Original articleEstimating Contraction Level Using Root Mean Square Amplitude in Control Subjects and Patients With Neuromuscular Disorders
Section snippets
Participants
Nine patients (age, 52±12y) with clinically probable or definite amyotrophic lateral sclerosis (ALS) as defined by the revised El Escorial criteria14 and 10 healthy control subjects (age, 27±4y) volunteered to participate in the study. Three of the 9 ALS patients were unable to perform the FDI portion of the study due to severely atrophied muscles characterized by unrecordable M waves. Due to this limitation, 5 additional patients (age, 37±11y), with Charcot-Marie-Tooth disease type X confirmed
FDI MUNE, MVC, and RMS Amplitude
MUNEs differed significantly between control subjects (n=10) and patients (n=11, Charcot-Marie-Tooth disease type X=5, ALS=6) (table 1). Despite this difference, the initial MVC values were similar between groups (see table 1). The addition of the Charcot-Marie-Tooth disease type X patients did not alter this finding, because the MVC values of both the Charcot-Marie-Tooth disease type X (21.4±10.5N) and the ALS (18.5±11.1N) patients did not differ compared with the control subjects
Discussion
The results of this study show that for these experimental conditions, the individual and grouped force−RMS amplitude relationships are best fit by a simple linear function for both the biceps brachii and FDI muscles. These relationships did not differ in comparing a sample of control subjects and patients with neuromuscular disease, in whom substantial motor unit loss and remodelling had occurred. Similar results were found across groups within each of the muscles studied, with higher levels
Conclusions
For the experimental conditions described for this study, linear force and RMS amplitude relationships were observed for the biceps brachii and FDI muscles in control subjects and patients with neuromuscular disease. These results are inclusive of the relationships derived for subjects and groups, although the establishment of the grouped relationships and their corresponding 95% CIs may have greater clinical applicability in estimating the level of contraction because they express the
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