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The factors that limit human endurance have received extensive scientific scrutiny. Traditionally these limiting factors have been attributed to physiological processes occurring within the muscles, the cardiovascular system, or spinal and supraspinal sites. Consequently, interventions designed to provoke alterations in endurance performance are generally tailored towards targeting these physiological processes. Recent research suggests that endurance performance is also limited by psychobiological influences: specifically perception of effort (RPE). On this basis the psychobiological model of endurance performance predicts that any physiological or psychological factor affecting RPE will alter endurance performance. As such, this thesis sought to elicit alterations in RPE, and consequently physical endurance, using psychobiological strategies that were implemented to directly target RPE. In Chapter 2 it was established that a two week motivational self-talk intervention significantly reduced RPE at 50% iso-time while enhancing cycling time to exhaustion (TTE) by 18%. This equated to a very likely beneficial practical effect on TTE (beneficial/trivial/harmful%; 99/1/0%). In Chapter 3, a six week cognitive training protocol was designed to repeatedly target the anterior cingulate cortex due to its neuro-cognitive connections with cognitive and physical effort. This approach did not significantly alter RPE or TTE at exercise intensities of 80% or 65% peak power output (PPO). A likely beneficial practical effect on TTE was nonetheless evident at 65% PPO (83/15/2%). Using subliminal affective priming in Chapter 4, RPE was significantly lower and TTE significantly greater when participants were subliminally primed with happy faces while cycling compared to an alternative visit when they were subliminally primed with sad faces. This difference in TTE was of possible practical value (70/30/0%). Following on from this, Chapter 5 implemented a single subject approach using a randomization tests design and illustrated that subliminally primed action words significantly reduced RPE and enhanced TTE compared to subliminally primed inaction words.

Locomotor muscle fatigue develops during endurance events and it is traditionally thought to limit performance despite no direct experimental evidence in favour of this hypothesis. Similarly, muscle damage is known to limiting strength and power performance, but there was no evidence that it can reduce endurance exercise performance. The aims of this thesis are to investigate the effects of locomotor muscle fatigue and damage on endurance performance and the physiological and perceptual response to exercise. In the first study, we tested the hypothesis that exercise-induced muscle damage can decrease performance during a 30 min running time trial. A significant relative 4%decrease in running performance was showed in subjects with exercise-induced muscle damage. In the second study locomotor muscle fatigue was induced with an eccentric exercise protocol to test its detrimental effect on time to exhaustion during high-intensity constant-power cycling independently of metabolic stress. A significant 15% drop in lower limb strength (compared to baseline) determined a shortening of the time to exhaustion from 750 ± 281 s to 636 ± 278 s. The third study provides a more in depth analysis of the effects of reduced locomotor muscle force per se on the physiological and perceptual response to high intensity endurance exercise. Locomotor muscle fatigue entailed an increase in heart rate, breathing frequency, and perceived exertion despite no change in the metabolic requirements. The same exercise protocol was used in the fourth study to investigate effects of locomotor muscle fatigue on incremental exercise performance and physiological/perceptual responses during cycling at di fferent intensities. Although no changes occurred in the physiological responses to incremental exercise, the 13% decrease in locomotor muscle force determined a 2% decrease in the peak power output (an overall difference of 21 W ) and a significant increase in the perceived leg effort. Overall, our findings show that both locomotor muscle fatigue and damage significantly and reliably impair endurance exercise performance between 10 and 30 minutes. However, the effects of increased central motor command to weaker locomotor muscles on cardiorespiratory responses seem to be dependent upon the degree of strength loss and the intensity of exercise. Finally, perception of effort is augmented by locomotor muscle fatigue and damage, and provides the most plausible explanation for the curtailment of endurance performance.

