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A. Koufman, M.D., Teresa A. Radomski, M.M., Ghazi M. Joharji, M.D,
Presented at the Annual Meeting of the American Academy of Otolaryngology -- Head and Neck Surgery - New Orleans, Louisiana, September 18, 1995
Visit The Wake Forest University Baptist Medical Center website
By transnasal fiberoptic laryngoscopy (TFL), patients with functional voice disorders often demonstrate abnormal laryngeal biomechanics, commonly supraglottic contraction. Appropriately, such conditions are sometimes termed "muscle tension dysphonias." Singers working at the limits of their voice may also transiently demonstrate comparable tension patterns. However, the biomechanics of "normal" singing, particularly for different singing styles have not previously been well characterized.
TFL was used to study 100 healthy singers in order to assess patterns of laryngeal tension during normal singing, and to determine whether factors such as gender, occupation, and style of singing, influence laryngeal muscle tension. Thirty-nine male and 61 female singers were studied: 48 professional singers and 52 amateurs.
Examinations of study subjects singing standardized and nonstandardized tasks were recorded on a laser disk and subsequently analyzed in a frame-by-frame fashion by a "blinded" otolaryngologist. Each vocal task was graded for muscle tension by previously established criteria, and objective muscle tension (MT) scores were computed. The MT score was expressed as a percentage of frames for each task showing one of the laryngeal muscle tension patterns.
The lowest MT scores were seen in female professional singers, and the highest MT scores were seen in amateur female singers. Male singers (professional and amateur) had intermediate MT scores. "Classical" singers had lower MT scores than "non-classical" singers, with the lowest MT scores being seen in those singing choral music (41%), art song (47%), and opera (57%), and the highest in those singing jazz/pop (65%), musical theater (74%), bluegrass/country & western (86%), and rock/gospel (94%).
Analyzed also were the influences of vocal nodules, prior vocal training, number of performance and practice hours per week, warm-up before singing, smoking, alcohol consumption, and race.
On television, almost everyone has seen ultra-slow-motion footage of runners, golfers and other athletes, in which the positions of the major joints and muscles are sequentially analyzed in a frame-by-frame fashion. "Biomechanical analysis" of athletic performance has become relatively familiar, and is accomplished by linking a video system to a computer system so that movement can be evaluated critically. Using this technology, patterns can be identified that are at one extreme optimally efficient, and at the other extreme, maladaptive, or even abusive.
Through the use of similar methods, laryngeal biomechanics were studied at the Center For Voice Disorders of Wake Forest University. The purpose of these studies was to determine the "normal" laryngeal biomechanics of healthy singers, and to analyze some of the factors (e.g., gender, vocal training, singing style) that may influence laryngeal biomechanics.
Materials And Methods
A collaboration between a laryngologist (JAK) and a vocal pedagogue (TAR) was established to carry out this study, and a custom computer-controlled laser disk recording system was employed so that video data could be retrieved and analyzed with precision.
Through media advertising, volunteer singers were solicited for study. To be included, singers had to be both medically and "vocally" healthy (i.e., they could not be experiencing any vocal problems at the time of enrollment in the study). Specifically excluded were subjects who had experienced any serious medical illness within 60 days of the study, or who were known to have vocal cord lesions, e.g., nodules, polyps, granulomas. Subjects were enrolled without regard to gender, race, or age, although an attempt was made to solicit and include a balance of professional and amateur singers, and singers of different styles of music.
Prior to inclusion, each subject completed a detailed history form. This information formed the preexamination database. Included were demographic information such as age, gender, race, occupation, professional status (full-time vocal professional, part-time vocal professional, voice student, other amateur singer), number of years of formal voice training (if any), average number of practice and performance hours per week, and style of singing. In addition, subjects were asked whether they were "currently" taking voice lessons, whether they warmed-up before singing, whether they experienced muscle tension when singing, and whether they exercised regularly.
The past medical history included the number of episodes of "laryngitis" in the past 5 years, any other history of vocal problems (specifically vocal cord lesions), tobacco usage, alcohol usage, medications, reflux symptoms, and any medical condition for which the subject saw a doctor regularly.
Demographic Description of the Study Population
All 100 of the subjects enrolled in the study were healthy, and none had any known voice problem. Thirty-nine were males and 61 were females. Forty-eight were professional singers, and 52 were amateurs. Ninety were caucasian and 10 were African-Americans. Their mean age was 37 ± 13.5 (mean ± standard deviation), with a range of 18-69 years. The primary singing style of the 100 subjects, broken down by gender and professional status, is shown in Table 1.
