For years, pitching coaches have talked about “staying closed” or “delaying the turn,” but until recently, the underlying science behind that advice wasn’t well quantified. A 2025 study by Koya Mine and colleagues, published in the Journal of Sports Sciences, examined this very concept in Australian pitchers—and the results provide one of the clearest biomechanical explanations yet for how trunk timing influences both performance and arm stress.

What the Study Found

Sixteen amateur Australian pitchers were analyzed using 3D motion capture to measure the sequencing of pelvic and upper trunk rotation during the pitching motion. The researchers specifically evaluated how the difference in timing between peak pelvic and trunk angular velocities—referred to as the “DTPAV”—related to throwing velocity, spin rate, and upper limb joint kinetics.

The results revealed a compelling performance-stress trade-off: pitchers who delayed their trunk rotation (larger DTPAV) threw harder and generated higher spin rates, but also exhibited greater shoulder forces.

Key Findings:

• Later upper trunk rotation correlated with increased shoulder proximal force (β = 5.5; p < 0.01).
  
  
• A larger timing gap between peak pelvis and trunk velocity was associated with higher ball velocity (β = 0.2; p = 0.01).
  
  
• The same delay was linked to increased spin rate (β = 0.1; p = 0.02).
  
  
• Velocity itself was a significant predictor of shoulder and elbow torque, reaffirming the kinetic cost of throwing harder.
  
  
• All kinematic and kinetic measures demonstrated excellent reliability (ICC > 0.90), validating the data’s precision.
  
  

In simple terms: pitchers who sequence their pelvis and trunk rotation more effectively—allowing the pelvis to rotate first, then the trunk—tend to create greater whip and energy transfer up the chain. That delayed trunk rotation enhances both ball velocity and spin efficiency. However, with greater separation and acceleration comes greater deceleration demand, which may elevate shoulder loading if the upper body can’t effectively control the motion.

Why This Matters

This finding refines our understanding of rotational sequencing beyond the “hip-shoulder separation” cliché. It’s not simply about achieving a large separation angle—it’s about timing how that separation is released. Efficient pitchers don’t rotate their trunk too early; they allow the pelvis to drive forward, store elastic energy, and then let the trunk fire at the right moment to maximize transfer.

However, this study also highlights the double-edged nature of that efficiency. Later trunk rotation produced the highest performance metrics but coincided with higher proximal shoulder forces, suggesting that the very mechanics that make a throw powerful also increase stress on the arm if not backed by adequate deceleration strength.

This aligns with Oyama et al. [2014], who showed that improper trunk rotation sequences increased shoulder forces, and Stodden et al. [2001], who linked torso–pelvis coordination directly with ball velocity. Together, these studies demonstrate that trunk timing may be one of the most critical—and overlooked—determinants of both performance and injury resilience.

How We Apply This at VeloU

At VeloU, we emphasize rotational timing as a trainable skill, not a fixed trait. Our programming focuses on sequencing drills that help athletes learn to delay trunk rotation without losing stability. This includes med-ball scoop tosses emphasizing pelvic lead, resisted trunk rotation drills to strengthen the decelerators, and eccentric posterior chain work to prepare the shoulder and trunk for the added forces associated with efficient separation.

We also stress that throwing harder isn’t just about generating more force—it’s about managing it. A pitcher can only exploit the benefits of delayed trunk rotation if the posterior shoulder, trunk, and lower half can absorb and decelerate that energy safely.

In essence, this study gives biomechanical backing to something elite pitchers have shown for years: the difference between efficient and dangerous velocity lies not in how much you separate, but when you do.

References

Mine, K., Jones, M., Saunders, S., Onofrio, B., Crowther, R.G., & Milanese, S. (2025). Associations between upper trunk rotation kinematics, shoulder and elbow joint kinetics, and pitching performance in Australian baseball pitchers. Journal of Sports Sciences. https://doi.org/10.1080/02640414.2025.2569008

Oyama, S., Yu, B., Blackburn, J.T., Padua, D.A., Li, L., & Myers, J.B. (2014). Improper trunk rotation sequence is associated with increased maximal shoulder external rotation angle and shoulder joint force in high school baseball pitchers. The American Journal of Sports Medicine, 42(9), 2089–2094.

Stodden, D.F., Fleisig, G.S., McLean, S.P., Lyman, S.L., & Andrews, J.R. (2001). Relationship of pelvis and upper torso kinematics to pitched baseball velocity. Journal of Applied Biomechanics, 17(2), 164–172.

Slowik, J.S., Aune, K.T., Diffendaffer, A.Z., Cain, E.L., Dugas, J.R., & Fleisig, G.S. (2019). Fastball velocity and elbow-varus torque in professional baseball pitchers. Journal of Athletic Training, 54(3), 296–301.