Il presente lavoro nasce dalla volontà di fornire una descrizione del processo di apprendimento di un compito motorio ad alta complessità esecutiva. Per fare ciò si è scelto di testare un gruppo eterogeneo di soggetti con un livello di esperienza da uno a ventidue anni. Il primo Lu del Tai Chi Ch’uan (TCC) è stato scelto come soggetto di indagine. Il TCC è un’antica arte marziale cinese, originariamente nata come tecnica di combattimento e sviluppatasi nei secoli in una raffinata forma di esercizio per la salute e per il benessere fisico. La pratica di questa particolare arte marziale consiste principalmente nell’esecuzione di movimenti lenti e circolari che ricordano una danza silenziosa, ma che in realtà mimano una lotta con un opponente immaginario. Il TCC può essere praticato a tutte le età, ma la lentezza esecutiva, il controllo del corpo e l’accoppiamento movimento-respirazione fanno del Tai Chi un efficace strumento per l’allenamento della popolazione anziana. La ricerca di indici quantitativi, capaci di rispecchiare il processo di apprendimento di questa particolare disciplina, si è snodata attraverso diverse teorie e numerosi campi di indagine. In questo approccio, marcatamente multidisciplinare, si sono utilizzati strumenti propri della biomeccanica, della bioenergetica, del controllo motorio e della analisi percettiva. Strumenti che hanno permesso di fornire una descrizione generale e scientifica degli aspetti cinematici, metabolici ed elettromiografici di questa forma di esercizio. La letteratura (principalmente in ambito del controllo motorio umano) mostra che i parametri muscolari, cardiaci, ventilatori e cinematici associati al movimento, risultano degli efficaci indicatori del livello di abilità motoria. Livello che sembra essere a sua volta un parametro quantificabile e percepibile da un qualsiasi osservatore; in generale chiunque è in grado di riconoscere il livello di “skill” anche se non ha competenze specifiche nella disciplina osservata. In altre parole, sembra esistere una relazione fra il livello tecnico della performance e il “senso di bellezza” legato e percepito nell’osservazione di questa. Ma quali sono le variabili bioenergetiche e/o biomeccaniche legate al movimento che permettono a un osservatore di riconoscere il livello di abilità? Quali le caratteristiche del moto percepite come “belle”? Questi due parametri sono distinti fra loro oppure coincidono? La bellezza sta negli occhi di chi osserva o esistono caratteristiche oggettive del movimento umano associate all’idea di “bellezza”? Questo lavoro si prefigge di rispondere anche a queste domande. Dopo un’introduzione generale, in cui sono riportati teorie e metodi utilizzati nel corso delle analisi (capitolo1), vengono riportati i risultati relativi ai tre studi condotti (capitoli 2, 3 e 4). Nel capitolo 5 infine, verranno presentate discussione e conclusioni generali. STUDIO 1- Nel primo studio, il primo Lu è stato analizzato da un punto di vista prettamente biomeccanico; tutte le variabili cinematiche calcolate si riferiscono all’andamento del centro di massa totale (BCOM), calcolato a partire dai centri di massa dei singoli segmenti corporei. Questi parametri oltre a fornire una descrizione cinematica di questa particolare sequenza di movimenti, rappresentano, in parte, degli indici capaci di riflettere il processo di apprendimento motorio. Sono stati testati 23 soggetti (10 esperti e 13 principianti), appartenenti alla stessa scuola di TCC (stile Yang). La raccolta dati è stata eseguita attraverso l’utilizzo di un sistema stereofotogrammetrico (Vicon) composto da 8 telecamere ad infrarosso; è stato utilizzato un full body marker set (e validato in letteratura) composto da 42 marcatori passivi posti in particolari punti di repere. Ad ogni soggetto, infine, è stato chiesto di ripetere l’esercizio due volte. Dai valori di spostamento del BCOM sono stati calcolati i valori di velocità, accelerazioni e jerk. Differenze significative (p<0.05) sono state trovate fra i due gruppi di soggetti; gli esperti eseguono la sequenza con una andatura