Answer:
His body is not as responsive to the level of exercise as it was initially
Step-by-step explanation:
The first change you can be aware of when doing exercise by the first time is that you are gonna start breathing faster, it is going to be even so difficult to breathe properly and you will also feel your pulse is high.
The first few weeks are so tough, but if you go along your body starts adapting to your workout and later you will feel that even doing the same routine you have no longer difficulty to do it. This happens because your body is already used to, then it's necessary to increase the level of difficulty in your daily workout. For doing this there are different ways, such as increasing the number of series, repetitions, increasing the weight and so on.