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Croake et al

priori significance level of α = .05 (

= 1,

= 5.71,

.054). This indicated that vocal intensity may play a role in

LEMG signal reliability. No interaction effects between

intensity and time factors were found.

To further evaluate the reliability of LEMG signals

across the 3 testing days, ICCs using a 2-factor mixed ran-

dom effect model were calculated. Average measures from

6 sample trials per participant were compared across the 3

testing sessions to evaluate reliability. The ICCs across

Sessions 1 through 3 were 0.56 for the 65 dB condition and

0.40 for the 75 dB condition. These between-session ICCs

were low, suggesting an interpretation of poor to, at best,

fair reliability across testing sessions. Although not stan-

dardized, typical calculated values for ICC interpretation

are as follows: less than 0.40 = poor reliability, 0.40 to

0.75 = fair to good reliability, and greater than 0.75 = excel-

lent reliability.

In addition, the SEM was calculated. The

SEM was then used to determine the MDC in microvolts

necessary to demonstrate a true difference if the muscle was

tested on multiple days with 95% confidence boundaries.

Results indicated that a change of 51µV would be necessary

to determine a true difference in LEMG activity between

testing sessions. Numerical results of ICC, SEM, and MDC

are presented in Table 5. Intraclass correlations for within-

session data revealed strong reliability among participants

ranging from 0.84 to 0.95 and from 0.88 to 0.98 for the 65

dB and 75 dB conditions, respectively. Comparisons of

within-session data are located in Table 6.

Discussion

The use of clinical in-office LEMG has been incorporated

into the diagnostic routine for the evaluation and treatment

of voice disorders in many practices across the country.

Although some evidence supports LEMG use in the

diagnosis and prognosis of certain neuromuscular disorders,

the general reliability of the LEMG signal in normal partici-

pants has not been carefully evaluated. This study measured

the reliability of the LEMG signal in normal, vocally healthy

participants over time with the central aim of determining if

significant LEMG signal variance occurred as a function of

multiple testing sessions. Our second aim was to determine

if vocalization intensity affected the LEMG signal. In limb

studies, control over the degree of muscle contraction is nec-

essary to achieve results that are comparable within and

across participants. Both maximal and submaximal contrac-

tions have been shown to demonstrate strong reliability in

limb muscle.

We used vocal intensity as a method to con-

trol laryngeal muscle contraction levels among participants.

Our results indicated that between-session LEMG reliability

was poor to fair and that control of vocal intensity may be an

important performance variable to help improve the reliabil-

ity of these measurements.

This study mirrored the University of Iowa head and

neck protocol for LEMG diagnostics.

In addition to this

basic protocol, we used vocal intensity control and a

Faraday booth to reduce ambient electrical noise to improve

the fidelity of the data and provide the optimal set of cir-

cumstances under which to perform our LEMG clinical

evaluation. The intent of this study was not to quantify

LEMG precisely but rather to use quantitative means to

measure LEMG in an ideal environment to test the hypoth-

esis that clinical LEMG data are variable across testing ses-

sions even with added control parameters in place.

Repeated measures analysis of variance indicated a non-

significant effect for time of testing, suggesting that LEMG

signals for pooled data did not vary significantly across test-

ing sessions. Intraclass correlation coefficient analysis for

within-session reliability was considered excellent for both

intensity conditions ranging from 0.84 to 0.95 and from

0.88 to 0.89 for the 65 dB and 75 dB conditions, respec-

tively. However, the between-session ICC revealed poor to

fair reliability for both intensity conditions. It should be

noted that the most qualitatively consistent data from our

study were collected when the participants vocalized at 65

dB, indicating a less reliable measure at greater loudness

levels. Data from Sessions 1 and 2 at 65 dB represented the

strongest reliability association with an

value of 0.048.

This indicated poor reliability even across the most consis-

tent recording sessions (see Figures 1 and 2).

Reliability debates concerning the clinical usefulness of

LEMG for diagnostic and prognostic applications have

been raised.

According to a recent evidence-based review

and clinical recommendations, LEMG data have been con-

sidered questionable for clinical uses such as diagnosing

paresis/paralysis from joint fixation, for accuracy diagnos-

ing diseases of the neuromuscular junction, and for provid-

ing accurate diagnostic information of neuropathic and

myopathic disorders.

1,8

To address these questions, it has

Table 5.

Intraclass Correlation Coefficients (ICCs) Between

Sessions, Standard Error of Measurement (SEM), and Minimum

Detectable Change (MDC) in µV Necessary to Detect True

Change Between Measurements.

ICC Sessions

1–3

SEM

Sessions 1–3

MDC in µV @

70% Confidence

MDC in µV @

95% Confidence

65 dB 0.56

18.57

26.26

51.47

75 dB 0.40

23.0

32.5

63.7

Table 6.

Intraclass Correlation Coefficients (ICCs) for Within-

Session Data.

Within-Session

ICC

Session 1

Session 2

Session 3

65 dB

0.95

0.93

0.84

75 dB

0.88

0.84

0.98