Influence of local massage application on fatigue scale and EMG power spectrum during sustained muscle contraction
Tim Hideaki Tanaka, Ph.D.
Gerry Leisman, MD., Ph.D.
Hidetoshi Mori, Ph.D.
Kazushi, Nishijo, Ph.D.
Paper presented at the34th Annual Meeting of Association for Applied Psychophysiology and Biofeedback, Jacksonville, Florida March 27-30, 2003.
There is not enough evidence to support the efficacy of massage for muscle fatigue despite wide utilization of the modality in various clinical settings. This study investigated the influence of massage application on localized back muscle fatigue.
Twenty-nine healthy subjects participated in two experimental sessions (massage and rest conditions). On each test day, subjects were asked to lie in the prone position on a treatment table and perform sustained back extension for 90 seconds (Load I). Subjects then either received massage on the lumbar region or rested for a 5 minute duration, then repeated the back extension movement (Load II). The median frequency (MDF), mean power frequency (MNF), and root mean square (RMS) amplitude of electromyographic signals during the 90 second sustained lumbar muscle contraction were analyzed. Immediately after each load, subjects were asked to evaluate their level of fatigue on the Visual Analogue Scale (VAS).
EMG signals were recorded during the entire sustained back extension using Biopac MP 150 with EMG amplifiers and Acqknowledge software. Bipolar silver-silver chloride electrodes (recording diameter = 10 mm.) filled with conductive jelly were placed on the left and right lumbar paraspinal muscles (LPM). Interelectrode impedance was reduced to less than 5 kW by cleaning and abrading the skin using abrasion paste.
The raw EMG signal was recorded at the sampling rate of 1,000 Hz and was band-pass filtered (10–500 Hz) and differentially amplified (gain: X2000, differential input impedance: 2 MW, common mode input impedance: 1000 MW, CMRR: >110 db). The frequency content of each recording in each 2 second segment was analyzed by Fast Fourier Transform analysis (FFT) and the power spectrum was quantified by measuring MNF and MDF. In addition, root mean square value of EMG amplitude was calculated in each 2 second segment. MNF, MDF, and RMS of the first and the last 5 segments recorded during the 90-second contraction stage were used for later analysis.
Reliability of EMG measurements
The recorded MNF EMG measurements were found to have good reliability of ICC2, 1 = 0.69, with 95% confidence interval of (0.44, 0.84). Good reliability of ICC2, 1 = 0.74, with 95% confidence interval of (0.53, 0.87) for MDN EMG; and ICC2, 1 = 0.73, with 95% confidence interval of (0.51, 0.87) for RMS EMG.
Test of the comparison between massage and rest
As shown in table 1, the principle effect found in this experiment was a general change of measurement with time. On ANOVA, there was an indication of significant treatment effect on the squared MNF measurement, however exact areas of change were not revealed on post hoc analysis. The first and last five segments of mean MNF, MDF, and RMS during the 90 second-contraction are presented in Figures 1-3.
Effect of massage and rest on fatigue VAS
The paired t-test indicated that there was a significant increase in fatigue VAS at the end of the second load compared to the end of the first load under rest. There was a significant difference in fatigue VAS change between massage and rest condition (Table 2).
This investigation was carried out to evaluate the possible effect of massage against localized muscle fatigue using EMG analysis and subjective fatigue evaluation. On VAS, there was a significant increase in the degree of lumbar muscle fatigue following the second load under rest condition. The degree of VAS change was significantly different between massage and rest condition. However, mean difference in VAS changes between massage and rest condition was relatively small (-0.32 VS +0.86). It should be noted that while the vast majority of subjects reported less fatigue after massage, four subjects indicated a notable increase in fatigue ranging from +2 to +6 on VAS after the massage. This substantially contributed to the deviation of the mean second VAS score towards the positive side in the massage condition. The increase observed in some subjects after massage might be associated with the elicitation of a relaxation response. Several subjects commented that they felt “too relaxed” after the massage and that they had experienced difficulty lifting their trunk and sustaining the contraction. The relaxation response should be favourable in most clinical situations and after athletic events. However, this reaction may have caused autonomic alterations in some cases, and may have resulted in unfavourable physiological or psychological status (e.g., inhibition of blood flow to muscles, reduced muscle tone, and/or altered mental activity such as decreased alertness) for immediate strenuous activity. Although massage application showed positive influence on subjective feeling of fatigue, the study failed to demonstrate significant changes in any of the EMG parameters. The frequency analysis of the EMG signals in particular has been recognized as a useful tool for the measurement of local muscle fatigue [1, 2]. The lower EMG power spectrum shift during fatigue is considered to be related to biochemical by-product accumulation (H+ and lactic acid) in the muscle, which changes the action potential conduction velocity . Other factors, such as firing rate of motor units, motor unit synchronization, additional recruitment of motor units, and muscle temperature influence the frequency changes . If massage application helps increase local circulation and decrease metabolic waste products, it is reasonable to expect changes in EMG power spectrum (i.e., decreased MNF and MDF slope decline during the 90 second-contraction). In this study, significant change in EMG parameters (MNF, MDF, RMS) was attributed to a time effect. ANOVA detected some evidence that the Intervention (massage or rest) may have influenced the change in MNF. However, the post hoc analysis could not reveal further details, possibly due to the minute difference in MNF changes.
This study was supported by a research grant from the College of Massage Therapists of Ontario (the provincial regulatory body for the practice of massage therapy in Ontario).