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MILESTONES OF A CORRECT TECHNIQUE
- Landing of the foot under the pelvis to avoid contact points in front of our center of mass which would create a force opposite to our forward motion;
- Light foot supination to more activate the elastic response of the lower kinematic chain;
- Fall forward using the support foot as the pivot of the movement;
- Release of the elastic force accumulated in the tendon and muscle part through plyometric contractions through the extension of the rear leg;
- Recall of the inward foot through the activation of the hamstring muscles and the knee-driven advancement of the free leg to close the gait cycle.
RESONANCE
The resonant frequency is the frequency at which the input of external energy is minimized to keep the system in motion.
ELASTIC FORCE
Force developed by an elastic body subject to compression or stretching.
F=k*x
SPRING MASS MODEL (Mc Mahon e Cheng, 1990)
Running stores the kinetic energy of the fall from the flight phase in the tendon-muscular system (Shorten 1987, Alexander 1988) and returns it in the thrust phase with a stiffness K attributable to both the musculo-tendon stiffness of the leg extensor muscles and to the elastic foot structure (Kerr et al. 1987, Alexander 1988, Alexander 1997)
Resonant frequency in running:
it depends on the anatomy of the body and on stiffness.
Range for adults is from 170 to 185 bpm
Stiffness
It depends on neuro-muscular activation
TENDONS
Footbed - Achilles - Patellar
MUSCLES
Back kinematic chain is designed for propulsion while the front muscles for stabilization.
PLIOMETRIC CONTRACTION: The mechanical model most used for the muscle contains elastic components in series, and others in parallel, to the contractile component. The phenomenon mainly concerned is the so-called lengthening-shortening cycle, in which an elongation of the muscle beyond its resting length (eccentric contraction) is followed by an active shortening of the same (concentric contraction). The components in series with the contractile unit, namely the tendons and cross-bridges, are capable of storing the elastic energy due to elongation. (Wikipedia)
RESONANCE
Even a running body has its own resonant frequency at which it minimizes the external energy necessary to overcome the forces that oppose advancement.
(Cavagna e Franzetti 1982, Kaneko e coll. 1987)
The point of maximum efficiency does not correspond to the point of minimum energy consumption Cr of the stroke (Kaneko 1990) because it increases the mechanical work associated with high stiffness.
SOME CONSIDERATIONS
A supinated foot is more rigid than a pronated foot and how this implies a stiffening of the system during running (Viale et al. 1998)
The stiffness, even if it is strongly influenced by both the stiffness of the acto-myosin bridges and that of the tendons (Shorten 1987, Alexander 1988), can only be modulated through neuro-muscular activation
However Actual Frequency tends to identify itself with Resonance Frequency especially at low running speeds (Cavagna et al. 1988) while for higher speeds, which would cause an increase in stiffness with consequent greater shock to the locomotor system, the subject tends to adopt a frequency of 10% lower, in this way it seems that the athlete prefers a lower stroke frequency with a consequent higher Cr probably in order to optimize the compromise between the need to preserve one's anatomical structures and the maximization of performance linked to the minimum expenditure energy (Dalleau et al. 1988a, b).
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