Sclerostin and bone turnover markers response to cycling and running at the same moderate-to-vigorous exercise intensity in healthy men

Background: Recreational cycling is a popular activity which stimulates and improves cardiovascular fitness. The corresponding benefits for bone are unclear. Purpose: This study examined the effect of running (high-impact) vs. cycling (low-impact), at the same moderate-to-vigorous exercise intensity, on markers of bone formation (N-terminal propeptide of type I collagen, PINP) and bone resorption (C-telopeptide of type I collagen, CTX-1), a non-collagenous bone remodeling marker (osteocalcin), as well as bone-modulating factors, including parathyroid hormone (PTH), irisin (myokine) and sclerostin (osteokine). Methods: Thirteen healthy men (23.7 ± 1.0 y) performed two progressive exercise tests to exhaustion (peak VO₂) on a cycle ergometer (CE) and on a treadmill (TM). On subsequent separate days, in randomized order, participants performed 30-min continuous running or cycling at 70% heart rate reserve (HRR). Blood was drawn before, immediately post- and 1 h into recovery. Results: PTH transiently increased (CE, 51.7%; TM, 50.6%) immediately after exercise in both exercise modes. Sclerostin levels increased following running only (27.7%). Irisin increased following both running and cycling. In both exercise modes, CTX-1 decreased immediately after exercise, with no significant change in PINP and osteocalcin. Conclusion: At the same moderate-to-vigorous exercise intensity, running appears to result in a greater transient sclerostin response compared with cycling, while the responses of bone markers, PTH and irisin are similar. The longer-term implications of this differential bone response need to be further examined.