BONE MASS AND ENDOCRINE ADAPTATIONS TO TRAINING IN SPINAL-CORD INJURED INDIVIDUALS

To investigate whether exercise training can produce increases in bone mass in spinal cord-injured (SCI) individuals with established disuse osteopenia, nine subjects (age 28.2 years, time since injury 6.0 year s, level of injury C-5-T-7) were recruited for a 9-month training prog ram using functional electrical stimulation cycle ergometry (FES-CE), which produces active muscle contractions in the paralyzed limb, After training, bone mineral density (BMD, by X-ray absorptiometry) increas ed by 0.047 +/- 0.010 g/cm(2) at the lumbar spine; changes in BMD at t he femoral neck, distal femur, and proximal tibia were not significant for the group as a whole. In a subset of subjects training at greater than or equal to 18 W for at least 3 months (n = 4), BMD increased by 0.095 +/- 0.026 g/cm(2) (+18%) at the distal femur, By 6 months of tr aining, a 78% increase in serum osteocalcin was observed, indicating a n increase in bone turnover, Urinary calcium and hydroxyproline, indic ators of resorptive activity, did not change over the same period, Ser um PTH increased 75% over baseline values (from 2.98 +/- 0.15 to 5.22 +/- 0.62 pmol/L) after 6 months' training, with several individual val ues in hyperparathyroid range; PTH declined toward baseline values by 9 months, These data establish the feasibility of stimulating site-spe cific increases in bone mass in severely osteopenic bone with muscle c ontractions independent of weight-bearing for those subjects able to a chieve a threshold power output of 18 W with FES-CE, Calcium supplemen tation from the outset of training in osteopenic individuals may be ad visable to prevent training-induced increases in PTH.