Paul C. Henning

Physiological Employment Standards III: physiological challenges and consequences encountered during international military deployments

Modern international military deployments in austere environments (i.e., Iraq and Afghanistan) place considerable physiological demands on soldiers. Significant physiological challenges exist: maintenance of physical fitness and body composition, rigors of external load carriage, environmental extremes (heat, cold, and altitude), medical illnesses, musculoskeletal injuries, traumatic brain injuries, post-traumatic stress disorder, and environmental exposure hazards (i.e., burn pits, vehicle exhaust, etc.). To date there is very little published research and no comprehensive reviews on the physiological effects of deployments. The purpose of this paper is to overview what is currently known from the literature related mainly to current military conflicts with regard to the challenges and consequences from deployments. Summary findings include: (1) aerobic capacity declines while muscle strength, power and muscular endurance appear to be maintained, (2) load carriage continues to tax the physical capacities of the Soldier, (3) musculoskeletal injuries comprise the highest proportion of all injury categories, (4) environmental insults occur from both terrestrial extremes and pollutant exposure, and (5) post-deployment concerns linger for traumatic brain injury and post-traumatic stress disorder. A full understanding of these responses will assist in identifying the most effective risk mitigation strategies to ensure deployment readiness and to assist in establishment of military employment standards.

Physiological Decrements During Sustained Military Operational Stress

Missions conducted by the U.S. Military during combat involve a multitude of operational stressors that can cause deterioration in physical and military performance of soldiers. Physiological consequences of sustained operational stress include decrements in anabolic hormones, skeletal muscle mass, and loss of bone mineral density. The objective of this review is to examine the current literature and provide commanders with information on the physical and physiological decrements in soldiers conducting sustained operations. The intent is that this will provide commanders with insight on how to plan for missions to incorporate possible countermeasures to enhance or sustain warfighter performance.

Recovery of Endocrine and Inflammatory Mediators Following an Extended Energy Deficit

CONTEXT Due to current operational requirements, elite soldiers deploy quickly after completing arduous training courses. Therefore, it is imperative that endocrine and inflammatory mediators have fully recovered. OBJECTIVE Our objective was to determine whether a short-term (2-6 wk) recovery period was sufficient to restore endocrine and inflammatory homeostasis after sustained energy deficit. DESIGN Before and immediately after the course, serum concentrations of inflammatory and endocrine markers were taken along with anthropometric measures prior to and immediately after the Army Ranger course. In addition, nine soldiers were assessed between 2 and 6 weeks after the course. SETTING This research occurred in a field setting during an intensive 8-week military training course characterized by high-energy expenditure, energy restriction, and sleep deprivation (U.S. Army Ranger School). PARTICIPANTS Twenty-three male soldiers (23.0 ± 2.8 y; 177.6 ± 7.9 cm; 81.0 ± 9.6 kg, 16.8 ± 3.9% body fat) participated in this study. INTERVENTIONS There were no interventions used in this research. OUTCOME MEASURES AND RESULTS Significant changes occurred in circulating total testosterone (-70%), brain-derived neurotrophic factor (-33%), total IGF-1 (-38.7%), free IGF-1 (-41%), IGF binding protein (IGFBP-6; -23.4%), sex-hormone binding globulin (+46%), thyroid stimulating hormone (+85%), IGFBP-1 (+534.4%), IGFBP-2 (+98.3%), IGFBP-3 (+14.7%), IL-4 (+135%), IL-6 (+217%), and IL-8 (+101%). Significant changes in body mass (-8%), bicep (-14%), forearm (-5%), thigh (-7%), and calf (-2%) circumferences, sum of skinfolds (-52%), and percentage body fat (-54%). All anthropometric, inflammatory, and hormonal values, except T3, were restored to baseline levels within 2-6 weeks after the course. CONCLUSIONS Endocrine markers and anthropometric measures were degraded, and inflammatory mediators increased after an extended energy deficit. A short-term recovery of 2-6 weeks was sufficient to restore these mediators.

Effects of acute caloric restriction compared to caloric balance on the temporal response of the IGF-I system.

