Journalof Speech and HearingResearch, Volume 35, 1239-1245, December 1992
Tongue Strength and Endurance: Relation to Highly Skilled Movements Donald A. Robin Anuj Goel Lori B. Somodi Erich S. Luschei Laboratory of Speech and Language Neuroscience
Departmrnent of Speech Pathology and Audiology
and National Center for Voice and Speech University of Iowa Iowa City
Tongue strength and endurance (fatigue) were examined insubjects who have acquired high skill levels with their tongues (supranormal) and insubjects who use the tongue normally. The supranormal groups were trumpet players and high school debaters who were able to speak intelligibly at rates much faster than normal. Hand strength and fatigue were also assessed. Maximal strength was measured by recording how much pressure an individual could exert on an air-filled bulb. Endurance was measured by determining how long subjects could sustain 50% of their maximal pressure. Results showed that maximal strength of the tongue and hand did not differentiate the supranormal subjects from the normal subjects. Hand endurance did not differentiate the subjects either. However, the supranormal groups had significantly longer tongue endurance times than did the normal subjects. KEY WORDS: maximal strength, endurance, fatigue, speech motor control, sense of effort
The tongue is one of the principle articulators. During speech the tongue moves rapidly from one position to the next. In order to accomplish precise placement for accurate speech sound production, the neuromotor system must operate with enough strength and without substantial fatigue so that accurate placement of the tongue occurs within an appropriate timeframe. Some researchers have argued that maximal strength may not be a useful measure in the study of speech motor control and its disorders (e.g., Kent, Kent, & Rosenbek, 1987). More recently, however, this has been questioned (Luschei, 1991). The few data available on the relation between maximal tongue strength and speech suggest a relation between abnormal speech sound production and reduced tongue strength (Dworkin, 1980; Dworkin, Aronson, & Mulder, 1980; Robin, Somodi, & Luschei, 1991). That is, abnormally low tongue strength has been associated with reduced intelligibility. Even less is known about endurance and its relation to normal and abnormal speech motor control. Kent et al. (1987, p. 377) note that "Few, if any, data have been published on these or similar measures of endurance or fatigue although it could be important clinically to make these determinations, especially for clients with neurological disorders." One way to study the relation between maximal strength and endurance of the tongue and the performance of skilled movements, such as those required for speech, is to examine subjects with specific speech disorders (abnormal). For instance, preliminary data (Robin et al., 1991) have indicated that children with speech sound problems described as "apraxic" had significantly less endurance of the tongue (i.e., were more fatigable) than normally speaking children, even though maximal strength was within normal limits in some cases. In the case of a mixed dysarthric speaker, Robin et al. (1991) reported that tongue endurance was normal but strength was reduced. © 1992, American Speech-Language-Hearing Association
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Another approach to the study of strength and endurance and their relation to tongue movement is to examine "supranormal" subjects: individuals who are particularly skilled in the use of a given muscle group. For example, Titze (1991) enhances his study of the mechanisms underlying voice production by including data from professional singers in the data base. The present study explored two different groups of subjects demonstrating exceptional tongue movement skills: trumpet players and debaters. Trumpet players use precise tongue control to valve the instrument. Oftentimes, rapid tongue valving is required. Thus, the trumpet players were studied to examine the possible relations between practice resulting in exceptional skill and measures of strength and endurance. It was predicted that this group might be stronger and/or less fatigable than individuals who had no special training with the tongue. The second group of subjects, high school debaters, were studied in order to examine possible relations among speech, strength, and endurance. High-school-level debate in Iowa not only involves the ability to provide a coherent argument that logically strengthens or weakens a position, but also gives points for unrebutted arguments (related or not) made by a debater. Debaters therefore train themselves to speak very rapidly. It was hypothesized that debaters would be stronger and/or less fatigable than their nondebating cohorts. Method .__ .,._.. Subjects Trumpet players. The trumpet player sample consists of 12 musicians, 8 males (mean age 23.4 years, range 18-48) and 4 females (mean age 22.3 years, range 19-27), recruited from the University of Iowa School of Music. Trumpet players all had at least 8 years experience playing. Data on 12 control subjects, 8 males (mean age 29.3 years, range 18-49) and 4 females (mean age 22.5 years, range 20-25) was taken from the normal sample of a larger ongoing project aimed at the development of standards for tongue strength and endurance. Debaters. The supranormal speaker sample consisted of 5 debaters (3 males and 2 females) recruited from the debate team of a local high school. Since the larger data base noted above does not yet include subjects 16 to 17 years old, we recruited age- and sex-matched normal speakers from the high school. It was reasoned that the debaters' ability to speak at extremely rapid rates would be reflected in measures of tongue performance. In order to determine how rapidly the individuals in this study could speak and still maintain a high level of intelligibility, both the debaters and normal speakers were instructed to repeat the "Rainbow Passage" as quickly as possible, but maintain intelligible speech. Subjects were first asked to read the paragraph silently to become familiar with its contents. When ready, they were told to read out loud as quickly as possible, but making sure that they did not slur their words. Audio recordings of the speech samples were made. Both
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groups of speakers were able to maintain better than 98% intelligible speech as measured by transcriptions of the Rainbow Passage by two graduate student listeners. Neither listener was familiar with the subjects in the study or the passage. The listeners wrote the words they heard, and the intelligibility score was derived from the number of words correctly transcribed divided by the total number of words in the passage. The debaters maintained high intelligibility at an average rate of 414 words/min (SD = 44.3, range = 370-475 words per min) compared to the normal speaking group who maintained intelligible speech at an average rate of 313 words/min (SD = 59.8, range = 233-376 words per min). This difference was statistically significant (p < .01) as analyzed by a t test. Apparatus The present study examined the strength and endurance of both the tongue and hand using the Iowa Oral Performance Instrument (IOPI). The IOPI makes use of an air-filled bulb attached to a pressure transducer. The amount of pressure generated by squeezing the bulb with the tongue or hand is displayed on a digital readout that is calibrated in Pascals (Pa). The pressure bulbs for the tongue were made from 1 ml latex rubber pipette bulbs. The end of a 23 cm long silastic rubber tube (0.040 mm inside diameter) was sealed in the bulb. The unit was gas sterilized before each use. The bulb was then sheathed in a clean polyethylene sleeve, heat sealed at the intraoral end, for use with subjects. The hand bulbs were 10 ml rubber syringe bulbs. The IOPI and bulbs are described in a previous publication (Robin et al., 1991). Procedures Trumpet players. Procedures for the study involving trumpet players followed a standard protocol (Robin & Luschei, 1990; Robin et al., 1991). The procedures used have been shown to be reliable, with low intrasubject and intersubject variability (Robin et al., 1991). To obtain the maximal amount of tongue pressure (Pmax-t) that could be exerted on the bulb (i.e., maximal tongue strength), subjects were instructed to squeeze the bulb against the roof of the mouth as hard as they could with the front of the tongue (Figure 1). They were instructed not to use the tongue tip. After this maneuver was completed, the subjects were given a rest period of at least 1 min. Then a second Pmax-t trial was completed. Subjects were then asked to complete a third "motivated" trial in which they were encouraged to "really push as hard as you can" (accompanied by cheerleading from the examiner). These motivated trials did not elicit significantly different readings for the tongue or hand. Thus, the above method appears to result in an accurate index of maximal strength. The greatest pressure obtained from the three trials was taken to be the Pmax-t. Hand strength (Pmax-h) was then measured in a manner similar to that described for Pmax-t. Subjects used their preferred hand (typically the right). The bulb was placed in the palm of the hand in a standard position (Figure 2).
