What do diurnal rhythms pertain to?

Diurnal rhythms refer specifically to variations in body functions that occur every 24 hours. These rhythms are part of the body's internal clock, also known as the circadian rhythm, which regulates various physiological processes in response to the day-night cycle. For example, hormone levels, sleep-wake cycles, and body temperature can vary throughout the day, reflecting this 24-hour pattern.

Body weight fluctuations, changes in skin temperature, and daily exercise patterns might exhibit their own rhythms or variations, but they do not specifically relate to diurnal rhythms as classified within the context of biological rhythms influenced by light and darkness. Thus, the focus on 24-hour variations in physiological functions correctly illustrates the concept of diurnal rhythms.