1,720,963 research outputs found
An Investigation of Experimental Muscle Pain on Neuromuscular Fatigue and Endurance Performance
Full text linkThe determinants of exercise-induced fatigue are a contentious topic within exercise physiology and the limitations to endurance performance are still not fully understood. Exercise-induced pain is often present during high intensity exercise and typically occurs in parallel with exercise-induced fatigue. Therefore, it is possible that exercise-induced pain may be in part responsible for the development of neuromuscular fatigue and be a limitation to endurance performance. Therefore, the purpose of this thesis was to experimentally increase muscle pain and investigate the development of neuromuscular fatigue during endurance exercise. Experimental muscle pain was caused with an intramuscular injection of hypertonic saline into the vastus lateralis whereas an isotonic injection served as the non-painful control.Four experimental studies were conducted for this thesis. The first study aimed to investigate the test-retest reliability of an isometric time to task failure (TTF) of the knee extensors and measures of neuromuscular fatigue. This was to determine if these measures were sufficiently reliable to investigate the effects of pain on fatigue and endurance performance. The second study was to determine the effect of localised muscle pain on the performance of an isometric TTF of the knee extensors and measures of neuromuscular fatigue. Study three was to explore if non-local pain could also affect isometric endurance performance and the development of neuromuscular fatigue. The final study sought to investigate if whole-body, self-paced cycling exercise was also impaired by elevated muscle pain.
The results of study one showed that an isometric knee extensor TTF displayed good reliability displayed by a coefficient of variation = 5.1% [95% CI: 2.9 - 7.3] and standard error of measurement = 21 s. Similarly, measures of neuromuscular fatigue displayed good reliability in the presence of exercise-induced fatigue (all coefficient of variation < 10%). Study two revealed that elevated muscle pain reduced isometric endurance time by 16% and this was due to a reduction in maximal strength and a reduction in voluntary activation (exacerbated central fatigue). Similarly, study three showed that non-local pain can reduce endurance time by 10% due to a decreased voluntary activation. Short duration self-paced cycling exercise remained largely unaffected in the presence of elevated muscle pain and the development neuromuscular fatigue was also unaltered.
In conclusion, muscle pain appears to exacerbate the development of neuromuscular fatigue and impose a significant limitation to single-limb time to exhaustion exercise. However, self-paced exercise appears to be less affected by elevated pain and requires further investigation
Investigating the Neural Control of Muscle Torque Using High-Density Surface Electromyography
Full text linkThe use of high-density surface electromyography (HDsEMG) decomposition presents an opportunity to study the behaviour of individual motor units, the smallest functional components of the neuromuscular system involved in movement. The present thesis aimed to investigate the neural control of muscle torque during isometric exercise of the ankle dorsiflexors in healthy adults using decomposition of the tibialis anterior HDsEMG signal. The first experimental study (Chapter 4) investigated the methodological aspects of HDsEMG signal acquisition including the skin-electrode interface, ground electrode configuration, and decomposition processing criteria. No differences in motor unit yield were observed between skin treatments, and at least four ground electrodes resulted in significant reductions in baseline signal noise. The use of adjusted acceptance criteria during the decomposition process resulted in a greater motor unit yield when compared to the original conditions. Furthermore, the low motor unit yields observed with increasing contraction intensities meant that contractions in subsequent studies were performed below 50% maximal voluntary contraction (MVC). Study 2 (Chapter 5) then investigated the effects of fatiguing intermittent exercise performed with arterial occlusion at 30% MVC on the complexity of muscle torque output and the motor unit cumulative spike train. Reductions in the complexity of the tibialis anterior motor unit cumulative spike train were concomitant with a loss of dorsiflexor muscle torque complexity, indicating an increase in the transmission of common synaptic input relative to independent synaptic input to the muscle as task failure approaches. In Study 3 (Chapter 6), the critical torque concept was extended to the ankle dorsiflexors, and the end-test torque from the 5 min all-out test was compared to the critical torque estimated from the conventional method involving multiple submaximal exercise bouts performed until task failure. The 5 min all-out test overestimated the critical torque compared to the conventional method, and the critical torque of the dorsiflexors was shown to be higher than previously reported for the knee extensors. In the final study (Chapter 7), the performance of 6 min prior heavy-intensity exercise had no discernible effects on tibialis anterior motor unit behaviour, suggesting the 'priming' effects previously observed for the knee extensors are absent in the dorsiflexor muscles. Collectively, the findings of this thesis confirm the dorsiflexors as a highly fatigue-resistant muscle group, and suggest that the findings from HDsEMG studies involving the tibialis anterior are not necessarily generalisable to other muscles (such as the knee extensors)
Complexities of ageing: An investigation of age-group differences in neuromuscular complexity.