Biomechanical testing has been the cornerstone of sports bra research to date and the quantification of breast kinematics during exercise has received increasing interest. However, comparatively little research has been published regarding the development of biomechanical testing methodology and how this testing may inform the development of sports bra design. Thus, the overall research aim was the 'Development and application of methods used in the biomechanical assessment of sports bra performance with the end goal of better biomechanical tools for use in the sports bra design process'. Breast kinematics are typically measured relative to the torso, therefore, it is necessary to track both torso and breast motion. The absence of a universally accepted torso tracking model, and information regarding the sensitivity of breast kinematics to the selected torso model were identified as limitations to the existing research. The seven marker torso tracking model presented is the first to be specifically developed for analysing relative breast motion during activities such as treadmill running and is recommended to be implemented in future sports bra research. The torso segment used to calculate relative breast kinematics is assumed to be rigid, however, breast movement resulting from respiration has been reported for a static condition. The effect of breathing on breast kinematics during treadmill running was investigated. Significant differences were observed in the breast kinematics between breathing and non-breathing conditions, notably in the superior-inferior direction; however, they could not definitively be directly linked to breathing since significant differences in running gait were also observed. The results do suggest that increasing the number of gait cycles analysed may reduce any effects of breathing on breast kinematics due to phase-locking, the synchronisation of breathing with running locomotion. Analysing breast kinematics over 30 gait cycles may help minimise any potential effects of phase-locking across all commonly used phase-locking ratios. Further understanding of breast motion and whether markers placed on the bra represent the underlying breast were identified as pertinent to advancing biomechanical assessment of sports bra performance. Motion between the breast and bra (either during an initial bedding in phase or steady state running) has yet to be explored within the existing literature and is assumed to be negligible for a correctly fitted bra. A settling in period of ~30 seconds between the breast and bra was found to occur during the initial phase of treadmill running. Whilst the study is recognised to be exploratory in nature, the findings suggest future breast kinematic study should consider the possibility of a settling in effect. Therefore, experimental protocols may benefit from including a short period of activity after the subject has changed into the bra to help eliminate any settling in effect prior to data capture or application of over bra markers. The results also suggest that motion occurs between the breast and bra irrespective of bra size and that over bra markers underestimate superior-inferior (S-I) breast displacement and anterior-posterior (A-P) displacement at the upper breast. Markers positioned over the bra were found to be less sensitive to variation in A-P and S-I displacement in different regions of the breast. However, use of under bra markers is limited by current motion capture technology and until advances in technology are made the use of over bra markers remains current best practice. Future studies are recommended to state whether breast markers were located over or under the bra and recognise that over bra markers represent bra motion. Bra strap stiffness was identified as a potentially important factor in sports bra performance. The effect was investigated using a modified bra with removable strap sections of three differing stiffness. Bra strap mechanical properties were characterised using a specifically developed tensile testing protocol. Sports bra performance during treadmill running was assessed using biomechanical and perceptual measures. Increasing bra strap stiffness was found to improve sports bra performance with respect to bra kinematics (primarily in the superior-interior direction) and subjective perception ratings (in particular the perception of support), suggesting strap stiffness may have an important role to play in bra design.

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This mixed methods study, conducted in four sections, examined a number of key areas in relation to dentofacial discrepancy and orthognathic treatment: Chapter 1: Pre-treatment psychological characteristics of orthognathic patients This was a cross-sectional study using validated questionnaires to assess the pre-treatment psychological profile, personality, quality of life, and perceptions of appearance of 68 orthognathic patients. These factors were compared with normative values and significant differences were found between the patients and normative population for several psychological traits. Chapter 2: Impact, motivations, and expectations in relation to orthognathic treatment: A qualitative study This was a qualitative study exploring the impact of dentofacial deformity, orthognathic patients’ motivations for, and expectations of, treatment. Data were collected from 18 pre-treatment patients using in-depth interviews and these were analysed using the Critical Qualitative Theory method. The full range of impacts, motivations, and expectations was analysed and reported, together with a clinically useful typology of patients based on expectations. Chapter 3: Social anxiety in orthognathic patients This study involved assessing social anxiety in orthognathic patients. The Brief Fear of Negative Evaluation Scale was used. As no UK normative data existed, initially a national survey was conducted of a random sample of 1196 individuals from the general UK population to establish norms for social anxiety with which to compare the cohort of 61 pre-treatment orthognathic patients. The results revealed that orthognathic patients had significantly higher levels of social anxiety than the general population. Chapter 4: Shared decision-making in orthognathic treatment There is increasing evidence that the extent to which patients are involved in their treatment decisions may affect outcomes. In this study, the extent to which clinicians involved 61 orthognathic patients in treatment decision-making was assessed using the OPTION scale. The results revealed overall low levels of shared decision-making and reasons for this are discussed.

