Josh B. Kazman

Heat Tolerance Testing: Association Between Heat Intolerance and Anthropometric and Fitness Measurements

This study investigated associations between heat intolerance, as determined by performance on a heat tolerance test (HTT), and anthropometric measurements (body surface-to-mass ratio, percent body fat, body mass index, and waist circumference) and cardiorespiratory fitness (maximal oxygen uptake [VO2max]). Relationships between predictive variables and specific physiological measurements recorded during the HTT were examined. A total of 34 male and 12 female participants, recruited from the military community, underwent anthropometric measurements, a maximal aerobic exercise test, and a standardized HTT, which consisted of walking on a treadmill at 5 km/h at 2% grade for 120 minutes at 40°C and 40% relative humidity. VO2max negatively correlated with maximum core temperature (r = -0.30, p < 0.05) and heart rate (HR) (r = -0.48, p < 0.01) although percent body fat showed a positive correlation with maximum HR (r = 0.36, p < 0.05). VO2max was the only independent attribute that significantly influenced both the maximum HR and core temperature attained during HTT. Logistic regression analyses indicated that VO2max was the only independent parameter (OR = 0.89, p = 0.026) that significantly contributed to overall HTT performance. Low cardiorespiratory fitness was associated with heat intolerance, as defined by HTT performance, and can be addressed as a preventative measure for exertional heat illness. This study provides further evidence that the HTT can be an effective tool for assessment of thermoregulatory patterns.

Exertional Heat Illness: The Role of Heat Tolerance Testing

Exertional heat stroke (EHS) is a common clinical problem for both athletes and warriors; however, evidence-based guidance for return-to-play/duty (RTP/RTD) decisions is limited. Heat tolerance testing (HTT) has been proposed as a potential tool that, when combined with appropriate clinical information, may assist in RTP/RTD decisions. However, currently, no standard of care is available for performing HTT. The Israeli Defense Forces (IDF) HTT protocol, which was developed over decades of careful research, has proven useful for IDF warriors and is utilized by other militaries to assist in RTD decisions. The present case studies are used to discuss the efficacy of the IDF HTT in determining RTD for two warriors who experienced EHS. Strengths and limitations of the IDF HTT, along with current and potential roles in clinical decision-making and in future thermoregulation research, are discussed.

Family Functioning and Stress in African American Families: A Strength-Based Approach

Having social support substantially reduces the effects of stressful experiences. Family relationships are central components of social support for African Americans. In a community-based sample of African Americans (n = 255), the relationship between family functioning and stress was examined, as well as possible mediators of this relationship, independent of demographic variables. Using multiple regression analysis, close and flexible family relationships were linked to lower perceived stress levels. The association of family functioning and stress operated through the internal processes of anxiety, depression, daily hassles, and higher hardiness and explained more than half of the variance in stress levels. These findings also remained above and beyond the known stressor of discrimination and the known stress reducer of spirituality. These findings suggest that expanding traditional stress management programs to include strategies for bolstering family functioning could have significant benefits.

Obesity and African Americans: Physiologic and Behavioral Pathways

Although progress has been made to understand the association between physiological and lifestyle behaviors with regard to obesity, ethnic differences in markers of obesity and pathways towards obesity remain somewhat unexplained. However, obesity remains a serious growing concern. This paper highlights ethnic differences in African Americans and Caucasians that may contribute to the higher prevalence of obesity among African Americans. Understanding ethnic differences in metabolic syndrome criteria, functioning of the hypothalamic pituitary adrenal axis, variations in glucocorticoid sensitivity and insulin resistance, and physical activity and cardiovascular fitness levels may help to inform practical clinical and public health interventions and reduce obesity disparities.

