Elsevier

Clinical Neurophysiology

Volume 114, Issue 12, December 2003, Pages 2355-2361
Clinical Neurophysiology

Reliability of electromyographic and torque measures during isometric axial rotation exertions of the trunk

https://doi.org/10.1016/S1388-2457(03)00249-9Get rights and content

Abstract

Objective: The aim of the present study was to investigate the between-days reliability of electromyographic (EMG) measurement of 6 bilateral trunk muscles and also the torque output in 3 planes during isometric right and left axial rotation at different exertion levels.

Methods: Ten healthy subjects performed isometric right and left axial rotation at 100, 70, 50 and 30% maximum voluntary contractions in two testing sessions at least 7 days apart. EMG amplitude and frequency analyses of the recorded surface EMG signals were performed for rectus abdominis, external oblique, internal oblique, latissimus dorsi, iliocostalis lumborum and multifidus bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were measured.

Results: For both EMG amplitude and frequency values, good (intraclass correlation coefficient, ICC=0.75–0.89) to excellent (ICC≥0.90) reliability was found in the 6 trunk muscles at different exertion levels during axial rotation. The reliability of both maximal isometric axial rotation torque and coupling torques in sagittal and coronal planes were found to be excellent (ICC≥0.93).

Conclusions: Good to excellent reliability of EMG measures of trunk muscles and torque measurements during isometric axial rotation was demonstrated. This provides further confidence of using EMG and triaxial torque assessment as outcome measures in rehabilitation and in the evaluation of the human performance in the work place.

Introduction

In the last few decades, surface electromyographic (EMG) measurement has become a popular method of investigating muscle function. Recent reviews have confirmed the usefulness of EMG investigation in various clinical studies which have analyzed muscle function (Soderberg and Knutson, 2000), evaluated movement disorders (Pullman et al., 2000) and been applied to ergonomic applications (Kumar and Mital, 1996). Commonly, two characteristics of EMG signals have been investigated. They are the amplitude and frequency parameters of the EMG signals. The EMG amplitude is used to quantify the extent of the activation of the muscle which could give an indication of individual muscle force (Perry and Bekey, 1981). The EMG frequency parameter is considered to represent the recruitment of motor units of the muscle during set tasks (Moritani and Muro, 1987, Solomonow et al., 1990).

Surface EMG has commonly been used in the investigation of spinal or trunk muscles, but this usually has involved the examination of back muscles during trunk extension. Fewer studies have investigated abdominal and back muscle activity during axial rotation exertion of the trunk. This may be attributed to the fact that trunk axial rotation is a more complex exertion compared to contraction in sagittal plane. Axial rotation involved coupling of torques in 3 planes (Parnianpour et al., 1988, Parnianpour et al., 1991, Ng et al., 2001) and it is known that the coupling of torque was more evident during exertions in axial rotation than during exertions in flexion and extension (Parnianpour et al., 1988, Parnianpour et al., 1991). Furthermore, axial rotation involves a number of muscles, and the co-contractions of antagonists and synergists are higher than that in other planes of exertion (Marras and Granata, 1995, Marras and Granata, 1997, Thelen et al., 1995). There is not one agonist with a moment arm exclusively involved in axial rotation (McGill, 1991) and the contraction of these agonists usually results in torque in other planes (Dumas et al., 1991). Hence, the co-contractions of the antagonists and synergists are important in maintaining spinal position and stability during trunk axial rotation.

Axial rotation of the trunk is a common daily activity and has been identified as a risk factor associated with back pain (Frymoyer et al., 1980, Burdorf and Sorock, 1997). Previous studies have demonstrated that back pain patients exhibit different activation strategies in their trunk muscles during axial rotation (Wolf and Basmajian, 1978, Ahern et al., 1988, Ng et al., 2002a). A recent study demonstrated that EMG activity of rectus abdominis was less in back pain subjects compared to healthy controls only at high levels of axial rotation exertion (Ng et al., 2002a). In addition, during the fatigue process, abnormal changes in EMG amplitude and frequency parameters have been found in the abdominal and back muscles of back pain patients (Ng et al., 2002b).

In order to make practical conclusions for EMG studies, reliability investigations are essential. There are many reliability studies involving the evaluation of surface EMG in back muscles during trunk extension, including activation (e.g. Stokes et al., 1987, Lee and Stokes, 1992, Ng and Richardson, 1994) and frequency values (e.g. Biedermann et al., 1990, Ng and Richardson, 1996, van Dieën and Heijblom, 1996, Mannion et al., 1997, Peach et al., 1998, Elfving et al., 1999, Dedering et al., 2000, Larivière et al., 2000, Koumantakis et al., 2001). In addition, there are some recent studies on reliability investigations of EMG measurement in lateral flexion (e.g. Larivière et al., 2000, Thomas and Lee, 2000). While one previous study (Ahern et al., 1986) investigated the reliability of EMG amplitude during unresisted axial rotation movement, there have been no studies on the reliability of EMG measures and related torque output during isometric trunk axial rotation at different exertions levels. It is important that the reliability of EMG and torque measures should be established before they are adopted in clinical assessment of musculoskeletal disorders, occupational applications in work place design and used as outcome measures in rehabilitation. Therefore, the aim of the present study was to investigate the reliability of EMG measurement of 6 bilateral trunk muscles and also the torque output in 3 planes during isometric right and left axial rotation at different exertion levels.

Section snippets

Subjects

Ten healthy subjects without any history of back pain were recruited for this study. All the subjects were male and right-handed. Their mean (±standard deviation) age, height, weight were 27.1±7.3years, 1.76±0.07m, and 64.7±10.1kg, respectively. All subjects gave their written informed consent to participate. The study was approved by the Medical Research Ethics Committee of The University of Queensland.

Equipment

A triaxial dynamometer, B200 Isostation (Isotechnologies, Hillsborough, North Carolina, USA)

Results

Group mean (standard deviation) of EMG amplitude and frequency measures over two testing sessions as well as the reliability for EMG amplitude and frequency values are shown in Table 1, Table 2. For both EMG amplitude and frequency values, good (ICC=0.75–0.89) to excellent (ICC≥0.90) reliability was found in the 6 trunk muscles at different exertion levels during axial rotation. The reliability of maximal isometric axial rotation torque was found to be excellent, ICC=0.98. The ICC value for

EMG findings

The reliability of the EMG activity (RMS values) at different exertion levels in both abdominal and back muscles was found to be good (ICC=0.75–0.89) to excellent (ICC≥0.90) (Table 1). It should be noted that between-days reliability was examined in the present study. It has been demonstrated that reliability of EMG measurement between days is poorer than measures taken within the same day (Yang and Winter, 1983, Ahern et al., 1986). The higher variability in between-days reliability may be

Conclusion

The present study demonstrated that the between-days reliability of EMG measures of trunk muscles and torque measurements during isometric axial rotation exertion was good to excellent. Given the potential use of EMG in human performance assessment and industrial applications in work place design, the observed reliability of both amplitude and frequency measures of EMG are reassuring. These measurements would be valuable in the diagnosis of neuromuscular dysfunction of back pain patients and

Acknowledgements

This study was supported financially by the Dorothy Hopkins Award for Clinical Study and the research support grant of Manipulative Therapists Special Group of Queensland, Australia. The authors are grateful to the staff of the Workers' Compensation Board of Queensland for their invaluable assistance during the whole data collection process.

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