Neither is clearly better for building muscle or strength. A meta-analysis of 11 studies found strength and muscle-size gains were similar whether people trained in the morning or the evening4.
What does differ is when you are strongest. Strength tends to follow the time of day you train. Below is what the studies measured, where they disagree, and what "similar" does and does not mean.
What was studied
The main evidence is a 2019 meta-analysis, a review that pools the results of many studies into one estimate4. It included studies that trained people at a set time of day while keeping everything else, such as sessions per week and total sets, the same between groups. Eleven studies of moderate and good quality made the cut.
The review asked four questions4:
- Are people stronger in the morning or the evening before any training?
- After training, how strong are the morning and evening groups at each time of day?
- Overall, does one group gain more strength than the other?
- Does one group gain more muscle?
The clearest single trial is a 2018 randomised study, which we read in full2. Previously untrained young men were randomly assigned to train early in the morning (07:30 to 08:30), in the afternoon (16:00 to 17:00), or not at all.
| What | Morning group | Afternoon group | Control |
|---|---|---|---|
| Men | 11 | 7 | 7 |
| Sessions | 22 over 11 weeks | 22 over 11 weeks | none |
| Program | identical | identical | none |
| Muscle size measure | MRI of the thigh | MRI of the thigh | not scanned |
MRI is a scan that images the cross-section of a muscle, so its area can be measured directly.
In plain terms: the review compares training times with everything else held equal, and the trial is one clean example of that design.
What the studies found
The review's findings, in order4:
- Before training, people were significantly stronger in the evening than in the morning.
- Morning training "may increase strength assessed in the morning to similar levels as strength assessed in the evening".
- Evening training kept the usual gap: those groups stayed stronger in the evening.
- Overall strength gains were similar for the two groups, whichever time strength was tested.
- Muscle growth was similar "irrespective of the time of day at which the training is performed".
The 2018 trial showed the same pattern for size and strength2. Thigh muscle cross-sectional area grew 8.8% in the morning group and 11.9% in the afternoon group. Isometric strength (maximal force against an immovable resistance) rose 16.9% and 15.2%. Muscle fibres, measured in small tissue samples, grew 21% and 18%. The control group showed no significant changes. The difference between the two training groups was not statistically significant, meaning it was small enough that chance could explain it in a study this size.
Change over 11 weeks: early-morning vs afternoon training · %
Morning (07:30) Afternoon (16:00)
The authors concluded that "similar levels of muscle strength and hypertrophy could be achieved regardless of time of the day in previously untrained men"2.
In plain terms: the hour on the clock did not decide how much muscle or strength people gained.
Time-of-day specificity: strength follows the clock
The one consistent time effect is about when strength shows up, not how much is built. Researchers call this time-of-day specificity. The body gets better at producing force at the hour it usually trains.
The 2019 review found that morning training may close the usual morning-versus-evening gap, while evening training keeps it4. A 2023 review reached a similar conclusion across both strength and endurance training5. It found "evidence for larger effects when there is congruency between training and testing times", meaning when people were tested at the same time of day they trained.
This matters for how a result is read. A morning lifter tested in the evening may look a little weaker than their training suggests, and the reverse. It also matters for anyone who competes or tests at a fixed hour. That is a description of what the studies found, not a rule.
In plain terms: you tend to be strongest at the hour you usually train.
Where the studies disagree
Not every trial came out even. Two smaller studies leaned in opposite directions:
- Evening leaned ahead in a longer trial. In 2016, 42 young men did combined strength and endurance training in the morning or evening for 24 weeks1. All groups increased leg-press 1RM (the heaviest load lifted once) by similar amounts, 14% to 19% tested in the morning and 18% to 24% in the evening. Thigh muscle area rose 12% to 20% in all groups. In weeks 13 to 24, the evening groups gained more muscle. The authors noted that time of day seemed to matter only after 12 weeks.