The following equipment was employed: a Pentax (FNL-13S), 3.7-mm external diameter fiberscope; a Storz xenon light source; a Panasonic (model AG7300) super VHS video recorder; a Toshiba (model IK-C40) camera; a Pioneer (model TQ-3031F) optical disc recorder; and a Zenith microcomputer.
The optical disc recording system was under footswitch control via computer interface for hands-off operation by the examiner. Frame addresses were stored and labelled in the computer program for subsequent retrieval and analysis. (The advantages of the optical disc video system for this study were its high resolution of the video image, precision random access, and stability of freeze-frame fields.)
1: Laryngeal Biomechanics Of The Singing Voice:
* Country and Western
Technique of TFL
TFL was performed by the senior author (JAK) using the following technique: the procedure was explained; the subject's nose was topically anesthetized by spray with 2% cocaine and 1% ephedrine; the subject was positioned sitting with the neck in a modified "sniffing position," with the arms on the lap, chin up, and shoulders relaxed; and the fiberscope was introduced between the middle and inferior turbinates, and positioned in the hypopharynx so that it gave an unobstructed view of the endolarynx.
Each subject was asked to perform the following singing tasks: (1) the last line of the Star Spangled Banner ("O'er the land of the free, and the home of the brave") on key (provided by a keyboard); and (2) a selection of music in the subject's own style. (Throughout this report, the former will be referred to as "the standard task" and the latter as "the own-style task.")
The Star Spangled Banner line was selected as the standard singing task because it can be sung in six seconds or less (and matches our six-second recording window); it is familiar to every subject; it is relatively difficult to sing; and it includes the passaggio (the transition from the middle to the high registers of the voice). For the own-style singing task, each subject was instructed to select something that he or she considered to be technically difficult and that also included the passaggio. Prior to TFL examination, each of the tasks was "practiced" by the subject under the supervision of the examining team. This was done to evaluate the suitability of the piece selected by the subject for the "own style" task, and to encourage the subject to sing loudly, in "full voice."
For actual video recording (data collection), each task was performed at full voice and sufficiently quickly, so that the complete task was recorded within the six-second window. In some instances, tasks were repeated to ensure that they were completely recorded.
Statistical Methods and Analysis
For data analysis, the study population was broken down into gender, professional status, and singing style. Some of the singing styles were combined into three groups, because the numbers of subjects in the pop, jazz, bluegrass, country and western (C&W), rock, and gospel groups were small; these were pop/jazz, bluegrass/C&W, and rock/gospel. This gave a total of eight singing style groups for the purpose of statistical analysis. (The authors believe that it is appropriate to pair these groupings for that purpose because the paired styles demonstrated similar laryngeal biomechanics, i.e., they had similar MT scores.)
Frequencies and descriptive statistics were generated for demographic data. Pearson Product Moment Correlations and analysis of variance (ANOVA) were utilized to assess univariate relationships between MT scores and independent variables. Multiple linear regression with backward elimination was used to examine multivariate relations. Fisher's Exact Test was used to test for differences in categorical variables.
Both a univariate data analysis and a multivariate model for the outcomes of interest were analyzed in an effort to assess the impact of each variable individually, as well as in conjunction with the other variables observed. (The multivariate model takes every variable into account; however, it should be recognized that it is not unusual for univariately significant variables in such models not to be significant in a multivariate model.)
Laryngeal "Muscle Tension Patterns" (MTPs)
The operation of normal and abnormal laryngeal biomechanics as assessed by TFL examination of normal subjects and patients with voice disorders has been reported. Koufman and Blalock have previously characterized four discrete patterns of laryngeal muscle tension in patients with voice disorders. These basic patterns are termed muscle tension patterns (MTPs): type I is glottal, and types II-IV are supraglottal.
Muscle Tension Pattern I (MTP I)
MTP I was first described by Morrison and colleagues in 1986 as "an open glottic chink." The characteristic finding of MTP I is a gap between the vocal fold free-edges during phonation, with a more conspicuous posterior gap between the vocal processe s. MTP I has also been called a laryngeal isometric pattern, because it presumably is caused by the simultaneous and inappropriate overcontraction of the posterior cricoarytenoid muscles in opposition to the lateral cricoarytenoid muscles during phonation. (MTP I is common in patients who have vocal nodules.)
