so ya 50 miles per week wont improve your 400m time unless youre out of shape ( high body fat percentage skinny fat or fat). Might improve your 800 but so will 40 at your age. The mile, ya, run 50. The 400 is highly technical compated to distance events. You need a good 50 meter start, a long stride to cruise at high velocity for the next 150 meters, and high turnover for when your stride starts to shorten from fatigue. Get a jumprope, start doing drills, sprints. That or be a 800/mile guy running 50 (still skip rope and strength train if you do this. but ya, you caught the trolls, but what you might not catch is people here know next to nothing about the 400. its a whole different animal, intense anaerobic energy use. Bench pressing or flipping a tractor tire tire does more for your 400 than a long run. Even the 800 is a lot more aerobic, if guys here are good at the 400 its coincidence, high mileage is aerobic training. its like training for shotput by paddling a canoe, youll be fit, but not specifically for your event.