Full text linkNeuromuscular complexity quantifies the temporal structure of muscle torque or force signals, providing a non-invasive measure of the neuromuscular system's functionality. Ageing has been identified as a contributing factor to the loss of neuromuscular complexity, proposed to reflect an age-related reduction in neuromuscular function, specifically a reduced capacity to effectively control voluntary muscle contractions. Notable gaps remain in the current understanding of how age influences neuromuscular complexity, particularly in knee extensor (KE) muscles and small hand muscles involved in precision pinch grip (PG) tasks. Additionally, the neurophysiological mechanisms underpinning age-related changes in
neuromuscular complexity are not yet fully understood, and the functional importance of changes in neuromuscular complexity remains unclear. Therefore, the current thesis investigated age-group differences in the complexity of isometric KE torque and precision PG force signals, as well as the neural mechanism(s) underpinning the complexity of isometric muscle torque signals.
Chapter Four assessed the intra- and inter-day reliability of the complexity of isometric KE muscle torque signals in younger and middle-aged adults. The results indicated that measures of complexity exhibit moderate to excellent intra- and inter-day reliability across both age groups. These findings support neuromuscular complexity as a reliable, non-invasive technique for assessing and monitoring age-group related differences in neuromuscular function.
Chapter Five investigated age-group differences in the complexity of isometric KE muscle torque signals at 40% MVT and MVT. No differences in neuromuscular complexity were observed between middle-aged adults (58.6 ± 5.1 years) and younger adults (21.9 ± 3.7 years). However, age-related changes were evident in the temporal organisation of neuromuscular output, suggesting a possible restructuring of neuromuscular control strategies, that maintains motor performance with age.
Chapter Six investigated the effect of contraction intensity on age-group related differences in the complexity of isometric KE muscle torque signals. The study also examined the relationship between neuromuscular complexity and postural sway. Older adults (64.9 ± 11.3 years) demonstrated lower neuromuscular complexity across a range of contraction intensities (10% to 80% MVT) compared to younger adults (22.5 ± 3.4 years), with the most pronounced age-group related differences occurring above 20% MVT. These findings suggest that impairments in muscle torque regulation in older age are exacerbated at higher contraction intensities. Additionally, lower neuromuscular complexity was associated with greater postural sway, highlighting the potential functional relevance of complexity.
Chapter Seven investigated age-group differences in the neuromuscular complexity of isometric precision PG force signals. Adults over the age of 70 years exhibited lower neuromuscular complexity than younger adults, aged 18 to 30 years. However, no differences in neuromuscular complexity were observed between younger adults and those aged 50 to 70 years. These findings suggest that measurable changes in hand muscle force regulation begin to emerge in the eighth decade of life, providing insight into the potential time course of age related changes in hand muscle neuromuscular function.
Chapter Eight investigated the neural mechanism(s) that may underpin the complexity of isometric KE muscle torque signals. Chapter 8A investigated the association between the strength of common synaptic input to the motor neuron pool of the vastus lateralis muscle and the complexity of isometric KE torque in adults aged between 18 and 90 years. Stronger alpha
frequency band oscillations in common synaptic input were found to be associated with higher complexity isometric KE torque signals. Chapter 8B investigated whether fatigue-related changes in the strength of common synaptic input to the motor neuron pool could explain fatigue-related changes in isometric KE torque complexity. Fatigue-related changes in the strength of alpha band oscillations in common input accounted for a significant percentage of the fatigue-related changes in isometric KE torque complexity. These findings suggest that the complexity of isometric muscle torque is attributable, in part, to the strength of oscillations in common synaptic input (an adaptive neural response) and is therefore indicative of the neuromuscular system's strategy to adapt muscle torque to meet task demands.
In conclusion, the thesis demonstrates that older adults exhibit lower neuromuscular complexity in both lower and upper extremity muscle groups compared to younger adults. The observed age-related differences in neuromuscular complexity were likely attributable, in part, to alterations in the strength of oscillations in common synaptic input. These findings highlight the potential of neuromuscular complexity as a reliable, functionally relevant, non-invasive biomarker for assessing and monitoring age-related changes in aspects of neuromuscular system function
Exploring the relationships between terrain, structural foot morphology, and adaptive foot morphology
No full textThe arch of the foot is considered a principal element of the structure and function of the foot, and its claimed causative relationship with injuries has been commonly researched. The impact of terrain (Natural and Developed) on the development of the arch has not yet been clearly researched and could be a critical part in the structure-function-injury discussion. Collecting postcodes and Foot Flexibilities (FF) from a range of participants and data gathered using smart insoles allowed for relationships between terrain, foot structure, dynamic response, and the biophysics of the foot to be examined.
