These lines are where the elbow ends when finishing a move. In the 3 vertical lines (not the horizontal line) the elbow should be as low as possible on that line to maintain the 2nd centreline (see article).
Mai Jarn Punch (‘Elbow In’)
Jum Sao (combined with Juen Ma – Turning)
Mostly used for striking when staying frontal (i.e. shoulders square) with your opponent. If turning (Juen Ma) then this elbow line can be used to divert the attack (e.g. using Jum Da). If defending frontally (e.g. Fuk Sau), the elbow will be slightly lower than when attacking as the fist doesn’t need to be at the height of your opponent’s nose.
Gao Cha Sao (Cross Hands)
Wu Sao – when applied in practice (different in the form)
Mostly used for defending when staying frontal with your opponent. Your move will usually create a diagonal line with your forearm when viewed from the front.
However when using 2 arms forward together then your forearms can be straight (e.g. with Fun Sao, CK Seung Fuk Sao) – these moves are good for controlling your opponent’s balance.
‘Elbow Out’ Position
Fei Jarn Punch (‘Elbow Out’) – on the inside
Lap Sao (with Juen Ma/Turning)
Used for moves that aim to control your opponent’s arms instead of hitting them. This is because unlike the ‘braces’ line your elbows are not in front of your torso and are therefore less able to quickly transition into a strike.
Biu Ji Wang Jarn (Horizontal Elbow Strike)
Biu Ji Pek Sao (Horizontal Chop)
Only used in the above 2 high-risk strikes. The risk comes from the threat of losing your 2nd centreline by having someone put upwards pressure on your high elbow, resulting in the loss of balance. However the potential gain is high due to the strikes possessing good power.