Theory 048/Medicine & Health /Rehabilitation
Rehabilitation Has a Dose Threshold
Therapy is prescribed in small amounts and assumed to help proportionally. There may be a minimum dose below which nothing happens.
Rehabilitation gains follow a dose-response with a threshold below which no benefit accrues, so low-intensity programmes produce no measurable effect rather than a small one, and resources should be concentrated.
01The evidence
Rehabilitation trials show inconsistent dose-response, with some low-dose arms indistinguishable from control.
02The tension
Dose is assumed proportional on the model of drug trials, and null results at low dose are attributed to poor adherence rather than to a threshold.
03The mechanism
Recovery requires a sufficient training stimulus to drive plasticity. Below a threshold, the stimulus is accommodated without adaptation, so the outcome is unchanged rather than slightly improved.
That makes dose a step function, and predicts that splitting a therapeutic dose into small sessions should produce less than the same total given in fewer, larger sessions.
04What this is not
Linear models predict proportional benefit. This predicts a threshold and a step.
05Predictions
- P1Low-dose arms should match control.
- P2Fewer larger sessions should outperform many small ones at equal total.
- P3The threshold should shift with baseline capacity.
06Refutation
Proportional gains down to very low dose would remove the threshold.
07What it changes
It would concentrate rehabilitation resources.