Alan St Clair Gibson

The influence of sensory cues on the perception of exertion during exercise and central regulation of exercise performance

AbstractThe perception of effort during exercise and its relationship to fatigue is still not well understood. Although several scales have been developed to quantify exertion Borg’s 15-point ratings of perceived exertion (RPE) scale has been adopted as a valid and reliable instrument for evaluating whole body exertion during exercise. However, Borg’s category-ratio scale is useful in quantifying sensations of exertion related to those variables that rise exponentially with increases in exercise intensity. Previous research has examined the extent to which afferent feedback arising from cardiopulmonary and peripheral variables mediates the perception of exertionHowever, the literature has not identified a single variable that consistently explains exertion ratings. It is concluded that effort perception involves the integration of multiple afferent signals from a variety of perceptual cues. In a process defined as teleoanticipation, the changes in perceived exertion that result from these afferent signals may allow exercise performance to be precisely regulated such that a task can be completed within the biomechanical and metabolic limits of the body. The accuracy with which individuals can regulate exercise intensity based upon RPE values, the decrease in muscle recruitment (central drive) that occurs before fatigue, and the extent to which perceived exertion and heart rate can be altered with hypnosis and biofeedback training all provide evidence for the existence of such a regulatory system. Future research is needed to precisely quantify the extent to which efferent feed forward commands and afferent feedback determine pacing strategies such that an exercise event can be completed without irreversible tissue damage. However, the literature has not identified a single variable that consistently explains exertion ratings. It is concluded that effort perception involves the integration of multiple afferent signals from a variety of perceptual cues. In a process defined as teleoanticipation, the changes in perceived exertion that result from these afferent signals may allow exercise performance to be precisely regulated such that a task can be completed within the biomechanical and metabolic limits of the body. The accuracy with which individuals can regulate exercise intensity based upon RPE values, the decrease in muscle recruitment (central drive) that occurs before fatigue, and the extent to which perceived exertion and heart rate can be altered with hypnosis and biofeedback training all provide evidence for the existence of such a regulatory system. Future research is needed to precisely quantify the extent to which efferent feed forward commands and afferent feedback determine pacing strategies such that an exercise event can be completed without irreversible tissue damage.

The Conscious Perception of the Sensation of Fatigue

In this review, fatigue is described as a conscious sensation rather than a physiological occurrence. We suggest that the sensation of fatigue is the conscious awareness of changes in subconscious homeostatic control systems, and is derived from a temporal difference between subconscious representations of these homeostatic control systems in neural networks that are induced by changes in the level of activity. These mismatches are perceived by consciousness-producing structures in the brain as the sensation of fatigue. In this model, fatigue is a complex emotion affected by factors such as motivation and drive, other emotions such as anger and fear, and memory of prior activity. It is not clear whether the origin of the conscious sensation of fatigue is associated with particular localised brain structures, or is the result of electrophysiological synchronisation of entire brain activity.

Evidence for neuromuscular fatigue during high-intensity cycling in warm, humid conditions.

