Ito et al noted in 1992 that Lewis and Burrell did not differentiate themselves from 10.60-11.50 Japanese sprinters through ankle or knee extension velocity in the ground phase but rather through marked differences in hip extension velocity. This suggested highly disproportionate increases in hip extension velocity compared to ankle or knee extension velocity with increasing speed. Lewis’ reported knee extension velocity was near zero, which meant that a superior sprinter (with commensurate anthropometry), given disproportionate increases in hip extension velocity compared to ankle or knee extension velocity with increasing speed, was likely to eventually show negative knee extension values as hip extension velocity continued to gain and contact time and length changes were minimal.
–> The potential key to superior VMax is superior hip extension velocity.
(BUT these gains in “hip extension” depend upon pelvic orientation!)
Lombard’s Paradox is based upon the simple spring mass model, which is invalid with regards to the 100 metres. The importance of vertical (not spring-mass reliant) as opposed to leg stiffness (spring mass reliant) is becoming clear in the research, particularly regarding the 100 metres distance.
Also clear is that a pure focus on the ground phase and ground contacts and GRF’s etc is myopic with regards to sprint performance and increasing maximal speed as it seems contact time, contact distance etc are stable. Regarding touchdown distance (assuming a given anthropometry):
– Decreases will occur between markedly lower and markedly higher speeds
– At high speeds, further touchdown distance decreases must result in more extended leg at touchdown (unless we sit right down with big dorsiflexion, which may be undesiable :p ).
–> Potential decreases in stiffness.
I believe it is likely that top sprinters have optimized touchdown distance relative to their anthropometry (tibia/femur ratio will matter) and instead of addressing gains through knee and “hip” position, and further marginal gains may be most possible through subtle changes in lumbopelvic rhythm.
Implications for “pawing or “grab velocity”: Negative velocity of the foot is very likely related to hip extension velocity relative to horizontal velocity of the centre of mass.
The “pawing” appearance in better sprinters is very likely a result:
1. Disproportionate increases in hip extension velocity relative to horizontal velocity of the centre of mass.
2. Disproportionate increases in hip extension velocity compared to ankle or knee extension velocity with increasing speed.
A knee extension moment is present through the ground phase in sprinting, and as per the above there is highly physiological pre-activation and activation of vastus medialis to for a braking impulse.
Implications for research perspectives: The swing phase is part of the causative pathway that is the gait cycle, and should not be separated for analysis, or regarding as unimportant due to lack of GRF’s. The activation of various hip and knee extensors is very high throughout the swing phase and these actions are essential to the technical model of maximal running. To take away both preceding acceleration and analysis of output in swing phase, as with Weyand’s treadmill work, greatly inhibits a view of the context.
The functions of the hip and knee extensors are multiplanar and actions and interactions with other muscles will tell a similar story. More attention needs to be paid to the anatomy and the importance of the lumbopelvic rhythm rather than “hip” based measures.
In a similar vein, it must be noted that step width is the variable with the greatest correlation to maximal running mechanics compared with step frequency and length in the Helsinki data, and is most sensitive to changes in running speed as we approach maximal values. There is clear relevance for the attachments of the biceps femoris, and the actions of hip “extensors” and “flexors” in the frontal (and transverse) plane, and training modalities (wide box squats with a big arch = force production from an abducted position, anterior tilt, external not internal rotation with extension, I will draw up a post on other exercises as Bulgarian squats and muscled hang cleans, and wide catches on o-lifts, hip thrusts with a bar across the lower abdomen are not friendly to lumbo-pelvic rhythm and posture so for those going more than 40 yards, so caution is very much needed, see previous comments re “subtracting what hurts you vs adding new methods”).
These step width reductions result in force production from a very medial position that is dependent on angular momentum (from swing phase) and velocity at high levels and very likely unique to sprinting. We cannot replicate this medial position with static, slower velocity weight room work (lacking a swing phase for angular momentum) whether bilateral or unilateral, as a fixed flat foot means the knee shows the medial deviation as the foot stays close to under the ipsilateral shoulder for balance.
The spring-mass model and the Lombard paradox need to exit stage left, as sprinting is not a sit to stand and the kinematics are clearly demonstrating this now in elites, though for years we have known that hip extension velocity is hugely disproportionate. Focusing on lumbopelvic rhythm and footstrike to address overall kinematics (all planes), muscle activation and kinetics across the full gait cycle, to improve mechanics and stiffness seems a better direction. I am writing a more detailed look at effects on speed and fatigue with a specific case study and will post when done.
Reports of seemingly paradoxical “hip flexor cramping” at the bottom of a squat is likely due to increased anterior tilt to maintain balance.
“Booty Lock” or soreness at the glute-ham tie in for sprinters doing big upright volumes is likely related to big muscle activity in pelvic stabilization regarding glute/ham and posterior tilt in the gait cycle.