OBJECTIVE Insulin-like growth factor-I (IGF-I) is a key regulator of metabolism during altered energy states. The IGF-I system components respond to prolonged caloric restriction but it is not clear if this system responds similarly to acute caloric restriction. The purpose of this study was to characterize the IGF-I system response to acute caloric restriction with a secondary purpose of determining if two isocaloric diets with different ratios of carbohydrate to fat alter the IGF-I system under conditions of caloric balance. MATERIALS/METHODS A double-blind, placebo-controlled crossover design was used in which 27 subjects underwent three, 48-h experimental treatments: 1) caloric restriction 2) carbohydrate and 3) carbohydrate/fat. Blood was sampled periodically (6 time points total) for IGF-I (total and free), IGFBPs1-4, insulin and glucose. ANOVAs were used with significance set at P<0.05. RESULTS Total IGF-I decreased 7% during CR (P=0.051) and remained stable during CHO and CHO/F. Free IGF-I decreased 43% during CR (P<0.05) and remained stable during CHO and CHO/F. IGFBP-1 increased by 445% during CR (P<0.05) compared to CHO and CHO/F with no changes for IGFBP-2, IGFBP-3 and IGFBP-4. There was no change in glucose or insulin during CR over the course of the study. Insulin and glucose increased (P<0.05) after a meal in both the CHO and CHO/F groups with no difference between these two groups. CONCLUSION Our findings indicate that free IGF-I decreases and IGFBP-1 increases during caloric restriction, but they are not altered with diets differing in carbohydrate and fat content. Changes in free IGF-I and IGFBP-1 are sensitive to caloric restriction, and their measurement may be valuable in monitoring the physiological response to refeeding in those consuming suboptimal calories.

Effects of dynamic stretching on energy cost and running endurance performance in trained male runners.

Zourdos, MC, Wilson, JM, Sommer, BA, Lee, S-R, Park, Y-M, Henning, PC, Panton, LB, and Kim, J-S. Effects of dynamic stretching on energy cost and running endurance performance in trained male runners. J Strength Cond Res 26(2): 335–341, 2012—The purpose of this study was to examine the effects of dynamic stretching on running energy cost and endurance performance in trained male runners. Fourteen male runners performed both a 30-minute preload run at 65% &OV0312;O2max and a 30-minute time trial to assess running energy cost and performance, respectively. The subjects repeated both the trials after either 15 minutes of dynamic stretching (i.e., experimental condition) or quiet sitting (i.e., control condition) while the order was balanced between the subjects to avoid any order effect. The total calories expended were determined for the 30-minute preload run, whereas the distance covered was measured in the time trial. Average resting &OV0312;O2 increased significantly (p < 0.05) after dynamic stretching (prestretch: 6.2 ± 1.7 vs. poststretch: 8.4 ± 2.1 ml·kg−1·min−1) but not during the quiet-sitting condition. Caloric expenditure was significantly higher during the 30-minute preload run for the stretching (416.3 ± 44.9 kcal) compared with that during the quiet sitting (399.3 ± 50.4 kcal) (p < 0.05). There was no difference in the distance covered after quiet sitting (6.3 ± 1.1 km) compared with that for the stretching condition (6.1 ± 1.3 km). These findings suggest that dynamic stretching does not affect running endurance performance in trained male runners.

High protein diets do not attenuate decrements in testosterone and IGF-I during energy deficit ☆,☆☆

OBJECTIVE Energy deficit (ED) diminishes fat-free mass (FFM) with concomitant reductions in anabolic hormone secretion. A modest increase in protein to recommended dietary allowance (RDA) levels during ED minimally attenuates decrements in insulin-like growth factor-I (IGF-I). The impact of dietary protein above the RDA on circulating anabolic hormones and their relationships with FFM in response to ED are not well described. MATERIALS/METHODS Thirty-three adults were assigned diets providing protein at 0.8 (RDA), 1.6 (2×-RDA), and 2.4 (3×-RDA) g/kg/d for 31days. Testosterone, sex-hormone binding globulin (SHBG) and IGF-I system components were assessed after a 10-day period of weight-maintenance (WM) and after a 21-day period of ED (40%) achieved by an increase in energy expenditure and decreased energy intake. Associations between the change in FFM and anabolic hormone levels were determined. RESULTS As compared to WM and regardless of dietary protein intake, total and free testosterone, total IGF-I, and acid-labile subunit decreased (P<0.05), whereas SHBG and IGF binding proteins-1, -2, and -3 increased (P<0.05) during ED. There were no energy-by-protein interactions on any hormones or IGF-I system components measured. Changes in FFM in response to ED were negatively associated with acid-labile subunit (ALS) (r=-0.62, P<0.05) in 2×-RDA; however, no other relationships were observed. CONCLUSION Consuming a high protein diet does not impact the androgenic and IGF-I system response to ED. These data suggest that the protective effects of high protein diets on FFM during ED are likely not influenced by anabolic hormone concentrations.

