There is a condition described as Delayed Onset Muscle Soreness (DOMS). In most cases this is not a problem rather a normal process in building up muscle and fitness or after a differentiation in exercise. As with us, the muscles lack in strength for the next couple of days.
Tip 3 – Giving a couple of days rest allows the tissues to regenerate and repair. My recommendation is to work lightly the day after extremely intense work, then give your horse a days break.