Biomedical subjects

Harris R Lieberman

Publications and source records attributed to Harris R Lieberman.

At least 19 recordsLinked to original sources

PubMed2006

Mental energy: Assessing the cognition dimension.

The cognitive dimension of mental energy can be assessed by tests of vigilance and choice reaction time. These behaviors are relatively simple cognitive functions and can be measured with precision and reliability if carefully designed and implemented tests are used. Because the concept of mental energy is still evolving, the selection of appropriate tests to assess it must be tentative. However, vigilance and choice reaction time seem to have the necessary psychometric properties for assessing mental energy, including construct, predictive content, and face validity. Tests of reaction time and vigilance are correlated with questionnaires that measure mood states corresponding to mental energy--such as sleepiness, fatigue, and alertness--in the expected manner and are of approximately equivalent sensitivity.

Cognition↗

PubMed2006

Cognition during sustained operations: comparison of a laboratory simulation to field studies.

INTRODUCTION: Military operations, especially combat, expose individuals to multiple stressors, including sleep loss, food deprivation, and sustained physical activity. Civilians, such as woodland firefighters, disaster victims, and relief workers, are also exposed to such environments. Our laboratory developed a brief, intense, laboratory-based simulation of a multistressor environment which included sleep loss, continuous physical activity, and food deprivation. METHODS: During this sustained operations (SUSOPS) scenario, and a control period, cognitive performance and mood were measured in 13 volunteers. The scenario included road marches, battle drills, and land navigation. Physical activity and sleep were assessed with actigraphs. RESULTS: Significant decrements in visual vigilance, choice reaction time, and matching-to-sample, a test of short-term memory, were observed. Marksmanship was stable and physical activity significantly increased. Mood states assessed by the Profile of Mood States (POMS: Tension, Depression, Anger, Vigor, Fatigue and Confusion) also significantly deteriorated. DISCUSSION: Cognitive function declined more extensively and rapidly than physical performance. Decrements in cognitive performance were comparable to those in a field study conducted for an equivalent period of time in uncontrolled conditions. This demonstrates that decrements in cognitive function and increased physical activity, similar to those in highly stressful field environments, can be duplicated under controlled conditions. The simulated SUSOPS scenario is an appropriate paradigm for assessment of adverse effects of military and civilian multistressor environments on human performance, physiology, and interventions designed to mitigate them.

Adult↗

PubMed2006

Caffeinated tube food effect on pilot performance during a 9-hour, simulated nighttime U-2 mission.

INTRODUCTION: Interventions to maintain performance are necessary to meet demanding mission requirements during sustained and surge aviation operations. Tube foods are the only foods that can be consumed during a U-2 mission due to the confining and encapsulating nature of required support equipment. Caffeine is a safe and effective strategy to enhance cognitive performance and is an ingredient in some tube foods. The objective of this study was to determine whether moderate doses of caffeinated tube foods would enhance performance in a simulated U-2 mission. METHODS: Volunteers were 12 healthy USAF male pilots. The study used a double blind, placebo-controlled, two-factor, repeated-measures (five iterations per night) design. Caffeinated (200 mg each) or placebo tube food was consumed at 00:00 and 04:00. Dependent measures assessed included standardized tests of cognitive performance, vigilance, and mood designed to simulate the demands of a nighttime U-2 mission. RESULTS: Statistically significant (p < 0.05) improvements in performance due to caffeine administration compared with placebo were present in all five cognitive tasks either as main effects, interactions, or absence of significant degradation in the caffeine treatment condition compared with the placebo condition. A majority of sleep deprivation-induced performance decrements were attenuated by 200 mg of caffeine in tube food consumed every 4 h, and in some cases, performance was improved beyond baseline levels. CONCLUSIONS: Caffeinated tube food maintained cognitive performance representative of U-2 long-duration mission tasks at or near baseline levels for a 9-h overnight period in qualified USAF pilots. Side effects were minor and did not differ between placebo and caffeine conditions.

