The time of day your male clients train may affect their appetite and performance.

A small, preliminary study has found that middle-aged men can do a brief high-intensity interval workout at night without suffering sleep disruption. Researchers from Charles Sturt University in Bathhurst, Australia, conducted the study with 11 inactive men. The aim was to learn whether time of day—morning, afternoon or evening—would influence the effects of a 30-minute HIIT session on sleep levels and appetite.

Data analysis revealed little difference in sleep duration among the three exercise times. While no subjects perceived a variation in sleep or appetite, blood samples showed that evening exercise resulted in lower levels of the appetite-stimulating hormone ghrelin. The findings cannot be generalized to women or men of other ages.

“In the future, we hope to conduct similar studies recruiting women,” said lead study author Penelope Larsen, a PhD student at CSU School of Exercise Science, Health and Sport. “Interestingly, power output during the sprint efforts was higher for the afternoon and evening trials compared to the morning trial, indicating that participants were able to perform better during latter parts of the day. Therefore, time of day may also need to be considered when planning training schedules.”

The study is available in Experimental Physiology (2019; doi:10.1113/EP087455).

Shirley Archer, JD, MA

Shirley Archer, JD, MA, is an internationally acknowledged integrative health and mindfulness specialist, best-selling author of 16 fitness and wellness books translated into multiple languages and sold worldwide, award-winning health journalist, contributing editor to Fitness Journal, media spokesperson, and IDEA's 2008 Fitness Instructor of the Year. She's a 25-year industry veteran and former health and fitness educator at the Stanford Prevention Research Center, who has served on multiple industry committees and co-authored trade books and manuals for ACE, ACSM and YMCA of the USA. She has appeared on TV worldwide and was a featured trainer on America's Next Top Model.

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