This is a four part series-
- Why exercise helps
- A framework for why this matters
- How much is enough and practical guidelines
- Putting prevention in a new light
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How much is enough? It is *not* all relative
Continuing with colorectal cancer, from this study,
“Evaluating the combined effect of moderate and vigorous physical activity on the risk of colon and rectal cancer showed that high levels of vigorous activity reduced the risk at nearly every level of moderate activity (table 6). Evaluation of high levels of moderate activity at low levels of vigorous activity did not show a similar risk reduction.”
…
“Again, the strongest indicator of reduced risk was for vigorous physical activity performed at constant high levels over the past 20 years.”
This further clarifies the distinction. It’s not only whether you exercise, it’s how you exercise.
“In men with [prostate cancer], physical activity was associated with lower overall mortality and [prostate cancer] mortality. A modest amount of vigorous activity such as biking, tennis, jogging, or swimming for 3 hours a week may substantially improve [prostate cancer]-specific survival.”
When we tell people they should be exercising, and they have prostate cancer, are we being this specific with our advice? “You should be doing at least 3 hours a week of pretty vigorous activity. Examples of this type of activity include….”
Metabolic Equivalent of Task, MET, is how a lot of these studies assess physical activity. Examples include:

These are MET / minute. If we jog for two hours, that’s 7 METs * 120 minutes = 840 MET minutes. 840 / 60 = 14 MET hours.
Look at this chart carefully:
For those essentially sedentary, below 3 MET hours per week, that’s our baseline. If you’re someone who does SIX TIMES more than the sedentary group, you get essentially no difference in outcome.
If you’re someone who does more than six times -the lowest dotted line- you get a huge benefit in outcome (in colorectal cancer in this scenario).
The risk of death after colon cancer diagnosis in the above,
- 14.1% for less than 3 MET hours per week
- 14.4% for those between 3 to 17.9 MET hours per week
- 6.2% for those above 18 MET hours per week
If you get diagnosed with colon cancer, then start exercising, you can reduce your risk of death by more than half! But you need to be above a certain level of activity. How you feel is irrelevant. METs are not perception based outputs. They’re objective based outputs.
In Physical activity and cancer risk: dose-response and cancer, all sites and site-specific, a review of this topic, a demarcation is made between those who get activity requiring above 4.5 METs and those below. You need to get above to get the benefits.
For instance, from this paper on physical activity and lung cancer, incidence rate per 10,000 is the red circle:
(The kj/week are for kilojoules, which are used for energy. For context, 1000 kilojoules = 239 calories and 5,880 kilojoules = 1400 calories.)
Notice those who got no activity below 4.5 METs had an incidence rate of 12.5 per 10,000. For those who got a lot of activity, but still below a 4.5 MET intensity, they burned over 1400 calories per week! (they just did it slowly), their incidence rate was 13.3 per 10,000. All that activity didn’t matter because they didn’t get above a certain objective intensity.
Those who got no activity above 4.5 had an overall incidence rate of 16. However, those worked above 4.5 METs at something like at least 3 hours per week had an incidence rate of 7.2. No activity above 4.5 METs and you more than double your risk of lung cancer.
(Note we’re mixing relative risk and absolute risk. For instance, while the relative risk differences are large in the lung cancer example, the absolute is still quite low. However, the absolute difference is quite large in the colon cancer example.)
Look how many activities are below a 4.5 MET output:
We can’t go through every cancer in one post. What we can do is get some fairly solid thresholds we want to hit and or surpass. So far, it’s looks like we want at least get three hours or more of activity above 4.5 METs per week.
Let’s take a quick double check of this. There is a MET calculator from ExRx here. A speed of 3.8 miles per hour gives us 4.5 METs. For context, 4 to 4.5 miles per hour is when nearly everyone will start jogging rather than walking. Rather than worry about METs here, what we can say is you should get at least three hours per week of activity where you are at least right on the cusp of wanting to jog. Or walking at Manhattan speed.
But let’s double check the time. If we say a person is 180 pounds, rough American average, and walks at 3.8 miles per hour for 180 minutes (three hours), that gives us a caloric output of 1100 calories. In the one study above, greater than 1400 calories is when the optimal benefit was found. It’s only one study, but if we walk for 3.5 hours instead of 3, we just about hit 1400 calories.
