Acoustic myography as an indicator of force during sustained contractions of a small hand muscle

To test the hypothesis that muscle sound amplitudes would remain constant during sustained submaximal isometric contractions, we recorded acoustic myograms from the abductor digiti minimi muscle in 12 subjects at 15, 25, 50, and 75% of a maximum voluntary contraction (MVC). Muscle sounds were detected with an omni-directional electret microphone encased in closed-cell foam and attached to the skin over the muscle. Acoustic amplitudes from the middle and end of the sustained contractions were compared with the amplitudes from the beginning of contractions to determine whether acoustic amplitudes varied in magnitude as force remained constant. Physiological tremor was eliminated from the acoustic signal by use of a Fourier truncation at 14 Hz. The amplitudes of the acoustic signal at a contraction intensity of 75% MVC remained constant, reflecting force production over time. At 50% MVC, the root-mean-square amplitude decreased from the beginning to the end of the contraction (P less than 0.05). Acoustic amplitudes increased over time at 15 and 25% MVC and were significantly higher at the end of the contractions than at the beginning (P less than 0.05). Alterations in the acoustic amplitude, which reflect changes in the lateral vibrations of the muscle, may be indicative of the different recruitment strategies used to maintain force during sustained isometric contractions.     

Sound production in the red swamp crayfish Procambarus clarkii (Decapoda: Cambaridae)

Little is known about the acoustic behaviour of freshwater crustaceans. The present study is the first to describe the acoustic features and the sound production mechanisms of the crayfish Procambarus clarkii. Acoustic signalling was recorded and videotaped. When the animals were recorded in air, they produced a pulsed signal by beating the scaphognathite inside the chamber constituted by the efferent branchial channels. No sound was emitted after scaphognathite ablation. The acoustic features of the signals varied among individuals but were not correlated with body size. Several hypotheses on the functions of these sounds were discussed.     

Amplitude,latency, and habituation of the electrodermal response to acoustic stimuli in the frog

The electrodermal response (EDR) of frogs to various acoustic stimuli was measured in the form of the skin potential response (SPR). There was no correlation between the polarity of the SPR and the intensity of the stimuli. When different frequencies were presented at the same intensity, the amplitude of the SPR to each was inversely proportional to the sound pressure at which that frequency just elicited an SPR. The amplitude of the sound-induced SPR increased monotonically with increasing sound pressure. The latency of the SPR decreased with increasing intensity of the acoustic stimulus. Acoustic stimuli repeated at intervals of 1 and 2 min elicited responses with progressively decreased amplitude and increased latency; with 4 min intervals there was little habituation. Fatigue participates to only a very slight extent in reducing the amplitude of the SPR and increasing its latency. The results are compared with the published data on frogs and mammals, including humans.     

Courtship Sounds Advertise Species Identity and Male Quality in Sympatric Pomatoschistus spp. Gobies

Acoustic signals can encode crucial information about species identity and individual quality. We recorded and compared male courtship drum sounds of the sand goby Pomatoschistus minutus and the painted goby P. pictus and examined if they can function in species recognition within sympatric populations. We also examined which acoustic features are related to male quality and the factors that affect female courtship in the sand goby, to determine whether vocalisations potentially play a role in mate assessment. Drums produced by the painted goby showed significantly higher dominant frequencies, higher sound pulse repetition rates and longer intervals between sounds than those of the sand goby. In the sand goby, male quality was predicted by visual and acoustic courtship signals. Regression analyses showed that sound amplitude was a good predictor of male length, whereas the duration of nest behaviour and active calling rate (i.e. excluding silent periods) were good predictors of male condition factor and fat reserves respectively. In addition, the level of female courtship was predicted by male nest behaviour. The results suggest that the frequency and temporal patterns of sounds can encode species identity, whereas sound amplitude and calling activity reflects male size and fat reserves. Visual courtship duration (nest-related behaviour) also seems relevant to mate choice, since it reflects male condition and is related to female courtship. Our work suggests that acoustic communication can contribute to mate choice in the sand goby group, and invites further study.     

Effects of volatile anesthetics on elastic stiffness in isometrically contracting ferret ventricular myocardium.

The effects of halothane, isoflurane, and sevoflurane on elastic stiffness, which reflects the degree of cross-bridge attachment, were studied in intact cardiac muscle. Electrically stimulated (0.25 Hz, 25 degrees C), isometrically twitching right ventricular ferret papillary muscles (n = 15) at optimal length (L(max)) were subjected to sinusoidal length oscillations (40 Hz, 0.25- 0.50% of L(max) peak to peak). The amplitude and phase relationship with the resulting force oscillations was decomposed into elastic and viscous components of total stiffness in real time. Increasing extracellular Ca(2+) concentration in the presence of anesthetics to produce peak force equal to control increased elastic stiffness during relaxation, which suggests a direct effect of halothane and sevoflurane on cross bridges.     

