Assessment of Low Back Muscle Adalg

Assessment of Low Back Muscle

Adalgiso Coscrato Cardozo and Mauro Gonçalves

by Surface EMG

São Paulo State University

Brazil

Surface electromyography (EMG) is wide used to analyze back muscle activity. This tool is a

non-invasive technique that allows the evaluation of muscle activity. Extensive researches

were made to understand the surface EMG techniques and its application to the analysis of

low back muscles for classifying healthy subjects and low back pain (LBP) patients, trained

and non-trained subjects, subjects under rehabilitation treatments, as well as to access the

muscle activity during labor tasks, sports practice or daily life activities.

So, the development of biomechanical tests that enable identifying standards of muscular

activity characteristic of a fatigue process, one of the causes for spine muscular-skeletal

lesions, which emerges through the task repetitiveness and overload, may be a possibility of

The aim of this chapter is to provide a global understand of EMG parameters used to access

low back muscle. For this it will be presented some issues that affect the surface EMG for

low back muscle as: the reliability of low back muscle EMG; the behavior of low back

muscle EMG during isometric contractions by means the analysis of the root mean square

(RMS), median frequency (MF) and mean power frequency (MPF); the biomechanical

parameter to identify the fatigue threshold known as Electromyographic Fatigue Threshold

(EMGFT); the used of surface EMG to the assessing low back pain; and the influence of the

manual load lifting to the EMG signal in low back muscle.

2. Reliability of low back muscle EMG

EMG has been used to study physiological aspects of muscle activity. The reliability of the

EMG spectral parameters in low back muscles has been analyzed by different authors

(Bouillard et al., 2011, van Dieën & Heijblom, 1996, Dolan et al., 1995, Ng & Richardson,

1996). This reproducibility refers to the consistency in the measurement tool used, where a

reproducible method is one that has a small measurement error (Elfving et al., 1999). When

evaluating different methods of exercise, the reproducibility of the experiment is very

important, and the test/re-test methodology is used to estimate the variability of the

measures in repeated tests (Dedering et al., 2000).

Tools commonly used for analysis of reproducibility are the Standard Error of the

Measurement (SEM) and the Intra-class Correlation Coefficient (ICC), which appear to be

complementary of each other (Elfving et al., 1999). The first can be used to check the size of

152 Applications of EMG in Clinical and Sports Medicine

the error relative to the size of the changes in the variables analyzed while the second can be

used to consider the size of the error related to differences between measures (Keating &

The ICC rang from 0.00 to 1.00, were the perfect reliability is 1.00 and the poorest is 0.0. A

high ICC reflects a small within-subject variance compared to the between-subjects variance.

There are different ways to calculate the ICC depending on the experimental design and the

composition of the group being tested (Keating & Matyas, 1998), therefore, we must be

careful when comparing it in different groups, and extrapolates it to heterogeneous

Low back muscles EMG parameters are not easily comparable between studies of

reproducibility, since the methodology often varies. In several studies (van Dieën &

Heijblom, 1996, Dolan et al., 1995, Ng & Richardson, 1996) the number of subjects varies

between 4 and 28, mostly males. Also, different locations of electrodes, test positions and

levels of muscle contraction are used by different authors in testing low back muscles

The EMG signal is generally obtained in two locations ranging between T10 and L5

vertebrae. The positions of the test usually used are: prone (Mannion & Dolan, 1994,

Moffroid, 1993, Ng & Richardson, 1996, Coleman et al., 2011), sitting (Carpenter & Nelson,

1999, van Dieën & Heijblom, 1996, Elfving et al., 2003) and standing (Cardozo & Gonçalves,

2010, Cardozo et al., 2011). The time between test and re-test ranging from 5 to 60 minutes in

a comparison intra-day and 1 to 6 days in a comparison of day (Elfving et al., 1999).

Several authors have made studies to verify reliability of surface EMG methods. Spector

(1979) found correlation coefficients ranging from 0.73 and 0.97, while Komi & Buskirk

(1970) achieved a test-retest reliability of 0.88 for surface electrodes.

Danneels et al. (2002) have reported an excellent within-day ICC for EMG parameters

performed at the maximum voluntary contraction (MVC) for both healthy and LBP

During a sub-maximal protocol Dedering et al. (2000) have shown good reliability for EMG

parameters, corroborating with study performed by Fleiss (1986), who also demonstrated

good reliability for low back muscles. In his study he found ICCs ranging from 0.443 to

0.727 for the initial MF, and ranging from 0.273 to 0.734 for the MF slope. These better

results to the initial values comparing to the slope values is supported by study of Peach et

al (1998) performed to analyze back muscle fatigue.

Another measure of reproducibility of EMG parameters is intra and inter-subject coefficient

of variation (CV), where lower values represent greater repeatability (Knutson et al., 1994).

The CV reflects the dispersion of data around the mean and it is calculated by the root

square of the standard deviation divided by the mean. The high or low values are not

considered good or bad. Some degree of variability is necessary to demonstrate

reproducibility. A low CV suggests homogeneity of the group, which allows creating a

diagnostic or a model that can be compared to other assessments. This is the basis on which

the average dynamic electromyography has been considered as a normalization value when

Since EMG analysis have been an alternative to check the resistance of low back muscles due

to the contraction time, the reproducibility of these measures becomes paramount.

According to the studies presented in the current chapter, it is possible to note that during

isometric contractions surface EMG can access low back muscles with good reproducibility.