Early Elbow Extension in the Jump Smash: Speed Loss and Shoulder Pain

Sequential summation requires each segment to reach peak velocity in the correct order and at the correct moment, so the velocities add: hip and trunk rotation, then shoulder internal rotation, then elbow extension, then forearm pronation and wrist flexion. Racquet head speed is roughly the sum of those contributions, plus the whip effect when the racquet lags behind the hand and catches up at contact.

In Chan's action:

• Trunk rotation of only 20 degrees removes the largest contributor - the big muscle mass of hips and trunk - from the chain.
• Full elbow extension too early means the elbow's velocity peak happens before the shoulder internal rotators deliver theirs. The peaks are out of phase, so they cannot sum, and the arm ends up pushing the shuttle instead of throwing the racquet head at it.
• The stretch-shortening cycle is truncated. Early extension shortens the time the internal rotators spend on stretch during the cocking phase, so less elastic energy is stored and returned.
• The legs land together with no forward drive, so there is little ground reaction force and no forward transfer of the centre of mass to build on.

Fewer contributors, out of phase: that is a sound explanation for a 60 km/h deficit at the same height, although racquet, strings and contact point also contribute and should be checked.

Lever. Elbow extension is a third-class lever: the effort (triceps) acts between the fulcrum (elbow joint) and the load (hand and racquet). The effort arm is shorter than the load arm, so the system is mechanically disadvantaged in force but produces large range and speed - which is exactly why the timing of the chain matters more than raw strength. Shoulder internal rotation is also third-class.

Pain link (a reasoned hypothesis, not a diagnosis). When extension occurs early, the acceleration phase becomes dominated by internal rotation with the elbow already extended. In that pattern the humeral head tends to migrate and subacromial structures are repeatedly compressed, while the posterior cuff and capsule take eccentric load at the end of range. That is consistent with pain in the cocking phase and after 30 minutes of overhead work, settling with rest, rather than an acute tear. It also explains why 'more repetition' is the wrong prescription: it would repeat the faulty pattern under load.

Judgement. The technique fault and the pain are plausibly linked, but assessment by a physiotherapist is needed to confirm it. The coaching decision is to change the mechanics and manage the load, not to train through pain.

Plan (three sessions a week, quality over quantity).

• Replace 60 continuous smashes with blocks of 6–8 smashes at near-maximum effort with full recovery, 10–15 minutes total per session. Speed work needs full recovery; fatigue practice builds the wrong pattern.
• Add overhead throwing drills with a tennis ball or light medicine ball to rehearse hip and trunk rotation leading the arm.
• Use shadow smashes and footwork with an emphasis on trunk rotation and on the racquet lagging behind the hand, filmed every two weeks.
• Keep clears, drops and net play so he still trains and competes; band external rotation and scapular control work twice a week.
• Measure shuttle speed and compare elbow-extension timing on video rather than relying on feel.

Criteria for progression. A daily pain score of 0–2 out of 10 that settles overnight, technique holding in the last reps of a set when tired, and shuttle speed trending up. If pain exceeds 2 out of 10, or persists the next morning, reduce volume and refer.

Expectation setting. Four weeks can partially change a movement pattern but will not fully rebuild it; the semi-final should be planned around controlled smash volume, not a sudden return to 60 a day.