Holding a muscle stretched while pushing against something still makes it grow more than holding it short, even if you don’t move.
Evidence from Studies
Supporting (1)
Community contributions welcome
Differential changes in muscle architecture and neuromuscular fatigability induced by isometric resistance training at short and long muscle-tendon unit lengths.
This study found that doing muscle exercises while the muscle is stretched out (long length) made the muscle fibers grow longer, which usually means the muscle is getting bigger — while exercises done with the muscle shortened didn’t have the same effect.
Contradicting (2)
Community contributions welcome
The study found that doing isometric exercises with the hamstrings stretched out (long length) and bent (short length) both made the muscles grow just as much — so stretching more doesn’t give you bigger muscles in this case.
Does Muscle Length Influence Regional Hypertrophy? A Systematic Review and Meta-Analysis
The study found that training muscles at longer or shorter lengths doesn’t make a big difference in muscle growth — so stretching your muscle more during a static hold doesn’t help you grow bigger muscles any more than keeping it short.