Effects of 36-hour recovery on marksmanship and hormone concentrations during strenuous winter military survival training.

OBJECTIVES: Survival training can provide a unique setting for scientific examination of human stress responses and physical performance in a realistic operational military context. The aim of the present study was to observe effects of a 36-h recovery period on serum hormone concentrations, salivary cortisol, and marksmanship during 10-day winter military survival training in north of the Arctic Circle. DESIGN AND METHODS: Sixty-eight male soldiers were randomly divided into two groups; EXP (n = 26) and CON (n = 42). While CON performed the whole exercise phase in the field, EXP had 36-h recovery period between days 6 and 8. Several hormones were measured during the study to investigate recovery. RESULTS: Subjective physical and mental demand as well as catabolic hormone levels increased and anabolic hormones decreased in CON (p < 0.05), whereas in EXP, recovery period attenuated negative effects of survival training. Prone shooting performance decreased (87.5 ± 6.5 vs. 76.3 ± 8.8, points out of 100, p < 0.05) between days 6 and 8 in CON while EXP was able to maintain shooting performance throughout the study. CONCLUSION: A short recovery during a strenuous training can prevent the degradation in psychophysiological state and shooting performance in soldiers, which can be crucial for survival in demanding operational winter environment. In the present study, 36-h rest period during the field training seems to enhance recovery but the duration of the period was inadequate for full recovery from the accumulated operative stress. In conclusion, appropriate recovery periods should be implemented in order to optimize occupational performance during high operative stress.

Energy Balance, Hormonal Status, and Military Performance in Strenuous Winter Training.

Severe energy deficit may impair hormonal regulation and physical performance in military trainings. The aim of this study was to examine the associations between energy intake, expenditure, and balance, hormones and military performance during a winter survival training. Two groups were studied: the FEX group (n = 46) had 8-day garrison and field training, whereas the RECO group (n = 26) had a 36-h recovery period after the 6-day garrison and field training phase. Energy intake was assessed by food diaries, expenditure via heart rate variability, body composition by bioimpedance, and hormones by blood samples. Strength, endurance and shooting tests were done for evaluating military performance. PRE 0 d, MID 6 d, POST 8 d measurements were carried out. Energy balance was negative in PRE and MID (FEX -1070 ± 866, -4323 ± 1515; RECO -1427 ± 1200, -4635 ± 1742 kcal·d-1). In POST, energy balance differed between the groups (FEX -4222 ± 1815; RECO -608 ± 1107 kcal·d-1 (p < 0.001)), as well as leptin, testosterone/cortisol ratio, and endurance performance (p = 0.003, p < 0.001, p = 0.003, respectively). Changes in energy intake and expenditure were partially associated with changes in leptin and the testosterone/cortisol ratio, but not with physical performance variables. The 36-h recovery restored energy balance and hormonal status after strenuous military training, but these outcomes were not associated with strength or shooting performance.

Changes in Body Composition, Energy Metabolites and Electrolytes During Winter Survival Training in Male Soldiers.

The aim of this study was to examine changes in body composition, energy metabolites and electrolytes during a 10-day winter survival training period. Two groups of male soldiers were examined: the REC group (n = 26; age 19.7 ± 1.2 years; BMI 23.9 ± 2.7) had recovery period between days 6 and 8 in the survival training, whereas the EXC group (n = 42; age 19.6 ± 0.8 years; BMI 23.1 ± 2.8) did not. The following data were collected: body composition (bioimpedance), energy balance (food diaries, heart rate variability measurements), and biomarkers (blood samples). In survival training, estimated energy balance was highly negative: -4,323 ± 1,515 kcal/d (EXC) and -4,635 ± 1,742 kcal/d (REC). Between days 1 and 10, body mass decreased by 3.9% (EXC) and 3.0% (REC). On day 6, free fatty acid and urea levels increased, whereas leptin, glucose and potassium decreased in all. Recovery period temporarily reversed some of the changes (body mass, leptin, free fatty acids, and urea) toward baseline levels. Survival training caused a severe energy deficit and reductions in body mass. The early stage of military survival training seems to alter energy, hormonal and fluid metabolism, but these effects disappear after an active recovery period.

