Anticipatory, Feedforward and Central Regulation of Pacing Strategies in Time Trial Cycling

The aim of this thesis was to directly test the key underpinnings of recent propositions for systems of central control of exercise regulation. Fatigue and exercise tolerance have traditionally been explained through peripheral mechanisms, such as excitation-contraction coupling failure and the inability to supply sufficient metabolic substrate to contracting muscle in order to meet increasing energy demand. More recently, models of central control, which are proposed to regulate exercise intensity in an anticipatory/feedforward manner, with the ultimate aim of avoiding physiological ‘catastrophe’, have received a great deal of attention. This thesis investigated several of the key requirements and mechanisms stated in these models. The central governor model (CGM) and teleoanticipation are stated to use a combination of prior experience and distance knowledge of an exercise bout to work in a feedforward manner, so that a pacing strategy is set before exercise commences which ensures the bout is completed in an optimum time but in the absence of premature fatigue. Study one examined the influence of distance knowledge, prior experience and distance feedback on the setting and regulation of a pacing strategy in 4 km time trial (TT) cycling in trained cyclists (n = 18). When performing 4 × 4 km TT intervals, it was found that prior experience of the exercise (in the absence of distance feedback and distance knowledge) allowed the creation of a pacing strategy that produced a performance which was as competitive as cyclists who were provided with prior experience, distance knowledge and distance feedback. The difference in TT completion time between groups (CON = feedback group, EXP = no feedback group) was reduced with subsequent TT (CON TT1 367 ± 21 s; EXP TT1 409 ± 45 s; CON TT2 373 ± 19 s; EXP TT2 389 ± 30 s; CON TT3 375 ± 18 s; EXP TT3 383 ± 26 s; CON TT4 373 ± 20 s; EXP TT4 373 ± 14 s), so that by the final TT, completion time between groups was almost exactly the same. It was concluded that when sufficient prior experience is attained in the absence of distance knowledge and feedback, a successful pacing strategy can be set. In order for pacing to be set prior to an exercise bout and adjusted in a feedforward/anticipatory manner during exercise, an internal mechanism must exist which monitors the passage of time. Study two examined the accuracy and robustness of this ‘internal clock’ by assessing cyclist’s (n = 16) ability to gauge the distance they had cycled during repeated 4 km and 6 km TT. The internal clock was shown to be inaccurate to absolute measures of distance, but showed a calibration capacity following experience of a TT of unknown distance (24.6 ± 18.2 % error in distance judged completed vs. 8.2 ± 5.5 % error in distance judged completed). This process was fragile and occurred in the absence of any significant performance improvement. It was concluded that relative quantities appear more important in creating a pacing strategy, and that times are of greater importance than distances. Study three examined the influence of comparative performance feedback in a field setting in 4 km track TT cycling in trained cyclists (n = 5). Correct feedback produced a significantly faster TT time (t4 = -3.10, p < 0.05) than non-contingent feedback (341 ± 8 s vs. 350 ± 12 s), with differences in mean lap speed apparent between the conditions at the start of the TT (t4 = 4.71, p < 0.05) and at the end of the TT (t4= 3.45, p < 0.05; t4 = 3.30, p < 0.05). The study provided empirical support for the assumption that performance feedback is advantageous during exercise and provided insights into past and present exercise comparison and its role on the setting of a pacing strategy. A central component of the CGM and theories of central exercise regulation is the role of afferent feedback during exercise and the premature termination of exercise before a true maximum intensity has been reached. Study four used acetaminophen to blunt cyclists’ (n = 13) pain response during ten mile (16.1 km) TT in order to disrupt the afferent feedback processes. When using acetaminophen, cyclists produced significantly faster (t12 = 2.55, p 0.05) or pain scores (F1,12 = 0.30, p > 0.05). It was concluded that acetaminophen reduced levels of pain during the TT, thereby disrupting the comparative afferent feedback mechanism and allowing cyclists access to a ‘metabolic reserve’. The research presented has advanced our knowledge and supported propositions of models of central control and regulation during exercise. The research has provided further insight in the role of prior experience, distance knowledge, distance feedback, the internal clock, performance feedback and afferent feedback on the setting and maintenance of a pacing strategy in 4, 6 and 16.1 km TT cycling

The ergogenic effects of transcranial direct current stimulation on exercise performance