Muscle Tension Pattern II (MTP II)
MTP II is characterized by compression (medialward pressure) of the false vocal cords. In its mildest form, only the anterior portions of the false vocal cords are compressed -- almost approximating, or actually touching together. (When the false vocal cords come into contact and are used for phonation, this produces a severe, pitch-locked dysphonia. False-cord voice, sometimes termed plica ventricularis, is a relatively common functional voice disorder.)
Muscle Tension Pattern III (MTP III)
MTP III is characterized by partial anteroposterior contraction of the larynx during phonation. Typically, the arytenoids are pulled forward toward the petiole of the epiglottis, obscuring the posterior one-half to two-thirds of the vocal folds. (MTP III is seen in patients who speak using a very low-pitched voice, the so-called "Bogart-Bacall syndrome." Also, it is routinely seen when singers sing the lowest note of the vocal range.)
Muscle Tension Pattern IV (MTP IV)
Extreme anteroposterior contraction, i.e., complete sphincter-like closure of the larynx, in which the arytenoids actually contact and squeeze against the petiole, is characteristic of MTP IV. (This pattern is uncommon, but it is seen in severe functional voice disorders and in patients with spasmodic dysphonia.)
Grading and Calculation of the Muscle Tension (MT) Scores
An otolaryngologist, blinded to the demographic and clinical information, reviewed and graded each vocal task frame-by-frame. Frames in which the vocal cords were not in contact (e.g., during inspiration, before initiation of the task, and after completion of the task) were not scored. In addition, any obscured frames were not scored. Thus, the percent MT score was calculated:
Number of frames showing MTP x 100
Total number of scored frames for the task
Specific criteria were established for the actual classification and grading of each MTP:
For all subjects, the mean MT score for the standard task (the last line of the Star Spangled Banner) was 40.41% ± 45.9 (mean ± standard deviation). The mean MT score for the own-style task was 60.9% ± 41.9.
Influence of Singing Style (MT Scores For The "Own-Style" Task)
The mean MT scores for the different singing styles (in rank order) are shown Table 2. The differences among some of the groups were statistically significant.
* The P values in this table were calculated by comparing the MT score of each group with that of the choral group, which had the lowest MT score. The ** denotes statistical significance (P <0.05).
Influence Of Gender And Professional status
For male subjects, the mean MT score for the standard task was 40.1% ± 45.1, and for females, 40.6% ± 46.7 (P = 0.8379). The mean MT scores for male and female subjects for the own style task were also virtually identical (61.9% ± 39.6 and 60.3% ± 43.7 respectively) (P = 0.9999).
For professional subjects, the mean MT score for the standard task was 64.4% ± 42.6, and for amateurs 46.4% ± 46.3; however, the difference was not statistically significant (P = 0.1108). For professional subjects, the results for the own-style task were opposite from those observed for the standard task -- professionals had lower MT scores (33.9% ± 45.0), compared to amateurs (57.2% ± 41.4), but again, the difference was not statistically significant (P = 0.2131).
Interaction Between Gender And Professional Status
gender and professional status were treated as independent variables (as
above), neither appeared to correlate significantly with MT score;
however, when the study population was divided into four discrete cohorts
by gender and professional status, the MT score for each group was
significantly different from that for the other groups.
The P values in this table denote the difference among the groups. The ** denotes statistical significance (P <0.05).
Variables That Strongly Correlated With MT Scores
"Classical" styles of singing (choral, art song, and opera) had lower MT scores, than "non-classical" styles; subjects who were found to have vocal nodules had higher MT scores, than those who did not have them; and African-American subjects had higher MT scores, than caucasian subjects. These data are described below, and summarized in Table 4-A.
Classical Singing Styles
When the "classical" styles (choral, art song and opera) were combined into one group (n = 53) and compared to a group combining the other five singing style groups (n = 47), the MT scores for the classical group were lower for both tasks.
For the standard task, the mean MT score for the classical group was 28.11% ± 41.2, compared to 54.2% ± 47.4 for the non-classical group (P + 0.0040). For the own-style task, the mean MT score for the classical group was 45.9% ± 42. 6, compared to 74.9% ± 36.8 for the non-classical group (P = 0.0013).
During the laryngeal examination, 15 subjects were found to have "asymptomatic" vocal nodules on laryngeal examination: seven had "mature" (organized/keratinizing) nodules, and eight had "immature" mucosal swelling-type nodules. Both MT scores were higher for these subjects with nodules.
