The most reliable indicator to determine if you should modify activity for heat is the Wet Bulb Globe Temperature (WBGT). WBGT is considered the gold standard because it measures a combination of ambient temperature, humidity, wind speed, and radiant heat (such as sunlight), providing a comprehensive assessment of heat stress risk

. However, when WBGT measurement tools are not available, the Heat Index is a widely used and practical alternative. The Heat Index accounts for temperature and humidity to estimate how hot it feels, which helps guide activity modifications such as work-rest cycles and hydration breaks

Summary:

• Preferred indicator: Wet Bulb Globe Temperature (WBGT) - integrates temperature, humidity, wind, and radiant heat for accurate heat stress assessment

• Alternative indicator: Heat Index - combines temperature and humidity to estimate perceived heat, useful when WBGT is not accessible

• Both indicators help determine when to modify activity by adjusting work-rest ratios, hydration, clothing, and practice duration to prevent heat-related illnesses

In practice, many safety guidelines and organizations recommend using WBGT when possible, but rely on Heat Index charts for accessible and timely decisions regarding heat-related activity modifications