I’ve often heard that doctors recommend about 20-30 minutes of “sustained” cardio activity at least 3 times a week for good heart health. I was wondering how important the “sustained” part of that really is.
While I’m at work out here on the boat, instead of taking short little smoke breaks, I like to go running or using the eliptical in the rec room. It helps break up my day, and I can burn a few calories, and it makes me feel awake and alert. But is it doing anything to help my heart health? I’m talking about sprinting 1/4 mile every 30-40 minutes or so. Takes me about a minute and a half, gets my heart pumping and such. But it’s not sustained.
So I guess I’m looking for the medical facts and opinions here. Say I run 3 miles sustained, which usually takes me at least 25 minutes. How will this compare to me doing my short little sprints and racking up 3 miles over the course of a 12 hour work day? The amount of calories burned is going to be similar (although I believe sprinting burns more calories than jogging because it’s not as efficient of an exercise).
So what’s the deal here? Am I doing any good overall for my heart by doing these short bursts of 1-2 minute exercises spread throughout the day, as compared to just doing a 30 minute run all at once?
There is a lot of recent research that indicates that short bursts of high intensity exercise are more beneficial for improving health than the regularly cited 30 minutes several times a week. Here is a piece on one study. And another.
Recently I heard a spate of reports describing the cardiac danger of a sedentary lifestyle - stressed the importance of just standing briefly/walking around the office every hour or so.
I’m of the firm belief that something is better than nothing. Unless you are training for some particular competition or something, the main thing is to get that carcass moving!
IMHO, short bursts of activity might not cause your body to make physiological changes. With a burst, your body can just make due with what it has. But if you run for 20 minutes, your body has to deal with a lot more energy and waste issues. It has to continually get energy to your muscles and clear the waste products away. With a burst, your body can use the energy already in the muscle and there’s not too much waste to deal with.
So I would guess that longer sessions of exercise would cause greater changes to your muscles and circulatory system. It would force your body to become more efficient under greater stress. I would guess that the short burst would not tax your body enough to cause it to make changes.
His 1.5 minutes at a time separated by 30 to 40 minutes or so does not however meet any standard of high intensity interval training aka HIIT (and neither doe the first link’s falsely decribing it as 3 minutes per week). That does not mean it won’t accomplish quite a bit of good, but it is not covered by the evidence base of the HIIT literature which is all all about repeats of high intensity after partial recoveries. (See the Tabata protocol in the second link for one example.)
The CDC advises at least 10 minutes at a time but it does seem like that this is only because briefer sets have not been studied. 10 minute bouts three times spread out over the day have been compared directly to 30 minutes steady state and did actually did better on blood pressure control, for example.
That said my WAG is that the 3 miles spread out into twelve 1/4 mile sprints would do you more good than 25 minutes of steady state.
And, as always, the most effective exercise is the one you actually do. IMHO, the idea that “exercise” has to be a Jane Fonda style workout–where you have a warm up, 25 minutes of sustained elevated heart-rate, and then a cool down–does a great deal of damage. For years, doctors made is sound like if you didn’t do at least that three times a week, you were risking serious injury and you weren’t doing any good anyway. So it was really easy to find an excuse not to exercise at all, since it’s hard to find the time to meet that ideal routine.
I’ve been hearing the same reports. If I understand them correctly, it’s not good to sit all day even if you’re working out regularly - you still need the break in just sitting down. I’ve been doing well with both aerobic and strength training lately, but I sit at a desk 5+ hours every day. I’ve started setting a one hour timer on my phone when I sit down. When it goes off, I do 40 jumping jacks. Or 20 squats. Or something else. I don’t know how much it will help, but I figure it can’t hurt.
I work at home, BTW, so I have no office mates to speculate on my sanity when I stand up abruptly and do jumping jacks. My children sometimes see me, but they already think I’m weird.
On the boat out here, a lot of guys will just get up and do pushups right on the floor in front of everyone. I’ve also seen at least one other guy “sneaking” into the gym to do a bit of exercise as a short break.
All activity and exercise is good and beneficial in its own way. Aerobic exercise has specific benefits, which is way it is recommended several times a week (presumably to supplement other activity).
Sustained running or similar activity for at least 20 minutes helps you burn fat, because you deplete the readily available glycogen stored in your muscles, switching your body to more complex energy reserves. It also fully exercises your lungs and heart, and is more likely to give you the “runner’s high” that makes the awful feeling of exercise worth it.
Definitely continue short exercise throughout the day. Ideally, your day should be a mix of various physical activities.
You can’t deplete glycogen in 20 min. More like 90-120 min. or more, depending on your training and pacing.
What goes happen is at slower paces/lower exertion levels, the percentage of calories from fat increases. However, what really matters is total calories burned.
I remember Cecil writing about this (but I can’t find it), but the other thing that happens at that 20 minute threshold when your body starts to increase its use of fat is that it thinks the change is going to be necessary for a while. So if you exercise for 20 to 30 minutes, your body uses a carb/fat mix for the next few hours.
I can feel when this happens. Initially, exercise feels sluggish, tiring, and I want to stop. After about 20 minutes it gets easier, and I feel like I can keep going as long as I want to. It feels like going up a hill that levels off after about 20 minutes.
I appreciate it.