The effects of running-induced fatigue on some of lower limb muscles activity during stance phase

Running-induced fatigue is associated with alterations in running mechanics. Mechanisms of these alterations are not well known. The aim of this study was to determine the effects of running-induced fatigue on some of lower limb muscles activity during stance phase of running.
Twenty male runners participated in this study. Subjects along a 14m runway ran 6 times before and after the fatigue protocol. Surface electromyographic activity of Tibilalis anterior (Ta), Medial gastrocnemius (Mg), Lateral gastrocnemius (Lg), Soleus (Sol), Vastus lateralis (Vl) and Biceps femoris (Bf) was recorded before and after the fatigue protocol. Percentage of muscular activity, co-contraction index and time to peak muscle activity was calculated during stance phase of running. Data was analyzes using paired t-test at significant level of p The results of this study showed that in absorption phase, Mg (p=0.02) and Bf (p=0.02) activity, and Vl-Bf (p=0.02), Vl-Lg (p 0.001) and Ta-Mg (p=0.01) co-contraction index decreased after fatigue. In propulsion phase, after fatigue, Ta (p=0.001) activity decreased while activity of Mg muscle (p=0.01) was increased. In this phase Ta-Mg (p=0.0001) and Ta-Sol (p=0.005) co-contraction index decreased after fatigue. In pre-activation phase, fatigue increased Ta (p=0.01) and Bf (p=0.0001) activity. Also, fatigue increased time to peak activity of Bf, Gm and Gl muscles (p=0.001).
Fatigue can make alterations in running muscular mechanism indicating neural system attempt to reduce injury risk during fatigue. Therefore, in order to prevent running related injuries, we recommend considering percentage of muscular activity timing in novice runners.