significativamente inferiore (229 vs. 175 s), con spostamenti del BCOM più ampi (22.1 vs. 19.2 m) e più fluidi (i valor medi del jerk infatti risultano essere 1.82 m.s-3 per gli esperti contro i 2.57 m.s-3 per i principianti). Per questo particolare tipo di esercizio, la variabiltà è analizzata come una sorgente di errore e secondo le teorie del controllo motorio essa tende a diminuire all’aumentare dell’esperienza. A tal riguardo sono state calcolate e paragonate fra loro, le larghezze di banda per i valori di spostamento, velocità ed accelerazione nei due gruppi di soggetti (una deviazione standard rispetto al valore medio rappresenta l’indice qualitativo di variabilità motoria); l’analisi grafica mostra che la larghezza di banda risulta inferiore negli esperti per i valori di spostamento e accelerazione, mentre per la velocità il trend è opposto. Dai dati cinematici sono stati calcolati i valori di lavoro e potenza meccanica esterna. Sono state utilizzate due diverse metodologie per il computo di queste variabili: il “single mass model” e il “segmental model”. Per quanto riguarda il lavoro meccanico esterno non sono state trovate differenze significative nei due gruppi, mentre la potenza meccanica esterna risulta significativamente superiore negli esperti rispetto ai principianti (ciò è dovuto al fatto che la potenza è data dal rapporto fra lavoro e tempo d’esecuzione, e questo ultimo risulta significativamente maggiore nel gruppo degli esperti). Questi dati risultano circa dieci volte inferiori rispetto a quelli riportati in letteratura per la marcia (circa 1 m.s-1 self selected speed) e ciò è in accordo col fatto che anche le velocità in gioco differiscono dello stesso fattore. STUDY 2 –Scopo di questo studio è fornire una descrizione bioenergetica del primo Lu del Tai Chi Ch’uan, ma anche ricercare fra le variabili metaboliche ed elettromiografiche quelle capaci di riflettere il processo di apprendimento di un compito motorio complesso. Sono stati testati gli stessi soggetti presentati nel primo studio: 10 esperti e 13 principianti, appartenenti alla stessa scuola di TCC (stile Yang). Anche se non sono state trovate differenze significative nei valori di consumo di ossigeno (circa 12 ml.min-1.kg-1) e di ventilazione (circa 21.7 l.min-1) fra i due gruppi, gli esperti tuttavia si distinguono dai principianti per la “qualità” piuttosto che la “quantità” del pattern respiratorio: i primi infatti respirano più lentamente (11.0 vs. 15.4 b.min-1 , p<0.05) e più profondamente (2.28 vs. 1.53 l, p<0.05) rispetto ai secondi. Dai valori metabolici, risulta evidente che il Tai Chi Ch’uan è un esercizio a moderata intensità ma caratterizzato da lunghe fasi di co-attivazione a carico dei muscoli degli arti inferiori (le co-contrazioni variano da 50% a 80% rispetto all’intera durata dell’esercizio). Ci si aspettava che all’aumentare dei tempi di co-contrazione aumentasse anche la domanda metabolica ma questa ipotesi non è stata validata dai dati sperimentali. È noto che una delle cause principali d’inefficienza motoria è la presenza di alti tempi di co-attivazione muscolare; infatti i valori di efficienza meccanica risultano estremamente bassi in entrambi i gruppi (0.10 per gli esperti e 0.16 per i principianti rispetto a 0.25-0.30 in condizioni ottimali). Il TCC quindi risulta essere una “forma di locomozione poco efficiente”, e ciò è dimostrato dall’alto valore del costo energetico (circa 35 J.m-1.kg-1), tre volte superiore a quello calcolato per la marcia alla stessa velocità media (1 m.s-1). STUDIO 3 – Il terzo studio presenta un’analisi percettiva sul movimento umano; come nei precedenti lavori è stato analizzato il primo Lu del Tai Chi Ch’uan. Sono stati testati due gruppi di soggetti: il primo gruppo formato da 23 praticanti TCC, suddivisi in esperti e non-esperti, e il secondo gruppo composto da 56 osservatori, a loro volta suddivisi in osservatori esperti (OE) e osservatori naive (NEO). Il gruppo di OE è formato da soggetti praticanti TCC, mentre il gruppo di ONE è formato da soggetti con nessuna esperienza in questa particolare