Can Physiological and Psychological Factors Predict Dropout from Intense 10-Day Winter Military Survival Training?

Background: In the military context, high levels of physiological and psychological stress together can compromise individual's ability to complete given duty or mission and increase dropout rates. The purpose of this study was to investigate if baseline physical fitness, body composition, hormonal and psychological factors could predict dropout from a 10-day intense winter military survival training. Methods: 69 conscripts volunteered to participate in the study. Physical fitness (muscle strength and power, muscle endurance, and aerobic fitness), body composition and hormonal variables (BDNF, testosterone, cortisol, SHBG, DHEAS, IGF-1) together with self-reported psychological factors (short five personality, hardiness, sense of coherence, stress, depression) were assessed prior the survival training. Results: During the survival training, 20 conscripts (29%) dropped out. Baseline aerobic fitness (hazard ratio, HR: 0.997, 95% CI: 0.994-0.999, p = 0.006) and serum cortisol (HR: 1.0006, 95% CI: 1.001-1.011, p = 0.017) predicted dropout in Cox regression model. Each 10 m increase in the 12 min running test decreased the risk for dropout by 3%. Conclusion: Although most of the physiological and psychological variables at the baseline did not predict dropout during a short-term winter survival military training, baseline information of aerobic fitness and serum cortisol concentration may be useful to target support for individuals at higher potential risk for dropout.

Associations of nutrition and body composition with cardiovascular disease risk factors in soldiers during a 6-month deployment.

OBJECTIVES: This observational follow-up study investigated the associations of nutrition and body composition with cardiovascular disease (CVD) risk factors, including pro-inflammatory biomarkers, in soldiers during a 6-month deployment. MATERIAL AND METHODS: Thirty-five male soldiers were assessed at months 0, 3 and 6, and their parameters, i.e., M±SD, were as follows: age 30.0±8.7 years, height 179±6 cm, and BMI 24.2±2.5 kg/m2. Three-day food diaries were used for monitoring macronutrient intake. Body composition was estimated using bioimpedance. Fasting blood samples for lipids and pro-inflammatory biomarkers were collected, and blood pressure measurements were performed. RESULTS: Carbohydrate intake increased and protein intake decreased at month 3 (p = 0.034, p < 0.001), while body composition remained stable. Systolic blood pressure increased at month 6, while other CVD risk factors remained within the reference values. Fat mass and body fat percentage were associated positively with total and low density lipoprotein (LDL) cholesterol concentrations at all measurement points. A negative association was found between the change in fiber intake vs. the change in total (r = -0.36, p = 0.033) and LDL cholesterol (r = -0.39, p = 0.019). CONCLUSIONS: Lower fiber intake and a greater amount of body fat were associated with high total and LDL cholesterol concentrations. Nevertheless, the measured CVD risk factors remained within the reference values, except for the higher systolic blood pressure. A regular screening of body composition and a higher consumption of fiberrich foods may promote cardiometabolic health in soldiers. Int J Occup Med Environ Health. 2020;33(4):457-66.

Diet Macronutrient Composition, Physical Activity, and Body Composition in Soldiers During 6 Months Deployment.