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Robin et al.: Tongue Strength and Endurance
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FIGURE 1. Lateral view of the oral cavity showing the standard placement of tongue bulb. Subjects were instructed not to use their finger tips when squeezing the bulb. As with the tongue, intrasubject and intersubject variability was quite low for the hand trials (Robin et al., 1991). Tongue endurance was then measured. The IOPI has nine light-emitting diodes whose activation depends upon the amount of pressure exerted on the bulb relative to a full-scale pressure set by the examiner. The top light on the display represents the full scale. Each of the lower lights represents linear increments of the full scale. The middle light of the display is marked with a white line. Subjects' Pmax-t was the number entered to represent the full scale, so then the white line represented 50% Pmax-t. Subjects were instructed to watch the light display and were told to exert enough pressure to maintain activation of the middle light-emitting diode (at the white line) for as long as possible. The examiner measured this time, in sec, with a stop watch. Each trial began when the 50% point was achieved and ended when there was a persistent drop of greater than 10%. Most subjects stopped abruptly, saying they could no longer maintain the 50% Pmax-t. Endurance of the hand (50% Pmax-h) was measured in a similar manner to that used for the tongue. Subjects placed the bulb in their preferred hand in the standard grip and held 50% of Pmax-h for as long as they could. Debaters. For the debater study, tongue and hand strength were tested in the manner described above. However, subjects in this study performed endurance trials at three different levels of Pmax: 25%, 50%, and 75%. This difference in procedures is because the trumpet players were tested before the debaters, at an early stage in the development of the IOPI instrument and attendant procedures. Our standard method of measuring endurance at that time was at the 50% level. As well, before examining the control of speech, we studied trumpet players to determine if skilled performance would make a difference. When the debaters
FIGURE 2. A. Standard posture for hand bulb. B. Incorrect posture for hand bulb. Note that finger tips are pushing on bulb. were tested it was believed that a finer analysis of endurance (i.e., different levels of Pmax) was needed. Endurance was measured in the same manner as described above. If subjects sustained pressures for 500 sec a trial was stopped. Two debaters were stopped because of this criterion during the endurance trial at 25% Pmax-t.
StatisticalProcedures Statistical analyses involved a mixed design analysis of variance (ANOVA). The alpha level was set at .05. The dependent measures were pressure (in kPa) for the maximal strength trials and time (in sec) for the endurance trials. For the trumpet player study, group (normal or trumpet players) was the between-subject variable and structure (tongue or hand) was the within-subject variable. For the debater study the within-subject measures were structure (tongue or hand) and endurance level (25%, 50%, or 75% P-max). Post hoc testing was performed at the .05 level of significance using the Tukey procedure.
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1242 Journal of Speech and Hearing Research
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80
160 70
'7 ar,L I
140
o
:3 En Cn f~ L 0-
v
120
60
V
E
iz 100
50
80 40 60 TONGUE
.30
HAND
Structure FIGURE 3. Mean and standard deviation of maximal tongue and hand pressures of trumpet players (open bars) and normal controls (bars with horizontal bands). Results `----
Trumpet Players Mean Pmax-t and Pmax-h data for trumpet player (open bars) and normal (horizontal cross-hatched bars) groups are shown in Figure 3. ANOVA revealed a significant main effect for structure [F(1, 18) = 245.03, p < .0001]. The main effect for group and the interaction between structure and group were not significant. Post hoc analyses showed that within each group Pmax-t was significantly lower than Pmax-h. However, the between-group differences were not significant for hand or tongue strength. By contrast, between-group comparisons of endurance times, shown in Figure 4, were significantly different. ANOVA for 50% Pmax endurance trials revealed a significant interaction between group and structure [F(1, 18) = 14.87, p < .0009]. The main effects were not significant. Between-group comparisons revealed that tongue endurance was significantly shorter for the normal subjects than the trumpet players. The groups did not differ significantly in terms of hand endurance. Within-group comparisons showed that the normal group had tongue endurance times that were significantly shorter than hand endurance times, whereas trumpet players' hand and tongue endurance times did not differ significantly.
Debaters Mean group maximal strength data for the tongue and hand are shown in Figure 5. ANOVA on Pmax revealed a significant main effect for structure [F(1, 6) = 66.94, p < .0002]. The main effect for group and the interaction of group and structure were not significant. Within-group comparisons showed that for both groups the Pmax-t was significantly
TONGUE
Structure
HAND
FIGURE 4. Mean and standard deviation of endurance times at 50% maximal pressure for the tongue and hand of trumpet players (open bars) and normal controls (bars with horizontal bands). lower than Pmax-h. As with the trumpet player study above, the two groups did not differ significantly in terms of hand or tongue strength. Mean endurance times for both groups' tongue and hand at three levels of Pmax are shown in Figure 6. ANOVA revealed significant main effects for group [F(1, 4) = 8.89, p < .02] and endurance level [F(1, 4) = 15.51, p < .0003]. The main effect for structure was not significant. Significant
200
160 0-
o C,
120 a
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HAND
TONGUE Structure
FIGURE 5.Mean and standard devlation of maximal pressure of tongue and hand of debaters (open bars) and normal speakers (bars with horizontal bands).
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Robin et al.: Tongue Strengh and Endurance 500 450 400 350 300 E, 250
E .F
200 150 100 50
nv TONGUE
HAND
FIGURE 6. Mean and standard deviation of endurance times at 25%, 50%, and 75% maximal pressure of tongue and hand of debaters (open bars) and normal speakers (filled bars). interactions between group and endurance level [1, 4) = 12.26, p < .0003] and group and structure [F(1, 4) = 8.85, p < .02] were found. Post hoc testing revealed the following: (a) there were no significant group differences for hand endurance times at any of the three endurance levels, (b) tongue endurance times at 25% and 50% Pmax-t for debaters were significantly longer than normal speakers (although debaters' tongue endurance at 75% Pmax-t was twice that of normal speakers, this difference did not reach significance), (c) tongue endurance times for debaters were significantly longer at 25% Pmax-t than at 50% Pmax-t, which was in turn significantly longer than endurance at 75% Pmax-t, (d) normal speakers' tongue endurance was significantly longer at 25% Pmax-t than at 500/6 Pmax-t; however the difference in endurance times between 50%0/ and 75% Pmax-t was not significant, (e) for both groups, 25% Pmax-h was significantly longer than 50% Pmax-h, which was significantly longer than 75% Pmax-h, and (f) tongue endurance times for debaters were significantly longer than hand endurance times at 25% and 50% Pmax-t, whereas normal speakers' hand endurance times were significantly longer than tongue endurance times at all three levels of Pmax.