disciplina. Al gruppo di osservatori (esperti e non) è stato chiesto di guardare e giudicare 23 video, ognuno dei quali contenete l’esecuzione del primo Lu per ogni soggetto praticante TCC. Per ogni video è stata estratta la stessa sequenza di posture (dalla decima figura alla diciannovesima) in modo da avere tempi (circa 30 s) tali da ottenere sempre la massima attenzione da parte degli osservatori. La raccolta dati è stata eseguita attraverso una scala di valori validata in letteratura (VAS, visual analogic scale) in cui ogni giudice doveva fornire una votazione su qualità tecniche, rappresentate dalle voci “abilità tecnica” e “controllo dell’equilibrio”, e su qualità estetiche “grazia/bellezza” e “fluidità”. I dati ottenuti da questo esperimento indicano che esistono delle caratteristiche del movimento umano (o del Tai Chi Ch’uan) che sono riconosciute come “belle”; esse sono la fluidità, il ritmo e l’abilità motoria. Tutti gli osservatori (esperti e non) sono in grado di riconoscere il livello della performance osservata, ma solo quelli esperti riescono a distinguere le caratteristiche tecniche da quelle estetiche; i naive infatti forniscono lo stesso punteggio ai due tipi di qualità, dimostrando che per loro vale l’equivalenza bello uguale bravo o bravo uguale bello. In questo studio si è inoltre cercato di capire se esistesse una relazione fra le impressioni visive dei giudici e le variabili respiratorie dei soggetti praticanti TCC; i dati mostrano che i giudizi più alti sono stati dati (da entrambi i gruppi di osservatori e su tutti le qualità analizzate) ai soggetti che presentano una frequenza respiratoria minore (e quindi un tidal volume superiore), che hanno un numero di respiri inferiore e che eseguono l’esercizio ad un ritmo più basso. Infine ai soli osservatori non esperti (ONE) è stato chiesto di giudicare gli stessi video ad una velocità rallentata (metà) e accelerata (doppio) per verificare se la velocità di esecuzione influisse sulla valutazione della performance. I risultati mostrano un aumento generale nelle valutazioni delle performance a velocità rallentata dei soggetti non esperti (praticanti TCC); ciò può lasciar supporre che la bellezza del movimento è legata in qualche misura alla lentezza con cui esso viene eseguito. I dati riportati in questa tesi indicano che un qualsiasi tipo di osservatore è in grado di riconoscere il livello di una performance, anche se non ha nessuna competenza specifica nella disciplina osservata. Inoltre, una “skilled performance” è generalmente associata ad una percezione o idea di grazia e bellezza, qualità che sembrano essere quantificabili da un qualsiasi “spettatore”. Un altro obiettivo di questo lavoro è stato la ricerca di indici quantitativi capaci di descrivere il processo di apprendimento motorio di una sequenza di movimenti caratterizzati da una alta complessità esecutiva. Sembra inoltre ragionevole supporre che questi stessi indici possano influenzare il giudizio (sia tecnico che estetico) di un qualsiasi osservatore. Attraverso un’analisi biomeccanica, bioenergetica, elettromiografia e percettiva si è riusciti a individuare dei parametri capaci di riflettere il livello di esperienza/abilità (e quindi del processo di apprendimento motorio) dei soggetti analizzati e a fornire una descrizione generale e completa del primo Lu del Tai Chi Ch’uan. I tempi di esecuzione, i valori di spostamento, di velocità, di accelerazione e di jerk sono le principali variabili cinematiche che permettono di discriminare un atleta esperto da un principiante; la frequenza respiratoria e il numero di atti respiratori associati al movimento invece rappresentano i parametri metabolici più rilevanti per questa analisi. Dai dati bioenergetici (consumo di ossigeno, ventilazione e battito cardiaco) inoltre si è riusciti a classificare il TCC come un esercizio caratterizzato da una moderata intensità, da bassi livelli di efficienza meccanica (larga presenza di co-contrazioni) e da costi energetici molto alti (3 volte superiori a quelli calcolati nella marcia alla stessa velocità media).