Blood Hemostatic Changes During an Ultraendurance Road Cycling Event in a Hot Environment

OBJECTIVE This study aims to examine blood hemostatic responses to completing a 164-km road cycling event in a hot environment. METHODS Thirty-seven subjects (28 men and 9 women; 51.8±9.5 [mean±SD] y) completed the ride in 6.6±1.1 hours. Anthropometrics (height, body mass [taken also during morning of the ride], percent body fat [%]) were collected the day before the ride. Blood samples were collected on the morning of the ride (PRE) and immediately after (IP) the subject completed the ride. Concentrations of platelet, platelet activation, coagulation, and fibrinolytic markers (platelet factor 4, β-thromboglobulin, von Willebrand factor antigen, thrombin-antithrombin complex, thrombomodulin, and D-Dimer) were measured. Associations between changes from PRE- to IP-ride were examined as a function of event completion time and subject characteristics (demographics and anthropometrics). RESULTS All blood hemostatic markers increased significantly (P < .001) from PRE to IP. After controlling for PRE values, finishing time was negatively correlated with platelet factor 4 (r = 0.40; P = .017), while percent body fat (%BF) was negatively correlated with thrombin-antithrombin complex (r = -0.35; P = .038) and to thrombomodulin (r = -0.36; P = .036). In addition, male subjects had greater concentrations of thrombin-antithrombin complex (d = 0.63; P < .05) and natural logarithm thrombomodulin (d = 6.42; P < .05) than female subjects. CONCLUSION Completing the 164-km road cycling event in hot conditions resulted in increased concentrations of platelet, platelet activation, coagulation, and fibrinolytic markers in both men and women. Although platelet activation and coagulation occurred, the fibrinolytic system markers also increased, which appears to balance blood hemostasis and may prevent clot formation during exercise in a hot environment.

General health status in army personnel: relations with health behaviors and psychosocial variables

PurposePoor self-rated health (SRH) is linked to an increased risk of injury, future healthcare services utilization, and morbidity and mortality. This study aimed to identify correlates of a single-item measure of health in 8070 US Army personnel.MethodsResponses were collected from the Army’s global assessment tool (GAT) 2.0, an online questionnaire that assesses physical and psychosocial health. SRH was measured by the item, “How do you consider your health?” (four response categories: “poor,” “fair,” “good,” and “excellent”). Ordinal logistic regression (OLR) was used to evaluate how various health and psychosocial factors contribute to Soldiers’ ratings of SRH. Unadjusted and adjusted cumulative odds ratios (ORs) are presented and discussed.ResultsMost participants reported “good” health (57%), followed by “excellent” (24%), “fair” (17%), and “poor” (2%). Sleep quality (OR 2.48; 95% CI 2.34, 2.63) was the largest correlate of SRH, followed by obesity (OR 0.50; 95% CI 0.43, 0.58), emotional fitness (OR 1.68, 95% CI 1.56, 1.82), and Army physical fitness test (APFT) scores (OR 1.43; 95% CI 1.36, 1.51).ConclusionsSingle-item measures of self-reported health can cover a broad spectrum across physical and mental health. Among a large US Army sample, sleep quality was most strongly associated with SRH, followed by emotional fitness and APFT scores. In contrast, service-component and other sociodemographic characteristics had relatively small effects on general health. Military investigators and leaders who must rely on various subjective general health measures should interpret them as a combination of these factors.

Role of plasma adiponectin /C-reactive protein ratio in obesity and type 2 diabetes among African Americans

