Loss of muscle mass is poorly reflected in grip strength performance in healthy young men

Effects of a 10-d Military Field Exercise on Body Composition, Physical Performance, and Muscle Cells in Men and Women

PURPOSE

This study aimed to investigate the effects of a demanding military field exercise on physical performance, body composition, and muscle cellular outcomes in men and women.

METHODS

Ten men (20.5 ± 0.5 yr) and 8 women (21.4 ± 1.4 yr) completed a 10-d field exercise consisting of extensive physical activity with food and sleep restriction. Acquisition of body composition, physical performance, blood, and muscle biopsies samples were done before and 1, 7, and 14 d after the exercise.

RESULTS

There were no sex differences in the response to the exercise. Body mass was decreased with 5.6% ± 1.8% and fat mass with 31% ± 11% during the exercise. Both were still reduced after 14 d (2.5% ± 2.3%, P < 0.001, and 12.5% ± 7.7%, P < 0.001, respectively). Isometric leg strength did not change. Peak leg extension torque at 240°·s -1 and counter movement jump height were reduced with 4.6% ± 4.8% ( P = 0.012) and 6.7% ± 6.2% ( P < 0.001), respectively, and was still reduced after 14 d (4.3% ± 4.2%, P = 0.002, and 4.1% ± 4.7%, P = 0.030). No changes occurred in fiber CSA, fiber types, proteins involved in calcium handling, or HSP70. During the exercise, αB-crystallin levels decreased by 14% ± 19% ( P = 0.024) in the cytosolic fraction and staining intensity on muscle sections tended to increase (17% ± 25%, P = 0.076). MuRF1 levels in the cytosolic fraction tended to decrease (19% ± 35%) and increased with 85% ± 105% ( P = 0.003) in the cytoskeletal fraction 1 wk after the exercise.

CONCLUSIONS

The field exercise resulted in reduced body mass and physical performance in both sexes. The ability to produce force at high contraction velocities and explosive strength was more affected than isometric strength, but this was not related to any changes in fiber type composition, fiber area, Ca 2+ handling, or fiber type-specific muscle damage.

Effects of male paratroopers' initial body composition on changes in physical performance and recovery during a 20-day winter military field training

Changes in physiological markers and physical performance in relation to paratroopers' initial body composition were investigated during a 20-day winter military field training (MFT) and the subsequent 10-day recovery period. Body composition, serum hormone concentrations and enzymatic biomarkers, and physical performance of 58 soldiers were measured before, during, and after MFT. Comparisons were done according to soldiers' body fat percentage before MFT between low-fat (<12% body fat) and high-fat (>12% body fat) groups. Correlations between body fat percentage preceding MFT and changes in muscle mass, physical performance, and serum hormone concentrations and enzymatic biomarkers were investigated. It was hypothesized that soldiers with a higher fat percentage would have smaller decrements in muscle mass, physical performance, and serum testosterone concentration. The change in muscle and fat mass was different between groups (p < 0.001) as the low-fat group lost 0.8 kg of muscle mass and 2.0 kg of fat mass, while there was no change in muscle mass and a loss of 3.7 kg of fat mass in the high-fat group during MFT. Fat percentage before MFT correlated with the changes in muscle mass (R2 = 0.26, p < 0.001), serum testosterone concentration (R2 = 0.22, p < 0.001), and evacuation test time (R2 = 0.10, p < 0.05) during MFT. The change in muscle mass was correlated with the changes in evacuation test time (R2 = 0.11, p < 0.05) and countermovement jump test results (R2 = 0.13, p < 0.01) during MFT. Soldiers with a higher initial fat percentage lost less muscle mass, and had smaller decrements in some aspects of physical performance, as well as in serum testosterone concentration during MFT.

Alterations in Measures of Body Composition, Neuromuscular Performance, Hormonal Levels, Physiological Adaptations, and Psychometric Outcomes during Preparation for Physique Competition: A Systematic Review of Case Studies

The present paper aimed to systematically review case studies on physique athletes to evaluate longitudinal changes in measures of body composition, neuromuscular performance, chronic hormonal levels, physiological adaptations, and psychometric outcomes during pre-contest preparation. We included studies that (1) were classified as case studies involving physique athletes during the pre-contest phase of their competitive cycle; (2) involved adults (18+ years of age) as participants; (3) were published in an English-language peer-reviewed journal; (4) had a pre-contest duration of at least 3 months; (5) reported changes across contest preparation relating to measures of body composition (fat mass, lean mass, and bone mineral density), neuromuscular performance (strength and power), chronic hormonal levels (testosterone, estrogen, cortisol, leptin, and ghrelin), physiological adaptations (maximal aerobic capacity, resting energy expenditure, heart rate, blood pressure, menstrual function, and sleep quality), and/or psychometric outcomes (mood states and food desire). Our review ultimately included 11 case studies comprising 15 ostensibly drug-free athletes (male = 8, female = 7) who competed in various physique-oriented divisions including bodybuilding, figure, and bikini. The results indicated marked alterations across the array of analyzed outcomes, sometimes with high inter-individual variability and divergent sex-specific responses. The complexities and implications of these findings are discussed herein.

Microalgae Produce Antioxidant Molecules with Potential Preventive Effects on Mitochondrial Functions and Skeletal Muscular Oxidative Stress

In recent years, microalgae have become a source of molecules for a healthy life. Their composition of carbohydrates, peptides, lipids, vitamins and carotenoids makes them a promising new source of antioxidant molecules. Skeletal muscle is a tissue that requires constant remodeling via protein turnover, and its regular functioning consumes energy in the form of adenosine triphosphate (ATP), which is produced by mitochondria. Under conditions of traumatic exercise or muscular diseases, a high production of reactive oxygen species (ROS) at the origin of oxidative stress (OS) will lead to inflammation and muscle atrophy, with life-long consequences. In this review, we describe the potential antioxidant effects of microalgae and their biomolecules on mitochondrial functions and skeletal muscular oxidative stress during exercises or in musculoskeletal diseases, as in sarcopenia, chronic obstructive pulmonary disease (COPD) and Duchenne muscular dystrophy (DMD), through the increase in and regulation of antioxidant pathways and protein synthesis.

