What data are available? (Part two)

The following six studies have assessed the effects of training volume in strength-trained lifters. Here they are in order of appearance.

Ostrowski (1997) — assessed the effects of body part split training on changes in rectus femoris and triceps brachii muscle size. The intent of the researchers was to use 1, 2, and 4 sets per exercise, and 3 exercises per muscle group, to compare the effects of 3, 6, and 12 sets per workout (and per week). Yet, the use of only one exercise for the rectus femoris in the leg workout (squats and leg presses probably don’t work this muscle) resulted in that comparison being between 1, 2, and 4 sets per workout (and per week). The use of 3 triceps exercises in the arm workout and 4 in the chest/shoulders workout resulted in that comparison being between 7, 14, and 28 sets per week, albeit across 2 workouts. While there were no significant effects of training volume, rectus femoris size seemed to increase more after 4 sets per week than after 1 or 2 sets per week. Triceps muscle size increases were similar after 14 and 28 sets per week, indicating that a plateau was reached somewhere between those volumes.

Radaelli (2015) — assessed the effects of full body training, 3 times a week, on changes in biceps brachii and triceps brachii muscle size. Either 1, 3, or 5 sets were done for each exercise. Two exercises were done in each workout for the biceps, and three for the triceps. Thus, the number of sets per muscle group was 2, 6, or 10 per workout (6, 18, or 30 per week) for the biceps, and 3, 9, or 15 per workout (9, 27, or 45 per week) for the triceps. Increases in biceps and triceps muscle sizes were progressively greater with increasing volumes, with no obvious plateau.

Schoenfeld (2018) — assessed the effects of full body training, 3 times a week, on changes in biceps brachii, triceps brachii and leg muscle size. Either 1, 3, or 5 sets were done for each exercise. Two exercises were done in each workout for each arm muscle, and 3 for the leg muscles. Thus, the number of sets per muscle group was 2, 6, or 10 per workout (6, 18, or 30 per week) for each arm muscle, and 3, 9, or 15 per workout (9, 27, or 45 per week) for the legs. Increases in biceps and leg muscle sizes were progressively greater with increasing volumes, with no obvious plateau. Although not significant, the increases in triceps size showed the same pattern.

Heaselgrave (2018) — assessed the effects of training with either one or two workouts per week on increases in biceps brachii muscle size. One group did 1 workout per week with 3 sets of 3 exercises (9 sets per workout and per week). Another group did 2 of the same workout (9 sets per workout and 18 sets per week). A third group did 2 workouts with 4–5 sets per exercise, for a (13–14 sets per workout and 27 sets per week). While not taken to failure, each set was done with 2 repetitions in reserve (RIR). While not significant, the increases in biceps muscle size were greatest after 18 sets a week.

Barbalho (2019, March) — assessed the effects of training using a body part split routine on changes in biceps brachii, triceps brachii, pectoralis major, quadriceps, and gluteus maximus muscle size. Each body part was trained once per week. Depending on their group, subjects did either 5, 10, 15, or 20 total sets per workout (either 2, 4, 5, or 7 sets each on the first 2 exercises, and either 1, 2, 5 or 6 sets for the third exercise in the workout). Exercise selection was such that some of the muscles were indeed trained with 5, 10, 15, or 20 sets per workout (and per week), but others were only trained with 4, 8, 10, or 14 sets per workout (and per week). Even so, there was a clear plateau in the gains achieved above 4–5 sets per workout (and per week), and in fact the gains in size were greater after training using 5 or 10 total sets per workout than after training with 15 or 20 total sets per workout.

Barbalho (2019, June) — this study was the same in design as the one above, and there was again a clear plateau in the gains in muscle size that were achieved above 4–5 sets per workout (and per week). In this study, muscle size was measured at two time points. The two higher volume groups (15 and 20 sets per workout and per week) tended to display reductions in muscle size in the latter half of the study period. In contrast, the lower volume groups (5 and 10 sets per workout and per week) did not.

These results all seem very contradictory, so what does this all mean?