[Advantages and limitations of the motor unit number estimation techniques]

It is now 30 years since the first motor unit number estimation (MUNE) technique was introduced by Allan McComas as a way of providing an objective, sensitive and reproducible means of measuring the number of motor axons in living human muscle or muscle group. MUNE techniques have substantially evolved over the past decade and have been applied, with increasing frequency, to the study of age effects on motoneurone population and muscle denervating disorders such as amyotrophic lateral sclerosis (ALS), spinal muscular atrophy, poliomyelitis and different types of inherited and acquired peripheral neuropathies. In the future, one of the most important topics involving MUNE, will probably be its use in monitoring the progress of ALS patients undergoing experimental drug trials. However, among incremental, multiple point stimulation, spike-triggered averaging, F-wave analysis and statistical methods, there is no consensus about the best MUNE method. There is only a general feeling that some techniques are more valid than others. For this reason, in the present review, brief descriptions of the distinct MUNE methods are presented. In the second part of the paper, advantages and limitations (alternation, sampling errors, temporal registration etc...) of the most commonly employed procedures are considered.