Do circadian rhythms prefer to run long or short?

Circadian rhythms generally prefer to run long, approximately 24.2 to 25 hours. This intrinsic tendency is a result of natural biological processes that align with the Earth's day-night cycle, which has developed over millions of years. The average human circadian cycle tends to extend slightly beyond a 24-hour day, leading to a preference for slightly longer cycles. This pattern can be influenced by external cues such as light exposure, which helps regulate and synchronize the rhythm to the 24-hour day.

While there is variability in circadian rhythms across individuals, the overarching tendency of the biological clock across the population is to lean towards a longer duration. This concept helps explain why shift work and irregular schedules can disrupt sleep patterns and overall well-being, as they conflict with our natural rhythm. Therefore, recognizing that circadian rhythms prefer to run long is essential for understanding their impact on human factors in aviation and other fields.