Reflex responses at the human ankle: the importance of tendon compliance.

Rack, P. M. H.; Ross, H. F.; Thilmann, A. F.; Walters, D K

doi:10.1113/jphysiol.1983.sp014954

Cited by 95 publications

(68 citation statements)

References 22 publications

(31 reference statements)

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“…One possible cause of this would be multiple EMG bursting on each stretch cycle, as has been reported previously (Andrews et al 1973b;Rack et al 1983), but examination of the raw data provided no evidence for multiple bursting here. The raw data in Figure 2b show a case where harmonics were strongly present, taken from the subject whose spectra are shown in Figure 5, at an amplitude of 1.9 o and frequency of 8.5 Hz.…”

Section: Discussionmentioning

confidence: 77%

Entrainment to extinction of physiological tremor by spindle afferent input

2005

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In this study the systematic modulation of wrist flexor muscle activity by imposed joint movement was examined. Ten subjects maintained a constant contraction level (25% of maximum; trial duration: 20 s) in flexor carpi radialis while their wrists were perturbed with 50 different quasi-sinusoidal signals (frequency range: 0.5 -9.5 Hz; amplitude: 0.3° -4.2°). Frequency spectra of wrist position and the rectified and filtered electromyogram (EMG) were determined. The muscle activity was only weakly entrained to imposed movements of small amplitude and low frequency, as shown by a small peak in the EMG spectrum at the frequency of movement, while the most prominent peak in the spectrum was between 9 -15 Hz, corresponding to the frequency range of physiological tremor. The entrainment of muscle activity increased markedly as the amplitude and frequency of the imposed movement increased, to the point of saturation of modulation and harmonic peaks in the spectrum. In parallel with this increase in entrainment, the 9 -15 Hz tremor peak was progressively extinguished. The results are consistent with a coupled oscillator model in which the central oscillatory source(s) of tremor became fully entrained to the imposed movement at the highest amplitudes and frequencies. Such coupling depends on communication between the external forcing oscillator and the central oscillator(s), the Ia afferent signal from the imposed movement being the most likely candidate to provide the entraining signal for the central oscillator(s).

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Section: Discussionmentioning

confidence: 77%

Entrainment to extinction of physiological tremor by spindle afferent input

2005

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“…Moreover, such interactions seem unlikely to produce the right kind of effect. Stretching at frequencies close to that of the 'spontaneous' firing of a motoneurone (or to its harmonics) should more readily phase-lock its firing onto the stimulus cycle, and so evoke an unduly deep modulation of the EMG; such an action is well known for spindle afferents, and might contribute to tremor (Goodwin, Hulliger & Matthews, 1975;Rack, Ross, Thilmann & Walters, 1983). Thus motoneurone rhythmicity seems more likely to create a peak than a trough in the frequency response at 20-25 Hz.…”

Section: Behaviour Of Single Motor Unitsmentioning

confidence: 99%

Interaction between short‐ and long‐latency components of the human stretch reflex during sinusoidal stretching.

Matthews¹

1993

The Journal of Physiology

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SUMMARY1. Using wrist muscles, the subdivision of the human stretch reflex into separate components was examined with small amplitude sinusoidal stretching of relatively high frequency (10-40 Hz). The reflex was evoked by angular rotation of the wrist (below 1 deg amplitude), applied via the hand during maintained voluntary contraction of the muscle studied; both flexors and extensors were tested.2. The reflex response was recorded electromyographically rather than mechanically. For each condition, the surface EMG was rectified and averaged to give a cycle average showing the mean response evoked by a cycle of stretching. The cycle average was fitted with a sinusoid, the amplitude and phase of which were used to assess the reflex; their value reflects the combined action of its various subcomponents. Fourier analysis gave similar results (the EMG was then rectified but not averaged).3. The amplitude of the reflex response typically fell to a minimum in the region of 20-25 Hz. The phase lag of the response in relation to the stimulus increased approximately linearly with frequency, except in the region of the amplitude minimum. Here the lag tended to remain constant, or to decrease slightly; this created a discontinuity between the upper and lower limbs of the phase plot.4. Such effects are attributed to an interaction between two components of the reflex that differ in latency by 20-25 ms. These would progressively change their relative phase as the frequency increased. At first they would come to interfere with each other, but then the more delayed reflex produced by a given cycle of stretching would begin to sum with the shorter latency reflex evoked by the next stretch.5. At high and low frequencies the cycle averages were normally well fitted by a single sinusoid. Around 20-25 Hz, however, they typically showed appreciable harmonic distortion, with the second harmonic larger than the fundamental. The cycle average then showed two separate responses per cycle of stretching. These were considered to represent the uncancelled non-linear residua of separate components of the reflex response. Their relative timing shifted appropriately with change of frequency.6. These 'double responses' are unlikely to be due to mechanical resonance. First, the relative sizes of the two components could be altered by the reflex action of cutaneous afferents. Second, the same pattern of behaviour was found when the MS 1143 P. B. C. MATTHEWS mechanical stimuli were applied directly to the tendon of flexor carpi radialis while the hand remained fixed.7. Sinusoidal stretching thus provides an alternative to ramp stretching for fractionating the stretch reflex into components of different latency. A longer latency component has thereby been found to persist at frequencies above those at which muscle can respond mechanically; its central machinery can thus be expected to take part in the moment to moment control of muscle action.

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“…There is evidence that spindle afferent discharges are related to changes in the elastic properties of the tissues in which they are embedded 59 . Specifically, it has been reported that stiffer muscle-tendon elements ensure that the muscle spindles are more sensitive to imposed external forces 60 . Strength training has been shown to increase the stiffness not only of muscular but also of connective tissues surrounding the targeted joint 61,62 .…”

Section: Implications For Rehabilitationmentioning

confidence: 99%

“…or "Where on the object would you like to hit a ball?" Whether the objects were tennis rackets (ranging in length from 53 to 73cm) or wooden rods (44,60, and 75cm) with attached metal rings (at 1/3 or 2/3L), perceived sweet spot (center of percussion) was distinguished from perceived length. Both rods and rackets showed the familiar 1/3 scaling of perceived length to I xx albeit with a lower intercept than was found for young participants 52 .…”

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confidence: 99%