Athletes that can accelerate faster will often have an advantage. 

In most sports, the athlete that can get through the first few steps faster, will have a better chance of success.

A wide receiver getting past the defense, a midfielder getting a touch on the ball first to create a scoring opportunity, a defender stopping an attacking player from turning up field, the game applications are everywhere. 

Maximizing acceleration ability in athletes is a huge part of coaching speed. 

Below are my thoughts on some research that breaks this down further, focusing on the Ratio of Forces (RF).

What is the Ratio of Forces? 

The ratio of forces (RF) is a metric that represents the percentage of horizontal force relative to the total force generated during the initial acceleration phase of a sprint.

It indicates the efficiency with which an athlete is able to generate horizontal force to propel themselves forward. 

A higher RF value suggests a greater proportion of the total force is directed horizontally, which is desirable for maximizing early acceleration performance.

A study was conducted that featured fourteen male sprinters who participated in two maximal 60-meter sprints from a block start. The researchers collected kinematic and external kinetic data  from the first four steps of each sprint to analyze the relationships between various characteristics and the ability to achieve higher RF during the initial acceleration phase of sprinting. 

The researchers found several key factors that were significantly associated with higher RF. . .

Key Factors for Higher RF

1. Foot Placement

Placing the stance foot further behind the body's center of mass at touch-down was linked to higher RF. This suggests that a more negative touchdown distance, or having the foot land further back, can enhance initial acceleration performance.

2. Foot and Shank Orientation

 An anterior (forward) orientation of the proximal end (closer to the body) of the foot and shank segments at touch-down was also associated with higher RF. This highlights the importance of lower leg configurations in generating high RF during initial acceleration.

3. Ankle Dorsiflexion Range of Motion

Greater ankle dorsiflexion range of motion during early stance (when the foot is in contact with the ground) was found to be related to higher RF. 

Ankle dorsiflexion refers to the movement that allows the foot to be flexed upward toward the shin. It plays a crucial role in rotating the center of mass forward, which facilitates efficient sequential extension of the leg joints during acceleration.

Practical Implications 

Based on these findings, there are practical implications for coaches and athletes aiming to improve RF during the initial acceleration phase:

1. Foot Placement

Optimizing foot placement by having the stance foot land further behind the body's center of mass can contribute to improved RF and overall sprint performance. 

Attention should be given to optimizing technical ability and step frequency. This is why we spend time on the technical side of things. 

It’s something that takes practice, takes repetition. But, if an athlete commits to this part of their training, it could be a huge difference maker. 

2. Lower Leg Configurations

Encouraging a more forward-oriented position of the foot and shank segments at touch-down can help maximize RF during initial acceleration. Coaches and athletes should focus on developing proper foot and shank orientations.

3. Ankle Dorsiflexion

Considering the role of ankle dorsiflexion during early stance is important. Greater range of motion in ankle dorsiflexion can aid in rotating the center of mass forward, leading to higher RF. 

Strengthening and improving ankle dorsiflexion mobility may be beneficial.

Conclusion 

While this study provides valuable insights into the factors influencing initial acceleration in sprinting, further research is needed to fully understand the complex coordination of shank and foot motion during early stance. 

Investigating their interplay and overall contribution to sprint acceleration will help refine training strategies and unlock further performance improvements in sprinting. 

If anybody has any thoughts or questions on this, let us know. We think it’s important to share some of the technical and mechanical implications. If you’re curious to read more about the study or relationship, here’s the research: 

Kinga, D., Burnie, L., Nagahara, R., & Bezodis, N. E. (2023). Relationships between kinematic characteristics and ratio of forces during initial sprint acceleration. Sports Medicine and Biomechanics.

Or. . .

Here's a quick video where I explain horizontal vs. vertical force.