Exercising With Bad Knees — Low-Impact Training That Works
Knee pain stops more people from exercising than almost any other problem, and the advice they usually receive — 'just rest it' — is often the worst advice available. For the commonest knee problems, including osteoarthritis, the evidence is clear: the right exercise reduces pain and improves function, while inactivity weakens the muscles that protect the joint and makes the pain worse over time.
This guide covers the low-impact training that works for bad knees: the strength exercises that protect the joint, the cardio that does not aggravate it, and the movements to avoid. The principle throughout is the same as for back pain — graded, pain-monitored progress, starting with what does not hurt.
Use the calculator
Start with the numbers: try our step calorie calculator to work out your own figures before applying anything on this page. The worked examples below use round numbers so you can follow the maths; the calculator uses your real weight, height, age and goal.
Related reading: step calorie calculator, calorie calculator, Exercising With Back Pain, How to Start Walking for Fitness, full guides section.
The formula behind knee-friendly exercise
The most important number in knee exercise is the load on the joint. Walking loads the knee with roughly 2–3 times body weight per step; running loads it with 5–8 times; and stair climbing with about 3–4 times — so body weight itself is a major variable, and the Mifflin-St Jeor equation (Mifflin et al., American Journal of Clinical Nutrition, 1990) — 10 × weight (kg) + 6.25 × height (cm) − 5 × age, plus 5 for men or minus 161 for women, times an activity factor — frames the calorie side of any weight-management plan that reduces that load. A 10 kg weight loss, for example, reduces the load on the knee by roughly 20–30 kg per step. The exercise evidence is strong: a 2015 Cochrane review of exercise for knee osteoarthritis found it reduced pain and improved physical function, and the effect was larger for programmes that included quadriceps strengthening. The standard for judging a session is the pain rule used throughout rehabilitation: pain up to about 3/10 during exercise that settles within 24 hours is acceptable; pain above 5/10, or pain and swelling that linger into the next day, means the dose was too high. Strength targets are practical rather than formulaic: the goal is a quadriceps strong enough to control the knee through a step, a squat and a stair, which for most people means being able to do a controlled sit-to-stand from a chair ten times without using the hands.
The key points
Strengthen the quadriceps — it is the knee's shock absorber. The quadriceps is the main muscle controlling the knee, and strengthening it is the single most effective exercise intervention for knee osteoarthritis, according to a 2015 Cochrane review. Straight-leg raises, seated knee extensions with a light weight, and mini-squats to a chair all build quadriceps strength without loading the joint through a painful range. Two to three sessions a week, 2–3 sets of 10–15 reps, is the standard dose. Stronger quads mean less pain per step, measurably.
Cycling and swimming are your cardio. Low-impact cardio keeps fitness up without the joint loading of running: stationary cycling (low resistance, higher cadence), swimming, water aerobics and the elliptical all raise heart rate with minimal knee stress. Cycling is especially useful because it moves the knee through its range while strengthening the quadriceps. Start with 10–15 minutes and build to 30. Avoid running, jumping and deep lunges until the knee is stronger and quieter.
Lose weight if it is a factor — gently. Every kilogram of body weight adds roughly 2–3 kg of load to the knee per step, so weight loss is one of the most effective treatments for knee pain in people who carry excess weight. A modest deficit of 300–500 kcal/day, with protein at 1.6 g/kg to protect muscle, is the sustainable approach — and the safety floors of 1,200 kcal/day for women and 1,500 kcal/day for men apply. Crash diets are counterproductive: they lose muscle along with fat, and weaker muscles mean worse knees.
Avoid deep knee bending under load, for now. Deep squats, deep lunges, kneeling and high-impact jumping load the knee in its most compressed position, and they are the movements most likely to provoke pain early on. They are not banned forever — a healthy knee should eventually handle them — but the starting point is partial ranges: mini-squats to a chair, step-ups on a low step, and leg presses through a comfortable range. Increase the range gradually, one step at a time, watching the pain response over the next 24 hours.
Warm up the joint before you load it. A stiff, cold knee hurts more under load. Five to ten minutes of gentle cycling, walking or marching in place before strength work raises the temperature of the joint and the muscles around it, and a few minutes of gentle range-of-motion work — heel slides, seated knee bends — prepares the joint for the session. Ice after exercise can help if the knee swells, and a short rest day between strength sessions lets the joint recover.
Shoes and surfaces matter. Supportive, cushioned shoes reduce the impact transmitted to the knee, and soft, even surfaces (a track, a treadmill, grass) are kinder than concrete. Avoid worn-out shoes, high heels, and uneven ground while the knee is painful. If you walk for exercise, a flat route with good shoes is the right starting point — and a walking pole or stick can reduce knee load on hills if needed.
