Loading with a 1 Kg weight should result in a 1 Hz decrease in frequency in normal subjects and those with enhanced physiological tremor (EPT), whereas change in frequency in ET and PD is usually < 1 Hz1. An effect may also be seen in functional tremor.
The frequency shift is thought to appear because EPT is caused partly by mechanical reflex oscillation, which is dependent on the hand’s resonant frequency and therefore changes with increased inertial loading.
- PD: no effect (or less than 1 Hz decrease)
- ET: no effect (or less than 1 Hz decrease)
- Cerebellar disease, Holme’s tremor, drug induced tremor: effect from loading observed.
Example of mechanical tremor component. There is a peak on the right-side accelerometer at around 6 Hz that decreases in frequency after weight loading, and it does not have a clear EMG correlation. This is compatible with a mechanical tremor component.