The recently proposed topic on actual percentages of bent knee has affected Antonio Amigo, a researcher at the University of Barcelona.
We propose his report on this argument, accompanied by some photographs-graphics made on the occasion of a meeting with all the race walking Judges of Catalonia (ESP).
Needless to say, the Marcia dal Mondo thanks Antonio Amigo for the collaboration offered on this occasion to clarify this interesting topic.
In the high-level elite race walk (including U20 and U23 categories) virtually all red card for bent knee are false positives, and therefore sometime erroneous.
This is the reason why it is very difficult (except some exceptions) to find a picture in which you really see a knee flexion.
Many times for a mistake in judgment the judge always tends to overestimate the knee flexion and underestimate the loss of contact.
It is very easy that visual perception of the bent leg is maintained in the judge retina until after the final moment required by the rules (vertical) when the leg was actually fairly extended at the time of contact. Also with current style in race walk, the leg extends only shortly before the contact with the ground, and evaluating just that moment is visually very difficult.
So this is the reason because there are always many more red cards for ben knee flexion than real knee flexion.
On the other hand, beware with absolute certainty that loss of contact is something unattainable to the human eye with the high current rhythms.
For this reason, on the contrary to knee flexion, judges always tend to notice a lesser loss of contact than what is actually happening.
Let's see in figures: a step of a walker is about 250ms. (1/4 sec.). The time for contact loss is normally only about 10-12% of the total duration of the step.
"Visually" finding that short flight time is extremely difficult for the human eye.
On the other hand, a judge normally "sees" a bent leg of the walker for at least 66% of the total time of the step, and only 30-33% see it fully extended (time from the heel to the ground up to the vertical position).
With the modern style of walking, this extended leg time shrinks even further, and therefore the "feeling" of the folded leg is the one that still prevails in the judge's brain, as its retina does not even allow it to “see" the moment of the heel attaching to the ground.
That is, of this 30% of real extended leg, the court eye "loses" more or less a further 10% for simple "retinal visual inertia", this 10% corresponds exactly to the period of the heel attack to the ground.
Receiving detailed information on the characteristics and peculiarities of the human eye retina and its "real" ability to observe and/or appreciate something should be a fundamental part of the education of the race walking judges.
This is because the timing of the offenses occurring in the current walk is at the limits of human visual evaluation.
Antonio Amigo - Barcelona