Table 2.
WBSR | Local SR | Local sweat [Na+] | Comments | |
---|---|---|---|---|
Day-to-day (CVs) | 5–7% | 6–22% | 5–16% (WB: 11–17%) | Includes instrument variability (1–3%) |
Regional differences | ||||
Across body (% difference) | NA | 200–360% | 80–120% | Range includes anatomical sites typically used/accessible in field testing (back, chest, forearm, thigh, and forehead) |
Contralateral sides | NA | ↔ | ↔ | Forearms and scapulas |
Exercise intensity (absolute VO2) | Impacts E req | |||
High vs. moderate vs. low | ↑ | ↑ | ↑ | Directly related to metabolic energy expenditure (i.e. metabolic heat production) |
Environmental conditions | ||||
Temperature (↑) | ↑ | ↑ | ↑ | Impacts E req; ↑ radiant heat gain and therefore ↑ T c |
Solar radiation (↑) | ↑ | ↑ | ↑/? | Impacts E req; ↑ radiant heat gain and therefore ↑ T c |
Humidity (↑) | ↑ | ↑ | ↑/? | ↓ Water vapor gradient leads to ↓ evaporation of sweat, which ↑ T c and the need for higher SR than calculated from E req, but prolonged exposure can lead to hidromeiosis and decreased SR |
Wind (↑) | ↓ | ↓ | ↓/? | Impacts E req; ↑ convective/evaporative heat loss and therefore ↓ T c |
Body mass | ||||
Larger vs. smaller | ↑ | ? | ? | Related to metabolic heat production and possibly sweating efficiency |
Protective equipment | ↑ | ↑ | ? | ↓ Evaporative and radiant heat loss, ↑ metabolic heat gain and therefore ↑ T c |
Sex | ||||
Men vs. women | ↑ | ↑ | ↑/↔ | SR differences related to higher body mass and metabolic heat production of men, rather than sex per se; less wasteful sweating by women in humid heat |
Aging | ||||
Older vs. middle-aged vs. young adult | ↓ | ↓ | ↔/? | Related to decline in fitness (and associated decline in cholinergic sensitivity), rather than aging per se |
Maturation | ||||
Pre vs. post-pubertal | ↓ | ? | ↓ | Related to lower sweat gland sensitivity; SR differences in males only, suggesting testosterone may be involved (although direct evidence is lacking) |
Heat acclimation | ↑ | ↑ | ↓ | ↑ Cholinergic and aldosterone sensitivity; gland hypertrophy; ↑ slope of relation between SR and T c; ↓ T c threshold for sweat onset |
Aerobic capacity | ||||
Higher vs. lower VO2max | ↑ | ↑ | ↔/? | ↑ Cholinergic sensitivity; ↑ slope of relation between SR and T c; ↓ T c threshold for sweat onset |
Hydration status | ||||
2–3% BML vs. euhydration | ↓ | ↓ | ↑/? | Hypovolemia ↓ slope of relation between SR and T c; hyperosmolality ↑ T c threshold for sweat onset |
Menstrual cycle | ||||
Luteal vs. follicular | ↔ | ↓ | ↓/↔/? | Luteal phase ↑ T c threshold for sweat onset and ↓ slope of relation between SR and T c (thus LSR lower at a given T c); effect lessens with heat acclimation |
Dietary sodium | Studies involved 8–14 days on strictly controlled, modified diets | |||
Change from moderate to high intake (8–9 g Na+) | ↔ | ↔ | ↑ | ↓ Circulating aldosterone |
Change from moderate to low intake (1–2 g Na+) | ↔ | ↔ | ↓ | ↑ Circulating aldosterone |
Exercise duration (↑) | ||||
Low intensity | ↔ | ↔ | ↔ | Studies involved 3–7 h of exercise and low SR |
High intensity | ↓ | ↓ | ↓ | Related to effects of hidromeiosis with prolonged heavy sweating |
Race/ethnicity | ↔ | ↔ | ↔ | Indigenous environmental factors are more important than race or ethnicity per se. Heat habituation (lower, more efficient sweating) may occur in people indigenous to hot or tropical climates |
See text for discussion and supporting references
BML body mass loss, CV coefficient of variation, E req required rate of evaporation for heat balance, NA not applicable, [Na + ] sodium concentration, SR sweating rate, Tc body core temperature, VO 2 oxygen uptake, VO 2max maximal oxygen uptake, WB whole body, WBSR whole-body sweating rate, ↑ indicates increase in the sweating response, ↓ indicates decrease in the sweating response, ↔ indicates no effect on the sweating response, ? indicates limited data available