From Rugby Coach Weekly
All players can run faster and you can help them by steering as far as possible away from these three myths.
1. Knees up
Sprinting is about power generated when the foot drives off the ground. That does not come from “high” knees. In fact, making players get their knees up might reduce the power.
It is better to focus on driving the foot into the ground. It is best if the player lands on the ball of the foot, so the calf is in the best position to drive off.
2. 90-degree elbow bend
Making players run with a 90 degree bend at the elbow has no anatomical justification. It might actually make the player stiffen up.
Instead, let him run naturally, though the arms do need to go forwards and backwards, and not side to side.
3. Sprint interval training
Increasing speed comes from improvements in technique and power.
If the players are doing interval work, they should be fully rested before they do specific speed work.
That might mean an eight second burst at top speed and then a minute’s rest.
Lots of 100m sprints only helps to increase speed endurance.