Aviation↗

PubMed2005

A low-protein diet alters rat behavior and neurotransmission in normothermic and hyperthermic environments.

Dietary protein contains amino acids used in the brain for synthesis of neurotransmitters. Although information on pre- and post-natal exposure to low-protein diets in rodents is available, little is known about effects of such diets on adult animals. Therefore, the behavioral and neurochemical consequences of exposure to a brief (11 days), low (4%)-protein diet in animals exposed to normothermic and hyperthermic test conditions were examined. In separate groups of animals, the Porsolt Swim test and elevated plus maze were administered. These tasks are sensitive to nutritional and/or environmental manipulations. In other groups of rats exposed to the same dietary and environmental conditions, dopamine, norepinephrine, epinephrine, and serotonin in the striatum were assessed using microdialysis. In the Porsolt swim test, which assesses coping behavior, performance was impaired under normothermic and hyperthermic conditions in animals on the low-protein diet. Performance on the plus maze, a measure of exploration and anxiety, was altered in the hyperthermic condition by low protein, with the diet increasing exploration. Microdialysis detected increased norepinephrine in the striatum of hyperthermic animals on the low-protein diet. This study demonstrates that changes in stress-related behaviors of adult animals occur following brief exposure to low-protein diets.

Analysis of Variance↗

PubMed2005

Severe decrements in cognition function and mood induced by sleep loss, heat, dehydration, and undernutrition during simulated combat.

BACKGROUND: Military exercises generate high levels of stress to simulate combat, providing a unique opportunity to examine cognitive and physiologic responses of normal humans to acute stress. METHODS: Cognitive and physiologic markers of stress were evaluated before, during, and after an intense training exercise conducted for 53 hours in the heat. Cognitive performance, mood, physical activity, sleep, body composition, hydration, and saliva cortisol, testosterone, and melatonin were assessed. Volunteers were 31 male U.S. Army officers from an elite unit, aged 31.6 +/- .4 years. RESULTS: Wrist activity monitors documented that soldiers slept only 3.0 +/- .3 hours during the exercise and were active throughout. Volunteers lost 4.1 +/- .2 kg (p < .001) of weight, predominately water (3.1 +/- .3 L) (p < .001). Substantial degradation in cognitive function, assessed with computerized tests, occurred. Vigilance, reaction time, attention, memory, and reasoning were impaired (p < .001). Mood, including vigor (p < .001), fatigue (p < .001), confusion (p < .001), depression (p < .001), and tension (p < .002), assessed by questionnaire, deteriorated. The highest cortisol and testosterone levels were observed before the exercise. CONCLUSIONS: This study quantifies the overwhelmingly adverse impact of multiple stressors on cognitive performance, mood, and physiologic parameters, during a continuous but brief military exercise conducted by highly motivated, well-trained officers.

Adult↗

PubMed2005

The fog of war: decrements in cognitive performance and mood associated with combat-like stress.

INTRODUCTION: Anecdotal reports from military conflicts suggest cognitive performance and mood are severely degraded by the stress of combat. However, little objective information is available to confirm these observations. METHODS: Our laboratory had several unique opportunities to study cognitive function in warfighters engaged in exercises designed to simulate the stress of combat. These studies were conducted in different environments with two different types of military volunteers. In one study, subjects were officers, with an average 9 yr of military service, who were members of an elite U.S. Army unit, the Rangers. In the other study, participants were younger, mostly enlisted, trainees with only 3 yr of military experience on average, in training to determine if they would qualify for an elite U.S. Navy unit, the SEALS. We administered a variety of identical, computer-based cognitive tests to both groups. RESULTS: In both groups, during stressful combat-like training, every aspect of cognitive function assessed was severely degraded compared with baseline, pre-stress performance. Relatively simple cognitive functions such as reaction time and vigilance were significantly impaired, as were more complex functions, including memory and logical reasoning. DISCUSSION: The deficits observed were greater than those typically produced by alcohol intoxication, treatment with sedating drugs, or clinical hypoglycemia. Undoubtedly, such decrements would severely degrade operational effectiveness. Furthermore, it is likely such cognitive decrements would be greater during actual combat. War planners, doctrine developers, and warfighters, especially leaders, need to be aware that combat stress will result in extensive and severe deficits in cognitive performance.