- Morning leaned ahead in older women. In 2018, 31 healthy women aged about 66 trained in the morning or evening for 12 weeks3. Both groups improved leg-press and seated-row strength and every functional test. Only the morning group significantly increased muscle mass (3%, estimated by bioelectrical impedance, which passes a small current through the body). The authors concluded that time of day "did not have a major effect on outcome variables".
These results point in different directions, in different people, with different methods. That is part of why the pooled reviews land on "similar".
How the evidence on training time built up
- 2016Küüsmaa et al.42 young men, 24 weeks: similar strength; evening groups gained more muscle after week 12.
- 2018Sedliak et al.25 untrained men, 11 weeks: similar muscle growth and strength, morning vs afternoon.
- 2018Krčmárová et al.31 older women, 12 weeks: both gained strength; only the morning group added measurable muscle.
- 2019Grgic et al.11 studies pooled: similar strength and size gains; strength follows the training hour.
- 2023Bruggisser et al.26 studies reviewed: no time clearly better; larger effects when training and testing times match.
In plain terms: single trials sometimes tilt one way, but the tilts do not agree with each other.
What this means in practice
This is a description of the research, not a prescription. What the studies suggest:
- Consistency is the variable they held equal. Every study compared groups doing the same sessions and sets. None tested what happens when one time of day makes people skip sessions.
- Muscle and strength gains were similar across times, in the pooled review and the full-text trial42.
- Strength shows up best at the familiar hour. If you test or compete at a set time, the studies found larger effects when training and testing matched5.
How many sessions to fit into a week is covered in how many days a week should you lift. If you track your lifts, time-of-day specificity is one reason to compare numbers taken at a similar hour (see how to track strength progress); that is our reading, not a tested rule. Whether lifting late affects sleep is a separate question, with its own article on this site.
The studies at a glance
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Küüsmaa et al., *Appl Physiol Nutr Metab*1 | 42 young men, 24 weeks of combined strength and endurance training | Similar strength gains; evening groups gained more muscle in weeks 13 to 24 | 2016 |
| Sedliak et al., *Chronobiol Int*2 | 25 untrained young men, randomised, 11 weeks | Thigh muscle +8.8% (morning) vs +11.9% (afternoon); strength +16.9% vs +15.2%; not significantly different | 2018 |
| Krčmárová et al., *Chronobiol Int*3 | 31 healthy older women, 12 weeks | Both gained strength; only the morning group significantly increased muscle mass | 2018 |
| Grgic et al., *Chronobiol Int*4 | Meta-analysis of 11 studies | Strength and muscle-size gains similar for morning and evening training | 2019 |
| Bruggisser et al., *Sports Med Open*5 | Systematic review of 26 studies, 7 meta-analysed | Little evidence for or against any time of day; larger effects when training and testing times match | 2023 |
Limits worth knowing
- Small trials. The full-text trial had 11 and 7 men in its training groups2.
- Mostly young men. Only one of the trials here studied women, and they were older and previously untrained3.
- Afternoon, not late evening. The 2018 trial's later group trained at 16:00, and each group was tested only at its own training time2.
- High risk of bias. The 2023 review rated most studies in the field at high risk of bias5.
- Abstracts only for four papers. We read the full text of the 2018 trial and the abstracts of the other four. The 2019 review's abstract gives no effect sizes, so we cannot say how large the evening strength advantage is.
- Not measured. How time of day affects sticking with training over months.
Latest research
The newest study we opened is the 2023 systematic review in *Sports Medicine – Open*5. It screened 14,125 articles, included 26, and pooled 7. It found evidence "neither for nor against a specific time of the day being more beneficial", and larger effects when training and testing times matched. Its authors also set out how future studies should be designed, a sign the question is still open. When a larger trial appears, this page will be updated and its date will change.
The short version
- Morning and evening training produced similar muscle and strength gains in the pooled evidence.
- People start stronger in the evening; morning training may close that gap at the morning hour.
- Strength tends to show up best at the time of day you train.
- Single trials lean both ways, and most studies are small.
Educational overview only — not medical advice.
