Skeletal muscles are involved in numerous processes including postural maintenance, locomotion, ventilation of lungs and protection of the bones and viscera. Muscle also plays important roles in chronic diseases including sarcopenia, cachexia, insulin resistance and diabetes. The major component of muscle is the constituent muscle fibres. Muscle fibre cross-sectional area (CSA), fibre number, and proportion of fibre types are important determinants of muscle function, overall metabolism and the quality and quantity of meat in livestock. Genetic variation plays a substantial role in the variation observed in fibre traits. The underlying pathways and genes remain poorly understood; therefore a greater understanding can potentially lead to treatments of disease. The aim of this thesis was to gain a deeper understanding of the genetic mechanisms which underlie variation in the number, CSA and type of muscle fibres. Linkage analysis of soleus fibre properties was performed in an F2 intercross, and refined in the F34 intercross of two strains selected for high and low bodyweight, LG/J and SM/J respectively. Quantitative trait loci (QTL) were then integrated with LG/J and SM/J muscle transcriptome data to identify candidate genes. Genome-wide association analysis identified 6 QTL affecting properties of muscle fibres. Transcriptome analysis indicated a number of differentially expressed candidate genes within the QTL; Ppp1r16b, Gm826, Chd6, Alad, Akap2, E130308A19Rik, Gm9174 and Hdhd3. Functional testing of a mouse Chd6 knockout 5 model confirmed no involvement in fibre properties and has therefore been discounted from the candidate genes. The genetic mechanisms accounting for the differing fibre properties in the LG/J and SM/J strains have been elucidated in greater detail. Integration of QTL mapping and transcriptome data led to a manageable number of candidate genes which could underlie the effects of the QTL via differential expression or coding sequence differences. Available knockout models will facilitate validation of the candidate genes.

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Call number: LD2668 .T4 1950 N5 / Master of Science

A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Physiotherapy Johannesburg, 2017 / This research makes a meaningful contribution to the development of effective injury prevention strategies among adolescent cricket pace bowlers. This dissertation, specifically investigated two screening procedures, the Functional Movement Screen (FMS) and ultrasound measured abdominal wall muscle thickness, both of which aim to predict injury among the general and sporting population. More specifically, the dissertation investigated the applicability of these screening procedures to adolescent cricket pace bowlers. Adolescent pace bowlers are prone to injury due to the high load and complex nature of the bowling action as well the risk factors associated with the adolescent growth spurt. Studies related to the validity of the FMS in terms of the prediction of injuries among various sporting disciplines have been conducted but none among cricket pace bowlers. Studies related to the association between abdominal wall muscle morphometry (i.e. thickness at rest and during the performance of abdominal drawing in manoeuvre (ADIM), as measured by ultrasound imaging (USI), and injury among professional and amateur cricket pace bowlers have had conflicting results and limited research related to abdominal muscle morphometry among the adolescent pace bowlers exist. Adolescent pace bowlers that were injury free at the start of the season were recruited for this study. Details related to the nature of past injuries as well as injuries sustained during the season were monitored and recorded over a three month period. Included in this dissertation are three original papers. The first two investigated the association between prospective in-season injury and the two above mentioned screening procedures. The third investigated the concurrent validity of FMS overhead deep squat (DS) when observer rating was compared to kinematic analysis. The first paper (Chapter 4) investigated the association between muscle morphometry of transverse abdominis (TA), internal oblique (IO) and external oblique (EO), as measured by USI, at the start of the season and in-season injury. Results indicated that non-dominant internal oblique is thicker than dominant IO (p=0.01, effect size (ES) =0.65) in injury free pace bowlers but that non-dominant and dominant internal oblique (p=0.47; ES=0.24) is symmetrical in injured pace bowlers. Based on these findings we concluded that asymmetry in IO thickness may play a protective role against injury rather than being a predisposing risk factor to injury. The second paper (Chapter 5) investigated the association between pre-season total FMS score and in-season injury among adolescent pace bowlers. Results indicated that there was no significant difference in total pre-season FMS scores of bowlers that sustained injuries during the season and those that remained injury free (p=0.58). Also, a total FMS score of 14 (the score previously found to be an accurate cut-off score) does not provide the sensitivity needed to assess injury risk among adolescent pace bowlers. It was therefore concluded that the FMS was not associated with in-season injury among adolescent pace bowlers and that the usefulness of this tool in the prediction of injuries among these cricketers is doubtful Paper 3 (Chapter 7) investigated the concurrent validity of the overhead DS included in the FMS when observer rating is compared to kinematic analyses. The FMS attempts to systematically score the quality of movements, among other the DS, based on specific criteria. The developers of the FMS suggest that specific mechanics related to the DS differ between levels of scoring. There were significant differences in the degree to which the torso was flexed forward, away from the vertical (p=0.03), where groups 3 and 2 (i.e. those participants who scored a rating of 3 and 2 respectively for the performance of the DS) remained more upright compared to Group 1. There was also a significant difference in the degree to which the femur passed the horizontal line (p=0.05) between the three groups. At the point of deepest descent, the femurs of Groups 3 and 2 were below the horizontal while that of Group 1 remained above. The findings of this part of the study suggest that, while raters correctly identified differences in biomechanics between groups for two of the scoring criteria (femur below horizontal and feet remaining flat on floor or board) , they did not rate the groups correctly for the remaining criteria. The concurrent validity of the observer rating of the FMS DS is therefore questionable. In conclusion, the high load nature and complexity of the pace bowling action together with the intrinsic risk factors related to the adolescent growth spurt, expose school boy cricket pace bowlers to injury. The ability of these screening procedures to accurately identify individuals at risk of sustaining injuries are therefore of the utmost importance. Despite the popularity of the FMS, the concurrent validity of this screening tool and its lack of association with in- season injury among adolescent pace bowlers brings the use of FMS into question. Symmetry, not asymmetry, of the IO and under-, not over-activation of the dominant TA muscles were associated with in-season injuries among pace bowlers. All of the above conflicting findings pose uncertainty regarding the applicability of these screening procedures to injury prediction among adolescent cricket pace bowlers. / MT2017