Adult↗

PubMed2004

Tyrosine prevents effects of hyperthermia on behavior and increases norepinephrine.

Tyrosine (TYR) is the precursor of the catecholamine (CA) neurotransmitters, dopamine (DA) and norepinephrine (NE). Catecholamines, especially NE, participate in the response of the brain to acute stress. When animals are acutely stressed, NE neurons become more active and tyrosine availability may be rate-limiting. Tyrosine administration, before exposure to physical and/or environmental stressors including cold, reduces the adverse behavioral, physiological and neurochemical consequences of the exposure. In this study, the effects of tyrosine (400 mg/kg) were examined on rats exposed to heat stress, for which its effects have not been examined. Coping behavior and memory were assessed using the Porsolt swim test and the Morris water maze. Release of hippocampal NE and DA was assessed with in vivo microdialysis. In vehicle-treated animals, heat impaired coping and memory, and increased release of NE, but not DA. In heated animals receiving tyrosine, coping was not impaired and NE release was sustained, thus demonstrating tyrosine protects against the adverse effects of heat, and suggesting these effects result from increased central NE release. This study indicates the effects of tyrosine generalize across dissimilar stressors and that tyrosine administration may mitigate the adverse behavioral effects of heat and other stressors on humans. In addition, it demonstrates that moderate heat stress impairs coping behavior, as well as working and reference memory.

Analysis of Variance↗

PubMed2004

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.

Adult↗

PubMed2004

Branched-chain amino acid supplementation and human performance when hypohydrated in the heat.

The serotonin system may contribute to reduced human performance when hypohydrated in the heat. This study determined whether branched-chain amino acid (BCAA) supplementation could sustain exercise and cognitive performance in the heat (40 degrees C dry bulb, 20% relative humidity) when hypohydrated by 4% of body mass. Seven heat-acclimated men completed two experimental trials, each consisting of one preparation and one test day. On day 1, a low-carbohydrate diet was eaten and subjects performed exhaustive cycling (morning) and treadmill exercise in the heat (afternoon) to lower muscle glycogen and achieve the desired hypohydration level. On day 2, subjects consumed an isocaloric BCAA and carbohydrate (BC) or carbohydrate-only drink during exercise. Experimental trials included 60 min of cycle ergometry (50% peak oxygen uptake) followed by a 30-min time trial in the heat. A cognitive test battery was completed before and after exercise, and blood samples were taken. BC produced a 2.5-fold increase (P < 0.05) in plasma BCAA and lowered (P < 0.05) the ratios of total tryptophan to BCAA and large neutral amino acid. Blood prolactin, glucose, lactate, and osmolality were not different between trials but increased over time. Cardiovascular and thermoregulatory data were also similar between trials. BC did not alter time-trial performance, cognitive performance, mood, perceived exertion, or perceived thermal comfort. We conclude that BCAA does not alter exercise or cognitive performance in the heat when subjects are hypohydrated.

Adult↗

PubMed2004

Adequacy of Garrison feeding for Special Forces soldiers during training.

This study evaluated whether Special Forces (SF) soldiers training in garrison would meet nutrient intake recommendations using the available garrison dining facility. Dietary intakes were obtained by a visual estimation method and self-reported food records from 32 SF and 13 support soldiers for 9 days. Total energy expenditure (TEE) was measured in nine soldiers from each group using doubly labeled water. Mean (+/- SD) total energy expenditure of SF (4,099 +/- 740 kcal/day) was higher than support soldiers (3,361 +/- 939 kcal/day, p < 0.01). Energy intake did not differ between groups. Median energy intake for all soldiers was 3,204 kcal/day. The nutrient intake goals of SF soldiers were not fully met by eating in the dining facility. Extending meal times and providing additional meals or "take out" foods may allow energy needs of SF soldiers (approximately 4,200 kcal/day) to be met, while reducing the reliance on potentially less nutritious outside foods.

