Musculoskeletal responses of spinal cord injured individuals to functional neuromuscular stimulation-induced knee extension exercise training

This study was conducted to evaluate a newly designed functional neuromuscular stimulation (FNS)-induced knee extension (KE) exercise system that incorporates the most desired features of previously described systems by determining the musculoskeletal responses of spinal cord injured (SCI) individuals to training. A specially designed chair and electrical stimulator were fabricated for FNS-induced KE resistance exercise. Surface electrodes were placed over motor points of the quadriceps muscles, and KE was alternated between legs at an average rate of 6 KE/min/leg. KE testing protocols were developed for pre- and post-training evaluations of performance, and 12 SCI subjects exercise-trained up to three times per week for 36 sessions using a progressive resistance load at ankle level. Pre- and post-training evaluation data were statistically compared using a 0.05 level for significance. Quadriceps muscle performance (strength x repetitions) improved for both legs in all subjects as indicated by significant increases in load resistance and repetitions over the 36-session training period (right leg x̄= 1156.0 versus 1624.8 kg·reps, left leg x̄= 1127.3 versus 1721.1 kg·reps). In addition, knee range of motion significantly increased (right leg x̄= 134 versus 146 degrees, left leg x̄= 133 versus 144 degrees). Thigh skinfold, thigh girth, body weight and bone density were not significantly changed. The lack of decrease in bone density in some subjects suggests that the training may retard the rate of bone loss which typically occurs with SCI. No injuries or problems were encountered during testing and training. Therefore, this newly-designed FNS-KE exercise appears to be safe, easy to use, and effective for all subjects who participated in the study. The protocol developed for this form of FNS training of the quadriceps may be used to increase the integrity of muscles paralyzed due to SCI. In addition, the enhanced muscle performance reserve may better enable the SCI individual to accomplish more complex FNS tasks with less fatigue.