface electromyography (sEMG) (band pass filtered 50–500 Hz) of 7 lower limb muscles were made. Each trial was time normalised to 100% and the mean of 10 consecutive data points at 0, 20, 40, 60, 80 and 100% of the trial were determined to represent the dependant variables at each of these moments from start to finish of the trial. Dependant variables included ankle (A) and knee (K) joint angles (at initial contact (IC) and peak vertical ground reaction force (PvGRF)), ankle (AL) and knee (KL) excursion during loading and ankle-knee joint coupling (AKJC) in the frontal axis. A one-way repeated measure ANOVA was used to determine differences during the trials with Bonferroni correction used to reduce the risk of a type 1 error. Results: There was a significant decrease in AKJC (p 0.05). There was a significant increase towards ankle dorsiflexion of AKIC (p < 0.001) and APvGRF (p < 0.001) at the end of the trial and concomitant decrease in AL (p = 0.03). There was a converse significant decrease in KL (p < 0.001) even though there was a significant increase in KIC (p < 0.001) and KPvGRF (p = 0.028). Conclusion(s): Adaptations of ankle and knee joint angles at IC offset decreased KL (increased knee joint stiffness) and this may have allowed (i) a shift in optimal muscle activation characteristics between the prime movers (triceps surae and quadriceps femoris) and (ii) optimisation of the force-length relationship. Although there was synchronous adaption in the ankle and knee joints, this was not characterised by proportionate changes in neuro-mechanical changes at each joint or synergistic muscle group. Implications: Determination of the modulation of a gross motor pattern when motor performance remains unchanged is a factor which needs to be considered during training and rehabilitation during repetitive tasks which may be sensitive to the effects of fatigue and motor learning

Reliability of detecting medial gastrocnemius muscle activity during single-leg hopping

The onset of muscle activity in the MG during single-leg-hopping may be reliably determined and used with confidence to determine temporal characteristics of the sEMG signal recorded during a SSC muscle action