Effects Of An 8-week Nordic Hamstring Vs. Isokinetic Eccentric Training Intervention On Biceps Femoris Muscle-tendon Interactions

Abstract

Resistance eccentric training triggers adaptations in both active and passive elements of the muscle tendon unit (MTU). Previous research highlight the buffering role that tendinous tissues may play to mitigate muscle strain and to optimize operating fascicle lengths. However, the effects of eccentric training on the muscle-tendon interactions of the biceps femoris remain unexplored. PURPOSE: To evaluate the effects of eccentric training on torque and muscle-tendon interactions of the biceps femoris muscle during lengthening contractions. METHODS: Eighteen participants completed an 8-wk standardized eccentric training intervention comprising 15 sessions of Nordic Hamstring (NH) or isokinetic leg curl (IK; n=10) exercise. Pre and post training, torque and fascicle, tendinous tissue and MTU length of the biceps femoris muscle were measured during maximal 70° lengthening knee extensions at 60°.s-1. One sample t-test statistical parametric mapping (SPM) analyses were performed to evaluate fascicle and tendon behaviour during the contractions. Training effects were evaluated with two-way repeated measures ANOVA and paired t-test SPM. RESULTS: Both groups increased torque from 38% to 100% of the contraction duration, with greater improvements in IK from 78.5 to 100% (p < 0.001). The contribution of tendinous tissue to MTU length changes slightly increased only in IK at the last 2% of the contraction (p = 0.04). Despite opposite trend changes in NH, no training effects on fascicle or tendon behavior occurred. The tendinous tissues contribution to MTU lengthening was greater than fascicles up to 75% of the contraction. The fascicles contribution progressively augmented at the end of the contraction (p < 0.05). CONCLUSION: We provide novel findings on the muscle-tendon interactions of the biceps femoris muscle during lengthening contractions. A 15-session eccentric training program comprising NH or IK exercise does not seem to affect muscle-tendon interactions.