Comparison of the Effect of Hip, Knee, and Ankle Fatigue on Dynamic Balance of Armed Forces

Abstract

Background: Muscles of the lower limbs play a very important role in the control of balance and performance in military activities. Fatigue in these muscles results in a decrease in balance and increase in risk of damage. Thus, it is important to determine the group of muscles in which fatigue has more effect on dynamic balance in the armed forces. Therefore, this study was aimed at the investigation of the effects of fatigue in each group of lower limb muscles on dynamic balance of the armed forces and risk assessment of damage to the military. Methods: The participants of the current study included 15 military personnel with a mean age of 27.00 ± 2.12 years and mean height of 178.1 ± 3.1 cm. This study used star excursion balance test (SEBT) to measure balance and used the ankle plantar flexion system, knee extension system, knee flexion system, thigh abduction system, and thigh adduction system to assess fatigue. First, all the participants were asked to warm up for about 5 minutes. Then, using a annual dynamometer, the maximal voluntary contraction ‎(MVC) for the muscles was measured. A 50% reduction in MVC is associated with fatigue. Nevertheless, if the individual was able to continue exercise after 50 extensions, he was given a 4-minute rest and the measurement was performed again using the dynamometer. If MVC was reduced by 50%, the SEBT was immediately performed. To analyze data, descriptive statistics, paired t-test, and repeated measures analysis of variance (ANOVA) test were used at a significance level of P ≤ 0.05. Results: Comparison of the total mean of balance in the SEBT before and after fatigue showed that there was a significant decrease in balance after fatigue in all 5 groups of muscles (knee extensor, knee flexor, thigh abductor, thigh adductor, and ankle plantar flexor) (P ≤ 0.05). The results of ANOVA for the total mean score of muscles did not show a significant statistical difference (P ≥ 0.05). However, there was a significant difference between the thigh abductor muscles, ankle plantar flexor, and knee extensors in terms of the anterior and anterolateral direction scores (P ≤ 0.05). Conclusion: The findings of the current study showed an inverse relationship between lower limb fatigue and an individual’s balance; an increase in fatigue in the muscles resulted in a decrease in balance.