So let’s say our thresholds are an intensity of nearly jogging or more, for a total of 3.5 hours or more, every week. Or 30 minutes every day is another way to look at it.
Please again note 3.8 miles per hour is not a relative measure. We are not saying “do an activity hard enough you get out of breath.” We are saying “hit this speed for this long or else.”
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First, this is different than heart health. We’ve found, given similar energy expenditure, walking gives similar results to running. Run for an hour vs walk for an hour, and running is clearly better. The running will expend -we’ll say for simplicity- double the energy. But run for an hour vs walk for two hours -similar energy expenditure- and walking is just as good.
That’s not what we’re seeing with cancer though. This is what’s meant by structuring our exercise parameters based on disease. Perhaps heart health is your primary concern. Well, you don’t need the intensity of exercise as someone who is mainly worried about prostate cancer. (In reality, most are worried about heart and cancer health. This is addressed at the end.) You need to worry about doing enough overall.
Second, this is critical because how many geriatrics can’t even walk this fast? Above a 3.8 miles per hour pace? How many are so out of shape they can’t exercise intensely enough to get the benefits? Because it’s not only whether you go for a walk, it’s how fast you walk. Just telling your geriatric client they need to start exercising is as meaningless as telling someone to start taking a drug. How much of the drug? When? Days per week? Side effects? Contraindications? Give them too little of the drug and you can’t say the drug is useless. The prescription was useless!
-> My experience training a lot of older people is once around or above ~55 years old, it is hard work to get people to be able to get above 3.8 miles per hour on the treadmill. Jogging tends to not be easy for people upwards of 60 years old and older. Decades of deconditioning become more apparent.
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Weightlifting?
With something like resistance training, it’s a bit harder to give specific guidelines. In the study:
–Can Resistance Training Contribute to the Aerobic Components of the Physical Activity Guidelines?
It was found resistance training gives a moderate to vigorous heart rate response for about 50% of the time. So if you’re training with the intention to get stronger, with ~2 minute rest breaks, for an hour, that could count as roughly 30 minutes of working at a 3.8 mile per hour intensity.
So many go to the gym and sit on a bike. So many cruise on the elliptical as if they’re watching a kite. Sit on machines and keep the weight at its most lean. So many think having kids means they’re active. That when they go on vacation, because they walk a lot, they’re doing enough to stay attractive. So many are too quick to think hitting the gym once a week is enough. That because they have a standing desk, they don’t need to huff and puff. That walking the dog means they’re healthier than a hog. While this thinking may help you feel functional, it is no doubt delusional.
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Summarizing activity / practical implementation
- Strive for 10,000 steps a day, regardless of speed.
- This is a more general health goal, but also ideal for cardiovascular health.
- At least three and half hours per week, move at an intensity on the cusp of you needing to jog, or greater.
- These 3.5 hours of steps can be part of the 10,000 requirement.
- Ideally, this is spread over at least two days per week, rather than done all on one day.
- If strength training, it should be done enough to where a person is trying to get stronger i.e. lift more weight, for the entire body.
- In the study I linked earlier on resistance training, it was found lower body training gave an aerobic heart rate response for 75% of a session, compared to only 46% for upper body training. Don’t skip the leg work!
- If strength training is done but no faster walking / jogging / running is done, then we want the strength training to hit a total of at least seven hours per week.
- Good luck hitting this. It’s probably best you get tuh walkin’.
- (For those thinking I get my strength training in much faster than that, you’re probably not strength training then. That’s circuit training, which is ok. But the notion of “I get my exercise done in 30 minutes twice a week” is insufficient.)
- Other than the obsessive exercise types / marathon people, when in doubt, don’t only do more, but do it more intensely. It’s really hard to do too much, and for 99.9% of us, the more we do, the harder we do it, the better our health.
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kierfinnegan
May 10, 2016
Loving this series. Really interesting. One thing I’m wondering is, with the idea of ‘intensity’ and vigorous exercise, what are we striving for? Is it elevated heart rate? Mechanical tension? Overall metabolic stress on the body?