For the standard task, the mean MT score of the nodule group was 57.9% ± 49.3, compared to 37.3% ± 44.9 for the group without nodules (P = 0.0626). For the own-style task, the mean MT score of the nodule group was 93.3% ± 15.1, compared to 55.2% ± 42.6 for the group without nodules (P = 0.0082).
The singing styles ("own-style") of the 10 African-American subjects were opera (n = 4), gospel (n = 2), pop/jazz (n = 2), art song (n = 1), and bluegrass (n = 1). Compared to the caucasians, the African-Americans had significantly higher MT scores.
For the standard task, African-Americans subjects had a mean MT score of 88.0% ± 31.6, compared to 35.2% ± 44.2 for caucasian subjects (P = 0.0004). For the own-style task, the African Americans had a mean MT score of 99.1% ± 2.8, compared to 56.3% ± 41.9 for the caucasians (P = 0.0018).
Variables That Had Borderline Correlation With MT Scores
Lower MT scores were seen in those with vocal training, and those who warmed-up before singing. Compared to the amateurs, professional singers had lower MT scores for the own-style task, but higher MT scores for the standard task. In addition, there was a correlation between the number of practice hours per week and the MT score -- as the number of practice hours increased, so too did the MT score. These data are described below, and summarized in Table 4-B.
Seventy-three subjects had at least one year of vocal training (range 1 to 23 years). Vocal training was treated as a continuous variable, and it appeared to correlate with lower MT scores (P = 0.0838).
Forty-eight subjects were professional singers and 52 were amateurs. For the own-style task, the professionals had lower MT scores (33.9% ± 45.0) than amateurs (57.2% ± 41.4) (P = 0.2131). For the standard task, the professionals had higher MT scores (64.4% ± 42.6) than the amateurs (46.4% ± 46.3) (P = 0.1108).
Warm-Up Prior To Singing
Seventy-four of the 100 subjects reported that they warmed-up prior to singing. For the standard task, those who warmed-up have a mean MT score of 39.6% ± 46.1, compared to 48.5% ± 47.2 for those who did not (P = 0.1392). For the own-style task, those who warmed-up had a mean MT score of 57.8% ± 41.9, compared to 73.3% ± 38.9 for those who did not (P = 0.1250).
Number of Practice Hours Per Week
The number of practice hours per week was treated as a continuous variable, and it appeared to correlate with the MT scores for the own-style task -- as the number of practice hours increased, so too did the own-style MT score (P = 0.0838). For the standard task, however, there was no correlation (P = 0.8985).
Numerous variables were investigated, but none appeared to correlate with the MT scores (Table 4-C).
4: Summary Of Variables
Variables that STRONGLY CORRELATED with MT Scores (P<0.05)
Variables that WEAKLY CORRELATED with MT Scores (P = 0.05 to 0.15)
Variables that DID NOT CORRELATE with MT Scores (P >0.15)
Correlation Between MT Scores For The Standard Task and For The Own-Style Task
On cursory examination of the data, it may appear that the MT scores on the standard and own-style tasks are independent. However, when the MT scores of the two tasks are compared, the correlation is highly statistically significant (P = 0.0001).
Muscle Tension Pattern Data
In addition to collecting the total MT score data for each vocal task, each of the MT patterns was scored, and the data were analyzed. MTP I was by far the most common. For the standard task, the mean MTP values for all subjects were: MTP I 3.9% ± 18.1; MTP II 6.0% ± 22.2; MTP III 30.4% ± 42.6; and MTP IV 2.8% ± 15.0. For the own-style task, the mean MTP values for all subjects were: MTP I 3.4% ± 15.6; MTP II 10.8% ± 28.2; MTP III 46.5% ± 41.4; and MTP IV 4.0% ± 14.2.
The individual MTP patterns were analyzed to detect differences among professionals and amateurs, and men and women. None of the differences among the groups were statistically significant except that MTP II was more common in male singers (10.1% ± 27.3) than in female singers (3.4% ± 18.0) (P = 0.0365); and MTP III was more common in amateur singers (38.5% ± 45.5) than in professional singers (21.6% ± 37.8) (P = 0.0261).
The Mutivariate Model
A multivariate model used to investigate the interaction among the variables showed a significant correlation between MTP score and gender, race, classical singing style, professional status, practice hours per week, alcohol use, and vocal nodules. These data are shown in Table 5. (The implications and interpretation of this model are addressed in the discussion.)