Repeated Bout Effect in Muscle-Specific Exercise Variations

Abstract Zourdos, MC, Henning, PC, Jo, E, Khamoui, AV, Lee, S-R, Park, Y-M, Naimo, M, Panton, LB, Nosaka, K, and Kim, J-S. Repeated bout effect in muscle-specific exercise variations. J Strength Cond Res 29(8): 2270–2276, 2015—A single bout of unaccustomed exercise confers protective effect against muscle damage from a subsequent bout of similar activity, that is, repeated bout effect (RBE). It remains unknown whether varying muscle-specific exercise between sessions alters the magnitude of the RBE. This study examined the effects of muscle-specific exercise variation between consecutive sessions on the RBE. Twenty untrained males (21 ± 2 years) were assigned to one of 2 groups (n = 10 per group): (a) 2 sessions of incline curls, Fixed Exercise or (b) 1 session of incline curls followed by 1 session of preacher curls, Varied Exercise, with 7 days between sessions. Subjects performed 5 sets of 6 repetitions at ∼50% of maximal isometric elbow flexor strength during each session. Changes in maximal voluntary isometric and isokinetic torque, range of motion, muscle soreness, and serum creatine kinase were measured before, immediately after, and 24, 48, 72, and 96 hours after each exercise session, and the changes were compared between bouts and between groups. There were significant time effects (p < 0.05) for isometric maximal voluntary contraction, concentric maximal voluntary contraction, range of motion, and muscle soreness during sessions 1 and 2 with no between-group differences. Both groups demonstrated a significantly faster recovery of range of motion and soreness to baseline levels after session 2 compared with session 1. Overall, our findings suggest that incline curls conferred a protective effect during subsequent preacher curls in a similar way to repeating incline curls; therefore, the RBE was not exercise specific.

β-Hydroxy-β-methylbutyrate improves bone properties and attenuates the depression of protein synthesis during a simulated sustained operation.

OBJECTIVES Soldiers lose muscle and bone density during sustained operations. We investigated the impact of β-hydroxy-β-methylbutyrate (HMB) on bone properties, muscle mass, and markers of skeletal muscle regeneration under simulated military sustained operations. METHODS Male mice were divided into four groups (10/group): (1) ALT = ad libitum + trained (1h/d for 3 d/wk); (2) ALTH = ALT + HMB (0.5 g/kg BW/d); (3) C = caloric restricted (-30%) + trained (6h/d, 6d/wk); and (4) CH = C + HMB. Assessments included bone mineral density/content by dual-energy X-ray absorptiometry, muscle wet weight (quadriceps) and expression of selected genes regulating muscle mass and protein turnover. Analysis of variances were used with significance set at p < 0.05. RESULTS Bone mineral content increased in the ALT group (+16%) and decreased in the C group (-32%). Quadriceps muscle mass was lower in C (-27%) and CH (-19%) compared to ALT and ALTH. Myogenin mRNA expression was higher in C than ALT, ALTH and CH. Protein kinase B (Akt) mRNA expression was higher in both C and CH than ALT and ALTH. Mammalian target of rapamycin expression was higher in CH than ALT and ALTH. Muscle RING-finger protein-1 expression was higher in both C and CH than ALT and ALTH. CONCLUSION HMB intake improved bone properties and attenuated the depression of protein synthesis during a simulated sustained military operation.

Erratum to: Bone formation is suppressed with multi-stressor military training

immediate post-training measures. A repeated-measures ANOVA with time as the only factor was used to analyze data on the subset of 8 subjects who completed follow-up data collection. Results BAP and OCN significantly decreased by 22.8 ± 15.5 % (pre 41.9 ± 10.1; post 31.7 ± 7.8 ng/ml) and 21.0 ± 23.3 % (pre 15.0 ± 3.5; post 11.3 ± 2.1 ng/ ml), respectively, with training, suggesting suppressed bone formation. OCN returned to baseline, while BAP remained suppressed 2–6 weeks post-training. TRAP5b significantly increased by 57.5 ± 51.6 % (pre 3.0 ± 0.9; post 4.6 ± 1.4 ng/ml) from preto post-training, suggesting increased bone resorption, and returned to baseline 2–6 weeks post-training. PTH Increased significantly by 37.3 ± 45.2 % with training. No changes in CTX, calcium, or PTH were detected. Conclusions These data indicate that multi-stressor military training results in increased bone resorption and suppressed bone formation, with recovery of bone metabolism 2–6 weeks after completion of training.