Architecture of contracting human muscles and its functional significance

This paper reviews three of our recent studies on human muscle architecture in vivo. 1. Hypertrophic changes: From B-mode ultrasonograms, pennation an gles and thickness of triceps brachii were determined for normal subjects a nd highly-trained bodybuilders. There was a significant correlation between muscle thickness and pennation angles. It was confirmed that hypertrophy w as accompanied by an increase in pennation angles. 2. Variation of fascicle architecture: Fascicle lengths and pennation angles were obtained from dif ferent positions in the gastrocnemius muscle while the subjects relaxed and performed isometric planter flexion. The fascicle length was uniform throu ghout the muscle and shortened by contraction (30-34% at 50% of the maximal force). On the other hand, pennation angles differed among positions and i ncreased by contraction. The muscle thickness did not change by contraction . Pennation angles were significantly correlated with muscle thickness with in muscle. 3. Joint position-fascicle length relationships: Ultrasonic imag es of the gastrocnemius and soleus muscles were obtained while the subject performed maximal isometric plantarflexion at various joint positions, from which fascicle lengths and angles were determined. The length-force relati onship of each muscle was estimated. It was suggested that human muscle arc hitecture has an ability to make substantial changes to adapt to environmen tal conditions.