Changes in energy balance, body composition, metabolic profile and physical performance in a 62-day Army Ranger training in a hot-humid environment

OBJECTIVES

To determine the physiological effects of multiple stressors including energy deficit during a 62-day Ranger course in a hot-humid environment.

DESIGN

Prospective cohort design.

METHODS

Food intake data were collected daily and energy expenditure at each of the three phases of the course was estimated by the doubly-labeled water method. Anthropometry, hydration status, stress and metabolic hormones, handgrip strength and lower explosive power were measured at the start and at the end of each phase.

RESULTS

Seventeen male participants (age: 24.5 ± 3.2 years, height: 173.9 ± 5.1 cm, body mass: 69.3 ± 3.2 kg, BMI: 22.9 ± 0.9 kg/m², percent body fat: 14 ± 5%) completed the study. Mean total daily energy expenditure was 4756 kcal/day and mean daily energy intake was 3882 kcal/day. An 18% energy deficit resulted in an average body mass loss of 4.6 kg, comprising mostly fat mass. Participants with higher baseline adiposity (>15% body fat) lost more fat mass and gained (rather than lost) muscle mass compared to those with lower baseline adiposity. Handgrip strength declined only at the end of Phase I, while lower body explosive power declined progressively throughout the course. Lean mass in arms and legs was correlated with initial grip strength and lower body explosive power, but only at the start of the course.

CONCLUSIONS

Physiologically demanding Ranger training in an equatorial environment is at least as metabolically demanding and stressful as other similar high-risk training courses, as demonstrated by the stress and metabolic endocrine responses, changes in body composition, and reduction in explosive power. Moreover, the smaller body size of Asian soldiers may confer an energetic advantage over larger sized Western counterparts.

A Muscle-Centric Perspective on Intermittent Fasting: A Suboptimal Dietary Strategy for Supporting Muscle Protein Remodeling and Muscle Mass?

Muscle protein is constantly “turning over” through the breakdown of old/damaged proteins and the resynthesis of new functional proteins, the algebraic difference determining net muscle gain, maintenance, or loss. This turnover, which is sensitive to the nutritional environment, ultimately determines the mass, quality, and health of skeletal muscle over time. Intermittent fasting has become a topic of interest in the health community as an avenue to improve health and body composition primarily via caloric deficiency as well as enhanced lipolysis and fat oxidation secondary to attenuated daily insulin response. However, this approach belies the established anti-catabolic effect of insulin on skeletal muscle. More importantly, muscle protein synthesis, which is the primary regulated turnover variable in healthy humans, is stimulated by the consumption of dietary amino acids, a process that is saturated at a moderate protein intake. While limited research has explored the effect of intermittent fasting on muscle-related outcomes, we propose that infrequent meal feeding and periods of prolonged fasting characteristic of models of intermittent fasting may be counter-productive to optimizing muscle protein turnover and net muscle protein balance. The present commentary will discuss the regulation of muscle protein turnover across fasted and fed cycles and contrast it with studies exploring how dietary manipulation alters the partitioning of fat and lean body mass. It is our position that intermittent fasting likely represents a suboptimal dietary approach to remodel skeletal muscle, which could impact the ability to maintain or enhance muscle mass and quality, especially during periods of reduced energy availability.

Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial

Importance

The efficacy and safety of time-restricted eating have not been explored in large randomized clinical trials.

Objective

To determine the effect of 16:8-hour time-restricted eating on weight loss and metabolic risk markers.

Interventions

Participants were randomized such that the consistent meal timing (CMT) group was instructed to eat 3 structured meals per day, and the time-restricted eating (TRE) group was instructed to eat ad libitum from 12:00 pm until 8:00 pm and completely abstain from caloric intake from 8:00 pm until 12:00 pm the following day.

Design, Setting, and Participants

This 12-week randomized clinical trial including men and women aged 18 to 64 years with a body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) of 27 to 43 was conducted on a custom mobile study application. Participants received a Bluetooth scale. Participants lived anywhere in the United States, with a subset of 50 participants living near San Francisco, California, who underwent in-person testing.

Main Outcomes and Measures

The primary outcome was weight loss. Secondary outcomes from the in-person cohort included changes in weight, fat mass, lean mass, fasting insulin, fasting glucose, hemoglobin A1c levels, estimated energy intake, total energy expenditure, and resting energy expenditure.

Results

Overall, 116 participants (mean [SD] age, 46.5 [10.5] years; 70 [60.3%] men) were included in the study. There was a significant decrease in weight in the TRE (-0.94 kg; 95% CI, -1.68 to -0.20; P = .01), but no significant change in the CMT group (-0.68 kg; 95% CI, -1.41 to 0.05, P = .07) or between groups (-0.26 kg; 95% CI, -1.30 to 0.78; P = .63). In the in-person cohort (n = 25 TRE, n = 25 CMT), there was a significant within-group decrease in weight in the TRE group (-1.70 kg; 95% CI, -2.56 to -0.83; P < .001). There was also a significant difference in appendicular lean mass index between groups (-0.16 kg/m2; 95% CI, -0.27 to -0.05; P = .005). There were no significant changes in any of the other secondary outcomes within or between groups. There were no differences in estimated energy intake between groups.

Conclusions and Relevance

Time-restricted eating, in the absence of other interventions, is not more effective in weight loss than eating throughout the day.

Trial Registration

ClinicalTrials.gov Identifiers: NCT03393195 and NCT03637855.