Discussion The relationship between performance on nonspeech and speech tasks has been a controversial topic. Data from the present study suggest that some nonspeech or nonmusical measures of performance reflect speech or musical proficiency. The two measures tested in the present study were maximal strength and endurance. Maximal strength of the tongue did not differ as a function of skill level. Thus, the maximal amount of pressure that could be exerted upon a bulb with the tongue was no different for trumpet players or
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debaters and their respective normal controls. These data suggest that the development of supranormal skill that requires exercise of the tongue does not necessarily increase maximal strength. Thus, these findings support the view that some traditional measures of maximal performance, such as maximal strength, may not provide information that is predictive of submaximal performance levels (Kent et al., 1987). However, more data are needed to extend these findings to subjects with speech disorders. It may be that reductions in maximal strength compared to normal at some level do interfere with speech. The critical level of reduction in strength that will affect speech performance has not been studied. For instance, it may be that a 20% reduction in maximal strength has little effect on overall speech performance, but a 30% reduction may affect subjects' accurate production of speech sounds. Luschei (1991) notes that reductions in strength may be particularly related to the speed of tongue movement during speech. He argues that the tongue is a muscular hydrostat and contraction of tongue muscle fibers results in constriction of the compartments within the tongue in one dimension. This causes the tongue to operate against a large viscous load. Thus, according to this hypothesis, in order to get the tongue in the correct position at the right time, a significant fraction of the strength measured in the tongue during a static isometric behavior may be used during normal speech. As strength is decreased, maximal attainable shortening velocity of the muscle fibers decreases, which in turn decreases the rate of movement. The result of this decreased strength may be that articulatory targets are not reached in an appropriate timeframe. In contrast to the strength measures, it was the case that tongue endurance differentiated skilled performers from normal controls. Thus, supranormal subjects had tongues that were less fatigable than normal, although measures of hand endurance did not separate the two groups. These results suggest that practice with the tongue needed to develop high skill levels is related to fatigability. The underlying mechanism for the change in fatigability is not known. However, a number of different neural mechanisms can underlie reductions in performance or endurance times due to fatigue (Brooke, 1989; McClosky, 1981). One mechanism is peripheral fatigue, which results from faulty peripheral excitation or contractile mechanisms (Burke, Levine, Tsairis, & Zajac, 1973; Grimby, Hannerz, & Hedman, 1981; Kugelberg, 1973). Other peripheral mechanisms of fatigue include oxygen depletion or the reduction in, or shutdown of, the energy metabolic cycle (i.e., ATP supply) (Brooke, 1989). Performance may also be limited by central factors. Central fatigue is defined by Grimby et al. (1981) as a firing rate of single motor units that Is insufficient to achieve complete fusion and thus reduces the force output. Another central factor that may result in fatigue involves a "sense of effort" from motor commands that give rise to the sensation of force, timing, and effort independent of peripheral sensations (e.g., Gandevia, 1988; McCloskey, Gandevia, Potter, & Colebatch, 1983). If the sense of effort associated with a given level of motor unit recruitment increases, the subject may not be willing or able to sustain the muscle contraction.
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1244 Journal of Speech and Hearing Research
One important central factor that affects endurance is the ability to make motoneurons continue to discharge. Some studies have suggested that while motoneurons slow down during sustained contractions, they generally do not stop firing (e.g., Bigland-Richie, Johansson, Lippold, Smith, & Woods, 1983). While this could be true for some muscles, Grimby et al. (1981) have noted that motor units of short toe extensor muscles cease firing after a short period during maximal contraction. Further, they found that practicing these maximal contractions made it possible for the subjects (authors of the study) to keep motor units recruited during maximal response active for much longer periods of time. Associated with this practice effect was a marked reduction in the "sense of effort" reported by the subjects. Without practice, subjects could sustain maximal voluntary contraction for 2 sec or less. During the sustained voluntary contraction, tension decreased more rapidly than the decrease found when intermittent superimposed tetanization was applied. Tetanization was achieved by electrically stimulating the nerve. This difference between the decrease in tension during volitional and intermittent stimulation suggests that central fatigue is responsible for the decrease. After 6 months practice, these same subjects were able to sustain voluntary maximal contraction for as long as 20 sec. Moreover, after practice, tetanic tensions decreased at more rapid rates than in the pre-practice condition, suggesting that much of the central fatigue had been reduced by training and that subjects could maintain the maximal contraction for a longer period of time. Similar to the study by Grimby et al. (1981), skilled subjects in the present study were able to sustain volitional contractions for significantly longer periods of time than unskilled subjects. In the Grimby et al. study subjects were required to maintain maximal contractions. In the present study fatigue was measured at submaximal levels. The greatest differences between debaters and normals was at 25% Pmax-t. However, one may assume that the forces generated during speech or trumpet playing are less than maximal and that the effects of decreased central fatigue would occur for motor units activated at a much lower level than in the Grimby et al. experiment. In fact, Barlow and Abbs (1983) presented data that suggests that the force of the lips used during speech is approximately 20% of maximal force. This might allow for the prediction that the greatest changes related to practice would occur in that range, as was the case with debaters. It is also noteworthy that all the subjects in the present study, like those in the Grimby et al. study, reported on the amount of effort required to maintain a constant pressure level. All normal subjects commented that at the end of an endurance run they were exerting a great amount of effort. Moreover, subjects showed visible signs of extreme effort (e.g., squirming in the chair). These signs of effort often began only one-third of the way through a trial. The supranormal subjects showed no visible signs of effort (until the very end of a run), and many commented that the task was easy. After the endurance runs at 25% Pmax-t, some debaters reported that they never increased effort. In fact, as mentioned earlier, two of the debaters were stopped at 500 sec and claimed they could have continued indefinitely. These observations suggest that the sense of effort may be
