Developing Acceleration

“Burst” is a key performance indicator for many team sports. When attempting to make a tackle, evade a tackle, cut an offensive player off, score a goal, etc., it is important to get from point A to point B faster than your opponent. This requires a rapid change of velocity, which is known as acceleration. 

Physics of Acceleration

Let’s break down acceleration using Newton's laws of motion:

Law 1: An object will remain still or keep moving at a constant speed until acted upon by an unbalanced outside force. 

How does this apply to acceleration speed? Let’s use a wide receiver as an example. Pre-play, the receiver(object) is still. To begin movement, he must apply a force to the ground that is greater than his bodyweight. This is where relative strength comes into play. The extent of the receiver’s change in speed depends on the magnitude of excess force applied to the ground, relative to his bodyweight. We will get into the direction of force later in this article, but the relative strength plays a large role in accelerating from his stationary position. 

Law 2: Force= mass x acceleration (f=mxa)

This law describes the relationship between force, mass, and acceleration. Based on this equation, we know acceleration=force/mass. So, this tells us that the higher the mass of the object, the greater force required to accelerate it and vice versa. This further points to the importance of relative strength and body composition. In terms of sprinting, mass refers to body weight. So, acceleration speed depends on the ability to apply a force in excess of body weight. Get strong and don’t be fat. 

Law 3: Every action has an equal and opposite reaction

Let’s visualize this with a bouncy ball. If I slam a bouncy ball straight down as hard as I can, it will bounce back up with a lot of height. If I slam it straight down with less force, it will bounce back up to a lesser height. If I throw the ball straight forwards at a wall, it will bounce straight backwards towards me. The path of the ball after it bounces off the ground depends on the magnitude and direction of how I throw it. When accelerating, force needs to be applied horizontally to propel forward. 

Physics tells us effective acceleration requires high levels of relative strength, and the ability to apply this force in the proper direction.

Strength

As described above, acceleration performance begins with relative strength. Relative lower body strength levels have shown to be positively correlated with sprint speed (5,6). An athlete must produce force in excess of their bodyweight. This is improved through general strength training. Exercises that apply high load to large groups of muscle mass, through a full range of motion are most effective. Bilateral squats, unilateral squats, and hinges are the bread and butter here.

 Bilateral squatting trains a strong neural drive in a full body extension pattern. It is the most effective way to load the lower body, as the powerful leg extensor muscles (quads, glutes, hamstrings) are highly loaded through a full range of motion. They allow for long term progress and health. 

Unilateral squat variations are beneficial due to the fact sprinting is done on one leg. The first few steps of acceleration require the bodyweight to be supported on one leg in deep knee and hip flexion angles. Unilateral squats also develop smaller muscles more effectively than bilateral variations.

Hinges (RDLs) target hip extension to a greater degree, applying a high load to the posterior chain. The hamstrings are being loaded at a long muscle length, while simultaneously stressing the spinal erectors, which are responsible for maintaining postural integrity in the early phases of a sprint.

Squatting, lunging, and hinging are the most effective exercises to build strength in the lower body. The variations of each are not relevant, it's the stimulus that these heavy compound movements provide. If you want to sprint faster, you need to recruit high threshold motor units, improving neural drive. Squatting, lunging, and hinging with high intensity are effective strength exercises to do so.

Technique

High relative force production is only one part of the equation. The force must be applied in the proper direction. Degree of horizontal force appliaction has shown shown stronger correlations to sprint performacne than total force applicaiton. (1,2). Horizontal force application is a product of shapes and rhythm of the sprinter. The athlete must achieve timing and body position that allows for optimal direction of force. This is where technique comes into play. Two main elements to focus on with acceleration technique is projection of the center of mass, and fast/efficient switching of the legs. 

Project

Projection refers to full extension. As you can see in the image above, Bolt is maximizing horizontal displacement of his center of mass by fully extending at the hip, displaying a straight line from head to toe. Referring back to Newton’s 3rd law, every action has an equal and opposite reaction. Full extension provides the foot with a large angle of attack to the ground to produce a horizontal impulse by striking the ground directly underneath or slightly behind the hip. If the hips raise vertically out of the blocks, the foot will be attacking at a vertical angle, producing braking forces and slowing down horizontal acceleration.

