Acceleration is the rate at which speed changes.
The default acceleration setting in the Motion Analysis tool is global and forward, which measures an athlete’s acceleration down the pool.
Positive acceleration, or data points above 0, means the athlete is speeding up. Negative acceleration, or data points below 0, means the athlete is slowing down.
The goal is to maximize peaks above 0 and the duration in which the athlete is at a positive acceleration. And at the same time, minimize troughs below 0 and the duration in which the athlete is at a negative acceleration.
Drag creates negative acceleration, so it’s possible to see negative acceleration for an athlete pushing forward, but not quite overcoming drag. It is also not uncommon for faster swimmers to see bigger troughs than slower swimmers because the faster they go, the more drag they’ll see.
You can also see sideways and upward acceleration on the graph, and invert the direction, by clicking on the gear icon and turning on the toggles.