The effect of sex and protein supplementation on bone metabolism during a 36-hour military field exercise in energy deficit

Thomas J. O'Leary (Lead Author), Charlotte V. Coombs, Victoria C. Edwards, Sam D. Blacker, Rebecca L. Knight, Fiona N. Koivula, Jonathan C. Y. Tang, William D. Fraser, Sophie L. Wardle, Julie P. Greeves

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This study investigated sex differences in, and the effect of protein supplementation on, bone metabolism during a 36-h military field exercise. Forty-four British Army Officer cadets (14 women) completed a 36-h field exercise. Participants consumed either their habitual diet [n = 14 women (Women) and n = 15 men (Men Controls)] or the habitual diet with an additional 46.6 g·day−1 of protein for men [n = 15 men (Men Protein)]. Women and Men Protein were compared with Men Controls to examine the effect of sex and protein supplementation. Circulating markers of bone metabolism were measured before, 24 h after (postexercise), and 96 h after (recovery) the field exercise. Beta C-telopeptide cross links of type 1 collagen and cortisol were not different between time points or Women and Men Controls (P ≥ 0.094). Procollagen type I N-terminal propeptide decreased from baseline to postexercise (P < 0.001) and recovery (P < 0.001) in Women and Men Controls. Parathyroid hormone (PTH) increased from baseline to post-exercise (P = 0.006) and decreased from postexercise to recovery (P = 0.047) in Women and Men Controls. Total 25(OH)D increased from baseline to postexercise (P = 0.038) and recovery (P < 0.001) in Women and Men Controls. Testosterone decreased from baseline to post-exercise (P < 0.001) and recovery (P = 0.007) in Men Controls, but did not change for Women (all P = 1.000). Protein supplementation in men had no effect on any marker. Men and women experience similar changes to bone metabolism—decreased bone formation and increased PTH—following a short-field exercise. Protein had no protective effect likely because of the energy deficit.
Original languageEnglish
Pages (from-to)1481-1495
Number of pages15
JournalJournal of Applied Physiology
Issue number6
Early online date4 May 2023
Publication statusPublished - Jun 2023


  • bone remodeling
  • energy availability
  • female athlete triad
  • stress fracture

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