In water above 90 degrees Fahrenheit, what physiological change occurs?

In water above 90 degrees Fahrenheit, the body experiences increased circulation and fluid distribution as a physiological adaptation to help regulate body temperature and maintain homeostasis. The warm water expands blood vessels, promoting better blood flow throughout the body. This increased circulation can enhance the delivery of oxygen and nutrients to tissues, as well as aid in the removal of waste products from metabolism. Additionally, this flush of circulation may also help with the body's thermoregulation as it deals with higher external temperatures, ultimately supporting performance and endurance in warmer conditions.

The other options do not reflect accurate physiological responses in warm water. For instance, a decreased metabolic rate or a reduced heart rate would typically be observed in cooler conditions, where the body aims to conserve energy. Limited oxygen availability for muscles could occur in situations of extreme temperature, but with the warm water environment supporting circulation, this is less likely to be a dominant response. Thus, increased circulation and fluid distribution is the primary physiological change observed.