Forcing yourself to work out is one thing, but forcing yourself to wake up early and then work out? That is truly asking a lot. But, new and encouraging research suggests that, for some of us, sleeping in might be the best way to prep for exercise. In the small study, published earlier this month in Current Biology, 20 field hockey players were sorted into groups based on their sleep and wake-up times, both during the week (when they're at the mercy of an alarm) and on the weekend (when they're more able to follow natural rhythms). Nearly half of them were considered to have the "intermediate" circadian phenotype, meaning they tended to wake up around 9:30 a.m. and fall asleep around midnight on the weekends. Another 25% were sorted as early risers, and the remaining 25% were the night owls. Then, everyone had to perform a cardio endurance test at six different times of day. Overall, participants did their best on the test near the end of the day (at 4:00 and 7:00 p.m.) and their worst at the very beginning (7:00 a.m., yikes). However, personal bests for the cardio tests were dependent on participants' circadian phenotypes — especially the late risers, whose performance steadily improved as the day went on. Even if you're not a field hockey player, this suggests that your personal best can be affected by the timing of your workout and your natural sleep-wake cycle. (Speaking of sleep, previous research has shown that doing cardio in the morning and strength training later in the day can improve the quality of your sleep.) Although squeezing in an early morning jog is certainly better than not doing anything, this means it won't necessarily be the most productive workout. If your schedule allows, you could get better results if you time your sweat sessions based on your own internal schedule. So, for you night owls, try planning for an after-work sweat session and save the morning for some snoozing. Doesn't that sound more pleasant anyway?