At a glance
| Activity | Verdict | Notes |
|---|---|---|
| Stationary cycling (low resistance) | Best cardio | Moves the knee, builds quads |
| Swimming / water aerobics | Best cardio | Almost no joint load |
| Walking (flat, good shoes) | Safe | Start 10 min, build to 30 |
| Elliptical trainer | Safe | Low impact, full body |
| Straight-leg raises | Safe strength | Builds quads, no joint load |
| Mini-squats to a chair | Safe strength | Partial range, controlled |
| Step-ups (low step) | Safe after 2 weeks | Builds function for stairs |
| Running | Avoid for now | 5–8× body weight per step |
| Jumping / plyometrics | Avoid for now | High impact, high load |
| Deep squats / deep lunges | Avoid for now | Maximum compression |
A worked example: a knee-friendly week
Take a 55-year-old woman, 80 kg, 165 cm, with knee osteoarthritis, who currently walks little because it hurts. Her BMR by Mifflin-St Jeor is 10 × 80 + 6.25 × 165 − 5 × 55 − 161 = 800 + 1,031 − 275 − 161 = 1,395 kcal/day, and at a sedentary level her maintenance is about 1,674 kcal/day. A modest deficit of 300 kcal puts her at about 1,374 kcal/day — above the 1,200 kcal/day safety floor for women — predicting roughly 0.3 kg of fat loss per week, and every kilogram lost removes about 2–3 kg of load from the knee per step. Her protein target at 1.6 g/kg is 128 g per day. Her exercise week: three 15-minute stationary cycling sessions (low resistance, building to 30 minutes), two strength sessions (straight-leg raises, seated knee extensions, mini-squats to a chair, glute bridges — 2 sets of 12 reps each), daily 10-minute flat walks building to 20, and gentle range-of-motion work before each session. No running, no jumping, no deep squats for the first month. After eight weeks the expected result, based on the Cochrane evidence, is less pain, better walking tolerance and stronger quadriceps — and a knee that hurts less per step because it is both stronger and carrying less weight.
How to use this guide
Start with the pain rule and a notebook. Do the safe list for two weeks — cycling, walking, quadriceps strengthening — and record pain 0–10 during each session and the next morning. If pain stays below 3/10 and settles within a day, add a little: five more minutes of cycling, a third set, a slightly higher step. If pain exceeds 5/10 or lingers, drop back. See a clinician or physiotherapist if the knee locks, gives way, swells significantly, or the pain does not improve after six weeks of consistent work — those are signs that need assessment, not more of the same exercises. And keep the weight side of the plan gentle: a slow, sustainable deficit with enough protein protects the muscle that protects the knee, which is the whole point.
What this guide does NOT tell you
This guide covers the common, exercise-responsive knee problems — especially osteoarthritis and general knee pain — and it does not diagnose anything. Knee pain can also come from a meniscus tear, a ligament injury, a fracture, infection, inflammatory arthritis, or a problem referred from the hip or back, and those need medical assessment. Seek prompt care if the knee locks or gives way, if there is significant swelling after an injury, if you cannot bear weight, or if pain follows a trauma. The pain rule and the load figures are practical guides from the rehabilitation literature, not individual medical thresholds, and they do not account for medicines, other conditions or previous surgery. The calorie and protein figures are estimates for a generally healthy adult; kidney disease, diabetes and other conditions change the answer, so discuss targets with a clinician or dietitian. And this guide does not replace a physiotherapist: if pain persists or recurs, a professional assessment and an individualised programme are the right next step.
Frequently asked questions
Is exercise safe with knee osteoarthritis?
Yes — it is one of the most effective treatments. A 2015 Cochrane review found exercise reduced pain and improved function in knee osteoarthritis, with the largest effect from programmes including quadriceps strengthening. The key is the right dose: low-impact activity, strength work, and the pain rule (below 3/10, settling within a day). Inactivity weakens the muscles that protect the joint and makes pain worse over time.
What is the pain rule for knee exercise?
Pain up to about 3/10 during exercise that settles within 24 hours is acceptable. Pain above 5/10, or pain and swelling that linger into the next day, means the dose was too high — reduce the volume, range or load and try again. Pain that changes how you move, or a knee that locks or gives way, needs medical assessment.
Is cycling better than walking for bad knees?
For most people with knee pain, yes — stationary cycling moves the knee through its range and strengthens the quadriceps with almost no impact loading, while walking loads the knee with 2–3 times body weight per step. Both are useful; cycling is the better starting point when walking hurts, and walking can be built up as the knee strengthens.
Does losing weight really help knee pain?
Yes, significantly. Every kilogram of body weight adds roughly 2–3 kg of load to the knee per step, so a 10 kg loss removes about 20–30 kg of load per step. A modest deficit of 300–500 kcal/day with protein at 1.6 g/kg is the sustainable approach — and never go below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.
Should I avoid squats completely with bad knees?
Not forever, but avoid deep squats under load early on. Start with partial ranges — mini-squats to a chair, step-ups on a low step — and increase the range gradually as pain allows. A healthy knee should eventually handle a full squat, but the starting point is the range that is pain-free.
When should knee pain be checked by a doctor?
Promptly if the knee locks or gives way, swells significantly after an injury, you cannot bear weight, or pain follows a trauma. Also seek assessment if pain does not improve after about six weeks of consistent, sensible exercise, or if it keeps recurring and limiting daily life.
Estimates only, not medical advice. Minimum safe intakes: 1,200 kcal/day women, 1,500 kcal/day men — consult a healthcare professional before a very-low-calorie diet.