William J. Tharion

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.

Effects of caffeine or diphenhydramine on visual vigilance

The effects of two drugs having opposite effects on the central nervous system were investigated using a newly developed visual vigilance task. Twenty-four male volunteers (median age=20) performed the task on three separate occasions; after consuming placebo, caffeine (200 mg), or diphenhydramine (25 mg), in a double-blind, Latin Square design. At least 2 days intervened between drug administrations. Caffeine use was restricted for 10 h and smoking for 3 h before drug administration. When compared with placebo, caffeine significantly increased the number of correct responses and decreased response times, whereas diphenhydramine decreased the number of correct responses and increased response times. Low habitual consumers of caffeine (< 100 mg/day) and non-smokers had more correct responses than did high habitual caffeine consumers (> 100 mg/day) and smokers, but only in the placebo condition. Non-smokers had faster response times than smokers only in the placebo condition. Both caffeine and diphenhydramine altered certain aspects of mood.

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 x 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.

A Comparison of Injuries, Limited-Duty Days, and Injury Risk Factors in Infantry, Artillery, Construction Engineers, and Special Forces Soldiers

OBJECTIVES We compared injuries/risk factors in infantry soldiers (I), construction engineers (CE), combat artillery (CA), and Special Forces (SF) during their operational and fitness activities. METHODS Anthropometrics, ethnicity, and fitness data were collected before review of medical records. RESULTS Injury rates for I, CE, and CA were 4.0, 7.2, and 5.5 injuries/100 soldier-months, respectively; over 70% of them resulted from overuse. SF soldiers had an injury rate of 3.5 injuries/100 soldier-months, 50% of them reported as traumatic. Average limited-duty days (LDDs) were threefold higher in SF. Smoking, BMI > or =25, and APFT run time for 3.2 km >14 minutes were risk factors in I. Caucasian ethnicity, height <170.2 cm, weight > or =90 kg, and BMI > or =25 were risk factors in CE and CA. Age >27 years old was a risk factor in SF. CONCLUSIONS Greater emphasis should be placed on risk factor identification and testing strategies to reduce injuries among SF and other troops.

Dietary Tyrosine Benefits Cognitive and Psychomotor Performance During Body Cooling

Supplemental tyrosine is effective at limiting cold-induced decreases in working memory, presumably by augmenting brain catecholamine levels, since tyrosine is a precursor for catecholamine synthesis. The effectiveness of tyrosine for preventing cold-induced decreases in physical performance has not been examined. This study evaluated the effect of tyrosine supplementation on cognitive, psychomotor, and physical performance following a cold water immersion protocol that lowered body core temperature. Fifteen subjects completed a control trial (CON) in warm (35 degrees C) water and two cold water trials, each spaced a week apart. Subjects ingested an energy bar during each trial; on one cold trial (TYR) the bar contained tyrosine (300 mg/kg body weight), and on the other cold trial (PLB) and on CON the bar contained no tyrosine. Following each water immersion, subjects completed a battery of performance tasks in a cold air (10 degrees C) chamber. Core temperature was lower (p=0.0001) on PLB and TYR (both 35.5+/-0.6 degrees C) than CON (37.1+/-0.3 degrees C). On PLB, performance on a Match-to-Sample task decreased 18% (p=0.02) and marksmanship performance decreased 14% (p=0.002), compared to CON, but there was no difference between TYR and CON. Step test performance decreased by 11% (p=0.0001) on both cold trials, compared to CON. These data support previous findings that dietary tyrosine supplementation is effective for mitigating cold-induced cognitive performance such as working memory, even with reduced core temperature, and extends those findings to include the psychomotor task of marksmanship.

Antihistamine Effects on the Central Nervous System, Cognitive Performance and Subjective States

Diphenhydramine causes drowsiness and performance decrements in some tasks whereas terfenadine generally does not. This study examined central nervous system (CNS) differences in response to the administration of diphenhydramine (50 mg) and terfenadine (60 mg) up to 3 h after drug administration. Two evoked potential measures, the Brainstem Auditory Evoked Potential and the Pattern Reversal Evoked Potential (PREP), assessed CNS function. Other measures of CNS function, cognitive performance and subjective states administered included Critical Flicker Fusion, the Baddeley Grammatical Reasoning Test, Digit Symbol Substitution, the Profile of Mood States, and the Environmental Symptoms Questionnaire. Significant increases in PREP latencies (N75, P100 and N145) occurred after orally ingesting diphenhydramine. No other significant drug effects were observed. The significant increase in the PREP latencies indicate diphenhydramines presence in the cerebral cortex results in a slowing of visual information processing. The lack of significant findings for terfenadine is probably a result of its difficulty in penetrating the blood-brain barrier.

