Effects of rest intervals and training loads on metabolic stress and muscle hypertrophy.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 28032435 · doi:10.1111/cpf.12409
What was done
Twenty subjects were assigned to 8 weeks of volume-matched resistance training under one of two protocols: short rest (30 seconds) combined with low load (20 RM) (SL group, n=10) or long rest (3 minutes) combined with high load (8 RM) (LH group, n=10). Upper arm cross-sectional area (CSA) was assessed before and after the 8-week intervention using magnetic resonance imaging (MRI). Acute responses of growth hormone (GH) and muscle thickness (MT) were measured before and immediately after a single resistance training session.
What was found
Immediately following a single session, only the SL group demonstrated significant increases in GH (7704.20 ± 11833.49%, P < 0.05) and MT (35.2 ± 16.9%, P < 0.05). After 8 weeks, upper arm CSA increased significantly in both groups: 9.93 ± 4.86% in the SL group (P < 0.001) and 4.73 ± 3.01% in the LH group (P < 0.05). No significant correlation was observed between acute GH elevations and long-term CSA increases. Numeric strength values were not reported in the abstract.
Why it matters
These findings suggest that low-load resistance training combined with short rest intervals can stimulate substantial muscle hypertrophy, while reinforcing that transient exercise-induced growth hormone spikes do not correlate with long-term muscle growth.
Limits
The sample size is very small (n=20 total, 10 per group). Acute hormone measures exhibited extreme variance. The abstract does not report participant demographics, baseline training status, or quantitative strength data.