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a limiting factor in performance. However, studies are needed to test this hypothesis directly. Recently, it has been found that the sense of effort is highly calibrated in the tongue and hand of normal individuals, suggesting that the role of sense of effort in fatigue can be examined experimentally (Somodi, Robin, & Luschei, 1992). Although the discussion above has drawn attention to the fact that enhanced fatigue-resistance could result from an increased ability to sustain the discharge of motoneurons, it is also possible that exercise-related changes in the proportion of fatigue-resistant muscle fibers contributed to the observed differences in endurance times. It would be useful, in this regard, to know the composition of the human tongue in terms of the histochemical fiber-typing procedures that have been developed and used extensively in other muscle systems. Yet, to our knowledge, no such reports exist. The fiber composition of the cat (Hellstrand, 1980) and the rat (Sata, Suzuki, Sato, Sato, & Inokuchi, 1990) tongue has, however, been studied. In both of these species, most of the muscle fibers were of a fatigue-resistant type. The extrinsic tongue muscles of the cat have been studied physiologically (Hellstrand, 1982). It was observed that only about 20 to 25% of the initial strength of the muscle was lost during prolonged stimulation, consistent with the aforementioned muscle type suggested by histochemical studies. These data suggest that the tongue muscle may be "exercised" sufficiently by nonspeaking activity to maintain the fatigue-resistance of its muscle fibers. If this is the case, then the difference in the tongue fatigue measures of debaters and trumpet performances could more logically be ascribed to changes in the behavior of neural elements in the system (i.e., central fatigue) such as those noted above. Finally, the differences in endurance at 25%, 50%, and 75% Pmax bear comment. Subjects had longer endurance times at lower levels of Pmax. While one mechanism contributing to these differences may be related to central fatigue as discussed above, the properties of the motor units themselves may also contribute to these differences. Motor units are recruited generally by the size of their axons. At low levels of strength, units with small axons are recruited, and as higher levels of force are required, units with larger axons then become active (Henneman, Clamann, Gillies, & Skinner, 1974; Henneman, Somjen, & Carpenter, 1965). Moreover, units with small axons produce less tension and develop tension more slowly than those with large axons (Burke et al., 1973). The early recruited, weak motor units are fatigue resistant, whereas the late recruited, strong units are fatigable (Burke et al., 1973; Enoka & Stewart, 1984; Henneman, 1957). Thus, at 25% Pmax, small relatively fatigueresistant motor units are presumably activated and the motoneurons are "easy" to keep going centrally. In this case, endurance times are long. At 50% Pmax, larger motor units are presumably recruited; these are relatively more fatigable and less easy to keep activated by central mechanism than those used at 25% Pmax, so endurance times decrease. Finally, at 75% Pmax, units with large axons are presumably activated. These units are fatigable and less easy to activate centrally, so endurance time is relatively short.
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Robin et al.: Tongue Strength and Endurance
Summary Study of trumpet players and debaters showed that these subject groups have tongues that are less fatigable than those of normal subjects, even though hand fatigue did not differentiate the groups. It is hypothesized that the mechanisms underlying these differences relate to central fatigue, although the fiber type composition of the tongue may also contribute to the observed effects. The method used to study tongue strength and endurance may be useful in the study of individuals with speech disorders.
Acknowledgments This research was supported by NIDCD grant No. 1 R03 DC01182-1. We thank the subjects for their willingness to participate in the study. Sincere appreciation is extended to Paula Altmaier, Carlin Hagemann, Daryl Lorell, and Nancy Solomon for comments on an earlier version of the manuscript. Thanks are also extended to Colleen Gardner for her secretarial support.
References Barlow, S. M., & Abba, J. H. (1983). Force transducers force the evaluation of labial, lingual, and mandibular motor impairments. Journal of Speech and Hearing Research, 26, 616-621. Blgland-Rlchle, B., Johansson, R., Llppold, O. C. J., Smith, S., & Woods, J. J. (1983). Changes in motoneuron firing rates during sustained maximal voluntary contractions. Journal of Physiology, 340, 335-346. Brooke, M. H.(1989). Clinical measurements of fatigue and exercise in neuromuscular disease. In T. L. Munsat (Ed.), Quantification of neurologic deficit (pp. 101-118). Boston: Butterworths. Burke, R. E., Levine, D. N., Tealrls, P., & Zajac, F. E. (1973). Physiological types and histochemical profiles in motor units of the cat gastrocnemius. Journal of Physiology, 234, 723-748. Dworkin, J. P. (1980). Tongue strength measurement in patients with amyotrophic lateral sclerosis: Qualitative vs. quantitative procedures. Archives of Physical Medicine and Rehabilitation, 61, 422-444. Dworkin, J.P., Aronson, A., & Mulder, D.W. (1980). Tongue strength in normal subjects and dysarthric patients with amyotrophic lateral sclerosis. Journal of Speech and Hearing Research, 23, 828-837. Enoka, R. M., & Stewart, D. G. (1984). Henneman's "size principle": Current issues. Trends in Neuroscience, 7, 226-228. Gandevla, S. C. (1988). Physiological accompaniments of human muscle fatigue. Australian Paediatric Journal, 104-108. Grimby, L., Hannerz, J., Hedman, B. (1981). The fatigue and voluntary discharge properties of single motor units in man. Journal of Physiology, 316, 545-554. Hellstrand, E. (1980). Morphological and histochemical properties of
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tongue muscles incat. Acta Physiologica Scandanavia, 110, 187-198. Hellstrand, E. (1982). Reflex control of cat extrinsic and intrinsic tongue muscles exerted by intraoral receptors. Acta Physiologica Scandanavia, 115, 245-256. Henneman, E. (1957). Relation between size of neurons and their susceptibility to discharge. Science, 126, 1345-1346. Henneman, E., Clamann, H. P., Gillies, J. D., & Skinner, R. D. (1974). Rank order of motoneurons within a pool: Law of combination. Journal of Neurophysiology, 37, 1338-1349. Henneman, E., Somen, G., & Carpenter, D. 0. (1965). Functional significance of cell size in spinal motoneurons. Journal of Neurophysiology, 28, 560-580. Kent, R.D., Kent, J.F., & Rosenbek, J.C. (1987). Maximum performance tests of speech production. Journal of Speech and Hearing Disorders, 52, 367-387. Kugelberg, E. (1973). Histochemical composition, contraction speed and fatigability of rat soleus motor units. Journal of Neurological Science, 20, 177-198. Luchel, E. S. (1991). Development of objective standards of nonspeech oral strength and performance: An advocate's view. In C. A. Moore, K. M. Yorkston, & D. R. Beukelman (Eds.), Dysarthria and apraxia of speech: Perspectives on management (pp. 3-14). Baltimore: Paul H. Brookes Publishing Co. McCloskey, D. . (1981). Corollary discharges: Motor commands and perception. In V. B. Brookes (Ed.), Handbook of physiology: A critical, comprehensive presentation of physiological knowledge and concepts. Section : The nervous system (pp. 1415-1448). Bethesda: American Physiological Society. McCloskey, D. I., Gandevla, S., Potter, E. K., & Colebatch, J. G. (1983). Muscle sense and effort: Motor commands and judgments about muscular contractions. In J. E. Desmedt (Ed.), Motor control mechanisms in health and disease (pp. 151-170). New York: Raven Press. Robin, D.A., & Luschel, E. S. (1990). IOPI operators manual. Unpublished manuscript. University of Iowa. Robin, D.A., Somodli, L B., & Luschel, E. S. (1991). Measurement of strength and endurance in normal and articulation disordered subjects. In C.A. Moore, K. M. Yorkston, & D. R. Beukelman (Eds.), Dysarthria and apraxia ofspeech: Perspectives on management(pp. 173-184). Baltimore: Paul H. Brookes Publishing Co. Sate, I., Suzuki, M., Sato, M., Sato, T., & Inokuchl, S. (1990). A histochemical study of lingual muscle fibers in rat. Okajamas Folia Anatomica Japanica, 66, 405-415. Somodl, L B., Robin, D. A., & Luschel, E. S. (1992). Sense of effort in relation to the motor control of the tongue. Manuscript submitted for publication. Tltze, I. (1991, January). Studies of vocal production. Presentation at the Professional Seminar of the Department of Speech Pathology and Audiology, University of Iowa, Iowa City, IA. Received November 8, 1991 Accepted March 23, 1992 Contact author: Donald A. Robins, PhD, Department of Speech Pathology and Audiology, Wendell Johnson Speech and Hearing Center, University of Iowa, Iowa City, IA 52242.
