Mechanomyography And H-reflex Responses To Electrical Stimulation

Abstract

PURPOSE: The purpose of the present study was to examine the relationship between mechanomyography (MMG) and surface electromyography (SEMG) during electrically evoked muscle contraction. METHOD: Recruitment curves for H-reflex (H), M-wave (M), and peak-to-peak MMG (MMGp-p) were elicited through incremental tibial nerve stimulation (5.0 V increments with 10-second rest intervals until the maximum M-wave was established). Signals were collected (1000 Hz) using a uni-axial accelerometer placed mid-soleus between the SEMG recording electrodes. Sum of the H and M (HMsum) and root mean square MMG (MMGrms) were calculated, and the lag time (TTMax) between the stimulus and the peak MMGrms (Max) was measured. Data for 38 (6 males, 32 females) college-aged participants with measurable H-reflexes were analyzed. Informed consent was obtained, and the Hope College Human Subjects Review Board approved all procedures. Pearson's r among the pairs of dependent variables (HMsum, M, MMGp-p, and Max) was calculated using SPSS v17 statistical analysis software (a ≤ 0.05). RESULTS: Correlations between MMG and the H-reflex were low (r = 0.214, 0.304, 0.389, and 0.411 for MMGp-p:HMsum, Max:HMsum, MMGp-p:M, and Max:M, respectively, p < 0.001). Correlation coefficients for the individuals were on average stronger [ravg = 0.76 ± 0.24 (range: -0.25 to 0.98, 0.75 ± 0.28 (range: -0.10 to 0.97), 0.76 ± 0.31 (range: -0.48 to 0.98), and 0.76 ± 0.29 (range: -0.32 to 0.98) for MMGp-p:HMsum, Max:HMsum, MMGp-p:M, and Max:M, respectively, p < 0.001]. TTMax reflected the transition from a predominant H-reflex to the onset of the M-wave and demonstrated a decline in lag time as the stimulus intensity increased for nearly every participant. CONCLUSIONS: MMG recorded during electrical stimulation is similar to the H-reflex. MMG is not susceptible to stimulus artifact and appears to provide a complimentary signal source for H-reflex studies. While general patterns were apparent, sources of individual variability (e.g., body composition, muscle fiber composition, gender, training, etc.) warrant further study. In addition, the relationship between MMG and maximal twitch torque was not examined in this study. Examination of the latency times (TTMax) and amplitudes for the MMGrms may also be useful in distinguishing muscle fatigue from neural fatigue.