接触时的延伸
Also known as: 延伸, 完全延伸
延伸是指双臂在接触瞬间及之后继续伸展，而不是收缩贴向身体——在接触瞬间本身，后手臂通常仍保留一定弯曲，尤其是打内角球时，完全延伸会在撞击后一瞬间才完成。
当打者以双臂明显弯曲的状态完成接触时，力量会流失，棒速也会随之泄漏。理想状态下，对于本垒板范围内的球，接触点会略微靠前，双臂在贯穿击球的过程中伸直，而不是收缩折叠进躯干。可延伸的幅度取决于落点：内角球必须提早接触，双臂还来不及伸直；外角球则允许双臂在好球区内伸得更远。撞击之后发生的事情，会叠加放大所传递的力量。
二者是相互关联的：击球点的位置决定了双臂是否能够伸直。对于外侧半区的球，接触点在好球区内更深（更靠近捕手），这使得双臂在接触瞬间能够朝投手方向完全伸展。内角球则必须在更靠前的位置完成接触，因为它更早到达打者身前。此时双臂完全伸直既不可能也不理想——那需要在更深的位置接触球，双手会越过身体中线。
撞击之后继续把棒头贯穿球体，是与击球初速关联最直接的变量。那些在撞击后继续发力一两英尺的打者，其击球初速持续高于那些一触即收、立刻收臂的打者。这正是为什么强调“撞击后向投手方向伸展”的训练能提高击球初速——它们训练的是贯穿撞击的持续发力，而不是撞击瞬间保持的某个静态姿势。
After each swing in batting practice, hold your follow-through position and check that your arms are nearly straight. This means if they are still by a lot bent, you are collapsing rather than extending through the ball.
Practise reaching a foot further toward the pitcher after impact than feels natural — that overshoot builds the pattern behind higher exit velocity on well-struck pitches.
Example
她在本垒板前方接触外角速球时双臂完全伸直，把球线打向反方向空当。
How it shows up on video
On video, quality is judged at impact and across the first foot of barrel travel afterwards. Common errors include the arms collapsing toward the body at contact (producing a weak flick rather than a drive through the ball), contact occurring too deep in the zone with the arms still by a lot bent (usually caused by a late swing or a pitch that jams the hitter). A premature rollover where the top hand fires over the bottom hand just before or at the contact point rather than continuing through it.
Common mistakes
- Collapsing the front arm at the elbow during contact instead of driving through the ball. This leaks energy and reduces exit velocity on pitches across all zones of the plate
- Meeting an outer-half pitch too deep in the zone, which forces bent arms before they could geometrically straighten
- Rolling over the top hand immediately at contact rather than extending through. This converts what should be a line drive into a pull-side grounder from premature top-hand dominance
- Confusing the follow-through position with what happens at the ball, and drilling the finish before fixing the strike
In SwingVantage Motion Lab
SwingVantage measures elbow angle at impact and how much the arms stay driving across the following ten frames, flagging those that fold at or before the ball. It compares that across inner-half, middle and outer-half pitches, to identify whether the hitter is moving the meeting point with the location or using one fixed spot for everything.
Related terms
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