How to Run Faster: The Mechanics of the Acceleration Phase

Ask most runners how to get faster and they picture moving the legs quicker. In the acceleration phase, the first several strides where you build speed from a standstill, that picture is wrong. Acceleration is a force problem, and specifically a horizontal force problem. The athletes who pull away in the first 20 meters are the ones who push the ground backward hardest and keep pushing back, not just down, further into the run than everyone else. This article breaks down the mechanics of acceleration, why the direction of your force matters as much as its size, and how to train the whole pattern. If you want to watch your own start on video while you read, you can screen your stride with our free tool.

Why acceleration is a horizontal-force game

At top speed, faster running comes down to how much force you can put into the ground in a very short contact. Acceleration is different. Here you have more time on the ground, and the winning variable is not just the size of the force but its orientation. Morin and colleagues showed that what best predicts sprint acceleration performance is how effectively an athlete aims force backward into the ground as speed rises, rather than total force capacity alone.[2] They quantified this as the ratio of the horizontal force component to the total force applied, a measure of mechanical effectiveness.

Force-plate work on world-class athletes sharpened the point. Comparing elite and sub-elite sprinters over a reconstructed 40 m, Rabita and colleagues found that the ratio of force, how horizontally the athlete directs the ground reaction, was among the mechanical variables most strongly correlated with performance.[3] Elite sprinters produced more horizontal force at any given running velocity than sub-elite ones. The orientation of the total force applied to the ground during acceleration mattered more than its raw magnitude.[3]

This idea is captured in the force-velocity profile of a sprint. The horizontal force you can produce falls in a roughly straight line as your velocity climbs, from a theoretical maximum force at a dead stop to a theoretical maximum velocity where you can no longer add speed. Maximal horizontal power sits between the two, and an athlete can be limited more by the force end, the velocity end, or the ability to keep force pointed backward.[1] Knowing which one you lack tells you what to train, which is why coaches profile the acceleration rather than guess.

The mechanics, step by step

A big forward lean, then a gradual rise

To push the ground backward you have to be positioned behind it. Out of the start, sprinters lower the center of mass and lean the trunk forward so that the body is angled sharply, often near 45 degrees on the first steps if the athlete is strong enough to hold it.[4] That lean lets you angle force backward and down, producing forward propulsion instead of lift. Competitive sprinters can keep the center of mass in front of the support foot for the first three to four steps, which is exactly what a strong lean allows.[4]

The lean is not a fixed position, it is a progression. As you gain speed the trunk rises smoothly toward the upright posture of top-speed running. The common error is standing up too early, which points your force down instead of back and kills the acceleration. The opposite error, staying folded over too long or reaching the front foot out ahead of the body, leaks force the other way. Reviews of sprint mechanics describe this smooth transition from forward lean to upright running as a hallmark of well-trained acceleration.[5]

Push the ground back and down with powerful hip extension

Each acceleration stride is a coordinated extension of the hip, knee, and ankle, sometimes called triple extension, that drives the body forward and away.[4] The hip extensors carry a large share of that job. Gluteus maximus activity and peak concentric hip-extension torque are related to the horizontal force produced over the initial steps of acceleration, and the hamstrings are heavily involved in generating horizontal force as well.[6] The cue is not to reach and pull, it is to plant a positive shin angle and push the ground back and down behind you, letting the hip drive extend the whole chain.

Because the hamstrings work so hard producing horizontal force during acceleration, this phase places real demand on them. That is worth respecting in how you build volume, and it is the mechanical reason behind our piece on hamstring strains in sprinters.

The phase is not uniform

Acceleration itself changes shape as you go. Step-by-step analyses show that the first steps are dominated by increases in step frequency, while the middle of the acceleration is driven more by lengthening the stride, and the pattern reorganizes as you approach top speed rather than switching all at once.[9] Practically, that means the first two or three steps, the mid-acceleration strides, and the transition to upright running each ask for something slightly different, and your training should touch all of them rather than only the block start.

How to train the acceleration phase

The goal of acceleration training is to build the ability to produce large, backward-oriented force early, and to rehearse the posture that lets you deliver it. The table below maps the main methods onto the quality each mainly develops. As with all speed work, the pattern gets wired together by actually accelerating at full effort, so drills feed the sprint, they do not replace it.

Resisted sprinting deserves a closer look because it maps so cleanly onto acceleration. Systematic reviews report that resisted sprint training improves force, power, and sprint times over the first 5 to 20 m, and shifts the horizontal force-velocity profile toward greater force production.[7][8] The load is the dial. When you match horizontal force or power for a given speed, a heavily loaded sprint resembles the very first steps of a free acceleration, near 3 m per second, so heavy sleds train the early, high-force part of the phase, while lighter loads sit closer to mid-acceleration.[8] Resisted work may be favored over unresisted running specifically for improving early-to-mid acceleration and horizontal force.[7][8]

Strength is the foundation under all of it, since the force you orient backward has to be produced by the hips and legs first. If you are building that base, our guide to the best strength exercises for runners pairs well with this piece. And if you want the full picture of how acceleration connects to top-speed running and the classic drills, see sprint mechanics and drills.

Putting it together

Getting faster off the line is not about spinning the legs. It is about creating a strong forward lean so you can push the ground backward and down, extending the hip, knee, and ankle powerfully to drive the body forward, and then rising smoothly toward upright as speed climbs. The research is consistent that the orientation of your force, keeping it pointed backward as you accelerate, is one of the tightest correlates of sprint performance.[2][3] Train it with full-effort short accelerations for the pattern, resisted sled work and strength for the force behind it, and let the two feed each other. To see how your own lean, shin angle, and rise look on video, bring your footage to the CritchPitch Run Lab.