Why do my knees hurt when cycling?

Knee pain on a bike is usually caused by bike fit, and most often by the saddle height. Where the pain is tells you which way to adjust. If it's sharp, swelling, or still there after a few days off, see a doctor or physical therapist.

Where it hurts tells you what's wrong

• Front of the knee, around the kneecap. Usually the saddle is too low or too far forward, or you're pushing a big gear at low cadence. Raise the saddle a little and spin an easier gear.
• Back of the knee. Often the saddle is too high, so your leg overextends at the bottom of the stroke. Lower it slightly.
• Inside of the knee. Commonly related to cleat position or foot angle, so check the cleats are not forcing your feet to point in or out.
• Outside of the knee. Often a sign the saddle is too high or the cleats are rotated, and it can also come from tight outer thigh muscles.

Move one thing at a time, by a few millimeters, and ride on it for a few sessions before changing something else.

The easy checks

1. Saddle height. With the ball of your foot on the pedal at the bottom of the stroke, your knee should have a slight bend, roughly 25 to 35 degrees. A quick check is that your leg is nearly straight when your heel sits on the pedal.
2. Cadence. Aim for about 80 to 95 rpm. Grinding a big gear at 50 rpm loads the knee.
3. Cleats and shoes. Make sure the cleats are positioned under the ball of the foot, and that your float allows a little natural movement.
4. Crank length and bike size. If the bike is the wrong size, small adjustments won't fix it.

Build up more slowly

Doing too much too soon is the other big cause. If you've gone from 60 to 120 minutes a week, your knees may need time. Hold your weekly time steady for a couple of weeks.

Strengthening your quads, glutes and hips with squats, lunges and step-ups also helps, since those muscles take load off the joint.

While you sort out your fit, a shorter and easier spin is fine. Rides sync from Apple Health into League of Fitness and are scored by effort, so you don't need a big ride to count toward the day.

When to stop riding

Don't ride through sharp pain, swelling, clicking with pain, or the feeling that your knee gives way. A bike fitter can work out the details if your own changes don't help.