There is a lot more to marching band than just walking and playing an instrument. There is physics involved, just like any other sport. There is a lot of force that happens with marching band. Whether determining how far to push out your leg in order to meet the tempo. It could also be how hard to blow or how hard to beat the sticks on the drum in order to get the right amount of energy to get the right dynamic or the right sound. It could also be the body movement of the marching band show. You need to determine whether you should just flail your arms out to form an arc or should you gently and slowly move your arm into an arc.