Following some video analysis of elite play and using the principal of continuity we have formed this theory:

Theory: the direction of the follow through of a smash should be directly related to the direction of the smash.

This is different from some of the current coaching practice which advocates the follow through should always (or nearly always) follow through to the non-racket side.  To make analysis consistent we choose the hand/racket handle as the point that we followed.  The justification for this is that the distal body segment carries the resultant momentum of the smash and the racket head position can alter wildly depending on things like forearm rotation and wrist flexion and therefore is a poor general indicator.

In general we found that the lateral position (across the body) of the hand follow through varies from slightly outside the body on the racket side (for straight smashes) to towards the non-racket side hip (although not as far as is advised by some for all smashes).

Early analysis indicates a return around the elbow so that the arm becomes bent at the elbow during the initial follow through.  Also, at the end of the follow through we see a return around the shoulder and forearm from a pronated position so the racket moves to a position that points roughly horizontally across the body (pointing from racket side to non-racket side).

Our analysis showed we prepared straight smashes produced racket side straight follow throughs.  Other factors tended to drag the follow through towards the non-racket side.  These factors included:

• shot angle towards the non-racket side
• preparation court movement that required moving towards the non-racket side
• body weight shifted to the non racket side
• taking the shuttle out wide and low on the racket side.  This changes the plane of the shot such that the follow through swings naturally round

We predict that having a follow through that does not follow this pattern (e.g. the often advised follow through to completely the non-racket side) will cause slice on the shuttle and therefore reduce the transmitted power.

Early conclusions are that coaches should look for the players to play through the shuttle and allow the follow through to naturally progress in the related direction.

If it feels natural for the player to follow through on the non-racket side we have theorised that maybe this is because the early part of the shot is too stiff and instead of a kinetic link starting from body rotation, the body rotation is too dominant at impact time and drives the follow through round.  We have yet to test these ideas out.