THE RIDE IS STRAIGHT THRU ? 50hrs week/month to where ? Why not interesting place A to interesting place B at 50 miles ?
Check your shoe heels, worn ? add heel inserts pushing pelvis forward. Stretching exercises for lower back and situps, Place hands on ground, move feet back and aside a bit then see what the lower back and vastus medialus are doing today.
A flat terrain ride suggests longer cranks than a hilly routing.
If you ride BIG GEARS be warned knee cartilage separation may occur without warning or significant pain.
My experience suggests if you plan to ride 50 then train 80 4 times a week: time consuming.
If you can ride 50-80 4 times a week with a 60-75 pound load, do intervals....then not feel ANY strain during or after then go go go....
if not revise the so called plan.
How's the ticker ? wear a monitor...if your rate is down from average the morning after a ride or workout then take a break and/or review the exercise load as too grate.