What Nachemson actually measured

How pressure changes through the day

Alf Nachemson, a Swedish orthopaedic surgeon, threaded a tiny pressure transducer into a volunteer’s lumbar disc in the 1960s and recorded what happened as the volunteer changed posture. Standing relaxed became the reference point. Lying on your back dropped to about a quarter of that. Sitting upright rose to roughly 140%. Sitting and leaning forward, especially with weight in the hands, climbed past 200%.

Wilke and colleagues replicated the experiment in 1999 with newer instrumentation. The numbers shifted slightly — sitting upright came out closer to standing than Nachemson’s original figures suggested — but the shape of the curve held: forward-leaning postures load the lumbar disc more than balanced ones, and lying flat is the lightest load of all.

What that means at a desk

A sitting day isn’t a rest day for your discs — it’s the opposite of one. Standing breaks aren’t about burning calories; they’re about giving the disc a chance to rehydrate at lower pressure. Lying down at lunch, if your circumstances allow, does even more.

How Plumb uses this

Plumb doesn’t measure pressure — no consumer app can. But the postures that add pressure (forward lean, head jutting toward the screen) are exactly what the camera and AirPods modes flag. Catching drift early means less time at the high end of Nachemson’s curve.