Of all the misconceptions about strength training and weight lifting, one that comes up a lot is that they have no aerobic component. Therefore, the idea goes, if you do only weight training, you won’t build sufficient cardiorespiratory fitness, which you need to protect your heart and get the benefits of exercise. But weight lifting increases aerobic fitness, all on its own.
On at least two occasions, when a doctor has asked me what I do for exercise — after remarking that I was in great shape — and I told them weight lifting, they said I needed to add some aerobic exercise (cardio).
It’s obvious that these doctors never lifted weights. At my weight lifting sessions, I have to catch my breath after a set and my heart is often going at around 160 to 180 beats per minute.
It’s not just a couple doctors either. The view is widespread that you must do a very special form of exercise, called aerobics or cardio, to improve heart and lung function and raise VO2max, the most common measure of cardiorespiratory fitness.
On the contrary, weight lifting raises VO2max.
A review article looked at every study they could find on the relation between resistance training and VO2max: “Resistance training induced increase in VO2max in young and older subjects”.(1)
What they found was that the improvement in VO2 max caused by resistance training depended on the initial VO2max of the participants. See the following graph:
If the participants had a generally low VO2max initially, then they improved. But if they had generally good VO2max initially, no improvement was seen.
Now, take a look at the following chart of VO2max norms, for men, by age. (Chart from here.)
You can see that the VO2max level to which resistance training will get you (first chart) ranks from good to excellent for all age groups of men.
The studies that the reviewers compiled had great variation in number of sets, rest times between sets, and frequency of training.
Generally, the less time between sets, the greater the cardiorespiratory workout. So if increasing cardiorespiratory fitness is among your goals, take short rests between sets. A circuit-training scheme with short rests should be ideal for increasing fitness.
The caveat here is that if you are a trained runner or similar athlete, weight training won’t do much extra for your fitness level. Elite marathon runners, for example, have a VO2max in the upper 60s to 70s or even higher. Lance Armstrong clocked in at 84.0. It’s unlikely that weight training would increase his fitness.
As for other benefits that are ascribed to aerobic conditioning, weight training can do these too. For instance, artery diameter in young men increased in response to weight training.(2)
Blood flow in the legs in resistance-trained men aged 35 to 65 was not different from that of young resistance-trained men, while sedentary men aged 35 to 65 had only 30% as much leg blood flow as the young men.(3) Therefore resistance training looks to be a powerful way to keep the circulation young and healthy.
The moral of this story is that if you lift weights regularly and especially with intensity, then you probably don’t need to add cardio to your regimen to obtain good cardiorespiratory fitness.