Effects of military exercise tasks and a carbohydrate-electrolyte drink on rifle shooting performance in two shooting positions

The effect of exercise, consumption of a carbohydrate-electrolyte drink and shooting position (standing vs. prone) on marksmanship accuracy and sighting time were measured in 27 experienced marksmen. Participants ‘dry-fired’ a laser equipped rifle simulator system at a 2.3 cm circular target at a distance of 5 m. Marksmanship was assessed under the following conditions: (1) at rest; (2) after completing a 14.7 km road march (10.4 km with a 21 kg pack); and (3) after a combined timed rock climb and 700 m uphill run. The road march reduced marksmanship accuracy and sighting time (p < 0.05) while the climb and uphill run did not affect marksmanship. Consumption of a carbohydrate-electrolyte drink did not preserve marksmanship accuracy after exercise. Shooting prone was significantly more accurate and faster than shooting from the standing position (p < 0.05). The effects of drinking a carbohydrate-electrolyte drink and performing heavy work on a subsequent fine motor-visual vigilance type task was studied. Implications are for the military, but also for industries whose work involves tasks that are both physically demanding and require precision (e.g. linemen working for the telephone company climbing a pole and then cutting a small single wire).

The effects of gender, team size, and a shoulder harness on a stretcher-carry task and post-carry performance. Part I. A simulated carry from a remote site

This study examined the effects of gender, two- vs. four-person teams, and use of a shoulder harness vs. a hand carry on the ability of participants to simulate the transport of patients during a prolonged stretcher carry, and to simulate the defense and medical treatment of patients following the stretcher carry. Participants carried a 6.8-kg stretcher containing an 81.6-kg manikin at a constant rate of 4.8 km/h for as long as possible, up to a half hour. Dependent measures included carry time, weapon firing, fine-motor coordination, heart rate, oxygen uptake, perceived exertion, and subjective symptoms. Analysis of variance and post-hoc Newman-Keuls comparison of means revealed that men carried stretchers longer than women (p < 0.05). Harness use resulted in the stretcher being carried longer (23.1 ± 8.9 vs. 6.1 ± 5.9 min), at lower heart rates (141.9 ± 17.9 vs. 149.9 ± 14.7 beats per min), at slightly higher intensity (46 ± 8 vs. 42 ± 7% VdotO2max) (p < 0.05), and with less fatigue in the forearm and hand (p < 0.05). Four-person teams maintained pre-carry fine-motor and marksmanship scores and carried longer (16.9 ± 11.0 vs. 12.3 ± 11.4 min), while working at a slightly lower intensity (43 ± 8 vs. 45 ± 8% VdotO2max), compared with two-person teams (p < 0.05). Use of four-person teams with a harness resulted in an 8-fold increase in carry time, compared with two-person hand-carry teams (24.5 ± 9.0 vs. 3.0 ± 1.8 min). Four-person teams with a shoulder harness are therefore recommended for prolonged carries.

Hypohydration and muscular fatigue of the thumb alter median nerve somatosensory evoked potentials

The mechanisms by which dehydration impairs endurance performance remain unresolved but may involve alterations in afferent neural processing. The purpose of this study was to determine the effect of hypohydration on somatosensory evoked potentials (SEPs) at rest and during recovery from fatiguing exercise. Fourteen volunteers (12 men, 2 women) performed repetitive isometric thumb contractions (50% maximal voluntary contractions (MVC) and 100% MVC in a 5:1 ratio, each contraction separated by 5 s of rest) until exhaustion when euhydrated (EU) and when hypohydrated by 4% body mass (HY). SEPs were obtained from the median nerve. The results indicated that HY did not produce statistical differences in time to exhaustion (EU=754 (SD 255); HY=714 (SD 318) s; p=0.66) or rate of muscle fatigue. However, HY was associated with greater subjective feelings of fatigue and loss of vigor after exhaustive exercise (p<0.01). HY affected N20 latency with an interaction effect of hydration by fatigue state (EU-Rest: 18.5 (SD 1.6) ms; EU-Fatigue: 19.0 (SD 1.6) ms; HY-Rest: 18.3 (SD 1.3) ms; HY-Fatigue: 18.4 (SD 1.5) ms; p=0.034), but N20 and N20-P22 amplitude responses were similar between HY and EU trials. We concluded that moderate water deficits appear to alter afferent signal processing within the cerebral cortex.

Acceptability of a Wearable Vital Sign Detection System

This study assessed the human factors issues associated with wearing a Vital Sign Detection System (VSDS), a body worn physiological monitoring system. Experienced combat Soldiers (n = 27) participated in a combat training exercise of ∼ 120 hr while wearing the VSDS. They were then given a questionnaire to assess comfort, physical impact on the body, and acceptability of the VSDS as well as questions on fit, impact on performance, and durability of the VSDS. Comfort was impacted the most by the VSDS when in the prone position, possibly affecting sleep, and prone position rifle shooting. Skin irritation or discomfort was reported in 85% of respondents. Sixty-two percent thought the VSDS was not acceptable to wear for ≥ 8 hr. Yet, at the same time, 92% of Soldiers approved of the concept for health monitoring, and 89% said they would wear the VSDS as is if it could help save their life. The VSDS needs to be modified to be more comfortable before it can be fielded for medical monitoring of Soldiers in the field.