Shakey, it is never a good idea to hyperextend/flex any joints really (Not unless you a yoga master :lol: ) Your knees and kneejoints are supported by the legs biggest muscle which is your quads (thigh muscle) So strong quads=strong kneejoints for any type of exercise.
The normal range of flexion of the knee joint is well beyond 90 degrees and such movement does no harm at all; indeed it does all joints good to be moved through the entire range of normal movement from time to time. Harm to the knee joint occurs when there is frequent movement in the mid range when weight bearing (climbing ships' ladders for instance.) The RN sees lots of knee problems caused by such (necessary) activity, aggravated by soccer (unnecessary!)
or driving any aircraft moving tractor for 10 years!!
I have no knee cap in my stbd main oleo, it was removed at the age of 31 when the doctor told me the damage that had been done he would expect to see in someone in their 70s. Now at 46 my port main oleo is in the same boat & am a waiting my 7 op on knees. :sad: