When you move your ankle or push off your toes, your calf muscle doesn't work across its full strength range. Instead, it only uses a specific part of its strength curve, and this part is different for most people, with most using the rising part of the curve and only a few using the falling or flat part.

When you move your ankle normally, your calf muscle gets stronger the more it stretches, instead of reaching a maximum strength and then getting weaker. This means your calf muscle is designed to keep producing more force the more it's pulled during everyday movements.

People's calf muscles don't all work the same way when you push off your toes. Because everyone's muscles behave differently, one-size-fits-all computer models might not accurately predict how each person's leg will move.

When you move your ankle from pointing your toes down to pulling them up, the main calf muscle gets longer and generates more force in a straight-line pattern. This shows that how your calf muscle is built and how much power it produces directly changes as your ankle joint bends.

Your calf muscle works best at bending your knee when your leg is completely straight, and it loses strength very quickly as you start to bend it. This means how well your calf can help bend your knee depends entirely on the exact angle of your knee joint.

When you move your ankle, the tiny contractile units in your calf muscle stretch to a length that isn't quite ideal for producing maximum strength. This means your calf might not be able to generate its full potential force during normal ankle movements because of how the muscle fibers are stretched.