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Tongue Strength and Endurance: Relation to Highly Skilled Movements Donald A. Robin Anuj Goel Lori B. Somodi Erich S. Luschei Laboratory of Speech and Language Neuroscience
Departmrnent of Speech Pathology and Audiology
and National Center for Voice and Speech University of Iowa Iowa City
Tongue strength and endurance (fatigue) were examined insubjects who have acquired high skill levels with their tongues (supranormal) and insubjects who use the tongue normally. The supranormal groups were trumpet players and high school debaters who were able to speak intelligibly at rates much faster than normal. Hand strength and fatigue were also assessed. Maximal strength was measured by recording how much pressure an individual could exert on an air-filled bulb. Endurance was measured by determining how long subjects could sustain 50% of their maximal pressure. Results showed that maximal strength of the tongue and hand did not differentiate the supranormal subjects from the normal subjects. Hand endurance did not differentiate the subjects either. However, the supranormal groups had significantly longer tongue endurance times than did the normal subjects. KEY WORDS: maximal strength, endurance, fatigue, speech motor control, sense of effort
The tongue is one of the principle articulators. During speech the tongue moves rapidly from one position to the next. In order to accomplish precise placement for accurate speech sound production, the neuromotor system must operate with enough strength and without substantial fatigue so that accurate placement of the tongue occurs within an appropriate timeframe. Some researchers have argued that maximal strength may not be a useful measure in the study of speech motor control and its disorders (e.g., Kent, Kent, & Rosenbek, 1987). More recently, however, this has been questioned (Luschei, 1991). The few data available on the relation between maximal tongue strength and speech suggest a relation between abnormal speech sound production and reduced tongue strength (Dworkin, 1980; Dworkin, Aronson, & Mulder, 1980; Robin, Somodi, & Luschei, 1991). That is, abnormally low tongue strength has been associated with reduced intelligibility. Even less is known about endurance and its relation to normal and abnormal speech motor control. Kent et al. (1987, p. 377) note that "Few, if any, data have been published on these or similar measures of endurance or fatigue although it could be important clinically to make these determinations, especially for clients with neurological disorders." One way to study the relation between maximal strength and endurance of the tongue and the performance of skilled movements, such as those required for speech, is to examine subjects with specific speech disorders (abnormal). For instance, preliminary data (Robin et al., 1991) have indicated that children with speech sound problems described as "apraxic" had significantly less endurance of the tongue (i.e., were more fatigable) than normally speaking children, even though maximal strength was within normal limits in some cases. In the case of a mixed dysarthric speaker, Robin et al. (1991) reported that tongue endurance was normal but strength was reduced. © 1992, American Speech-Language-Hearing Association
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Another approach to the study of strength and endurance and their relation to tongue movement is to examine "supranormal" subjects: individuals who are particularly skilled in the use of a given muscle group. For example, Titze (1991) enhances his study of the mechanisms underlying voice production by including data from professional singers in the data base. The present study explored two different groups of subjects demonstrating exceptional tongue movement skills: trumpet players and debaters. Trumpet players use precise tongue control to valve the instrument. Oftentimes, rapid tongue valving is required. Thus, the trumpet players were studied to examine the possible relations between practice resulting in exceptional skill and measures of strength and endurance. It was predicted that this group might be stronger and/or less fatigable than individuals who had no special training with the tongue. The second group of subjects, high school debaters, were studied in order to examine possible relations among speech, strength, and endurance. High-school-level debate in Iowa not only involves the ability to provide a coherent argument that logically strengthens or weakens a position, but also gives points for unrebutted arguments (related or not) made by a debater. Debaters therefore train themselves to speak very rapidly. It was hypothesized that debaters would be stronger and/or less fatigable than their nondebating cohorts. Method .__ .,._.. Subjects Trumpet players. The trumpet player sample consists of 12 musicians, 8 males (mean age 23.4 years, range 18-48) and 4 females (mean age 22.3 years, range 19-27), recruited from the University of Iowa School of Music. Trumpet players all had at least 8 years experience playing. Data on 12 control subjects, 8 males (mean age 29.3 years, range 18-49) and 4 females (mean age 22.5 years, range 20-25) was taken from the normal sample of a larger ongoing project aimed at the development of standards for tongue strength and endurance. Debaters. The supranormal speaker sample consisted of 5 debaters (3 males and 2 females) recruited from the debate team of a local high school. Since the larger data base noted above does not yet include subjects 16 to 17 years old, we recruited age- and sex-matched normal speakers from the high school. It was reasoned that the debaters' ability to speak at extremely rapid rates would be reflected in measures of tongue performance. In order to determine how rapidly the individuals in this study could speak and still maintain a high level of intelligibility, both the debaters and normal speakers were instructed to repeat the "Rainbow Passage" as quickly as possible, but maintain intelligible speech. Subjects were first asked to read the paragraph silently to become familiar with its contents. When ready, they were told to read out loud as quickly as possible, but making sure that they did not slur their words. Audio recordings of the speech samples were made. Both
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groups of speakers were able to maintain better than 98% intelligible speech as measured by transcriptions of the Rainbow Passage by two graduate student listeners. Neither listener was familiar with the subjects in the study or the passage. The listeners wrote the words they heard, and the intelligibility score was derived from the number of words correctly transcribed divided by the total number of words in the passage. The debaters maintained high intelligibility at an average rate of 414 words/min (SD = 44.3, range = 370-475 words per min) compared to the normal speaking group who maintained intelligible speech at an average rate of 313 words/min (SD = 59.8, range = 233-376 words per min). This difference was statistically significant (p < .01) as analyzed by a t test. Apparatus The present study examined the strength and endurance of both the tongue and hand using the Iowa Oral Performance Instrument (IOPI). The IOPI makes use of an air-filled bulb attached to a pressure transducer. The amount of pressure generated by squeezing the bulb with the tongue or hand is displayed on a digital readout that is calibrated in Pascals (Pa). The pressure bulbs for the tongue were made from 1 ml latex rubber pipette bulbs. The end of a 23 cm long silastic rubber tube (0.040 mm inside diameter) was sealed in the bulb. The unit was gas sterilized before each use. The bulb was then sheathed in a clean polyethylene sleeve, heat sealed at the intraoral end, for use with subjects. The hand bulbs were 10 ml rubber syringe bulbs. The IOPI and bulbs are described in a previous publication (Robin et al., 1991). Procedures Trumpet players. Procedures for the study involving trumpet players followed a standard protocol (Robin & Luschei, 1990; Robin et al., 1991). The procedures used have been shown to be reliable, with low intrasubject and intersubject variability (Robin et al., 1991). To obtain the maximal amount of tongue pressure (Pmax-t) that could be exerted on the bulb (i.e., maximal tongue strength), subjects were instructed to squeeze the bulb against the roof of the mouth as hard as they could with the front of the tongue (Figure 1). They were instructed not to use the tongue tip. After this maneuver was completed, the subjects were given a rest period of at least 1 min. Then a second Pmax-t trial was completed. Subjects were then asked to complete a third "motivated" trial in which they were encouraged to "really push as hard as you can" (accompanied by cheerleading from the examiner). These motivated trials did not elicit significantly different readings for the tongue or hand. Thus, the above method appears to result in an accurate index of maximal strength. The greatest pressure obtained from the three trials was taken to be the Pmax-t. Hand strength (Pmax-h) was then measured in a manner similar to that described for Pmax-t. Subjects used their preferred hand (typically the right). The bulb was placed in the palm of the hand in a standard position (Figure 2).
