Kent B. Pandolf

PERCEPTUAL AND PHYSIOLOGICAL RESPONSES DURING EXERCISE IN COOL AND COLD WATER

This investigation examined the interaction of exposure to cold water stress with both perceived exertion and thermal sensation during exercise. Eight male volunteers performed arm, leg, and combined arm and leg exercise for 45 min. in water at 20 and 26°C. Exercise was performed at a low (n = 7) and a high (n = 8) intensity relative to the ergometer specific peak oxygen uptake (VO2 peak). In general, percent VOz peak did not differ between types of exercise in either 20 or 26°C water. During low intensity exercise when power output was matched across water temperatures (Tw), percent VO2 peak was greater in 20°C water (52%) compared to 26°C water (42%). Ratings of perceived exertion (RPE) did not differ between Tw. During high intensity exercise when percent VO2 peak was matched across Tw, RPE was lower during exercise in 20°C compared to 26°C. Multiple correlation analyses comparing both final RPE and thermal sensation (TS) with physiological and thermal measures were performed across type of exercise and Tw. RPE was moderately correlated with heart rate (r = 0.68) and ventilation (r = 0.61), whereas very slight relationships were established with TS (r = 0.16), skin and rectal temperatures (r = 0.10 and r = 0.20). TS was moderately correlated with skin and rectal temperatures (r = 0.64 and r = 0.73), whereas low correlations existed between TS and both heart rate (r = 0.32) and ventilation (r = —0.12). These data suggest that the change in oxygen uptake associated with exercise in cold water does not add to the over-all perception of exertion. This perception appears to be related to cardiopulmonary variables rather than thermal measures, whereas thermal sensation is related to thermal measures and not cardiopulmonary variables.

Comparison of Rated Perceived Exertion and Constant Effort During Cycling Exercise

Overall sense of effort during muscular exercise has been described as having local and central components. Both components are thought to be involved in the determination of rated perceived exertion (RPE) and constant effort (CE) during physical exercise; however, RPE and CE power output have not been directly compared. The present study examined the relationship between RPE during steady-state exercise and power output during CE exercise in ten male volunteers. Steady-state exercise (~60% peak oxygen uptake, \(\dot{V}{{O}_{2}}\)) and CE exercise (initial exercise intensity ~70% peak \(\dot{V}{{O}_{2}}\)) were each performed for 30 min on a cycle ergometer. During steady-state exercise, RPE increased as the exercise duration increased (p<.05). During CE exercise, power output (W) decreased as exercise duration increased (p<.05). When W during CE exercise was plotted as a function of RPE during steady-state exercise for identical time intervals, the following linear relationship (y = b x + a) was obtained: W = b × RPE + a (r = −.47) where a is 196.6 and b is −3.14 (p<.10). These findings indicate that RPE and CE power output are related and, when studied collectively, may someday help explain the mechanism(s) responsible for the buildup of muscular fatigue during physical exercise.

Recent heat and cold strain predictive indices

Recent heat and cold strain predictive indices have been developed. The physiological strain index (PSI), based on rectal temperature and heart rate, is capable of indicating heat strain online and analyzing existing databases. Six studies, containing eight databases were analyzed to evaluate PSI for different climates, hydration levels, clothing, exercise intensities, gender, and aging. PSI was capable of differentiating (p<0.05) between all of these conditions and some combinations of conditions. Our cold strain index (CSI), based on core and mean skin temperatures, is able to indicate cold strain in real time and analyze existing databases. There studies containing three databases were analyzed in order to evaluate CSI for different cold air and cold-water immersion conditions. CSI differentiated (p<0.01) between the conditions for two of these three databases. However, further study is required to possibly adjust CSI for a wider range of cold air and water temperatures, and to consider the effects of physical exercise. Both PSI and CSI rate heat and cold strain on a universal scale of 0–10. Both indices have the potential to be widely accepted and used universally for many scenarios.

Validation of the environmental stress index (ESI) for physiological variables

A new environmental stress index (ESI), based on ambient temperature (Ta), relative humidity (RH) and solar radiation (SR), was recently suggested as a potential substitute for the wet-bulb globe temperature (WBGT) index. The purpose of this study was to evaluate and validate ESI for three different physiological variables including rectal temperature (Tre), heart rate (HR), and sweat rate (msw). A database was taken from a previous study where 12 young men (21±1 y) served as subjects exposed to 120 min of 12 different combinations consisting of three metabolic rates (rest and treadmill walking at 5 km·h−1 at 0% and 5% grades), two clothing ensembles (BDU and protective MOPP gear) and two outdoor solar radiation levels (shade and open sky). ESI was calculated as follows: ESI=0.63Ta-0.03RH+0.002SR+0.0054(TaRH)-0.073(0.1+SR)−1. Significant differences of about 2 units (p 0.838) were found between ESI and Tre, HR, or msw. These results indicate that ESI is strongly correlated to the physiological strain, whereby higher stress is reflected in higher strain. Therefore, evaluating heat stress by ESI, which uses the more common, fast response and accurate climatic measures, becomes more predominant.