Training is three dials: how fast, how heavy, how much fuel. These tools set all three — pace and race predictions for the run, percentages for the weight room, macros and zones for everything in between.
Within a few percent — if you train for the marathon. The Riegel formula assumes equivalent preparation; it cannot give you endurance you never built. Use it as a target, then respect the mileage.
Because Zone 2 builds the aerobic engine that everything else runs on, and most athletes train it too fast to get the adaptation. The heart rate zone calculator shows your honest Zone 2 ceiling — staying under it feels embarrassingly easy at first.
Yes — heavy low-rep work (85%+ of 1RM) improves running economy and injury resistance without adding bulk. The one-rep max calculator gives you the loads without ever testing a true max.