Stretch reflex instability compared in three different human muscles

Abstract

The possibility of causing instability in the stretch reflex has been examined in three different human muscles: biceps, first dorsal interosseous (FDI) of the hand and digastric. Tremor recorded as fluctuation of isometric force was compared with that occurring during contraction against a spring load. The spring compliance was selected to make the natural frequency of the part in each case appropriate for oscillations in the short latency stretch reflex. A computer model of the whole system was used to predict the frequency at which oscillations should be expected and to estimate the reflex gain required in each case to cause sustained oscillations. Estimates were computed of the autospectra of the force records and of the rectified surface EMG signals and of the coherence functions. Normal subjects showed no evidence of a distinct spectral peak during isometric recording from any of the three muscles. However, in anisometric conditions regular oscillations in force occurred in biceps, but not in FDI or digastric. The oscillations in biceps at 8-9 Hz were accompanied by similar oscillations in the EMG which were highly coherent with the force signal. The results are consistent with the presence of a strong segmental stretch reflex effect in biceps and weak or absent reflex in FDI. Digastric is known to contain no muscle spindles and therefore to lack a stretch reflex. In two subjects who volunteered that they had more tremor than normal, but had no known neurological abnormality, there was a distinct peak in the force spectrum at 8-9 Hz in biceps and FDI in isometric conditions with coherent EMG activity. The peak increased in size in anisometric conditions in biceps but not in FDI. This component appears to be of central rather than of reflex origin. No equivalent component was found in digastric records. The results are discussed in relation to the possible role of the short latency stretch reflex in the genesis of physiological tremor in different muscles.

Effect of mental fatigue on induced tremor in human knee extensors

“…In fact, although the presence of muscle spindles is necessary to generate instability [Durbaba et al 2005], in order to obtain an optimal resonance, the delay around the feedback loop [Lippold 1970] and the inertia of the oscillating part [Halliday et al 1956] are also of primary importance. These last two components (inertia of the system and delay around the feedback loop) might be more relevant in terms of effects on tremor amplitude with the stretch reflex response only acting as a pacemaker ensuring the timing for optimal entrainment.…”

“…Various studies have shown that self maintaining force fluctuations (hereafter referred to as instability) can be revealed when contracting against a compliant load, such as a spring, and can be attributed to instability of the stretch reflex pathway [Durbaba et al, 2005;Joyce and Rack, 1974;Lippold, 1970;Matthews and Muir, 1980]. 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].…”

“…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].…”

Analysis of the effects of mechanically induced tremor on EEG-EMG coherence using wavelet and partial directed coherence

“…The amplitude of ~10 Hz oscillations was considerably enhanced by the introduction of a spring of appropriate stiffness (3.22 Nmm -1 ) in series between the load cell and the handle [5]. This effect is attributed to the onset of stretch reflex instability around the short latency reflex loop [6]. Surface EMG was recorded from the biceps brachii.…”

Exertion dependent alternations in force fluctuation and limb acceleration during sustained fatiguing contraction

“…The oscillatory activities can be easily featured with a force-recording device coupled to a strain gauge (Oda and Kida 2001;Durbaba et al 2005) or accelerometers placed on limb segments (McAuley et al 1997;Shinohara et al 2005) that measure force fluctuation (FF) and limb acceleration (LA), respectively. Tremulous movements develop across a wide spectral range, consisting of a low frequency resonance of less than 3 Hz (Christou et al 2004;Kouzaki et al 2004), a 6-12 Hz range of possible central origins (Semmler and Nordstrom 1995;Durbaba et al 2005), and higher spectral components larger than 20 Hz (McAuley et al 1997;Takanokura and Sakamoto 2005). The continuous oscillatory activities inherently have a neurogenic basis, granting that electromyographic signals exhibit correlated discharge and alternating firing of antagonist pairs when force tremor is present (Halliday et al 1999;Taylor et al 2003).…”