Abstract The purpose of this study was to examine and describe the neuromuscular changes associated with fatigue using a self-paced cycling protocol of 60-min duration, under warm, humid conditions. Eleven subjects [mean (SE) age 21.8 (0.8) years; height 174.9 (3.0) cm; body mass 74.8 (2.7) kg; maximum oxygen consumption 50.3 (1.8) ml · kg · min−1] performed one 60-min self-paced cycling time trial punctuated with six 1-min “all out” sprints at 10-min intervals, while 4 subjects repeated the trial for the purpose of determining reproducibility. Power output, integrated electromyographic signal (IEMG), and mean percentile frequency shifts (MPFS) were recorded at the mid-point of each sprint. There were no differences between trials for EMG variables, distance cycled, mean heart rate, and subjective rating of perceived exertion for the subjects who repeated the trial (n=4). The results from the repeated trials suggest that neuromuscular responses to self-paced cycling are reproducible between trials. The mean heart rate for the 11 subjects was 163.6 (0.71) beats · min−1. Values for power output and IEMG expressed as a percentage of that recorded for the initial sprint decreased during sprints 2–5, with normalised values being 94%, 91%, 87% and 87%, respectively, and 71%, 71%, 73%, and 77%, respectively. However, during the final sprint normalised power output and IEMG increased to 94% and 90% of initial values, respectively. MPFS displayed an increase with time; however, this was not significant (P=0.06). The main finding of this investigation is the ability of subjects to return power output to near initial values during the final of six maximal effort sprints that were included as part of a self-paced cycling protocol. This appears to be due to a combination of changes in neuromuscular recruitment, central or peripheral control systems, or the EMG signal itself. Further investigations in which changes in multiple physiological systems are assessed systematically are required so that the underlying mechanisms related to the development of fatigue during normal dynamic movements such as cycling can be more clearly delineated.

Neural control of force output during maximal and submaximal exercise.

AbstractA common belief in exercise physiology is that fatigue during exercise is caused by changes in skeletal muscle metabolism. This ‘periphera’ fatigue results either from substrate depletion during submaximal exercise or metabolite accumulation during maximal exercise in the exercising muscles. However, if substrate depletion alone caused fatigue, intracellular ATP levels would decrease and lead to rigor and cellular death. Alternatively, metabolite accumulation would prevent any increase in exercise intensity near the end of exercise. At present, neither of these effects has been shown to occur, which suggests that fatigue may be controlled by changes in efferent neural command, generally described as ‘central’ fatigue.In this review, we examine neural efferent command mechanisms involved in fatigue, including the concepts of muscle wisdom during short term maximal activity, and muscle unit rotation and teleoanticipation during submaximal endurance activity. We propose that neural strategies exist to maintain muscle reserve, and inhibit exercise activity before any irreparable damage to muscles and organs occurs. The finding that symptoms of fatigue occur in the nonexercising state in individuals with chronic fatigue syndrome indicates that fatigue is probably not a physiological entity, but rather a sensory manifestation of these neural regulatory mechanisms.

Acute milk-based protein–CHO supplementation attenuates exercise-induced muscle damage

Exercise-induced muscle damage (EIMD) leads to the degradation of protein structures within the muscle. This may subsequently lead to decrements in muscle performance and increases in intramuscular enzymes and delayed-onset muscle soreness (DOMS). Milk, which provides protein and carbohydrate (CHO), may lead to the attenuation of protein degradation and (or) an increase in protein synthesis that would limit the consequential effects of EIMD. This study examined the effects of acute milk and milk-based protein-CHO (CHO-P) supplementation on attenuating EIMD. Four independent groups of 6 healthy males consumed water (CON), CHO sports drink, milk-based CHO-P or milk (M), post EIMD. DOMS, isokinetic muscle performance, creatine kinase (CK), and myoglobin (Mb) were assessed immediately before and 24 and 48 h after EIMD. DOMS was not significantly different (p > 0.05) between groups at any time point. Peak torque (dominant) was significantly higher (p < 0.05) 48 h after CHO-P compared with CHO and CON, and M compared with CHO. Total work of the set (dominant) was significantly higher (p < 0.05) 48 h after CHO-P and M compared with CHO and CON. CK was significantly lower (p < 0.05) 48 h after CHO-P and M compared with CHO. Mb was significantly lower (p < 0.05) 48 h after CHO-P compared with CHO. At 48 h post-EIMD, milk and milk-based protein-CHO supplementation resulted in the attenuation of decreases in isokinetic muscle performance and increases in CK and Mb.

