1. The glycogen-depletion patterns were studied as a measure of muscle-fibre recruitment in patients after leg injuries (fractures, ligament injuries). Intermittent isometric and dynamic isokinetic knee extension were performed with 30 and 50% of the maximal isometric torque of the injured leg. In a third group isokinetic and dynamic exercise with weights were compared by using maximal effort procedures.
2. The 30% maximal voluntary contraction programme, which corresponded to 16% of maximal voluntary contraction of the non-injured leg, resulted in glycogen depletion of type I fibres, which was significant only in the isometric exercise. In the 50% maximal voluntary contraction programme (41% of maximal voluntary contraction of the non-injured leg) depletion of type II fibres dominated and was significant with isometric exercises. In the maximal effort programmes there was a significant depletion of type II fibres.
3. Subjects with a relatively large reduction in strength or a small number of type I fibres demonstrated more depletion of these fibres than other subjects.
4. In patients with moderately reduced muscle strength and muscle fibre atrophy static or dynamic exercises using at least 50% of the actual maximal voluntary contraction can thus be used to recruit and train type II fibres.