By Christopher Kent, DC
November 16, 2005
An important issue when selecting a clinical examination procedure is
reliability. Reliability is a measure of the ability to reproduce a
measurement, which is expressed as a coefficient ranging from 0.00 to
1.00. Perfect reliability results in a coefficient of 1.00, while
chance agreement would be 0.0.
As an example, Hass and Panzer (1) noted that the inter-examiner
reliability of palpation for muscle tension is poor, with coefficients
ranging 0.07 to 0.20. As presented below, research data indicates
that the reliability of SEMG is clearly superior to palpation for
muscle tension.
Decades of research by independent investigators show that surface
electrode electromyography exhibits very good to excellent test-retest
reliability. Spector (2) conducted a study at New York Chiropractic
College which yielded correlation coefficients ranging from 0.73 and
0.97. Komi and Buskirk (3) compared the test-retest reliability of
surface electrodes vs. needle electrodes in the deltoid muscle. The
average test-retest reliability for surface electrodes was 0.88
compared to 0.62 for inserted electrodes.
Giroux and Lamontagne (4) compared the reliability of surface vs.
intramuscular wire EMG of the trapezius and deltoid muscles during
isometric and dynamic contractions. The statistical analysis on the
integrated EMG was a factorial analysis model with repeated measures.
They found that surface EMG was more reliable than inserted wire EMG
on day-to-day investigations.
Andersson et al (5) compared the electrical activity in lumbar erector
spinae muscles using inserted electrodes and surface electrodes. They
found that the standard deviations and coefficients of variation for
wire electrodes were greater than those for surface electrodes. They
concluded, "Wire electrodes are more sensitive to electrode location
and give estimates with less precision than surface electrodes."
Other investigators have evaluated the reliability of surface
electrode techniques using hand-held electrodes. This method is
referred to as surface EMG scanning. Thompson et al (6) of the Mayo
clinic found that the scanning electrode technique correlated well
with the "gold standard" of attached electrode technique. Cram et al
(7) evaluated the reliability of surface EMG scanning in 102 subjects
in the sitting and standing positions. SEMG scans were performed on
three occasions approximately one hour apart on the same day. The
median correlation was 0.64. The authors concluded, "With adequate
attention given to skin preparation, EMG sensors held in place by hand
with a light pressure provide reliable results."
In a review of surface EMG, Lofland et al (8) state that "Recent
methodologically sound research has shown modern multichannel surface
EMG to be reliable and valid."
The most exciting recent study examining surface EMG reliability (9)
was conducted at the NZCA School of Chiropractic in New Zealand. The
study involved chiropractic care provided by 19 chiropractic interns
in a teaching clinic. The equipment used was an Insight Subluxation
Station.
Each of the 30 patients involved in the study received chiropractic
examinations including static and motion palpation, joint play and end
feel, Derefield-Thompson leg length assessment, and muscle challenge
testing. Full spine x-rays were taken and analyzed when evidence of
spinal dysfunction was determined.
One or more adjusting procedures, including Palmer Upper Cervical,
Diversified, Gonstead, and Thompson Terminal Point Technique were used.
Baseline SEMG scans were performed prior to initiation of chiropractic
care. Follow up SEMG scans were performed one week after the first
adjustment, and four weeks after the first adjustment.
To evaluate intra-examiner reliability, a two-tailed paired t-test was
used to compare means of the intra-examiner trial population samples.
This approach was used because correlation coefficients could reveal a
high level of self-consistency, but mask examiner error. The
objective was to determine if there was so much variability in the
samples that they could be distinguished as different. The article
reported that in 99.7% of the paired trials, variation was not
sufficient to distinguish the samples as significantly different.
This suggests an acceptable level of examiner consistency.
The investigators further concluded, "Under the conditions of this
study, it is concluded that SEMG is an objective measure of change
which can be used as an assessment of patient progress."
REFERENCES
1. Haas M, Panzer DM: Palpatory diagnosis of subluxation. In:
Gatterman M (ed): Foundations of Chiropractic Subluxation. St. Louis,
MO, Mosby, 1995.
2. Spector B: Surface electromyography as a model for the
development of standardized procedures and reliability
testing. JMPT 1979;2(4):214.
3. Komi P, Buskirk E: Reproducibility of electromyographic
measurements with inserted wire electrodes and surface
electrodes. Electromyography 1970;10:357.
4. Giroux B, Lamontagne M: Comparisons between surface electrodes and
intramuscular wire electrodes in isometric and dynamic conditions.
Electromyogr Clin Neurophysiol 1990;30:397.
5. Andersson G, Jonsson B, Ortengren R: Myoelectric activity in
individual lumbar erector spinae muscles in sitting. A study with
surface and wire electrodes. Scand J Rehab Med 1974 Suppl;3:91.
6. Thompson J, Erickson R, Offord K: EMG muscle scanning:
stability of hand-held electrodes. Biofeedback Self Regul
1989;14(1):55.
7. Cram JR, Lloyd J, Cahn TS: The reliability of EMG muscle scanning.
Int J Psychosomatics 1994;41:41.
8. Lofland KR, Mumby PB, Cassisi JE, et al: Assessment of lumbar EMG
during static and dynamic activity in pain-free normals: implications
for muscle scanning protocols. Biofeedback and Self-Regulation
1995;20(1):3.
9. Kelly S, Boone WR: The clinical application of surface
electromyography as an objective measure of change in the chiropractic
assessment of patient progress: a pilot study. Journal of Vertebral
Subluxation Research 1998;2(4):175.