INTRODUCTION: Optimal diet together with good physical fitness maintains readiness and military performance during longer deployments. The purpose of this study was to describe changes in dietary macronutrient and energy intake, total physical activity and body composition during a 6-month deployment in South Lebanon. Furthermore, associations of diet macronutrient intake and physical activity on body composition were also studied. MATERIALS AND METHODS: Forty male soldiers kept a 3-day food diary and their body composition was measured via bioimpedance and ultrasonography. Total physical activity was evaluated by accelerometers in a subgroup of participants. Measurements were conducted in the PRE-, MID-, and POST-deployment. RESULTS: Mean carbohydrate intakes were 39.5-42.6 E%, protein intakes 18.7-22.3 E%, and fat intakes 34.9-35.7 E%. Daily energy intake remained stable (10.1-10.3 MJ/D). Total physical activity was decreased during deployment (e.g., step count from 9,835 ± 2,743 to 8,388 ± 2,875 steps/day, p = 0.007). Skeletal muscle mass and subcutaneous fat increased by 1.3% (p = 0.019) and 1.9% (p = 0.006), respectively. Energy and fat intake associated positively with body mass and skeletal muscle mass (r = 0.31-0.48, p < 0.05-0.001). CONCLUSIONS: Carbohydrate intakes and physical activity were low, compared with the general recommendations. Protein intakes were relatively high. Skeletal muscle mass and subcutaneous fat increased. Suboptimal diet together with low level of physical activity may have a negative impact on body composition, physical performance, and cardiometabolic health. Consequently, soldiers should be encouraged to consume more fiber-rich carbohydrates and less saturated fatty acids as well as maintain a high level of physical fitness to sustain military readiness during long-term deployments.

Free amino acid pool and muscle protein balance after resistance exercise.

PURPOSE: The aim of this study was to assess the effects of a resistance exercise session (RES) on free amino acid concentrations and protein synthesis and breakdown of the vastus lateralis (VL) muscle during recovery in male subjects. METHODS: Both the exercise group (EG) and the control group (CG) consisted of six healthy physically active men. On the experiment day in fasting conditions, a stable isotopic tracer of L-[ring-2H(5)] phenylalanine was infused and EG started a heavy 50-min hypertrophic RES for lower extremities after 55 min of infusion. At the same time, CG was at rest. During recovery of 195 min after RES, several blood samples were drawn from the femoral artery (FA) and the femoral vein (FV) and muscle samples from the VL muscle. The enrichment was analyzed by GC/MS and leg muscle amino acid kinetics determined by three-pool compartment model between FA, FV, and VL. RESULTS: During recovery at 60 min after RES, there was no difference in muscle protein synthesis or muscle protein breakdown between the groups, but at 195 min, both muscle protein synthesis (P < 0.05) and muscle protein breakdown (P < 0.05) were increased in EG compared with CG. The protein net balance was negative and similar in both groups. Simultaneously in serum concentrations, there was a decrease in leucine (P < 0.05) associated with an increase in aspartate (P < 0.05). Furthermore, the exercise-induced increase in alanine concentration decreased both in serum and muscle. CONCLUSION: In fasting conditions, protein net balance is negative and RES induces an increase in muscle protein synthesis and breakdown at 195 min but not yet at 60 min of recovery.

IGF-I, IgA, and IgG responses to bovine colostrum supplementation during training.

This study examined the effect of bovine colostrum (Dynamic colostrum) supplementation on blood and saliva variables (study 1) and the absorption of orally administered human recombinant insulin-like growth factor (IGF)-I (rhIGF-I) labeled with 123I (123I-rhIGF-I) (study 2). In study 1, adult male and female athletes were randomly assigned in a double-blind fashion to either an experimental (Dynamic; n = 19) or a control (Placebo; n = 11) group. The former consumed daily 20 g of Dynamic supplement, and the latter 20 g of maltodextrin during a 2-wk training period. After bovine colostrum supplementation, significant increases were noticed in serum IGF-I (P < 0.01) and saliva IgA (P < 0.01) in Dynamic compared with Placebo. In study 2, gel electrophoresis was carried out in 12 adult subjects with serum samples taken 60 min after ingestion of 123I-rhIGF-I and showed peaks at 0.6 and at 40-90 kDa, with the former inducing 96% and the latter 4% of the total radioactivity. It was concluded that a long-term supplementation of bovine colostrum (Dynamic) increases serum IGF-I and saliva IgA concentration in athletes during training. Absorption data show that ingested 123I-rhIGF-I is fragmented in circulation and that no radioactive IGF-I is eluted at the positions of free, or the IGF, binding proteins, giving no support to the absorption of IGF-I from bovine colostrum.