Vastus Lateralis Fascicle Length Isometricity at Different Knee Extensor Torques and Angles

Muscle fascicle lengths change as a function of muscle length and muscle force. The effect of these two factors may be balanced to maintain the same fascicle length at different joint angles during in vivo muscle function. The aim of this study was to determine the relationship between knee flexion angles, knee extensor torques and fascicle lengths of the Vastus Lateralis muscle. We found that a constant fascicle length can be maintained across a range of 60° of knee flexion if knee extensor forces are varied appropriately. Fascicle length isometricity has been found for some functional movements. For example, fascicle lengths in cat [1] and human [2,3] medial gastrocnemius muscles were shown to remain at virtually constant lengths in the midstance phase of walking despite substantial changes in joint angles and torques. Fascicle length isometricity may offer important functional advantages in a variety of situations, such as increased force production in “concentric” contractions and savings of metabolic energy [4].