Tom M. McLellan’s research while affiliated with University of Ontario Institute of Technology and other places

Objectives: Combat deployments are characterized by high operational demands with limited opportunities for sleep leading to fatigue and degraded cognitive and operational performance. Caffeine in moderate doses is recognized as an effective intervention for physical and cognitive decrements associated with sleep loss. Methods: This report is based on data collected by two separate, independently conducted surveys administered in Afghanistan in 2011–2012. It assessed caffeine use and sleep disruption among U.S. Army combat soldiers (J-MHAT 8; n = 518) and among deployed soldiers with different military assignments (USARIEM Deployment Survey; n = 260). Results: Daily caffeine intake assessed in the J-MHAT 8 survey averaged 404 ± 18 mg. In the USARIEM Deployment Survey, intake was 303 ± 29 mg and was significantly higher among combat arms soldiers (483 ± 100 mg) compared to combat service support personnel (235 ± 23 mg). In both surveys, over 55% of total caffeine intake was from energy drinks. Additional sources of caffeine included coffee, tea, sodas, gum, candy, and over-the-counter medications. Higher caffeine intake was not associated with ability to fall asleep at night or wake-up in the morning (J-MHAT 8 survey). Higher caffeine consumption was associated with disrupted sleep from high operational tempo and nighttime duties of combat operations. Discussion: Overall caffeine consumption and energy drink use in Afghanistan was greater than among non-deployed soldiers and civilians. Caffeine was frequently used as a countermeasure during night operations to offset adverse effects of sleep loss on physical and cognitive function, consistent with current Department of the Army recommendations.

Background. Firefighting requires tremendous cognitive demands including assessing emergency scenes, executing critical decisions, and situational awareness of their surroundings. The aim of this study was to determine the effects of differing rates of increasing core temperature on cognitive function during exercise-induced heat stress. Methods. Nineteen male firefighters were exposed to repeated cognitive assessments, randomized and counter-balanced, in 30°C and 35°C and 50% humidity. Participants performed treadmill walking (4.5 km . h ⁻¹ and 2.5% grade) with cognitive function assessed before exercise (PRE), after mounting the treadmill (Cog 1), at core temperatures of 37.8°C (Cog 2), 38.5°C (Cog 3), and 39.0°C (Cog 4), after dismounting the treadmill (POST), and following an active cooling recovery to a core temperature of 37.8°C (REC). The cognitive tests implemented at PRE and POST were spatial working memory (SWM), rapid visual information processing (RVP), and reaction time (RTI) while paired associates learning (PAL) and spatial span (SSP) were assessed at Cog 1, Cog 2, Cog 3, and Cog 4. All five cognitive tests were assessed at REC. Results. Planned contrasts revealed that SSP and PAL were impaired at Cog 3, with SSP also impaired at Cog 4 compared to Cog 1. REC revealed no difference compared to Cog 1, but increased errors compared to Cog 2 for PAL. Conclusions. The decrements in cognitive function observed at a core temperature of 38.5°C are likely attributed to the cognitive resources required to maintain performance being overloaded due to increasing task complexity and external stimuli from exercise-induced heat stress. The addition of an active cooling recovery restored cognitive function to initial levels.

Background. Firefighting requires tremendous cognitive demands including assessing emergency scenes, executing critical decisions, and situational awareness of their surroundings. The aim of this study was to determine the effects of differing rates of increasing core temperature on cognitive function during exercise-induced heat stress. Methods. Nineteen male firefighters were exposed to repeated cognitive assessments, randomized and counter-balanced, in 30°C and 35°C and 50% humidity. Participants performed treadmill walking (4.5 km . h ⁻¹ and 2.5% grade) with cognitive function assessed before exercise (PRE), after mounting the treadmill (Cog 1), at core temperatures of 37.8°C (Cog 2), 38.5°C (Cog 3), and 39.0°C (Cog 4), after dismounting the treadmill (POST), and following an active cooling recovery to a core temperature of 37.8°C (REC). The cognitive tests implemented at PRE and POST were spatial working memory (SWM), rapid visual information processing (RVP), and reaction time (RTI) while paired associates learning (PAL) and spatial span (SSP) were assessed at Cog 1, Cog 2, Cog 3, and Cog 4. All five cognitive tests were assessed at REC. Results. Planned contrasts revealed that SSP and PAL were impaired at Cog 3, with SSP also impaired at Cog 4 compared to Cog 1. REC revealed no difference compared to Cog 1, but increased errors compared to Cog 2 for PAL. Conclusions. The decrements in cognitive function observed at a core temperature of 38.5°C are likely attributed to the cognitive resources required to maintain performance being overloaded due to increasing task complexity and external stimuli from exercise-induced heat stress. The addition of an active cooling recovery restored cognitive function to initial levels.

Caffeine is consumed by over 80% of U.S. adults. This review examines the effects caffeine has on cognitive and physical function, since most real-world activities require complex decision making, motor processing and movement. Caffeine exerts its effects by blocking adenosine receptors. Following low (∼40mg or ∼0.5 mg·kg(-1)) to moderate (∼300mg or 4 mg·kg(-1)) caffeine doses, alertness, vigilance, attention, reaction time and attention improve, but less consistent effects are observed on memory and higher-order executive function, such as judgement and decision making. Effects on physical performance on a vast array of physical performance metrics such as time-to-exhaustion, time-trial, muscle strength and endurance, and high-intensity sprints typical of team sports are evident following doses that exceed about 200mg (∼3mg·kg(-1)). Many occupations, including military, first responders, transport workers and factory shift workers, require optimal physical and cognitive function to ensure success, workplace safety and productivity. In these circumstances, that may include restricted sleep, repeated administration of caffeine is an effective strategy to maintain physical and cognitive capabilities.

