Is it better to run in the morning or night?

This question is about Running
Sarah Achleithner
Some research shows the best time to run is between 4 and 5 PM [1]. This is because at night, the body experiences its peak core temperature, which translates to an increase in energy metabolism, flexibility, range of motion, speed, agility, and endurance [2]. And no need to worry about insomnia; research has shown that running approximately four hours before bedtime can improve sleep quality [3, 4]. 
Don’t fret if that timeframe doesn’t work for you - adaptations to training are greater at the time of day at which training is regularly performed [1].
woman with ponytail running along road against a fenced background

References: 

  1. Chtourou, H. & Souissi, N. (2012). The Effect of Training at a Specific Time of Day. The Journal of Strength and Conditioning Research. 26(7), 1984-2005. doi: 10.1519/JSC.0b013e31825770a7 
  2. Teo, W., Newton, M. J., & McGuigan, M. R. (2011). Circadian rhythms in exercise performance: implications for hormonal and muscular adaptation. Journal of sports science & medicine, 10(4), 600–606. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3761508/
  3. Saidi, O., Davenne, D., Lehorgne, C., & Duché, P. (2020). Effects of timing of moderate exercise in the evening on sleep and subsequent dietary intake in lean, young, healthy adults: randomized crossover study. European journal of applied physiology, 120(7), 1551–1562. https://doi.org/10.1007/s00421-020-04386-6
  4. Youngstedt, S. D., Kripke, D. F., & Elliott, J. A. (1999). Is sleep disturbed by vigorous late-night exercise?. Medicine and science in sports and exercise, 31(6), 864–869. https://doi.org/10.1097/00005768-199906000-00015