The physical limits of the human performance have been the object of study for a considerable time. Most of the research has focused on the locomotor muscles, lungs and heart. As a consequence, much of the contemporary literature has ignored the importance of the brain in the regulation of exercise performance. With the introduction and development of new non-invasive devices, the knowledge regarding the behaviour of the central nervous system during exercise has advanced. A first step has been provided from studies involving neuroimaging techniques where the role of specific brain areas have been identified during isolated muscle or whole-body exercise. Furthermore, a new interesting approach has been provided by studies involving non-invasive techniques to manipulate specific brain areas. These techniques most commonly involve the use of an electrical or magnetic field crossing the brain. In this regard, there has been emerging literature demonstrating the possibility to influence exercise outcomes in healthy people following stimulation of specific brain areas. Specifically, transcranial direct current stimulation (tDCS) has been recently used prior to exercise in order to improve exercise performance under a wide range of exercise types. In this review article, we discuss the evidence provided from experimental studies involving tDCS. The aim of this review is to provide a critical analysis of the experimental studies investigating the application of tDCS prior to exercise and how it influences brain function and performance. Finally, we provide a critical opinion of the usage of tDCS for exercise enhancement. This will consequently progress the current knowledge base regarding the effect of tDCS on exercise and provides both a methodological and theoretical foundation on which future research can be based

Prediction of overuse injuries in professional U18-U21 footballers using metrics of training distance and intensity

The most common injury in professional football is an overuse injury to the lower limb. A significant external risk factor of this injury is the mismanagement of training and match loads. The aim of the current study was to examine the predictability of overuse injuries in professional youth soccer players using volume and intensity variables derived from Global Positioning Systems (GPS). A total of 41 players (Age - 17.8 yrs±1.1 yrs) training and match loads were assessed. These external loads were measured over two competitive seasons for every training session and match for each individual. A linear regression was used to test the predictability of the injury based on load, which were grouped using loading groups calculated from squad weekly averages. The load groupings assigned were: Low load = 1 SD below the squad mean score; Normal load = ±1 SD from the squad mean; High load = 1 SD above squad mean. The analysis demonstrated that total distance significantly predicted overuse injury incidence rates (F(1, 39) = 6.482, p = 0.015), whereas high speed running meters could not (F(1, 39) = 1.003, p = 0.323). This study demonstrated that distance covered in training and matches can impact on the incidence of overuse injury in youth soccer players. Coaches should seek to monitor player training loads and incorporate this metric into their decision making for protecting players from overuse injury

Prescribing 6-weeks of running training using parameters from a self-paced maximal oxygen uptake protocol

The self-paced maximal oxygen uptake test (SPV) may offer effective training prescription metrics for athletes. This study aimed to examine whether SPV-derived data could be used for training prescription. Twenty-four recreationally active male and female runners were randomly assigned between two training groups: (1) Standardised (STND) and (2) Self-Paced (S-P). Participants completed 4 running sessions a week using a global positioning system-enabled (GPS) watch: 2 × interval sessions; 1 × recovery run; and 1 × tempo run. STND had training prescribed via graded exercise test (GXT) data, whereas S-P had training prescribed via SPV data. In STND, intervals were prescribed as 6 × 60% of the time that velocity at [Formula: see text] ([Formula: see text]) could be maintained (T ). In S-P, intervals were prescribed as 7 × 120 s at the mean velocity of rating of perceived exertion 20 ( RPE20). Both groups used 1:2 work:recovery ratio. Maximal oxygen uptake ([Formula: see text]), [Formula: see text], T RPE20, critical speed (CS), and lactate threshold (LT) were determined before and after the 6-week training. STND and S-P training significantly improved [Formula: see text] by 4 ± 8 and 6 ± 6%, CS by 7 ± 7 and 3 ± 3%; LT by 5 ± 4% and 7 ± 8%, respectively (all P < .05), with no differences observed between groups. Novel metrics obtained from the SPV can offer similar training prescription and improvement in [Formula: see text], CS and LT compared to training derived from a traditional GXT

Alpha band oscillations in common synaptic input are explanatory of the complexity of isometric knee extensor muscle torque signals

We investigated whether the strength of oscillations in common synaptic input was explanatory of knee extensor (KE) torque signal complexity during fresh and fatigued submaximal isometric contractions, in adults aged from 18 to 90 years. The discharge times of motor units were derived from the vastus lateralis muscle of 60 participants using high-density surface EMG, during 20 s isometric KE contractions at 20% of maximal voluntary contraction, performed before and after a fatiguing repeated isometric KE contraction protocol at 60% of maximal voluntary contraction. Within-muscle coherence Z-scores were estimated using frequency-domain coherence analysis, and muscle torque complexity was assessed using multiscale entropy analysis and detrended fluctuation analysis. Alpha band (5–15 Hz) coherence was found to predict 23.1% and 31.4% of the variance in the complexity index under 28-scales (CI-28) and detrended fluctuation analysis α complexity metrics, respectively, during the fresh contractions. Delta, alpha and low beta band coherence were significantly increased due to fatigue. Fatigue-related changes in alpha coherence were significantly predictive of the fatigue-related changes in CI-28 and detrended fluctuation analysis α. The fatigue-related increase in sample entropy from scales 11 to 28 of the multiscale entropy analysis curves was significantly predicted by the increase in the alpha band coherence. Age was not a contributory factor to the fatigue-related changes in within-muscle coherence and torque signal complexity. These findings indicate that the strength of alpha band oscillations in common synaptic input can explain, in part, isometric KE torque signal complexity and the fatigue-related changes in torque signal complexity

