Finger gesture recognition using glove-like interfaces are very accurate for sensing individual finger positions by employing a gamut of sensors. However, for the same reason, they are also very costly, cumbersome and unaesthetic for use in artistic scenarios such as gesture based music composition platforms like Virginia Tech's Linux Laptop Orchestra. Wearable computing has shown promising results in increasing portability as well as enhancing proprioceptive perception of the wearers' body. In this thesis, we present the proof-of-concept for designing a novel muscle-machine interface for interpreting human thumb motion as a 2-dimensional joystick employing mechanomyographic signals. Infrared camera based systems such as Microsoft Digits and ultrasound sensor based systems such as Chirp Microsystems' Chirp gesture recognizers are elegant solutions, but have line-of-sight sensing limitations. Here, we present a low-cost and wearable joystick designed as a wristband which captures muscle sounds, also called mechanomyographic signals. The interface learns from user's thumb gestures and finally interprets these motions as one of the four kinds of thumb movements. We obtained an overall classification accuracy of 81.5% for all motions and 90.5% on a modified metric. Results obtained from the user study indicate that mechanomyography based wearable thumb-joystick is a feasible design idea worthy of further study. / Master of Science

Individuals with severe physical disabilities and minimal motor behaviour may benefit from access technologies that harness the volitional activity of muscles. In this thesis, we investigate the use of muscle activity, indicated by the mechanomyogram (MMG), as a binary and multifunction control signal for access devices. A challenge in the design of a binary MMG switch is to reliably recognize the timing of voluntary muscle contractions, and to subsequently translate the MMG signal into a switch-activation signal. A continuous wavelet transform (CWT) algorithm based on a simplified MMG generation model of recurring impulsive morphological patterns was proposed for automatic detection of muscle activity from MMG signals. CWT coefficients of the MMG signal were compared to scale-specific thresholds derived from the baseline signal to estimate the timings of muscle activity. The automatic detection algorithm was implemented as a binary switch controlled by a single muscle site at the forehead, shoulders or forearm. The binary control algorithm was verified on able-bodied participants, and the switch was tested on individuals with neuromuscular and neurological disabilities. The switch showed very high sensitivity and specificity when the muscle and its control were minimally affected by spasticity, involuntary movement, or involuntary muscle activity. We further investigate the potential of improving the functionality of the MMG-controlled switching interface. We demonstrate the practical use of the vibratory artefact measured at the forehead during vocalization to control a second switch. The proposed integrated MMG-vocalization access solution may augment access alternatives for individuals with physical disabilities using a single access site. Further, we show that multi-site MMG signals exhibit distinctive patterns of forearm muscle activity, and 7+/-1 hand movements can be identified with an accuracy of 90+/-4%. This suggests that MMG may have applications in multi-function body-machine interfaces when multiple muscle sites are available. However, MMG signal features vary with sensor location. We show that sensor displacements significantly diminish classification accuracy, emphasizing the importance of consistent sensor placement between MMG classifier training and deployment for accurate control of switching interfaces. Collectively, the findings and developments of this thesis lay the foundation for future research on wearable, MMG-driven access technologies.