Young participants growing up on a Natural terrain were found to have a more flexible arch; however, the same was not observed in an adult population. High FF feet and low FF feet did not yield significantly different values for walking characteristics, nor did they show a difference in adaptability to walking on varying terrains. Moreover, no correlations could be found between FF and walking characteristics. It was found, however, that the dynamic response of the foot differs between varying terrains. Few correlations were observed between terrains per walking characteristic, and the characteristics themselves did not appear interrelated either. Lastly, it was shown that a more deforming arch stores more energy than a rigid arch.
Terrain has been shown to influence the foot structure of a developing foot, but a standardised protocol to classify terrains is required to observe this trend consistently. Pronation was often found to be the outlier in general trends, facilitating development of the theory that pronation is inherent to the foot, undecided by environmental factors or correlated to certain intrinsic classifications. The vertical displacement of the arch was found to be the main cause of higher energy storage in flexible arches, although calculations leading to this observation were based on simplifications of the mechanisms
Exploring the Psychopysiological Indices of Perceived Effort and its Self-Regulation
Full text linkEffort involves the application of physical and mental resources towards a task. Individuals perceive effort during task engagement like exercise with a conscious sensation of how hard, heavy, and strenuous the exercise consciously feels to drive the working muscles and for breathing. Accordingly, individuals' decisions are thought to be guided by their perceived effort. In turn, there are numerous psychophysiological characteristics that underpin the perceived effort phenomenon which can also play a role in the overall decision-making processes and self-regulation of behaviour. However, it is often difficult to capture the underlying mechanisms of decision-making processes due to their erratic and complex nature. Consequently, there is scant literature on the psychophysiological indices of set perceived effort intensities and underlying decision-making processes during self-regulation of perceived effort. Yet, a small sample of studies have demonstrated that concurrent mixed-methods/process-tracing approaches can delve more into complex decision-making processes involved with regulating perceived effort and exercise behaviour. Subsequently, the main aim of the present thesis was to explore the psychophysiological indices of perceived effort and its self-regulation.
This thesis comprises three separate studies. In Study 1, the reliability of a novel fixed perceived effort cycling task was investigated. Results demonstrated that a novel fixed perceived effort trial that corresponded ratings of perceived effort to a known physiological threshold was reliably produced over numerous bouts and elicited a consistent psychophysiological response for each perceived effort intensity. A following study (Study 2, Part A) also probed the psychophysiological responses associated with two intensities of fixed perceived effort. During these studies it appeared that physical outputs at a set perceived effort intensity would decrease over time to maintain the same perception of effort. Meanwhile, certain psychophysiological markers showed characteristic increases (e.g., heart rate) or decreases (e.g., affective valence) as the fixed perceived effort exercise progressed. As a result, specific intensities of perceived effort appear to exhibit different power output and psychophysiological responses in terms of magnitude and changes over time. This could possibly then be linked to different ways that perceived effort is self-regulated.
It was also of interest how individuals self-regulated during fixed perceived effort exercise. To achieve this, Study 2 utilised a think aloud protocol to understand the behavioural and cognitive self-regulatory strategies that were used by participants at different fixed perceived effort intensities (Part A) as well as any differences in self-regulation between experienced and inexperienced cyclists (Part B). Within Part A, it was found that there was a greater change in power output during the higher intensity fixed perceived effort cycle, signifying a greater amount of behavioural self-regulation. Furthermore, the activation of cognitive strategies was also greater in the higher intensity fixed perceived effort task. When assessing differences between experience levels of participants, there were no significant differences in power output or major secondary themes of the think aloud protocol suggesting participants of any experience level may self-regulate perceived effort similarly. However, closer examination of the primary themes from the think aloud data suggest experience level may affect the cognitive self-regulatory strategies that are used during a prolonged fixed perceived effort intensity exercise.
Finally, this thesis then explored any changes in self-regulation of perceived effort after an intervention which involved experimentally induced muscle pain. In addition, this study also incorporated the use of functional near infrared spectroscopy to assess the cognitive effort applied to activate cognitive self-regulation strategies during fixed perceived effort exercise. It was found that the presence of elevated muscle pain due to an intramuscular hypertonic saline injection cause a significantly lower power output than an isotonic placebo-control condition. In addition, near infrared spectroscopy data showed a greater change in deoxyhaemoglobin between condition suggesting a greater use of cognitive self-regulatory strategies as part of executive function when experiencing elevated muscle pain compared to a placebo-control.
