Free-running period

The free-running period is the natural cycle length of an organism's internal clock when it is not influenced by external cues like light or dark. For humans, this internal rhythm averages around 24.2 hours, slightly longer than the 24-hour day. Without environmental signals, the internal clock would drift, causing sleep and activity patterns to shift gradually. This concept helps scientists understand how biological rhythms maintain regularity and how external factors, such as artificial light, help synchronize (or entrain) our internal clocks to the 24-hour day-night cycle.