Foot friction blisters are one of the most common dermatological injuries experienced by those actively involved in outdoor physical pursuits. The frictional interaction between the human skin and textile fabric is acknowledged as being an important aspect in blister development. Despite growing research in this area, relatively little is known about the friction interaction between plantar skin and textiles. The ultimate aim of this thesis is to achieve enhanced understanding of the complex tribological interactions between human plantar skin and sock textiles. The first part of this thesis primarily focusses on experimental studies conducted on the sock-insole and skin-sock interfaces. Due to the lack of existing standard testing protocols, novel testing protocols were developed and used as a standard testing procedure throughout the experimental studies. The friction study on the entire plantar region was conducted in dry textile conditions whereas the friction study on the plantar aspect of the first metatarsal head (1MTH) was carried out in three significantly different moisture conditions (dry, low moisture and wet). Findings gained from a friction study on the 1MTH region of the foot were then used for validations in the second half of this thesis which concerns the development of a range of prototype biofidelic test-beds to mimic the frictional behaviour of 1MTH region. A set of prototype biofidelic test-beds were developed after considering the appropriate geometry, materials and manufacturing processes. Each test-bed is a two-layer polymer-based physical skin model, with the outer layer representing the epidermal dermal tissue and the inner layer representing the dermal subcutaneous tissues. A steel hemisphere was also embedded within the test-bed to simulate the 1MTH bone. Nine test-beds of differing inner Young’s modulus were made with four of them having texture on their surface layer, obtained from a mould of an actual human foot. All test-beds were subjected to deformation and friction tests in order to validate their performances in the respective aspects, when compared with data obtained from human testing. It is hoped that the understanding gained from the study will close the gaps in the existing knowledge of plantar skin – sock textile friction which can be applied into future foot friction blister studies.

Kyphoscoliosis peptidase (KY) is a Z-disc protein essential for muscle maintenance and its absence underlies a unique type of muscular dystrophy in humans and mice (1–3). The function of KY remains uncharacterised, thus there is limited understanding about the mechanisms underlying the muscle pathology observed due to KY deficiency. Immunoglobulin-like and fibronectin type III domain containing 1 (IGFN1) was identified as a KY interaction partner which in turn interacts with MLK-like mitogen-activated protein triple kinase (MLTK) (4). This thesis aimed to develop further understanding of these interaction partners to gain novel insights into mechanisms of muscle maintenance. In this thesis, the specific interactions between IGFN1_V1 and MLTK isoforms were confirmed for the first time via immunoprecipitation and pull down assays. In addition, MLTKβ is confirmed as the primary isoform in skeletal muscle. The effects of ectopic expression of IGFN1_V1 and MTLK isoforms in mouse skeletal muscle are examined. The Z-disc localisation of these proteins is confirmed, along with nuclear localisation for IGFN1_V1. In addition, expression of IGFN1_V1 drives both ectopically and endogenously expressed MLTKβ to the nucleus. This data shows that the z-disc is the likely site for IGFN1-MLTK interactions, and suggests a function for IGFN1_V1 in the shuttling of MLTKβ to the nucleus. Overexpression of recombinant MLTKβ results in skeletal muscle fibre cross sectional area increases, and some overexpressing fibres showed disorganized myofibrils. Together with the previous finding that overexpression (5) or reduction (6) of MLTKβ causes myofibril disorganization in either cardiac or skeletal muscles, this indicates that a certain expression level of MLTKβ is important for maintaining muscle health. This thesis also describes the generation of IGFN1-deficient mouse myoblasts, which show abnormal differentiation patterns, including short myotube formation and globular differentiation bodies, indicating that IGFN1 is important for regulation of muscle myogenesis.