The main purpose of this Thesis was to describe the learning process of a complex motor task: the First Lu of Tai Chi Ch’uan (TCC). TCC is a branch of traditional Chinese martial arts and, as is the case for all martial arts, one of its most important characteristic is the deep interaction between mind and body: the body is naturally relaxed, the mind is tranquil but alert, the body movements are slow, smooth, and well coordinated. It is composed by a complex sequence of movements that needs several years of practice to be learned and which is characterized by “an high aesthetic content”. There are different styles of TCC, the more diffused ones are Chen, Yang, Wu and Sun. In this Thesis we focused our attention on the Yang style. In the Yang school the main exercise is composed by 108 posture (or figures) divided into four sections called “Lu”. In this Thesis we analyzed in detail the Fist Lu of the Yang style, composed by 22 postures. We tried to provide a general description of this martial art focusing our attention on the bioenergetic, biomechanic and perceptive aspects of this “form of exercise”. Motor control literature proved that muscular, cardiac, ventilatory, electromyographyc and mechanical variables can be used as indicators of skill and, in some cases, as indexes of learning (however these studies are generally referred to discrete movements or, at most, to cyclic tasks). Moreover, the skill level seems to be a “quantity” that can be perceived by anyone even if the observer has no specific competence in that discipline. When observing a skilled movement a “sense of beauty” is also perceived. Indeed millions of people like to watch the Olympic games not only because of the competition excitement, the national pride and the media coverage but also because of the simple pleasure of looking at movements that could be considered as an example of “perfection”. Thus, there seems to be a relationship between the technical skill of the performer and the sense of “beauty” perceived by an observer (whether an expert or not in that discipline). But, which are the variables (bioenergetical and/or biomechanical) of human movement that allow an observer to recognize the level of the athlete’s performance? Which are the features of human movement that are perceived as “beautiful”? Are these related to those that reflect the level of expertise? Is beauty in the eyes of the beholder or are there common objective characteristics of motion associated to the idea of “beauty”? In this work we attempted to answer these questions by means of a multidisciplinary approach. In this Thesis we tried to understand which were the variables involved in the learning process of a complex and not repetitive sequence of movements. To do this a heterogeneous group of 23 TCC practitioners, with a level of expertise from one to twenty-two years, were analyzed; they were recruited on a voluntary basis through different TCC schools and the inclusion criteria included that subjects had practiced the Yang style of TCC for at least one year and could correctly and properly complete the First Lu (the first 22 postures of TCC). In this Thesis, after a general introduction of the topics of interest (Chapter 1), the results obtained in the three studies we performed are presented (Chapter 2, 3, and 4). The general discussion and the conclusions are reported in Chapter 5. STUDY 1 - The aim of this study was to give a biomechanical description of the First Lu of Tai Chi Ch’uan and to investigate which kinematic variables associated to the body centre of mass (BCOM) movements could describe the learning process of this complex motor task. Twenty-three subjects (10 experts: 15.0 ± 5.1 yrs of practice; 13 beginners: 2.3 ± 1.1 yrs of practice) were recruited through the same TCC school (Yang style). Practitioners were asked to perform the exercise twice and kinematic data were collected through a stereophotogrammetryc system. From the values of displacement of BCOM, velocities, accelerations and jerk were calculated. Significant differences between groups (p<0.05) were observed for most of the parameters of interest: experts performed the movements at a significantly lower pace (229 and 175 s), with wider movements (22.1 vs. 19.2 m) of total BCOM displacement and with a lower jerk (1.82 vs. 2.57 m.s-3) than beginners. According with the theories of motor learning, variability of movement decreased with the increase of expertise. The bandwidth for displacement and acceleration of BCOM (1 SD about the average