Obviously, neither one has a weight-loss advantage. If Uncle Leo slowed his pace down just a little bit, he would still be working at a challenging pace, but he could probably maintain it for close to 30 minutes. Exercise intensity is an individual kind of thing-don't go comparing your pace to anyone else's. Pain is an indication that you're working too hard, and there's plenty to gain from comfortable exercise. For those of you who think you have to sweat to get a good workout, think again.
Sweat is a body coolant, plain and simple.
It has nothing to do with the quality of your exercise. An intense jog in the Arctic while wearing nothing but a bathing suit probably won't produce a lot of sweat, but you may still be getting plenty of good exercise. Likewise, simply standing in line at an amusement park in the summer sun could cause you to break a sweat, but you're hardly getting any exercise. There are a number of good ways to measure your exercise intensity, from the scientific to the subjective. This test measures the quantity of oxygen that the cells of your body are consuming during exercise.