Which action is not a recommended personal measure to prevent heat injuries?

Increasing physical activity is not a recommended personal measure to prevent heat injuries, particularly in situations where heat stress is a concern. In fact, during periods of high temperature and humidity, participating in vigorous physical activities can elevate body temperature and lead to heat-related illnesses such as heat exhaustion or heat stroke.

The other options serve as important strategies for minimizing the risk of heat injuries. Modifying your uniform for comfort can help improve ventilation and moisture management, thereby facilitating body temperature regulation. Drinking plenty of water is critical for maintaining hydration, as dehydration is a key factor that can contribute to heat stress. Eating all meals helps to replace lost salts and maintain electrolyte balance, which is essential for proper physiological function during heat exposure. Thus, the emphasis should always be on managing activity level in hot conditions to ensure safety and prevent heat injuries.