Using heart rate as a physical activity metric

Eckard et al. (2019) strapped a heart-rate watch on one neurotypical child during free-play sessions. They wanted to know if the watch could tell the difference between light, moderate, and hard physical activity.

The team set color zones on the watch: green for light, yellow for moderate, red for vigorous. They filmed the child and checked whether the colors matched how active the child looked.

The watch worked well for spotting moderate activity. When the child saw yellow, researchers saw moderate movement.

Red (vigorous) only showed up when staff added loud prompts like "run faster." Without prompts, the child stayed in yellow even while playing hard.

McCabe et al. (2023) looked at heart rate during functional analyses and said "don’t bother"—HR added no value over watching reinforcers. That sounds like the opposite of Eckard’s positive view, but the two studies asked different questions. Eckard checked if HR matches activity level; McCabe checked if HR predicts problem behavior. Same tool, different jobs.

Schaaf et al. (2015) stretched HR use further. They showed that kids at risk for developmental coordination disorder have flatter heart-rate changes when tasks get harder. Together with Eckard, this tells us HR can flag both physical effort and cognitive load in typical and at-risk children.

Zamunér et al. (2011) studied kids with cerebral palsy and found lower heart-rate variability as motor problems increased. Their work extends Eckard’s idea: once you know HR tracks activity in typical kids, you can use it to spot stress during transitions for kids with motor impairments.

You can use a cheap heart-rate watch to check if your client is really working at the intensity you want. Aim for yellow zone for moderate activity. If you need vigorous bursts, plan extra prompts—music, races, or timed sprints. The watch won’t replace your eyes, but it gives you a quick, objective backup.