You put a lot of stress on your hip flexors when you sprint or kick. Thatâs why athletes, especially runners, soccer players, and martial artists, are especially prone to hip flexor injuries that result in hip flexor pain. Hip flexor pain is usually felt in the upper groin region, where the thigh meets the pelvis. To avoid hip flexor pain, you should pay more attention to these muscles, Dr. Siegrist explains. When you are seated, your knees are bent and your hip muscles are flexed and often tighten up or become shortened.
Walking and bicycling are good exercises for bad knees because they aren't high-impact. If you belong to a gym, the elliptical machine is another good option; the machine has pedals instead of a flat, treadmill-like surface and allows you to simulate running and walking without the impact on the joints.
1 Another cause of knee pain is using too high a gear. Try to use a gear that allows you to pedal quickly, from 70 to 100 strokes per minute.  Neck pain is another common cycling complaint and is usually the result of riding a bike that is too long or having handlebars that are too low.