Answer: Knee pain accounts for approximately one third of non traumatic musculoskeletal problems seen in a family physician's office. This complaint is most prevalent in physically active patients, with as many as 54 percent of athletes having some degree of knee pain each year.
As there was no acute trauma or sudden onset of the pain during a ride, it is almost certainly an overuse syndrome. To quote from excellent article on knee pain reprinted from the The Physician and Sports Medicine, posterior knee pain is "most often attributed to biceps tendinosis or, less frequently, medial hamstring tendinosis. Cyclists who have biceps tendinosis report insidious onset of point tenderness at the tendinous attachment of the biceps femoris where it inserts on the fibular head.7 Saddles that are too high or too far back can stress the biceps tendon. Excessive internal rotation of the cleats will also increase stress. Varus alignment of the knees or leg-length discrepancies may also contribute to posterior knee pain. If the saddle height is set for the longer leg, the shorter leg will be forced to stretch farther with each pedal stroke, increasing posterior knee stress. "
Increased susceptibility to this injury may be from inadequate stretching during warm-up exercises, decreased flexibility, and muscle fatigue. Endurance sports, such as running or cycling, are also associated with injury to the biceps femoris tendon. Overuse injuries are most likely when an athlete changes the mode, intensity, or duration of training. Biomechanic (intrinsic) factors and equipment or training (extrinsic) issues are also contributors to overuse injuries.
Treatment would include