Energy Deficiency in Soldiers: The Risk of the Athlete Triad and Relative Energy Deficiency in Sport Syndromes in the Military

Military personnel experience energy deficit (total energy expenditure higher than energy intake), particularly during combat training and field exercises where exercising energy expenditures are high and energy intake is reduced. Low energy availability (energy intake minus exercising energy expenditure expressed relative to fat free mass) impairs endocrine function and bone health, as recognized in female athletes as the Female Athlete Triad syndrome. More recently, the Relative Energy Deficiency in Sport (RED-S) syndrome encompasses broader health outcomes, physical and cognitive performance, non-athletes, and men. This review summarizes the evidence for the effect of low energy availability and energy deficiency in military training and operations on health and performance outcomes. Energy availability is difficult to measure in free-living individuals but doubly labeled water studies demonstrate high total energy expenditures during military training; studies that have concurrently measured energy intake, or measured body composition changes with DXA, suggest severe and/or prolonged energy deficits. Military training in energy deficit disturbs endocrine and metabolic function, menstrual function, bone health, immune function, gastrointestinal health, iron status, mood, and physical and cognitive performance. There are more data for men than women, and little evidence on the chronic effects of repeated exposures to energy deficit. Military training impairs indices of health and performance, indicative of the Triad and RED-S, but the multi-stressor environment makes it difficult to isolate the independent effects of energy deficiency. Studies supplementing with energy to attenuate the energy deficit suggest an independent effect of energy deficiency in the disturbances to metabolic, endocrine and immune function, and physical performance, but randomized controlled trials are lacking.

Comparison between grip strength and grip strength divided by body weight in their relationship with metabolic syndrome and quality of life in the elderly

Strength measures should be normalized by body mass; however, the definition of sarcopenia includes only simple grip strength. Thus, we compared the relationship of grip strength and grip strength divided by body weight or body mass index to two major consequences of sarcopenia, namely metabolic syndrome and poor quality of life. Data from the participants (aged 60 years or older) of the Sixth Korea National Health and Nutrition Examination were analyzed. Metabolic syndrome was defined according to the Adult Treatment Panel III guidelines with some modifications appropriate for Koreans. Quality of life was assessed using the EuroQoL Five-dimension questionnaire. Multiple logistic regression models were used to evaluate the association of grip strength and grip strength divided by body weight with metabolic syndrome and quality of life. A total of 1273 men and 1436 women were included in the analyses. Grip strength was not related to metabolic syndrome, whereas grip strength divided by body weight and grip strength normalized by body mass index revealed a dense dose-response relationship. All measures showed a similar correlation with quality of life. Grip strength divided by body weight can be superior to simple grip strength and grip strength normalized by body mass index in representing the metabolic aspects of sarcopenia.

Muscularity and Strength Affect Individual Variation in Self-Perception of Fighting Ability in Men

Objective: There is evidence that competitive conflicts are the main form of intrasexual competition among men. The capacity to recognize visual cues of fighting ability in competitors is thought to be an important characteristic that allows men to avoid the costs of contest competition. However, for an accurate comparison to take place, individuals need to compare the fighting ability of their competitors to their own to assess this asymmetry.

Methods: In order to improve our understanding of this self-assessment process, here we study the relationship between visual fighting ability cues, namely (i) muscularity, as measured with a bioimpedance device, (ii) the real capacity to inflict cost to a rival based on strength, as measured with a hand grip dynamometer (HGS), and (iii) self-perceived fighting ability, as determined with a questionnaire. The study sample was 364 men between 18 and 38 years of age (M ± SD = 22.27 ± 3.99).

Results: Our results confirm the expected positive relationship between upper-body muscularity and strength, while controlling for body mass index (BMI). However, muscularity explained only around 30.2% of the variance in strength. In addition, muscularity was related to self-perception of fighting ability in our sample, its effect being partially mediated by strength.

Conclusion: The more muscular men perceive their fighting ability as being greater, and not only because they are stronger (at least in the HGS task). Accordingly, it seems that men take into account the overestimation the robustness of the relationship between strength and muscularity that prevails within his peers.

Psychophysiological Monitorization in a Special Operation Selection Course

The present research aimed: i. to analyse the psychophysiological response of soldiers undertaking a special operation selection course; ii. to study the relationship between fat and muscle loss and the psychophysiological response of soldiers undertaking a special operation selection course. We analysed 46 professional soldiers from a special operations unit (25.1 ± 5.0 years, 1.8 ± 0.1 cm, 76.8 ± 7.9 kg, 24.4 ± 2.5 kg/m²) undertaking the last phase of their 10 weeks special operation selection course. Before and immediately after the exercise the following variables were assessed: Stress subjective perception, fatigue subjective perception, rating of perceived perception, cortical arousal, body temperature, blood oxygen saturation, spirometry, isometric hand strength, lower body muscular strength, urine, body composition, life engagement test, coping flexibility scale, acceptance and action questionnaire, perceived stress scale, anxiety state, visual analogue scale and differential aptitude test. A special operation selection course induced an intense stress and physical response as suggested by the psychophysiological changes with a significant (p < 0.05) increase in fatigue and stress subjective perception, blood oxygen saturation, Ph, cognitive impairment and motivation-loss. Moreover, decreased leg strength, peak expiratory flow, cortical arousal, body composition, body weight, fat and muscle mass, anxiety stress, alertness, sadness and tension decreased after the exercise. Regarding body composition, higher muscle mass loss participants were related to a higher cognitive impairment and similar psychophysiological response than lower fat mass loss participants.

Physical fitness, hormonal, and immunological responses during prolonged military field training

Physical fitness is crucial to warfighters' performance in the battlefield. Previous studies have shown negative changes in their hormonal and neuromuscular responses induced by military field training (MFT). The purpose of this study was to investigate the changes in hormonal and immunological values and body composition during a prolonged MFT and to find out how warfighters' physical condition influences these changes. Conscripts (n = 49, age 20 ± 1 years, height 179 ± 9 cm, body mass 73.8 ± 7.8 kg, fat 12.6 ± 3.7% and BMI 23 kg/m²) were measured before, during, after MFT, and after a 4-day recovery period. Serum insulin-like growth factor-1 (IGF-1), tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6) concentrations, creatine kinase (CK) activity and leptin concentration were analyzed as well as body composition throughout MFT. Neuromuscular performance was assessed via lower and upper body muscle endurance at the beginning of the study. During MFT, there was a significant decrease (P < 0.05) in body mass (2.3%), fat mass (7.7%) and in muscle mass (2.2%), but all of these values recovered to PRE-levels after the recovery period. Serum IGF-1 (22%) and leptin decreased (66%) while CK increased (88%) significantly (P < 0.05) during MFT but recovered at the end of MFT. Upper body dynamic and trunk isometric muscular endurance had a positive correlation (r = 0.37. P < 0.05) with the change in IGF-1 during MFT and a negative correlation with the changes in CK (-0.34, P < 0.05). The results show that there were negative changes in conscript's body composition and hormonal and immunological values during the prolonged MFT. These changes suggest that the physiological stress was high during MFT. High levels of upper body and trunk muscular strength were negatively correlated with warfighters' physiological effects and should therefore be developed prior to actual deployment to reduce the physical decline experienced during prolonged MFTs.

