This study aimed to determine the influence of sport type and training volume during adolescence on low bone mineral density (BMD) in long-distance runners. In total, 125 competitive long-distance runners (64 males; 21.3 ± 4.2 years, 61 females; 21.4 ± 3.1 years) participated in this retrospective cohort study. We collected training history data during adolescence using a questionnaire and measured BMD of the lumbar spine and whole body using dual-energy X-ray absorptiometry (DXA). Male runners with low BMD ran for more hours (p = 0.02) and had a smaller proportion of multidirectional loading activity (p = 0.03) in elementary school than those with normal BMD. Although female runners with low BMD performed multidirectional activity for more hours in middle school than those with normal BMD (p = 0.01), running volume was similar between groups. There was an increasing trend in the total number of hours of physical activity in middle school in female runners with low BMD (p = 0.05). These results suggest that avoiding specialization in long-distance running, increasing the proportion of multidirectional sports, and preventing overload during the bone growth phase may reduce the risk of low BMD among runners.

男性長距離走選手を対象にシーズン中の骨代謝回転の変化を明らかにすることを目的とした.大学生男性長距離走選手66名を対象に2022年シーズンの開始から終了までに5回測定を行い,最終的に25名が解析対象となった.測定項目は血液検査で骨形成マーカーとして骨型アルカリフォスファターゼ(BAP),骨吸収マーカーとして酒石酸低抵抗性酸フォスファターゼ(TRACP-5b),遊離テストステロン(free testosterone),黄体化ホルモン(LH),コルチゾール(cortisol)とし,骨形成と骨吸収のバランスを示すuncoupling index(UI)を算出した.さらに身体組成測定とトレーニング量として走行距離を集計し,混合モデルを用いて各項目の変化を検討した.また,トレーニング量と骨代謝マーカーの関係を各時点において検討した.その結果,BAPがシーズン中に低値を示した.運動は骨形成を亢進させることが報告されているが,本研究では先行研究とは異なる結果を示した.さらに,トレーニング量と骨代謝マーカーの間にはすべての時点において関連が認められなかった.骨代謝マーカーが変化する要因に低エナジー・アベイラビリティ(LEA)が挙げられる.本研究においてトレーニング量との関連が認められなかったことから,今後はエネルギー摂取量を評価するとともに,LEAと骨代謝マーカーの関連について検討する必要がある.(著者抄録)

INTRODUCTION: The bone metabolism of male endurance runners during a competitive season has been little studied. Furthermore, Japanese runners have a special competitive season. This study aimed to investigate the change of bone turnover markers (BTMs) and other hormones in Japanese male endurance runners. MATERIALS AND METHODS: We investigated biochemical markers, bone formation and resorption markers and sex hormones, body composition using dual-energy X-ray absorptiometry (DXA), and training volume during a competitive season. 11 (age: 24.0 ± 4.3 years) Japanese male endurance runners were analyzed in this study. They participated in all measurements three times a year: the baseline (BL), the post-track period (PT), and the road race period (RR). RESULTS: Fat mass (FM) and percentage of body fat (% body fat) at RR (p = 0.009, p = 0.009) were lower than at BL. Specific bone alkaline phosphatase (BAP) decreased at PT (p = 0.004) and RR (p = 0.004) compared with BL. However, the bone resorption marker did not change. Free testosterone at PT (p = 0.032) was lower than BL. There was no correlation with blood variables and body composition or training volume. CONCLUSION: BAP and testosterone in Japanese male endurance runners decreased during the competitive season. However, there was no correlation between blood variables and training volume.