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The focus in this clip is on the racket arm during the smash.
As the racket is drawn back the elbow is in a low V position. This allows the shoulder to be relaxed before the big hit.
The strings should be facing downwards to ensure a clean full-face contact with the shuttle.
Watch the elbow and racket preparation highlighted here
At the point of weight transfer, the elbow is extended upwards and forwards so that the shuttle can be intercepted early just in front of the body (an L position).
This high contact point will also give you the option of a steeper smash if required.
In your smash practice please take some time to concentrate on your elbow shapes. V to L!