A Muscle’s Functional Role Influences Movement Accuracy Before and After Eccentric Exercise

Abstract

Eccentric muscle contractions, especially if unaccustomed and intense, can cause fatigue and muscle damage that contributes to acute decrements in motor performance. Because performance of motor tasks requires the precise coordination of agonist and antagonist musculature, the effect of the eccentric activity on accuracy will likely depend on the damaged muscle’s functional role as an agonist or antagonist in the task. PURPOSE: To compare the effect of fatiguing eccentric exercise (EE) on the accuracy of aiming movements when the EE muscle group’s function is that of an agonist or antagonist. METHODS: 16 untrained subjects (9 M, 7 F; 27 ± 3 yrs.) completed discrete horizontal pointing movements between 2 targets (13mm diameter) that required 40° of elbow movement. Twenty elbow-extension and 20 elbow-flexion pointing movements were performed with their right arm before and immediately after eccentric exercise of the elbow extensor muscles standardized by isokinetic dynamometry. Movement accuracy was quantified by the incidence (overall accuracy) and duration to initiation (magnitude of error) of secondary submovements that were identified by zero crossings in the tangential velocity and acceleration profiles. RESULTS: When the exercised muscles performed the pointing task as the agonist (i.e. extension movements), movement times (MT) were longer and peak velocity (PV) decreased after EE compared with before EE (MT= 222 ± 40, 248 ± 37ms, p<0.05; PV= 3.4 ± 0.6, 3.1 ± 0.6m/s, p<0.05). However, when the exercised muscle was the antagonist (i.e. flexion movements), MT and PV remained unchanged. There were more trials with no corrective submovements (i.e. more accurate) for the extension compared with flexion movements before EE (92% vs. 62%, p<0.001), but there was a greater decline in accurate trials after EE for the extension movements (78% vs. 41% decline p<0.0001). Furthermore, although initially similar, the duration of the primary submovement was shorter (further from target) after EE for the movements in which the agonist was the exercised muscle compared with an antagonistic role (62% vs. 73% of total movement time, p<0.001). CONCLUSIONS: There is a greater effect of EE-induced muscle fatigue and damage on movement kinematics and accuracy when the muscle’s functional role is agonistic.