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Here's the Minimum Amount of Exercise You Really Need

April 03, 2015

Story at-a-glance

  • Women who exercise just a few times a week have a lower risk of heart disease, stroke, and blood clots
  • For moderate-exercise activities, the health benefits peaked at four to six sessions per week
  • For more strenuous exercise, the health benefits peaked at just two to three times per week

By Dr. Mercola

Eighty percent of Americans fail to meet the recommended amount of exercise, which is 2.5 hours of moderate-intensity activity or 1.25 hours of vigorous-intensity activity each week… along with twice weekly strength-training workouts.1

These are the “official” US government exercise recommendations, but they are not the last word on fitness. How much exercise you need depends on a number of factors, not the least of which is the type of activity you do. The more intense you work out, the less frequently you should do it (and the shorter the duration should be).

It’s entirely possible to get a phenomenal workout in just 20 minutes two or three times a week if you’re using, for instance, high-intensity interval training (HIIT) or super-slow weight training. But this doesn’t mean you should simply sit around for the rest of the week.

Regular walking (upwards of 7,000 steps a day) is also important, in addition to regular exercise. But before I get into the details, here’s something you should know: even small amounts of exercise matter… and any amount of exercise is better than none at all.

The Minimal Amount of Exercise You Should Strive For…

The greatest health gains among exercisers are often seen when a person goes from not exercising at all to getting physically active. And it doesn’t take much to see significant benefits. Compared to women who don’t exercise at all, for instance, women who exercise just a few times a week have a lower risk of heart disease, stroke and blood clots.2

For moderate-exercise activities, which included walking, gardening, and housework, the health benefits peaked at four to six sessions per week. For more strenuous exercise (defined as exercise that caused sweating and a fast heartbeat), the benefits peaked at just two to three times per week.

Those who engaged in the more strenuous exercise two to three times a week lowered their risk of heart disease, stroke, and blood clots by 20 percent. Interestingly, less is more in this case, as women who exercised strenuously more than three times per week had increased vascular risk.3

It’s quite clear that if you engage in intense exercise, overdoing it can cause serious problems, which is often seen in marathon runners. According to a study presented at the Canadian Cardiovascular Congress 2010 in Montreal, regular exercise reduces cardiovascular risk by a factor of two or three, but the extended vigorous exercise performed during a marathon raises your cardiac risk seven-fold!

Even Minimal Amounts of Exercise May Improve Your Health

Exercise is not “all or nothing” when it comes to your health. If you don’t fit in three workouts one week, but do just one instead, you’ll still benefit – albeit not quite as much as if you had done more. According to researcher Philipe de Souto Barreto from the University Hospital of Toulouse:4,5

“Getting inactive people to do a little bit of physical activity, even if they don’t meet the recommendations, might provide greater population health gains… Achieving target physical activity recommendations should remain as a goal but not the core public health message surrounding physical activity.”

For instance, just one hour of moderate activity a week may lower your risk of premature death by 15 percent, while just 20 minutes of vigorous intensity once a week may lower it by 23 percent.6 Research also suggests that walking for one to 74 minutes a week may lower your risk of premature death by 19 percent compared to those who are sedentary.7

So if you’re feeling intimidated about starting an exercise program, feeling you simply don’t have enough time… if you can carve out 20 minutes a week, you can experience some health benefits of exercise.

That being said, there is a dose-response relationship between physical activity and premature death as well as at least seven chronic diseases (cardiovascular disease, stroke, hypertension, colon cancer, breast cancer, type 2 diabetes, and osteoporosis).8

In other words, the more exercise you do, the greater the benefits will be. This is true only to a point, because once you get past a certain threshold then more exercise will only cause harm.

Most people are not at risk of over-exercising… but, as mentioned, the general guideline to remember is the more intense you exercise, the more recovery time you will need. One of the many positive aspects of intense exercise is that you can “max out” your exercise requirements in a very short (and very achievable) amount of time.

The Benefits of Shorter, More Intense Workouts

When you exercise intensely, you can reap greater rewards in a shorter period of time. For starters, high-intensity interval training burns more calories in less time – a mere 2.5 minutes, divided into five 30-second sprint intervals at maximum exertion, each followed by four minutes of light pedaling to recuperate, can burn as much as 220 calories.9

Besides burning more calories, HIIT has also been shown to produce greater health benefits overall than conventional aerobic training, such as increasing insulin sensitivity and glucose tolerance – both of which are critical components of optimal health.

One study that found doing just three minutes of high-intensity exercise per week for four weeks could lead to a 24 percent improvement in insulin sensitivity.

Another important benefit of high-intensity interval training is its ability to naturally increase your body's production of human growth hormone (HGH), also known as "the fitness hormone."

HGH is a synergistic, foundational biochemical underpinning that promotes muscle and effectively burns excessive fat. A study published in the journal Cell Metabolism even showed that when healthy but inactive people exercise intensely, even if the exercise is brief, it produces an immediate change in their DNA.10

While the underlying genetic code in the muscle remains unchanged, exercise causes important structural and chemical changes to the DNA molecules within your muscles. This contraction-induced gene activation appears to be early events leading to the genetic reprogramming of muscle for strength, and to the structural and metabolic benefits of exercise.