Anthropometry↗

PubMed2003

Nutrition, brain function and cognitive performance.

Military interest in the effects of nutritional factors on cognitive function has stimulated considerable research on a variety of food constituents. This paper will review the research on the amino acids tryptophan and tyrosine, caffeine and carbohydrate. It will focus on research that addresses the potential utility of these compounds in military applications, particularly the acute, as opposed to chronic, effects of these substances on cognitive functions such as alertness, vigilance and resistance to stress. Caffeine, the most intensively studied food constituent, has unequivocal beneficial effects on vigilance, and in sleep deprived individuals it enhances other cognitive functions as well. Tryptophan, although it clearly has sedative-like properties, has not been extensively studied by military laboratories for use as a hypnotic, due to safety concerns. Tyrosine has been examined in animal models and human studies, and appears to prevent the substantial decline in various aspects of cognitive performance and mood associated with many kinds of acute stress. Carbohydrate supplementation appears to enhance cognitive performance in soldiers engaged in sustained, intense physical activities that expend high levels of energy.

Adult↗

PubMed2003

A comparison of tyrosine against placebo, phentermine, caffeine, and D-amphetamine during sleep deprivation.

Sleep deprivation can impair alertness and cognitive and motor performance. We hypothesized that the amino acid tyrosine might reduce deleterious effects of sleep deprivation. Seventy-six healthy males, age 18-35 years, participated in a four-day protocol that included a habituation night, a baseline night, a 40.5 h period without sleep, and a recovery night. Tyrosine 150 mg/kg, caffeine 300 mg/70 kg, phentermine 37.5 mg, D-amphetamine 20 mg and placebo were administered in a double-blind, randomized fashion to compare their effects on the time it took to fall asleep, on endocrine responses during sleep deprivation, and on sleep quantity, quality and architecture as measured by polysomnography during recovery sleep. When given after 36 h without sleep, tyrosine had no significant effect on any parameter of sleep. D-amphetamine produced marked decrease in sleep drive but caused deleterious effects on many aspects of recovery sleep. Still, D-amphetamine was associated with increased alertness on the first recovery day. Phentermine and caffeine both decreased sleep drive during sleep deprivation, but phentermine impaired rapid-eye-movement (REM) recovery sleep. Tyrosine (when compared to placebo) had no effect on any sleep related measure, but it did stimulate prolactin release.

Adolescent↗

PubMed2003

Effects of tyrosine, phentermine, caffeine D-amphetamine, and placebo on cognitive and motor performance deficits during sleep deprivation.

Cognitive and motor performance are critical in many circumstances and are impaired by sleep deprivation. We administered placebo, tyrosine 150 mg/kg, caffeine 300 mg/70 kg, phentermine 37.5 mg and D-amphetamine 20 mg at 15.30 h following overnight sleep deprivation and compare their effects on cognitive and motor performance in healthy young men. Tests of visual scanning, running memory, logical reasoning, mathematical processing, the Stroop task, four-choice serial reaction time, time wall take, pursuit tracking, visual vigilance, Trails (B) task and long-term memory were evaluated at standardized intervals before, during and after sleep deprivation and drugs. Performance decrements with sleep deprivation occurred in visual scanning, running memory, logical reasoning, mathematical processing, the Stroop test, the time wall test, tracking and visual vigilance. Interestingly, with sleep deprivation some tests improved and others did not deteriorate. Improvements with medication following sleep deprivation were seen in running memory, logical reasoning, mathematical processing, tracking and visual vigilance. Although less effective than D-amphetamine, tyrosine improved performance on several tests. We conclude that all drugs tested improved at least some aspects of cognitive and motor performance after sleep deprivation. As a naturally occurring amino acid, and thus amenable to nutritional strategies, tyrosine may deserve further testing.

Adolescent↗

PubMed2003

Caffeine effects on marksmanship during high-stress military training with 72 hour sleep deprivation.

