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Context: Dynamic stability is a necessary requirement in many sports competitions. Muscle fatigue, which can impair stability, may be occurred in many sports competitions in which lateral movements and landing repeated frequently. Objective: To assess the effects of peroneal muscles fatigue on dynamic stability following lateral hop landing through measuring time to stabilization (TTS) and dynamic postural stability index (DPSI). Design: Quasi-experimental. Setting: Laboratory study. Participants: A total of 20 recreationally active, healthy males with no lower-extremity injury during the previous 6 months participated in this study. Intervention: Participants performed a lateral hop on a force plate before and immediately after a fatigue intervention using a Biodex dynamometer. For inducing fatigue, the participant made a prolonged eversion effort with 40% of the maximal voluntary contraction. Fatigue was met when the eversion torque declined by 50% of the initial value. TTS and DPSI were calculated using sequential averaging method and relevant formulas, respectively. Main Outcome Measures: Premeasures and postmeasures of TTS in the anteroposterior, mediolateral and vertical directions, resultant vector of TTS, stability indices in the anteroposterior, mediolateral and vertical directions, and DPSI. Results: Means of the DPSI or its components did not change significantly due to fatigue (P >.05). Means of the TTS in the anteroposterior and mediolateral directions, and the mean of the resultant vector of the TTS increased significantly after fatigue (P <.05). Conclusions: The question that the dynamic stability is affected or not affected by fatigue depends on which of the TTS or DPSI is used for analysis. The TTS may be a sensitive measure to detect subtle changes in postural stability due to fatigue. But, the DPSI which may be changed after a more strenuous fatigue may be related to actual fatiguing situations. [ABSTRACT FROM AUTHOR]

Context: Cyclic movements and muscle fatigue may result in musculoskeletal injuries by inducing changes in neuromuscular control. Ankle frontal-plane neuromuscular control has rarely been studied in spite of its importance. Objective: To compare the effects of peroneal muscle fatigue and a cyclic passive-inversion (CPI) protocol on ankle neuromuscular control during a lateral hop. Design: Quasi-experimental, repeated measures. Setting: University laboratory. Participants: 22 recreationally active, healthy men with no history of ankle sprain or giving way. Interventions: Participants performed a lateral hop before and after 2 interventions on a Biodex dynamometer. They were randomly assigned to intervention order and interventions were I wk apart. A passive intervention included 40 CPIs at 5°/s through 80% of maximum range of motion, and a fatigue intervention involved an isometric eversion at 40% of the maximal voluntary isometric contraction until the torque decreased to 50% o f its initial value. Main Outcome Measures: Median frequency o f the peroneus longus during the fatigue protocol, energy absorption by the viscoelastic tissues during the CPI protocol, and feedforward onset and reaction time o f the peroneus longus during landing. Results: A significant fall in median frequency (P < .05) and a significant decrease in energy absorption (P < .05) confirmed fatigue and a change in viscoelastic behavior, respectively. There was a significant main effect of condition on feedforward onset and reaction time {P < .05). No significant main effect of intervention or intervention x condition interaction was noted (P > .05). There was a significant difference between pre- and postintervention measures (P < .0125), but no significant difference was found between postintervention measures (P > .0125). Conclusions: Both fatigue and the CPI may similarly impair ankle neuromuscular control. Thus, in prolonged sports competitions and exercises, the ankle may be injured due to either fatigue or changes in the biomechanical properties o f the viscoelastic tissues. [ABSTRACT FROM AUTHOR]

Context: Flat foot is one of the lower extremity deformities that might change kinetic variables of gait. Fatigue is one of the factors that can alter the vertical ground-reaction force (GRF). The effect of a fatiguing condition on vertical GRF has not been documented in individuals with flat feet. Objective: To examine the fatigue effect on vertical GRF in individuals with flat feet compared with a normal group during barefoot walking. Design: Repeated-measure ANOVA for the effects of fatigue on individuals with flat feet and normal feet. Setting: Biomechanics laboratory. Participants: 17 subjects with flat feet and 17 normal subjects (recruited according to their arch-height ratio). Main Outcome Measures: Three vertical GRF measures (F1, the first peak force; F2, minimum force; and F3, the second peak force) were extracted before and after a functional fatigue protocol. Results: No significant interaction between fatigue and group was observed for the 3 vertical GRF measures. For F2, fatigue and group effects were significant (P = .001 and P = .02, respectively). Furthermore, F2 was higher in the flat-feet group than in the normal group; F2 also increased after fatigue. For F3, only a significant fatigue effect was observed (P = .004). F3 decreased after fatigue in both groups. Conclusions: In the flat-feet group, a decrease in the variation of vertical GRF might be due to more flexible foot joints. After fatigue, muscles might lose their ability to control the foot joints and cause higher F2 in the flat-feet group. [ABSTRACT FROM AUTHOR]

BACKGROUND: The single-leg squat (SLS) is a common strengthening exercise after anterior cruciate ligament reconstruction (ACLR) surgery. The multi-joint nature of squatting may allow patients to shift the demand from the target muscle group to its synergies, thus reducing the strengthening effect of the SLS exercise. OBJECTIVE: To compare the muscular contribution in the involved and uninvolved side of the ACLR patients and both sides of the ACLR patients with the matched control group during SLS exercise. METHOD: Seventeen athletic men with unilateral ACL reconstruction and 16 athletic healthy men participated. Integrated Electromyography was used to calculate the relative contributions of, Vastus Medialis (VM), Vastus Lateralis (VL), rectus femoris (RF), Gluteus maximus (GMax) and Soleus (SOL) muscles to SLS performance and squat peak force was measured with a Biodex System 3 isokinetic dynamometer. RESULTS: The VM muscle contribution was significantly lower and the VL and GMax contribution was higher on the involved side of the ACLR patients compared to their uninvolved side and the control group. The SLS peak force was significantly lower on the involved side compared to the uninvolved side. CONCLUSION: The increased VL and GMax muscle contribution might be a compensatory mechanism for the reduced VM contribution on the involved side. [ABSTRACT FROM AUTHOR]