BackgroundAdipose tissue regulates postprandial lipid metabolism by storing dietary fat through lipoprotein lipase-mediated hydrolysis of exogenous triglycerides, and by inhibiting delivery of endogenous non-esterified fatty acid to nonadipose tissues. Animal studies show that acute hypoxia, a model of obstructive sleep apnea, reduces adipose tissue lipoprotein lipase activity and increases non-esterified fatty acid release, adversely affecting postprandial lipemia. These observations remain to be tested in humans.MethodsWe used differentiated human preadipocytes exposed to acute hypoxia as well as adipose tissue biopsies obtained from 10 healthy men exposed for 6 h to either normoxia or intermittent hypoxia following an isocaloric high-fat meal.ResultsIn differentiated preadipocytes, acute hypoxia induced a 6-fold reduction in lipoprotein lipase activity. In humans, the rise in postprandial triglyceride levels did not differ between normoxia and intermittent hypoxia. Non-esterified fatty acid levels were higher during intermittent hypoxia session. Intermittent hypoxia did not affect subcutaneous abdominal adipose tissue lipoprotein lipase activity. No differences were observed in lipolytic responses of isolated subcutaneous abdominal adipocytes between normoxia and intermittent hypoxia sessions.ConclusionsAcute hypoxia strongly inhibits lipoprotein lipase activity in differentiated human preadipocytes. Acute intermittent hypoxia increases circulating plasma non-esterified fatty acid in young healthy men, but does not seem to affect postprandial triglyceride levels, nor subcutaneous abdominal adipose tissue lipoprotein lipase activity and adipocyte lipolysis.

Circulating fatty acids are a major systemic energy source in the fasting state as well as a determinant of hepatic triglycerides (TG)-rich very-low-density lipoprotein production. Upon acute hypoxia, sympathetic arousal induces adipose tissue lipolysis, resulting in an increase in circulating nonesterified fatty acids (NEFA). Animal studies suggest that TG clearance may also be strongly reduced under hypoxia, though this effect has been shown to be dependent on temperature. Whether the hypoxia-induced rise in blood fatty acid concentrations affects fasting TG levels in humans under thermoneutral conditions remains unknown. TG, NEFA, and glycerol levels were measured in fasted healthy young men (n = 10) exposed for 6 h to either normoxia (ambient air) or acute hypoxia (fraction of inspired oxygen = 0.12) in a randomized, crossover design. Participants were casually clothed and rested in front of a fan in an environmental chamber maintained at 28 °C during each trial. Under hypoxia, a significantly greater increase in NEFA occurred (condition × time interaction, p = 0.049) and glycerol levels tended to be higher (condition × time, p = 0.104), suggesting an increase in adipose tissue lipolysis. However, plasma TG levels did not change over time and did not differ between the normoxia and hypoxia conditions. In conclusion, acute exposure to normobaric hypoxia under thermoneutral condition in healthy men during fasting state increased lipolysis without affecting circulating TG.

Introduction Elevated plasma triglyceride (TG) concentrations are an important contributor to deleterious metabolic alterations. Evidence in animals suggest that acute exposure to an environment with reduced oxygen inhibits plasma TG clearance and causes important rise in plasma TG, especially in the postprandial state. The objective of this study was to characterize the effects of an acute exposure to normobaric hypoxia on prandial TG levels in 2 distinct lipoprotein subtypes in healthy humans: chylomicrons which are secreted by the intestine and carry dietary lipids, and denser TG carriers (mainly VLDL), which are secreted by the liver and carry endogenous lipids. Plasma lipolytic activity was also assessed. It was hypothesized that hypoxia would reduce prandial plasma lipolytic activity and raise prandial TG levels in both lipoprotein subtypes. Methods Using a randomized crossover design, 9 healthy young men were studied for 6 h in a constantly fed state while being exposed to either normobaric hypoxia (FiO 2 = 0.12) and normoxic conditions on two different days. Prandial glucose, TG, non-esterified fatty acid (NEFA), and post-heparin plasma lipolytic activity were measured during each session. Results Six hours of exposure to hypoxia marginally increase prandial glycemia (+5%, p = 0.06) while increasing insulinemia by 40% ( p = 0.04). Hypoxia induced a 30% rise in prandial NEFA levels and tended to slightly increased total prandial TG levels by 15% ( p = 0.11). No difference was observed in TG concentrations and metabolism of chylomicrons between conditions. However, TG in the VLDL containing fraction decreased significantly overtime under normoxia but not under hypoxia (time × condition interaction, p = 0.02). No difference was observed in post-heparin plasmatic lipolytic activity between conditions. Conclusion Acute hypoxia in healthy men tends to increase prandial VLDL-TG levels. These results lend support to the increased blood lipid levels reported in animals exposed acutely to lower partial pressures of oxygen.

