DEAR DR. DONOHUE: I would like to read what you have to say on interval training. I do the treadmill for 50 minutes to 60 minutes. When I’m on it, I walk for five minutes and then run for five minutes. I have the treadmill on a fairly steep incline, so I feel I am getting a good workout. I would love to learn more about interval training. – V.B.

ANSWER: I just wrote about fartlek, a variant of interval training. But the subject of interval training is important enough to merit a repeat. It’s not a new technique. It was first described in the 1940s by trainers trying to improve the overall conditioning of swimmers, runners and other Olympic-level athletes.

It’s a method that permits people to perform strenuous exercise without having to completely stop from exhaustion. The idea is to intersperse periods of less-intense exercise between periods of all-out exercise. During the less-intense phases, the body rids itself of lactic acid, whose accumulation puts an end to exercise.

For example, most people can’t run a mile in six minutes. That’s too exhausting a pace. However, if they break down the mile into segments of fast and slow running, they can manage to complete the distance without being totally wasted and in a much faster time than they ordinarily would have.

Exercise segments are done continuously, but the exerciser divides the entire exercise session into periods of intense exercise alternating with periods of relatively easy exercise. A starting ratio could be a ratio of 1:3, 10 seconds of hard exercise and 30 seconds of less-intense exercise. You can choose minutes if you’re up to it. During the relatively restful periods, the heart rate should not return to its resting rate. As a person becomes better conditioned, the intense periods can be lengthened and the less-intense periods shortened.

As with all exercise, the usual warning has to be issued. Older people should not attempt strenuous exercise without their doctor’s approval.

DEAR DR. DONOHUE: In reply to the reader who got knee and back pain after a week of biking, I wonder why you did not tell him to get a recumbent bicycle. The rider sits in a full-size seat in a reclined position with less strain on back and buttocks. – H.M.

ANSWER: Consider readers informed. It’s a good idea. I have seen only stationary recumbent bikes. Are there ones for the outdoors?

DEAR DR. DONOHUE: I am 80 and fairly fit. I walk 45 minutes every other day and do resistance (weightlifting) exercise on the alternate days.

My problem is getting up and out of a soft chair. I fear I will sit down with a book and my family will find me three days later. What kind of exercise do I need to do? – G.T.

ANSWER: Yours is a common problem with older people. When the seat of a chair is low and causes the knees to be on a higher level than the buttocks, it’s difficult to rise from that position. It takes strong thigh muscles to hoist the body upward. You have to do thigh exercises.

A simple exercise is rising out of and lowering yourself into a firm chair. Rising and sitting, 10 successive times, will exercise those muscles. If the chair has arms, you can use them to push yourself up at first, but gradually eliminate arm use so the thighs get all the work.

In your weightlifting sessions, do you have access to any weightlifting machines? If so, start using the ones that are designed for thigh exercises, both the front and the back thigh muscles.

If you don’t have access to those machines, then the standard squat exercise is a good one.

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