The effect of localized leg muscle fatigue on tibial impact acceleration

Objective. The objective of this study was to assess the effect of localized leg muscle fatigue on tibial acceleration following impact. Background. Peak tibial accelerations measured just distal to the knee joint during running have been shown to increase with general body fatigue. However, the role that local leg muscle fatigue plays in shock attenuation is not clear. Methods. The unshod, dominant foot of 24 healthy women in two different age groups was impacted into a vertical force plate, using a human pendulum method. Impact velocity and force approximated that found in running. EMG activity of the gastrocnemius and tibialis anterior muscles was monitored during fatiguing isometric exercise to assess fatigue, and quantified at impact as a measure of muscle activation level. A skin-mounted uni-axial accelerometer, was located at the tibial tubercle under pre-load, to measure tibial acceleration at impact. Results. There was a significant decrease in peak tibial acceleration (P=0.008) and acceleration slope (P=0.033) following fatigue. There were no significant main effects or interactions for age group or muscle group for all tibial response variables. Conclusion. The reduction in peak tibial acceleration following fatigue (for the test performed) is contrary to the response documented following whole-body fatigue.