Q: My trainer has me doing lots of heavy weights for things like squats and shoulder presses (well, heavy for me), followed on most days by some high-intensity movements like pushups and pull-ups, or plyometrics, or even pushing or pulling metal sleds around. I asked him what we’d be doing for cardio, and he said that “this is your cardio”. I thought that cardio had to last at least 20 minutes, and most of the time the absolute longest we go is 10-15 minutes before we rest, if that. Do I need to start doing my cardio on my own time? – N.R., Parker
A: For decades, since Dr. Kenneth Cooper published his groundbreaking book Aerobics in 1968, it has been thought that long (20 minutes or more) slow (heart rate in a “target zone” of 65-80% of maximum) exercise is the cornerstone of both heart health and fat loss.
Over the last several years, however, both research and the experience of athletes and trainers has shown that the long-lasting effects of higher-intensity exercise may have a greater effect on physical benchmarks than running 5k or spending an hour on the elliptical machine. (1)
In general:
- "Cardio" is very specific as to what benefits it brings. Running helps you be a better runner. Biking helps you be a better cyclist. Lance Armstrong, who probably has the best VO2 max (the ability to utilize oxygen – the primary benchmark of cardiovascular fitness) in human history, found that his time on a bike didn't help nearly as much as he thought in running a marathon. In other words, while squatting or plyometrics won’t help your running as much as running will (although they will make a significant difference), neither do bicycling or jumping rope.
- Both steady-state cardio (such as running, aerobic dance, elliptical machines, etc) and weight training improve your metabolic conditioning by means of developing an oxygen deficit in your cells (primarily your muscles), from which your body needs to recover.
During cardiovascular exercise, this is very mild (by definition, it's an oxygen deficiency that you can maintain for extended periods of time), and lasts as long as the exercise is going.
A session of high-intensity weight training (or sprinting, or kettlebell swings, or sled pushing) puts your muscles in a significant state of oxygen debt resulting in everything being ramped up trying to recover for hours after you’ve finished your session (referred to as EPOC, or “Excess Post-exercise Oxygen Consumption”). So essentially, during the exercise itself, you're in an anaerobic training zone. During your rest time between exercises, and during the recovery time afterward, you're in an aerobic zone for much longer – up to 38 hours according to some research (2) – than you would be if you had gone for a run.
- About the only thing steady-state cardio does that weight training doesn't is increase the density of mitochondria (organelles that produce energy via aerobic pathways) in the muscle cells, since our muscle cells adapt specifically to use. If you train in distance running, your muscles will develop more mitochondria to utilize oxygen to produce energy. If you do more weight training, they will get better at utilizing creatine phosphate and glycogen to produce energy.
What this all comes down to is that it depends on your goals; if you want to improve in long-distance running or cycling, you’ve got to practice running or cycling. If, however, you’re looking for the best results for long-term heart health or fat loss, your trainer has you on the right track.
(1) Melby, C.L. et al. 1993. Effects of acute resistance exercise on post-exercise energy expenditure and resting metabolic rate. Journal of Applied Physiology, 75, 1847-53.
(2) Schuenke MD, Mikat RP, McBride JM, Effect of an acute period of resistance exercise on excess post-exercise oxygen consumption: implications for body mass management, Eur J Appl Physiol. 2002 Mar;86(5):411-7. Epub 2002 Jan 29.
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