I've been cycling long-term in hills and over the last few years without clipless pedals. Over time I have found the hills to be easier to climb, but have noticed a dramatic decrease in my running ability, and recently on holiday found it difficult to walk long distances as well without pain and stiffness. Is this because of increased leg muscle (weight)? Should I get clipless pedals again? Any thoughts? Thanks in advance!
Is this because of increased leg muscle (weight)?
I am confident that no, bicycling has not packed so much muscle onto your legs that they are now too heavy to walk normally and comfortably.
I don't think they are related and I don't think clip-less pedal will change anything. It's probably age or lack of running training that make it harder to run.
Anecdotal evidence : my friend is running and cycling pretty fast, but I can only cycle fast, I'm an abysmal runner. He runs multiple times a week while I rarely run more than once a month.
Think of triathletes who run and cycle pretty fast, if cycling would be bad for running, they wouldn't be able to do both of them at that level.