BACKGROUND Obesity is a modifiable risk factor for hypertension and T2D. Objective(s): We examined relations between fasting plasma adiponectin (ADIP), C-reactive protein (CRP) concentrations and markers of T2D in African Americans (AA). METHODS Fasting plasma ADIP, CRP, Insulin (IN), HOMA-IR, lipid profiles, body fat percent (%BF), waist circumference (WC), body mass index (BMI) and blood pressure measures were determined in AA women (W: n=77) and men (M: n=34). Participants were classified into: 1) Normal fasting glucose (FG) and Normal %BF; 2) Normal FG and High %BF; and 3) High FG. RESULTS Compared to men, women had significantly higher mean ADIP (W: 31.4±2.9 vs. M: 18.0±4.4 ng/L), CRP (W: 3.2±0.3 vs. M: 2.0±0.5 mg/L), %BF (W: 41.2±0.9 vs. M: 27.2±1.3), and BMI (W: 32.3±0.7 vs. M: 29.2±1.1 kg/m2). Women with normal FG and %BF had significantly higher ADIP (64.0±6.0) and lower CRP (1.3±0.6) concentrations than normal FG/ high %BF (ADIP: 37.0±5.0 and CRP: 3.1 ±0.5) and high FG (ADIP: 15.1±4.1 and CRP: 4.0 ± 0.5) groups. Women with high ADIP to CRP ratio had favorable metabolic and anthropometric profiles. CONCLUSION Low ADIP and high CRP are associated with excessive %BF and FG in AA women. ADIP/CRP, may be useful for detecting metabolic dysregulation.

Exertional Heat Illness in the Military: Risk Mitigation

This chapter focuses on exertional heat illness (EHI) in the military and covers common scenarios of EHI, the epidemiology, and guidelines related to risk mitigation and physical activity modifications. EHI risk is particularly high among new military recruits and those in combat occupational specialties. Other extrinsic and intrinsic factors are reviewed, including sickle cell trait and medications, which have received more attention recently. Military leaders are responsible for mitigating EHI risk at both the unit and individual level. The five steps of risk management are identify hazards, assess hazards, develop controls and make risk decisions, implement controls, and supervise and evaluate. Each step is discussed and elucidated with examples of work/rest hydration cycles by heat categories and Army risk management matrices. Military leaders need to remain vigilant and adapt risk management strategies; as the military’s demographic/occupational makeup changes, the evidence base for EHI risk mitigation evolves, and new technologies become available.

Heat Tolerance Testing

Exertional Heat Stroke (EHS) is a life-threatening illness that affects both athletic and military populations. It continues to be among one of the top three leading causes of death in these cohorts and remains largely preventable. Although clear guidelines have been established for the successful treatment of EHS, the process of returning individuals who have survived EHS is much less clear. However the use of a heat tolerance test (HTT) has shown promise and utility within both the military and athletic models.

Individualized estimation of human core body temperature using non-invasive measurements

A rising core body temperature (Tc) during strenuous physical activity is a leading indicator of heat-injury risk. Hence, a system that can estimate Tc in real time and provide early warning of an impending temperature rise may enable proactive interventions to reduce the risk of heat injuries. However, real-time field assessment of Tc requires impractical invasive technologies. To address this problem, we developed a mathematical model that describes the relationships between Tc and noninvasive measurements of an individual’s physical activity, heart rate, and skin temperature, and two environmental variables (ambient temperature and relative humidity). A Kalman filter adapts the model parameters to each individual and provides real-time personalized Tc estimates. Using data from three distinct studies, comprising 166 subjects who performed treadmill and cycle ergometer tasks under different experimental conditions, we assessed model performance via the root mean squared error (RMSE). The individualized model yielded an overall average RMSE of 0.33 (SD = 0.18)°C, allowing us to reach the same conclusions in each study as those obtained using the Tc measurements. Furthermore, for 22 unique subjects whose Tc exceeded 38.5°C, a potential lower Tc limit of clinical relevance, the average RMSE decreased to 0.25 (SD = 0.20)°C. Importantly, these results remained robust in the presence of simulated real-world operational conditions, yielding no more than 16% worse RMSEs when measurements were missing (40%) or laden with added noise. Hence, the individualized model provides a practical means to develop an early warning system for reducing heat-injury risk. NEW & NOTEWORTHY A model that uses an individual’s noninvasive measurements and environmental variables can continually “learn” the individual’s heat-stress response by automatically adapting the model parameters on the fly to provide real-time individualized core body temperature estimates. This individualized model can replace impractical invasive sensors, serving as a practical and effective surrogate for core temperature monitoring.