Thesis (M.A.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Models of muscle relevant to the study of the active state have been reviewed. Some of the implications of the existing force-velocity equations have been examined preliminary to the presentation of a new method for determining the active state curve and the formulation of a general active state equation. It has been demonstrated, both theoretically and experimentally, that the intensity of the active state at any instant can be determined from a set of isometric myograms recorded rapidly but with different external compliances. The length of the muscle must be kept constant while these myograms are being recorded. From such sets of isometric myograms taken at 25uC and at different resting tensions, regression lines of developed tension against compliance were calculated at 10 msec intervals after the stimulus. The tension, independent of external compliance, was calculated from such regression lines. The extension of the series elastic component at any instant was determined according to the method of MacPherson (1953) while the compliance of the series elastic component was determined by dividing this extension by P t' the intensity of the active state at that instant. Substituting this compliance in the corresponding regression equation, a general equation Pt - Ptpt - a Lt = 0 (where P t is the intensity of the active state, pt is the isometric tension at zero external compliance, a is the regression coefficient and Lt is the extension of the series elastic component at time t after the stimulus) was developed. Pt was obtained by solving this equation. The active state curves determined according to this method rise much more gradually than those previously proposed. / 2031-01-01

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Master of Science / A mechanical stimulus producing stretch in human or animal muscle may evoke a reflex response in the muscle that tends to oppose the length change. In decerebrate preparations, limb flexion generates a tonic stretch reflex that manifests as a sustained increase in resistance (Liddell and Sherrington, 1924; Widmalm, 1976b). This tonic response is not readily apparent in the conscious human subject, however, the phasic response may be observed as a burst of action potentials produced by the synchronous firing of several motor units, and as such represents the classic tendon reflex. The analogous compound action potential in the jaw musculature may be demonstrated following a sudden downward mechanical impulse to the mandible in the human or animal subject (Goodwill, 1968; Matthews, 1976) and has been termed the jaw-closing reflex or the jaw jerk reflex, the latter so named in view of its similarity to the knee-jerk and other tendon reflexes induced by sudden stretch (Goodwill, 1968; Munro and Griffin, 1971; Tardieu, Tabary and Tardieu, 1973). The use of the term “jaw jerk” to describe this reflex may be inappropriate as it has been used to describe a sudden opening movement (Riblet and Mitchell, 1971). It would appear preferable therefore to avoid the term “jaw jerk” in in favour of less ambiguous terminology such as “jaw-closing” reflex or monosynaptic myotatic reflex potential (MSP; Widlam, 1976a and b). The jaw-closing reflex is considered a fundamental phenomenon of the facial and oropharyngeal areas (Dubner, Sessle and Stoery, 1978) as it utilises afferent and efferent components involved in the generation, learning and modulation of programmed jaw movement sequences. Thus the reflex would appear to form the basis of more complex functions such as mastication and swallowing (Sessle, 1981), although the response itself probably appears only infrequently in normal function. A downwards tap delivered to the chin in a relaxed human subject causes muscle stretch and this produces an afferent projection along group Ia and group II pathways (Figure:1) which in turn exert monsynaptic and polysynaptic influences on motoneurones in the trigeminal motor nucleus. Inter-segmental and suprasegmental projections onto alpha and fusimotoneurones located in this motor nucleus (Greenwood and Sessle, 1976; Sessle, 1977a and b) modulate ongoing motoneurone excitability thus influencing the mainifestation of evoked monosynaptic reflexes.

Master of Dental Surgery / A study of the masticatory apparatus can be divided into the following sections:- Bony structure Teeth and supporting structures Temporomandibular articulation (and ligaments) Muscles of mastication (elevation and depression) Muscles of facial expression and deglutition Neurology Vascular and lymphatic supply This work is concerned with the muscles of mastication and the positions and movements of the mandible for which they are responsible. It is of course impossible to divorce this particular aspect from the others, as they are all completely interdependent, and, in particular, a study of the neurology is essential for an understanding of the function of the muscles of mastication. When all parts of the apparatus are in the correct functional relationship they operate with the greatest efficiency and the least effort. The jaws and neuromuscular system should be in correct relationship to avoid neuromuscular tension and damage to the component parts of the masticatory system.