Electrical stimulation paradigms on muscle quality and bone mineral density after spinal cord injury

Abstract

The goal of the work was to determine the effects of altering muscle quality (peak torque and muscle CSA) via NMES-RT on bone mineral density (BMD) following application of FES-lower extremity cycling. Components of muscle quality were altered and attenuated the decline in BMD after SCI.

Introduction: Spinal cord injury (SCI) negatively impacts muscle quality and bone health. Neuromuscular electrical stimulation-resistance training (NMES-RT) has been shown to enhance muscle quality. It is unclear whether adding NMES-RT to functional electrical stimulation (FES)-lower extremity cycling may further augment muscle quality and subsequently enhance bone mineral density (BMD).

Methods: Thirty-two participants were randomized into either 12 weeks of NMES-RT followed by 12 weeks of FES- lower extremity cycling (NMES-RT + FES; n = 16) or 12 weeks of passive movement training (PMT) followed by 12 weeks of FES-lower extremity cycling (PMT + FES; n = 16). Measurements were conducted at baseline (BL), post-interventions 1 and 2 (P1 and P2) separated evenly by 12 weeks. Left thigh muscle isometric and isokinetic torques were measured using an isokinetic dynamometer. Magnetic resonance imaging measured whole thigh and knee extensor (KE) muscle CSAs. Dual energy X-ray absorptiometry measured total and regional BMD.

Results: NMES-RT elicited a trend towards greater isometric torque at 80 Hz (P = 0.057) and isokinetic torque (60 deg/s; P = 0.009 and 180 deg/s; P = 0.003) compared to PMT. Muscle CSA was greater in left whole thigh (F (2,20) = 9.1; P = 0.007) and KE (F (2,20) = 15.5; P = 0.001) by 11.0 and 8.0 cm² respectively at P1 in the NMES-RT + FES compared to PMT + FES. In the NMES-RT + FES, ankle weights were positively associated with muscle CSA, isometric and isokinetic torques as well as muscle quality following P1. Compared to PMT + FES, NMES-RT + FES maintained BMD at the distal femur.

Conclusion: NMES-RT + FES enhanced muscle quality as measured by torque production and muscle CSA as result of increasing ankle weights. The addition of FES- lower extremity cycling to NMES-RT maintained but did not further augment muscle quality. Furthermore, NMES-RT + FES may help maintain BMD after SCI.

Clinical trial registration: Registered with clinicaltrials.gov: NCT02660073.

Keywords: BMD; Muscle quality; Peak torque; Rehabilitation; SCI.