Physiological and psychological determinants of whole-body endurance exercise following short-term sustained operations with partial sleep deprivation

Purpose

The study examined the effects of short-term field-based military training with partial sleep deprivation on whole-body endurance performance in well-trained individuals.

Methods

Before and after a 2-day sustained operations (SUSOPS), 14 cadets performed a 15-min constant-load cycling at 65% of peak power output (PPO; CLT₆₅), followed by an exhaustive constant-load trial at 85% of PPO (CLT₈₅). Physiological [oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot {V}$$\end{document}V˙O₂), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), and regional oxygenation (TOI) in the frontal cerebral cortex and vastus lateralis muscle] and psychological [effort perception (RPE), affective valence (FS), and perceived activation (FAS)] variables were monitored during exercise.

Results

SUSOPS reduced time to exhaustion in CLT₈₅ by 29.1% (p = 0.01). During the CLT₆₅ trial, SUSOPS potentiated the exercise-induced elevations in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot {V}$$\end{document}V˙O₂ and HR (p < 0.05), and blunted MAP (p = 0.001). CO did not differ between trials. Yet, towards the end of both CLT₈₅ trials, CO tended to decline (p ≤ 0.08); a response that occurred at an earlier stage in the SUSOPS trial. During CLT₆₅, SUSOPS altered neither cerebral nor muscle TOI. The SUSOPS CLT₈₅ trial, however, was terminated at similar leg-muscle deoxygenation (p > 0.05) and lower prefrontal cortex deoxygenation (p < 0.01). SUSOPS increased RPE at submaximal intensities (p = 0.05), and suppressed FAS and FS throughout (p < 0.01).

Conclusions

The present findings indicate, therefore, that a brief period of military sustained operations with partial sleep deprivation augment cardiorespiratory and psychological strain, limiting high-intensity endurance capacity.

Preserving Healthy Muscle during Weight Loss

Weight loss is the cornerstone of therapy for people with obesity because it can ameliorate or completely resolve the metabolic risk factors for diabetes, coronary artery disease, and obesity-associated cancers. The potential health benefits of diet-induced weight loss are thought to be compromised by the weight-loss-associated loss of lean body mass, which could increase the risk of sarcopenia (low muscle mass and impaired muscle function). The objective of this review is to provide an overview of what is known about weight-loss-induced muscle loss and its implications for overall physical function (e.g., ability to lift items, walk, and climb stairs). The currently available data in the literature show the following: 1) compared with persons with normal weight, those with obesity have more muscle mass but poor muscle quality; 2) diet-induced weight loss reduces muscle mass without adversely affecting muscle strength; 3) weight loss improves global physical function, most likely because of reduced fat mass; 4) high protein intake helps preserve lean body and muscle mass during weight loss but does not improve muscle strength and could have adverse effects on metabolic function; 5) both endurance- and resistance-type exercise help preserve muscle mass during weight loss, and resistance-type exercise also improves muscle strength. We therefore conclude that weight-loss therapy, including a hypocaloric diet with adequate (but not excessive) protein intake and increased physical activity (particularly resistance-type exercise), should be promoted to maintain muscle mass and improve muscle strength and physical function in persons with obesity.

Effects of winter military training on energy balance, whole-body protein balance, muscle damage, soreness, and physical performance

Physiological consequences of winter military operations are not well described. This study examined Norwegian soldiers (n = 21 males) participating in a physically demanding winter training program to evaluate whether short-term military training alters energy and whole-body protein balance, muscle damage, soreness, and performance. Energy expenditure (D218O) and intake were measured daily, and postabsorptive whole-body protein turnover ([15N]-glycine), muscle damage, soreness, and performance (vertical jump) were assessed at baseline, following a 4-day, military task training phase (MTT) and after a 3-day, 54-km ski march (SKI). Energy intake (kcal·day−1) increased (P < 0.01) from (mean ± SD (95% confidence interval)) 3098 ± 236 (2985, 3212) during MTT to 3461 ± 586 (3178, 3743) during SKI, while protein (g·kg−1·day−1) intake remained constant (MTT, 1.59 ± 0.33 (1.51, 1.66); and SKI, 1.71 ± 0.55 (1.58, 1.85)). Energy expenditure increased (P < 0.05) during SKI (6851 ± 562 (6580, 7122)) compared with MTT (5480 ± 389 (5293, 5668)) and exceeded energy intake. Protein flux, synthesis, and breakdown were all increased (P < 0.05) 24%, 18%, and 27%, respectively, during SKI compared with baseline and MTT. Whole-body protein balance was lower (P < 0.05) during SKI (–1.41 ± 1.11 (–1.98, –0.84) g·kg−1·10 h) than MTT and baseline. Muscle damage and soreness increased and performance decreased progressively (P < 0.05). The physiological consequences observed during short-term winter military training provide the basis for future studies to evaluate nutritional strategies that attenuate protein loss and sustain performance during severe energy deficits.