Acoustic Myography as a Noninvasive Technique for Assessing Muscle Function: Historical Aspects and Possibilities for Application in Clinical Practice

Neurophysiology - Acoustic myography is a technique for detecting and measuring mechanical oscillations of a sound/infrasound-range frequency produced during muscle contractions; such oscillations...     

The effects of pH on force and stiffness development in mouse muscles

Changes in force and stiffness during contractions of mouse extensor digitorum longus and soleus muscles were measured over a range of extracellular pH from 6.4 to 7.4. Muscle stiffness was measured using small amplitude (less than 0.1% of muscle length), high frequency (1.5 kHz) oscillations in length. Twitch force was not significantly affected by changes in pH, but the peak force during repetitive stimulation (2, 3, and 20 pulses) was decreased significantly as the pH was reduced. Changes in muscle stiffness with pH were in the same direction, but smaller in extent. If the number of attached cross-bridges in the muscle can be determined from the measurement of small amplitude, high frequency muscle stiffness, then these findings suggest that (a) the number of cross-bridges between thick and thin filaments declines in low pH and (b) the average force per cross-bridge also declines in low pH. The decline in force per cross-bridge could arise from a reduction in the ability of cross-bridges to generate force during their state of active force production and (or) in an increased percentage of bonds in a low force, "rigor" state.     

Size Distribution of Sperm Whales Acoustically Identified during Long Term Deep-Sea Monitoring in the Ionian Sea

The sperm whale (Physeter macrocephalus) emits a typical short acoustic signal, defined as a “click”, almost continuously while diving. It is produced in different time patterns to acoustically explore the environment and communicate with conspecifics. Each emitted click has a multi-pulse structure, resulting from the production of the sound within the sperm whale’s head. A Stable Inter Pulse Interval (Stable IPI) can be identified among the pulses that compose a single click. Applying specific algorithms, the measurement of this interval provides useful information to assess the total length of the animal recorded. In January 2005, a cabled hydrophone array was deployed at a depth of 2,100 m in the Central Mediterranean Sea, 25 km offshore Catania (Ionian Sea). The acoustic antenna, named OνDE (Ocean noise Detection Experiment), was in operation until November 2006. OνDE provided real time acoustic data used to perform Passive Acoustic Monitoring (PAM) of cetacean sound emissions. In this work, an innovative approach was applied to automatically measure the Stable IPI of the clicks, performing a cepstrum analysis to the energy (square amplitude) of the signals. About 2,100 five-minute recordings were processed to study the size distribution of the sperm whales detected during the OνDE long term deep-sea acoustic monitoring. Stable IPIs were measured in the range between 2.1 ms and 6.4 ms. The equations of Gordon (1991) and of Growcott (2011) were used to convert the IPIs into measures of size. The results revealed that the sperm whales recorded were distributed in length from about 7.5 m to 14 m. The size category most represented was from 9 m to 12 m (adult females or juvenile males) and specimens longer than 14 m (old males) seemed to be absent.     

Timbal muscle physiology in the endothermic cicada Tibicen winnemanna (Homoptera: Cicadidae).

The operative muscle temperature and contraction kinetics are described for the endothermic cicada Tibicen winnemanna (Davis). Measurements of timbal muscle temperature in the field demonstrate that timbal muscle temperature is elevated above ambient temperature during activity. Timbal muscle temperature increases as the acoustic output progresses from a 'warm-up' buzz (27.9-29.7 degrees C) to full song production (36.3-39.5 degrees C). Mean muscle-ambient temperature difference increases from 5.8 degrees C in buzzing animals to 13.1 degrees C in animals producing a full calling song. Twitch rise time and onset to 50% relaxation time decrease while tension production increases with increasing temperature to 40 degrees C. Mean force production at 20 degrees C was determined to be 0.22+/-0.06 N/cm(2). The characteristics of T. winnemanna muscle are similar to those reported in other cicada species. Analysis of the songs produced by animals with one timbal destroyed and the sounds produced by mechanical manipulation suggest that the timbals alternately contract and relax in the sequence IN(1)-IN(2)-OUT(1)-OUT(2). Measurements of the inferred period of muscle contraction from song recordings and the contraction kinetics of isolated timbal muscles measured in the laboratory show that the temperature of the timbal muscle must be elevated in order for the cicada to be able to produce the calling song.     

