FASCICLE LENGTH AND PENNATION ANGLE OF THE HUMAN BICEPS FEMORIS MUSCLE AT REST AND DURING SUBMAXIMAL CONTRACTION

Abstract

The purpose of this study was to determine the changes in fascicle length and pennation angle of the long head of the biceps femoris muscle (BFlh) between active contraction and resting muscle at various combinations of hip and knee position using ultrasonography. Ultrasound images of the BFlh in 19 females (23.5 ± 1.7 years) were recorded in 5 different combinations of hip and knee positioning representing a wide range of overall muscle length change. The 5 positions were (hip/knee in degrees): 0/90, 0/0, 90/90, 90/45, and 90/0. At each of the positions, ultrasound images were recorded when the subject was relaxed and then during a muscle contraction at 30% of the maximal isometric voluntary contraction at that position. Fascicle length increased and pennation angle decreased as the hip and knee positions were progressed from the 0/90 to the 90/0 positions in the order shown above. Fascicle length increase from 5.64 ± 2.06 cm at 0/90 to 12.95 ± 1.65cm at 90/0 with the muscle at rest. Comparing active to resting muscle at each of the positions, fascicle length decreased by 8–12%, and the pennation angle increased from 10–70% with the magnitude of the increase dependent upon position. Based on the sarcomere length of the BFlh from cadavers fixed at the 0/0 position and the percentage change in fascicle length from 0/0 to each of the positions, a length-tension diagram relative to joint positions was calculated. The human BFlh muscle occupies a portion of the ascending, plateau, and descending limbs of the length-tension relationship in the range of motion studied. The architecture of the human BFlh muscle (a biarticular muscle) is influenced by both hip and knee position and whether the muscle is active or at rest.