Individuals with severe physical disabilities and minimal motor behaviour may benefit from access technologies that harness the volitional activity of muscles. In this thesis, we investigate the use of muscle activity, indicated by the mechanomyogram (MMG), as a binary and multifunction control signal for access devices. A challenge in the design of a binary MMG switch is to reliably recognize the timing of voluntary muscle contractions, and to subsequently translate the MMG signal into a switch-activation signal. A continuous wavelet transform (CWT) algorithm based on a simplified MMG generation model of recurring impulsive morphological patterns was proposed for automatic detection of muscle activity from MMG signals. CWT coefficients of the MMG signal were compared to scale-specific thresholds derived from the baseline signal to estimate the timings of muscle activity. The automatic detection algorithm was implemented as a binary switch controlled by a single muscle site at the forehead, shoulders or forearm. The binary control algorithm was verified on able-bodied participants, and the switch was tested on individuals with neuromuscular and neurological disabilities. The switch showed very high sensitivity and specificity when the muscle and its control were minimally affected by spasticity, involuntary movement, or involuntary muscle activity. We further investigate the potential of improving the functionality of the MMG-controlled switching interface. We demonstrate the practical use of the vibratory artefact measured at the forehead during vocalization to control a second switch. The proposed integrated MMG-vocalization access solution may augment access alternatives for individuals with physical disabilities using a single access site. Further, we show that multi-site MMG signals exhibit distinctive patterns of forearm muscle activity, and 7+/-1 hand movements can be identified with an accuracy of 90+/-4%. This suggests that MMG may have applications in multi-function body-machine interfaces when multiple muscle sites are available. However, MMG signal features vary with sensor location. We show that sensor displacements significantly diminish classification accuracy, emphasizing the importance of consistent sensor placement between MMG classifier training and deployment for accurate control of switching interfaces. Collectively, the findings and developments of this thesis lay the foundation for future research on wearable, MMG-driven access technologies.

No description available.

Background: Epidemiological studies suggest an increased incidence of osteoarthritis among workers in occupations requiring squat-lifting such as in construction, mining and farming. Squat-lifting postures can induce heavy mechanical loads on the joint, causing the articulating surfaces to deform. This can result in changes of vibration characteristics of the joint surfaces. Differences in the vibration characteristics of normal and pathological joints have been established and used in the past for classifying severity of disease. The purpose of this study was to examine the influence of cumulative mechanical load on the vibration properties of the knee joint and to gain an understanding of how these properties may relate to an increase in cumulative load placed on the joint. Methods: In this study, cumulative load was measured as the resultant knee joint torque during squat lifting, while a piezoelectric accelerometer was used to capture vibration signals from points on the knee during flexion and extension. Twelve university students were recruited for a repeated measures study. Each participant attended one session where they had to perform a series of six squat-lifting tasks on a force platform. Motion capture equipment was used to obtain kinematic data. The cumulative 3-D moment on the joint was calculated using inverse dynamics. Results: A visual inspection of an ensemble average constructed for the frequency spectrum of all participants revealed that differences may exist in the 750 Hz - 2000 Hz bandwidth for vibrations coming from the patella during flexion. Further statistical analysis by a t-test and ANOVA showed a decrease in the RMS power of the signal captured in this bandwidth before and after mechanical load was induced by squat lifting. A linear regression analysis indicated a significant correlation between cumulative 3-D moment on the knee joint and the median frequency of vibration signals from the patella during flexion in the 1000 Hz - 2500 Hz range. Conclusions: Overall, the results of this study indicate the possibility of a relationship between mechanical exposure on the knee joint and its vibration properties during joint movement. Despite the small sample size, a declining trend was observed in the normalized RMS power of signals with increase in loading. However, the quantitative nature of this relationship is not clear and the current study points towards a non-linear relationship between joint exposure and knee vibrations. Future studies must investigate this possibility using direct measures of joint loading, cartilage deformation and their relation to joint vibrations. / Master of Science

Surface electromyography (sEMG) and mechanomyography (MMG) are well-studied signals that can reveal information about the physiological behavior of muscles during contraction. The purpose of this study was to quantify, characterize, and analyze the electrical and mechanical muscle responses to submaximal, isometric contractions in the rectus femoris in adults. Previous studies have investigated the use of EMG to monitor muscle fatigue. However, more information appears to be needed about the use of MMG to measure muscle fatigue during submaximal isometric contraction in the rectus femoris. In this study, the utility of MMG as a measure of muscle fatigue or muscle state was investigated. After studying 10 adult subjects (6 females, 4 males) during 2 consecutive fatiguing isometric contractions at 50% MVIC, there was a total sample of 20 contractions. The RMS, frequency, and electromechanical efficiency (EME) were calculated as an average over 2s samples at the beginning, middle and end of the fatiguing contraction for both EMG and MMG. Electrical efficiency and contraction duration were also measured. EMG RMS. MMG RMS, and electrical efficiency showed significant increasing trends during fatiguing exercise (p=0.0001 and p=0.005 respectively). EMG frequency had a significant decreasing trend (p=0.0016). There was also a significant decrease in the contraction duration when fatiguing exercises were repeated in the same session (p=0.0228). EME and MMG frequency did not have significant trends. However, further studies of these parameters during different fatiguing exercises may help expand their utility in monitoring muscle state. Overall, this study suggests that sEMG and MMG may have utility in monitoring muscle fatigue in submaximal, isometric contractions in the rectus femoris. sEMG and MMG may also find future applications in monitoring patients with muscle conditions.