PURPOSE: Navy SEALs (sea, air, land) are elite special warfare units that conduct unconventional warfare primarily in marine environments. Marksmanship accuracy and sighting time were quantified with 62 male trainees during Navy SEAL Hell Week, which involves the combined stress of sleep loss, operational combat scenarios, and cold-wet environmental conditions. Caffeine was administered to minimize deficits due to sleep deprivation. METHODS: Volunteers dry-fired a disabled rifle equipped with a laser-based marksmanship simulator system to measure shooting speed and accuracy. The target was a 2.3-cm diameter circle at a distance of 5 m, simulating a 46 cm target at a distance of 50 m. Marksmanship was assessed prior to training, and at 73 and 80 h into Hell Week. Volunteers were randomly assigned to 1 of 4 treatments: 100, 200, or 300 mg of caffeine or a placebo. Dosing occurred 72 h after training commenced. RESULTS: The combined effects of almost 73 h of total sleep deprivation and operational and environmental stress degraded all marksmanship accuracy measures (p < 0.05) as shown by the 37.5% increase in percent of targets missed, 38% increase in distance from center of mass of the target, and the 235% increase in shot group tightness. Sighting time increased by 53% or 3.1 s after 73 h of sleep deprivation (p < 0.05). Sighting time was significantly faster in sleep deprived individuals after taking 200 or 300 mg of caffeine compared with placebo or 100 mg of caffeine. No differences in accuracy measures between caffeine treatment groups were evident at any test period. CONCLUSION: During periods of sleep deprivation combined with other stressors, the use of 200 or 300 mg of caffeine enabled SEAL trainees to sight the target and pull the trigger faster without compromising shooting accuracy.

Adult↗

PubMed2003

Nutrition knowledge and supplement use among elite U.S. army soldiers.

A U.S. Army Special Forces (SF) unit was studied to determine characteristics of supplement users, assess nutrition knowledge, and identify nutrition information sources. SF-qualified (n = 119) and non-SF, support soldiers (n = 38) participated. Most soldiers (87%) reported current supplement use with more SF (90%) than non-SF, support soldiers (76%) using supplements (p < or = 0.05). Supplements SF reported using most were multivitamins, sports bars/drinks, and vitamin C. The mean nutrition knowledge score for all soldiers was 48.5 +/- 15.2% correct responses. Most soldiers incorrectly believe protein is used for energy for short-term athletic events (64%) and that vitamins provide energy (58%). The most common information sources reportedly used were popular magazines/books (75%), friends/teammates (55%), physicians/nurses, radio/television (34%), and the Internet (31%).

Adult↗

PubMed2002

Effects of caffeine, sleep loss, and stress on cognitive performance and mood during U.S. Navy SEAL training. Sea-Air-Land.

RATIONALE: When humans are acutely exposed to multiple stressors, cognitive performance is substantially degraded. Few practical strategies are available to sustain performance under such conditions. OBJECTIVE: This study examined whether moderate doses of caffeine would reduce adverse effects of sleep deprivation and exposure to severe environmental and operational stress on cognitive performance. METHODS: Volunteers were 68 U.S. Navy Sea-Air-Land (SEAL) trainees, randomly assigned to receive either 100, 200, or 300 mg caffeine or placebo in capsule form after 72 h of sleep deprivation and continuous exposure to other stressors. Cognitive tests administered included scanning visual vigilance, four-choice visual reaction time, a matching-to-sample working memory task and a repeated acquisition test of motor learning and memory. Mood state, marksmanship, and saliva caffeine were also assessed. Testing was conducted 1 and 8 h after treatment. RESULTS: Sleep deprivation and environmental stress adversely affected performance and mood. Caffeine, in a dose-dependent manner, mitigated many adverse effects of exposure to multiple stressors. Caffeine (200 and 300 mg) significantly improved visual vigilance, choice reaction time, repeated acquisition, self-reported fatigue and sleepiness with the greatest effects on tests of vigilance, reaction time, and alertness. Marksmanship, a task that requires fine motor coordination and steadiness, was not affected by caffeine. The greatest effects of caffeine were present 1 h post-administration, but significant effects persisted for 8 h. CONCLUSIONS: Even in the most adverse circumstances, moderate doses of caffeine can improve cognitive function, including vigilance, learning, memory, and mood state. When cognitive performance is critical and must be maintained during exposure to severe stress, administration of caffeine may provide a significant advantage. A dose of 200 mg appears to be optimal under such conditions.

