When you work out, different parts of the same muscle can grow at different rates. Some exercises might make the far ends of your muscles grow more than the middle parts.

Your muscles grow bigger not because of just one thing like lifting heavy weights or doing lots of reps, but because of how all the workout factors—like how hard you push, how often you train, and how well you recover—work together.

Muscle hypertrophic responses to training at different lengths may vary across muscle groups due to differences in architecture, biarticulation, and sarcomere number.

If you're already strength training, doing more sets and reps doesn't always mean your arms and shoulders will grow much bigger—other things like rest, diet, and genetics also play a big role.

Total training volume, training intensity, and consistency are more significant determinants of muscle hypertrophy than the specific muscle length at which training occurs.

Lifting weights makes your muscles bigger, and the main reason is how much total work you do—like how heavy the weights are, how many sets and reps you do, and how long you hold the tension. More total work = bigger muscles.