What is the correct dose and frequency of aerobic exercise for unconditioned middle age people?

Question

This is the general question:

How often and how long should do soft aerobic exercise a middle-aged man in his 40s, provided that he his healthy but out of shape? If possible, please focus your answer specifically on fast walking as exercise

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Now, after the general question, I would like to add some particular details that may help the readers understand better what I want to know:

I am 41, quite out of shape but I have permission from the doctors to do aerobic exercise. Because several months ago I returned to weight training improperly after 18 years of sedentary computer work, and then aggravated it by improperly stretching my pecs and carrying my 16 kg doughter always on the same arm, I am still recovering from several tendonitis in both shoulders.

In the meantime, I am doing some aerobic exercise every day. But, after having injured myself so badly, this time I want to be sure that I am doing the aerobic exercise properly and that I am not going to die suddenly in the middle of the street because I was stressing my heart too much, or who knows what may happen this time...

This is exactly what I have been doing in the last 11 days:

I start walking very fast, just at a pace where it seems that I should instead start running. But I don't run, I just stay walking. I do this uninterruptedly for up to 45 min. I wear a fairly good running shoes. I check my pulse at least twice during the walk, and it always stays between 120 and 150 bpm (I never let it go over 14 beats in six seconds). I breath correctly. I don't feel it is exhausting, but rather slightly challenging. I think I could say some sentences aloud while walking, as long as they were short and there were enough pauses to breathe in between. I sweat a bit but not too much. At the end, I stretch my quads a bit.

I have written down how long I do this every day. This are the times up to yesterday: 25, 30, 36, 45, 45, 41, 45, 45, 43, 42 and 45 min.

Is that wrong? Should I insert rest days or something?

If this question seems too localized because of the additional details I gave, please feel free to answer only to the general question at the beginning, and I will try to derive the appropriate adaptation to my personal circumstances. Nevertheless, I think that explaining the correct way of starting a soft aerobic walking program for middle-aged unconditioned people is something of a general interest, and the personal details I added are valuable as an example of how it should (or how it should not) be done.

Answer 1

For your general question, according to the 2008 Physical Activity Guidelines for Americans, you need:

1. 2 hours and 30 minutes (150 minutes) of moderate-intensity aerobic activity (i.e., brisk walking) every week and weight training muscle-strengthening activities on 2 or more days a week that work all major muscle groups (legs, hips, back, abdomen, chest, shoulders, and arms).

For you the strength training is currently on hold, so the following is about cardio-vascular or aerobic exercise:

• Moderate Intensity Aerobic Activity ranges from 55% to 75% of your MHR (max heart rate); or a level of exertion of 12 to 16 (somewhat hard to hard at a steady pace) on the Borg Scale when exercising. Calculate your target heart rate to optimize your workouts. Since you say that you are "quite out of shape", begin in the 55% to 65% range and work your way up. ("Quite out of shape" means different things to different people so that figure may or may not be a good starting point.) Your doctor may also give you guideline targets.

  If my calculations are correct, your MHR (maximum heart rate) is 179, making 120 - 150 bpm in the 67% to 85% range, which may be overly enthusiastic given your level of fitness and recent injury history. To be more accurate, use your RHR (resting heart rate), to calculate your exercise target heart rate using the Karvonen Method.

  The best way to avoid injury is to begin modestly and progress gradually. A dynamic warm-up before walking (being careful not to aggravate any current injuries) will lubricate soft tissues and joints, increase circulation to the muscles, increase the heart rate and prime the nervous system.

  Remember that you may not know that you have overdone until after you finish exercise, (or even the next day or two). Be cautious until you know how your body reacts. Make notes on your exercise log about how you feel. Pay attention to little annoyances that may become worse with the repetitive movements of walking.

Once you have safely progressed from the above recommended level without injury, gradually increase to:

• 5 hours (300 minutes) each week of moderate-intensity aerobic activity and weight training muscle-strengthening activities on 2 or more days a week that work all major muscle groups (legs, hips, back, abdomen, chest, shoulders, and arms).

  If you add up your walking weekly times you have already reached the progression to 300 minutes per week recommendation. How your body feels will tell you if you have progressed too quickly or are on schedule. Given that you are beginning a process to get back in shape and want to avoid injury, you may be more prudent to lower the intensity and progress more gradually. 1-2 rest days per week can help with recovery. For the necessary patience, think of getting back in shape as a lifelong healthy lifestyle.

• Flexibility - A regular gentle stretching program after you walk will help to keep you flexible. In addition to your quads, include your hamstrings and gastroc/soleus.

• Measurements - Tracking your physical progress will also help you judge if you are benefiting from your exercise program, and whether or not you need to make changes. Measurements also help with motivation (which does not appear to be your problem. ;)