Testing your scrums in training using a scrum machine / sled helps to ensure all of your pack practice the correct body position and timing in cooperation with their team mates. This is a great time to try out new combinations of players before match day.
With the brakes on, the scrum is more realistic to game situations, and the players must apply power at the same time to achieve any movement.
The roles of each player in channelling the ball to the number 8
Performance Analysis - Scrum 8 use
A progression from the 3 man scrum - developing body shape and positions
Each player should understand how their individual contribution affects the scrum as a whole
Develop the front row as a foundation for the building of the scrum
Building the scrum to the full 8 man - focusing on body shape