Electrical stimulation training is known to alter skeletal muscle characteristics after a spinal cord injury, but the effect of load on optimizing the training protocol has not been fully investigated. This study investigated two electrical-stimulation training regimes with different loads on intramuscular parameters of the paralyzed lower limbs. Six paraplegic individuals with a spinal cord injury underwent electrical stimulation training (45 min daily for 3 days per week for 10 weeks). One leg was trained statically with load, and the contralateral leg was trained dynamically with minimal load. Isometric force assessed with 35-HZ stimuli increased significantly in both legs from baseline, with the static-trained leg also being significantly higher than the dynamic-trained leg. The vastus lateralis muscle of the statically trained leg showed a significant increase in type I fibers, fiber cross-sectional area, capillary-to-fiber ratio, and citrate synthase activity when compared to both baseline and the dynamically trained leg. Relative oxygenation of the vastus lateralis muscle as determined by near infrared spectroscopy was also significantly greater after static training. This study indicates that the load that is applied to paralyzed muscle during an electrical stimulation training program is an important factor in determining the amount of muscle adaptation that can be achieved.

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Experiments are described in which a fatigue index is determined for the latissimus dorsi muscle of sheep in situ, using capacitive strain gauges. Parallel experiments for invasive and non-invasive measurements are conducted, measuring global contraction and relaxation rates and shortening duration for paced muscle. The results show that, above one pulse per burst (5 V, 100 microseconds pulsewidth), contraction rates (62 +/- 11 mm s-1) and relaxation rates (50 +/- 7 mm s-1) are constant for unloaded muscle. For one animal, fatigue testing with a 2.5 kg load at six pulses per burst shows shortening rates increasing to a maximum (80 mm s-1) after 30 s and reducing to 5 mm s-1 after 150 s. The decrease in shortening amplitude is used as a fatigue index, log displacement against time. Power output is load dependent, measuring 4.7 W kg-1 with a 2.5 kg load. There is good agreement between the invasive and non-invasive measurements, thus providing a method for monitoring changes in muscle parameters non-invasively during future pacing transformation.

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