values, considered as an indicator of control and accuracy of movement) was indeed lower in experts than in beginners. Based on kinematic data, external mechanical work and power were computed. External mechanical work (WEXT) was calculated by means of two independent methods (the “single mass model” and the “segmental model”) and was found not to differ between groups; on the other hand, mechanical power (W’EXT = WEXT / TEXE) was significantly larger in experts compared to beginners due to the significant difference in TEXE. The values of WEXT and W’EXT were found to be 10 times lower than those reported for walking at the self selected speed (about 1 m.s-1), according to the fact that average speed maintained during the execution of the First Lu of TCC is ten times lower (about 0.1 m.s-1). STUDY 2 - The aim of this study was to give a bioenergetic description of the First Lu of Tai Chi Ch’uan and to investigate which metabolic and electromyographic variables are involved in the learning process of this complex motor task. Twenty-three subjects, divided into two groups based on their expertise, were recruited through the same TCC school (Yang style). Even if no differences in oxygen uptake (about 12 ml.min-1.kg-1) and expired ventilation (about 21.7 l.min-1) were detected between groups, results show that expert and non expert TCC practitioners can be differentiated based on the “quality” instead of the “quantity” of their breathing: expert practitioners breathed slowly (11.0 and 15.4 b.min-1, respectively) and more deeply (2.28 and 1.53 l, respectively) than beginners. TCC is thus an exercise of moderate intensity but it is characterized by a long duration of co-activation of the lower limb muscles (from 50 to 80 % of total exercise duration). We expected that longer co-contraction times were related to higher metabolic demands, but this was not verified. It is well known that one of the main causes of inefficiency is the presence of a large % of co-contractions and indeed the values of mechanical efficiency as measured in this study are rather low (from 0.10 to 0.16, compared to 0.25 at the muscular level). TCC is thus an un-efficient “type of locomotion” and this is also demonstrated by the high values of energy cost (about 35 J.m kg-1) that are three times larger that those reported for walking (about 12 J.m kg-1) at the same “average velocity” (about 0.10 m.s-1). STUDY 3 – In the third study we performed a perceptive analysis (visual perception) of this type of movement. Two groups of subjects were recruited: one group of practitioners (10 experts: with more than 8 years of practice; 15 non experts: with less than 4 years of practice) and one group of observers (26 experts of this motor task and 30 naïve observers). The observers were asked to rate the performance of practitioners for aesthetic (beauty/grace and fluidity/continuity) and technical (skill and balance control) qualities of movement. Data reported in this study indicate that: 1) there are indeed features of human motion (or at least of TCC) that are recognised as “beautiful”: fluency, rhythm and technical skill; and 2) differences in the perception of movement are indeed recognizable between expert and naïve observers. Thus, as for the aesthetic evaluation of a static object (e. g. visual arts), beauty in human motion seems to be a function of both the quality of the “object” and of the observer. We also found a significant relationship between metabolic parameters (e. g. the breathing pattern) and aesthetic/technical scores and this further suggest that action performance is the final mergence of the coalition of all these components. Data reported in this Thesis indicate that any observer should be able to recognise the “level” of a movement performance (TCC, in our case) even if he has no specific competence in that discipline, since skilled performance is often associated with a perception (or idea) of grace and beauty, which are movement qualities that anyone seems to be “able to rate”. In this Thesis we also tried to understand which are the quantitative indexes that could characterize the performance of expert and non-expert TCC practitioners and thus play a significant role in the learning process of this complex sequence of movements. It is reasonable to think that these variables influence also the judgement of the observers (both technical and aesthetical). This was done through a kinematic, metabolic and EMG analysis. Longer time of execution (228 vs. 174 s), lower velocities (0.10 vs. 