Twenty-one Shipibo Indian men were compared to 21 Mestizo men in a study of heat tolerance in the Amazon jungle of Peru, both groups walked together in the afternoon sun for 12 days. The first six were at a slow rate (5 km/hr); the second six at a faster rate (8.5 km/hr). At the 5 km/hr rate the Shipibo sweated more and showed less cardiovascular stress than the Mestizos. At the 8.5 km/hr walking rate the Shipibo still sweated more, but did not differ in other measures. Since both groups seemed well acclimatized at the outset, the Shipibo may have a propensity to be less stressed at lower work loads in the heat.
Hanna, Joel M. and Baker, Paul T.
"Comparative Heat Tolerance of Shipibo Indians and Peruvian Mestizos,"
1, Article 8.
Available at: https://digitalcommons.wayne.edu/humbiol/vol46/iss1/8