Sound Characteristics and Outcome of Contests in Male Croaking Gouramis (Teleostei)

A correlative study using similar-sized males of the croaking gourami Trichopsis vittata was carried out to investigate whether sound characteristics influenced winning and if relative fighting ability was assessed by acoustic signals. Pair-wise contests between males were decided using lateral displays (LD) and vocalization in 26 cases, whereas 66 fights escalated to the frontal display (FD) phase. Physical fighting (mouth wrestling) and injuries were rarely observed in this species. Winners were generally larger than their opponents, and this effect was more pronounced in non-escalated than in escalated contests. Sounds of fight winners had a higher sound pressure level and also a lower dominant frequency. Neither number of acoustic signals nor duration of lateral and frontal displays were predictors of contest outcome. Acoustic measures were highly correlated to body weight. These results indicate that traits correlated with RHP (such as sound pressure level and dominant frequency) were predictors of the outcome, while traits not correlated with size (such as number and duration of displays) did not influence winning. In accordance with the main prediction of assessment models, the contest duration (cost) increased with the decrease in asymmetry of body length as well as sound pressure level. No such relationships were found for weight and dominant frequencies in LD- and FD-contests. The present study indicates that morphological and sound characteristics influence winning in fish. Moreover, the results suggest that croaking gouramis settle conflicts without damaging combats by assessing asymmetries in different components of RHP such as body weight and length, which may reliably be signalled by acoustic and visual assessment signals.     

Beak gape dynamics during song in the zebra finch

Bird song is a complex communication behavior that requires the coordination of several motor systems. Sound is produced in the syrinx and then modified by the upper vocal tract, but the specific nature and dynamics of this modification are not well understood. To determine the contribution of beak movements to sound modification, we studied the beak gape patterns in zebra finches (Taeniopygia guttata). Subsyringeal air sac pressure and song were recorded together with changes in beak gape, which were monitored with a magneto-sensitive transducer. Beak gape was positively correlated with fundamental frequency, peak frequency, and subsyringeal air sac pressure in all but one bird. For harmonic stacks, peak frequency increased with increasing beak gape, and the relationship between fundamental frequency and beak gape was no longer significant. Experimentally holding the beak open or closed had acoustic consequences consistent with the model in which beak movements change upper vocal tract length and, thus, the filter properties. Beak gape was positively correlated with sound amplitude in all but two birds. The relationship between beak aperture and amplitude may, however, be indirect because air sac pressure is correlated with amplitude and beak gape. The beak is opened quickly and to its widest aperture immediately prior to the onset of sound and at rapid transitions in sound, suggesting that beak movements may affect vibratory behavior of the labia.     

Changes of muscular sound during sustained isometric contraction up to exhaustion

The sound (SMG) generated by the biceps muscle during isometric exercise at 20, 40, 60, and 80% of maximum voluntary contraction (MVC) up to exhaustion has been recorded by a contact transducer and integrated (iSMG), together with the surface electromyogram (EMG) in eight young untrained men. At the onset of exercise, iSMG and integrated surface EMG (iEMG) amplitude increased linearly with exercise. iSMG remained constant for 253 +/- 73 (SD), 45 +/- 16, 21 +/- 5, and 0 s at the four levels of contraction. Then iSMG increased linearly at 20% MVC, fluctuated at 40% MVC, and decreased exponentially at 60 and 80% MVC. iSMG exhaustion-to-onset ratio was 5.0 at 20%, 1.0 at 40%, and 0.2 at 60 and 80% MVC. On the contrary, independently of exercise intensity, iEMG increased with time, being 1.4 higher at exhaustion than at the onset. The nonunivocal iSMG changes with time and effort of exercise suggest that the sound may be a useful tool to acquire different information to EMG and output force during muscle contraction up to fatigue.     

The mechanism of low-frequency sound production in muscle.

Frog gastrocnemius muscles stimulated isometrically in a saline bath at 20 degrees C were found to produce a single ringing sound event beginning just before the tension record began to rise. The sound event was substantially over by the time the isometric tension began to fall. Results from studies correlating the spatial pattern of the sound, the amplitude and frequency of the sound as a function of the muscle length, and the response of both the passive and active muscle to a transverse pluck were found to be consistent with the conclusion that the sounds in these muscles are caused primarily by transverse resonant vibrations. As the muscle develops force, its lack of cylindrical symmetry gives rise to lateral motions, which are most likely the initiators of the bending vibrations detected as sound.     