0.12 m.s-1), wider movements (23.8 vs. 21.1 m), and a better control of movement (lower SDs) were the main kinematic features that characterized the performance of an expert TCC practitioner in comparison to a beginner. The increase in the time of execution was found to depend, in part, from the breathing pattern; TCC is considered as a form of “meditation in movement” thus, as in other forms of meditation, a deeper and slower breathing pattern is generally achieved with practice. Indeed, expert practitioners were characterized by a slower breathing frequency (11.0 vs. 15.4 b.min-1) and a larger tidal volume (2.28 vs. 1.53 l) than beginners; moreover, in experts, the number of breaths was found to be smaller (36 vs. 44) and closer to the number of postures (22) than in non experts (in TCC opening movements should correspond to an inspiration, closing movements to an expiration). Metabolic data indicated that TCC is an exercise of moderate intensity ad that no significant differences could be detected (between expert and non expert practitioners) for the values of ventilation (about 21.7 l.min-1), heart rate (about 116 bpm) and oxygen consumption (about 12.0 ml.min-1.kg-1). Data reported in this Thesis also indicate that this “form of exercise” is characterized by long co-activation times of the lower limb muscles (from 50 to 80 % of total exercise duration). It is well known that one of the main causes of inefficiency is the presence of a large proportion of co-contractions; in fact mechanical efficiency in TCC was found to be of about 0.10 - 0.15 (compared to 0.25 at the muscular level). TCC also appears to be a very expensive “form of locomotion”, with values of energy cost being three times greater with respect to walking (34 vs. 11 J.m-1.kg-1) at the same “average velocity” (about 0.1 m.s-1). In conclusion, we found metabolic and kinematic indexes able to explain and describe the improvement of “skill” with the years of practice. We also demonstrated that technical skill is strictly related to the perception of beauty. This study therefore underlines the interplay between technical, metabolic, kinematic and perceptive data.
Quantitative analysis of motor activities with an elevated "aesthetic content": the case of Tai Chi Ch'uan
ZORZI, Elena
2011-01-01
Abstract
The main purpose of this Thesis was to describe the learning process of a complex motor task: the First Lu of Tai Chi Ch’uan (TCC). TCC is a branch of traditional Chinese martial arts and, as is the case for all martial arts, one of its most important characteristic is the deep interaction between mind and body: the body is naturally relaxed, the mind is tranquil but alert, the body movements are slow, smooth, and well coordinated. It is composed by a complex sequence of movements that needs several years of practice to be learned and which is characterized by “an high aesthetic content”. There are different styles of TCC, the more diffused ones are Chen, Yang, Wu and Sun. In this Thesis we focused our attention on the Yang style. In the Yang school the main exercise is composed by 108 posture (or figures) divided into four sections called “Lu”. In this Thesis we analyzed in detail the Fist Lu of the Yang style, composed by 22 postures. We tried to provide a general description of this martial art focusing our attention on the bioenergetic, biomechanic and perceptive aspects of this “form of exercise”. Motor control literature proved that muscular, cardiac, ventilatory, electromyographyc and mechanical variables can be used as indicators of skill and, in some cases, as indexes of learning (however these studies are generally referred to discrete movements or, at most, to cyclic tasks). Moreover, the skill level seems to be a “quantity” that can be perceived by anyone even if the observer has no specific competence in that discipline. When observing a skilled movement a “sense of beauty” is also perceived. Indeed millions of people like to watch the Olympic games not only because of the competition excitement, the national pride and the media coverage but also because of the simple pleasure of looking at movements that could be considered as an example of “perfection”. Thus, there seems to be a relationship between the technical skill of the performer and the sense of “beauty” perceived by an observer (whether an expert or not in that discipline). But, which are the variables (bioenergetical and/or biomechanical) of human movement that allow an observer to recognize the level of the athlete’s performance? Which