A series of case studies aimed to assess bone and stress fractures in a 768-km ultra-trail race for 11 days. Four nonprofessional male athletes completed the event without diagnosing any stress fracture. Bone turnover markers (osteocalcin (OC), serum C-terminal cross-linking telopeptide of type I collagen (CTX), bone-specific alkaline phosphatase (BALP), and serum turnover calcium (Ca2+)) were assessed before (pre) and after the race (post) and on days two and nine during the recovery period (rec2 and rec9), respectively. Results showed: post-pre-OC = -45.78%, BALP = -61.74%, CTX = +37.28% and Ca2+ = -3.60%. At rec2 and rec9, the four parameters did not return to their pre-run levels: OC, -48.31%; BALP, -61.66%; CTX, +11.93% and Ca2+, -3.38%; and OC = -25.12%, BALP = -54.65%, CTX = +93.41% and Ca2+ = +3.15%), respectively. Our results indicated that the ultra-trail race induced several changes in bone turnover markers, uncoupling of bone metabolism, increased bone resorption: OC and BALP and suppressed bone formation: CTX and Ca2+. Bone turnover markers can help determine the response of bone to extreme effort and might also help predict the risk of stress fractures.
Keywords: bone formation; bone mass density; bone remodelling markers; bone resorption; ultra-endurance.