I'm 50 years old, have been riding about 500 miles per year. This year I plan to ride more...have about 500 miles in 2 months. Typically have been taking 10-15 miles rides with a longer ride one time per week (increasing distances each week). Yesterday I tried my first 50 miler. About at the 35 mile mark I experienced either cramping or muscle fatigue in front of my upper leg muscles...especially the right leg. Does anyone have an opinion whether this was cramping or muscle fatigue (which I never experience on shorter rides). I had taken in water/electrolytes/carbs prior to riding and about 40 oz. of fluid during the ride. Any thoughts would be appreciated.