Watch the best runners in the world race, and you’ll notice that almost all of them look supremely relaxed at almost all times. The grimacers and grunters and strainers are the exceptions (and usually the ones finishing behind). Sprinters are especially adept at running relaxed and letting the speed come out.
It might be natural to think that because you’re working harder you should feel tenser. But it’s not helpful. Straining while you run causes unnecessary muscle tightness and fatigue, and wastes energy that could better be used on getting to the finish line faster.
Everyone can get better at running fast but relaxed through practice. On your harder workouts, frequently run through a mental checklist: Are my shoulders low and even? Are my hands cupped loosely? Is my face, especially my jaw, free of strain?
Doing striders is an excellent opportunity to consciously work on running fast but relaxed. On each strider, think about one element of a flowing, relaxed running gait. Over time, practicing these desirable movement patterns will come naturally, even when you’re under duress in the last third of a race.