Skeletal Responses To An All-female Unsupported Antarctic Expedition

Abstract

Arduous training can result in an energy deficit, the consequences of which include impaired bone health and increased stress fracture risk, as determined by acute interventional or cross-sectional studies. Women are more prone to stress fractures than men, and possibly more susceptible to metabolic perturbations associated with reduced energy availability. No study has longitudinally examined the effect of a prolonged severe energy deficit on bone in women. PURPOSE: To investigate the skeletal effects of the first all-female trans-Antarctic expedition. METHODS: Six women (mean ± SD, age 32 ± 3 years, height 1.72 ± 0.07 m, body mass 72.1 ± 3.8 kg) each hauled an 80 kg sledge over 1700 km in 61 days from coast-to-coast across the Antarctic. Whole-body areal bone mineral density (aBMD) (dual energy x-ray absorptiometry) and tibial volumetric BMD (vBMD), geometry, microarchitecture and mechanical properties (high-resolution peripheral quantitative computed tomography) were assessed 39 days before (pre-expedition) and 15 days after (post-expedition) the expedition. Serum and plasma markers of bone turnover were assessed pre-expedition, and 4 and 15 days after the expedition. RESULTS: There were reductions in trunk (−2.6%), ribs (−5.0%) and spine (−3.4%) aBMD from pre- to post-expedition (all P ≤ 0.046); arms, legs, pelvis and total body aBMD were not different (all P ≥ 0.075). Tibial vBMD, geometry, microarchitecture and mechanical properties at the distal metaphysis (4% site) and diaphysis (30% site) were not different between pre- and post-expedition (all P ≥ 0.082). Bone-specific alkaline phosphatase was higher 15 days post- than 4 days post-expedition (18.0 vs 16.3 μg∙l-1, respectively, P = 0.028). Total 25(OH)D decreased markedly from pre- to 4 days post-expedition (112 vs 76 nmol∙l-1, respectively, P = 0.008). Sclerostin, procollagen 1 N-terminal propeptide, C-telopeptide cross-links of type 1 collagen and adjusted calcium were unchanged (all P ≥ 0.154). CONCLUSION: The deleterious effect of the expedition on aBMD may be due to indirect and direct effects of prolonged energy deficit on bone turnover. We propose that weight-bearing exercise was protective against the effects of low energy availability on tibial vBMD, geometry, microarchitecture and strength. Supported by UK Ministry of Defence (Army)