are the features of human movement that are perceived as “beautiful”? Are these related to those that reflect the level of expertise? Is beauty in the eyes of the beholder or are there common objective characteristics of motion associated to the idea of “beauty”? In this work we attempted to answer these questions by means of a multidisciplinary approach. In this Thesis we tried to understand which were the variables involved in the learning process of a complex and not repetitive sequence of movements. To do this a heterogeneous group of 23 TCC practitioners, with a level of expertise from one to twenty-two years, were analyzed; they were recruited on a voluntary basis through different TCC schools and the inclusion criteria included that subjects had practiced the Yang style of TCC for at least one year and could correctly and properly complete the First Lu (the first 22 postures of TCC). In this Thesis, after a general introduction of the topics of interest (Chapter 1), the results obtained in the three studies we performed are presented (Chapter 2, 3, and 4). The general discussion and the conclusions are reported in Chapter 5. STUDY 1 - The aim of this study was to give a biomechanical description of the First Lu of Tai Chi Ch’uan and to investigate which kinematic variables associated to the body centre of mass (BCOM) movements could describe the learning process of this complex motor task. Twenty-three subjects (10 experts: 15.0 ± 5.1 yrs of practice; 13 beginners: 2.3 ± 1.1 yrs of practice) were recruited through the same TCC school (Yang style). Practitioners were asked to perform the exercise twice and kinematic data were collected through a stereophotogrammetryc system. From the values of displacement of BCOM, velocities, accelerations and jerk were calculated. Significant differences between groups (p<0.05) were observed for most of the parameters of interest: experts performed the movements at a significantly lower pace (229 and 175 s), with wider movements (22.1 vs. 19.2 m) of total BCOM displacement and with a lower jerk (1.82 vs. 2.57 m.s-3) than beginners. According with the theories of motor learning, variability of movement decreased with the increase of expertise. The bandwidth for displacement and acceleration of BCOM (1 SD about the average values, considered as an indicator of control and accuracy of movement) was indeed lower in experts than in beginners. Based on kinematic data, external mechanical work and power were computed. External mechanical work (WEXT) was calculated by means of two independent methods (the “single mass model” and the “segmental model”) and was found not to differ between groups; on the other hand, mechanical power (W’EXT = WEXT / TEXE) was significantly larger in experts compared to beginners due to the significant difference in TEXE. The values of WEXT and W’EXT were found to be 10 times lower than those reported for walking at the self selected speed (about 1 m.s-1), according to the fact that average speed maintained during the execution of the First Lu of TCC is ten times lower (about 0.1 m.s-1). STUDY 2 - The aim of this study was to give a bioenergetic description of the First Lu of Tai Chi Ch’uan and to investigate which metabolic and electromyographic variables are involved in the learning process of this complex motor task. Twenty-three subjects, divided into two groups based on their expertise, were recruited through the same TCC school (Yang style). Even if no differences in oxygen uptake (about 12 ml.min-1.kg-1) and expired ventilation (about 21.7 l.min-1) were detected between groups, results show that expert and non expert TCC practitioners can be differentiated based on the “quality” instead of the “quantity” of their breathing: expert practitioners breathed slowly (11.0 and 15.4 b.min-1, respectively) and more deeply (2.28 and 1.53 l, respectively) than beginners. TCC is thus an exercise of moderate intensity but it is characterized by a long duration of co-activation of the lower limb muscles (from 50 to 80 % of total exercise duration). We expected that longer co-contraction times were related to higher metabolic demands, but this was not verified. It is well known that one of the main causes of inefficiency is the presence of a large % of co-contractions and indeed the values of mechanical efficiency as measured in this study are rather low (from 0.10 to 0.16, compared to 0.25 at the muscular level). TCC is thus an un-efficient “type of locomotion” and this is also demonstrated by the high values of