Broadcasts of wing-fanning vibrations recorded from calling male Ceratitis capitata (Diptera: Tephritidae) increase captures of females in traps

Female Mediterranean fruit flies, Ceratitis capitata (Wiedemann), from the sterile-male rearing facility in El Pino, Guatemala, were exposed to broadcasts of wing-fanning vibrations recorded from males engaged in calling behavior to investigate the feasibility of developing a female-selective acoustic trap. The recorded signals had frequent amplitude fluctuations and peak frequencies approximately 350 Hz, typical of signals observed in previous studies of Mediterranean fruit fly acoustic behavior. Females did not exhibit long-distance phonotaxis, but remained near a speaker significantly longer when the sounds were broadcast at 103-107 dB than when the speaker was silent. In addition, significantly higher percentages of females were captured by yellow adhesive traps next to a broadcasting speaker than by traps next to a silent mimic. Additional bioassays were conducted with synthetic, 350-Hz tones produced by a thermoacoustic tube as well as with silent mimics of the different sound sources to examine the relative responsiveness of female Mediterranean fruit flies to traps with different acoustic and visual features. The visual attributes of the different sound source assemblies significantly affected capture rates. The range over which the broadcast significantly increased the percentage of female captures was <0.5 m, which may limit the utility of these acoustic cues in large-scale trapping programs. However, the findings of this study do justify further testing of whether optimized short-range acoustic signals could be used to augment longer range pheromonal and visual cues to improve the efficacy of female-selective traps.     

Variation and repeatability of ultrasonic sexual advertisement signals inAchroia grisella (Lepidoptera: Pyralidae)

MaleAchroia grisella (Lepidoptera: Pyralidae) produce ultrasonic advertisement signals for pair formation. The signals are generated by wing-fanning and consist of pairs of approximately 100-μs pulses of 70- to 130-kHz sound. In a previous study, playback experiments showed that femaleA. grisella preferred signals whose pulses were louder, longer, and delivered at a higher rate and included longer silent (asynchrony) intervals within pairs. To understand the variation and repeatability of these signal characters, acoustic signals of 18A. grisella males were recorded twice daily on the first 4 days and the seventh day after adult eclosion. ANOVA and MANOVA revealed significant among-individual and among-age variation for all signal characters. Peak amplitude, average amplitude, rate, and pulse length peaked 2–3 days after eclosion and then decreased. Asynchrony interval, however, continued to increase as males aged. Repeatabilities of peak amplitude, average amplitude, rate, and asynchrony interval were all relatively high (>0.5).     

Geographical variation in the vocalizations of the suboscine Thorn‐tailed Rayadito Aphrastura spinicauda

Structural variation in acoustic signals may be related either to the factors affecting sound production such as bird morphology, or to vocal adaptations to improve sound transmission in different environments. Thus, variation in acoustic signals can influence intraspecific communication processes. This will ultimately influence divergence in allopatric populations. The study of geographical variation in vocalizations of suboscines provides an opportunity to compare acoustic signals from different populations, without additional biases caused by song learning and cultural evolution typical of oscines. The aim of this study was to compare vocalizations of distinct populations of a suboscine species, the Thorn‐tailed Rayadito. Four types of vocalizations were recorded in five populations, including all three currently accepted subspecies. Comparisons of each type of vocalization among the five populations showed that some variation existed in the repetitive trill, whereas no differences were found among alarm calls and loud trills. Variation in repetitive trills among populations and forest types suggests that sound transmission is involved in vocal differences in suboscines. Acoustic differences are also consistent with distinguishing subspecies bullocki from spinicauda and fulva, but not the two latter subspecies from each other. Our results suggest that the geographical differentiation in vocalizations observed among Thorn‐tailed Rayadito populations is likely to be a consequence of different ecological pressures. Therefore, incipient genetic isolation of these populations is suggested, based on the innate origin of suboscine vocalizations.     

