LAUSR

PURPOSE The present study compared the effects of contraction intensity (submaximal vs. maximal) and mode (concentric vs. eccentric) on biceps femoris long head (BFlh) fascicle lengthening, rotation, and architectural gear ratio at long and short muscle lengths. METHODS Data were captured from 18 healthy adults (10 men and 8 women) without history of right hamstring strain injury were used in the study. BFlh fascicle length (Lf) and angle (FA) and muscle thickness (MT) were assessed in real time using two serially aligned ultrasound devices whilst submaximal and maximal concentric and eccentric isokinetic knee flexions were performed at 30°/s. Ultrasound videos were exported and edited to create a single, synchronized video and three fascicles were analyzed through the range of motion (10°-80°). Changes (Δ) in Lf, FA, MT and muscle gear at long (60-80° knee angle; 0° = full knee extension) and short (10°-30°) muscle lengths and across the full knee flexion range were measured and compared. RESULTS Greater ΔLf was observed at long muscle length (p < 0.001) during both submaximal and maximal eccentric and concentric contractions. When the full length range was analyzed, a slightly greater ΔMT was observed in concentric contractions (p = 0.03). No significant differences between submaximal and maximal contractions were observed for ΔLf, ΔFA or ΔMT. No changes were detected in the calculated muscle gear between muscle lengths, intensities or conditions (p > 0.05). CONCLUSIONS Although gear ratio ranged ~1.0-1.1 under most conditions, the increased fascicle lengthening observed at long muscle lengths might influence acute myofiber damage risk but also speculatively play a role in chronic hypertrophic responses to training.