The dog that is being trained needs to feel normal, i.e., be in good shape, according to the trainer’s evaluation.
Do as follows:
Stage 1: Is my dog okay?
Examine what shape your dog is in at that moment and evaluate if everything is okay. Is he eating normally? Is he standing or moving in a way typical to him? Is your dog healthy and eager to learn new things? If you’re not entirely sure that your dog is okay or you suspect that he’s ill, turn to a vet or some other professional for help.
Stage 2: Take your dog out and do a warm up if necessary
Go for a little walk before training so that your dog is able to relieve himself. If your training is physically demanding, do a warm up before training, just like an elite athlete would. A good warm up is about 20 minutes long, and includes small spurts and bends.