Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position

Abstract

The biarticular triceps brachii long head (TB_Long) is lengthened more in the overhead than neutral arm position. We compared triceps brachii hypertrophy after elbow extension training performed in the overhead vs. neutral arm position. Using a cable machine, 21 adults conducted elbow extensions (90−0°) with one arm in the overhead (Overhead-Arm) and the other arm in the neutral (Neutral-Arm) position at 70% one-repetition maximum (1RM), 10 reps/set, 5 sets/session, 2 sessions/week for 12 weeks. Training load was gradually increased (+5% 1RM/session) when the preceding session was completed without repetition failure. 1RM of the assigned condition and MRI-measured muscle volume of the TB_Long, monoarticular lateral and medial heads (TB_Lat+Med), and whole triceps brachii (Whole-TB) were assessed pre- and post-training. Training load and 1RM increased in both arms similarly (+62−71% at post, P = 0.285), while their absolute values/weights were always lower in Overhead-Arm (-34−39%, P < 0.001). Changes in muscle volume in Overhead-Arm compared to Neutral-Arm were 1.5-fold greater for the TB_Long (+28.5% vs. +19.6%, Cohen's d = 0.61, P < 0.001), 1.4-fold greater for the TB_Lat+Med (+14.6% vs. +10.5%, d = 0.39, P = 0.002), and 1.4-fold greater for the Whole-TB (+19.9% vs. +13.9%, d = 0.54, P < 0.001). In conclusion, triceps brachii hypertrophy was substantially greater after elbow extension training performed in the overhead versus neutral arm position, even with lower absolute loads used during the training.