How much is this actually helping you?
Research obviously shows that exercise does wonders for alleviating stress. But research also shows that if you are forced to do something you don't want to do (actually, this also works of you're forced to do something you do want to do as well) then the resultant stress can negate any of the positive effects that the activity might have had.
The Helpless Mouse
In one study, they had two mice exercising in different running wheels, in different cages. Mouse one (let's call him Voluntary Mouse) was subjected to various stimuli that the researches know induces stress related illness in these rodents - annoying sounds, flashing lights, cats circling the cage - that sort of thing. Now, if Voluntary Mouse is supplied with a running wheel and allowed to use it whenever he wants, the exercise almost completely deletes all of the stress related illness and response that mice usually get in these situations.
But let's take a look at what happens in the second cage, with Mouse Two (let's call him Involuntary Mouse). Involuntary Mouse is 'yoked' to his friend, Voluntary Mouse. What this means is that whenever Voluntary Mouse runs on the wheel, Involuntary Mouse is forced to run on his own wheel as well. Involuntary Mouse is effectively trapped in the wheel, and when Voluntary Mouse starts running, Involuntary Mouse's wheel also starts spinning, forcing him to run as well.
What happens to Involuntary Mouse? He gets stress related illness and symptoms - even though he is not experiencing the stress inducing stimuli (the lights, noise, cats) that is happening in the other cage. In other words, Involuntary Mouse, gets the stress related reactions simply because he is forced to do something - even though that something would otherwise be good for him (incidentally, mice actually love running on these wheels, so in any other circumstance, Involuntary Mouse would be happy).
The message is pretty clear: stress-reducing activities are really only completely beneficial, when we do them voluntarily, when we aren't forced to do them and they are most effective when we actually like doing them. If you hate boot camp, then maybe tennis is more appealing.
Whatever you are doing to de-stress, you'd better like it.... and if you don't, then find something else that still fits the bill.