Loaded inter-set stretch may selectively enhance muscular adaptations of the plantar flexors.
Level 2 - randomized trial
Individual randomized within-subject trial
PubMed 36048793 · doi:10.1371/journal.pone.0273451
What was done
Twenty-one young, healthy men underwent an 8-week resistance training program performing calf raises (plantar flexion) twice weekly. In a randomized within-subject design, one leg performed traditional resistance training with passive rest between sets (TRAD), while the contralateral leg received the same training protocol combined with a 20-second loaded inter-set stretch (STRETCH). Outcomes evaluated were muscle thickness of the lateral gastrocnemius (LG), medial gastrocnemius (MG), and soleus (SOL), as well as isometric strength of the plantar flexors.
What was found
STRETCH showed a potential hypertrophic advantage over TRAD for the soleus (mean difference 0.7 mm, 90% CI: 0 to 1.6 mm). Differences were ambiguous for the lateral gastrocnemius (0.4 mm, 90% CI: -0.4 to 1.3 mm) and equivocal for the medial gastrocnemius (0.0 mm, 90% CI: -0.6 to 0.7 mm). Standardized growth across legs was higher for LG (z = 1.1, 90% CI: 1.0 to 1.3) than for MG (z = 0.3, 90% CI: 0.2 to 0.5) and SOL (z = 0.3, 90% CI: 0.2 to 0.5). Isometric strength showed a modest advantage favoring STRETCH, though specific numerical values were not provided in the abstract.
Why it matters
This trial suggests that incorporating loaded stretching between sets can selectively enhance hypertrophy in the soleus without clear added benefit for the gastrocnemius muscles.
Limits
The sample was small (n = 21) and restricted entirely to young, healthy men. The 90% confidence intervals for muscle thickness changes were wide and crossed or touched zero. Specific numerical values and confidence intervals for the isometric strength measurements were not reported in the abstract.
Cited by
- supports A 20-second loaded interset stretch between sets of calf raises promoted greater hypertrophy in the soleus muscle, with no substantial difference in the gastrocnemius.