The indoor bike was the single best form of exercise for me to increase knee flexion. From around 8 weeks post op, I rode the bike every single day. Here’s how I progressed the exercise to improve flexion and strength / tolerance in the tissues in the knee. When I started this program I could only just get enough bend to get the pedals to go round.
I borrowed a spin bike from work in the first instance.
This is the type of spin bike I used. Spin bikes differ from normal stationary bikes: their flywheel spins faster and their seat posts are more upright, meaning more flexion is needed.
Seat height as high as possible so you can get the pedals to rotate. ZERO resistance. Pedal until it STOPS hurting. The first time I tried this it took over 45 mins.
repeat this until you get on and it stops hurting within a few mins.
Gradually start lowering the seat. you might need to do a warm up at a higher seat height first before trying this. lower 1 notch at a time. max 3 notches in 1 sitting
Add speed intervals. Still little or no resistance. I.E pedal faster like you’re sprinting. You will need to build this up in speed and in time – start with short intervals and longer rests
Gradually start adding resistance. This needs to be VERY gradual and there should be NO direct pain through the knee joint. If there is, dial it back a little. NO STANDING UP.
Add standing intervals with the resistance back to easy. Only do this if its pain free in the knee joint.
Progression to an actual bike. The next step was to put my bike on the indoor trainer.
I have one that looks a bit like this. It lifts the back wheel: the bike is held in a frame and the back wheel is on a roller on mine. So I pedal as normal, my speedo works as normal, but its in effect turned into a stationary bike.
Back to the same as stage 1: pedal until it stops hurting, bike on the easiest gear possible / zero resistance. From there, then add a bit of speed in the legs as intervals.
Once you can pedal without it hurting at the start, practice getting on and off while the bike is attached to the trainer.
start gradually adding a little bit of resistance, but it should all still be relatively pain free.
Stage 5: the open road
At this point, I started by having my husband on stand by on the drive and I made sure I could pedal forwards and stop safely. Once I was sure I could do that, I started with my mountain bike and just trainers on my feet and did very short loops of the block. It was flat, back roads and all left turns. I was able to free wheel when my leg got tired (which was very frequently!)
Have fun, be patient and most importantly stay safe!