In exercise science research, muscle groups deemed prime movers during multi-joint and single-joint exercises are classified the same from a set standpoint.[1] For example, one set of a lat pulldown is counted as one set when considering biceps brachii hypertrophy, and the same goes for one set of bench press when considering triceps brachii hypertrophy. Similarly, one set of a barbell back squat and one set of leg extensions are both counted as one set when examining quadriceps hypertrophy, although in the former, other muscles such as the gluteus maximus are heavily involved.
This information is critical for interpreting the results of meta-analyses on the relationship between volume and muscle hypertrophy, particularly for the limb muscles. One meta-analysis found that around 12–20 sets per muscle group per week is optimal for muscle growth; however, that should not be interpreted to mean 12–20 sets of single-joint biceps or triceps movements should be performed to maximize the growth of these muscle groups.[2] Rather, based on the studies included in the meta-analysis and how these studies calculated training volume, this set range implies a myriad of possible combinations of single-joint and multi-joint exercises (e.g., five sets of biceps curls, five sets of lat pulldowns, and five sets of cable rows, totaling 15 sets for the biceps per week).
There are good reasons, both biomechanically and physiologically, to suggest that single-joint exercises may be more effective for hypertrophy of the limb muscles than multi-joint exercises,[3][4] and as such, one set of an upper-body multi-joint exercise should count less toward the volume for the limb muscles than one set of a single-joint exercise. However, it’s difficult to pinpoint the precise amount of volume that should be assigned to multi-joint exercises due to differences in exercise selection (e.g., narrow vs. wide grip), training experience, and anatomical structure and mobility (which influences range of motion about a given joint and thus muscle activation).[5]
As a general rule of thumb, one set of a multi-joint press (i.e., bench press or shoulder press) can be counted as half a set for the triceps,[4][6][7][8] and the same can be said for a multi-joint pull (i.e., row or pulldown) and the biceps.[3][9][10]
Whether an individual chooses to count one set of an upper-body multi-joint exercise as one set or half a set toward the limb muscles is less important than being consistent with the method used to quantify training volume, although the latter may be more accurate in terms of the stimulus the limb muscles are receiving.