Effects of length on the catchlike property of human quadriceps femoris muscle.

BACKGROUND AND PURPOSE: Recent reports have suggested that electrical stimulation trains that take advantage of the catchlike property of skeletal muscle can produce higher forces from skeletal muscle than traditionally used constant-frequency trains. This study investigated the effects of catchlike-inducing trains on human quadriceps femoris muscles while the kneejoint was held at 15 degrees of flexion. SUBJECTS AND METHODS: Subjects (N=12) were tested with constant-frequency trains that had interpulse intervals ranging from 10 to 160 milliseconds and comparable catchlike-inducing trains. Data were collected during the control condition (1 train every 10 seconds) and during repetitive contractions (1 train per second). RESULTS: During control and repetitive activation conditions, catchlike-inducing trains produced approximately 5% to 110% greater peak forces than comparable constant-frequency trains, depending on the frequencies being compared. Total forces produced (ie, force-time integrals) were increased up to 59% and 49% during the control and repetitive activation conditions, respectively. CONCLUSION AND DISCUSSION: These results support earlier findings that catchlike-inducing trains may be advantageous in functional electrical stimulation applications.