The reason I ask is because, as you know, I strive to add weight or reps to exercises as often as I can. There may be days, though, where I haven’t slept as well, or I’ve pigged out a bit and I’m heavier than usual or maybe there are other sources of stress in my life, and the gym sessions feel a lot harder; more sweat/higher heart rate than normal/fatigue sets in quicker….
In these instances I may be forced to drop the weight a little or not get as many reps in, maybe even fewer sets. My point is, my overall fitness level is unlikely to change drastically from one workout to the next but it feels more intense. Am I still reaping the same benefits because it’s still at a high intensity or is it less because I’m actually doing less work?
I’ve wondered about this since the whole HIIT thing kicked off. If you take person A – very fit and person B – overweight and unfit, and they work at the same level of perceived ‘intensity’, person A will clearly be doing more work/distance, but are they getting the same training effect? Similarly, for overweight people who are very fit, do they get more of a training effect because they’re heavier?
It’s difficult to articulate but hopefully you understand what I mean!
reddyb
May 12, 2016
Hey Kier,
That one paper looked at heart rate comparisons between aerobic activity and resistance training. That’d be absolute intensity, not relative.
While there is often a relationship between how something feels and how much the heart is beating, this isn’t always so. A tired person may feel exhausted just warming up, but that doesn’t mean they’re working at a significant *absolute* intensity. Perhaps one way to look at this is the context of the human body. Nobody argues a four minute mile is hard on the body just like nobody argues a 15 minute mile is not hard on the body. Sure, relatively speaking it can change. But for a healthy human body, it’s obvious.
I hit on it being hard to know what we’re shooting for in the “Why” post. Is it increased circulation / heart rate, something psychological, getting the muscles to pump, increased insulin sensitivity, it’s practically an infinite list of variables which can’t all possibly be controlled for to iron out the most important one(s). We don’t even know all the factors to look at.
The person A and person B is what was meant by looking at things objectively vs subjectively. It doesn’t appear to matter if walking at 4 miles per hour feels hard. It matters how fast they’re moving. So, if for a person 3.5 mile per hour happened to feel very hard that day, that may be irrelevant in that it doesn’t hit the threshold. Don’t believe this has been explicitly looked at e.g. perform a study where you assess exercise intensity and cancer rate based on perceived exertion compared to absolute exertion. So it’s best to err and focus on absolute instead of relative.
This is one reason I made the remark about resistance training with the intention to get stronger with ~2 minutes rest breaks or so. For most, it shouldn’t take too long until this hits the threshold. Similar to if a person was always walking with the intention of going faster, it wouldn’t take too long to hit 3.8 miles per hour. (i.e. It shouldn’t take long to hit a 3.8 mph walk intensity when lifting weights.) It’s an insurance policy, but overall with resistance training it is guessing, as we 1) haven’t studied it (so far as I know) 2) don’t know what variable(s) we’re really going after.
There is a notion in the fitness world resistance training / anaerobic activity can supplant aerobic activity. In many ways, this either hasn’t been found to be true i.e. it hasn’t been rigorously looked at yet. Cancer and Alzheimer’s are two examples, though the evidence isn’t looking good for resistance training. (See last link in mailbag here: https://b-reddy.org/2016/04/15/emptying-out-the-mailbag-and-clearing-the-history-13/ .) Or it’s been found to not be true. “Why Zebras Don’t Get Ulcers?” hits on this regarding handling stress, with aerobic being better. Personally, with my in person clients, I always have them moving. The idea of perform a set of weights, then sit down for a couple minutes, then go again, we don’t do that. It’s do a set, take a lap, do a set, next exercise in the circuit, take a couple laps. I want people moving consistently for a while.
Thinking about someone who is in shape having an off day- The thresholds we’re talking about, again in the context of the human body, are pretty damn low. Like if you’re non-elderly, nothing abnormal, then being able to do a brisk walk for a few hours a week should either not be hard or not take long to work up to. To where a person should be in good enough shape that an off day still has them above the threshold.
For instance, if you’re able to do a low level jog, like 6 miles per hour, then even the most tired of days should keep you at the ability to do a fast walk.
That felt jumbled typing. Hope it’s clear.