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Robin et al.: Tongue Strength and Endurance
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FIGURE 1. Lateral view of the oral cavity showing the standard placement of tongue bulb. Subjects were instructed not to use their finger tips when squeezing the bulb. As with the tongue, intrasubject and intersubject variability was quite low for the hand trials (Robin et al., 1991). Tongue endurance was then measured. The IOPI has nine light-emitting diodes whose activation depends upon the amount of pressure exerted on the bulb relative to a full-scale pressure set by the examiner. The top light on the display represents the full scale. Each of the lower lights represents linear increments of the full scale. The middle light of the display is marked with a white line. Subjects' Pmax-t was the number entered to represent the full scale, so then the white line represented 50% Pmax-t. Subjects were instructed to watch the light display and were told to exert enough pressure to maintain activation of the middle light-emitting diode (at the white line) for as long as possible. The examiner measured this time, in sec, with a stop watch. Each trial began when the 50% point was achieved and ended when there was a persistent drop of greater than 10%. Most subjects stopped abruptly, saying they could no longer maintain the 50% Pmax-t. Endurance of the hand (50% Pmax-h) was measured in a similar manner to that used for the tongue. Subjects placed the bulb in their preferred hand in the standard grip and held 50% of Pmax-h for as long as they could. Debaters. For the debater study, tongue and hand strength were tested in the manner described above. However, subjects in this study performed endurance trials at three different levels of Pmax: 25%, 50%, and 75%. This difference in procedures is because the trumpet players were tested before the debaters, at an early stage in the development of the IOPI instrument and attendant procedures. Our standard method of measuring endurance at that time was at the 50% level. As well, before examining the control of speech, we studied trumpet players to determine if skilled performance would make a difference. When the debaters
FIGURE 2. A. Standard posture for hand bulb. B. Incorrect posture for hand bulb. Note that finger tips are pushing on bulb. were tested it was believed that a finer analysis of endurance (i.e., different levels of Pmax) was needed. Endurance was measured in the same manner as described above. If subjects sustained pressures for 500 sec a trial was stopped. Two debaters were stopped because of this criterion during the endurance trial at 25% Pmax-t.
StatisticalProcedures Statistical analyses involved a mixed design analysis of variance (ANOVA). The alpha level was set at .05. The dependent measures were pressure (in kPa) for the maximal strength trials and time (in sec) for the endurance trials. For the trumpet player study, group (normal or trumpet players) was the between-subject variable and structure (tongue or hand) was the within-subject variable. For the debater study the within-subject measures were structure (tongue or hand) and endurance level (25%, 50%, or 75% P-max). Post hoc testing was performed at the .05 level of significance using the Tukey procedure.
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1242 Journal of Speech and Hearing Research
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'7 ar,L I
140
o
:3 En Cn f~ L 0-
v
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V
E
iz 100
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Structure FIGURE 3. Mean and standard deviation of maximal tongue and hand pressures of trumpet players (open bars) and normal controls (bars with horizontal bands). Results `----
Trumpet Players Mean Pmax-t and Pmax-h data for trumpet player (open bars) and normal (horizontal cross-hatched bars) groups are shown in Figure 3. ANOVA revealed a significant main effect for structure [F(1, 18) = 245.03, p < .0001]. The main effect for group and the interaction between structure and group were not significant. Post hoc analyses showed that within each group Pmax-t was significantly lower than Pmax-h. However, the between-group differences were not significant for hand or tongue strength. By contrast, between-group comparisons of endurance times, shown in Figure 4, were significantly different. ANOVA for 50% Pmax endurance trials revealed a significant interaction between group and structure [F(1, 18) = 14.87, p < .0009]. The main effects were not significant. Between-group comparisons revealed that tongue endurance was significantly shorter for the normal subjects than the trumpet players. The groups did not differ significantly in terms of hand endurance. Within-group comparisons showed that the normal group had tongue endurance times that were significantly shorter than hand endurance times, whereas trumpet players' hand and tongue endurance times did not differ significantly.
Debaters Mean group maximal strength data for the tongue and hand are shown in Figure 5. ANOVA on Pmax revealed a significant main effect for structure [F(1, 6) = 66.94, p < .0002]. The main effect for group and the interaction of group and structure were not significant. Within-group comparisons showed that for both groups the Pmax-t was significantly
TONGUE
Structure
HAND
FIGURE 4. Mean and standard deviation of endurance times at 50% maximal pressure for the tongue and hand of trumpet players (open bars) and normal controls (bars with horizontal bands). lower than Pmax-h. As with the trumpet player study above, the two groups did not differ significantly in terms of hand or tongue strength. Mean endurance times for both groups' tongue and hand at three levels of Pmax are shown in Figure 6. ANOVA revealed significant main effects for group [F(1, 4) = 8.89, p < .02] and endurance level [F(1, 4) = 15.51, p < .0003]. The main effect for structure was not significant. Significant
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o C,
120 a
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TONGUE Structure
FIGURE 5.Mean and standard devlation of maximal pressure of tongue and hand of debaters (open bars) and normal speakers (bars with horizontal bands).
