By B. Hague

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The amplitude of individual F waves is normally that of a single motor unit. This is because the axon hillock is reactivated in only a small number of motoneurones (usually 1–2) in response to the stimulus. The variability of latency and morphology results from different motoneurones ‘backfiring’ in different trials. (v) Chronodispersion. Clinical studies ordinarily assume that the minimal and maximal F wave latencies represent the fastest and slowest motor conduction times to and from the spinal cord, respectively.

6 General Methodology the less likely is the recorded activity to come from only the muscle underlying the ‘active’ electrode. Measurement (i) Reflex latency is measured to the first deflection of the H wave from baseline, regardless of polarity (see the vertical dashed line in Fig. 2(e)–(g)). (ii) In practice it makes little difference whether the amplitude or the surface area of the reflex is assessed or whether amplitude is measured for the negative phase only or from negative peak to the following positive peak.

1951b; Paillard, 1955). However, such long recovery cycles are no longer used, because too many overlapping and uncontrollable phenomena are responsible for the changes: HD (p. 87), presynaptic inhibition of Ia terminals activated by the conditioning volley (p. 304), afterhyperpolarisation and recurrent inhibition of motoneurones (p. 05 mV Soleus EMG 50 s 10 180 (b) Threshold tracking 0 Rest Contraction –10 1 10 100 Normalised amplitude (% of control) Normalised threshold (% of control) 10 (c) Amplitude tracking 120 60 0 -60 1 10 100 Conditioning-test interval (ms) Fig.

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