A functional electrical stimulation rowing exercise program interrupts expected bone loss after SCI
1Lambach R, 2Stafford N, 1Kolesar J, 1Kiratli J, 1Creasey G, 3Gibbons R, 4Andrews B, 1Beaupre G
1VA Palo Alto Health Care System, Palo Alto, CA, USA; 2Stanford University, Stanford, CA, USA; 3University College London, London, , United kingdom; 4University of Warwick, Coventry, , United kingdom
Objective: Rapid and substantial bone loss which occurs after spinal cord injury (SCI) results in elevated fracture risk. To reduce the incidence of fracture there is a need to identify effective countermeasures such as interventions that provide lower limb skeletal forces of sufficient magnitude and repetition to slow or reverse bone loss after SCI. We investigated the use of a functional electrical stimulation (FES) rowing exercise program to reduce expected bone loss within the first two years after SCI.
Design/Method: Participants rowed three times each week on a modified indoor rowing ergometer using FES controlled by a button on the ergometer handle that allowed rowers to activate their quadriceps and hamstrings muscles. Bone mineral density (BMD) in the distal femur (4% of bone length proximal to the knee joint) was measured using peripheral quantitative computed tomography (pQCT) at enrollment and after 3, 6, and 9 months of FES training. Three dimensional motion and force data from each foot were collected during FES rowing at 3, 6, and 9 months. The bone stimulus for each rower at each time point was calculated using the average number of weekly lower limb loading cycles during the previous three months, the peak reaction force (under one foot) produced during FES rowing, and the initial bone mineral content at the 4% distal femur site in the leg of interest. A regression analysis was used to determine the relationship between the calculated bone stimulus and the change in BMD between time points.
Results: Four individuals with SCI (23-43 years old; 7-16 months post-SCI; level C7-T9; ASIA A or B) completed the nine-month FES rowing exercise program. Trabecular bone density decreased for all participants during the first three months (range: -10.5 to -25.0 mg/cm3), but during months 3-6 the rate of loss slowed substantially for two participants (from -17.8 to -8.9 and from -10.5 to -0.4 mg/cm3) and bone density increased for the remaining two participants (+13.2 and +11.6 mg/cm3). Three participants continued to experience little or no bone loss during months 6-9 (range: -2.0 to +2.4 mg/cm3). The fourth participant, who had the fewest training sessions and a decreased number of lower limb loading cycles during months 6-9, experienced a return of bone loss (-23.5 mg/cm3), although at a slower rate than prior to entry into the rowing program. The calculated bone stimulus was significantly correlated with the change in BMD (p = 0.04; r2 = 0.36). The average number of loading cycles per week varied among subjects and also within subjects (between time points) throughout the nine-month program (range: 902 to 2146 cycles per week). Despite substantial variations in SCI level and body mass (63.4-108.1 kg), forces per foot during FES rowing were approximately 20% of bodyweight for all participants (average: 20.3%, range: 17.7-26.2%).
Conclusion: Consistent participation in an FES rowing exercise program provided sufficient forces and repetitions to prevent the expected bone loss at the distal femur within the first two years after SCI. The calculated bone stimulus was a significant predictor of change in BMD over each three month time window.
Support: VA RR&D Pilot Project I21RX001410; PVA Endowment to Stanford University
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