TI and exercise - naive question?

[KarenK]

I've just begun practicing TI and find that - because of all the amazing efficiencies gained - I am not tired even after swimming for an hour. This would be great if my main interests were speed, preserving energy, and the exquisite feel of swimming like a fish. However, the reality is that a primary reason I swim is for exercise. In other words, I want a work out in which I burn calories and strengthen muscles.

Is TI less effective for this purpose than traditional, inefficient swimming where you pull with your arms and kick hard with your legs? I tried to find the answer to this in the freestyle forum posts, but had no luck. Thanks.