Can body weight supported treadmill training increase bone mass and reverse muscle atrophy in individuals with chronic incomplete spinal cord injury?

This study evaluates the impact of 12 months of body weight supported treadmill training (BWSTT) on muscle and bone in individuals with spinal cord injury (SCI). Fourteen individuals who sustained an incomplete SCI at least 12 months before the study were recruited to participate in BWSTT 3 times/week for a total of 144 sessions. Thirteen individuals completed the study. The average age of subjects was 29 y, average time post-injury was 7.70 y (range: 1-24 y). Areal bone densities of the proximal and distal femur, proximal tibia, spine, and whole body were measured using dual-energy X-ray absorptiometry. Muscle cross-sectional area (CSA), volumetric bone density, and bone geometry at mid-femur and proximal tibia were measured using computed tomography. Serum osteocalcin and urinary deoxypyridinoline were measured at baseline and after 6 and 12 months of training. All other measures were made before and after training. Participants experienced significant increases in whole-body lean mass, from 45.9 +/- 8.7 kg to 47.8 +/- 8.9 kg (mean +/- SD; p < 0.003). Muscle CSAs increased by an average of 4.9% and 8.2% at the thigh and lower leg sites, respectively. No significant changes occurred in bone density or bone geometry at any site, or in bone biochemical markers. Whole-body bone density exhibited a small but statistically significant decrease (p < 0.006). BWSTT may therefore be a promising intervention for increasing muscle mass. Although 12 months of BWSTT did not increase bone density in individuals with chronic incomplete SCI, it did not appear to decrease bone density at fracture-prone sites.