Muskeln oszillieren nachgewiesener Weise mit einer Frequenz um 10 Hz. Doch was geschieht mit myofaszialen Oszillationen, wenn zwei neuromuskuläre Systeme interagieren? Die Dissertation widmet sich dieser Fragestellung bei isometrischer Interaktion. Während der Testmessungen ergaben sich Hinweise für das Vorhandensein von möglicherweise zwei verschiedenen Formen der Isometrie. Arbeiten zwei Personen isometrisch gegeneinander, können subjektiv zwei Modi eingenommen werden: man kann entweder isometrisch halten – der Kraft des Partners widerstehen – oder isometrisch drücken – gegen den isometrischen Widerstand des Partners arbeiten. Daher wurde zusätzlich zu den Messungen zur Interaktion zweier Personen an einzelnen Individuen geprüft, ob möglicherweise zwei Formen der Isometrie existieren. Die Promotion besteht demnach aus zwei inhaltlich und methodisch getrennten Teilen: I „Single-Isometrie“ und II „Paar-Isometrie“. Für Teil I wurden mithilfe eines pneumatisch betriebenen Systems die hypothetischen Messmodi Halten und Drücken während isometrischer Aktion untersucht. Bei n = 10 Probanden erfolgte parallel zur Aufzeichnung des Drucksignals während der Messungen die Erfassung der Kraft (DMS) und der Beschleunigung sowie die Aufnahme der mechanischen Muskeloszillationen folgender myotendinöser Strukturen via Mechanomyo- (MMG) bzw. Mechanotendografie (MTG): M. triceps brachii (MMGtri), Trizepssehne (MTGtri), M. obliquus externus abdominis (MMGobl). Pro Proband wurden bei 80 % der MVC sowohl sechs 15-Sekunden-Messungen (jeweils drei im haltenden bzw. drückenden Modus; Pause: 1 Minute) als auch vier Ermüdungsmessungen (jeweils zwei im haltenden bzw. drückenden Modus; Pause: 2 Minuten) durchgeführt. Zum Vergleich der Messmodi Halten und Drücken wurden die Amplituden der myofaszialen Oszillationen sowie die Kraftausdauer herangezogen. Signifikante Unterschiede zwischen dem haltenden und dem drückenden Modus zeigten sich insbesondere im Bereich der Ermüdungscharakteristik. So lassen Probanden im haltenden Modus signifikant früher nach als im drückenden Modus (t(9) = 3,716; p = .005). Im drückenden Modus macht das längste isometrische Plateau durchschnittlich 59,4 % der Gesamtdauer aus, im haltenden sind es 31,6 % (t(19) = 5,265, p = .000). Die Amplituden der Single-Isometrie-Messungen unterscheiden sich nicht signifikant. Allerdings variieren die Amplituden des MMGobl zwischen den Messungen im drückenden Modus signifikant stärker als im haltenden Modus. Aufgrund dieser teils signifikanten Unterschiede zwischen den beiden Messmodi wurde dieses Setting auch im zweiten Teil „Paar-Isometrie“ berücksichtigt. Dort wurden n = 20 Probanden – eingeteilt in zehn gleichgeschlechtliche Paare – während isometrischer Interaktion untersucht. Die Sensorplatzierung erfolgte analog zu Teil I. Die Oszillationen der erfassten MTG- sowie MMG-Signale wurden u.a. mit Algorithmen der Nichtlinearen Dynamik auf ihre Kohärenz hin untersucht. Durch die Paar-Isometrie-Messungen zeigte sich, dass die Muskeln und die Sehnen beider neuromuskulärer Systeme bei Interaktion im bekannten Frequenzbereich von 10 Hz oszillieren. Außerdem waren sie in der Lage, sich bei Interaktion so aufeinander abzustimmen, dass sich eine signifikante Kohärenz entwickelte, die sich von Zufallspaarungen signifikant unterscheidet (Patchanzahl: t(29) = 3,477; p = .002; Summe der 4 längsten Patches: t(29) = 7,505; p = .000). Es wird der Schluss gezogen, dass neuromuskuläre Komplementärpartner in der Lage sind, sich im Sinne kohärenten Verhaltens zu synchronisieren. Bezüglich der Parameter zur Untersuchung der möglicherweise vorhandenen zwei Formen der Isometrie zeigte sich bei den Paar-Isometrie-Messungen zwischen Halten und Drücken ein signifikanter Unterschied bei