Abstract
BackgroundThe peak-to-peak (P-P) amplitude of the maximum M-wave and the area of the negative phase of the curve are important measures that serve as methodological controls in H-reflex studies, motor unit number estimation (MUNE) procedures, and normalization factors for voluntary electromyographic (EMG) activity. These methodologies assume, with little evidence, that M-wave variability is minimal. This study therefore examined the intraclass reliability of these measures for the biceps brachii.MethodsTwenty-two healthy adults (4 males and 18 females) participated in 5 separate days of electrical stimulation of the musculocutaneous nerve supplying the biceps brachii muscle. A total of 10 stimulations were recorded on each of the 5 test sessions: a total of fifty trials were used for analysis. A two-factor repeated measures analysis of variance (ANOVA) evaluated the stability of the group means across test sessions. The consistency of scores within individuals was determined by calculating the intraclass correlation coefficient (ICC). The variance ratio (VR) was then used to assess the reproducibility of the shape of the maximum M-wave within individual subjects.ResultsThe P-P amplitude means ranged from 12.62 ± 4.33 mV to 13.45 ± 4.07 mV across test sessions. The group means were highly stable. ICC analysis also revealed that the scores were very consistent (ICC = 0.98). The group means for the area of the negative phase of the maximum M-wave were also stable (117 to 126 mV·ms). The ICC analysis also indicated a high degree of consistency (ICC = 0.96). The VR for the sample was 0.244 ± 0.169, which suggests that the biceps brachii maximum M-wave shape was in general very reproducible for each subject.ConclusionThe results support the use of P-P amplitude of the maximum M-wave as a methodological control in H-reflex studies, and as a normalization factor for voluntary EMG. The area of the negative phase of the maximum M-wave is both stable and consistent, and the shape of the entire waveform is highly reproducible and may be used for MUNE procedures.
Highlights
The peak-to-peak (P-P) amplitude of the maximum M-wave and the area of the negative phase of the curve are important measures that serve as methodological controls in Hreflex studies, motor unit number estimation (MUNE) procedures, and normalization factors for voluntary electromyographic (EMG) activity
The day × subjects interaction term was significant, indicating that not all subjects exhibited the same magnitude of increase in PP amplitude across test sessions
The percentage of the variance attributed to trial-to-trial variability (σ2e1) was 1%, which was much lower than the 8% day-to-day variability (σ2e2)
Summary
The peak-to-peak (P-P) amplitude of the maximum M-wave and the area of the negative phase of the curve are important measures that serve as methodological controls in Hreflex studies, motor unit number estimation (MUNE) procedures, and normalization factors for voluntary electromyographic (EMG) activity. These methodologies assume, with little evidence, that M-wave variability is minimal. The PP amplitude of the maximum M-wave is used in Hoffman reflex (H-reflex) studies to accurately conclude that variations in the H-reflex arise from a neural origin, and are not caused by changes in the muscle, recording conditions, or problems with instrumentation [3]. The M-wave is used as a normalization factor to correct for day-to-day fluctuations in voluntary electromyographic (EMG) activity due to slight differences in electrode placement, muscle temperature, and other such considerations [6,7]
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