Comparison between concentric-eccentric and concentric-only plantar flexor exercise training with body weight for changes in muscle strength, range of motion, and muscle architecture.

Purpose: The present study tested the hypothesis that inclusion of prolonged eccentric (lengthening muscle) contractions would increase muscle adaptations greater than concentric-only contractions.

Methods: Fifteen sedentary men (20-21 years) underwent 16 resistance exercise sessions in 8 weeks (twice a week) using their body weight. They used two legs to raise heels in 1 s (concentric-only plantar flexions: CON) and used only one leg to lower the heel in 3 s (concentric-eccentric plantar flexions: CON-ECC). The number of contractions was 5 or 10 in a set and was increased gradually from 5 to 70 repetitions a session over 16 sessions. In addition, 10 participants (19-24 years) were recruited as a control group without resistance exercise. Outcome measures consisted of maximal voluntary isometric contraction (MVIC) torque of plantar flexors, triceps surae muscle thickness (MT) and architecture, and dorsiflexion range of motion (ROM) measured at baseline and 3-5 days after the last training session or with an 8-week interval (control group). Changes in the measures were compared between legs by a split-plot analysis of variance.

Results: No significant differences between legs were evident at baseline for the measures between legs as well as the leg in the control group. The CON-ECC leg showed increases (P < 0.05) in MVIC torque (32.9 ± 25.0%), MT (9.1 ± 7.0%), and ROM (30.4 ± 31.8%), but no such increases were evident for the CON leg and the leg in the control group.

Conclusion: These results supported the hypothesis and showed that inserting eccentric contractions in the resistance exercise were critical to maximize muscle adaptations.