Answer:
If he has managed to meet his target heart rate, he should be able to maintain his current intensity, taking into account if he does not have a heart defect or was working harder in a shorter period of time to meet his target heart rate.
If there was any other choice you could choose from, it would be to decrease his intensity level, but I would choose to have him maintain.
Explanation:
Stopping a workout immediately can be detrimental to a person if there is no serious reason as to why (heart attack, inability to breathe, etc.) as you body needs time to cool down. Stopping immediately may cause cramps and circulation issues.
Increasing his workout intensity may cause him to go over his target heart rate. This could make Demetri uncomfortable and to prone to excessive soreness and exhaustion.
