Effect of Fatigue at Heart Rate Deflection Point on Ankle Muscle Co-Contraction during Running in Healthy Individuals and Those with a Pronated Foot

Pronated foot, as one of the common foot deformities, can affect the biomechanics of running and risk of lower extremity injury. Fatigue, as a result of doing heavy tasks, can also change biomechanical parameters of locomotion. Under the fatigue conditions, the biomechanical differences between individuals with pronated and healthy feet are more easily identified. Thus, the main objective of the present study was to examine the effects of fatigue at heart rate deflection point on ankle muscle co-contraction between pronated and healthy feet during running.

A total of 14 young men with pronated feet and 14 individuals with healthy feet participated in the study. Electromyographic activities of the selected muscles before and after fatigue protocol were recorded. The statistical analysis was performed using the SPSS software and running ANOVA (p≤0.05).

Findings in the pronated foot compared with the healthy footgroup showed that the ankle general co-contraction was significantly lower in the mid-stance phase (p=0.049; d=0.81) and the directed co-contraction was significantly more in the heel off phase (p=0.038; d=0.85). Other components did not show any significant differences (P > 0.05).

The general co-contraction of the pronated feet was less than that in the healthy group in the middle phase. Weakness of the muscles around the joint may be one of the reasons for the change in the direction of the bones of the sole of the foot. An increase in directional co-contraction in people with pronated feet indicates an increase in pressure on the internal structures of the ankle. Long-term running may expose the internal structures of the foot to the risk of overload and injury. Therefore, it is suggested that rehabilitation programs be considered for these individuals, which will also increase the general co-contraction, especially in the mid-stance phase.