Why It’s Important to Keep Moving
First and foremost, aerobic exercise is an important part of a healthy lifestyle. That's why the government recommends you do 150 to 300 minutes of moderate physical activity per week. When you sweat regularly, your heart grows stronger and you maintain the strength and mobility you need to move through your daily life, according to a June 2014 study in JAMA. Plus, cardio helps keep your weight under control, which can ease pressure on your knees, according to a November 2018 study in the journal Arthritis Care & Research.
When you're injured, movement can boost the flow of fluids through your lymphatic system, a vital part of your immune system, says Galina Denzel, a restorative exercise specialist and personal trainer with a special interest in chronic pain. The circulation of both lymphatic fluid and blood speeds healing by shuttling vital nutrients to the site of your injury, then carrying away waste products.
Physical activity also prevents short-term injuries — say, torn ligaments or tendinitis — from lingering, Denzel says. When you first get hurt, damaged tissues cause pain. But if you avoid movement for too long, your brain can tag the entire area as dangerous, even after it's healed. That's when your pain becomes chronic and far more difficult to treat.
Even if you have a progressive condition like osteoarthritis, research shows exercise can ease your pain and form a critical competent of your treatment plan. In fact, one recent research review published in June 2019 in the journal Osteoarthritis and Cartilage called the body of evidence on the topic so robust that no further studies are needed to bolster the case.
Finally, cardio serves another critical purpose: It's a stress reliever and mood-booster, says Keli Roberts, a personal trainer based in the Los Angeles area. Even if you need to choose a different exercise than what you'd prefer, such as cycling instead of running, you'll still produce many of the same feel-good chemicals that make up the so-called "runner's high."
And maintaining a mindset based on curiosity — wondering what you can do, instead of dwelling on your limitations — can improve the effectiveness of your entire rehab program, she says. Exercise may also prevent the depression that often accompanies injury, according to a research review published in April 2018 in the Cochrane Database of Systematic Reviews.
The Best Cardio for a Knee Injury
The type of aerobic exercise that works best for you will depend, in part, on the cause of your knee problems. Your physical therapist is the best source of information on what's right for your body and your injury. But generally speaking, any type of exercise that doesn't exacerbate your symptoms will probably get a green light— and many people do best when they mix it up and try several different movements. Some ideas:
Take up cycling. For most knee injuries, lower-impact activities are better than high-impact moves like running and jumping. Cycling is often not only safe, but beneficial. If you need to have surgery for an injury like an ACL tear, your physical therapist may include time on the bike as part of your rehab to improve your range of motion, says David Reavy, a physical therapist and founder of React Physical Therapy in Chicago.
Cycling can also help many people with patellofemoral pain syndrome or runner's knee, a pain under the kneecap that often occurs when the kneecap moves out of alignment. Weakness or imbalance in the quadriceps muscles contributes to this condition, Reavy says. Cycling can fire up all four of the muscles that make up your quads, returning your knee to the right track.
Hop on the elliptical. Other low-impact choices include the elliptical machine and walking on the treadmill, provided you can do so without limping or an altered gait. Setting the incline high makes the workout more challenging and activates the muscles on the backs of your legs, which are often neglected in regular walking or running, Reavy says. Just don't cheat and hold onto the handrails.
Go for a swim. You don't need to do formal laps if you don't want to; you can grab a board and kick, use a pool buoy to work on your arm movements, walk or jog through shallow or deep water, do aerobics or take aqua spin classes, Roberts says. If your injury required surgery, you might need to wait a bit to get into the water, but once you're cleared, swimming can be a mentally soothing, low-impact workout.
Row your boat. Rowing is another low-impact workout, but keep in mind that 60 percent of the effort comes from your legs, not your upper-body, Roberts says. Rowing works for some people with knee problems. but if you feel pain, try another option.
Try an arm bike. If your knee injury completely restricts your movement, you can try machines that focus on your upper body, such as arm bikes. You won't gain quite as much fitness as you would if you engaged your lower body, since your leg muscles are much larger, Reavy says, but you'll reap many of the same benefits.
How to Exercise Safely
No matter which cardio workout you choose, make sure you do a dynamic warm-up beforehand. This activates the muscles around your knee so you take some pressure off the joint, Reavy says.
And some words of warning: Post-exercise muscle soreness is normal — that's a sign you're gaining fitness or strength — but if you feel a sharp, stabbing pain mid-workout, stop what you're doing. If your joint is unexpectedly sore or swollen following your workout, you might not be ready for that activity just yet. Try something different, shorter or less intense until you gain back more of your strength and function.
Speak with your doctor about your use of medications, too. Reavy suggests not using pain relievers while you're exercising, so you can keep in touch with the signals your body is sending you. If you use them to mask pain and push harder, you might delay or set back your recovery.
- Office of Disease Prevention and Health Promotion: "Top 10 Things to Know About the Second Edition of the Physical Activity Guidelines for Americans"
- JAMA: "Effect of Structured Physical Activity on Prevention of Major Mobility Disability in Older Adults"
- Arthritis Care & Research: "Intentional Weight Loss in Overweight and Obese Patients With Knee Osteoarthritis: Is More Better?"
- Osteoarthritis Cartilage: "Do We Need Another Trial on Exercise in Patients With Knee Osteoarthritis?: No New Trials on Exercise in Knee OA."
- Cochrane Database of Systematic Reviews: "Exercise Interventions and Patient Beliefs for People with Hip, Knee or Hip and Knee Osteoarthritis: a Mixed Methods Review"