By Dr. Robert L. Janda, MA, DC

A study published last month in JAMA Internal Medicine tested twelve commercial fitness trackers against laboratory-grade measurement of energy expenditure. The result was unflattering. Some devices underestimated calories burned by nearly 600 per day. Others overestimated by 200. The decimal-point precision on the screen — 482 calories, 9,317 steps, 73 active minutes — turned out to be theatre on top of an instrument that could be off by the equivalent of a meal in either direction.

The conventional response to that finding is incremental: better sensors, more data, machine learning to clean up the noise. Within a few years the trackers will be more accurate. Wait for v3.

The more useful question is one the technology can’t answer. Why did people start trusting a wrist device’s number more than the body’s own moment-to-moment signal in the first place?

Interoception: the data stream the tracker can’t see

There is a clinical word for the body’s perception of its own internal state — heart rate, breath rate, hunger, fullness, fatigue, the difference between thirsty and tired. Interoception. It is the slowest sense to mature in childhood and the first to atrophy in adulthood when we stop trusting it. Like any sense, it gets sharper with attention and duller without.

A wearable is, in the best case, a coarse and lagging approximation of one or two interoceptive channels. Heart rate, maybe step count. It does not know whether you slept well. It cannot tell that your blood sugar dropped. It cannot read the tension in the diaphragm. The signal it gives you is a calorie estimate; the signal your body is giving you, if you can still hear it, is a far richer set of variables it has been monitoring without instrumentation for two hundred thousand years.

What Applied Kinesiology actually tests

I’ve written before about Applied Kinesiology — the practice of using a muscle’s response to load as a real-time readout of the nervous system’s state. AK isn’t a strength test. It’s a question put to the body in a language the body still speaks. When a previously strong muscle weakens in response to a specific challenge — a food held in the mouth, a thought spoken aloud, a vertebral level palpated — the body has answered. The wearable, sitting on the same wrist, has no idea any of that happened.

That gap between what the body knows and what the device measures is the gap most patients come to me to navigate. They’ve been listening to the wrong instrument for so long that the loud, fast-moving, articulate signal of the body has gone quiet for lack of attention. The work is partly muscular and partly perceptual: rebuild the channel.

Hidden dysfunction and the data-trust loop

The Hidden Dysfunction chain — stressor → dysfunction → compensation → symptom → diagnosis — gets distorted in a particular way when the patient has outsourced their interoception to a device. The downstream symptoms (poor sleep, mid-afternoon crash, weight that won’t move) are real. But the diagnostic instrument has been turned the wrong way around. The patient is trying to manage the symptom using a metric (steps, calories, sleep score) that doesn’t measure the upstream stressor.

I see it most often in athletic patients. They are training hard, hitting their numbers, and getting injured. The numbers report compliance; the body has been reporting overtraining for weeks and no one was reading. Or in patients trying to lose weight: they’re eating fewer calories than the tracker says they’re burning, and the weight doesn’t move, because the tracker is off by 400 calories and they’re actually in a maintenance band. The fix is rarely a better device. The fix is a recalibration of what counts as a signal.

Who this is for

This piece is for the patient who has more data about their body than ever and feels further from it than ever. For the patient whose Apple Watch knows their heart rate to the beat but who can’t tell if they’re hungry. For the athlete whose programming spreadsheet is meticulous and whose hip has been asking, quietly, for a different question entirely.

The fitness tracker is not the enemy. It is a coarse instrument that has been mistaken for a precise one, and the cost of the mistake is that we stop listening to the precise instrument we were born with. The first task in a clinic like this one is to put the loud, lagging device back in its proper place — a rough record of motion — and turn the dial back up on the body that has been quietly transmitting all along.

Call the office for an intake. We’ll find out together what your body has been trying to tell you while you were checking your wrist.

— Dr. Robert L. Janda, MA, DC