According to studies, after how many hours of inactivity does fitness begin to decline?

The correct response is based on research indicating that physical fitness can begin to decline after 72 hours of inactivity. This timeframe reflects the body's adaptive responses to a lack of physical activity. When individuals remain inactive for an extended period, muscle mass and strength can decrease, cardiovascular fitness can diminish, and other aspects of physical health may also deteriorate.

This phenomenon emphasizes the importance of maintaining regular physical activity to preserve fitness levels. Staying active not only supports muscular strength and endurance but also enhances cardiovascular health and metabolic function. Thus, understanding that significant declines in fitness can occur after three days of inactivity highlights the necessity for consistent exercise routines to maintain health and fitness levels.

In contrast, the other durations mentioned—48 hours, 96 hours, and 120 hours—do not align with the established timeframe for noticeable declines in physical fitness, as fitness changes become measurable after about three days of inactivity, making the recognition of the 72-hour mark critical for individuals aiming to stay fit.