Biceps femoris fascicle behavior during submaximal and maximal slow speed contractions
Medicine & Science in Sports & Exercise
Centre for Human Performance / School of Medical and Health Sciences
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)–Brazil (Programa de Doutorado Sanduíche / Edith Cowan University
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. BFlh fascicle length ( Lf ), fascicle angle (FA), and muscle thickness (MT) were assessed in real time using two serially aligned ultrasound devices while submaximal and maximal concentric and eccentric isokinetic knee flexions were performed at 30°·s -1 . Ultrasound videos were exported and edited to create a single, synchronized video, and three fascicles were analyzed through the range of motion (10° to 80°). Changes ( ) in Lf , FA, MT, and muscle gear at long (60° to 80° knee angle; 0° = full knee extension) and short (10° to 30°) muscle lengths and across the full knee flexion range were measured and compared. RESULTS: Greater Lf 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 MT was observed in concentric contractions ( P = 0.03). No significant differences between submaximal and maximal contractions were observed for Lf , FA, or MT. 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 to 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. Copyright © 2023 by the American College of Sports Medicine.