When people train with their muscles stretched out, the longer their muscle fibers get, the more quickly they tire out during repeated efforts.

When people train with their muscles bunched up, the more their muscle fibers angle upward, the longer they can keep pushing hard before getting tired.

Doing 8 weeks of strength training with your muscle either stretched or bunched up doesn’t make you much better at resisting fatigue — the improvement is very small and not clearly real.

Doing strength exercises with your muscle stretched out for 8 weeks can make the muscle fibers longer, but doing them with your muscle bunched up doesn’t change their length.

After doing leg exercises with your knee bent all the way back, your muscles are weaker not just at that angle—but even more so when you try to use them with your knee only slightly bent, as if your muscle fibers got stretched out and lost their normal power.

If new guys lift weights for 15 weeks using only part of the movement—focusing on the shorter muscle position—they build more muscle size in that specific area and get stronger at certain joint angles, according to this claim.