If you read my recent article on the effects of snacking, then you got a brief introduction to the field of chrono-nutrition and the influence of circadian rhythms on daily functioning. These approximate 24-hour rhythms in metabolism, physiology, and behavior not only play a crucial role when it comes to optimizing our dietary patterns but our performance as well.
Numerous time-of-day fluctuations have been recorded for indices that influence our ability to execute different tasks at our maximum capacity. This applies to different modes of exercise as well as cognitive tasks.
For example, mental performance tends to deteriorate with time awake. In principle, this means that mental performance tends to be best in the morning and will incrementally decrease over the course of the day. Indeed, research has shown that performance in complex tasks such as mental arithmetic and short-term memory have been shown to peak in the early hours of the day.
In terms of physical tasks, pursuits that require fine motor control (i.e. balancing on a wobble board), appear to be better performed in the morning due to lower levels of arousal.
In a study on tennis performance, it was found that serve accuracy at 9 a.m. and 2 p.m. were significantly better than at 6 p.m. In conjunction with this finding, an inverse relationship for velocity was reported with greater serving speeds later in the day.
This tendency for tasks that require a greater degree of motor control to be better performed earlier in the day seems to ring true for other sports as well. Badminton serve accuracy was observed to be better at 2 p.m. than 8 p.m. For soccer, the performance of tasks that require finer motor control, such as juggling and chipping, was shown to peak earlier in the day (4 p.m.) than tasks that involved more gross motor functions such as dribbling speed and volley tests (8 p.m.).
Taken together, this information suggests that more technical aspects of sports performance peak earlier in the day. In addition, an individual may learn a new skill quicker if it is practiced in the morning.
In contrast to cognitive tasks and endeavors that require precise motor coordination, muscle strength and power have consistently shown to peak in the later hours of the day.
From this body of evidence, it’s clear that we are primed to perform different tasks at different times of the day. As such, a time-of-day effect on responses to exercise training might exist. This would mean that the greatest adaptations to training may coincide with a particular time of day depending on the specific trait you are trying to improve.
For the remainder of this article, we’ll be focusing on time-of-day effects on short-term maximal exercise performance and muscle hypertrophy. This includes modes of exercise up to one minute in duration which mainly involves anaerobic metabolism. This research is most relevant to strength and physique athletes which is the area I’m most interested in and the same likely applies to you if you follow my work.
Time-Of-Day Effects on Training Performance
It’s a common understanding that in order to grow muscle, some form of progressive overload needs to take place over time. Simply put, to drive hypertrophic adaptations, you need to be putting more weight on the bar or performing more reps with the same weight. In addition, it appears there is a dose-response relationship between training volume and muscle hypertrophy.
With these fundamentals of resistance exercise in mind, it seems logical that if a specific time of day facilitates better training performance (the ability to express greater strength), this will lead to the accumulation of a greater amount of training volume (specifically, volume load, or sets x reps x weight) within a session and superior gains over time. To assess the efficacy of this hypothesis, we need to figure out if there is a significant difference in anaerobic performance between different times of the day. If this is indeed the case, we would then need to see if these acute differences in performance do in fact lead to better outcomes over time. Let’s see what science has to offer on the matter.
To begin, we’ll take a look at indirect research utilizing modes of exercise similar in nature to bodybuilding-style training. A pretty good example is the Wingate Test. The Wingate Test is a 30-second (s) maximal sprint against constant resistance on a friction loaded cycle ergometer.
The duration of this exercise is both too short to exhaust the anaerobic energy system and not long enough for the contribution of aerobic metabolism to be negligible. As such, I would say this type of test is comparable to something like a set of 10-15 reps to failure on a multi-joint lift like squats or deadlifts, exercises that utilize a large amount of muscle mass and possess a significant cardiovascular component, especially when performed for high repetitions to muscular failure.
In this study, performance on the Wingate Test was assessed at 6 a.m. and 6 p.m. It was found that peak power (the highest amount of force produced during the 30-s test), mean power (the average amount of force produced during the 30-s test), and total work performed were significantly lower in the morning than the afternoon session.
The researchers also found that power decline was greater in the morning which suggests increased susceptibility to fatigue when maximum effort is exerted earlier in the day.
