hip and knee pain
Hi,
There are many reasons why you may be getting hip and knee pain on a training bike (with identical dimensions) used on an indoor trainer. The pedal forces (at different stages of rotation) measured on an indoor trainer differ significantly from those measured while out on the road. This load also varies according to the brand and mechanism of resistance (for example air, magnetic, or hydraulic).
With the the information given, it is speculation to come up with one or more contributing factors to your hip and knee pain. However, I can suggest some possible scenarios. I am assuming that pedals, shoes, saddle (and age of saddle), handlebars, BB width etc are identical.
1) Your warm-up on the trainer may be different to that of your road bike. Most people do a shorter, higher intensity warm-up on a trainer relative to the road bike. Try to approximate the same warm-up, and note any changes to your hip or knee pain.
2) If you have a heart rate monitor, compare the intensity and duration of workouts on the trainer relative to the road bike. A power monitor would be ideal but these are less common than heart rate monitors. You may be surprised at the difference. If you do more 'quality' efforts on the trainer, which is usual, you may for instance be exceeding the capacity of your vastus medialis to repeatedly control the movement of your patella during extension (straightening) and therefore develop patello-femoral pain syndrome (or sore knees). Hip pain at higher intensities may be due to aggravation of the sciatic nerve or simply lactic acidosis and failing contraction/ischaemia. As I said before these are just possibilities.
My recomendations would be to see a local physiotherapist who has a passion for cycling, and to try to reproduce the same warm-up on the trainer as you do on the road bike. This would include getting off the bike for a stretch after 15 minutes if this is what you do on the road bike. Remember that out on the road you are often getting out of the saddle for long hills, pot holes, sprints, traffic lights etc, and these regular changes of position alter muscle usage patterns and intensity and reduce fatigue. As a generalisation, indoor training sessions are usually shorter, sharper, and (barring discomfort that you describe) also give you a greater training response for the time allocated.
The fact that you are pain free on the road bike is very reassuring and it is less likely that there are serious issues. It is more likely to be a case of carefully comparing your activity on the bikes.
My qualifications are undergraduate exercise physiology and physiotherapy degrees, masters in pain management, and medical student (and 10 years in bike shops). Raced at track nationals (without merit) and a couple of top ten national road results.