Quantification of Extent of Muscle-skin Shifting by Traversal sEMG Analysis Using High-density sEMG Sensor

Averaging electromyographic activity prior to muscle synergy computation is a common method employed to compensate for the inter-repetition variability usually associated with this kind of physiological recording. Capturing muscle synergies requires the preservation of accurate temporal and spatial information for muscle activity. The natural variation in electromyography data across consecutive repetitions of the same task raises several related challenges that make averaging a non-trivial process. Duration and triggering times of muscle activity generally vary across different repetitions of the same task. Therefore, it is necessary to define a robust methodology to segment and average muscle activity that deals with these issues. Emerging from this need, the present work proposes a standard protocol for segmenting and averaging muscle activations from periodic motions in a way that accurately preserves the temporal and spatial information contained in the original data and enables the isolation of a single averaged motion period. This protocol has been validated with muscle activity data recorded from 15 participants performing elbow flexion/extension motions, a series of actions driven by well-established muscle synergies. Using the averaged data, muscle synergies were computed, permitting their behavior to be compared with previous results related to the evaluated task. The comparison between the method proposed and a widely used methodology based on motion flags, shown the benefits of our system maintaining the consistency of muscle activation timings and synergie

Quantification of Extent of Muscle-skin Shifting by Traversal sEMG Analysis Using High-density sEMG Sensor

Surface electromyography(sEMG) measurement has been an essential approach to analyze human behaviors because we can generally consider that sEMG signals represent the muscle activities as the final output of our nerve system. One of the most serious problems for considering sEMG signal as the muscle activity is the shift of the relative position between muscles and skin depending on a posture. The motion of forearm rotation is the prominent example of muscle-skin shifting depending on postural changes. The sEMG signal from a sensor may represent the different muscle activity when the muscle-skin shifting is happened. In this study, we discuss a method to quantify the muscle-skin shift from the sEMG signals in response to the postural changes. We use the high density sEMG sensor that is possible to measure sEMG signal as the potential map. We proposed the computation algorithm to quantify the amount of muscle-skin shifting based on the change of the sEMG signals in response to the postural changes. We conducted the experiments of wrist extension motions under three different forearm postures: forearm pronation, natural posture and forearm supination. Experimental results from three healthy subjects show that we can quantify the extent of muscle-skin shifting as an angle by using proposed algorithm

Acute neuromuscular, kinetic, and kinematic responses to accentuated eccentric load resistance exercise

