The benefits of regular exercise are very well known:  it boosts the immune system and brain function, and improves mood and heart function.  Many people go to a gym to jog on a treadmill, or do aerobic exercises that are low-intensity but do them for a relatively long period of time.
The lowdown on low-intensity workouts
But lately there?s been a debate about whether this is a good practice. Some people believe that low-intensity exercise for a relatively long period of time doesn’t do any good. Their rationale is: in the animal kingdom, there is no such thing as low-intensity, sustained exercise (have you ever seen a monkey in a gym?). They believe that the problem with low-intensity exercise is that it doesn’t raise the metabolic rate very much. If you want to raise your metabolic rate significantly, you need to have a high-intensity exercise for a short period of time–like animals do. They chase their prey in short bursts of time and then enjoy the meal and rest for the remainder of the day. Could it be applied to humans?
High intensity equals high risk
There?s some proof that high-intensity, short-term exercise appears to be better for your body than low-intensity, extended periods of exercise (http://online.wsj.com/article/SB10001424127887323689604578221730011383620.html?mod=djemHL_t). And according to some researchers, the metabolic rate is going much higher with high-intensity exercise than with low-intensity exercise. High-intensity, short periods of exercise looks attractive to many doctors and patients, and many doctors and patients opt for this type of exercise.
But I don?t recommend this type of exercise to my patients even though I am very well aware of benefits of it.
The reason is very simple: high-intensity, short periods of exercise may be good for a perfectly healthy person. But how can anyone be sure that he’s perfectly healthy? Even athletes die while exercising at high-intensity levels.  According to some research the risk of adverse events secondary to exercise in presumably health athletes is underestimated (http://eurheartj.oxfordjournals.org/content/29/15/1903).
Finding a happy medium
In my opinion, it?s not worth risking your life for the benefits of having a high base metabolic rate.  It?s like sticking with a Paleolithic diet while having digestive problems. The diet is good?but it?s not for everyone.
On the other hand, low-intensity, long periods of exercise may put too much burden on your body. For instance, jogging for many miles may put too much pressure on your hips knees and ankles.
So what?s the solution?
MY THOUGHTS ABOUT EXERCISE CAUTION:
Move naturally rather than stick to certain exercises.
Make sure that you enjoy what you are doing.
Opt for your chores rather than gym.
Remember that s.e.x. is an exercise too.  What would you prefer:  running a treadmill or having s.e.x.?  Wouldn?t you opt for the latter?
Do not make any health decisions without consulting with your doctor.  For some people even such small exercise like s.e.x. is not an option.
Good luck!