The normal biomechanical configuration for effortless phonation is that the vocal cords approximate "like two hands clapping on a hinge"; vocal cord closure is achieved along the length of the vocal cords, without the participation of supraglottic structures. (There is neither front-to-back foreshortening nor side-to-side compression of the larynx, and the aryepiglottic folds remain thin and rounded.) "Effortless phonation," however, is not always what singers exhibit when they are singing.
It must be emphasized that the data we present here do not suggest that singing styles associated with high MT scores should be avoided, nor do they suggest that a high MT score is in any way abnormal or pathologic. They do, however, make one assumption (which is supported by clinical experience): High MT scores imply high levels of laryngeal work, whereas low MT scores imply relative vocal/laryngeal efficiency.
It would be premature to speculate about the specific implications of MT scores, except to say that a very high MT score represents the laryngeal mechanism working at maximal effort. In some singers this may be necessary and acceptable to achieve a desired vocal result, and in others it may be a precursor to a voice disorder. In other words, in a patient with a voice disorder, observed MT patterns appear to have pathologic significance; however, in an asymptomatic singer, a high MT score may simply indicate an elevated level of laryngeal work for a specific vocal task, and nothing more.
It is on the basis of our experience with patients having vocal nodules that we can extrapolate the possible significance of prolonged and excessive high levels of laryngeal tension/work. Fifteen of the patients in this series had "asymptomatic" vocal nodules (incidentally found at the time of examination). Although this group (by univariate statistical analysis) had higher MT scores compared to subjects without nodules, when the multivariate model was used, nodules were not associated with increased MT scores for those subjects' own-style tasks (see Table 5).
5: Results Using A Multivariate Model:
(Shown are the P values of a backward stepwise regression; see the statistical methods and results sections of the text for analysis and definition of terms.)
denotes statistical significance (P <0.05)
A possible explanation for this finding is exemplified by one of the study subjects, a professional "club" singer. Her MT score on the standard task was very high, but when she sang her own style, her MT score was 0.0% -- she sang "Misty" using a soft, breathy glottal attack.
In professional singers, with few exceptions, we found a matching of the singer with his or her own singing style. In the multivariate model, professionals had relatively high MT scores for the standard task, but not for the own-style task. Vocal training and warming-up before singing, for example, may be useful in increasing laryngeal efficiency; however, the multivariate model demonstrated that the MT score is a result of the complex interactions of many variables.
Some of the variables that influence the MT score interact in ways that may be interpreted. There was no difference between the MT scores of male and female subjects, or between professionals and amateurs, and yet the "gender/pro-status" cohorts were significantly different from each other, see Table 3. The explanation is simply that the variables that influence MT score interact in complex ways. For example, a higher proportion of professional females sang classical styles, warmed-up before singing, and had had vocal training than professional males and amateur females.
Variables That Favorably Influence Laryngeal Biomechanics
Generally, some variables appear to decrease the MT score, or "protect against excessive laryngeal tension," and these include: (1) vocal training; (2) singing classical styles of music; and (3) warming-up before singing. Intuitively, each of these variables should exert a score-lowering influence.
It is presumed, particularly by vocal pedagogues, that the purposes of vocal training are to teach good vocal technique ("vocal hygiene"), to teach an appropriate repertoire, and to increase the efficiency of the laryngeal mechanism. While "good vocal technique" may vary from teacher to teacher, good breath support, good posture, and relaxation of the vocal tract and its supporting musculature are among its professed elements.
In other words, reduction of excess laryngeal tension is one of the primary goals of training. In particular, many voice teachers focus on avoiding laryngeal elevation during singing. This makes sense because excessive tension of the suprahyoid musculature is associated with supraglottic contraction (MTPs II-IV). In this study, 79% of the subjects had some vocal training, and the MT data appear to affirm the proposition that vocal training does to some degree increase laryngeal/vocal efficiency, i.e., decrease MT scores.
Classical vs Non-Classical Singing Styles
The complexity of the model makes it difficult to determine the relative contribution of every variable, and it appears that classical singing may be associated with other MT-score-reducing variables. However, when a classical singer sang a non-classical style, such as musical theater or gospel, we observed that the MT scores increased dramatically. (As part of a related study, some subjects did sing more than one style, but herein we are just reporting the results of a subject's primary singing style.)
