Human Striated Muscle Ultrastructural Changes Accompanying Increased Strength without Hypertrophy

Skeletal muscle was obtained from the vastus lateralis of three normal college male students. Two biopsies were obtained prior to a training period and one after the training period. Subjects participated in an intense weight training program involving isometric and isotonic exercises. The subjects participated in the exercise regimen five days in each week for a period of 10 weeks. Muscle tissue was processed immediately for electron microscope examination. The following parameters were measured from micrographs of longitudinal sections: sarcomere length, sarcomere width, intracellular fat, mitochondria number and mitochondria length. The following parameters were measured from micrographs of cross sections: myosin filament concentration, distance between myosin filaments, myosin filament diameter, the number of actin filaments in orbit around a myosin filament, and gross cell size. Major findings included significant changes in myosin filament concentration, distance between myosin filaments, and the number of actin filaments in orbit around a myosin filament.