NMES-Resistance Training Enhances Oxygen Uptake and Ventilatory Efficiency Independent of Mitochondrial Complexes after SCI: A Randomized Clinical Trial.

The purpose of the study was to determine whether neuromuscular electrical stimulation resistance training (NMES-RT) evoked muscle hypertrophy is accompanied by increased VO2 peak, ventilatory efficiency and mitochondrial respiration in individuals with chronic spinal cord injury (SCI). Thirty-three men and women with chronic, predominantly traumatic, SCI were randomized to either NMES-RT (n=20) or passive movement training (PMT; n=13). Functional electrical stimulation-lower extremity cycling (FES-LEC) was used to test leg VO2 peak, VE/VCO2 ratio and substrate utilization prior to and post-intervention. Magnetic resonance imaging was used to measure muscle cross-sectional area (CSA). Finally, muscle biopsy was performed to measure mitochondrial complexes and respiration. The NMES-RT group showed a significant increase in post-intervention VO2 peak compared to baseline (∆ VO2 = 14%, P < 0.01) with no changes in the PMT group (∆ VO2 = 1.6%, P= 0.47). Similarly, thigh (∆ CSA Thigh = 19%) and knee extensor (∆ CSA Knee = 30.4 %, P < 0.01) CSAs increased following NMES-RT but not after PMT. The changes in thigh and knee extensor muscle CSAs were positively related with the change in VO2 peak. Neither NMES-RT nor PMT changed mitochondrial complex tissue levels; however, changes in peak VO2 were related to complex I. In conclusion, in persons with SCI, NMES-RT-induced skeletal muscle hypertrophy was accompanied with increased peak VO2 consumption which may partially be explained by enhanced activity of mitochondrial complex I.