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 high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial

The purpose of this work was to determine the effects of varying levels of dietary protein on body composition and muscle protein synthesis during energy deficit (ED). A randomized controlled trial of 39 adults assigned the subjects diets providing protein at 0.8 (recommended dietary allowance; RDA), 1.6 (2×-RDA), and 2.4 (3×-RDA) g kg(-1) d(-1) for 31 d. A 10-d weight-maintenance (WM) period was followed by a 21 d, 40% ED. Body composition and postabsorptive and postprandial muscle protein synthesis were assessed during WM (d 9-10) and ED (d 30-31). Volunteers lost (P<0.05) 3.2 ± 0.2 kg body weight during ED regardless of dietary protein. The proportion of weight loss due to reductions in fat-free mass was lower (P<0.05) and the loss of fat mass was higher (P<0.05) in those receiving 2×-RDA and 3×-RDA compared to RDA. The anabolic muscle response to a protein-rich meal during ED was not different (P>0.05) from WM for 2×-RDA and 3×-RDA, but was lower during ED than WM for those consuming RDA levels of protein (energy × protein interaction, P<0.05). To assess muscle protein metabolic responses to varied protein intakes during ED, RDA served as the study control. In summary, we determined that consuming dietary protein at levels exceeding the RDA may protect fat-free mass during short-term weight loss.

Associations of maximal strength and muscular endurance test scores with cardiorespiratory fitness and body composition

The purpose of the present study was to assess the relationships between maximal strength and muscular endurance test scores additionally to previously widely studied measures of body composition and maximal aerobic capacity. 846 young men (25.5 ± 5.0 yrs) participated in the study. Maximal strength was measured using isometric bench press, leg extension and grip strength. Muscular endurance tests consisted of push-ups, sit-ups and repeated squats. An indirect graded cycle ergometer test was used to estimate maximal aerobic capacity (V(O2)max). Body composition was determined with bioelectrical impedance. Moreover, waist circumference (WC) and height were measured and body mass index (BMI) calculated. Maximal bench press was positively correlated with push-ups (r = 0.61, p < 0.001), grip strength (r = 0.34, p < 0.001) and sit-ups (r = 0.37, p < 0.001) while maximal leg extension force revealed only a weak positive correlation with repeated squats (r = 0.23, p < 0.001). However, moderate correlation between repeated squats and V(O2)max was found (r = 0.55, p < 0.001) In addition, BM and body fat correlated negatively with muscular endurance (r = -0.25 - -0.47, p < 0.001), while FFM and maximal isometric strength correlated positively (r = 0.36-0.44, p < 0.001). In conclusion, muscular endurance test scores were related to maximal aerobic capacity and body fat content, while fat free mass was associated with maximal strength test scores and thus is a major determinant for maximal strength. A contributive role of maximal strength to muscular endurance tests could be identified for the upper, but not the lower extremities. These findings suggest that push-up test is not only indicative of body fat content and maximal aerobic capacity but also maximal strength of upper body, whereas repeated squat test is mainly indicative of body fat content and maximal aerobic capacity, but not maximal strength of lower extremities.

Effects of easy-to-use protein-rich energy bar on energy balance, physical activity and performance during 8 days of sustained physical exertion

BACKGROUND

Previous military studies have shown an energy deficit during a strenuous field training course (TC). This study aimed to determine the effects of energy bar supplementation on energy balance, physical activity (PA), physical performance and well-being and to evaluate ad libitum fluid intake during wintertime 8-day strenuous TC.

METHODS

Twenty-six men (age 20±1 yr.) were randomly divided into two groups: The control group (n = 12) had traditional field rations and the experimental (Ebar) group (n = 14) field rations plus energy bars of 4.1 MJ•day(-1). Energy (EI) and water intake was recorded. Fat-free mass and water loss were measured with deuterium dilution and elimination, respectively. The energy expenditure was calculated using the intake/balance method and energy availability as (EI/estimated basal metabolic rate). PA was monitored using an accelerometer. Physical performance was measured and questionnaires of upper respiratory tract infections (URTI), hunger and mood state were recorded before, during and after TC.

RESULTS

Ebar had a higher EI and energy availability than the controls. However, decreases in body mass and fat mass were similar in both groups representing an energy deficit. No differences were observed between the groups in PA, water balance, URTI symptoms and changes in physical performance and fat-free mass. Ebar felt less hunger after TC than the controls and they had improved positive mood state during the latter part of TC while controls did not. Water deficit associated to higher PA. Furthermore, URTI symptoms and negative mood state associated negatively with energy availability and PA.

CONCLUSION

An easy-to-use protein-rich energy bars did not prevent energy deficit nor influence PA during an 8-day TC. The high content of protein in the bars might have induced satiation decreasing energy intake from field rations. PA and energy intake seems to be primarily affected by other factors than energy supplementation such as mood state.

Effects of a daily mixed nutritional supplement on physical performance, body composition, and circulating anabolic hormones during 8 weeks of arduous military training

The aim of this work was to investigate the effect of a daily mixed nutritional supplement upon body composition, physical performance, and circulating anabolic hormones in soldiers undergoing arduous training. Thirty males received either a habitual diet alone (CON, n = 15) or with the addition of a daily mixed supplement (SUP, n = 15) of ∼5.1 MJ·d⁻¹ during 8 weeks of training. Body composition (DEXA), maximal dynamic lift strength (MDLS), and vertical jump (VJ) were assessed, and resting blood samples were collected before and after training. Blood analysis included insulin-like growth factors (IGF-1, IGF BP-1, and IGF BP-3), testosterone, and cortisol. There were no group differences at baseline. Body mass loss (mean ± SD) (CON 5.0 ± 2.3, SUP 1.6 ± 1.5 kg), lean mass loss (CON 2.0 ± 1.5, SUP 0.7 ± 1.5 kg), and fat mass loss (CON 3.0 ± 1.6, SUP 0.9 ± 1.8 kg) were significantly blunted by SUP. CON experienced significant decrements in MDLS (14%), VJ (10%), and explosive leg power (11%) that were prevented by SUP. Military training significantly reduced circulating IGF-1 (28%), testosterone (19%), and the testosterone:cortisol ratio (24%) with no effect of SUP. Circulating IGF BP-1 concentration and cortisol remained unchanged throughout, although SUP abolished the significant decrease in circulating IGF BP-3 (20%) on CON. In conclusion, a daily mixed nutritional supplement attenuated decreases in body mass and lean mass and prevented the decrease in physical performance during an arduous military training program.

