drawings of muscles and exercise apparatus

Wednesday, April 18, 2007

Some thoughts on engagement under the new rugby scrum law

An email I received from Colin Astley reads:

"With the new scrum engagement rules everybody's looking for that little something to get the advantage. What are your views on my theory that if you use a quick 'squat' on the engage call, this would give you that extra 'bang' and you would be coming in at a rising angle. As there is only a split second to utilise this technique, the player would have to train the stretch-shortening of the muscle.

"Look forward to your thoughts,


I think that Colin is really onto something significant here. What we are observing under the new rules is a tendency to revert to the practice of the No. 8 pulling back on the locks while the referee goes through his " Crouch - Touch - Pause - Engage" chant. On "Engage" the No. 8 pushes with straightened arms against the buttocks of the locks before attempting to wedge his head between the locks' hips.

Prior to the "Engage" the front seven of the pack are pulling forward or leaning forward against the restraint of the No. 8. Once that brake is released they are pitched forward. Apart from the difficulty of coordinating the transmission and timing of force through the three rows of players, there are other problems from a biomechanical viewpoint.

In conventional scrummaging, front rowers typically crouch so that they maintain a stable position while being positioned to generate a powerful shove. By contrast, if they are being pulled backward their natural tendency is to adopt a very different body configuration. They will be more erect, and in particular their hips will be higher. That is what seems to be happening since the introduction of the new law - front rows are falling forward into the engagement with a consequent increase in collapses and resets.

I think that Colin has not thought through issues of timing when he suggests "a quick 'squat' on the engage call". That is far too late in the sequence. However, if around the time of the "Pause" call all forwards crouch or sink, they will be in an ideal position to rapidly generate a cohesive and coordinated upward-slanting shove on the "Engage". The structured and measured sequencing of the referee's calls under the new law makes such a technique very feasible.

What Colin is talking about when he refers to "stretch-shortening" is a phenomenon utilised by jumpers and gymnasts to increase jumping height and also observable in the ballistic back swing or pre-stretch of throwers and racquet game players:

"The stretch-shorten cycle (SSC) describes a period in which a muscle undergoes eccentric work, is stretched, contracts isometrically to stop the counter movement, and follows immediately with maximal contraction with the intention of applying a maximal force. The cycle utilises the principle of stretch reflex, of the length-tension relationship of muscle, storage of elastic energy in the muscle-tendon complex, enhanced potentiation of muscle, and chemical energy from the preload effect." (Doug McClymont and Mike Cron, "Total impact method: a variation on engagement technique in the rugby scrum" http://www.coachesinfo.com/category/rugby/84/)

There is absolutely no doubt that a pack which is trained to utilise stretch-shortening from a low crouch position will generate much more effective and purposeful force than one that one that adopts the "pull-back-then-release-the-brakes" method.

I believe that the new scrum law is potentially a significant improvement, subject to two conditions. Firstly, referees must rigidly enforce Law 20.2 (b) which requires of front rowers that "each player's shoulders must be no lower than the hips". Secondly, the practice of No. 8s pulling back the pack should be outlawed as it has been clearly demonstrated that its effect is directly contrary to the primary intent of the new law, i.e., to produce safer engagements and to minimise resets.