[read time ~3 minutes]
“I worry that I’m going to end up with an injury,” Elizabeth explained to me over the phone. “I just want to be able to go for a hike or a jog, or take an exercise class with a friend, and not be afraid that I’m going to hurt myself.”
Elizabeth was in her 40s with a full-time job that sometimes required her to work extra hours or to travel. That’s why she liked running. She could lace up her shoes, step outside and start her workout. She worked up a good sweat in 20 to 30 minutes, so it felt efficient-- regardless of where she was: home, office, or hotel.
But lately Elizabeth was experiencing more aches and pains. Last month, she went kayaking with a friend, and her left shoulder hurt for almost a week afterwards.
“This probably shouldn’t have surprised me,” she admitted, “because I don’t do arm exercises all that often.”
When her shoulder was feeling better, she took an indoor rock climbing class. And since then, her right knee and hip are both painful when she runs more than a mile. She also feels the pain when taking the stairs instead of the elevator.
“I don’t want to believe this is just a part of getting older,” she sighed. “Can you help me?”
Aerobic exercise--often referred to as “cardio”-- is any physical activity that elevates your heart rate and requires you to breathe faster. It includes everything from brisk walking or running, to cycling, dancing, or jumping rope. For centuries, this type of activity has been recommended as an essential part of being fit and healthy.
Muscle strengthening is also a critical component of good fitness. The Centers for Disease Control and Prevention (CDC) recommends adults participate in muscle strengthening activities at least twice a week.
When I asked Elizabeth what type of strengthening she did for her legs, she wondered aloud: “Well, my legs get really tired when I run, especially on longer runs. Doesn’t this count as strengthening?”
The mistake many active people make is counting cardio as muscle strengthening.
Muscle strengthening involves doing something for a prescribed number of times (usually in the range of 6 to 15 times) over a short period of time to produce a lot of muscle fatigue. An example of muscle strengthening is lifting a weight overhead 8 times in 30 seconds, achieving a level of 80% fatigue (on a scale where 0% represents no fatigue, and 100% equates to the inability to repeat the action again).
Cardio, by contrast, involves doing something repetitively for a lengthy period of time. If a cardio activity causes fatigue in the muscles, it increases muscle endurance--the ability of the muscles to work over and over again--but it doesn’t increase muscle strength--the ability to generate a maximal amount of force.
Elizabeth’s pain was not simply a part of getting older. An absence of muscle strengthening made her more susceptible to injuries, aches and pains, and these made her feel old.
Mistaking Cardio for Muscle Strengthening:
Both cardio and muscle strengthening are critical components of physical fitness.
Both cardio and muscle strengthening cause fatigue, but only muscle strengthening makes your muscles stronger.
Stronger muscles prevent pain and injuries, allowing you to feel younger.