Neurological and morphological adaptations are responsible for the increases in strength that occur following the completion of resistance exercise training interventions. There are a number of benefits that can occur as a result of completing resistance exercise training interventions, these include: (i) reduced risk of developing metabolic health issues; (ii) decreased risk and incidence of falling; (iii) improved cardiovascular health; (iv) elevated mobility; (v) enhanced athletic performance; and (vi) injury prevention. Traditional resistance exercise (constant load resistance exercise (CL)) involves equally loaded eccentric and concentric phases, performed in an alternating manner. However, eccentric muscle actions have unique physiological characteristics, namely greater force production capacity and lower energy requirements, compared to concentric actions. These characteristics have led to the exploration of eccentric-focused resistance exercise for the purposes of injury prevention, rehabilitation, and enhancement of functional capacity. Accentuated eccentric load resistance exercise (AEL) is one form of eccentric-focused resistance exercise. This type of resistance exercise involves a heavier absolute external eccentric phase load than during the subsequent concentric portion of a repetition. Existing training study interventions comparing AEL to CL have demonstrated enhancements in concentric, eccentric, and isometric strength with AEL. However, no differences in strength adaptations have been reported in other AEL vs. CL training studies. Only 7 d intensified AEL training interventions have measured neuromuscular variables, providing evidence that enhanced neuromuscular adaptations may occur when AEL is compared to CL. Therefore, a lack of information is currently available regarding how AEL may differentially affect neuromuscular control when compared to CL. Furthermore, the equivocal findings regarding the efficacy of AEL make it difficult for exercise professionals to decide if they should employ AEL with their athletes or patients and during which training phase this type of resistance exercise could be implemented. Therefore, the aims of this thesis were: (i) to examine differences in acute neuromuscular, kinetic, and kinematic responses between AEL and CL during both lower-body single-joint resistance exercise and multiple-joint free weight resistance exercise; (ii) to assess acute force production and contractile characteristics following AEL and CL conditions; (iii) to investigate the influence of eccentric phase velocity (and time under tension) on acute force production and contractile characteristics following AEL and CL conditions; and (iv) to compare common drive and motor unit firing rate responses after single- and multiple-joint AEL and CL. Before investigating neuromuscular, kinetic, and kinematic responses to AEL it was deemed necessary to evaluate normalisation methods for a multiple-joint free weight resistance exercise that would permit the implementation of AEL. Therefore, the aim of the first study of the thesis was to evaluate voluntary maximal (dynamometer- and isometric squat-based) isometric and submaximal dynamic (60%, 70%, and 80% of three repetition maximum) electromyography (EMG) normalisation methods for the back squat resistance exercise. The absolute reliability (limits of agreement and coefficient of variation), relative reliability (intraclass correlation coefficient), and sensitivity of each method was assessed. Strength-trained males completed four testing sessions on separate days, the final three test days were used to evaluate the different normalisation methods. Overall, dynamic normalisation methods demonstrated better absolute reliability and sensitivity for reporting vastus lateralis and biceps femoris EMG compared to maximal isometric methods. Following the methodological study conducted in Chapter 2, the next study began to address the main aims of the thesis. The purpose of the third chapter of the thesis was to compare acute neuromuscular, kinetic, and kinematic responses between single-joint AEL and CL knee extension efforts that included two different eccentric phase velocities. Ten males who were completing recreational resistance exercise attended four experimental test day sessions where knee extension repetitions (AEL or CL) were performed at two different eccentric phase velocities (2 or 4 s). Elevated vastus lateralis eccentric neuromuscular activation was observed in both AEL conditions (p= 0.004, f= 5.73). No differences between conditions were detected for concentric neuromuscular or concentric kinematic variables during knee extension efforts. Similarly, no differences in after-intervention rate of torque development or contractile charactersitics were observed between conditions. To extend the findings of the third chapter of the thesis and provide mechanistic information regarding how AEL may differentially effect acute neuromuscular variables that have been reported to be undergo chronic adaptations, additional measures that were taken before and after the intervention described in the previous chapter were analysed. Therefore, the purpose of the fourth chapter of the thesis was to compare motor unit firing rate and common drive responses following single-joint AEL and CL knee extension efforts during a submaximal isometric knee extension trapezoid force trace effort. In addition, motor unit firing rate reliability during the before-intervention trapezoid force trace efforts was assessed. No differences in the maximum number of detected motor units were observed between conditions. A condition-time-point interaction effect (p= 0.025, f= 3.65) for firing rate in later-recruited motor units occurred, with a decrease in firing rate observed in after-intervention measures in the AEL condition that was completed with a shorter duration eccentric phase. However, no differences in common drive were detected from before- to after-intervention measures in any of the conditions. The time period toward the end of the plateau phase of before-intervention trapezoid force trace efforts displayed the greatest absolute and relative reliability and was therefore used for motor unit firing rate and common drive analysis. The purpose of the fifth chapter was to compare acute neuromuscular and kinetic responses between multiple-joint AEL and CL back squats. Strength-trained males completed two experimental test day sessions where back squat repetitions (AEL or CL) were performed. Neuromuscular and kinetic responses were measured during each condition. No differences in concentric neuromuscular or concentric kinetic variables during back squat repetitions were detected between conditions. Elevated eccentric phase neuromuscular activation was observed during the AEL compared to the CL condition in two to three of the four sets performed for the following lower-body muscles: (i) vastus lateralis (p< 0.001, f= 15.58); (ii) vastus medialis (p< 0.001, f= 10.77); (iii) biceps femoris (p= 0.003, f= 6.10); and (iv) gluteus maximus (p= 0.001, f= 7.98). There were no clear differences in terms of the neuromuscular activation contributions between muscles within AEL or CL conditions during eccentric or concentric muscle actions. Following the investigation of acute motor unit firing rate and common drive responses to lower limb single-joint AEL and CL in the fourth chapter of the thesis, the question arose as to whether or not similar responses would occur in a more complex model, such as a multiple-joint resistance exercise. Multiple-joint resistance exercise poses different neuromuscular activation, coordination, and stabilisation demands. Therefore, the purpose of the sixth chapter of the thesis was to compare acute motor unit firing rate and common drive responses following multiple-joint lower-body free weight AEL and CL. In addition, motor unit firing rate reliability during the before-intervention trapezoid force trace efforts, performed on a custom-built dynamometer, was assessed. No differences in motor unit firing rate or the number of motor units detected were observed between conditions. Condition-time-point interaction effects were observed for maximum peak cross-correlation coefficients (p= 0.028, f= 8.24), with a decrease from before to after intervention measures in the CL condition. However, differences in mean peak cross-correaltion coefficients and cross-correlation histogram distributions were not detected between conditions. As in Chapter 4 the time period toward the end of the plateau phase of before-intervention trapezoid force trace efforts displayed the greatest absolute reliability and was therefore used for motor unit firing rate and common drive analysis. Whereas, relative reliability was shown to be “poor” across all time phases. The results of the studies that comprise this thesis contribute new knowledge to the AEL research literature. In particular, the way that motor unit recruitment strategy responses were investigated following interventions provided new information regarding the acute neuromuscular effects of AEL and a new potential approach to investigating the hypothesised similarities between motor learning and resistance exercise. Previously, only transcranial magnetic stimulation had been used for this purpose. However, the contrasting motor unit firing rate and common drive response results of Chapter 4 and 6 of the thesis indicate further research is required to ascertain how acute measures quantified through the decomposition of surface EMG (such as motor unit firing rate and common drive) are related to chronic neuromuscualr adaptations following resistance exercise. The findings presented in the thesis also add to the existing body of AEL research literature by providing practitioners with novel data regarding the acute neuromuscular, kinetic, and kinematic responses during AEL. The results presented in Chapter 3 and 5 of the thesis suggest that AEL resistance exercise implemented in both single- and multiple-joint resistance exercise models presents no negative acute variable responses. Neither of the AEL models investigated acutely reduced concentric kinetic outputs, decreased neuromuscular contributions or activation from key agonist muscles during concentric or eccentric phases, or caused after-intervention lower-body force production or contractile characteristics to decline more than following CL. In addition, both AEL models involved greater eccentric phase knee extensor muscle contributions compared to CL. Therefore, given these findings exercise professionals who prescribe training interventions may want to consider the use of AEL depending on the characteristics and training goals of the individuals they work with. Despite these encouraging acute neuromuscular, kinetic, and kinematic responses to AEL further research is clearly required to confirm the efficacy of AEL on a longitudinal basis. Specifically, the efficacy of AEL for the concurrent enhancement of both chronic concentric and eccentric knee and hip extensor strength, eliciting chronic neuromuscular adaptations in these muscles, and preventing injury in a range of populations remains unclear