Application of Decision-Making Theory to the Regulation of Muscular Work Rate during Self-Paced Competitive Endurance Activity

Successful participation in competitive endurance activities requires continual regulation of muscular work rate in order to maximise physiological performance capacities, meaning that individuals must make numerous decisions with regards to the muscular work rate selected at any point in time. Decisions relating to the setting of appropriate goals and the overall strategic approach to be utilised are made prior to the commencement of an event, whereas tactical decisions are made during the event itself. This review examines current theories of decision-making in an attempt to explain the manner in which regulation of muscular work is achieved during athletic activity. We describe rational and heuristic theories, and relate these to current models of regulatory processes during self-paced exercise in an attempt to explain observations made in both laboratory and competitive environments. Additionally, we use rational and heuristic theories in an attempt to explain the influence of the presence of direct competitors on the quality of the decisions made during these activities. We hypothesise that although both rational and heuristic models can plausibly explain many observed behaviours in competitive endurance activities, the complexity of the environment in which such activities occur would imply that effective rational decision-making is unlikely. However, at present, many proposed models of the regulatory process share similarities with rational models. We suggest enhanced understanding of the decision-making process during self-paced activities is crucial in order to improve the ability to understand regulation of performance and performance outcomes during athletic activity.

Voluntary Running Provides Neuroprotection in Rats After 6-Hydroxydopamine Injection into the Medial Forebrain Bundle

Neurotoxic drugs such as 6-hydroxydopamine (6-OHDA) have been used to mimic a Parkinsonian state in a rat model. The toxic effect of 6-OHDA has been shown to be reduced in rats that were forced to use the impaired limb immediately after unilateral 6-OHDA injection. The aim of this study was to determine whether dopamine neurons in the substantia nigra are spared in rats that exercise voluntary. Two groups of rats were placed in cages with attached running wheels 7 days prior to injection of 6-OHDA (10 μg/4 μL saline) into the medial forebrain bundle. The running wheels of the control group were immobilized for the duration of the study. After 6-OHDA injection, the rats were returned to their respective cages where they remained for a further period of 14 days. Wheel revolutions during free running were recorded daily in the experimental group. At the end of this period the rats were injected with apomorphine (0.5 mg/kg, s.c.) and the number and direction of rotations was recorded. Rats that exercised in the running wheels did not rotate contralaterally in response to apomorphine injection, suggesting that dopamine neurons had been spared sufficiently from the toxic effects of 6-OHDA injection to prevent upregulation of postsynaptic dopamine receptors in the striatum.

Post-operative gait analysis in total hip replacement patients—A review of current literature and meta-analysis

Gait analysis has been used to measure gait adaptations following total hip replacement (THR) for many years. In this time, advances have been made in implant technology and surgical procedure. However, gait adaptations persist after surgery. This review of seven published studies, where gait characteristics were compared between post-operative THR patients and healthy controls, had the objective of investigating current practice in gait analysis of this patient population and to determine if there is a consensus on post-operative gait changes associated with THR. Levels of methodological quality and study design were found to be variable. Meta-analyses were performed on all gait variables reported by at least three studies to determine overall Cohens d effect sizes and 95% confidence intervals. Reductions in walking velocity (d=-0.79; CI=-1.54, -0.04), stride length (d=-1.06; CI=-1.62, -0.49) and sagittal hip range of motion (d=-1.58; CI=-2.12, -1.04) were observed. Increases in peak hip flexion (d=0.52; CI=-0.01, 1.09) and extension (d=0.54; CI=-0.10, 1.09) moments were found, although these were likely to be of less clinical significance. Reduced peak hip abduction was also observed (d=-0.58; CI=-1.09, -0.06). Future developments in THR technology and surgical methods should therefore aim to reduce the differences between patients and controls in terms of walking velocity, stride length, hip range of motion and hip abduction moments.

