Title: The effect of sex and protein supplementation on bone metabolism during a 36-hour military field exercise in energy deficit
Presenting author’s name: John Smith, British Army
Presenting author’s email address: email@example.com.
Author names and affiliations: Doe, Jane, British Army; Body, Nicola E, British Army.
ABSTRACT MAIN BODY
Purpose: Acute periods of low energy availability during military field exercise can decrease circulating markers of bone formation, but the sex difference in this bone metabolic response is poorly understood. Protein plays a structural role in the bone matrix, and protein feeding increases intestinal calcium absorption and may attenuate changes in concentrations of anabolic and metabolic hormones during energy deficit. This study investigated sex differences in, and the effect of supplementary protein on, bone metabolism during a 36-hour military field exercise.
Methods: Forty-four British Army Officer cadets (14 women) completed a 36-hour field exercise. Participants consumed their habitual diet (n = 14 women [Women] and n = 15 men [Men Controls]) or the habitual diet and an additional 46.6 g·d–1 protein in supplemental bar form (n = 15 men [Men Protein]). Women and Men Protein were independently compared with Men Controls to examine the effect of sex and protein supplementation. Circulating markers of bone and calcium metabolism were measured before, 24 hours after (post-exercise), and 96 hours after (recovery) the field exercise. Women and Men Controls, and Men Controls and Men Protein were compared over time with linear mixed effects models.
Results: βCTX, 1,25(OH)2D, and cortisol were not different between timepoints or Women and Men Controls (p ≥ 0.094). PINP decreased from baseline to post-exercise (mean difference [95% CI], −13.5 [10.3, 16.8] μg∙L-1, p < 0.001) and recovery (−7.6 [3.3, 11.8] μg∙L-1, p < 0.001) in Women and Men Controls. PTH increased from baseline to postexercise (0.7 [0.3, 1.1] pmol∙L-1, p = 0.006) and decreased from post-exercise to recovery (−0.5 [−1.0, −0.1] pmol∙L-1, p = 0.047) in Women and Men Controls. Total 25(OH)D increased from baseline to post-exercise (4.5 [0.8, 8.3] nmol∙L-1, p = 0.038) and recovery (9.5 [5.7, 13.3] nmol∙L-1, p < 0.001) in Women and Men Controls. Testosterone decreased from baseline to post-exercise (−7.0 [−8.9, −5.2] nmol∙L-1, p <0.001) and recovery (−2.2 [−4.7, 0.3] nmol∙L-1, p = 0.007) in Men Controls, but did not change for Women (all p = 1.000). Protein supplementation had no effect on any biochemical marker.
Conclusions: Men and women experience similar changes to bone metabolism—decreased bone formation and increased PTH—following a short arduous field exercise. Supplementary protein had no protective effect likely because of the severity of energy deficit.
Military Impact: Recovery should be managed following arduous field exercise in energy deficit to allow the recovery of bone formation.