Improving relative strength plays a large role in the ability to maintain this optimal body angle and explosively extend out of deep flexion angles. However, the athelte must learn how to apply their strength horizontally. Drilling the athletes into projection allows them to feel the body angles required to produce horizontal force. Below is a list and example progression drills that assist with this "feel" of projection.

Level 1	Level 2
Prowler march	Prowler bound
Split stance broad jump	Single leg broad jump
Half-kneeling start	Half kneeling broad jump
Chain/sled sprints (10-30% BW)	Chain/sled sprints(10-40% BW)
Slingshot start

Prowler variations slow down movement, allowing the athelete to feel the angles of projection. Half kneeling starts slow down the 0 step, while also forcing deeper flexion angles. Slingshot starts force the athlete to fully project from the hip, then attack back with a low heel recovery. The broad jump variations apply an explosive strength stimlulus, while stressing the coordination aspect of unilateral projection.

Switch

The only way to move forward is to push off the ground. Therefore, projection needs to be followed by a rapid switching off the limbs to get the foot back on the ground. This refers to thigh angular velocity. Faster sprinters show higher thigh angular velocities compared to their slower counterparts (3,4). The switch should be initiated from the hips. Hip flexion and extension should drive movement of the legs, as it allows for the greatest attack angle for the foot, maximizing ground reaction force. Below are examples of drills to emphasize proper switching. 

Level 1	Level 2	Level 3	Level 4
Hands on hips A march	Hands on hips A skip	Hands on hips single switch	Continous switch
A March	A Skip	Single switch	Lunge switch

Hands on hips variations are useful for lower-level sprinters, as it emphasizes initaiting movement from the hip. Hip flexion and extension should drive movement of the lower extremties. This allows for muscular effciency, increases thigh displacement (in turn thigh angular velocity), and ensures proper foot path. Once this pattern is established, the arms are incorported to stress rhythm and relaxation.

It is important to note that team-sport atheltes will not exhibit elite-level acceleration mechanics due to tactical and technical elements of the game. However, to maxmize the acceleration training stimulus, we want to reach the highest speeds possible. Proper technique allows us to reach the highest speeds possible.

Conclusion 

Acceleration requires the application of high amounts of force applied in the proper direction. Producing high force is simply improved by strength training. Applying strength in the proper direction is accomplished via proper technique of projecting and switching.

References

1. Morin JB, Edouard P, Samozino P. Technical ability of force application as a determinant factor of sprint performance. Med Sci Sports Exerc. 2011 Sep;43(9):1680-8. doi: 10.1249/MSS.0b013e318216ea37. PMID: 21364480.

2. Morin JB, Bourdin M, Edouard P, Peyrot N, Samozino P, Lacour JR. Mechanical determinants of 100-m sprint running performance. Eur J Appl Physiol. 2012 Nov;112(11):3921-30. doi: 10.1007/s00421-012-2379-8. Epub 2012 Mar 16. PMID: 22422028.

3. Clark, K. P., Meng, C. R., & Stearne, D. J. (2020). 'Whip from the hip': thigh angular motion, ground contact mechanics, and running speed. Biology open, 9(10), bio053546.

4. Kunz, H., & Kaufmann, D. A. (1981). Biomechanical analysis of sprinting: decathletes versus champions. British journal of sports medicine, 15(3), 177–181. https://doi.org/10.1136/bjsm.15.3.177

   
   

5. Keiner, M., Brauner, T., Kadlubowski, B., Sander, A., & Wirth, K. (2022). The Influence of Maximum Squatting Strength on Jump and Sprint Performance: A Cross-Sectional Analysis of 492 Youth Soccer Players. International journal of environmental research and public health, 19(10), 5835. https://doi.org/10.3390/ijerph19105835

6. Conan, R., & DeBeliso, M. (2020). The relationship between back squat strength and sprint times among male NCAA track athletes. Int. J. Sports Sci. Coach, 10, 38-42.