Distribution of power output during cycling : Impact and mechanisms

We aim to summarise the impact and mechanisms of work-rate pacing during individual cycling time trials (TTs). Unlike time-to-exhaustion tests, a TT provides an externally valid model for examining how an initial work rate is chosen and maintained by an athlete during self-selected exercise.The selection and distribution of work rate is one of many factors that influence cycling speed. Mathematical models are available to predict the impact of factors such as gradient and wind velocity on cycling speed, but only a few researchers have examined the inter-relationships between these factors and work-rate distribution within a TT.When environmental conditions are relatively stable (e.g. in a velodrome) and the TT is >10 minutes, then an even distribution of work rate is optimal. For a shorter TT (≤10 minutes), work rate should be increased during the starting effort because this proportion of total race time is significant. For a very short TT (≤2 minutes), the starting effort should be maximal, since the time saved during the starting phase is predicted to outweight any time lost during the final metres because of fatigue. A similar ‘time-saving’ rationale underpins the advice that work rate should vary in parallel with any changes in gradient or wind speed during a road TT. Increasing work rate in headwind and uphill sections, and vice versa, decreases the variability in speed and, therefore, the total race time.It seems that even experienced cyclists naturally select a supraoptimal work rate at the start of a longer TT. Whether such a start can be blunted through coaching or the monitoring of psychophysiological variables is unknown. Similarly, the extent to which cyclists can vary and monitor work rate during a TT is unclear. There is evidence that sub-elite cyclists can vary work rate by ±5% the average for a TT lasting 25–60 minutes, but such variability might be difficult with high-performance cyclists whose average work rate during a TT is already extremely high (>350 watts).During a TT, pacing strategy is regulated in a complex anticipatory system that monitors afferent feedback from various physiological systems, and then regulates the work rate so that potentially limiting changes do not occur before the endpoint of exercise is reached. It is critical that the endpoint of exercise is known by the cyclist so that adjustments to exercise work rate can be made within the context of an estimated finish time. Pacing strategies are thus the consequence of complex regulation and serve a dual role: they are both the result of homeostatic regulation by the brain, as well as being the means by which such regulation is achieved.The pacing strategy ‘algorithm’ is sited in the brain and would need afferent input from interoceptors, such as heart rate and respiratory rate, as well as exteroceptors providing information on local environmental conditions. Such inputs have been shown to induce activity in the thalamus, hypothalamus and the parietal somatosensory cortex. Knowledge of time, modulated by the cerebellum, basal ganglia and primary somatosensory cortex, would also input to the pacing algorithm as would information stored in memory about previous similar exercise bouts. How all this information is assimilated by the different regions of the brain is not known at present.

Pre-operative patient education reduces length of stay after knee joint arthroplasty

INTRODUCTION The aim of this study was to evaluate the impact of a pre-operative education programme on length of hospital stay after surgery for primary and revision knee arthroplasty patients. The programme was introduced at our hospital in October 2006 to encourage patients to play an active role in their recovery process after surgery. PATIENTS AND METHODS A multidisciplinary team educated knee arthroplasty patients about their care pathway, knee surgery, pain management, expected discharge goals, in-patient and out-patient arthroplasty rehabilitation. Prospective data were collected from 472 consecutive patients who underwent (primary or revision) knee arthroplasty in the period between January 2006 and November 2007. Patients were separated into two groups, one that received conventional pre-operative treatment (n = 150; Conventional group) and another that received the pre-operative education (n = 322; Education group). Length of hospital stay was compare using the Mann Whitney U test. In-patient complications, hospital re-admissions within 24 h and 3 months of hospital discharge were compared using the chi-squared test. RESULTS The mean length of stay was significantly reduced from 7 days in the Conventional group to 5 days in the Education group (P < 0.01). In addition, 20% more patients were discharged early (within 1-4 days) in the Education group compared to the Conventional group (P < 0.01). There was no difference in the percentage of in-patient complications and re-admissions in 24 h (P = 1.00) and 3 months of discharge (P = 0.92) between the two groups. CONCLUSIONS The results suggest that pre-operative education is a safe and effective method of reducing length of stay for knee arthroplasty patients.