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.

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.

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

Lifting weights until you can't do another rep leaves you much more tired during and after the workout than stopping a few reps short — even if both methods build muscle equally.

If you lift weights until you can't do another rep, or stop just before failure, your thigh muscles grow about the same amount after eight weeks — but stopping short feels less exhausting each time.

If you do leg exercises with your knee only slightly bent, your muscles stay strong at that angle—even right after the workout—but if you do them with your knee fully bent, your muscles get weaker at that angle and also at other angles.