der Ermüdungscharakteristik sowie bezüglich der Amplitude der MMGobl. Die Ergebnisse beider Teilstudien bestärken die Hypothese, dass zwei Formen der Isometrie existieren. Fraglich ist, ob man überhaupt von Isometrie sprechen kann, da jede isometrische Muskelaktion aus feinen Oszillationen besteht, die eine per Definition postulierte Isometrie ausschließen. Es wird der Vorschlag unterbreitet, die Isometrie durch den Begriff der Homöometrie auszutauschen. Die Ergebnisse der Paar-Isometrie-Messungen zeigen u.a., dass neuromuskuläre Systeme in der Lage sind, ihre myotendinösen Oszillationen so aufeinander abzustimmen, dass kohärentes Verhalten entsteht. Es wird angenommen, dass hierzu beide neuromuskulären Systeme funktionell intakt sein müssen. Das Verfahren könnte für die Diagnostik funktioneller Störungen relevant werden. / Muscles oscillate with a frequency of about 10 Hz. But what happens with myofascial oscillations if two neuromuscular systems interact? The dissertation is devoted to this question during isometric interaction. The test measurements provide hints for the presence of possibly two different forms of isometric muscle action. When two persons work against each other, each individual can subjectively choose to take up one of two modes: one can either hold isometrically – thus resist the force of the partner – or one can push isometrically – and therefore work against the resistance of the partner. In addition to the measurements to determine the interaction of neuromuscular systems, measurements with single individuals were done to evaluate the question, if probably two forms of isometric muscle action exist. The doctoral thesis consists of two separate parts concerning the content and methodology: I “Single Isometric” and II “Coupled Isometric”. For part I the hypothetical measurement modes - “holding” and “pushing” during isometric muscle action - were examined using a pneumatic system. During the measurements of n = 10 subjects the signal of pressure, force (strain gauge) and acceleration were recorded. Furthermore, the detection of the mechanic muscle oscillations of the following myotendinal structures occurred via Mechanomyo- (MMG) and Mechanotendography (MTG), respectively: triceps brachii muscle (MMGtri), tendon of triceps brachii muscle (MTGtri) and obliquus externus abdominis muscle (MMGobl). Each test person performed at 80 % of MVC six 15-seconds-measurements (three at holding and three at pushing mode, respectively; break: 1 min.) as well as four fatigue measurements (two at holding and two at pushing mode, respectively; break: 2 min.). In order to compare the two measurement modes holding and pushing, the amplitude of the myofascial oscillations as well as the force endurance were used. Significant differences between the holding and the pushing mode appeared especially when looking at the characteristics of fatigue. Subjects in the holding mode yielded earlier than during the pushing one (t(9) = 3.716; p = .005). In the pushing mode the longest isometric plateau amounts 59.4 % of the overall duration of the measurement. During holding it lasted 31.6 % (t(19) = 5.265, p = .000). The amplitudes of the single-isometric-measurements did not differ significantly. But the amplitude of the MMGobl varied significantly stronger during the pushing mode comparing to the holding one. Due to these partly significant differences between both measurement modes, this setting was considered for the second part „Coupled-Isometric“, too. For the coupled-isometric-measurements n = 20 subjects – divided into same-sex couples – were investigated during isometric interaction. The placement of the sensors is analogous to part I. The oscillations of the recorded MMG- and MTG-signals were