Multiple lead electromyograms were recorded simultaneously with motion-picture studies of normal subjects during exercise on a stationary bicycle. Action potentials were picked up by surface electrodes from the sacrospinalis, rectus abdominis, glutaeus maximus and glutaeus medius, tensor fasciae latae, sartorius, gracilis, rectus femoris, vastus medialis, vastus lateralis, semitendinosus, biceps femoris, tibialis anterior, and gastrocnemius. Bicycling was performed against resistance of varying degree with the seat twenty-one and twenty-five inches from the center of the pedal sprocket. The evidence presented supports time following conclusions:

1. During bicycling, muscles contract in a pattern which is orderly and coordinated. This was unchanged even when the resistance was so great that assistance was needed to help initiate rotation of the pedals.

2. The pattern muscle activity is highly reproducible in each individual subject and among the three different subjects under test.

3. Varying the height of the bicycle seat does not influence, in general, the timing of muscle activity, but the exercise is performed with less effort when the seat is high.

4. As the resistance to muscle action increases, electrical activity intensifies in each muscle and develops in other muscles. Exercise against no resistance evokes action potentials primarily in the muscles acting on the foot and ankle.

5. The bicycle is a useful therapeutic device for increasing the range of motion in the hip, knee, and ankle within certain limits. The ankle moves through its complete range of motion, while considerably less motion occurs in the knee, and still less in time hip.

6. Of the muscles studied, those most necessary for pedaling a stationary bicycle are the tensor fasciae latae, sartorius, quadriceps femoris, and tibialis anterior as demonstrated by multiple lead electromyography.