Overall, this thesis firstly found a novel fixed perceived effort exercise to be reliable. Using this task paradigm, additional studies show that specific intensities of perceived effort seem to elicit different power output and psychophysiological responses in terms of magnitude (e.g., higher/lower between intensities) and changes over time (condition x time interactions). Subsequently, data concerning the self-regulation of perceived effort shows that participants employ a mixture of behavioural (i.e., changing power output) and cognitive (i.e., engaging in reappraisal and/or self-talk) strategies to self-regulate perceived effort. In addition, there was a difference in self-regulatory strategies between conditions which involved elevated muscle pain (hypertonic saline injection) or a no elevated muscle pain (isotonic saline injection). Therefore, the self-regulation of perceived effort is likely context dependent and there are also likely to be some individual preferences towards how perceived effort is self-regulated
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The use of a self-paced cardiopulmonary exercise test in the pre and post-operative care of patients with cardiovascular disease
Full text linkThe aim of this thesis was to assess the ability of a self-paced (SPV) cardiopulmonary exercise test (CPET) in assessing patient fitness prior to elective surgery, and its ability to predict postoperative outcomes. The SPV is a 10 minute test which is comprised of 5 × 2 minute stages. Each stage is fixed to a level on the ratings of perceived exertion (RPE) scale, in an incremental format (RPE: 11, 13, 15, 17 and 20). This test eliminates the need of practitioners having to choose the most appropriate work rate increments to ensure a patient reaches volitional exhaustion within the recommended time period (8-12 min).
Study 1 aimed to assess the reliability of the maximal exercise test parameters obtained from the SPV. Twenty-five (12 females, 13 males) healthy participants completed three SPV tests on three separate occasions. Results demonstrated a coefficient of variation (CV) for V?O2peak (ml·kg-1·min-1) of 4.2% (95% CI: 3.4-5.6%) for trials 2-1, and 5.1% (95% CI: 4.2-6.8%) for trials 3-2. Repeated measures ANOVA analysis demonstrated no significant difference in V?O2peak across the repeated tests (p > 0.05). The limits of agreement (LOA) were ± 5.59 ml·kg-1·min-1 for trials 2-1, and ± 5.86 ml·kg-1·min-1 for trials 3-2. The mean intraclass correlation coefficient (ICC) was 0.95, which represents good reproducibility. It was concluded that the SPV is a reliable indicator of the main CPET derived variables in a healthy population, with comparable values to previous work on standard CPET protocols.
Study 2 investigated the physiological responses between the SPV and a standard CPET (sCPET) protocol between a young (18-30 years) and a middle aged to older adult (50-75 years) population. This was in the attempt to gain an understanding of the response to the protocol and whether these responses differ with age. Expired gases, Q, SV, muscular deoxyhaemoglobin (deoxyHb) and electromyography (EMG) at the vastus lateralis were recorded throughout both tests. Results demonstrated a significantly higher V?O2max in the SPV (49.68 ± 10.26 ml·kg-1·min-1) vs. a sCPET (47.70 ± 9.98 ml·kg-1·min-1) in the young, but no differences in the middle aged to older adult group (> 0.05). Q and SV were significantly higher in the SPV vs. a sCPET in the young ( 0.05). No differences were seen in both age groups in the deoxyHb and EMG response (> 0.05). Findings from this study suggest that in the young group, the SPV produces higher V?O2max values as a result of an increase in oxygen delivery (enhanced Q). However, likely due to age-related differences, particularly in the cardiovascular response to exercise, the middle aged to older adult group achieved similar V?O2max values regardless of them reaching a higher physiological workload.
Study 3 aimed to assess the validity and reliability of the SPV in post myocardial infarction (post-MI) patients, this was the first study to assess the use of the SPV in a clinical population. Twenty-eight post-MI patients completed one sCPET and two SPVs in a randomised, counterbalanced crossover design. Each patient completed one sCPET and two SPVs. Results demonstrated the SPV to have a coefficient of variation for V?O2peak of 8.2%. The limits of agreement were ± 4.22 ml·kg-1·min-1, with intraclass correlation coefficient of 0.89. There was a significantly higher V?O2peak achieved in the SPV (23.07 ± 4.90 ml·kg-1·min-1) against the sCPET (21.29 ± 4.93 ml·kg-1·min-1). It was concluded that the SPV is a safe and valid test of exercise capacity in post-MI patients, with acceptable levels of reliability when compared to previous work on sCPET protocols.