analyzed regarding their coherence inter alia by algorithms of non-linear dynamics. Through the coupled-isometric-measurements it was shown, that also during isometric interaction the muscles and the tendons of both neuromuscular systems oscillate at the known frequency range of 10 Hz. Moreover, the systems are able to coordinate them in such a manner, that a significant coherence appears. This differed significantly from random pairings (number of patches: t(29) = 3.477; p = .002; Sum of 4 longest patches: t(29) = 7.505; p = .000). Thus it is concluded that neuromuscular complementary partners are able to synchronize themselves in the sense of coherent behavior. Regarding the parameters concerning the possibly existing forms of isometric muscle action, a significant difference at the coupled-isometric-measurements between holding and pushing appeared with respect to the characteristics of fatigue as well as the amplitudes of the MMGobl. The results of both sub studies strengthen the hypothesis that two forms of isometric muscle action exist. It is questionable whether one can talk of isometry at all, since each isometric muscle action consists of fine oscillations. This excludes a by definition postulated isometry. It is proposed to exchange this term with homeometry. The results of the coupled-isometric-measurements show inter alia, that neuromuscular systems are able to coordinate their myotendinal oscillations, so that coherent behavior arises. It is supposed that for this both systems have to be functionally intact. This procedure could become relevant for diagnostics of functional disorders.

Mechanomyography (MMG) has been proposed as a control modality for alternative access technologies for individuals with disabilities. However, MMG recordings are highly susceptible to contamination from limb movements. Pressure-based transducers are touted to be the most robust to external movement although there is some debate about their optimal chamber geometry, in terms of low frequency gain and spectral flatness. To investigate the question of preferred geometry, transducers with varying chamber shapes were designed, manufactured and tested. The best performance was achieved with a transducer consisting of a low-frequency MEMS microphone, a 4 micron thick aluminized mylar membrane and a rigid conical chamber 7 mm in diameter and 5 mm in height. Furthermore, microphone-derived MMG spectra were found to be less influenced by motion artifact than corresponding accelerometer-derived spectra. However, artifact harmonics were present in both spectra, suggesting that bandpass filtering may not remove artifact influences permeating into MMG frequency bands.

Mechanomyography (MMG) has been proposed as a control modality for alternative access technologies for individuals with disabilities. However, MMG recordings are highly susceptible to contamination from limb movements. Pressure-based transducers are touted to be the most robust to external movement although there is some debate about their optimal chamber geometry, in terms of low frequency gain and spectral flatness. To investigate the question of preferred geometry, transducers with varying chamber shapes were designed, manufactured and tested. The best performance was achieved with a transducer consisting of a low-frequency MEMS microphone, a 4 micron thick aluminized mylar membrane and a rigid conical chamber 7 mm in diameter and 5 mm in height. Furthermore, microphone-derived MMG spectra were found to be less influenced by motion artifact than corresponding accelerometer-derived spectra. However, artifact harmonics were present in both spectra, suggesting that bandpass filtering may not remove artifact influences permeating into MMG frequency bands.