Author(s): NOSAKA, K., YOSHIDA, R.1, MURAKAMI, Y.2, KASAHARA, K.2, SATO, S.3, NAKAMURA, M.4 , Institution: EDITH COWAN UNIVERSITY, Country: AUSTRALIA, Abstract-ID: 380

INTRODUCTION:
We reported that one 3-s maximal eccentric contraction of the elbow flexors performed on an isokinetic dynamometer 5 days a week for 4 weeks increased maximal voluntary isometric (MVC-ISO), concentric (MVC-CON), and eccentric contraction (MVC-ECC) torque of the elbow flexors by 10.2±6.4%, 12.8±9.6% and 12.2±7.8%, respectively [Sato et al. Scand J Med Sci Sports. 32:833-43, 2022]. However, these effects were not produced by one 3-s maximal isometric nor concentric contraction in the same format. Our other study showed that daily six maximal eccentric contractions that were performed on an isokinetic dynamometer 5 days a week for 4 weeks increased MVC-ISO (9.3±5.5%), MVC-CON (11.1±7.4%), and MVC-ECC torque of the elbow flexors (13.5±11.5%), and muscle thickness (MT) of biceps brachii and brachialis (10.4±4.4%) [Yoshida et al. Scand J Med Sci Sports. 32:1602-14, 2022.]. To perform maximal eccentric contraction(s), a specific device such as an isokinetic dynamometer is necessary, which is difficult to be accessed practically. The present study examined whether the muscle strength and MT would still be increased when a dumbbell was used with the training intensity of six eccentric contractions being reduced to 2/3 or 1/3 of the peak MVC-ECC torque.
METHODS:
Thirty-six healthy young (19-24 y) adults who had not performed resistance training were placed to three groups (n=12/group): 2/3MVC or 1/3MVC that performed the six eccentric contractions with a dumbbell set at 2/3 or 1/3 MVC-ECC load 5 days a week or control group that did not perform any training for 4 weeks. Changes in MVC-ISO, MVC-CON, MVC-ECC torque of the elbow flexors, and MT before and after the 4-week period were compared among the groups and with the group of the previous study [Yoshida et al. Scand J Med Sci Sports. 2022.] in which six maximal eccentric contractions were performed 5 days a week for 4 weeks (MVC group; n=12) by two-way repeated measured ANOVA.
RESULTS:
All participants reported to the laboratory to perform the training without any missing sessions. The control and 1/3MVC groups showed no significant changes in any measures. Significant (p<0.05) increases in MVC-ISO (10.3±11.4%), MVC-CON (10.9±9.5%), and MVC-ECC (9.3±8.8%) torque and MT (10.1±9.2%) were observed for the 2/3MVC group. When comparing the 2/3 MVC and MVC groups, no significant differences in the changes in the measures were found. This may be due to that the dumbbell set at 2/3 of MVC-ECC torque was close to the MVC-ECC at elbow extended angles.
CONCLUSION:
These results suggest that submaximal-intensity at 2/3 MVC-ECC is still effective for the six maximal eccentric contractions to increase muscle strength and MT, and the “submaximal” intensity using a dumbbell produced the same effects as those by maximal intensity protocol using an isokinetic dynamometer. The present study together with the previous studies show potent effects of daily small volume eccentric contractions on muscle adaptations, which could be used in practice.