One of the questions that comes up as people get further along in their own exercise programs is the relative merits of doing strength training two versus three days a week. There is no right or wrong answer to this. It’s purely a question of what you are looking to get out of your fitness program. As long as you stick with six days a week, either one is fine, but they will leave you with mildly different benefits.

The key thing to remember about strength training is that, done right, it exhausts your muscles to the point where you need a full day off between strength training sessions. So if you are going to do three days a week make sure they are alternate days and not consecutive days. If you enjoy the strength training more than the aerobic training, or if you want to focus on strength for other reasons -- say, an upcoming ski season, or recovery from an injury, then certainly go ahead and make it three days of strength training and three days of aerobics.

If, on the other hand, you enjoy the aerobic training or aerobic sports more, such as biking, hiking, kayaking, etc., then you will probably want to stick with four days of aerobic training to maintain your aerobic fitness base, and in that case, two days a week of strength training will do everything you need it to do.

Purely because most people enjoy the aerobic training more than the strength training, we made the rule: four days a week of aerobics and two days a week of strength. Interestingly, it appears that your body, to a fairly large extent, only really builds growth in either the strength or the aerobic direction, on a given day. So putting in a significant aerobic work out and strength work out on the same day, while it will bring you some fitness benefits in both areas, is not as productive as alternating the days.

On your strength days, I suggest a five-to-ten minute aerobic warm up, to reduce your risk of injury, and then go straight ahead with the strength training. So obviously, if you are doing three days a week of strength you are only going to be getting in three days a week of aerobics. What to do on those three days should be guided in large part by how fully you have recovered from the previous day’s strength training episode. If it was a fairly demanding strength work out you may find that your aerobic day is best used for a long and slow day at 60% of maximum heart rate, rather than pushing for a hard aerobic day at 80-85% of maximum heart rate.

On the other hand, if you feel charged up from the previous day’s work out and back on top of your game, feel free to go ahead with a hard day of aerobics, without any concerns.

Another thing that seems to work well, from a scheduling perspective, for many people, is to do an aerobic work out six days a week, and to alternate a certain amount of strength training at the end of those days. So, for instance, people will do half an hour of aerobics and then do either their legs or their back, stomach and arms, on alternate days. There’s nothing wrong with this strategy, and a lot of people who don’t like strength training per se find that it is easier to go ahead and stick with the routine this way (remember that it’s all about showing up, so if this works best for you, that’s great!). It is mildly less effective, because your body is ramped up for aerobic growth, and then you ask it to do some strength training – but it certainly does work. If you find that this strategy works best for you, go ahead with it. You are only giving up 5 or 10% in the efficiency of your overall training program.