Measuring Acceleration

Acceleration can be measured in several ways, and each answers a slightly different question. This article explains the acceleration metrics the 1080 software calculates for a sprint, how they differ, and how to read the acceleration curves in the result chart.

Ways to measure acceleration

The 1080 software gives you four ways to look at how an athlete accelerates:

The first three are calculated for every linear sprint. See Linear Sprint Metrics for their exact definitions. The force-velocity profile needs a dedicated test; see Force-Velocity Profiling.

All of these are based on the smooth speed curve, which removes the speed variation within each step. See Acceleration curves below for why.

0-5 m compared with Max Acceleration

0-5 m and Max Acceleration both describe the start of a sprint, but they measure different things:

• 0-5 m is a time. It covers everything from the first movement until the athlete has covered 5 meters, so it reflects the whole start, including how quickly the athlete gets going. A lower value is better.
• Max Acceleration is a rate, in m/s². The software finds the 0.5-second period where the smooth speed increases the most, and divides that speed increase by 0.5 seconds. It shows the athlete's peak ability to gain speed. A higher value is better.

The charts in this section all show the same 40 m resisted sprint. In each chart, the blue area is the 0-5 m range and the violet area is the Max Acceleration window.

In this sprint:

• The athlete reached 5 meters after 1.53 s, so the 0-5 m time is 1.53 s.
• The steepest 0.5 seconds of the speed curve was the very first 0.5 seconds. Speed rose from standstill to 2.6 m/s, which gives a Max Acceleration of 5.1 m/s².

Speed over time

Max Acceleration is the slope of the dashed line: the speed gained across the window, divided by 0.5 seconds. The window is usually at the very start of the run, where the speed curve is steepest. It can occur later, for example after a slow first step.

Speed over distance

Plotted over distance, the difference in scale is clear. The Max Acceleration window covers only the first 0.7 meters of the run, while the 0-5 m time covers the first 5 meters.

Acceleration over time

The acceleration curve shows the same run as a rate. Max Acceleration is the average of the acceleration curve across the window, which is why it is lower than the highest point of the curve. Acceleration then falls steadily, and is close to zero from about 3 seconds as the athlete approaches Top Speed.

Acceleration over distance

Over distance, almost all of the hard acceleration happens within the first few meters.

Why the two metrics differ

0-5 m and Max Acceleration do not always move together. Covering 5 meters in 1.53 s corresponds to an average acceleration of about 4.3 m/s² over that range, which is lower than the 5.1 m/s² peak. An athlete can improve one without the other: a sharper first push raises Max Acceleration, while holding acceleration for longer improves the 0-5 m time.

Max Deceleration is calculated in the same way as Max Acceleration, from the 0.5-second period where the smooth speed decreases the most.

Acceleration curves

The result chart can show acceleration over time or over distance, in three views:

• Smooth shows the athlete's overall acceleration. The variation within each step is filtered out, leaving a curve that starts high, drops as the athlete approaches Top Speed, and is close to zero once the speed levels off.
• Steps shows one peak for each step the athlete takes. Use it to see when the steps happened, but not for the values themselves: they are much larger than the athlete's real acceleration.
• Raw shows the acceleration exactly as the machine measured it, several hundred times per second, with no filtering.

Why the peak of the smooth curve differs from Max Acceleration

The highest point of the smooth acceleration curve is usually higher than the Max Acceleration value. In the example above, the curve peaks at about 5.7 m/s² after 0.25 seconds, while Max Acceleration is 5.1 m/s².

The two measure different things:

• The peak of the curve is the acceleration at a single moment.
• Max Acceleration is the speed gained over the best 0.5 seconds, divided by 0.5 seconds. This is the same as the average of the acceleration curve across that window. The window includes the rise to the peak and part of the drop after it, so the average is lower than the peak.

The 0.5-second window is used because it measures acceleration that the athlete sustains, which is what drives sprint performance. A single moment is more sensitive to the exact shape of the curve. This is especially true at the very start of the run, where the filter has no data from before the athlete started moving. Max Acceleration therefore gives a more repeatable value for comparing runs and athletes.

Why raw acceleration is not useful

The raw acceleration is dominated by things other than the athlete's acceleration:

• Every step shows up as a spike. Each foot contact makes the athlete speed up and slow down slightly, and the line follows that movement. The raw acceleration swings between large positive and negative values several times per second, even when the athlete's overall speed barely changes.
• The line itself adds movement. Line sway and small vibrations in the line add rapid changes that have nothing to do with the athlete's acceleration.
• Acceleration magnifies small errors. Acceleration is the rate of change of speed, so tiny variations in speed from one sample to the next become large values.

The chart below shows the raw and smooth acceleration for the same sprint. The raw values swing between about −24 m/s² and +43 m/s² with every step, all the way to the finish. Over the same run, the athlete's "real" acceleration never goes above 6 m/s².

As a result, the highest raw value reflects a single jerk of the line rather than how well the athlete accelerates, and it cannot be compared between runs or athletes.

Related articles

• Linear Sprint Metrics
• Sample Filtering
• Force-Velocity Profiling