Adaptation of Muscles With Different Physiological Properties to Resistance Training With and Without Bloodflow Restriction

Background: Low-load bloodflow-restricted (BFR) resistance training (LLBFR-RT) has been shown to elicit muscular hypertrophy comparable with high-load resistance training (HL-RT). We aimed to explore the differential impact of LLBFR-RT and HL-RT on hypertrophy of the triceps surae. Hypothesis: LLBFR-RT would be more effective than HL-RT for soleus muscle hypertrophy. In addition, it was hypothesized that HL-RT would be more effective than LLBFR-RT for the hypertrophy of both gastrocnemii. Study Design: An active controlled trial. Level of Evidence: Level 2. Methods: A total of 28 healthy adults were assigned randomly to 2 unilateral plantar-flexion training regimens: HL-RT (75% of 1-repetition maximum [1RM], 4 sets, 10 repetitions) and LLBFR-RT (20% of 1RM, 4 sets, 30+15+15+15 repetitions). Maximal voluntary isometric contractions (MVIC), 1RM, and panoramic ultrasound assessments of the triceps surae were obtained pre- as well and post-4 weeks of intervention (5 sessions per week). Results: MVIC and 1RM improved statistically from pre- to post-training ( P < 0.05), and this occurred similarly between interventions (gains of ~20% to 30%). Both regimens were similarly effective for the hypertrophy of the soleus muscle (gains of ~12% to 15%). Conversely, the lateral gastrocnemius only responded to HL-RT (gains of ~12%; P < 0.05 vs 4% with LLBFR-RT), and the medial gastrocnemius did not manifest statistical changes with either training regimen. Conclusion: HL-RT is more effective for eliciting size gains in the lateral gastrocnemius (muscle with a mixed fiber type composition) over a period of high-frequency training. The soleus (muscle with predominant oxidative fibers) adapts to both training regimens in a similar fashion. Clinical Relevance: High-frequency plantar-flexion exercise with HL-RT (5 days per week) is preferable to LLBFR-RT when aiming to elicit plantar-flexor strength gains accompanied by more comprehensive hypertrophy of the triceps surae muscle.