Exercise has been shown to relieve depressive symptoms, yet optimal exercise intensity for treating depression has not been established. The mechanisms that explain the antidepressant effect of exercise also require investigation. The purpose of this study was to test (a) the effect of two different exercise intensities prescribed for aerobic training on depressive symptoms, and (b) a previously proposed psychological mechanism for this effect: self-efficacy. Sedentary women scoring ≥14 on the Beck Depression Inventory-II (BDI-II) were randomized to one of two aerobic training groups that differed on exercise intensity (high [65–75% MaxVO2 reserve] or low [40–55% MaxVO2 reserve]), or to a stretching control group for 10 weeks. Main outcome variables included depressive symptoms (BDI-II) and self-efficacy (exercise self-efficacy [ESE] and depression coping self-efficacy [DCSE]), which were measured at study entry, 5 and 10 weeks later. Participants in all groups (high, n = 18; low, n = 18; stretching, n = 18) had significant reductions in depressive symptoms at Week 5 (p < .001) and Week 10 (p < .001). The BDI-II change scores did not differ significantly among the groups (p = .066). Follow-up analyses controlling for baseline BDI-II scores showed that the high intensity group had significantly fewer depressive symptoms than the low intensity and stretching control groups at weeks 5 and 10 (p < .05). There was no significant association between changes in aerobic capacity and changes in depressive symptoms (r = −.099, p = .491). At 10 weeks, both ESE (p = .013) and DCSE (p < .001) increased significantly for the whole sample, with no significant group difference (p = .613 for ESE, p = .277 for DCSE). Controlling for baseline scores, the increase remained significant for ESE (p = .005) but not for DCSE (p = .629). Partial correlations showed significant negative relationships between both types of self-efficacy and depressive symptoms at Week 5 and Week 10 (p < .02). We concluded that both high and low intensity aerobic exercise, as well as stretching exercise were associated with reductions in mild to moderate depressive symptoms in initially sedentary women. Changes in depression were associated with changes in ESE and DCSE.
CHOOSING YOUR EXERCISE INTENSITY
How do you know how hard you should be exercising? For most healthy adults, the Department of Health and Human Services recommends these exercise guidelines:
- Aerobic activity. Get at least 150 minutes a week of moderate aerobic activity — such as brisk walking, swimming or mowing the lawn — or 75 minutes a week of vigorous aerobic activity — such as running or aerobic dancing. You can also do a combination of moderate and vigorous activity, preferably spread throughout the course of a week.
- Strength training. Do strength training exercises at least twice a week. Consider free weights, weight machines or activities that use your own body weight — such as rock climbing or heavy gardening. The amount of time for each session is up to you.
To reap the most health benefits from exercise, your exercise intensity must generally be at a moderate or vigorous level. For weight loss, the more intense your exercise, or the longer you exercise, the more calories you burn.
However, balance is important. Overdoing it can increase your risk of soreness, injury and burnout. If you’re new to regular exercise and physical activity, you may need to start out at a light intensity and gradually build up to a moderate or vigorous intensity.
So think about your reasons for exercising. Do you want to improve your fitness, lose weight, train for a competition or do a combination of these? Your answer will help determine the appropriate level of exercise intensity. Be realistic and don’t push yourself too hard, too fast. Fitness is a lifetime project, not a sprint. Of course, if you have any medical conditions or you’re not sure what your exercise intensity should be, talk to your doctor.
UNDERSTANDING EXERCISE INTENSITY
When you’re doing aerobic activity, such as walking or biking, exercise intensity correlates with how hard the activity feels to you. Exercise intensity also is reflected in your breathing and heart rate, whether you’re sweating, and how tired your muscles feel.
There are two basic ways to measure exercise intensity:
- How you feel. Exercise intensity is a subjective measure of how hard physical activity feels to you while you’re doing it — your perceived exertion. Your perceived level of exertion may be different from what someone else feels doing the same exercise. For example, what feels to you like a hard run can feel like an easy workout to someone who’s more fit.
- Your heart rate. Your heart rate offers a more objective look at exercise intensity. In general, the higher your heart rate during physical activity, the higher the exercise intensity.
Studies show that your perceived exertion correlates well with your heart rate. So if you think you’re working hard, your heart rate is likely elevated.
You can use either way of gauging exercise intensity. If you like technology and care about the numbers, a heart rate monitor might be a useful device for you. If you feel you’re in tune with your body and your level of exertion, you likely will do fine without a monitor.
GAUGING INTENSITY USING YOUR HEART RATE
Another way to gauge your exercise intensity is to see how hard your heart is beating during physical activity. To use this method, you first have to figure out your maximum heart rate — the upper limit of what your cardiovascular system can handle during physical activity.
The basic way to calculate your maximum heart rate is to subtract your age from 220. For example, if you’re 45 years old, subtract 45 from 220 to get a maximum heart rate of 175. This is the maximum number of times your heart should beat per minute while you’re exercising.
Once you know your maximum heart rate, you can calculate your desired target heart rate zone — the level at which your heart is being exercised and conditioned but not overworked.
Here’s how heart rate matches up with exercise intensity levels:
- Moderate exercise intensity: 50 to 70 percent of your maximum heart rate
- Vigorous exercise intensity: 70 to 85 percent of your maximum heart rate
If you’re not fit or you’re just beginning an exercise program, aim for the lower end of your target zone (50 percent). Then, gradually build up the intensity. If you’re healthy and want a vigorous intensity, opt for the higher end of the zone.
MODERATE EXERCISE INTENSITY
Moderate activity feels somewhat hard. Here are clues that your exercise intensity is at a moderate level:
- Your breathing quickens, but you’re not out of breath.
- You develop a light sweat after about 10 minutes of activity.
- You can carry on a conversation, but you can’t sing.
VIGOROUS EXERCISE INTENSITY
Vigorous activity feels challenging. Here are clues that your exercise intensity is at a vigorous level:
- Your breathing is deep and rapid.
- You develop a sweat after a few minutes of activity.
- You can’t say more than a few words without pausing for breath.
Beware of pushing yourself too hard too often. If you’re short of breath, in pain or can’t work out as long as you’d planned, your exercise intensity is probably higher than your fitness level allows. Back off a bit and build intensity gradually.