Table 3.

Equations linking physical work capacity to the thermal climate

Heat stress metric	Range	Equation: PWC=	R2	RMSE	Index accounts for solar radiation?
Ta and humidity	Ta 15–50°C RH 20–80%	$\frac{100}{1+{\left[\frac{\left(-12.28\mathit{Ln}(\mathrm{RH}\right)+87.99}{T_{\mathrm{a}}}\right]}^{\left[-2.21\mathit{Ln}\left(\mathrm{RH}\right)+2.63\right]}}$	.98	3.09	No
Heat index	14–85°C	$\frac{100}{1+{\left(\frac{55.47}{\text{heat index}}\right)}^{-2.90}}$	.97	4.10	No
Humidex	13–71°C	$\frac{100}{1+{\left(\frac{54.50}{\text{humidex}}\right)}^{-4.10}}$	.96	4.86	No
Twb	10–39°C	$\frac{100}{1+{\left(\frac{30.98}{T_{\mathrm{wb}}}\right)}^{-5.90}}$	.95	5.60	No
UTCI	15–63°C	$\frac{100}{1+{\left(\frac{45.33}{\text{UTCI}}\right)}^{-4.30}}$	.94	5.90	Yes
WBGT	12–40°C	$\frac{100}{1+{\left(\frac{33.63}{\text{WBGT}}\right)}^{-6.33}}$	.94	5.94	Yes

WBGT wet bulb globe temperature, T_wb aspirated wet bulb temperature, UTCI universal thermal climate index, T_a air temperature, RMSE root-mean-square error, Ln natural logarithm