I have a very mild case of patellar tendonitis. But, it is a chronic and recurring problem I have been dealing with since 2011. I get it mainly from playing tennis. But, I notice that when biking I can also agravate it a little. I bike on a touring bike with fixies type pedals that fit pretty well. What should I watch for in my pedalling technique to heal my patellar tendonitis?
I ended up researching this topic with other sources. And, the feedback I got from a very avid biker (frequently bikes 80 miles a day on his own on the weekend) and a tennis colleague of mine that suffers from the same condition is described below.
The pedaling technique is key. The majority of bikers push down on their pedals with their toes first, so the feet when coming down are at a 45 degree angle (the heel being up and the toes down). That actually stresses out the patellar tendon. What you want to do is pedal by pushing down with your heel first. When you do that correctly, your foot should remain as parallel to the ground throughout the entire pedaling circle. A friend of mine described this technique as think of dragging your foot flush on the floor as if you want to remove some clay under your sole that is stuck throughout the entire sole of your shoe including the heel.
I have started this technique, and it seems to work pretty well. I also noticed that indeed the majority of bikers do not bike that way. Well they are young and don't have patellar tendonitis issues, so they are fine (until they are not).
What's your cadence? If you're running a large gear at a lower cadence, switch gears so that you're able to (consistently) spin about 90 rpm. This will reduce the stress on your knees.
As for the legs being straight at the bottom of the stroke, you don't want it completely straight -- maybe 175° vs. 180°.