Im a fairly new runner and ran a marathon my first marathon last year and didn't really meet my expectations with a 3:03 time. I ran well until about mile 18 and then cracked hard. My training going into the race maxed out just of 50 mpw, and I think that low volume was likely my issue (for example, I have run half marathon at a pace that would predict a marathon quite a bit faster).
If I incorporate a lot more volume, consistently running 50 mpw, and ramping up to 60-70, how do I incorporate speed? If I'm doing that kind of volume, I would probably be mostly endurance and some tempo. I think I might really ware myself down with any significant threshold efforts. Would that volume alone get me faster? Do I need speed at all?
How do you balance speed with volume?