Knee Injuries from Badminton

During my studies in badminton I completed a study on Hongyan Pi, a Chinese player who plays for France.  Hongyan often had her knee strapped, and I found this fascinating.  It is common to see this strapping on many badminton players.  Recently, an Irish player told me about the damage to the menisci in his knees.  They were torn and he was in severe pain because of them.  I've watched him play on a number of occasions and it seems to me that he bends his knees a lot.  In a recent post I mentioned the angles that knees work best at.  That constitutes a bend of less than 50°.  Once the angle of the knee is greater than 50° the stresses on the knee increase rapidly.  Here's a video of Mikhail Koklyaev deadlifting over 400kg.  Look closely at the angles that he bends his knees to.  You can see that the angle that his knees are bent to when he starts the lift is about 45°.  His back on the other hand is at 90° to his thighs.  He is using his lower back and gluteal muscles to do most of the lifting.

I think we would all agree that the fundamental aim for a singles player is to reach a shuttle in good time and quickly move back to the centre of play in anticipation of the next shot.  Think then that in order to move quickly back to the centre of play, the last step away from the centre of play should be made when the player has a low speed or momentum away from the centre of play, in order that the player can easily accelerate back to the centre of play.  If you think that the movement around the court is like the motion of a marble inside a bowl; slow on the outside of the bowl and quick towards the centre of the bowl.  Ideally, the last step away typically involves engaging the myotatic reflex.  This is the same reflex that doctors test for with little hammers and the one that people use when they run.  A high degree of force is engaged during the engagement of the myotatic reflex.  In larger movements around the court, it is obviously used by the top players. 
The timing of the shuttle strike that accommodates this footwork best is that the shuttle is struck just before the last step away from the centre of play.  This means that the body is not changing direction, which allows a better shot.  Importantly though, it means that when the foot lands on the floor, the body is ready to accelerate back to the centre of play.

The flip side of the coin is when the player places their foot on the floor first and then strikes the shuttle.  The myotatic reflex is lost, and the knee is bending all the time the foot is in contact with the floor prior to striking the shuttle.  That is a big load on the knee joint and often the knee is bent past 90° before the player moves off.  The shuffle step is often foregone for some sprinting.  Another excellent badminton coach described it as the Ground Contact Time ( GCT ).  He postulates that the better players are in contact with the ground for less time in these steps.  I've included a link to a video of a match to hopefully illustrate what I mean.

2011 WC WSQF Hongyan Pi v Yihan Wang