Ever felt seriously out of breath when doing heavy lifting and wondered why you’re finding high-rep strength training so hard aerobically? A new study suggests that it’s because performing squats at a high volume (more than 15 reps) could actually count as cardio, with weight training stimulating cardiovascular health benefits similar to those experienced during endurance exercise.
22 participants aged between 20 and 39 who had over one year’s experience performing resistance exercise tested for their 1-rep max (1RM), and then on a separate day, when they were well rested, performed five sets of 10 full-rep squats at 65% of their 1RM, with a three-minute rest between intervals.
Maximal oxygen consumption, or how much oxygen you are capable of utilising during intense or maximal exercise (the higher the better), otherwise known as VO2 max, was measured. Prior to the squats, they had performed warm-up sets at increasing percentages of their 1RM (50%, 60%, 70% etc).
During the five sets of squats, the highest heart rate was observed at the fifth set, at 166 – 184 beats per minute (BPM), which was 89.7% of maximal heart rate.
In terms of VO2 max, participants with more strength experienced an increase in VO2 up to 108% of their max. This was because they had more muscle mass, and muscles need oxygen to produce energy. Meanwhile, the highest VO2 of participants with lower strength was 93.7% of their VO2 max, measured immediately after the final set.
When the highest VO2 achieved during each set of five sets was averaged across all groups, it showed that participants were exercising at 92.2% of their VO2 max, which was very close to 100% of their predetermined VO2 max. Therefore regardless of their training status, oxygen demand during squat exercises was extremely high.
Do high-rep squats count as cardio, then?
The jury’s out, it seems. If we look simply at the large volume of oxygen the body is using and the increase in heart rate, then squats could technically count as cardio, as could other strength-training exercises: ‘The levels of VO2’ and ‘the highest heart rate’ ‘clearly showed that multiple sets of resistance exercise could be considered as vigorous- or high-intensity cardiovascular activity,’ the study’s authors say.
However, the squats were not performed for long enough to count as aerobic activity, because of the rest periods. As the authors explain, ‘Since vigorous- or high-intensity aerobic activity is defined as an activity sustained for a prolonged period (10 minutes or longer) of time, squat exercise does not meet this criterion given the rest-interval period.’ So even though heart rate was elevated, the squat sets needed to be performed closer together to be classified as cardio.
The study therefore could have manipulated the workout – perhaps asking participants to use lighter weights, longer rep ranges, and decreasing the rest time, so people were exercising more continuously, with shorter breaks – to see if there was a point at which the programme counted as cardio from both a heart-and-lungs and rest-period point of view.
Speaking to Men’s Health, coach and athlete Louisa Sondergaard said: ‘The high-rep squat study is not able to support the conclusion that “squats are cardio”. It only shows that it is possible to elevate your oxygen consumption rate for a very short period of time if you do heavy high-rep squats. It doesn’t show that squats can be an adequate aerobic stimulus for cardiovascular adaptation.’
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