Prevalence and patterns of dietary supplement (DS) use by U.S. Army soldiers differ from the civilian population. Longitudinal trends in use of DSs by civilians have been examined, but are unavailable in subpopulations such as military service members. The present study examined longitudinal changes in DS use by soldiers. A standardized questionnaire on DS use was administered in 2006–2007 (N = 989) and 2010–2011 (N = 1196) to convenience samples of active duty soldiers. Data were weighted for total population demographics of age, sex, and rank. Regular use of DSs by soldiers increased significantly (56% ± 1.6% vs. 64% ± 1.7%; p ≤ 0.001) over the 4 years primarily because of an increase of DS use among the youngest 18- to 24-year-old soldiers (43.0% ± 2.5% vs 62.3% ± 2.4%; p ≤ 0.01). Protein (22% ± 1.4% vs. 26% ± 1.5%; p ≤ 0.001) and combination (10.0% ± 1.0% vs. 24% ± 1.4%; p ≤ 0.001) product consumption also increased over the 4 years. Individual vitamin and mineral use — including iron, magnesium, selenium, and vitamins A, B6, B12, and D — significantly increased as well (p ≤ 0.05). In addition, expenditures on DSs by soldiers increased over time (p < 0.01). Reasons reported by soldiers for DS use suggest use increased to meet the occupational demands of military service. Educational interventions to minimize inappropriate use of DSs by soldiers are necessary to reduce adverse events resulting from unnecessary use of DSs and the financial burden associated with their use.

Physical employment standards (PESs) exist for certain occupational groups that also require the use of protective clothing ensembles (PCEs) during their normal work. This review addresses whether these current PESs appropriately incorporate the physiological burden associated with wearing PCEs during respective tasks. Metabolic heat production increases because of wearing PCE; this increase is greater than that because of simply the weight of the clothing and can vary 2-fold among individuals. This variation negates a simple adjustment to the PES for the effect of the clothing on metabolic rate. As a result, PES testing that only simulates the weight of the clothing and protective equipment does not adequately accommodate this effect. The physiological heat strain associated with the use of PCEs is also not addressed with current PESs. Typically the selection tests of a PES lasts less than 20 min, whereas the requirement for use of PCE in the workplace may approach 1 h before cooling strategies can be employed. One option that might be considered is to construct a heat stress test that requires new recruits and incumbents to work for a predetermined duration while exposed to a warm environmental temperature while wearing the PCE.

United States Army personnel in garrison who are not deployed to combat theater report using dietary supplements (DSs) to promote health, increase physical and mental strength, and improve energy levels. Given the substantial physical and cognitive demands of combat, DS use may increase during deployment. This study compared DS use by garrison soldiers with DS use by personnel deployed to a combat theater in Afghanistan. Prevalence and patterns of DS use, demographic factors, and health behaviors were assessed by survey (deployed n = 221; garrison n = 1001). Eighty-two percent of deployed and 74% of garrison soldiers used DSs ≥1 time·week–1. Logistic regression analyses, adjusted for significant demographic and health predictors of DS use, showed deployed personnel were more likely than garrison soldiers to use protein, amino acids, and combination products. Deployed females were more likely to use protein supplements and deployed males were more likely to use multivitamins, combination products, protein, and body building supplements than garrison respondents. Significantly more deployed (17%) than garrison (10%) personnel spent more than $50∙month–1 on DSs. Higher protein supplement use among deployed personnel was associated with higher frequency of strength training and lower amounts of aerobic exercise for males but similar amounts of strength training and aerobic exercise for females. Protein supplements and combination products are used more frequently by deployed than garrison soldiers with the intent of enhancing strength and energy.

Various occupational groups are required to maintain optimal physical and cognitive function during overnight periods of wakefulness, often with less than optimal sleep. Strategies are required to help mitigate the impairments in cognitive function to help sustain workplace safety and productivity. To test the effectiveness of repeated 200 mg doses of caffeine on cognitive function and live-fire marksmanship with soldiers during three successive nights of sustained wakefulness followed by 4-h afternoon sleep periods. Twenty Special Forces personnel (28.6 ± 4.7 years, 177.6 ± 7.5 cm and 81.2 ± 8.0 kg) were randomly assigned to receive four 200-mg doses of caffeine (n = 10) or placebo (n = 10) during the late evening and early morning hours during three successive days. An afternoon 4-h sleep period followed. The psychomotor (PVT) and field (FVT) vigilance, logical reasoning (LRT) tests and a vigilance monitor assessed cognitive function throughout the study. Live-fire marksmanship requiring friend-foe discrimination was assessed. Caffeine maintained speed on the PVT (p < 0.02), improved detection of events during FVT (p < 0.001), increased number of correct responses to stimuli as assessed by the vigilance monitor (p < 0.001) and increased response speed during the LRT (p < 0.001) throughout the three overnight testing periods. Live-fire marksmanship was not altered by caffeine. A total daily dose of 800 mg caffeine during successive overnight periods of wakefulness is an effective strategy to maintain cognitive function when optimal sleep periods during the day are not available.