Is Your Virtual Self as Sensational as Your Real? Virtual Reality: The Effect of Body Consciousness on the Experience of Exercise Sensations

Objectives: Past research has shown that Virtual Reality (VR) is an effective method for reducing the perception of pain and effort associated with exercise. As pain and effort are subjective feelings, they are influenced by a variety of psychological factors, including one’s awareness of internal body sensations, known as Private Body Consciousness (PBC). The goal of the present study was to investigate whether the effectiveness of VR in reducing the feeling of exercise pain and effort is moderated by PBC. Design and Methods: Eighty participants were recruited to this study and were randomly assigned to a VR or a non-VR control group. All participants were required to maintain a 20% 1RM isometric bicep curl, whilst reporting ratings of pain intensity and perception of effort. Participants in the VR group completed the isometric bicep curl task whilst wearing a VR device which simulated an exercising environment. Participants in the non-VR group completed a conventional isometric bicep curl exercise without VR. Participants’ heart rate was continuously monitored along with time to exhaustion. A questionnaire was used to assess PBC. Results: Participants in the VR group reported significantly lower pain and effort and exhibited longer time to exhaustion compared to the non-VR group. Notably, PBC had no effect on these measures and did not interact with the VR manipulation. Conclusions: Results verified that VR during exercise could reduce negative sensations associated with exercise regardless of the levels of PBC

Test-retest reliability of a 30-minute fixed perceived effort cycling exercise

Purpose: Using exercise protocols at a fixed rating of perceived effort (RPE) is a useful method for exploring the psychophysical influences on exercise performance. However, studies that have employed this protocol have arbitrarily selected RPE values without considering how these values correspond to exercise intensity thresholds and domains. Therefore, aligning RPE intensities with established physiological thresholds seems more appropriate, although the reliability of this method has not been assessed. Methods: Eight recreationally active cyclists completed two identical ramped incremental trials on a cycle ergometer to identify gas exchange threshold (GET). A linear regression model plotted RPE responses during this test alongside gas parameters to establish an RPE corresponding to GET (RPEGET) and 15% above GET (RPE+15%GET). Participants then completed three trials at each intensity, in which performance, physiological, and psychological measures were averaged into five-minute time zone (TZ) intervals and 30-minute ‘overall’ averages. Data were assessed for reliability using intraclass correlation coefficients (ICC) and accompanying standard error measurements (SEM), 95% confidence intervals, and coefficient of variations (CoV). Results: All performance and gas parameters showed excellent levels of test-retest reliability (ICCs = >.900) across both intensities. Performance, gas-related measures, and heart rate averaged over the entire 30-minute exercise demonstrated good intra-individual reliability (CoV = <5%). Conclusion: Recreationally active cyclists can reliably replicate fixed perceived effort exercise across multiple visits when RPE is aligned to physiological thresholds. Some evidence suggests that exercise at RPE+15%GET is more reliable than RPEGET

Reliability and Validity of a Self-paced Cardiopulmonary Exercise Test in Post-MI Patients

A self-paced peak oxygen uptake (V?O2peak) test (SPV) has been shown to produce higher V?O2peak values compared to standard cardiopulmonary exercise tests (sCPET), but has not been tested on any clinical population. This study aimed to assess the reliability of the SPV in a healthy population (study 1), and the validity and reliability of the SPV in post Myocardial Infarction (post-MI) patients (study 2). For study 1, twenty-five healthy participants completed three SPV’s. For study 2, twenty-eight post-MI patients completed one sCPET and two SPV’s. The SPV consisted of 5 x 2- min stages where participants were able to self-regulate their effort by using incremental ‘clamps’ in ratings of perceived exertion. The sCPET consisted of a 20 W/min ramp. Results demonstrated the SPV to have a coefficient of variation for V?O2peak of 4.7% for the healthy population, and 8.2% for the post-MI patients. Limits of agreement ranged between ± 4.22-5.86 ml·kg-1·min-1, with the intraclass correlation coefficient ranging between 0.89-0.95. In study 2, 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 is concluded that these results provide initial evidence that the SPV may be a safe, valid and reliable method for determining exercise capacity in post-MI patients