Does training a weak body part first make it grow more?

Short answer

Not for size. Strength rose more in the exercise done first, but an analysis that pooled 11 studies found no difference in muscle size by exercise order. For size, there is no need to put a weak part first.

Does training a weak body part first make it grow more?
'Go first → more energy → more growth.' Is that right?
A common tip is to put a weak body part at the very start of the workout. The logic: with fresh energy, you lift heavier and do more, so it grows more. We checked this formula one step at a time.
Do you get more reps on the exercise done first?
Yes, reps dropped the later the exercise came
18 people did 5 upper-body exercises twice, changing only the order. With 3 sets of each exercise taken until they could not do another rep, both big-muscle and small-muscle exercises got fewer reps when done later. The biggest drop was in the third set of the last exercise.
So strength rose more in the exercise done first
This held for big and small exercises alike
In an analysis that pooled 11 studies on exercise order, multi-joint big exercises gained more strength when done first, and single-joint small exercises also gained more strength when done first. The 2026 American College of Sports Medicine review, which combined 137 analyses covering more than 30,000 people, also concluded that strength rises more when an exercise is done early in the session.
But muscle size did not depend on order
Strength and size gave different answers
In the same 11-study analysis, muscle size showed no difference whether big or small exercises came first. The 2026 American College of Sports Medicine review also found that size did not change with exercise order. In a study where 29 people changed only the order for 12 weeks, muscle mass rose 7.5% and 6.1%, with no difference.
Measured by body part, the upper arm was the same
Front upper arm: 14.2% vs 13.8%
36 people trained for 6 weeks with either big exercises first or small exercises first. Front upper-arm muscle thickness rose 14.2% and 13.8%, with no difference. For the thigh, only the big-exercise-first group grew meaningfully (7.2%, versus 3.9% with the reverse order).
Looking only at studies that put small muscles first
Only the triceps-first group grew its triceps from the start
In two 12-week studies that put biceps and triceps exercises at the very start, the triceps grew from the start only when done first (one study found no gap between orders), and the biceps showed no difference by order. Pooled into the 11-study analysis, they showed no size difference. In a study where 22 people only swapped the order of a triceps exercise and the bench press, chest and triceps size also showed no difference.
Summary: putting a weak part first builds more strength
Size did not change with order
Training a weak body part first raised strength more on that exercise. Muscle size did not change with order. If size is the goal, the order can be whatever is convenient.