Does splitting strength training into two sessions a day build more muscle?

Short answer

Not if you only split the same amount. In a 3-week trial that randomly assigned the same workload to one or two sessions a day, muscle size showed no difference, and an analysis of 25 studies found no muscle difference from training more often when the workload was the same. What built more muscle was the total number of sets per week.

Does splitting strength training into two sessions a day build more muscle?
'Two sessions → less fatigue each time → more muscle': does this formula hold?
Some say that splitting the same workout into a morning and an evening session builds more muscle because you are less tired each time. We checked trials comparing two sessions a day directly, and analyses of how often training is split up overall.
The randomized trial found no difference
Same workload, once versus twice a day, 3 weeks
10 people with an average of 5.5 years of lifting were randomly split to do the same workload once a day or in two sessions a day for 3 weeks. Thigh muscle size, holding strength, jump power and lifting results showed no difference between the two methods.
The study where muscle grew used a fixed order
3 weeks once a day, then 3 weeks twice a day
10 people trained once a day for the first 3 weeks, then split the same amount into two sessions a day for the next 3 weeks. Thigh muscle size and strength grew only in the later 3 weeks of two sessions. The same people did both methods in a fixed order; it was not a randomized comparison.
Splitting training more often did not change muscle
Same workload: once a week or more than 5 times
A 2019 analysis that pooled 25 studies found that when the workload was matched, training a muscle more often made no difference in muscle size. The same held for people who already lifted. The 2026 American College of Sports Medicine guideline also concluded that with the same workload, 1 day a week and more than 5 days a week did not differ for muscle.
What built more muscle was the total
More sets per week meant more muscle
A 2026 analysis that pooled 67 studies with 2,058 people found that muscle grew more as weekly sets increased, with the gains getting smaller along the way. In the same analysis, how often people trained had almost no effect on muscle. The guideline named 10 or more sets a week as a way to build muscle.
Strength was a bit different
Training more often raised strength more, with shrinking gains
In the same 2026 analysis, strength rose more as training sessions increased, with the gains getting smaller along the way. For muscle, this effect of how often you train was almost absent. This strength effect came from comparing sessions per week; in the 3-week trial with two sessions a day, strength showed no difference either.
Summary: splitting the same amount did not build more muscle
Muscle followed the total number of sets per week
Splitting the same workload into two sessions a day made no muscle difference in a randomized trial, and training more often had almost no effect on muscle by itself. What built more muscle was the total number of sets. Whether once or twice a day, getting 10 or more sets a week is enough.