Train to sprint with sled and parachute running modes

In this article, we will analyse what a sprint is from a biomechanical point of view, trying to highlight all the factors that intervene in the execution and how that affects the development of the performance.

In order to introduce what a sprint is and the importance of sprint training for running in general, it is necessary to understand what running is and what factors characterise it.

Definitions of sprint

The sprint is an expression of running and can be defined in several ways. It can be understood as a sudden sprint with rapid acceleration made by an athlete during a race, at the start or near the finish line or as the ability to run at high speed for short distances.

According to Prof. Di Prampero’s definition, the sprint is the high instantaneous metabolic power that takes into account speed and acceleration but also the short and intense effort of an athlete to reach and/or overtake an opponent.

From an observation of the various definitions, it is clear that the performance of a sprinter is linked to his ability to accelerate to reach and maintain maximum speed for the required time, whether he is a fast athletics runner, a cyclist or a team sports player.

There are 4 measurable factors for improving running and sprinting:

• Stride Frequency SF: the number of supports in a given time (by convection the unit of time).
• Stride Length SL: the distance between 2 supports.
• Contact Time CT
• Fly Time FT

these elements act directly on the mechanics of the gesture, influencing its performance.

In order to better understand how acceleration and speed are developed, we will analyse the technical-biomechanical model proposed by C. Vittori, on the performance of the 100 meters, which he defined as the quintessence of speed, because they summarise the set of characteristics required of a sprinter, allowing the purest and truest evaluation of speed performance.

6 factors to analyse to train the sprint: the propulsion

The propulsion that develops from the first support and is the result of 2 force components that are mixed:

• Explosive Force, defined as the ability to accelerate and develop speed rapidly, the greatest demand for which occurs mainly in the first bearings and where the horizontal component of the force is crucial to move the centre of gravity forward on the sagittal axis. This horizontal component acts at the start stage where the force requirement is maximum to reach 50-60% of the maximum speed. In the acceleration phase, in order to reach the maximum speed and in the speed maintenance phase, the horizontal force requirement is reduced to a minimum in order to leave room for the vertical force component and allow the maximum speed to be maintained.

• Elastic Force, defined as the ability to develop high absolute speed peaks, the maximum demand for which occurs instead in the launched phase of speed maintenance, once the maximum speed is reached, where the vertical component of the force, the one that allows to move the centre of gravity upwards on the longitudinal axis, ensures the maintenance of the propulsion. The vertical component of the force also intervenes during the start phase to raise the centre of gravity upwards and support the weight of the athlete's body.

When, on the other hand, the vertical force component exceeds the horizontal force component, the maximum speed has been reached and can no longer be increased because there is no longer any possibility of expressing horizontal force, in this phase the elastic force becomes dominant and remains the only one responsible for propulsion.

The contact time

The contact time (CT) is the moment when the foot makes contact with the ground and the moment when it detaches from the ground. This parameter progressively decreases during the acceleration phase and then stabilises to 90 milliseconds.

The step frequency

Stride Frequency (SF) also called Cadence: the number of supports in the time unit. This parameter is closely related to the previous one because, decreasing the contact time increases the frequency. However, this link is not linear because the frequency increases faster than the reduction of the contact time and then stabilises (already between the end of the start phase and the beginning of the transition that coincides between the second and third support, the frequency stabilizes around 5 supports per second).

 The stride length

Stride Length (SL) is the distance between 2 supports that increases as the frequency increases, growing in a more linear and progressive way with respect to the frequency trend. This is due to the progressive raising of the centre of gravity and the increase in the development of the vertical force thanks to the intervention of the elastic component.

The fly time

Fly time is the time when both feet are detached from the ground. This parameter is a critical factor, to be handled carefully because it affects length and frequency. Increasing the flight time increases the pitch length and speed, on the other hand you risk decreasing the pitch frequency. Necessary to manage the flight time without reducing the frequency, maintaining the mechanical efficiency guaranteed by the elastic component.

Foot positioning

During the development of the first supports, the foot is under and slightly behind the centre of gravity, allowing the advance along the sagittal axis. As the speed increases, the foot will position itself below and slightly ahead of the centre of gravity, ensuring the intervention of vertical force in the face of increased demand for the elastic component of the same. The correct positioning of the foot, allows the correct intervention of the explosive and elastic forces that, interacting correctly with each other, ensure the good development of the propulsion force.

The best choices to train for sprinting: feet and strength

In short, during the sprint the correct positioning of the foot acts on the propulsion force which is the result of the correct integration between explosive and elastic force. Improving performance in a sprint cannot be done without training the foot to make it stronger and more responsive.

Training the perception and good use of the foot increases awareness of its use by improving the mechanics of walking, running and sprinting. More specifically in sprinting, having an "active" foot means being able to rely on a strong and reactive foot, allowing you to make the most of the competent forces that intervene directly in the propulsion.

A "strong and stable" foot actively acts in the development phase of the explosive force, the one that improves the ability to accelerate and reach top speed first. The stability of the foot can be trained with static strength exercises (maintaining an upright position on the forefoot, keeping the heel raised off the ground), with static-dynamic exercises (pushing up on the forefoot, with or without overloading without resting the heel on the ground during the return phase), with dynamic exercises (mono breech leap forward), with balance exercises using sagging rather than unstable bases, to actively stimulate the work of the meso-foot (plantar arch) and forefoot (metatarsis and fingers).

A "reactive" foot intervenes directly in the good development of the elastic force, the one that allows to express high-speed forces, maintaining the maximum speed for the necessary time.

The reactivity of the foot can be trained with dynamic exercises using all the gaits that provide for the "flight" phase (jumping on even feet in advance, trotting, jumping, alternating jumping, etc.).

The advantages of parachute and sled training

The means and devices that can be used in resisted sprint training are:

• Uphill running
• The sleigh
• The elastic bands
• The ballasted jackets
• or The parachute

But which of these devices gives the best results? An analysis of various studies done by The Journal of Strength and Conditioning Reasearch shows how:

Sledge, vest and parachute are appropriate tools to train the top speed phase of the sprint. These devices exert such an overload that they reduce the length of the pace and speed of the run, without substantial changes in the correct running technique.

The correct positioning of the load makes it possible not to alter the correct running mechanics, maintaining the correct torso and support leg angles during contact with the ground, so that they are as close as possible to the sprint without load.

The extent of the optimal overload has not yet been established, but it seems clear that a resistance that reduces the speed of the athlete by more than 10% from the empty sprint would lead to substantial changes in the sprint mechanics.

Skillrun is the perfect treadmill to unleash athletic potential, providing incredible insights into running efficiency with its advanced Biofeedback. Its precise sensors can detect the differences between left and right leg action by exploring stride length and ground contact time during running or determining maximum power during SLED and PARACHUTE training.

With Skillrun you can train as if you were pushing a real sled in Sled Training mode, to reproduce in detail the feeling of pushing a sled on grass, including inertia. Start with more resistance on the Slat Belt surface, which decreases at a steady pace as you increase speed. Parachute Training, on the other hand, increases resistance as you increase speed.

The large parachute seems to be the most suitable tool to improve speed in the acceleration phase and in the maximum speed phase of traction against resistance. Among the tools used to improve speed in the acceleration phase, the parachute seems to be the most suitable training method to increase speed in the maximum speed phase. Compared to sprint training without endurance, training with the large parachute improves:

• The running speed throughout the acceleration phase;
• The pitch length (SL) in the acceleration phase;
• The pitch frequency (SF) during maximum speed.