After intense rides I suffer from extremely painful quads/thighs. Yesterday I rode 75km including about 35km with a bunch at about 45-50kp/h and a couple of 3km 8% climbs on the way home. Today they are extremely tender. Even after mild riding they can be quite sore. It's been this way for me over my last 3 bikes so I'm not sure the cause. It is often accompanied by lower back pain later in my rides too. If anyone has any clues that'd be great! Cheers.