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Robin et al.: Tongue Strengh and Endurance 500 450 400 350 300 E, 250
E .F
200 150 100 50
nv TONGUE
HAND
FIGURE 6. Mean and standard deviation of endurance times at 25%, 50%, and 75% maximal pressure of tongue and hand of debaters (open bars) and normal speakers (filled bars). interactions between group and endurance level [1, 4) = 12.26, p < .0003] and group and structure [F(1, 4) = 8.85, p < .02] were found. Post hoc testing revealed the following: (a) there were no significant group differences for hand endurance times at any of the three endurance levels, (b) tongue endurance times at 25% and 50% Pmax-t for debaters were significantly longer than normal speakers (although debaters' tongue endurance at 75% Pmax-t was twice that of normal speakers, this difference did not reach significance), (c) tongue endurance times for debaters were significantly longer at 25% Pmax-t than at 50% Pmax-t, which was in turn significantly longer than endurance at 75% Pmax-t, (d) normal speakers' tongue endurance was significantly longer at 25% Pmax-t than at 500/6 Pmax-t; however the difference in endurance times between 50%0/ and 75% Pmax-t was not significant, (e) for both groups, 25% Pmax-h was significantly longer than 50% Pmax-h, which was significantly longer than 75% Pmax-h, and (f) tongue endurance times for debaters were significantly longer than hand endurance times at 25% and 50% Pmax-t, whereas normal speakers' hand endurance times were significantly longer than tongue endurance times at all three levels of Pmax.
Discussion The relationship between performance on nonspeech and speech tasks has been a controversial topic. Data from the present study suggest that some nonspeech or nonmusical measures of performance reflect speech or musical proficiency. The two measures tested in the present study were maximal strength and endurance. Maximal strength of the tongue did not differ as a function of skill level. Thus, the maximal amount of pressure that could be exerted upon a bulb with the tongue was no different for trumpet players or
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debaters and their respective normal controls. These data suggest that the development of supranormal skill that requires exercise of the tongue does not necessarily increase maximal strength. Thus, these findings support the view that some traditional measures of maximal performance, such as maximal strength, may not provide information that is predictive of submaximal performance levels (Kent et al., 1987). However, more data are needed to extend these findings to subjects with speech disorders. It may be that reductions in maximal strength compared to normal at some level do interfere with speech. The critical level of reduction in strength that will affect speech performance has not been studied. For instance, it may be that a 20% reduction in maximal strength has little effect on overall speech performance, but a 30% reduction may affect subjects' accurate production of speech sounds. Luschei (1991) notes that reductions in strength may be particularly related to the speed of tongue movement during speech. He argues that the tongue is a muscular hydrostat and contraction of tongue muscle fibers results in constriction of the compartments within the tongue in one dimension. This causes the tongue to operate against a large viscous load. Thus, according to this hypothesis, in order to get the tongue in the correct position at the right time, a significant fraction of the strength measured in the tongue during a static isometric behavior may be used during normal speech. As strength is decreased, maximal attainable shortening velocity of the muscle fibers decreases, which in turn decreases the rate of movement. The result of this decreased strength may be that articulatory targets are not reached in an appropriate timeframe. In contrast to the strength measures, it was the case that tongue endurance differentiated skilled performers from normal controls. Thus, supranormal subjects had tongues that were less fatigable than normal, although measures of hand endurance did not separate the two groups. These results suggest that practice with the tongue needed to develop high skill levels is related to fatigability. The underlying mechanism for the change in fatigability is not known. However, a number of different neural mechanisms can underlie reductions in performance or endurance times due to fatigue (Brooke, 1989; McClosky, 1981). One mechanism is peripheral fatigue, which results from faulty peripheral excitation or contractile mechanisms (Burke, Levine, Tsairis, & Zajac, 1973; Grimby, Hannerz, & Hedman, 1981; Kugelberg, 1973). Other peripheral mechanisms of fatigue include oxygen depletion or the reduction in, or shutdown of, the energy metabolic cycle (i.e., ATP supply) (Brooke, 1989). Performance may also be limited by central factors. Central fatigue is defined by Grimby et al. (1981) as a firing rate of single motor units that Is insufficient to achieve complete fusion and thus reduces the force output. Another central factor that may result in fatigue involves a "sense of effort" from motor commands that give rise to the sensation of force, timing, and effort independent of peripheral sensations (e.g., Gandevia, 1988; McCloskey, Gandevia, Potter, & Colebatch, 1983). If the sense of effort associated with a given level of motor unit recruitment increases, the subject may not be willing or able to sustain the muscle contraction.
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1244 Journal of Speech and Hearing Research
One important central factor that affects endurance is the ability to make motoneurons continue to discharge. Some studies have suggested that while motoneurons slow down during sustained contractions, they generally do not stop firing (e.g., Bigland-Richie, Johansson, Lippold, Smith, & Woods, 1983). While this could be true for some muscles, Grimby et al. (1981) have noted that motor units of short toe extensor muscles cease firing after a short period during maximal contraction. Further, they found that practicing these maximal contractions made it possible for the subjects (authors of the study) to keep motor units recruited during maximal response active for much longer periods of time. Associated with this practice effect was a marked reduction in the "sense of effort" reported by the subjects. Without practice, subjects could sustain maximal voluntary contraction for 2 sec or less. During the sustained voluntary contraction, tension decreased more rapidly than the decrease found when intermittent superimposed tetanization was applied. Tetanization was achieved by electrically stimulating the nerve. This difference between the decrease in tension during volitional and intermittent stimulation suggests that central fatigue is responsible for the decrease. After 6 months practice, these same subjects were able to sustain voluntary maximal contraction for as long as 20 sec. Moreover, after practice, tetanic tensions decreased at more rapid rates than in the pre-practice condition, suggesting that much of the central fatigue had been reduced by training and that subjects could maintain the maximal contraction for a longer period of time. Similar to the study by Grimby et al. (1981), skilled subjects in the present study were able to sustain volitional contractions for significantly longer periods of time than unskilled subjects. In the Grimby et al. study subjects were required to maintain maximal contractions. In the present study fatigue was measured at submaximal levels. The greatest differences between debaters and normals was at 25% Pmax-t. However, one may assume that the forces generated during speech or trumpet playing are less than maximal and that the effects of decreased central fatigue would occur for motor units activated at a much lower level than in the Grimby et al. experiment. In fact, Barlow and Abbs (1983) presented data that suggests that the force of the lips used during speech is approximately 20% of maximal force. This might allow for the prediction that the greatest changes related to practice would occur in that range, as was the case with debaters. It is also noteworthy that all the subjects in the present study, like those in the Grimby et al. study, reported on the amount of effort required to maintain a constant pressure level. All normal subjects commented that at the end of an endurance run they were exerting a great amount of effort. Moreover, subjects showed visible signs of extreme effort (e.g., squirming in the chair). These signs of effort often began only one-third of the way through a trial. The supranormal subjects showed no visible signs of effort (until the very end of a run), and many commented that the task was easy. After the endurance runs at 25% Pmax-t, some debaters reported that they never increased effort. In fact, as mentioned earlier, two of the debaters were stopped at 500 sec and claimed they could have continued indefinitely. These observations suggest that the sense of effort may be