Adult↗

PubMed2002

Carbohydrate administration during a day of sustained aerobic activity improves vigilance, as assessed by a novel ambulatory monitoring device, and mood.

BACKGROUND: The brain requires a continuous supply of glucose to function adequately. During aerobic exercise, peripheral glucose requirements increase and carbohydrate supplementation improves physical performance. The brain's utilization of glucose also increases during aerobic exercise. However, the effects of energy supplementation on cognitive function during sustained aerobic exercise are not well characterized. OBJECTIVE: The effects of energy supplementation, as liquid carbohydrate, on cognitive function during sustained aerobic activity were examined. DESIGN: A double-blind, placebo-controlled, between-subjects design was used. Young, healthy men (n = 143) were randomly assigned to 1 of 3 treatment groups. The groups received either a 6% (by vol) carbohydrate (35.1 kJ/kg), 12% (by vol) carbohydrate (70.2 kJ/kg), or placebo beverage in 6 isovolumic doses, and all groups consumed 2 meals (3200 kJ). Over the 10-h study, the subjects performed physically demanding tasks, including a 19.3-km road march and two 4.8-km runs, interspersed with rest and other activities. Wrist-worn vigilance monitors, which emitted auditory stimuli (20/h) to which the subjects responded as rapidly as possible, and a standardized self-report mood questionnaire were used to assess cognitive function. RESULTS: Vigilance consistently improved with supplemental carbohydrates in a dose-related manner; the 12% carbohydrate group performed the best and the placebo group the worst (P < 0.001). Mood-questionnaire results corroborated the results from the monitors; the subjects who received carbohydrates reported less confusion (P = 0.040) and greater vigor (P = 0.025) than did those who received the placebo. CONCLUSIONS: Supplemental carbohydrate beverages enhance vigilance and mood during sustained physical activity and interspersed rest. In addition, ambulatory monitoring devices can continuously assess the effects of nutritional factors on cognition as individuals conduct their daily activities or participate in experiments.

Acoustic Stimulation↗

PubMed2002

The effect of creatine monohydrate supplementation on obstacle course and multiple bench press performance.

Dietary creatine (Cr) supplementation has been shown to enhance muscular strength and endurance. This study determined the effects of Cr supplementation on performance of military training tasks. Two groups (Cr and placebo [Pl]) of 13 male soldiers each performed 3 consecutive military obstacle course runs ( approximately 3 minutes over 7 obstacles with a 2-minute rest between runs) followed by a rifle marksmanship task on 3 occasions (T(1), T(2), and T(3)), each separated by 5 days. They also completed a bench press protocol (5 sets to failure at 70% of 1 repetition maximum) and answered the Profile of Mood States questionnaire during each test session. Testing was done 3 times. No supplementation was given before T(1). Supplementation was provided using sports bars, with both groups receiving Pl bars between T(1) and T(2), whereas from T(2) to T(3) the Cr group consumed 24 g per day of Cr monohydrate in sports bars and the Pl group consumed an equal amount (kilocalories) of Pl sports bars. Creatine usage resulted in a significant (14%) increase in total bench press repetitions (p </= 0.05), but no difference between groups in obstacle course run times for the 3 runs from T(2) to T(3). Marksmanship or mood was not affected by Cr supplementation. An increase of 1.4 kg in body mass (p </= 0.005) and a 0.5% decrease in percent body fat (p </= 0.05) were observed after Cr ingestion. Creatine supplementation over 5 days improved performance during a controlled strength test but did not significantly improve military obstacle course performance.

Adult↗