The Piper rhythm–a phenomenon related to muscle resonance characteristics?

Abstract

The purpose of the present work is to examine the causes of the Piper rhythm, i.e. the tendency towards rhytmical 40-60 Hz grouping of motor unit potentials in steadily contracting human muscles. At weak or moderate contraction strength individual motor units exhibited preferred firing rates which were subharmonically related to the Piper rhythm in the gross EMG. Microelectrode muscle nerve recordings provided no support for the hypothesis that the Piper rhythm is dependent on resonance-induced rhythmical volleys of afferent spindle impulses causing reflex entrainment of motor impulses. This hypothesis also seems inconsistent with the findings that Piper rhythms of similar frequency appear in muscles with widely different mechanical properties and that the rhythms are about equally prominent in muscles with brisk as in muscles with weak or absent stretch reflexes. The results suggest that the Piper rhythm is dependent on some kind of pace-maker in the spinal cord or the cerebrum which tends to entrain and synchronize motor impulses.

Frequency peaks of tremor, muscle vibration and electromyographic activity at 10 Hz, 20 Hz and 40 Hz during human finger muscle contraction may reflect rhythmicities of central neural firing

“…Findings of peaks of oscillatory EMG activity in a similar broad frequency range of 40-70 Hz have been confirmed by many studies on different muscles under different conditions (Adrian 1925;Fex and Krakau 1957;Komi and Viitasalo 1975;Hagbarth et al 1983;Bruce and Ackerson 1986). Adrian (1925) suggested that the origin of EMG synchronization at the Piper frequency could lie in mechanical resonance at this frequency producing afferent responses entraining the EMG at the same frequency via reflex action.…”

“…Many previous studies, including those by Vallbo and Wessberg (1993), Farmer et al (1993a,b), Hagbarth et al (1983), Keidel and Keidel (1990), Murthy and Fetz (1992) and Conway et al (1995), also favour such an origin for peripheral rhythms; the latter three reports have directly demonstrated a correlation between central and peripheral oscillations. The importance of high-level processing in the production of tremor frequency peaks is clearly illustrated by studies showing that they can be influenced by visual feedback (Sutton and Sykes 1967), implying a central modulation of peripheral tremor.…”

“…50 Synchronization of motor units Adrian (1925) Different muscles Strong contraction 35-60 Mechanical resonances Fex and Krakau Different muscles Contraction ca. 50 Active motor unit (1957) synchronization [13][14][15][16][17][18][19][20][21][22] Lower frequency is synchronized (1976) Hagbarth et al (1983) Different muscles Steady voluntary ca. 50 (Piper rhythm) Synchronization by CNS contraction + single units at rhythms subharmonics Homberg et al (1986) Finger and arm Isometric contraction 8-10 (finger), Motor unit firing muscles (+ force tremor) 8-20 (arm) Farmer et al 1DI Correlation between single 1-12, 18-32 Mechanical and CNS, (1993a, b) motor units on weak respectively contraction Muscle vibration frequency Wollaston (1810) Muscle belly Contraction ca.…”

“…Moreover, loading the limb with moderate weights sufficient to cause a profound drop in mechanical resonant frequencies and increasing the elastic force, which would increase resonant frequencies, had little effect on the main peak frequencies. Hagbarth et al (1983) recorded single nerve afferents during runs of Piper rhythm and found no modulation of these afferent signals at this frequency, similarly suggesting that Piper rhythm is not generated by peripheral feedback transmitting mechanical resonances or setting up a feedback loop resonance. In summary, there is no evidence to support a mechanical origin of any of the three main peaks at 10 Hz, 20 Hz and 40 Hz described in this study.…”

“…Adrian (1925) suggested that the origin of EMG synchronization at the Piper frequency could lie in mechanical resonance at this frequency producing afferent responses entraining the EMG at the same frequency via reflex action. However, microneurographic recording of afferent nerves has revealed no such rhythmic behaviour correlated with EMG Piper rhythms (Hagbarth et al 1983), suggesting that the rhythms are centrally driven. Piper rhythm frequencies have not been found in studies correlating activity between single motor units.…”