Looks like LocalFluff also talked about centrifuges. Here's my take, which is on similar lines.
It would be limiting for individuals to allow their physiology to weaken from lack of gravity (as long as a return trip to a higher gravity at a later date was possible or desired). It may be ok to let the plants and animals adapt, however, which reduces the scope of the problem to maintaining the health of human beings.
Carnival rides on Earth can create higher than earth gravity effects. NASA is already looking into applications of this.
One possible solution for a colony on a lower mass planet like Mars, where there is some gravity but it is still weaker than earth, is to provide centrifuge style exercise areas as big as ferris wheels that spin constantly (except for planned maintenance or no-use time periods).
A pod (that traces an identical circular path) could be spun up to speed to match the centrifuge and docked magnetically. The people inside the pod could be spun up to speed, dock, jog for an hour or lift weights or do squats, then get back in the pod and go home. All this, of course, would need to be refined a fair amount for safety and convenience. However, as long as the centrifuge had a ceiling that was no higher than, say, 12 feet, a person could safely fall to the "ceiling" in the event that the centrifuge lost power (due to the lighter gravity making a fall like this safer than it would be on Earth).
I would imagine that the exercise chamber, if designed like a ferris wheel, would have highest gs when a person standing still has their feet pointed at the Martian ground and the least gs when their feet point toward the Martian sky. So it would require an adjustment period so that people don't injure themselves by miscalculating the amount of gravity at any one moment (i.e. landing too hard). This assumes the exercise chamber doesn't have smart enough motor programming to speed up and slow down to manage the changing gravity.
That would help solve the problem of the whole-body effects of gravity, unlike wearing ankle weights. You could even choose your amount of gravity to be a little higher than earth if that would reduce the time needed for a person to stay strong.
Another NASA article on their explorations with centrifuges.