Effects of long-term anabolic androgenic steroid administration on respiratory function

The purpose of this study was to investigate the effects of resistance training and long-term anabolic androgenic steroids (AASs) administration on respiratory function. Subject groups consisted of AAS users (n = 9) who were still using AAS at time of testing (SU); AAS users (n = 6) who had been abstinent for > 3 months (SA), bodybuilding controls (n = 8) (BC), and (n = 8) sedentary male controls (SC). FEV(1), FVC, and PEF were measured. The results found that all subjects were within normal range, and there were no differences between groups. Maximum inspiratory pressure (MIP), and grip strength were both significantly greater in SU (P < 0.05) compared with SC; no significant difference was found between the other groups. Their MIP and grip strength was significantly correlated (r = 0.57; P < 0.05). The data from this study suggest that the combination of resistance training and AAS administration produce a significant increase in MIP in a cohort of long-term AAS users.

Following 2 diet-restricted male outdoor rock climbers: impact on oxidative stress and improvements in markers of cardiovascular risk

Lower body fat percentage is positively associated with climbing performance. This may lead climbers to practice unhealthy diet restriction when no sport-specific nutrition information exists. This study examined whether prolonged diet restriction affects body composition, oxidative stress, or other potential health risks in outdoor rock climbers. Two healthy male climbers conducted a 5 week rock climbing trip with a limited food budget ($1 each per day). Subjects underwent an energy restriction of approximately 40%. Loss of body weight and fat mass at week 5 were 5.8% and 16.1%, respectively, and were accompanied by significant subcutaneous fat loss in the iliac crest and abdomen. Triacylglycerols (TG), free fatty acids and C-reactive protein (CRP) dramatically decreased from baseline to week 2, and then maintained the lower level until week 5. Plasma vitamin C was below the normal range, and F2-isoprostanes, a marker of oxidative stress, continuously increased to week 5. Superoxide dismutase and glutathione peroxidase increased to week 2, but had returned to baseline levels at week 5. These results indicate that prolonged reduced energy intake while climbing may have an impact on weight loss and fat mass loss, which may contribute to low circulating TG and CRP, indicating improvements in markers of cardiovascular risk, and may lead to increased oxidative stress and reduced circulating antioxidants. Further studies are warranted to determine whether antioxidant supplementation or increased energy intake reduce oxidative stress.

Effects of dietary protein content on IGF-I, testosterone, and body composition during 8 days of severe energy deficit and arduous physical activity

Energy restriction coupled with high energy expenditure from arduous work is associated with an altered insulin-like growth factor-I (IGF-I) system and androgens that are coincident with losses of fat-free mass. The aim of this study was to determine the effects of two levels of dietary protein content and its effects on IGF-I, androgens, and losses of fat-free mass accompanying energy deficit. We hypothesized that higher dietary protein content would attenuate the decline of anabolic hormones and, thus, prevent losses of fat-free mass. Thirty-four men [24 (SD 0.3) yr, 180.1 (SD 1.1) cm, and 83.0 (SD 1.4) kg] participated in an 8-day military exercise characterized by high energy expenditure (16.5 MJ/day), low energy intake (6.5 MJ/day), and sleep deprivation (4 h/24 h) and were randomly divided into two dietary groups: 0.9 and 0.5 g/kg dietary protein intake. IGF-I system analytes, androgens, and body composition were assessed before and on days 4 and 8 of the intervention. Total, free, and nonternary IGF-I and testosterone declined 50%, 64%, 55%, and 45%, respectively, with similar reductions in both groups. There was, however, a diet × time interaction on day 8 for total IGF-I and sex hormone-binding globulin. Decreases in body mass (3.2 kg), fat-free mass (1.2 kg), fat mass (2.0 kg), and percent body fat (1.5%) were similar in both groups ( P = 0.01). Dietary protein content of 0.5 and 0.9 g/kg minimally attenuated the decline of IGF-I, the androgenic system, and fat-free mass during 8 days of negative energy balance associated with high energy expenditure and low energy intake.

Physiological consequences of U.S. Army Ranger training

PURPOSE

Soldiers are expected to maintain a high degree of physical readiness as operational demands can severely degrade performance capabilities. This study examined the physiological consequences of U.S. Army Ranger training on strength, power, body composition, and somatotrophic hormones.

METHODS

In an intensive 8-wk military training course that included an average daily energy deficit of 1000 kcal.d, lower-body power output, maximal lifting strength, body composition, and serum concentrations of several somatotrophic hormones were measured in 50 male soldiers (24.6 +/- 4.4 y; 176.1 +/- 7.8 cm; 78.4 +/- 8.7 kg; 14.7 +/- 4.2% body fat) before and after the course.

RESULTS

Vertical jump height (-16%), explosive power output (-21%), maximal lifting strength. (-20%), body mass (-13%), fat-free mass (-6%), and fat mass (-50%) declined (P < 0.05) after the training course. Circulating total testosterone and insulin-like growth factor-I (IGF-I) experienced significant (P < 0.05) declines, and cortisol was significantly increased. Lower-body power output, but not maximal lifting strength, correlated with changes in fat-free mass. IGF-I and cortisol, but not total testosterone, were correlated with losses of tissue mass.

CONCLUSION

Lower-body power output, estimated from vertical jump height and body mass, is a sensitive and field expedient measure that can be used to assess the influence of caloric deficit on physical performance after 8 wk of U.S. Army Ranger training. With severe weight loss (>or=13% of body mass), IGF-I and cortisol correlate more closely with soft-tissue tissue adaptations than does testosterone.

