An ultrasonic method is described to measure changes in width of the anterolateral leg compartment in its lower third following exercise. In 20 normal subjects, compartment widths increased an average of 8.6% following exercise, with joggers' compartments increasing 10.1%, as compared to 7.4% in nonjoggers. Control measurements of the compartment width in a cadaver leg showed excellent correlation with the ultrasound measurement. Following exercise, vascular responses and fluid transfers caused an increase in volume of the compartment contents, which is reflected in compartment widening. Because the compartment contents are usually contained by a complete but only moderately compliant wall, intracompartmental pressure will normally rise, and symptoms of a compartment syndrome will result. Diagnosis of exertional compartment syndrome in the leg has usually been made at clinical examination. Measurement of compartment width increase is intended to complement intracompartmental pressure and aid in differentiating the diagnosis of exertional compartment syndrome from shin splints, stress fracture, and tendonitis. Additionally, muscle atrophy, hypertrophy and growth can be recorded by the ultrasound technique.