energy cost (about 35 J.m kg-1) that are three times larger that those reported for walking (about 12 J.m kg-1) at the same “average velocity” (about 0.10 m.s-1). STUDY 3 – In the third study we performed a perceptive analysis (visual perception) of this type of movement. Two groups of subjects were recruited: one group of practitioners (10 experts: with more than 8 years of practice; 15 non experts: with less than 4 years of practice) and one group of observers (26 experts of this motor task and 30 naïve observers). The observers were asked to rate the performance of practitioners for aesthetic (beauty/grace and fluidity/continuity) and technical (skill and balance control) qualities of movement. Data reported in this study indicate that: 1) there are indeed features of human motion (or at least of TCC) that are recognised as “beautiful”: fluency, rhythm and technical skill; and 2) differences in the perception of movement are indeed recognizable between expert and naïve observers. Thus, as for the aesthetic evaluation of a static object (e. g. visual arts), beauty in human motion seems to be a function of both the quality of the “object” and of the observer. We also found a significant relationship between metabolic parameters (e. g. the breathing pattern) and aesthetic/technical scores and this further suggest that action performance is the final mergence of the coalition of all these components. Data reported in this Thesis indicate that any observer should be able to recognise the “level” of a movement performance (TCC, in our case) even if he has no specific competence in that discipline, since skilled performance is often associated with a perception (or idea) of grace and beauty, which are movement qualities that anyone seems to be “able to rate”. In this Thesis we also tried to understand which are the quantitative indexes that could characterize the performance of expert and non-expert TCC practitioners and thus play a significant role in the learning process of this complex sequence of movements. It is reasonable to think that these variables influence also the judgement of the observers (both technical and aesthetical). This was done through a kinematic, metabolic and EMG analysis. Longer time of execution (228 vs. 174 s), lower velocities (0.10 vs. 0.12 m.s-1), wider movements (23.8 vs. 21.1 m), and a better control of movement (lower SDs) were the main kinematic features that characterized the performance of an expert TCC practitioner in comparison to a beginner. The increase in the time of execution was found to depend, in part, from the breathing pattern; TCC is considered as a form of “meditation in movement” thus, as in other forms of meditation, a deeper and slower breathing pattern is generally achieved with practice. Indeed, expert practitioners were characterized by a slower breathing frequency (11.0 vs. 15.4 b.min-1) and a larger tidal volume (2.28 vs. 1.53 l) than beginners; moreover, in experts, the number of breaths was found to be smaller (36 vs. 44) and closer to the number of postures (22) than in non experts (in TCC opening movements should correspond to an inspiration, closing movements to an expiration). Metabolic data indicated that TCC is an exercise of moderate intensity ad that no significant differences could be detected (between expert and non expert practitioners) for the values of ventilation (about 21.7 l.min-1), heart rate (about 116 bpm) and oxygen consumption (about 12.0 ml.min-1.kg-1). Data reported in this Thesis also indicate that this “form of exercise” is characterized by long co-activation times of the lower limb muscles (from 50 to 80 % of total exercise duration). It is well known that one of the main causes of inefficiency is the presence of a large proportion of co-contractions; in fact mechanical efficiency in TCC was found to be of about 0.10 - 0.15 (compared to 0.25 at the muscular level). TCC also appears to be a very expensive “form of locomotion”, with values of energy cost being three times greater with respect to walking (34 vs. 11 J.m-1.kg-1) at the same “average velocity” (about 0.1 m.s-1). In conclusion, we found metabolic and kinematic indexes able to explain and describe the improvement of “skill” with the years of practice. We also demonstrated that technical skill is strictly related to the perception of beauty. This study therefore underlines the interplay between technical, metabolic, kinematic and perceptive data.File | Dimensione | Formato | |
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