Moran et al developed the physiological strain index (PSI) to evaluate a person's response to heat strain during exertion. If accurate temperature data is not available, then heart rate (HR) data alone can be used to calculate the PSI-HR. The authors are from the US Army Research Institute of Environmental Medicine in Natick, Massachusetts, and universities in Israel.
Parameters:
(1) heart rate at baseline in beats per minute
(2) heart rate during heat stress in beats per minute
physiological strain index based on heart rate alone (PSI-HR) =
= (5 * ((heart rate under heat stress) - (heart rate at baseline)) / (180 - (heart rate at baseline)))
PSI-HR |
Physiological Strain |
0 |
none |
1 |
minimal |
2 |
low |
3 |
moderate |
4 |
high |
5 |
very high |
If the person's physical fitness is taken into account:
PSI-HR Zone |
Heart Rate for Low Fitness |
Heart Rate for Moderately Fit |
Heart Rate for High Fitness |
0 to 1.0 |
70 - 96 |
60 - 88 |
50 - 80 |
1.01 to 2.0 |
97 - 122 |
89 - 116 |
81 - 110 |
2.01 to 3.0 |
123 - 148 |
117 - 144 |
111 - 140 |
3.01 to 4.0 |
149 - 174 |
145 - 172 |
141 - 170 |
4.01 to 5.0 |
175 - 200 |
173 - 200 |
171 - 200 |
The maximum of 200 beats per minute assumes a 20 year old male.
Specialty: Emergency Medicine, Critical Care
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