The efficiency of the lower half is dependent on utilizing your functional anatomy. When a muscle contracts it loads the tendons like a spring allowing for the tendon to recoil and produce efficient energy. Lack of optimal strength while running will cause a decrease in the tendons inherent capabilities to act like a spring, thus causing more of a metabolic demand that will ultimately decrease endurance. The more you load your tendons with strong forceful contractions from the muscles, the more efficient your strides become.
It also holds true with proper knee, foot and ankle alignment; the more you utilize proper alignment, the less unnecessary movements will occur, ultimately leading to a preservation of energy leading to greater endurance.
It comes down to the metabolic demand of the muscle: if you can’t move properly the demand goes up, and if you move more efficiently the metabolic demand goes down, ultimately leading to greater endurance. Think of it like pushing a car up hill versus downhill, which would you rather do? Exactly, you’d much rather push the car downhill because it takes little to no effort depending on the grade of the slope. When your movements are flawed and your muscles are weak, your movements become like pushing the car uphill, a massive waste of energy. If we utilize proper biomechanics and decrease our muscles metabolic demand by increasing strength, our stored energy and endurance is greatly increased.