From the Coach guide
Hard repeats with easy jogs between.
Intervals raise your VO₂ max, the most oxygen your body can use.
Warm up easy. Run each repeat hard but in control. The last one should be about as fast as the first. Jog easy between them.
A small share of hard running gives a large gain. Plans keep hard days to 2 a week or fewer.
Strides: short and fast, but not tiring. Tempo: longer and steadier.
8-week randomized trial; 40 moderately trained men
4 × 4 min intervals at 90–95% of max heart rate raised VO₂ max more than threshold running or easy running that did the same total work.
The study was small and short, and all the runners were young men. Threshold running still has other uses, such as race pace.
Coach