In a similar trial, subjects performed ten 6-second all-out sprints with 30-s of rest between bouts on a cycle ergometer. In a random counterbalanced order, subjects performed the test in the morning (between 8 a.m. and 10 a.m.) and in the afternoon (between 5 p.m. and 7 p.m.).
The results displayed a higher maximal power output in the afternoon. In conjunction with this finding, there was an observed greater decrease in power from sprint 1 to sprint 10 in the afternoon training, but total power output from sprint 1 to 10 was still significantly higher than in the morning. Also, subjects tended to still have a higher power output at sprint 10 when training in the afternoon.
To phrase these outcomes a bit differently, while power output was more consistent when training in the morning, total power output and peak power output were still significantly less than when training in the afternoon.
This research, in combination with the observed diurnal variations in strength reported in the introduction, suggests an ability to produce higher levels of peak force and the ability to sustain higher levels of force for longer when training later in the day. In the context of resistance exercise, this increase in total work found when training later in the day could potentially translate into vastly superior outcomes for muscle hypertrophy.
Moving on to the second half of our hypothesis, do longer-term trials report greater increases in muscle size from training later in the day? If so, is this effect explained by the performance of more training volume?
Time-Of-Day Effects on Muscle Hypertrophy
When it comes to examining time-of-day effects on training, we have lots of research examining different metrics of performance, but when it comes to muscle hypertrophy, specifically, it’s slim pickings. This area of research is still quite raw, but there are a couple of trials available with some pretty interesting results.
In this study, which focused on changes in the knee extensor muscles, subjects underwent a 10-week preparatory period where all training was performed between 5 p.m. and 7 p.m. Subjects were then matched based on their improvements in the 1RM half squat and randomized to 10 weeks of either morning (sessions performed between 7 a.m. and 9 a.m.) or afternoon (sessions performed between 5 p.m. and 7 p.m.) training.
In weeks 11-15, training frequency was bumped up from 2 sessions per week to 2.5 sessions per week (5 sessions completed over 2 weeks). In weeks 16-20, training frequency was increased again to 3 sessions per week.
Training consisted of squat jumps, leg presses, knee extensions, and half squats. Training volume and intensity was divided between hypertrophy oriented (40%), heavy-load maximum strength (38%), and high-speed training (22%).
From the mid-point of the intervention (week 10) to the end, it was found that maximal voluntary isometric strength of the knee extensors increased by 6.3% in the afternoon group and 4.7% in the morning group. In addition, 1RM half-squat increased by 4.5% in the morning group and 3.6% in the afternoon training group, respectively.
More importantly, while quadriceps femoris size increased significantly in both groups with no significant differences between interventions, there were in fact greater average gains in quadriceps femoris cross-sectional area and volume in the afternoon group (3.5% vs. 2.7%).
Moving on to a longer trial, in this one, subjects were randomized to one of four groups for 24 weeks: morning training (sessions performed between 6:30 a.m. and 10 a.m.) with strength training performed before endurance training, morning training with endurance training performed before strength training, evening training (sessions performed between 4:30 p.m. and 8 p.m.) with strength training performed before endurance training, and evening training with endurance training performed before strength training.
The training intervention was split into two 12-week periods. For the strength training intervention, each 12-week period consisted of three 4-week blocks dedicated to a different fitness component. Block one focused on circuit training (40-70% 1RM with minimal rest), block two was termed “hypertrophic” (70-85% 1RM), and block three was maximal strength (75-95% 1RM). During the first 12 weeks, subjects performed 2 sessions per week. During the second 12-week period, 2.5 strength training sessions were performed per week (5 sessions over 2-weeks).
For the endurance training intervention, continuous (30-50 minutes at 65-80% of maximal heart rate) and interval (4×4 minute intervals at 85-100% of maximum heart rate followed by 4 minutes of active rest at 70% of maximum heart rate) protocols on a cycle ergometer were utilized. During the first 12-week period, both interval and continuous training sessions were performed once per week. During the second 12-week period, an additional interval session was added resulting in 3 endurance training sessions per week.
The results showed that all training groups, except the morning training group that performed endurance training before their strength training, improved 1RM leg press force compared to the control group (no training).
For endurance performance, all groups increased time to exhaustion during the first 12 weeks of training, but during the second 12 weeks, only the morning and evening groups that performed their endurance training before their strength training continued to experience significant improvements. This finding indicates the importance of the law of specificity. If you want to get better at something, you should prioritize completing that work while in the freshest state possible in order to maximize performance.
