Principal component analysis demonstrates trunk muscle pattern variation with fall direction

Abstract

This study examined the role of the direction of a fall on neuromuscular response. Electromyography sensors were positioned on the erector spinae of twenty subjects. Falls, simulating slips, occurred in the anterior, posterior, and medial-lateral directions. The average activation curves for the four different fall directions displayed different characteristics. Observations were supported by principal component analysis (PCA). PCA coefficients related all fall directions to a single reflex-like response. Analysis of variance on the coefficients demonstrated that anterior falls had a significantly (p<0.05) stronger reflex-like response than posterior falls. There was also a significant (p<0.05) difference for the interaction between side of the erector spinae and fall direction for the medial-lateral fall directions. Here the contra-lateral muscle had a stronger reflex-like response than the ipsi-lateral muscle. Possible reasons for the observations could be to increase time available for active responses or decrease the energy transferred if the head impacted the ground.