When men who don't usually exercise start lifting weights, the angle of their muscle fibers changes by about 9% in 12 weeks. It doesn't matter if they lift heavy or light weights, or if they push until they can't do any more reps or not.

After doing 12 weeks of static strength exercises, whether your quadriceps muscle fibers change their angle doesn’t seem to affect how much stronger you get.

Doing strength exercises with your muscle bunched up for 8 weeks can make the muscle fibers angle more sharply, which might help them generate more force.

Whether you use machines that change resistance as you lift or keep the same weight all the way through, after 20 weeks of training, healthy men gain about the same strength and muscle size either way.

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.

Using machines or bands that change how hard they feel as you move might make your muscles work more evenly during an exercise, but that doesn’t always mean you’ll grow bigger muscles faster than with regular weights—especially if you’re just starting out.