AM vs PM – Is there a ‘best’ time to exercise?

Simple answer: yes. Longer answer: read below.

Circadian Rhythms

Your body has its own circadian rhythm (commonly known as your biological clock) that manages numerous mechanisms in the body including hormone production and body temperature. In our previous post on optimizing sleep, we explained how your circadian rhythm regulates sleep by adjusting levels of melatonin. When it comes to exercise, there are 4 key factors: body temperature and 3 hormones (testosterone, growth hormone and cortisol).

1. Body Temperature

The temperature of your muscles, joints and connective tissue (ligaments & tendons) has a direct impact on their effectiveness and performance. When they’re cold, they are stiff, less flexible and more likely to get injured. When they are warm, they are primed for a workout. This explains the prudent advice to warm up prior to your workout. How does your body temperature change during the day? Its lowest in the middle of the night while you sleep, and then it gradually increases from the time you wake up until it peaks mid-afternoon (2-3pm). In the afternoon, your body temperature is optimal for exercise. Accordingly, research says that midday or early evenings is the ideal time to schedule your workout. What about those that workout in the morning (like myself)? Are we wasting our time and putting ourselves at greater risk of injury? Not necessarily. Studies have shown that adding a 20min warm up prior to a morning workout can adequately prime your body by raising your body temperature.

2. Testosterone, Growth Hormone & Cortisol

Let’s give a quick introduction of each. Everyone’s familiar with testosterone, its an anabolic hormone (meaning that it promotes muscle growth and strength). It peaks in the morning and declines throughout the day. Growth hormone is also anabolic and is mostly produced at night to help rebuild and maintain your muscles. Cortisol, alternatively, is a stress hormone that is catabolic (meaning it breaks down muscle). Cortisol is also responsible for your level of alertness (think of your fight or flight response). It peaks in the morning and declines throughout the day. The research, in terms of ideal training time, is less definitive as compared to body temperature. It’s agreed that higher levels of testosterone/growth hormone is preferred for muscle gain and performance and lower levels of cortisol. However, testosterone peaks in the morning together with cortisol. Does this mean mornings are the best time to train? No. Research again concludes that that the optimal time to train is midafternoon or early evenings when testosterone is relatively elevated, and cortisol has declined. This explains why most sporting events and matches are played in the afternoons.


Based on both of the above factors, It’s clear that the ideal training time is in the midafternoon or early evenings. How much better is performance between morning and evenings? Roughly 2-3%. Is that a worthwhile difference for the average person? Not really. Unless you’re a professional athlete, you won’t notice the benefit of that marginal improvement. All this discussion so far has missed a critical factor: personal preference. What matters most when it comes to planning your workouts are two things: when time of day you feel at your best and when you actually have time to train. If you feel full of energy first thing in the morning and don’t have time to train in the evenings, stick to morning workouts. If you feel slow and lazy in the mornings, then workout during lunch or after work.

Bottomline: The worst workout is the one that didn’t happen! Find the time that works for you. Our personal trainers are there for you in the morning, evenings and weekends!

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