Why You Should Implement the 90/90 Sprint Start
The start is the most important component of a well executed sprint. The first few steps will tell you everything you need to know about the torque, projection, and trajectory of the sprint.
In earlier phases of acceleration the objective is to generate as much force in a horizontal manner as possible.
This includes:
Given this information, anatomically, where are we the most “powerful”?
If you are unfamiliar with the limb arc model (propulsion arc), this concept has been made more popular by the likes of bill hartman and the PRI community.
Essentially, gravity, stress, your respiration biases have a significant impact on your gait/propulsion at different degrees of freedom.
The Limb Arc Model
0-60 degrees (Early Propulsion)
- Inhalation/expansion
- Flexion, abduction, external rotation, plantar flexion, supination
60-120 degrees (Mid Propulsion)
- Exhalation/compression
- Extension, adduction, internal rotation, dorsiflexion, pronation
120-180 degrees (Late Propulsion)
- Inhalation/expansion
- Flexion, abduction, external rotation, plantar flexion, supination
Furthermore, anatomically we know that Internal rotators & adductors have most leverage to work at 90 degrees of hip flexion due to ↑ length-tension relationships (Neumann, 2010).
The piriformis switches its moment arm to internal rotation at 90 degrees of hip flexion (Levangie, 2011)
Hamstrings’ optimal length-tension relationship is at 90 degrees of hip & knee flexion (Levangie, 2011).
All of which are prime movers in sprinting.
With this information we can see that during the 60-120 degree (mid propulsion), preferably at 90 degrees, will be where the most leverage/length will occur, A muscle at greater length will have the opportunity to contract and generate greater levers of torque.