Study 4 aimed to determine if the SPV can assess patient's preoperative risk similar to sCPET and if exercise variables obtained from the test can accurately predict post-operative outcome. Fifty patients with cardiovascular related co-morbidities completed one sCPET and one SPV, although only thirty of those patients when ahead with surgery. Post-surgery, patients were monitored for incidence of morbidity on postoperative days 3 and 5, length of hospital stay, and incidence of mortality in the 30 days after surgery. Patients achieved a significantly higher V?O2peak, HR, V?E, peak PO and TTE in the SPV compared to the sCPET (P 0.05). Although when combining postoperative morbidity at days 3 and 5, logistic regression analysis showed that oxygen pulse at AT obtained from the SPV was significantly related to postoperative complications (P < 0.05). ROC curve analysis demonstrated oxygen pulse at AT to provide an AUC of 0.72 a.u. (95%CI 0.51 to 0.92), with an optimal cut-off point of 8.5 ml/beat-1 which provided 72.7% sensitivity and 71.4% specificity. It was concluded that the SPV was able to assess preoperative fitness comparable to the sCPET. Although none of the CPET variable from either test were associated with postoperative morbidity, which is likely a result of the small sample size.
The conclusion for this thesis is that a self-paced CPET test is able to reliably assess cardiovascular patient's fitness comparable to traditional methods. This type of test may be seen as advantageous, this is because the SPV takes away the need of clinicians having to choose the most appropriate work rate increments, it allows patients to have full control over the test, and it ensures that regardless of fitness all patients will be exercise for the recommended test time. The fixed test duration of 10 minutes may also help to improve the efficiency of running busy CPET clinics. There are clear benefits to using the SPV, although further research is required first to assess its ability of predicting postoperative outcome in a much larger sample, and to determine if it can be used to the same advantages sCPET protocols have previously demonstrated
An investigation into the test-retest reliability of the pain response to hypertonic saline injections and the impact of added muscle contraction
Full text linkBackground/Aims: Intramuscular Hypertonic Saline (HS) injections induce pain that resembles exercise-induced pain. The reliability and the impact that parallel exercise may have on this pain sensation is unestablished. Therefore, the aims of this research were to assess the test-retest reliability of this model's pain response and the influence of additional muscle contractions to the pain experience, in terms of both Pain Intensity (PI) and Pain Quality (PQ). Methodology: 8 male and 6 female participants (25 ± 5 years, 172.9 ± 8.5 cm, 71.9 ± 12.7 kg) completed the two studies. Study 1.1 assessed test-retest reliability with 3 separate visits, in which 1 ml of 5.85% HS was injected into the right vastus lateralis and differences in PI and PQ were measured. In Study 1.2, participants attended 3 separate visits, where they completed an isometric exercise task with 3 separate 10-second contractions at different intensities (10%/15%/20%). This was done with either HS, a placebo or no injection as control. Results: Study 1.1: Intraclass Correlation Coefficient scores for all PI measures indicated at least 'moderate' to 'good' test-retest reliability (0.68 - 0.814). Cronbach's Alpha scores for all PQ measures indicated 'acceptable' to 'good' test-retest reliability (0.806 - 0.933), except for the affective dimension (0.397 - 0.601). Study 1.2: Paired samples t-tests revealed no differences between exercise and rest, for any of the PI measures or PQ measures, except for the Present Pain Index (PPI) of the Long-form McGill Pain Questionnaire (P = 0.048). ANOVA analyses revealed no differences in PI or PQ measures between contraction intensities. Discussion: In Summary, HS provides a 'moderate' to 'good' reliable pain response, except for the affective dimension of pain. PI response is not affected by the addition of exercise or exercise intensity. PQ response is only affected in terms of different descriptive words, when exercise is introduced
Physical Therapists' and Fitness Professionals' Perceptions of Stretching in their Professional Practice
Full text linkDespite the central role of mobility and flexibility in daily function and injury rehabilitation, the impact and clinical applications of stretching remain poorly understood. Existing research has largely concentrated on stretching's effects on athletic performance or injury outcomes, rather than its use and interpretation by practitioners. This thesis adopts phenomenological and self-reflexive methodologies to explore how the lived experiences of physical therapists and fitness professionals shape their perceptions and implementation of stretching. An Interpretative Phenomenological Analysis (IPA) was employed to identify and interpret themes arising from these lived experiences
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