Abstract
High rate stimulations of the neuromuscular system, such as continuous whole body vibration, tonic vibration reflex and high frequency electrical stimulation, are used in the physiological research with an increasing interest. In these studies, the neuronal circuitries underlying the reflex responses remain unclear due to the problem of determining the exact reflex latencies. We present a novel “cumulated average method” to determine the reflex latency during high rate stimulation of the nervous system which was proven to be significantly more accurate than the classical method. The classical method, cumulant density analysis, reveals the relationship between the two synchronously recorded signals as a function of the lag between the signals. The comparison of new method with the classical technique and their relative accuracy was tested using a computer simulation. In the simulated signals the EMG response latency was constructed to be exactly 40 ms. The new method accurately indicated the value of the simulated reflex latency (40 ms). However, the classical method showed that the lag time between the simulated triggers and the simulated signals was 49 ms. Simulation results illustrated that the cumulated average method is a reliable and more accurate method compared with the classical method. We therefore suggest that the new cumulated average method is able to determine the high rate stimulation induced reflex latencies more accurately than the classical method.
Highlights
High frequency mechanical and electrical stimulation of the neuromuscular system is becoming increasingly popular in scientific research (Fornari and Kohn, 2008; Nakajima et al, 2009)
REFLEX LATENCY In the new technique, we first determined the position of the effective stimulus so that it could be used as the stimulus onset point for further analyses
As described in the Methods section, we used the peaks in the time derivatives of surface electromyography (SEMG) and Multi motor unit (MMU) traces as the trigger and force trace as the source to perform a spike triggered averaging (STA) process for all the six whole body vibration (WBV) frequencies tested
Summary
High frequency mechanical and electrical stimulation of the neuromuscular system is becoming increasingly popular in scientific research (Fornari and Kohn, 2008; Nakajima et al, 2009) This is because it opens up new avenues of investigating neuronal pathways and neuromuscular performance. If the experimental procedure requires high rate of stimuli, such as the WBV, which is the subject of this paper, the relationship between the stimulus time and the induced response becomes obscure. This is because in high rate stimulations the interval between the stimulus and the response becomes contaminated with many events such as responses from the previous stimuli and the occurrence of the subsequent stimuli (and possibly the corresponding stimulus artifacts). The high rate of WBV stimulation is faster than the reflex latency expected in a neuronal circuit and vibration induced reflex latency cannot be determined using the conventional manual methods
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