There is no question, for example, that "belting" singing styles require more work than classical styles, and it appears that the ranking of singing styles by MT score in Table 2 probably represents real differences in laryngeal tension/work. (We should point out that "belting" is sometimes used in the classical (operatic) repertoire; but, by comparison with musical theater and other "non-classical" styles, it is infrequent.)
Even when all variables are considered, certain singing styles demand increased laryngeal work, and increased MT scores appear to correlate with certain singing styles. One subject, an amateur bluegrass singer, stated, "if it don't hurt, it ain't bluegrass." (He had a very high MT score for his own style task.) Clearly, there may be social and cultural factors that impact on how certain styles of music are sung. To the trained ear, what you see (on TFL) is what you hear.
Warm-up Before Singing
Most athletes warm-up before performing, and vocal athletes appear to be no different. It is likely that vocal warm-up limbers up the laryngeal musculature much like stretching does for other muscles. This is evidenced by the data of the study.
Variables That Unfavorably Influence Laryngeal Biomechanics
Several variables appear to correlate with the MT score and have the "unfavorable" effect of increasing MT scores, or of "generating" increased laryngeal tension. These include vocal nodules, race, and an increased number practice hours per week.
Virtually, by definition, vocal nodules are associated with aberrant laryngeal biomechanics, namely higher than normal vocal fold tension/stiffness, i.e., increased laryngeal muscle tension. Among voice clinicians, it is presumed that nodules are the result of vocal abuse (too loud, too long), an excessively hard glottal attack, poor breath support, and/or excessive vocal cord tension/stiffness.
In addition, nodules appear to be self-perpetuating. The mass of the nodules themselves prevents complete closure of the cords along their free edges. As a consequence, in an attempt to achieve closure for certain vocal tasks, a person with nodules will automatically increase the tension of the vocal cords and increase the subglottic pressure to drive the stiffened cords. Thus, increased laryngeal work can create a vicious cycle in which additional vocal cord trauma and swelling are a consequence of compensatory biomechanical adjustments for the nodules.
It is important to emphasize that the study subjects with vocal nodules were "asymptomatic," i.e., they had no vocal complaints. In addition, more often than not, vocal nodules in singers result from problems with the speaking, and not the singing, voice. Consequently, voice clinicians working with nodule patients must establish the cause of nodules -- speaking voice, singing style, or both -- if therapy is to be effective.
When asymptomatic nodules are found, they should be addressed by a similar approach, namely, establishing why they are there by surveying laryngeal biomechanics during TFL with an assortment of vocal tasks. Observing how MTP patterns change with different tasks is essential to understanding laryngeal biomechanics and to determining a person's vocal strengths and weaknesses from a biomechanical point of view. (This can be likened to a tennis coach examining each of his pupils' different strokes.)
This concept is basic -- laryngeal biomechanics (MTPs) both reveal and forecast the vocal output. Some people with asymptomatic nodules are healthy, and others are potential voice disorder patients. The difference between the two groups may be related to whether the nodules are "wanted." In any case, vocal nodules appear to be associated with increased MT scores.
In summary, we have attempted to characterize and quantify laryngeal biomechanics so that some of the variables that may affect them could be studied. In view of the obvious complexity of these interactions, we do not believe that the influence of each individual variable can be fully described. Nevertheless, the methods used for this study appear to be useful for analysis of laryngeal biomechanics.
Muscle tension (MT) scores for male and female singers were not significantly different.
MT scores for professional and amateur singers were not significantly different.
Singers of classical styles of music, such as art song, opera, and choral music, appeared to have lower MT scores than singers of non-classical styles.
The mean MT scores for eight singing styles (in increasing order of muscle tension) were: choral music 41%, art song 47%, opera 58%, barbershop 61%, popular/jazz 65%, musical theater 74%, bluegrass/country and western 87%, and rock/gospel 94%.
The most common biomechanical alteration during singing was contraction of the supraglottis in an anteroposterior direction, i.e., MT pattern III.
Singers who had had formal vocal training appeared to have significantly lower MT scores than those who had not.
Singers who warmed-up prior to singing appeared to have significantly lower MT scores than those who did not.
Singers with vocal nodules appeared to have significantly higher MT scores than those who did not.
The African-American singers appeared to have significantly higher MT scores than the caucasian singers.
Alcohol use, tobacco use, prior vocal problems, and regular exercise did not appear to influence the MT scores.
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