The same reason you do, to move and be strong.
To swim.
Big muscles
Frogs need a strong layer of muscles to help them move and jump efficiently. The muscles in their limbs and body provide the strength and power needed for these movements. Additionally, the strong muscles support the frog's body structure and allow it to maintain its posture and balance.
the neck and head, because their neck muscles can't support their head.
muscles
The best way to keep your muscles strong and working efficiently is through exercises. Diet also plays an important role in keeping muscles healthy and efficient.
For girls lacrosse, you need to be fast and able to keep up with the ball wherever it goes. You need to be fit enough that you don't run out of breathe to easily, and you need to have strong arm muscles for throwing and strong leg muscles for running.
To form an attachment for the swim muscles.
If muscles are not properly fueled with the proteins and nutrients they need to be strong and health they will be more apt to tear, rip, and weaken.
very very strong they need SO much muscle to run at top speed
So they can go faster!