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Guys - I’ve briefly read the discussion in “Biomechanics” and “Your Strokes” and conclude Eric and Phil are relentless – a good thing. I’m running between cities so won’t be able to engage in an extended discussion but thought I’d chime in with a single observation.
I believe part of the discrepancy between your observations and the literature is semantics. Somersault is a forward pike at the waist, cartwheel is a lateral pike at the lower trunk, and twisting is trunk rotation about a curved spine.
It seems what you refer to as “cartwheeling” is what I measure as Trunk twist (shoulders rotating about the upper spine). Based on my research, only the twisting action of the trunk has any real impact on racquet speed.
Cartwheeling occurs late in the back swing and early in the upward swing as an effort to laterally tilt the trunk. This allows for increased trunk TWISTING rotation speed because the post-tilt trunk configuration aligns it better with the forward angular momentum axis (about which the overwhelming majority of angular momentum on the serve is generated) – as forward momentum is transferred to the trunk, aligning the trunk twisting axis in that direction allows faster twist rotation due to a lower reluctance to rotate (lower moment of inertia).
This position, along with the associated relative positions of the arm segments and racquet to attain acceptable contact height, are variable and alter the momentum transfer mechanisms. Therefore, different alignment strategies DRASTICALLY alter the amount of angular momentum transferred to the racquet at impact – ironically a large part of the subject matter of my dissertation –
gotta run – have fun - Brian
I believe part of the discrepancy between your observations and the literature is semantics. Somersault is a forward pike at the waist, cartwheel is a lateral pike at the lower trunk, and twisting is trunk rotation about a curved spine.
It seems what you refer to as “cartwheeling” is what I measure as Trunk twist (shoulders rotating about the upper spine). Based on my research, only the twisting action of the trunk has any real impact on racquet speed.
Cartwheeling occurs late in the back swing and early in the upward swing as an effort to laterally tilt the trunk. This allows for increased trunk TWISTING rotation speed because the post-tilt trunk configuration aligns it better with the forward angular momentum axis (about which the overwhelming majority of angular momentum on the serve is generated) – as forward momentum is transferred to the trunk, aligning the trunk twisting axis in that direction allows faster twist rotation due to a lower reluctance to rotate (lower moment of inertia).
This position, along with the associated relative positions of the arm segments and racquet to attain acceptable contact height, are variable and alter the momentum transfer mechanisms. Therefore, different alignment strategies DRASTICALLY alter the amount of angular momentum transferred to the racquet at impact – ironically a large part of the subject matter of my dissertation –
gotta run – have fun - Brian