SPECIAL COMMUNICATIONS: Letters to the Editor-in-Chief
Munn and colleagues (3) investigated the effects of the number of sets and movement velocity (contraction speed) for an exercise on strength. Munn et al. randomized 115 previously untrained participants (21 male, 94 female) to a nontreated control group or one of four treatments. The treatment groups trained elbow flexion three times per week for 18 sessions over 6-7 wk. One group trained with 1 set with a 6-8 RM of "slow" repetitions (∼3 s concentric, ∼3 s eccentric) while a second group used the same protocol for 3 sets. A third group trained with 1 set with a 6-8 RM of "fast" repetitions (∼1 s concentric, ∼1 s eccentric) while a fourth group used the same protocol for 3 sets.
Based on the data reported in their Table 1 (p. 1624) and linear regression analyses reported in Table 2 (p. 1625), Munn et al. indicated that compared with the control group, the 1-set slow group increased strength by 25%. The groups training with three sets increased strength by 48%. Munn et al. reported that fast training increased strength by 11% compared with slow training.
The data from Munn et al.'s Figure 2 (p. 1624) suggest more cautious interpretations. Figure 2 showed the distribution of strength change scores in each group. There clearly are outliers; that is, high responders. The data indicated that the 1-set fast group with three outliers, the 3-set slow group with two outliers, and the 3-set fast group with two outliers had more outliers than the 1-set slow group with one outlier. Eliminating the outliers, including one inexplicably in the control group, resulted in the following absolute change in each group compared with the control group: 1-set slow, ∼1.28 kg, 1-set fast, ∼1.62 kg; 3-set slow, ∼1.94 kg; and 3-set fast, ∼2.15 kg. The percentage changes (change kg/pretraining kg) for each group are 1-set slow,∼24%; 1-set fast, ∼28%; 3-set slow, ∼34%; and 3-set fast, ∼38%. Without the outliers, the absolute mean changes, the percentage changes, and the absolute differences between the 1-set slow group and the three other training groups are smaller, albeit with smaller group SDs.
Despite randomization, the 1-set slow group had fewer high responders than the other training groups. Strength increases and muscular hypertrophy with resistance training show considerable variation that is most likely attributable to genetic factors (2).
Munn et al. found that all four training groups showed a small increase in biceps circumference. Referring to a prior study by Hass et al. (1), they noted that an increase in biceps circumference was only found when the study participants trained with 3 sets compared to 1 set. Hass et al. reported that both 1-set and 3-set training groups showed within group changes in body composition with experienced trainees. While the within group patterns were different, there were no significant differences between groups.
Munn et al. concluded that 1 set with slow repetitions produces some favorable outcomes, but 3 sets of slow repetitions or training with fast repetitions produces superior outcomes. Their conclusions concerning 3 sets or fast training have minimal support.
Richard A. Winett, Ph.D.
Department of Psychology
1. Hass, C. J., L. Garzarella, D. De Hoyas, and M. L. Pollock. Single versus multiple sets in long-term recreational weightlifters. Med. Sci. Sports Exerc.
2. Hubal, M. T., H. G. Dressman, P. D. Thompson, et al. Variability in muscle size and strength gain under unilateral resistance training. Med. Sci. Sports Exerc.
3. Munn, J., R. D. Herbert, M. J. Hancock, and S. C. Gandevia. Resistance training for strength: effect of number of sets and contraction speed. Med. Sci. Sport Exerc.