Several of the genes affected by an acute bout of intense exercise are genes involved in fat metabolism. Specifically, the study suggests that when you exercise, your body almost immediately experiences genetic activation that increases the production of fat-busting proteins HIIT also plays an important part in promoting overall health and longevity. This too is something you cannot get from conventional, aerobic endurance training. Other benefits associated with high-intensity interval training include:

Decrease in body fat Improved muscle tone
Improved athletic speed and performance Ability to achieve your fitness goals much faster
Increase in energy and sexual desire Firmer skin and reduces wrinkles

How to Get the Most Exercise Benefits in the Shortest Amount of Time


The HIIT approach I personally use and recommend is the Peak Fitness method, which consists of 30 seconds of maximum effort followed by 90 seconds of recuperation, for a total of eight repetitions. Super Slow strength training is another high-intensity exercise, which may even be more effective than Peak Fitness cardio. While they both are highly effective, you can generate a higher cardiac output with Super Slow training as discussed in my interview with Dr. McGuff.

By slowing your movements down, you're actually turning them into high intensity exercise. The super-slow movement allows your muscle, at the microscopic level, to access the maximum number of cross-bridges between the protein filaments that produce movement in the muscle. You can perform the super-slow technique with hand weights, resistance machines, bodyweight exercises, or resistance bands.

You only need about 12 to 15 minutes of super-slow strength training once a week to achieve the same HGH production as you would from 20 minutes of Peak Fitness sprints, which is why fitness experts like Dr. Doug McGuff are such avid proponents of this technique. The key to making this work for you is intensity, which needs to be high enough that you reach muscle fatigue. If you've selected the appropriate weight for your strength and fitness level, your goal is to have enough weight that you cannot do more than 12 reps, but not so much that you can't complete at least four. Ideally, you will be somewhere in the neighborhood of seven to eight.

When the intensity is this high, you can decrease the frequency of your strength training sessions. In fact, the higher your fitness level, the less often you should do them. I also recommend incorporating Buteyko breathing, which involves breathing only through your nose while working out. This raises the challenge to another level. As a guideline, when you start out, allow your body at least two days to rest, recover, and repair between high-intensity sessions, and do not exercise the same muscle groups each time.

As your strength and endurance increases, decrease how often you do the sessions, as each one is placing greater stress on your body (provided you keep pushing yourself to the max). As a rule, avoid doing high-intensity exercises more than twice or three times a week. You can enjoy other activities on the off-days, such as swimming, Pilates, yoga, biking, gardening, or whatever other activities tickle your fancy. I also encourage you to use a pedometer and walk as much as possible, ideally 7,000 to 15,000 steps daily.

Not Exercising May Be Worse Than Smoking

If you’re looking for motivation to get moving, consider this: research shows that inactivity is lined to more than 5 million deaths each year, which is similar to the death toll taken by smoking.11 Data also suggests that at least twice as many deaths occur due to a lack of exercise than due to obesity. This is really astounding, considering one in five US deaths are associated with obesity. Study author Ulf Ekelund from the Medical Research Council Epidemiology Unit at the University of Cambridge told TIME:12

“This is a simple message: just a small amount of physical activity each day could have substantial health benefits for people who are physically inactive.”

As stated by Dr. Timothy Church, director of preventive medicine research at the Pennington Biomedical Research Center in Baton Rouge, exercise indeed affects your entire body—from head to toe—in beneficial ways.13 This includes changes in your:

  • Muscles, which use glucose and ATP for contraction and movement. Tiny tears in your muscles make them grow bigger and stronger as they heal. Gaining more muscle through resistance exercises has many benefits, from losing excess fat to maintaining healthy bone mass and preventing age-related muscle loss as you age. The intensity of your resistance training can achieve a number of beneficial changes on the molecular, enzymatic, hormonal, and chemical level in your body.
  • Lungs. As your muscles call for more oxygen, your breathing rate increases. The higher your VO2 max—your maximum capacity of oxygen use—the fitter you are.
  • Heart. Your heart rate increases with physical activity to supply more oxygenated blood to your muscles. The fitter you are, the more efficiently your heart can do this, allowing you to work out longer and harder. Your blood pressure will also decrease as a result of new blood vessels forming.
  • Brain. The increased blood flow also benefits your brain, allowing it to almost immediately function better. Exercising regularly also promotes the growth of new brain cells, boosting your capacity for memory and learning. A number of neurotransmitters are also triggered, such as endorphins, serotonin, dopamine, glutamate, and GABA. Some of these are well-known for their role in mood control. Exercise, in fact, is one of the most effective prevention and treatment strategies for depression.
  • Joints and Bones. Exercise can place as much as five or six times more than your body weight on them. Weight-bearing exercise is one of the most effective remedies against osteoporosis, as your bones are very porous and soft, and as you get older your bones can easily become less dense and hence, more brittle -- especially if you are inactive.

The simple take-home message is this: if you are currently living a sedentary lifestyle, the mere act of incorporating some high-intensity activity two or three days a week, along with regular walking, can significantly reduce your mortality rate.

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Sources and References

  • 1 CBS News May 3, 2013
  • 2 Circulation February 16, 2015
  • 3 TIME February 16, 2015
  • 4 TIME January 22, 2015
  • 5 BMJ 2015;350:h725
  • 6 Daily Mail January 21, 2015
  • 7 TIME January 22, 2015
  • 8 International Journal of Behavioral Nutrition and Physical Activity 2010, 7:39
  • 9 Integrative Biology of Exercise VI meeting, Oct. 10-13, 2012, Westminster, Colorado
  • 10 Cell Metabolism March 7, 2012: 15(3);405-411
  • 11 The Lancet July 18, 2012
  • 12 TIME January 15, 2015
  • 13 DailyComet.com December 30, 2013
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