Study design: Pretest-posttest, single factor design.
Objectives: To compare several indices that might be used to depict muscle size.
Background: The particular strategy used during heavy-resistance training may determine the magnitude of hypertrophic adaptations. At the same time, assorted measures supposedly reflecting muscle size may provide different results.
Methods and measures: Four groups of men (n = 38, mean age = 21.1 years, SD = 2.1) were exposed to conditions designed to elicit differential hypertrophic adaptations following 21 sessions of squat training. Three of the groups performed 4 sets of multiple repetitions maximum (RM): group I, 3-5 RM; group II, 13-15 RM; and group III, 23-25 RM. A control (C) group did no formal physical training. Tests used to represent muscle size included body weight, thigh girth, net thigh girth, and quadriceps femoris and hamstring thicknesses via B-mode ultrasound.
Results: Changes in the groups subsequent to training were similar for body weight and hamstring thickness. Results differed for the remaining 3 dependent variables (mean +/- SD): thigh girth was greater in groups II (1.42 +/- 1.00) and III (1.35 +/- 1.16) than in group C (0.24 +/- 0.69); net thigh girth was greater in groups II (1.33 +/- 0.77) and III (1.40 +/- 1.03) than in group C (0.10 +/- 0.84); and quadriceps femoris thickness was greater in all 3 training groups (I, 0.61 +/- 0.54; II, 0.43 +/- 0.30; III, 0.55 +/- 0.39) than in group C (0.05 +/- 0.11).
Conclusions: Observed muscle mass change following heavy-resistance training is dependent upon both the training intervention and tool used for measurement.