Exercise performance tends to be better in the late afternoon/early evening (1–8 p.m.) than the morning (8–10 a.m.),^[104] particularly for short-duration maximal exercise (e.g., a 30-second Wingate test or tests of jump height, repeated sprint ability, or maximal voluntary contraction).^{[105][106][104]} Currently, there is limited evidence to suggest that a specific time of day is best for endurance exercise performance.^[104]

The main mechanism that underlies this finding is core body temperature, which reaches a peak in the evening hours.^[107][108] An increase in core body temperature may improve exercise performance by enhancing metabolic reactions, increasing the extensibility of connective tissue, reducing muscle viscosity, and increasing the conduction velocity of action potentials.^[109] Moreover, using cold water immersion to decrease core body temperature before evening exercise has been shown to decrease muscular strength and repeated sprint ability.^{[110][111][112]}

While exercise performance may be better in the evening than the morning at baseline, consistently training in the morning can offset this natural diurnal variation in performance. Indeed, long-term resistance exercise interventions that have participants train in the morning or evening report similar increases in strength and hypertrophy.^[106] This suggests that training at a consistent time each day is more important than the time of day training takes place. Therefore, an individual interested in maximizing exercise adaptations should choose a time of day that suits their preferences and will facilitate long-term training adherence.

Besides consistently training in the morning, there are acute strategies that can diminish the natural diurnal variation in exercise performance, including exercising in a warm and humid environment,^[113][114] performing an extended warm-up (e.g., 12 minutes of cycling at 50% of VO₂max interspersed with brief accelerations of 5 seconds),^{[115][116][117]} ingesting caffeine,^[118][119] and listening to music.^[120][121]

While there is a general consensus that exercising in the morning or afternoon benefits sleep, it’s often recommended to avoid exercising, especially at a high intensity, in the evening in fear of it negatively affecting sleep.

However, according to a meta-analysis published in 2021, an acute bout of high-intensity exercise performed 2–4 hours before bedtime does not disrupt sleep.^[122] In fact, performing high-intensity exercise 2 hours before bedtime tends to increase total sleep time (+16 minutes) and decrease the time it takes to fall asleep (−5 minutes). However, longer duration high-intensity exercise (>30–60 minutes) may decrease rapid-eye movement sleep to a small extent (−3%).

In a 7-week study in elite youth soccer players, an evening high-intensity exercise session did not affect sleep quality and slightly increased sleepiness at bedtime, compared to nights where no exercise was performed.^[123]

In sum, high-intensity evening exercise does not appear to negatively affect sleep. Careful consideration should be given to pre-workout supplements when exercising in the evening, as products containing caffeine can negatively affect sleep.

The evidence is mixed, but the preponderance of the evidence suggests that it’s unlikely that creatine will increase your testosterone levels.

Three randomized controlled trials conducted in healthy young men reported that supplementing with creatine for 1–3 weeks produced small increases in the levels of testosterone or dihydrotestosterone (DHT; a highly active androgen converted from testosterone).^{[124][125][126]} One of the 3 trials looked at the effect of creatine loading (25 grams/day for 1 week) followed by a maintenance phase (5 grams/day for 2 weeks) on testosterone and DHT in 20 young, healthy rugby players. Although no effect on testosterone was found, creatine increased the levels of DHT by 12 nanograms of DHT per deciliter of blood (ng/dL).^[124] The other 2 trials found that supplementation with creatine for 1 week in healthy, active young men increased the concentrations of testosterone by 57 ng/dL and 150 ng/dL.^[125][126]

Conversely, 10 other trials (involving a total of 218 participants) looking at the effect of supplemental creatine at daily doses of 3–25 grams on testosterone levels for up to 12 weeks have found no statistically significant effect.^{[127][128][129][124][130][131][132][133][134][135]} The participants in the majority of these trials were healthy, active young men. With regard to the form of creatine used, 9 trials administered creatine monohydrate, whereas 1 trial administered creatine malate. It’s worth noting that no trials have looked at the effect of creatine on testosterone in men with abnormally low testosterone levels.

Taken together, the available evidence suggests that supplementing with creatine is unlikely to increase testosterone levels, at least in young healthy men whose testosterone levels are within the normal range.