Lower extremity muscle size and strength and aerobic capacity decrease with caloric restriction but not with exercise-induced weight loss

Caloric restriction (CR) results in fat loss; however, it may also result in loss of muscle and thereby reduce strength and aerobic capacity (VO2 max). These effects may not occur with exercise-induced weight loss (EX) because of the anabolic effects of exercise on heart and skeletal muscle. We tested the hypothesis that CR reduces muscle size and strength and VO2 max, whereas EX preserves or improves these parameters. Healthy 50- to 60-yr-old men and women (body mass index of 23.5-29.9 kg/m2) were studied before and after 12 mo of weight loss by CR (n = 18) or EX (n = 16). Lean mass was assessed by dual-energy X-ray absorptiometry, thigh muscle volume by MRI, isometric and isokinetic knee flexor strength by dynamometry, and treadmill VO2 max by indirect calorimetry. Both interventions caused significant decreases in body weight (CR: -10.7 +/- 1.4%, EX: -9.5 +/- 1.5%) and lean mass (CR: -3.5 +/- 0.7%, EX: -2.2 +/- 0.8%), with no significant differences between groups. Significant decreases in thigh muscle volume (-6.9 +/- 0.8%) and composite knee flexion strength (-7.2 +/- 3%) occurred in the CR group only. Absolute VO2 max decreased significantly in the CR group (-6.8 +/- 2.3%), whereas the EX group had significant increases in both absolute (+15.5 +/- 2.4%) and relative (+28.3 +/- 3.0%) VO2 max. These data provide evidence that muscle mass and absolute physical work capacity decrease in response to 12 mo of CR but not in response to a similar weight loss induced by exercise. These findings suggest that, during EX, the body adapts to maintain or even enhance physical performance capacity.

Three weeks of caloric restriction alters protein metabolism in normal-weight, young men

The effects of prolonged caloric restriction (CR) on protein kinetics in lean subjects has not been investigated previously. The purpose of this study was to test the hypotheses that 21 days of CR in lean subjects would 1) result in significant losses of lean mass despite a suppression in leucine turnover and oxidation and 2) negatively impact exercise performance. Nine young, normal-weight men [23 +/- 5 y, 78.6 +/- 5.7 kg, peak oxygen consumption (Vo2 peak) 45.2 +/- 7.3 ml.kg(-1).min(-1), mean +/- SD] were underfed by 40% of the calories required to maintain body weight for 21 days and lost 3.8 +/- 0.3 kg body wt and 2.0 +/- 0.4 kg lean mass. Protein intake was kept at 1.2 g.kg(-1).day(-1). Leucine kinetics were measured using alpha-ketoisocaproic acid reciprocal pool model in the postabsorptive state during rest and 50 min of exercise (EX) at 50% of Vo2 peak). Body composition, basal metabolic rate (BMR), and exercise performance were measured throughout the intervention. At rest, leucine flux (approximately 131 micromol.kg(-1).h(-1)) and oxidation (R(ox); approximately 19 micromol.kg(-1).h(-1)) did not differ pre- and post-CR. During EX, leucine flux (129 +/- 6 vs. 121 +/- 6) and R(ox) (54 +/- 6 vs. 46 +/- 8) were lower after CR than they were pre-CR. Nitrogen balance was negative throughout the intervention ( approximately 3.0 g N/day), and BMR declined from 1,898 +/- 262 to 1,670 +/- 203 kcal/day. Aerobic performance (Vo2 peak, endurance cycling) was not impacted by CR, but arm flexion endurance decreased by 20%. In conclusion, 3 wk of caloric restriction reduced leucine flux and R(ox) during exercise in normal-weight young men. However, despite negative nitrogen balance and loss of lean mass, whole body exercise performance was well maintained in response to CR.

Energy requirements of military personnel

Energy requirements of military personnel (Soldiers, Sailors, Airmen, and Marines) have been measured in garrison and in field training under a variety of climatic conditions. Group mean total energy expenditures for 424 male military personnel from various units engaged in diverse missions ranged from 13.0 to 29.8 MJ (3109-7131 kcal) per day. The overall mean was 19.3+/-2.7 MJ (mean+/-SD) (4610+/-650 kcal) per day measured over an average of 12.2 days (range 2.25-69 days). For the 77 female military personnel studied, mean total energy expenditures for individual experimental groups ranged from 9.8 to 23.4 MJ (2332-5597 kcal) per day, with an overall mean of 11.9+/-2.6 MJ (2850+/-620 kcal) per day, measured over an average of 8.8 days (range 2.25-14 days). Women, presumably due to their lower lean body mass, resting metabolic rate, and absolute work rates, had lower total energy expenditures. Combat training produced higher energy requirements than non-combat training or support activities. Compared to temperate conditions, total energy expenditures did not appear to be influenced by hot weather, but tended to be higher in the cold or high altitude conditions.

Diet and physical performance

This paper provides a historical summary of military nutrition research into the role of diet for sustaining soldier physical performance. Studies of underfeeding document that physical performance is preserved during several days of underfeeding provided sufficient carbohydrate and minerals are consumed to minimize the diuresis associated with semi-starvation diets and serial intake of carbohydrate is available to support metabolism during prolonged work. The Military Recommended Dietary Allowances, AR 40-25, currently recommends that when restricted rations are required, that the ration contain at least 1,100-1,500 kcal, 50-70 g of protein, and a minimum of 100 g of carbohydrate on a daily basis. This low energy diet, however, is not recommended for subsistence for longer than 10 consecutive days. Dietary carbohydrate intakes of approximately 300-400 g will more closely match the quantity of carbohydrate oxidized to meet daily energy requirements during field operations. Research into the potential advantages of dietary supplements has generally not proved advantageous when compared to eating a well balanced diet. Future investigations of the role of diet for sustaining soldier health and performance should be directed toward a better understanding of the influence of energy intake and macro-nutrient composition for preserving lean body mass, reducing susceptibility to illness and injury and enhancing recovery during and after sustained operations.

Physical performance responses during 72 h of military operational stress

PURPOSE

To characterize the impact of prolonged work, underfeeding, and sleep deprivation (i.e., sustained operations; SUSOPS) on physical and occupational related performance during military operational stress.

METHODS

Ten male soldiers were tested on days 1 (D1), 3 (D3), and 4 (D4) of a control and an experimental week that included prolonged physical work (total daily energy expenditure approximately 4,500 kcal x d(-1)), underfeeding (approximately 1,600 kcal x d(-1)), and sleep deprivation (approximately 2 h x d(-1)). Body composition was measured with dual-energy x-ray absorptiometry (DEXA). Ballistic power was assessed by 30 repetitive squat jumps and bench-press throws. Military-relevant occupational performance was evaluated with a 10-min box lift, obstacle course, grenade throw, rifle marksmanship, and a 25-min wall-build task.

