Randomised trial — 2021 — Hypertrophy · Resistance training
Single-Joint Exercise Results in Higher Hypertrophy of Elbow Flexors Than Multijoint Exercise
What did the researchers investigate?
Unilateral dumbbell rows (multi-joint) versus biceps curls (single-joint) for elbow-flexor growth, in 10 untrained men, one arm each, for 8 weeks.
What did they find?
Curls produced more elbow-flexor growth than rows. Strength improved most in whichever exercise each arm trained.
What does this mean for training?
Compound lifts train helping muscles, but not as much as direct work does.
How does FitX AI use this evidence?
FitX AI counts a row as a full set for the back but only half a set for the biceps, and includes direct work for smaller muscles.
Where FitX AI's own choices go beyond this paper
Weekly sets per muscle. The bands (8-12, 12-16 or 16-20 sets) and the half-set counting are FitX AI choices; the research gives trends, not individual prescriptions.
Limitations
10 untrained men, one muscle group, 8 weeks.