No, its not my knees after the cycle but my bicycle itself.
Thought something was completely knackered when I cycled to and from work yesterday as there was an ominous creaking from the crank. Found out it was my left pedal last night so thought I had worn the bearings out but thankfully I haven’t.
When spannering the pedal to get it off I realised it was quite lose so tighten it and the other one up and hey presto! No more creaks.
Hoooorah!