Purpose: Following spinal cord injury (SCI), atrophy is often observed in muscles innervated from spinal segments below the lesion. We used the twitch interpolation technique to estimate the total force capacity of the first dorsal interosseus muscle (FDI, index finger abductor) and compared these data to the maximal voluntary contraction (MVC) actually produced by the subject. Methods: Four SCI subjects who had partial voluntary control over their hand muscles, 7 control SCI subjects with intact hand function and 10 able-bodied subjects (AB) performed 3 MVCs and 3 voluntary contractions at 10, 30, 50 and 70% MVC with the right FDI muscle. During the contractions the ulnar nerve was electrically activated (two pulses, interval 10 ms). Muscle force evoked by the stimulation was expressed as a percentage of the potentiated rest twitch and plotted against the background force. Results: MVCs were smaller in the incomplete SCI-group (19.1±3.5N, p<0.005) compared to the control SCI group (40.8±9.1N) and AB-controls (38.1±10.2N). However, the total force capacity as estimated on the basis of regression analysis between the superimposed twitch and background forces resulted in similar forces for all groups (incomplete SCI: 28.5±7.3N, control SCI: 36.4±16.0N, AB-controls: 30.3±6.2N). Conclusion: Comparable total force capacity for all groups suggests that muscle atrophy was insignificant in the SCI-subjects with incomplete injuries.