Effect of cycle frequency and excursion amplitude on work done by rat diaphragm muscle

Strips of isolated rat diaphragm muscle were attached to a servomotor-transducer apparatus, and the muscle length was cycled in a sinusoidal fashion about the length at which maximum isometric twitch force was developed, Lo. The amplitude of the length displacement (excursion amplitude) and rate of cycling were varied between 3 and 13% Lo and 1-4 Hz respectively. The muscle was tetanically stimulated (100 Hz, supramaximal voltage, stimulus duration (duty cycle) 20% of the length cycle period) during the shortening stage of the imposed length cycle at the phase that yielded maximum net positive work. The force and displacement of the muscle were recorded. Work per cycle was calculated from the area of the loop formed by plotting force against length for one full stretch-shorten cycle. Work per cycle decreased, but power increased, as cycle frequency was increased from 1 to 4 Hz. Maximum work done per cycle was about 12.8 J/kg at a cycle frequency of 1 Hz. Maximum mean power developed was about 27 W/kg and occurred at a cycle frequency of 4 Hz. Work and power were maximum at an excursion amplitude of 13% of Lo (i.e., Lo +/- 6.5%). Measured work and power output are considerably less than values estimated from length-tension and force-velocity curves.     

Relationship between mechanomyogram signals and changes in force of human forefinger flexor muscles during voluntary contraction

In previous studies on mechanomyogram (MMG) signals no analysis of these signals accompanying force generation has been performed. Therefore, we have recorded MMG signals (previously referred to as muscle sound or acoustomyographic signals) during voluntary contractions of forefinger flexor muscles in 31 young subjects. These subjects made contractions to produce force records of triangular or trapeziform shape. The peak target force amounted to 10, 20 or 40 N which represented less than 40% of maximal voluntary contraction. The MMG signals during the transient phases of force generation at three different rates were analysed. The MMG intensity level calculated for MMG records and the peak-to-peak amplitude of MMG signals correlated with both the velocity of force increase and the contraction force. The occurrence of the strongest MMG signals corresponded to changes in contractile force. Therefore, it is suggested that measurements of these parameters could be a useful tool in studies of changes in contractile force. Accepted: 11 March 1998     

EMG and MMG of agonist and antagonist muscles as a function of age and joint angle.

The aim of this study was to determine the effect of elbow joint position on electromyographic (EMG) and mechanomyographic (MMG) activities of agonist and antagonist muscles in young and old women. Surface EMG and MMG were recorded from the triceps and biceps brachii, and brachioradialis muscles during isometric elbow extensions in young and old women. The measurements were carried out at an optimal joint angle (A(o)), as well as at smaller (A(s) = A(o) - 30 degrees ) and larger (A(l) = A(o) + 30 degrees ) angles. The normalized to force EMG amplitude (RMS-EMG/F) was smaller in old women compared to young in all muscles. The RMS-EMG/F of the triceps brachii muscle was not affected by muscle length while that of the biceps brachii and brachioradialis muscles increased at shortest muscle length in both groups. The normalized to force MMG amplitude (RMS-MMG/F) was smaller in old than in young in the triceps brachii muscle only. There was an increase in RMS-MMG/F with triceps brachii and biceps brachii muscle shortening in both groups, and in the brachioradialis muscle -- in young only. Compared to young, older women exhibited a bigger force fluctuation during maximum voluntary contraction, but these did not contribute significantly to the RMS-MMG. Skinfold thickness accounted for the RMS-EMG/F and RMS-MMG/F differences seen between old and young women in the biceps brachii muscle only. It is concluded that, the EMG and MMG response to muscles length change in agonist and antagonist muscles is generally similar in old and young women but the optimal angle shifts toward a bigger value in older women.     

Surface mechanomyogram reflects the changes in the mechanical properties of muscle at fatigue

The contractile properties of muscle are usually investigated by analysing the force signal recorded during electrically elicited contractions. The electrically stimulated muscle shows surface oscillations that can be detected by an accelerometer; the acceleration signal is termed the surface mechanomyogram (MMG). In the study described here we compared, in the human tibialis anterior muscle, changes in the MMG and force signal characteristics before, and immediately after fatigue, as well as during 6 min of recovery, when changes in the contractile properties of muscle occur. Fatigue was induced by sustained electrical stimulation. The final aim was to evaluate the reliability of the MMG as a tool to follow the changes in the mechanical properties of muscle caused by fatigue. Because of fatigue, the parameters of the force peak, the peak rate of force production and the peak of the acceleration of force production (d2F/dt2) decreased, while the contraction time and the half-relaxation time (1/2-RT) increased. The MMG peak-to-peak (p-p) also decreased. The attenuation rate of the force oscillation amplitude and MMG p-p at increasing stimulation frequency was greater after fatigue. With the exception of 1/2-RT, all of the force and MMG parameters were restored within 2 min of recovery. A high correlation was found between MMG and d2F/dt2 in un-fatigued muscle and during recovery. In conclusion, the MMG reflects specific aspects of muscle mechanics and can be used to follow the changes in the contractile properties of muscle caused by localised muscle fatigue.