ABSTRACT

　The triceps brachii long head （TBL） is a biarticular muscle that crosses the shoulder and elbow joints, and therefore its length is influenced by the position（angle） of each of these two joints. With this background of the biarticular nature of the TBL, this study examined the effect of muscle length during resistance training on muscle hypertrophy, by comparing two elbow extension training regimes performed at different, otherwise identical, shoulder joint positions. Using a cable machine, 21 healthy young adults conducted dynamic elbow extension （range of motion: 90-0ﾟ） training, with the shoulder joint of one side fixed at 180ﾟ flexion and the other at 0ﾟ （i.e. the elbow facing upwards and downwards, respectively）， whereby the TBL was in a long （L）and short （S） length condition, respectively. The training was performed with the load of 70% of one-repetition maximum, 10 reps/set, 5 sets/session, 2 sessions/week, for 12 weeks. After the intervention, MRI-based cross-sectional area （CSA） of the total triceps brachii （the sum of the three muscles）significantly increased in both conditions, with a greater degree for the L （23%） than S （16%）．On an individual muscle basis, the CSA significantly increased in all muscles for both conditions, with a significant difference in the degree between conditions only found in the TBL （L: 33% vs S: 21%） and not in the other two （monoarticular） muscles. These results suggest that the muscle hypertrophic effect of resistance training can be enhanced by conducting training at a long muscle length position.

DECENTE SPORTS SCIENCE Vol.41/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE