>>> I want to make sure I understand the idea of back arm bend/L idea correctly -- this research has found that the back elbow stays in an L at contact if the pitch is straightaway, but that on an inside pitch, there might be more arm extension? It seems like you could generate more force by extending based on the principle of having a longer "arm," but watching the slo-mo videos definitely shows hitters keeping their elbows in. Interesting <<<
Mark's post below correctly notes that the back-elbow must extend more to reach outside pitches. I would point out that keeping the elbow back in the "L" position supplies more power than relying on the extension of the arm. Ask yourself this question: had you rather be hit by a boxer's 'right hook' or his 'jab'? With the 'hook', the elbow maintains a constant angle and is driven by the rotation of the body.
The same is true for swing mechanics. The arm remains back in an "L" position and is powered forward by the major muscles of the legs and torso (via shoulder rotation). This is why analysis shows the best hitter's bats are brought to contact as shoulder rotation is depleted. In evaluating the efficiency of a batter's mechanics, the first thing I look for is, 'where was the bat when shoulder rotation was depleted.'
With efficient mechanics, the angular acceleration of the bat stays in sync with the rotation of the shoulders. Therefore, their bats arrive at contact as shoulder rotation is depleted. With less efficient mechanics, the bat remains 30 to 90 degrees from contact (bat drag) as shoulder rotation ceases. Once the shoulders stop rotating, the only muscles left to power the bat to contact is the smaller muscles of the arms.
The video clip below illustrates an inefficient mechanic that depletes shoulder rotation without producing a corresponding acceleration of the bat.
Role of the lead-arm