Moving on to the more interesting findings (all about that muscle), during the first 12-weeks, all groups increased vastus lateralis cross-sectional area similarly. In contrast, during the second 12-week period, only the evening training groups continued to experience significant gains in cross-sectional area.
These results are extremely fascinating because they would suggest that the impact of time-of-day on training adaptations is more important than the law of specificity. This is evidenced by the fact that the evening group that performed endurance exercise before their strength training experienced greater muscle gains than the morning group that performed their strength training first.
Another puzzling finding of this paper was that significant correlations between individual changes in the cross-sectional area of the vastus lateralis and the strength of the lower extremities were only found in the evening group that performed their strength training before their endurance exercise.
This means that strength gains could not primarily explain the significant differences in hypertrophy between the evening group that performed endurance training before strength training and the morning groups. This would invalidate our hypothesis from earlier that if training later in the day resulted in being able to utilize heavier loads, this would result in more total work performed and thus superior hypertrophy.
Before we throw the baby out with the bathwater on this idea, it is worthwhile to mention that the authors did speculate this finding (or lack thereof) could simply be a statistical error as a product of a low number of subjects.
In further consideration, rather than the law of specificity being completely ostracized by this data, the authors speculated that the specific form of endurance training utilized may have provided an additional hypertrophic stimulus rather than an interference-effect.
When examining these two trials, there is a very compelling difference worthy of additional thought. When looking at the intervention duration, the subjects in study one only spent 10-weeks in their respective protocol, while in study two, subjects spent over double that amount of time. Consequently, study two also reported significantly greater gains in muscle hypertrophy when training in the evening, even when endurance training was performed prior to strength training.
While study one also suggested greater muscular gains training in the afternoon, the percent increase was not significantly different from the group training in the morning. If there truly is a time-of-day effect for training for muscle hypertrophy, this would make sense. We know that the accretion of muscle mass is a painstakingly slow process. As such, 10-weeks may have simply not been enough time to detect significant differences, while 24-weeks was.
As I mentioned at the beginning of this section, this is a very young field of research. We simply need more long-term studies to tease out whether it’s worth reorganizing our schedules to train in the afternoon/evening. Nonetheless, these findings are quite captivating.
With a dearth of direct data on the topic, it’s worth exploring potential physiological mechanisms that might explain why performance and muscle hypertrophy adaptations are superior later in the day.
Why Might Training Performance be Better Later in the Day?
Several theories have been postulated as to why performance might be better later in the day. This includes enhanced calcium release from the sarcoplasmic reticulum and increased calcium sensitivity of contractile proteins in the afternoon leading to increased force production.
There’s also the idea that the hormonal response to exercise is superior later in the day. The primary players in this equation are testosterone and cortisol. Concerning the critical role these complementary hormones play in tissue growth and remodeling, many have speculated that training at a time of day which elicits the greatest increases in these markers will maximize training adaptations. Indeed, greater increases in cortisol and testosterone have been observed following evening training, but this doesn’t appear to lead to greater gains over time.
As it stands, it seems the primary mechanism explaining improved performance later in the day is body temperature. Body temperature falls to a minimum during sleep and begins to rise before wakefulness. This rise usually continues until it reaches a peak at around 6 p.m. which coincides with an observed nadir in joint stiffness.
It has been postulated that an increase in body temperature may lead to benefits such as an increase in carbohydrate utilization over fat as a fuel source, better muscle contractile properties (as evidenced by a higher mechanical response to an electrical stimulation of the motor nerve), and facilitate actin-myosin cross-bridge mechanics within the musculoskeletal unit.
When it comes to short-term maximal performances during continuous and intermittent exercises or very brief all-out efforts, performance tends to be best in the late afternoon/early evening. This is not only evidenced by direct research on the topic but indirect research on sports performance. Indeed, it has been shown that the performance of competitive cyclists is typically superior when races are held in the afternoon and evening compared to the morning and the same goes for swimming and weight throwing.
Is that it then? In order to maximize adaptations to training, we should exercise in the late afternoon/early evening? Not necessarily.
If you’re part of team early bird (#riseandgrind), you’re in luck, for the second portion of this series, we’ll be exploring other important factors to consider when picking a time-of-day to exercise in addition to potential strategies to blunt the aforementioned diurnal variations in physical performance.