Bill Robertson: Which physical activity uses your heart the most? Which activity increases your stamina levels the most? Which area of the abdominals does rowing target (upper or lower)?Terry O'Neill: You have to qualify what you mean when you start to compare different forms of exercise. Running is the easiest and most natural and there are no skills to be mastered. Because you are upright you will achieve a higher maximum heart rate. However, for a lot of people running is not an option because of weight or joint problems. It's not just the exercise but the amount of time you can carry out the exercise, so although running is a good way to exercise, you may be better off doing something else. There are three other main options that are non-impact and non-load bearing - swimming, cycling and rowing. Cycling will result in a higher maximum heart rate than the other two mainly because the body position is almost vertical and rowing will have a higher rate than swimming.Rowing involves more major muscle groups than the others and is more balanced in terms of physical development. The lower abdominals are used towards the end of the stroke when the body swings back and recovers and the upper abdominals are used throughout the stroke by the action of the diaphragm taking in large quantities of air.