The role of cardiopulmonary exercise testing for identifying possible silent myocardial ischaemia in people with coronary heart disease

This thesis investigates the utility of cardiopulmonary exercise testing (CPET) in assessing and managing patients with coronary artery disease (CAD), particularly focusing on the significance of oxygen pulse (O2Pulse) inflections as a marker for myocardial ischemia. The research encompasses a comprehensive analysis of O2Pulse morphology, inflection point identification, and the impact of exercise-based cardiac rehabilitation (exCR) programs, specifically high-intensity interval training (HIIT) and moderate-intensity steady-state (MISS) training, on patients with CHD.Chapter 3 examines the reliability of CPET in detecting suspected myocardial ischemia through O2Pulse and ΔV̇O2/ΔWR inflections in chronic total occlusion (CTO) patients. This study was considerable hampered by poor recruitment and the outbreak of COVID-19. Subsequently only four patients were enrolled, three of whom exhibited no inflections in O2Pulse. In the one patient who did have O2Pulse inflections they occurred at similar work rates (10W) and heart rates (5bpm). Chapter 5 extends the inquiry into the short-term reliability and agreement of O2Pulse curve parameters in a healthy cohort demonstrating that the mean percent minimal detectable change for filtered O2Pulse was 13.5 ± 3.2. Building on these findings, Chapter 6 evaluates the inter- and intra-rater reliability in identifying O2Pulse inflections, comparing subjective assessments with an objective algorithmic method. Almost perfect agreement between the algorithm and human raters was demonstrated, with a Fleiss’ Kappa statistic of 0.89. Chapter 7, a subset analysis from the HIIT or MISS UK trial, delves into the rate of O2Pulse inflections in outpatient cardiac rehabilitation (16%) and how different exercise interventions affect O2Pulse inflections in CAD patients.The results highlight a considerable potential for CPET, particularly O2Pulse inflections, in the diagnosis, treatment, and management of CAD. The research underscores the potential reliability of O2Pulse as a diagnostic tool, the effectiveness of exCR in improving cardiopulmonary fitness, and the relevance of O2Pulse inflections as a surrogate marker for myocardial ischemia. The findings suggest that both HIIT and MISS can positively influence O2Pulse inflections, offering a non-invasive means to monitor and potentially improve the health outcomes of CAD patients.This thesis contributes to the understanding of CPET in clinical settings, advocating for its broader application in cardiac rehabilitation. It identifies areas for further research, including the exploration of different exercise modalities, to optimize exCR programs and enhance patient care