Physiologic tremor is a

tremor A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, fa ...

or trembling of a limb or other body part. The recorded frequency is in the range of 8-12Hz. It occurs in normal individuals, especially when they are stressed by

anxiety Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...

fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...

. It is therefore common in sports such as

rock-climbing Rock climbing is a sport in which participants Climbing, climb up, across, or down natural Rock (geology), rock formations. The goal is to reach the Summit (topography), summit of a formation or the endpoint of a usually pre-defined Climbing ro ...

where it is known by names such as Elvis leg or sewing machine leg. It may occur in an enhanced form as a pathological symptom of conditions such as

hyperthyroidism Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidism ...

or stimulants such as

caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine t ...

References

Symptoms and signs: Nervous system {{med-diagnostic-stub