Treadmill Versus Stationary Cycling On The Bone Biomarker Response To Endurance Exercise In Older Veterans

Both weight-bearing (e.g., treadmill walking, TM) and weight-supported (e.g., cycle ergometry, CE) endurance exercise can cause a decrease in serum ionized calcium (iCa) and increases in parathyroid hormone (PTH) and c-terminal telopeptides of type I collagen (CTX; marker of bone resorption). Prior studies suggested that weight-bearing exercise may provoke a smaller increase in PTH and CTX than weight-supported exercise, but exercise mode has not been evaluated in the same participants. This research is of special importance to older Veterans who may have orthopedic injuries that prevent participation in some forms of exercise. PURPOSE: Determine whether there are different iCa, PTH, CTX, and procollagen type 1 n-terminal propeptide (P1NP; marker of bone formation) responses to 60 minutes of weight-bearing versus weight-supported endurance exercise. METHODS: Older Veterans (n = 9, 71 ± 3 years) performed two identical 60-min endurance exercise bouts (1 TM, 1 CE) at least 1 week apart at 70-80% of the peak heart rate measure during a maximal TM cardiopulmonary exercise test. Order of the exercise mode was randomized. iCa, PTH, CTX, and P1NP were measured before, during, and up to 24 hours after exercise. Paired t-tests compared the changes between modes in iCa, PTH, CTX, and P1NP from 15 minutes before to immediately after exercise. RESULTS: All results are mean ± SD. Average heart rate was similar between exercise modes (TW: 117 ± 6 bpm, SC: 118 ± 10 bpm, p = 0.78). Changes from before to immediately after exercise were similar for both exercise modes for iCa (TW: -0.12 ± 0.10 mg/dL, CE: -0.09 ± 0.13 mg/dL, p = 0.70), PTH (TW: 16.6 ± 11.7 pg/mL, CE: 15.4 ± 14.2 pg/mL, p = 0.87), CTX (TW: 0.05 ± 0.02 ng/mL, CE: 0.06 ± 0.04 ng/mL, p = 0.75), and P1NP (TW: 6.5 ± 6.8 ng/mL, CE: 7.4 ± 8.4 ng/mL, p = 0.45). CONCLUSION: Single bouts of TM and CE exercise generated a similar decrease in iCa and increases in PTH, CTX, and P1NP from before to after exercise. Further research is needed to determine if both exercise modes have a similar biomarker profile with repeated exercise bouts, such as with regular exercise participation or exercise training. Supported by: I21RX003593, IK2RX003820