Introduction Musculoskeletal injuries (MSKIs) and recruitment are major challenges faced by modern military forces. The Canadian Armed Forces uses a physical employment standard (PES) proxy to determine occupational fitness and job suitability. It is unknown whether the performance on the PES proxy can be also used as predictor of MSKIs. The purpose of this study was to investigate for relationships between age, sex, body composition, aerobic fitness, performance on the Canadian Armed Forces PES proxy (FORCE evaluation), and risk of sustaining a MSKI requiring intervention in the Training Rehabilitation Program (MSKI-TRP1) during Canadian Basic Military Qualification. Materials and Methods This was a retrospective analysis of MSKIs in recruits introduced in the Training Rehabilitation Program (TRP1) in 2016 and 2017. A two-tailed t-test and a multivariate stepwise logistic regression were completed to investigate the interrelationships of sex, age, FORCE performance (20 m rushes, sandbag lift, intermittent loaded shuttles, sandbag drag) and health-related characteristics (waist circumference, predicted peak oxygen consumption [$\dot{V}$O2peak]), and odds for sustaining a MSKI-TRP. Results The MSKI-TRP1 intervention rate observed was 4.3%. Rehabilitation duration was an average (SD) of 87 (76) days; nearly 80% of MSKI-TRP were lower body injuries. MSKI-TRP recruits were older, had a lower score on FORCE, and had a larger mean waist circumference and lower $\dot{V}$O2peak than non-TRP1 recruits (all P < 0.01). Recruits with performance lower than 1 SD below mean on the 20 m rushes, intermittent loaded shuttle, or sandbag drag were 2.69 (1.89–3.83), 2.74 (1.91–3.95), and 2.26 (1.52–3.37) times more likely to sustain a MSKI-TRP1, respectively (all P < 0.01). Recruits with $\dot{V}$O2peak lower than 1 SD below mean were also 2.19 (1.30–3.70) times more likely to sustain a MSKI-TRP. Neither sex, age, nor waist circumference impacted the risk of MSKI-TRP1 when controlling for FORCE performance. Conclusions The Canadian Armed Forces PES proxy performance can be used to assess the odds of sustaining a MSKI-TRP1 in Canadian military recruit training.

Introduction This study was conducted to determine what physical and physiological characteristics contribute to the performance of an urban operation casualty evacuation (UO) and its predictive test, FORCE combat (FC) and describe the metabolic demand of the UO in female soldiers. Methods Seventeen military members (9 M and 8 F) completed a loaded walking maximal aerobic test, the UO and FC. Heart rate reserve (HRR) and completion time were used as efficiency/performance measures. Oxygen consumption (VO2) was directly measured for UO on five female participants with a portable indirect calorimetry system, and analyzed using descriptive statistics. Stepwise multiple regression analysis was used to determine the contribution of the non-modifiable (age, sex, height) and modifiable characteristics (lean body mass to dead mass ratio (LBM:DM), VO2max corrected for load (L.VO2max), peak force (PF) measured on an isometric mid-thigh pull (IMTP) and medicine ball chest throw distance (Dist) on to the performance of each exercise. Results LBM:DM and PF were the only factors included in the stepwise regression model for UO, predicting 70% of UO performance (p < 0.01). For FC, L.VO2max only was included in the stepwise regression model predicting 54% of FC performance (p < 0.01). Sex, age and height were not included in the regression model. The average metabolic cost of UO was 21.4 mL of O2*kg−1*min−1 in female soldiers while wearing PPE. Conclusion This study showed that modifiable factors such as body composition, PF on IMTP and L.VO2max are key contributors to performance on UO and FC performance.