Can muscles grow with just one workout a week?

Short answer

Yes, with 6~9 sets in one session. In studies doing 6~9 sets for a body part once a week, muscle grew over 9~11 weeks, no different from splitting the same amount over 3 days. With only 5 sets once a week for 6 weeks, it did not grow.

Can muscles grow with just one workout a week?
Is "once a week is worse than nothing" true?
Many busy people can train a body part only once a week. We checked whether that is enough for muscle to grow, and the minimum to do in one session.
Muscle grew even once a week
9 sets in one go, no different from the leg split over 3 days
24 people trained for 9 weeks: one leg did 9 sets of leg press once a week, the other leg 3 sets 3 times a week. With the total weight lifted matched, front thigh muscle area grew 2.1% in the once-a-week leg and 2.0% in the 3-times-a-week leg, with no difference.
Doing 6 sets at once still thickened the muscle
Strength rose more when split up
20 people did leg extensions for 11 weeks, either 6 sets once a week or 2 sets 3 times a week. Both groups gained thigh girth and muscle thickness. Strength rose 65.2% in the 3-times group and 43.5% in the once group, and the once group found the workouts harder.
But too little, too short did not grow it
5 sets once a week for 6 weeks did not thicken the muscle
30 people did the same 30 sets of leg press on a flywheel machine over 6 weeks. The group doing 5 sets once a week did not gain muscle thickness meaningfully, while the group doing 1 set 5 times a week gained 9.8%. The all-at-once group had more soreness and found it harder.
Sets mattered more than sessions
Pooling many studies, the same amount split differently made no difference
In an analysis that pooled 25 studies, with weekly training amount matched, there was no difference in muscle growth between once a week and more often. In a 2026 analysis that pooled 67 studies with 2,058 people, muscle grew more as weekly sets rose, with smaller added gains each step. The number of sessions itself had almost no effect on muscle growth.
Muscle already built was kept with much less
Ages 20~35 held it even when training dropped to 1/9
70 people trained 3 times a week for 16 weeks, then cut their training to 1/3 or 1/9 for 32 weeks. Ages 20~35 kept the muscle they had built in both cases, and the 1/3 group's muscle fibers grew further. Ages 60~75 did not keep their muscle on the reduced amounts.
Summary: yes, 6~9 sets in one session built muscle
To grow more, add weekly sets
Even once a week, 6~9 sets for a body part grew muscle over 9~11 weeks, no different from splitting the same amount over 3 days. With only 5 sets once a week for 6 weeks, it did not. To grow more, raising a body part's weekly sets works, and with 6 or more sets per session, the number of sessions can be whatever fits.