A relative strength calculator measures your strength compared with your body weight. It usually divides your 1RM (one-rep max) by your body weight to calculate your strength-to-weight ratio.
The best time-efficient strength plan for a marathon runner is 2 short sessions per week, focusing on squats, single-leg exercises, calf raises, core exercises, and upper-body strength.
Balance strength and running by doing 2 strength sessions per week, preferably on hard running days. Keep easy days for recovery and reduce strength volume as your marathon mileage increases.
A 16-week strength plan is generally safer for most runners because it gives your muscles, joints, and tendons more time to adapt before heavier training.