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a limiting factor in performance. However, studies are needed to test this hypothesis directly. Recently, it has been found that the sense of effort is highly calibrated in the tongue and hand of normal individuals, suggesting that the role of sense of effort in fatigue can be examined experimentally (Somodi, Robin, & Luschei, 1992). Although the discussion above has drawn attention to the fact that enhanced fatigue-resistance could result from an increased ability to sustain the discharge of motoneurons, it is also possible that exercise-related changes in the proportion of fatigue-resistant muscle fibers contributed to the observed differences in endurance times. It would be useful, in this regard, to know the composition of the human tongue in terms of the histochemical fiber-typing procedures that have been developed and used extensively in other muscle systems. Yet, to our knowledge, no such reports exist. The fiber composition of the cat (Hellstrand, 1980) and the rat (Sata, Suzuki, Sato, Sato, & Inokuchi, 1990) tongue has, however, been studied. In both of these species, most of the muscle fibers were of a fatigue-resistant type. The extrinsic tongue muscles of the cat have been studied physiologically (Hellstrand, 1982). It was observed that only about 20 to 25% of the initial strength of the muscle was lost during prolonged stimulation, consistent with the aforementioned muscle type suggested by histochemical studies. These data suggest that the tongue muscle may be "exercised" sufficiently by nonspeaking activity to maintain the fatigue-resistance of its muscle fibers. If this is the case, then the difference in the tongue fatigue measures of debaters and trumpet performances could more logically be ascribed to changes in the behavior of neural elements in the system (i.e., central fatigue) such as those noted above. Finally, the differences in endurance at 25%, 50%, and 75% Pmax bear comment. Subjects had longer endurance times at lower levels of Pmax. While one mechanism contributing to these differences may be related to central fatigue as discussed above, the properties of the motor units themselves may also contribute to these differences. Motor units are recruited generally by the size of their axons. At low levels of strength, units with small axons are recruited, and as higher levels of force are required, units with larger axons then become active (Henneman, Clamann, Gillies, & Skinner, 1974; Henneman, Somjen, & Carpenter, 1965). Moreover, units with small axons produce less tension and develop tension more slowly than those with large axons (Burke et al., 1973). The early recruited, weak motor units are fatigue resistant, whereas the late recruited, strong units are fatigable (Burke et al., 1973; Enoka & Stewart, 1984; Henneman, 1957). Thus, at 25% Pmax, small relatively fatigueresistant motor units are presumably activated and the motoneurons are "easy" to keep going centrally. In this case, endurance times are long. At 50% Pmax, larger motor units are presumably recruited; these are relatively more fatigable and less easy to keep activated by central mechanism than those used at 25% Pmax, so endurance times decrease. Finally, at 75% Pmax, units with large axons are presumably activated. These units are fatigable and less easy to activate centrally, so endurance time is relatively short.
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Robin et al.: Tongue Strength and Endurance
Summary Study of trumpet players and debaters showed that these subject groups have tongues that are less fatigable than those of normal subjects, even though hand fatigue did not differentiate the groups. It is hypothesized that the mechanisms underlying these differences relate to central fatigue, although the fiber type composition of the tongue may also contribute to the observed effects. The method used to study tongue strength and endurance may be useful in the study of individuals with speech disorders.
Acknowledgments This research was supported by NIDCD grant No. 1 R03 DC01182-1. We thank the subjects for their willingness to participate in the study. Sincere appreciation is extended to Paula Altmaier, Carlin Hagemann, Daryl Lorell, and Nancy Solomon for comments on an earlier version of the manuscript. Thanks are also extended to Colleen Gardner for her secretarial support.
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tongue muscles incat. Acta Physiologica Scandanavia, 110, 187-198. Hellstrand, E. (1982). Reflex control of cat extrinsic and intrinsic tongue muscles exerted by intraoral receptors. Acta Physiologica Scandanavia, 115, 245-256. Henneman, E. (1957). Relation between size of neurons and their susceptibility to discharge. Science, 126, 1345-1346. Henneman, E., Clamann, H. P., Gillies, J. D., & Skinner, R. D. (1974). Rank order of motoneurons within a pool: Law of combination. Journal of Neurophysiology, 37, 1338-1349. Henneman, E., Somen, G., & Carpenter, D. 0. (1965). Functional significance of cell size in spinal motoneurons. Journal of Neurophysiology, 28, 560-580. Kent, R.D., Kent, J.F., & Rosenbek, J.C. (1987). Maximum performance tests of speech production. Journal of Speech and Hearing Disorders, 52, 367-387. Kugelberg, E. (1973). Histochemical composition, contraction speed and fatigability of rat soleus motor units. Journal of Neurological Science, 20, 177-198. Luchel, E. S. (1991). Development of objective standards of nonspeech oral strength and performance: An advocate's view. In C. A. Moore, K. M. Yorkston, & D. R. Beukelman (Eds.), Dysarthria and apraxia of speech: Perspectives on management (pp. 3-14). Baltimore: Paul H. Brookes Publishing Co. McCloskey, D. . (1981). Corollary discharges: Motor commands and perception. In V. B. Brookes (Ed.), Handbook of physiology: A critical, comprehensive presentation of physiological knowledge and concepts. Section : The nervous system (pp. 1415-1448). Bethesda: American Physiological Society. McCloskey, D. I., Gandevla, S., Potter, E. K., & Colebatch, J. G. (1983). Muscle sense and effort: Motor commands and judgments about muscular contractions. In J. E. Desmedt (Ed.), Motor control mechanisms in health and disease (pp. 151-170). New York: Raven Press. Robin, D.A., & Luschel, E. S. (1990). IOPI operators manual. Unpublished manuscript. University of Iowa. Robin, D.A., Somodli, L B., & Luschel, E. S. (1991). Measurement of strength and endurance in normal and articulation disordered subjects. In C.A. Moore, K. M. Yorkston, & D. R. Beukelman (Eds.), Dysarthria and apraxia ofspeech: Perspectives on management(pp. 173-184). Baltimore: Paul H. Brookes Publishing Co. Sate, I., Suzuki, M., Sato, M., Sato, T., & Inokuchl, S. (1990). A histochemical study of lingual muscle fibers in rat. Okajamas Folia Anatomica Japanica, 66, 405-415. Somodl, L B., Robin, D. A., & Luschel, E. S. (1992). Sense of effort in relation to the motor control of the tongue. Manuscript submitted for publication. Tltze, I. (1991, January). Studies of vocal production. Presentation at the Professional Seminar of the Department of Speech Pathology and Audiology, University of Iowa, Iowa City, IA. Received November 8, 1991 Accepted March 23, 1992 Contact author: Donald A. Robins, PhD, Department of Speech Pathology and Audiology, Wendell Johnson Speech and Hearing Center, University of Iowa, Iowa City, IA 52242.
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