Different types of tremor in the human thumb.

Abstract

1. The upper limbs of normal subjects were immobilized in a way that allowed measurement of forces and movements at the thumb interphalangeal joint without significant movement elsewhere in the limb. 2. When the subject attempted to maintain a steady flexing force at the joint against a rigid stop, the actual force showed the irregular 8‐11 Hz fluctuations characteristic of a ‘physiological tremor'. This force fluctuation increased when the mean flexing force increased. 3. If the subject exerted his flexing force against a light complaint spring, there was an analogous irregular 8‐11 Hz movement at the joint. 4. When, however, an extra inertial load was added to the terminal phalanx, flexion against a complaint spring was often accompanied by a different type of tremor. This was a more regular oscillation, of lower frequency (3‐6 Hz), and of much larger amplitude. 5. The precise frequency and amplitude of this type of tremor depended on the characteristics of the added inertia and spring, in a way that could have been predicted from the responses of the joint to an imposed sinusoidal movement (Brown, Rack & Ross, 1982a). The movement appeared to arise from re‐excitation within stretch reflex pathways. 6. The irregular 8‐11 Hz tremor at this joint could not be attributed to reflex re‐excitation, since the responses to sinusoidal movement indicated a stretch reflex whose timing would not support a movement at that frequency. It is, however, emphasized that other joints of the hand and fingers may behave in different ways.

Entrainment to extinction of physiological tremor by spindle afferent input

“…However, when the frequency of the mechanical component of physiological tremor is reduced by increasing the mass loading of the limb (Joyce and Rack 1974;Brown et al 1982a), a component at 8 -12 Hz remains constant or even shifts to slightly higher frequencies (Elble and Randall 1976;Elble and Randall 1978), suggesting that it has a neural origin. There is a tendency for unfused or partially fused motor unit twitches to cause tremor and while the mean motor unit firing frequency is somewhat higher than the frequency of physiological tremor, there is a tendency for short-term clustering of firing in the range of 8 -12 Hz (Elble and Randall 1976;Elble and Koller 1990; see also Halliday et al 1999).…”

“…A number of sources of physiological tremor have been suggested, including mechanical resonance of the limb (Joyce and Rack 1974;Elble andRandall 1976, 1978;Brown et al 1982a;Burne et al 1984), synchronisation of motor unit firing (Elble and Randall 1976;Allum et al 1978;Marsden 1984;Elble and Koller 1990;Matthews 1997;Timmer et al 1998a,b; see also Halliday et al 1999) and instability within the stretch reflex arc (Lippold 1970(Lippold , 1971Young and Hagbarth 1980;Zahalak and Cannon 1983;Burne et al 1984;Young 1984, Graham andRedman 1993;Miao and Sakamoto 1997;Sakamoto et al 1998;Santillan et al 2003). The multifactorial nature of tremor was emphasised by Llinas who described it as an "emerging property of various components" (Llinas 1984, p.178).…”

Effect of mental fatigue on induced tremor in human knee extensors

“…Also, modelling and experimental studies have shown that the frequency of oscillation of the instability is linked to whether the short (spinal) or long (transcortical) latency pathway of the stretch reflex is predominantly activated [Brown et al, 1982;De Serres et al, 2002;Durbaba et al 2005Durbaba et al , 2013Lippold, 1970;Matthews and Muir, 1980;Stein and Oguztöreli, 1976].…”

Influence of Force Tremor on Mechanomyographic Signals Recorded with an Accelerometer and a Condenser Microphone during Measurement of Agonist and Antagonist Muscles in Voluntary Submaximal Isometric Contractions

“…Isometric muscle contraction is accompanied by FT (Allum et al, 1978;Brown et al, 1982). The FT has a broad frequency bandwidth of between 1 and 25 Hz (Allum et al, 1978) and the majority of the FT's frequency bandwidth is in the 3-6 Hz bandwidth related to reflex activity, while the 8-12 Hz bandwidth is related to physiological tremor (Brown et al, 1982;Prochazka and Trend, 1988). Since the main frequency content of the MMG is below 100 Hz (Oster and Jaffe, 1980), it is possible that the frequency spectrums of the FT and the MMG signals overlap.…”