The organization of upper limb physiological tremor.

The objectives of this study are (1) to assess the relationship between tremor displacement of different segments of the upper limb, (2) to assess whether an attempt to voluntarily reduce tremor amplitude affects this relationship. Twenty-five young healthy participants were tested. Tremor of the finger, hand, arm and shoulder was assessed using laser displacement sensors while the upper limb was in a postural position. Results show strong correlations (r > 0.90), high coherence (>0.9) and in-phase movement between tremor displacement oscillations of different segments. The majority of finger tremor amplitude can be predicted by angular movement generated at the shoulder joint (r(2) > 0.86). Participants were able to voluntarily reduce tremor amplitude, but no change in the relationship between segments was observed. Tremor of all segments of the upper limb was mechanically driven by the angular movement generated at the shoulder joint. This study provides evidence that there is no compensatory organization of physiological tremor. This lays the groundwork to evaluate whether pathological tremors also lack this organization.