Aging and assessment of physiological strain during exercise-heat stress

Abstract

. Aging and assessment of physiological strain during exercise-heat stress. Am J Physiol Regulatory Integrative Comp Physiol 282: R1063-R1069, 2002 10.1152/ajpregu.00364.2001.-The purpose of this study was to evaluate the physiological strain index (PSI) for different age groups during exercise-heat stress (EHS). PSI was applied to three different databases. First, from young and middle-age men (21 Ϯ 2 and 46 Ϯ 5 yr, respectively) matched (n ϭ 9 each, P Ͼ 0.05) for maximal aerobic power. Subjects were heat acclimated by daily treadmill walking for two 50-min bouts separated by 10-min rest for 10 days in a hot-dry environment [49°C, 20% relative humidity (RH)]. The second database involved a group (n ϭ 8) of young (YA) and a group (n ϭ 7) of older (OA) men (26 Ϯ 1 and 69 Ϯ 1 yr, respectively) who underwent 16 wk of aerobic training and two control groups (n ϭ 7 each) who were matched for age to YA and OA. These four groups performed EHS at 36°C, 40% RH on a cycle ergometer for 60 min at 60% maximal aerobic power before and after training. The third database was obtained from three groups of postmenopausal women and a group of 10 men. Two groups of women (n ϭ 8 each) were undergoing hormone replacement therapy, estrogen or estrogen plus progesterone, and the third group (n ϭ 9) received no hormone replacement. Subjects were over 50 yr and performed the same EHS: exercising at 36°C, 40% RH on a cycle ergometer for 60 min. PSI assessed the strain for all three databases and reported differences were significant at P Ͻ 0.05. This index rated the strain in rank order, whereas the postacclimation and posttraining groups were assessed as having less strain than the preacclimation and pretraining groups. Furthermore, middle-aged women on estrogen replacement therapy had less strain than estrogen ϩ progesterone and no hormone therapy. PSI evaluation was extended for men and women of different ages (50-70 yr) during acute EHS, heat acclimation, after aerobic training, and inclusive of women undergoing hormone replacement therapy. esophageal temperature; heart rate; predictive indexes; rectal temperature COLLECTIVELY, THE LITERATURE on heat tolerance for the general population suggests that middle-aged and older men and women are more exercise-heat intolerant, suffering more physiological strain during exposure to a hot environment than younger individuals (6, 27). Older men and women have been reported to have higher heart rates (HR), higher mean skin and core (T c ) temperatures, and lower sweat rates than younger men and women during exercise-heat stress (EHS). However, it is unclear from these studies whether the exercise-heat intolerance observed with aging was related to age per se or associated with other factors such as certain disease states, decreased physical activity, and/or lowered aerobic fitness (21).In 1965, Robinson et al. (22) were the first to imply that "habitually active" middle-aged men displayed the same acute exercise-heat tolerance and acclimated to heat at about the same rate and degree as when th...

Heat balance and cumulative heat storage during exercise performed in the heat in physically active younger and middle-aged men

“…Noteworthy, reports suggest that even short-term exercise training programs which elicit improvements in cardiorespiratory function may have a beneficial effect on thermoregulatory function during a heat stress. Moran et al (2002) showed that older (69 years) men who underwent a 16-week aerobic exercise training demonstrated a significantly reduced level of physiological strain during exercise-induced heat stress compared with younger (26 years) individuals. When combined, these studies demonstrate that physical fitness (as indicated by _ V O 2max ) rather than age is a more important indicator of work-heat tolerance.…”

“…An increasing number of studies show that aerobic fitness and selected morphological factors can profoundly influence an individual's capacity to thermoregulate during work in the heat and may be more important determinants than aging per se in influencing work-heat tolerance (Cheung et al 2000;Moran et al 2002;Pandolf 1991Pandolf , 1997. Typically, older people have lower maximal aerobic power, higher adiposity and smaller stature and body mass compared with younger adults (Kenny et al 2008).…”

“…The resultant decrease in overall functional capacity will ultimately impact a worker's ability to thermoregulate in the heat and potentially have important repercussions with regards to day to day operations and productivity in arduous environments. Factors, such as aerobic fitness (aerobic training and/or fitness level) and selected morphological factors (i.e., body weight, percent body fat, body surface area, body surface area to weight ratio) appear in fact to play a key role in relation to an individual's ability to thermoregulate during work in the heat and may be more important than aging per se in maintaining work-heat tolerance (Cheung et al 2000;Moran et al 2002;Pandolf 1991Pandolf , 1997. To date, relatively few studies have attempted to delineate the effects of chronological age from concomitant factors such as certain disease states, reduced habitual physical activity levels, decreases in aerobic capacity and/or alterations in body mass/composition.…”

Determining an optimal recovery time for construction rebar workers after working to exhaustion in a hot and humid environment

“…PSI is therefore applied in this study to measure how rest breaks influence the recovery of the heat strain process. PSI has been shown to effectively differentiate the heat strain associated with different climatic conditions, hydration levels, types of clothing including protective clothing, different exercise intensities, gender and the effects of aging [36][37][38]. It is an algorithm combining data from the heart rate and core temperature, in which output is scaled from 0 to 10 where 0 represents "no strain" and 10 "very high physiological strain".…”

The Effect of Body Weight on Heat Strain Indices in Hot and Dry Climatic Conditions

“…BMI is a useful factor for determining obesity (9). The PSI was developed to evaluate heat and physiological strain by measuring heart rate (HR) and core body temperature (10). The HSSI, established and evaluated by Dehghan et al is an index that evaluates emotional and perceptual variables using questionnaire.…”