Background: The resistance training promotes hypertrophy and muscular strength, from mechanical, metabolic and hormonal processes. The execution speed of movement during the
resistance training is a variable that can influence the effectiveness of the training. However, it is not clear the effects of different speeds on the muscular strength and hypertrophy associated
with isotonic resistance training. Therefore, the present study aimed to compare both fast and slow speed of isotonic resistance training on muscular strength and hypertrophy in subjects with
experience in resistance training.
Methods: Twelve healthy adults were randomly divided into two groups, the Fast Speed (FS) or Slow Speed (SS) group. The FS group performed the resistance training performing the
concentric and eccentric repetitions at a maximum speed, and the SS group performed the resistance training performing the repetitions at a controlled speed. Before the beginning of the resistance
training all subjects performed an ultrasound examination of the biceps brachial to check the cross-sectional area and underwent tests of 1 repetition maximum (1RM). The training lasted 12 weeks of
resistance training of Scott curl exercise and the subjects were told to perform 3 sets of 8 repetition maximum, totaling 6 series per week. After 12 weeks of training volunteers were again subjected
to an ultrasound of the biceps brachial and remade the 1 RM tests. To check the possible differences in strength and hypertrophy among times and between the groups it was used two-way ANOVA for
repeated measurements. The effect size (ES) was calculated for the 1RM test and cross-sectional area of the biceps brachial muscle.
Results: The General features of the FS and SS groups demonstrated no significant differences (P≥0.05) between groups before the start of training. When comparing the pre/post
training times and between the groups, was verified in the SS group, significant difference between pre and post training moments in the cross-sectional area (P=0.019) and muscular strength (P=0.021).
The ES was greater for the SS group than FS group. The SS group presented great magnitude in the 1RM test (ES = 2.19) and moderate magnitude for the cross-sectional area (1.43).
Conclusions: In summary, no significant differences were found between the groups for hypertrophy and muscular strength. However, the effect size for the resistance training with SS
is greater than the resistance training with FS, pointing to a possible greater effectiveness of slow muscular actions for the induction of muscular strength and hypertrophy. In future studies, it
would be interesting to analyze the metabolic adaptations and degree of muscular activation promoted by different speeds of implementation of resistance training.