Hayward Live.

Carter shows his powerful startup while showing off.

Bolt.

Not much less.

Or.

This guy's mind.

There is no concept of "let".

During the squat phase, the forefoot bears a static load of about 60% of the body weight.

From the perspective of the human body's motor chain, this load distribution is closely related to the human body's anatomy and muscle function.

The forefoot connects the anterior calf muscle group and the small muscle group of the foot, which play an important role in maintaining body posture and providing initial support.

Since the center of gravity of the body leans forward during the sprint start, the forefoot acts as the front-end support point and needs to bear greater load to maintain body balance.

From a mechanical principle, this load distribution makes the body's center of gravity located in a relatively stable area, laying the foundation for subsequent start-up actions.

According to the principle of torque balance—

The torque generated by the body's gravity needs to be balanced by the counter moment generated by the support force of the forefoot and the hind foot. The large load bearing of the forefoot helps reduce the moment generated by the support force of the hind foot, so it is easier to maintain the stable posture of the body during the squatting stage.

Why say this?

This is because...this is what Bolt does now.

It was also what Mills told him, called the migration trajectory of the bipedal pressure center.

For example, the hindfoot pressure center is moved backward during startup.

That is, the center of the hind foot pressure moves backward 2-3cm along the sagittal plane.

This phenomenon has deep neuromuscular control and mechanical logic.

It's not random.

Mills is definitely a good person.

During the transition from squat to activate, the neuromuscular system will make fine adjustments to the body posture.

The center of the hindfoot pressure is due to the pre-activation and contraction preparation of the posterior calf muscles such as the calf triceps.

The contraction of these muscles causes the hindfoot to force behind and downward, causing the pressure center to move backward.

From the perspective of kinematics, the backward movement of the pressure center of the hindfoot changes the action line of the support force of the hindfoot.

This changes the direction of the torque generated by the support force of the hindfoot.

This helps provide a backward and lower pedal force at the start moment.

Provides high-quality reaction force for the body to accelerate forward.

In addition, this backward movement also adjusts the shape and size of the overall support surface of the body.

It is equivalent to further optimizing the body's equilibrium state before starting, and once again improving the stability of starting in disguise.

Of course, Bolt didn't understand these things.

He also doesn't need to understand.

Mills understands it.

When the reaction reaches the threshold of 180-220ms, the peak pressure forefoot can reach 3.5 times the body weight and the back foot is 2.8BW.

This is because at the moment of initiation, the neuromuscular system is activated rapidly and the muscles undergo strong contraction.

The peak pressure of the forefoot mainly comes from explosive contraction of the anterior calf muscle group and the extensor muscles of the foot. These muscles produce huge strength in a short period of time, pushing the forefoot downward to press the starter.

The peak pressure of the hindfoot is mainly caused by the strong contraction of the posterior calf muscles, especially the triceps of the calf.

According to the mechanics of muscle contraction, when muscles contract rapidly, they can produce greater force than static contraction.

Then at the critical moment of sprinting, the rapid contraction of these muscles can cause the pressure on the feet to increase sharply, forming a pressure peak.

Then...the pressure gradient difference enters to form a propulsion couple.

This is the key mechanism for generating forward propulsion during sprint start.

Because the pressure peaks of each person's forefoot and hindfoot are different, a pressure gradient along the sagittal plane is formed.

According to the mechanical definition of force couples, force couples are a force system composed of two forces of equal magnitude, opposite directions and non-collinearity. Their effect is to make the object rotate.

In sprint start, the greater pressure of the forefoot and the relatively smaller pressure of the hind foot form a force couple. The effect of this force couple is to rotate the body forward around a horizontal axis, thereby generating forward propulsion force.

From the perspective of motor chain conduction, this propulsion couple is transmitted upward to the trunk and upper limbs through the lower limb joints, including the ankle joint, knee joint and hip joint, driving the entire body to accelerate forward.

The subsequent formation of the propulsion couple is also closely related to the coordinated control of the bifoot pushing and stretching movements by the neuromuscular system.

Only when the pedal and extension force of both feet and timing are precisely coordinated can an effective propulsion couple be formed and an efficient sprint start can be achieved.

Mills.

One of the optimizations for Bolt's winter training this year.

That's what's arranged.

Then, based on the principle of peak power output of the ankle joint.

The Bolt ankle joint produces a peak power output of about 2800W at the moment of treading, which is due to the efficient work-making of the calf muscles.

The gastrocnemius and soleus muscles on the posterior side of the calf are the main sources of plantar flexion of the ankle joint.

During the priming phase, these muscles contract rapidly, producing powerful forces to plantar flex the ankle joint.

At the moment of treading, the force generated by the contraction of the calf muscles reaches a peak, and the speed of plantar flexion of the ankle joint is also at a high level. The product of the two causes the power output to reach the maximum.

When muscle contracts, the crossbridge between actin and myosin is constantly bound, dissociated and recombined, and this process consumes energy and generates force.

That is to say, when the muscles perform cross-bridge circulation at a higher rate, it can not only generate a greater force, but also accelerate the shortening of the muscles, thereby achieving high power output.

The core is that Mills is increasing the power output of Bolt's ankle joint!

After this winter training.

Before Bolt starts, the nervous system will pre-activate the calf muscles and adjust the initial state of the muscles to make it in the optimal state of contraction ready.

When the starting signal is sent, nerve impulses are quickly transmitted to the muscles, causing the muscles to contract simultaneously.

This precise nerve control ensures muscle contraction at the right time and intensity, improving energy utilization efficiency.

Good neuromuscular coordination can also allow muscles to recruit more motor units to participate in the work during the contraction process, further enhancing the muscle's contraction strength and power output ability.

Do you think this is over?

That's too underestimating Mills's super coaching identity.

In Jamaica, where the technological level of science and technology is not many years behind Ameika, such epoch-making super athletes can be cultivated.

More than one more.

Of course, there is real ability.

The above is just the beginning.

What follows is the key point.

Only when the top is done can there be a bottom.

Bolt takes the lead!

The knee joint stretching torque reaches 3.1Nm/kg!

This is mainly caused by the contraction of knee extension muscle groups such as the quadriceps femoris. The quadriceps femoris include rectus femoris, mesofemoris, lateral femoris and medial femoris. These muscles work together to stretch the knee joint during startup.

The magnitude of the knee extension moment depends on the force generated by muscle contraction and the length of the force arm.

During the initiation stage, the force generated by the contraction of the quadriceps femoris is transmitted to the calf bone through the patellar tendon, and the force arm is the vertical distance from the center of the knee joint to the attachment point of the patellar tendon.

According to the calculation formula of torque (moment = force x force arm), Mills finally found the powerful contraction force of the Bolt quadriceps and the appropriate force arm length!

This allows the knee joint to generate a larger stretching moment when Bolt is started.

Reinforce other muscles and connective tissue around the knee joint.

This plays a role in assisting stability and synergy.

Ensure the smooth progress of knee extension.

Through the principle of knee joint stretching moment, muscle synergy and torque generation are completed.

Then joint stability improves the efficiency of starting movement.

Bang!

Bolt's first step to achieve a larger knee extension moment not only helps the body move forward, but is also crucial to maintaining the stability of the knee joint.

This is because when the sprint starts, the body is subjected to a large ground reaction force and inertia force, and the knee joint needs to bear a lot of load.

These reinforcements arranged by Mills can resist these external forces through strong knee extension moments.
To be continued...