Trunk Muscle Fatigue and Activation are Associated with Drop Jump Performance

Abstract

Although the importance of core muscles on human motions has been recognized, little is known about the effect of trunk muscle fatigue and activation on drop jump (DJ) performance. PURPOSE: To examine how trunk muscle fatigue and activation relate to DJ performance. METHODS: The study included 7 healthy, well-trained males (age 20.8±1.4 years, height 168.4±5.7 cm, weight 67.1±8.0 kg). Subjects held vertical trunk position against a wire with one end attached to the posterior thorax, pulling the trunk posteriorly, with the other end attached to a weight corresponding to 25% of maximal voluntary isometric contraction force. Before and after this fatiguing task, maximum voluntary isometric trunk flexor contraction force (MVIC), and double- and single-leg DJ height (DJH), contact time (CT), and DJ index (DJI; DJH/CT) were measured. Surface electromyography was recorded from the dominant side of the anterior and posterior trunk musculature during DJs. Mean differences before and after the fatiguing task were examined using paired-sample t-tests. Simple linear regression analyses tested the relation of relative changes before and after the fatiguing task in the jump performance index and trunk muscle activation during preactivation, braking, and push off phase of each DJ. RESULTS: After the fatiguing task, MVIC was significantly decreased to 68.8±11.5% (p<0.01). DJI (Pre vs. Post fatigue for double- and single-leg DJ: 1.18±0.31 vs. 0.94±0.36, 0.52±0.13 vs. 0.41±0.15) and DJH (Pre vs. Post fatigue for double- and single-leg DJ: 22.12±5.09 cm vs. 20.01±5.24 cm, 13.21±3.04 cm vs. 11.07±3.64 cm) were significantly decreased (p<0.01), and CT (0.19±0.02 s vs. 0.22±0.03 s) was significantly extended (p<0.01). Regression analyses revealed that greater ensemble trunk muscle preactivation reduction rate was associated with CT lengthening rate in double-leg DJ (R2=0.582, B=-0.257, p=0.046), and DJI reductions rate in single-leg DJ (R2=0.910, B=0.309, p=0.001) and that greater rectus abdominus (R2=0.779, B=0.138, p=0.008) and external oblique activations reduction rate during breaking phase (R2=0.703, B=0.276, p=0.018) were associated with greater DJI reduction rate. CONCLUSIONS: Trunk muscle fatigue and decreased trunk flexor muscle activation during DJ have negative effects on both double- and single-leg DJ.