LAUSR

We evaluated the effects of differential muscle architectural adaptations on neuromuscular fatigue resistance. Seven young males and 6 females participated in this study. Using a longitudinal within-subject design, legs were randomly assigned to perform isometric training of the tibialis anterior (TA) 3× per week for 8 weeks at a short (S-Group) or long muscle-tendon unit length (L-Group). Before and following training, fascicle length (FL) and pennation angle (PA) of the TA were assessed. As well, fatigue-related time-course changes in isometric maximal voluntary contraction (MVC) torque and isotonic peak power (20%MVC resistance) were determined before, immediately, 1, 2, 5, and 10 min following task failure. The fatiguing task consisted of repeated maximal effort isotonic (20%MVC resistance) contractions over a 40° range of motion, until the participant reached a 40% reduction in peak power. Although there was no clear improvement of neuromuscular fatigue resistance following training in both groups (P = 0.081; S-Group: ~20%, L-Group: ~51%), the change in neuromuscular fatigue resistance was related positively to the training-induced increase in PA (~6%, P < 0.001) in the S-Group (r = 0.739, P = 0.004) and negatively to the training-induced increase in FL (~4%, P = 0.001) in the L-Group (r = -0.568, P = 0.043). Both groups recovered similarly for MVC torque and peak power after the fatiguing task as compared to before training. We suggest that the relationships between the changes in muscle architecture and neuromuscular fatigue resistance depend on the muscle-tendon unit lengths at which the training is performed.