What Should Lifters Do for Cardio?

I had a good conversation recently with some of our members about cardio for lifters – more specifically, why “lifting weights faster” isn’t cardio and whether cardio is actually important if you want to get stronger.

My exercise science Master’s program was basically a funnel for people to work in cardiac rehab, so our focus was largely on exercise for adults with cardiovascular disease. The heavy dose of anatomy and physiology courses helped me understand the way the heart and lungs adapt to both strength training and endurance training. To give away the ending: lifting weights isn’t enough and what most people think of as cardio (going for a run, interval training on a bike/sled, etc.) probably isn’t the best choice either.

First, let’s define cardio as training designed specifically to improve the ability of the heart and lungs to deliver oxygenated blood to working tissues. I’ll use the terms “aerobic system” and “aerobic training” interchangeably with “heart and lungs” and “cardio”, respectively. It’s not perfect, but for this discussion it’s OK.

Lifting doesn’t do a good job of improving your body’s ability to pump blood and consume oxygen efficiently. Lifting is anaerobic exercise, after all, because it’s too intense for oxygen to provide all the energy while lifting. No matter how light the weights are or how slow you do the reps, lifting physiologically can’t be “aerobic,” “oxidative” or “cardio” no matter what your dorkwad coach says.

Lifting and Increased Heart Rate

“But my heart rate goes through the roof when I lift!”

Yes, but increased heart rate and breathing rate while lifting doesn’t equal positive changes to your aerobic system. When you lift, blood gets trapped in the working muscles and can’t return to the heart until you put the weights down, rest and relax. This is called a decreased in venous return. When you reduce venous return, there’s less blood in circulation to go around and supply oxygen to other tissues. Therefore, it takes more heart beats (increased heart rate) and more forceful pumps (increased blood pressure) to deliver blood throughout the body.

Effective cardio should be cyclical in nature, meaning there’s repetitive movement with no “trapping” of blood in working muscles (e.g., running, cycling, swimming, etc.) and no “failure” point where you can’t keep going, such as the end of a set of squats, push-ups, etc. This maintains venous return and lets blood keep making it its journey to and from the heart, delivering oxygen all around the body where and when it’s needed.

After years of heavy strength training, you may develop some degree of left ventricular hypertrophy (LVH). The walls of the left ventricle of your heart grow thicker as an adaptation to increased blood pressure while lifting. The heart can’t fill with as much blood due to the thicker walls, so blood pressure must increase to pump the same amount of blood. Sounds scary, but it’s not inherently dangerous. Just inefficient.

On the other hand, endurance athletes (runners, cyclists, long-distance swimmers, etc.) experience a different adaption in their left ventricle: it learns to become more elastic so it can fill with more blood and pump more blood with each heartbeat. Increased efficiency. Lifters should care (at least a little bit) about cardio, not just because LVH leads to a less-than-efficient heart. As the saying goes, “all recovery is aerobic.” All the processes that replenish ATP (our body’s energy currency) and repair/rebuild tissue broken down during training become more effective with a well-developed aerobic system. If you want to recover faster (between workouts AND sets), grow muscle tissue more rapidly, and more effectively use the food you eat as fuel for exercise, you’re gonna want a robust aerobic system.

So what the hell should you do?

Going for a jog might be OK, but for those of us who lift heavy and consider walking to the fridge for another double IPA as cardio, it might actually be TOO intense (even at a slow pace) to actually develop the aerobic system. Believe it or not, you DO have to “get in shape” first for running be an effective form of cardio.

High Intensity Interval Training (HIIT)? Can’t that build up your cardio in a fraction of the time? Yes, it’s true that interval training (such as sled pushes or bike sprints with incomplete rest) has been shown to lead to the same main adaptations as aerobic training: 1) grow new capillaries (so there are more “roads” by which you can deliver blood/oxygen), 2) increased mitochondrial density (so you can produce more ATP) and 3) increased aerobic enzymes (also to improve ATP production). However, you have to go REALLY, REALLY HARD on your HIIT to see these adaptations. So hard, in fact, that the recovery cost of HIIT in terms muscle damage and energy use is pretty similar to lifting. So if you want to come back strong for your next lifting session, best not to tack on too many sled pushes or bike sprints at the end of your workout. Or at least make sure you get a full day of rest before your next lift.

The solution? Go for a walk. Every day if you can. Better to do a little a lot than a lot a little.

Walking won’t kill your gains. Or cause shin splits. Or make you want to puke. It’s easy and it works. For exercise to be truly aerobic and have a direct impact on your cardiovascular system, it has to be way easier than you think. So don’t jog. Don’t speed walk. Don’t walk up the steepest hill you can find. Just walk. Outside if you can. Get some fresh air, spend time with a loved one and/or your dog (or your cat, if you’re one of those weird people who walks their cat). Ten thousand steps a day has certainly been shown to be associated with improved health outcomes, no doubt because of how it enhances your aerobic system.

A leisurely bike ride would work too. Just wear your helmet.

TL;DR: strength training isn’t cardio. And most things we think are “cardio” are actually too intense (if you’re not already well-trained in them) and are kinda like just lifting more. If you want to live a long, healthy life while improving recovery between lifting sessions, go for lots and lots of walks.