RESULTS

Fat-free mass (-2.3%) and fat mass (-7.3%) declined (P </= 0.05) during SUSOPS. Squat-jump mean power (-9%) and total work (-15%) declined (P </= 0.05) during SUSOPS. Bench-press power output, grenade throw, and marksmanship for pop-up targets were not affected. Obstacle course and box-lift performances were lower (P </= 0.05) on D3 but showed some recovery on D4. Wall building was approximately 25% lower (P </= 0.05) during SUSOPS.

CONCLUSION

Decrements in performance during SUSOPS are primarily restricted to tasks that recruit muscles that are over-utilized without adequate recovery. General military skill tasks and occupational physical performance tasks are fairly well maintained.

Physical fitness of young women: carrying simulated patients

An evaluation of physical fitness prior to employment appears to be mandatory for several occupations in order to protect the employee from overburdening and the employer from placing excess demands on the employee. One such occupation seems to be that of the field medical specialist who needs special physical strength since terrain conditions deny wheel-assisted transport of stretcher patients. The anthropometric and isometric force data of a total of 62 female and 48 male recruits for the medical service of the Bundeswehr were evaluated, together with their ability to carry a patient on a stretcher (weight = 14 kg) within a gymnasium. Initially the 'casualties' were simulated by sandbags weighing 60, 70, 80 and 90 kg each on stretchers; subsequently equivalent-weight water cans were used. The tests were administered at the beginning and at the end of the general Basic Military Training (BMT). While all males were able to carry the simulated 90 kg patient, only 22 out of 62 female recruits were able to do so at the beginning of BMT. At the end, the number had improved to 29 out of 55 women soldiers completing training. At the beginning of BMT 22.5% of the women soldiers were unable to rescue a simulated 70 kg patient; at the end of BMT the number had fallen to 18%. The isometric force values as measured revealed the hand grip strength as the best predictor for the capacity to carry simulated 90 kg patients. It is, therefore, suggested that a hand strength test be administered prior to field medical specialist training in order to channel unsuitable candidates into other training schemes.

Endocrine markers of semistarvation in healthy lean men in a multistressor environment

We tested the hypothesis that key endocrine responses to semistarvation would be attenuated by changing only the food intake in a multistressor environment that also included sustained workload, inadequate sleep, and thermal strain. Serum hormones were compared within and between two groups of healthy young male volunteers participating in the 8-wk US Army Ranger course, with four repeated cycles of restricted energy intakes and refeeding: group 1 (n = 49) and group 2 (n = 48); energy deficits averaged 1,200 and 1,000 kcal/day, respectively. After 8 wk, most of group 1 achieved a minimum body fat, serum 3,5,3'-triiodothyronine (T(3)) was below normal (78 +/- 20 ng/dl), testosterone (T) approached castrate levels (4.5 +/- 3.9 nmol/l), insulin-like growth factor I (IGF-I) declined by one-half (75 +/- 25 microg/l), and cholesterol rose from 158 +/- 31 to 217 +/- 39 mg/dl. Bioavailable T(3) and T were further reduced by increases in their specific binding proteins in response to declining insulin. Refeeding, even with continuation of the other stressors, produced prompt recovery of T(3), T, and IGF-I. Higher energy intakes in group 2 attenuated the subclinical hypothyroidism and hypercholesterolemia, whereas consistent luteinizing hormone suppression indicated centrally mediated threshold effects on gonadal hormone suppression. We conclude that low T, T(3), and IGF-I remained reliable markers of acute energy deficits in the presence of other stressors; elevated cholesterol and cortisol provided information about chronic status, corresponding to diminishing body fat stores.

Effects of team size on the maximum weight bar lifting strength of military personnel

Teamwork is an essential element in the majority of critical Army lifting tasks. Therefore, an understanding of the relationship between individual and team lifting capacity is of great tactical importance. Twenty-three male and 17 female U.S. Army soldiers were randomly assigned to single- and mixed-gender teams of two, three, and four persons. Individual lifting strength was the one-repetition-maximum (1RM) load lifted from floor to knuckle height using a weight bar. A square-shaped bar was used for two- and four-person lifting, and a triangular-shaped bar was used for three-person lifting. Team lifting strength as a percentage of the sum of individual lifting strength (%sum) did not change with team size. The %sum for teams of men (87.3%) was less than for teams of women (91.1%, p < 0.05). The %sums for both single-gender teams (all men and all women) were greater (p < 0.01) than for mixed-gender teams (80.2%). The number of people lifting a large object was increased to four with no decrease in the effectiveness of the individual lifter beyond that found for two persons. The 1RM loads presented in this paper were lifted under ideal conditions by young soldiers and do not represent norms for an industrial population.

Muscle mass and strength: relation to function in population studies

The use of the term sarcopenia to describe the age-related loss in skeletal muscle and its functional consequences is relatively recent. However, interest in the relationship of muscle mass to strength and function predates the concept of sarcopenia as researchers have attempted to understand differences in mass and strength between men and women, young and old. Most of these studies are cross-sectional comparisons in which muscle mass and strength tend to be linearly related, so that those with more muscle tend to be stronger. This article focuses instead on some potential problems with the sarcopenia-function association in old age and presents what little data exist from longitudinal population studies addressing the effect of sarcopenia over time.

Development and biomedical testing of military operational rations

This article gives a brief history of military nutrition research in this century and reviews recent advances made through field testing. Although modern rations are nutritionally complete, ration developers are challenged to improve palatability to promote increased intakes in field training and combat settings. The principal goal for military nutritionists is to identify the optimal macronutrient mix and specific ration components that sustain a soldier's performance in the face of operational stressors such as sleep deprivation, intense physical activity, climatic extremes, and hypobaric hypoxia. Energy expenditures during typical field-training exercises average approximately 4000 kcal/day, whereas energy intakes are usually 3000 kcal/day or less when operational rations are consumed. One way to ameliorate the effects of this shortfall is to provide soldiers with a carbohydrate beverage supplement.