4 Surprising Reasons to Do Cardio While You’re Weight Training

by ben greenfield

If you were to go with me to a weight training session at the gym, you’d often see me darting off to the bicycle, treadmill or elliptical trainer in between weight lifting sets – and sometimes just throwing in a round of jumping jacks.

This isn’t because I have some rare form of exercise attention deficit hyperactivity disorder. It’s instead because there are multiple benefits to injecting strategically timed cardio sessions into your weight training routine – AKA “cardio with weights”.

Here are four surprising reasons to do cardio while you’re weight training (and a bonus video at the end):

Reason #1: Removal of Lactic Acid:

Multiple studies have shown that you can complete more reps, produce greater force, and experience far less lactic acid accumulation when you use the strategy of doing easy aerobics during your recovery between weight lifting sets, rather than just watching TV or reading a magazine.

Here’s why:

In most weight lifting scenarios, you are primarily utilizing an energy system in your body called anaerobic glycolysis. This is the process via which your body breaks down sugars into useable fuel for a forceful muscle contraction. But use of glycolysis results in significant accumulation of lactic acid. Too much lactic acid in a muscle decreases force production capability.

This is where easy aerobic exercise between your weight lifting sets comes in handy.

Light aerobic exercise, such as cycling, jogging, or even jumping jacks, can increase blood flow, which could increase the amount of oxygen that is available to either convert lactic acid to pyruvate (which can then be used as fuel) or to convert lactic acid to sugar in the liver, via a process called gluconeogenesis.

Reason #2: Hormonal Release:

When you lift weights, you get a release of growth-related hormones that help your muscles to grow or get stronger. These hormones include growth hormones, insulin-like growth factor, testosterone, and epinephrine. Depending on the type of weight training that you do these hormones can stay very significantly elevated for up to 30 minutes after you finish your exercise session (for example, higher-volume bodybuilding-style training results in a higher release of these hormones than short, explosive lifting).

But weight training isn’t the only form of exercise that causes a significant hormonal release. Brief and hard bicycling bouts in particular have been shown to cause a very similar amplification of growth hormones.

So why not get the best of both worlds and combine the last reason with this reason?

You can do your weight training set, then do a brief and intense 30-60 second bicycling bout, recover with easy aerobic cycling until you’re breathing easily (indicating lactic acid has been significantly buffered), then go back to the next weight training set.

Reason #3: Maintain Ideal Muscle Temperature

Your muscle’s force production capability are enhanced when your muscle is at specific temperatures. When you keep a muscle warm, you slightly decrease the muscle stiffness. While it may seem that a more “stiff” muscle would be capable of producing higher force, a slightly less stiff muscle can actually increase the responsiveness of the muscle’s tendons and the mechanical force production capabilities.

So while something like static stretching is not a good idea between, for example, a set of squats (it is too much stretching for your hamstrings and too much reduction in force production capability), riding the bike can keep your muscle just warm enough to allow for optimum muscle contraction.

Reason #4: Improved Nerve Speed

When you feel tired or exhausted towards the end of a weight lifting set, it is not just failure of your muscles that you are experiencing, but also a fatigue of your nervous system – as you lose the neural ability to recruit units of muscle and the firing frequency of your neurons.. But your nervous system not only operates at peak speed at specific ideal muscle temperatures described above, but it also recovers faster than your muscles do.

This means that if you’re just sitting around between your weight training sets, you’re allowing your nervous system to “cool-down” more than it actually needs to, and to an extent that may hinder your strength for the next set. By doing some type of aerobic activity, or by using the strategy above to combine a hard cycling bout with easy cycling recovery, you can keep your muscle temperatures high enough to ensure ideal neuromuscular activity for your next set.

So whether you want to remove lactic acid, enhance hormonal release, maintain your muscle’s ideal temperature or improve your neuromuscular capability, you’ve now got some good reasons to do something other than just sit there after you finish a bench press, squat, deadliest or some other weight training exercise. Mix it up with cardio and you’ll get better results.