Biomedical subjects

Alan St Clair Gibson

Publications and source records attributed to Alan St Clair Gibson.

16 recordsLinked to original sources

PubMed2006

The role of information processing between the brain and peripheral physiological systems in pacing and perception of effort.

This article examines how pacing strategies during exercise are controlled by information processing between the brain and peripheral physiological systems. It is suggested that, although several different pacing strategies can be used by athletes for events of different distance or duration, the underlying principle of how these different overall pacing strategies are controlled is similar. Perhaps the most important factor allowing the establishment of a pacing strategy is knowledge of the endpoint of a particular event. The brain centre controlling pace incorporates knowledge of the endpoint into an algorithm, together with memory of prior events of similar distance or duration, and knowledge of external (environmental) and internal (metabolic) conditions to set a particular optimal pacing strategy for a particular exercise bout. It is proposed that an internal clock, which appears to use scalar rather than absolute time scales, is used by the brain to generate knowledge of the duration or distance still to be covered, so that power output and metabolic rate can be altered appropriately throughout an event of a particular duration or distance. Although the initial pace is set at the beginning of an event in a feedforward manner, no event or internal physiological state will be identical to what has occurred previously. Therefore, continuous adjustments to the power output in the context of the overall pacing strategy occur throughout the exercise bout using feedback information from internal and external receptors. These continuous adjustments in power output require a specific length of time for afferent information to be assessed by the brain's pace control algorithm, and for efferent neural commands to be generated, and we suggest that it is this time lag that crates the fluctuations in power output that occur during an exercise bout. These non-monotonic changes in power output during exercise, associated with information processing between the brain and peripheral physiological systems, are crucial to maintain the overall pacing strategy chosen by the brain algorithm of each athlete at the start of the exercise bout.

Adaptation, Psychological↗

PubMed2005

Short-latency afferent inhibition during selective finger movement.

During individual finger movement, two opposite phenomena occur at the level of the central nervous system that could affect other intrinsic hand muscle representations, unintentional co-activation, and surround inhibition (SI). At rest, excitability in the motor cortex (M1) is inhibited at about 20 ms after electric stimulation of a peripheral nerve [short-latency afferent inhibition (SAI)]. We sought to determine whether SAI changes during selective index finger movement. Effects were measured by the response to transcranial magnetic stimulation in two functionally distinct target muscles of the hand [abductor digiti minimi muscle (ADM), first dorsal interosseus muscle (FDI)]. An increase in SAI in the ADM during index finger movement compared to at rest could help explain the genesis of SI. Electrical stimulation was applied to either the little finger (homotopic for ADM, heterotopic for FDI) or the index finger (heterotopic for ADM, homotopic for FDI). During index finger movement, homotopic SAI was present only in the ADM, and the effect of peripheral stimulation was greater when there was less co-activation. Heterotopic SAI found at rest disappeared with movement. We conclude that during movement, homotopic SAI on the muscle in the surround of the intended movement may contribute to SI.

Adult↗

PubMed2005

Effects of elevated plasma adrenaline levels on substrate metabolism, effort perception and muscle activation during low-to-moderate intensity exercise.

The aim of this study was to differentiate the role of raised plasma adrenaline (Adr) concentrations from sympathoadrenal activation associated with moderate-intensity exercise, on muscle activation, cardiopulmonary responses, fuel metabolism, and ratings of perceived exertion (RPE) during low-intensity exercise. Two groups of subjects (MOD, n=6; LOW, n=7) cycled on two occasions for 90 min. MOD cycled at 68% VO(2max) with saline infusion, and at 34% VO(2max) with Adr infusion. LOW cycled twice at 34% VO(2max), with either Adr or saline infusion. Infusions (0.015 g Adr/kg/min) started at 15 min and increased plasma [Adr] somewhat higher than during exercise at 68% VO(2max) (approximately 1.9 vs. 1.4 nM, at 75 min). Mean plasma glucose and lactate concentrations during LOW were significantly higher with Adr than saline infusion (5.1+/-0.6 vs. 4.4+/-0.3 mmol/l, P<0.01 and 2.1+/-0.8 vs. 1.3+/-0.5 mmol/l, P<0.01, respectively). Elevated [Adr], without increased exercise intensity, did not alter glycogenolysis. There were also no effects of Adr infusion at 34% VO(2max) on heart rate, oxygen consumption, [FFA], respiratory exchange ratio, intramuscular triglyceride utilization, muscle activation or RPE. In conclusion, elevated [Adr] similar to those found during moderate-intensity exercise increased plasma glucose and lactate availability, but did not alter intramuscular fuel utilization, effort perception or muscle activation.

Adolescent↗

PubMed2005

Submaximal force production during perceptually guided isometric exercise.

The aim of this study was to examine submaximal isometric force production guided by perceptual feelings of exertion. Thirty young adults performed isometric knee extensions on an isokinetic dynamometer. Subjects performed five different tests; the first test was the same for all subjects (standard naïve test). During the standard naïve test, subjects were asked to randomly produce force at perceived contraction intensities (25%, 50% and 75% of their maximum voluntary contraction (MVC)), with 100% MVC performed as the final intensity. All intensities, including the 100% MVC, were randomly performed in the other four tests (control tests 1 and 2, post 20% MVC and post 100% MVC tests). Post 20% MVC and post 100% MVC tests included fatiguing isometric exercise at 20% and 100% MVC respectively, which were performed prior to the test protocol. Results show that absolute peak force increased with increasing intensity (P<0.001) during all tests. During the standard naïve test, absolute peak force at 25% and 50% MVC was significantly lower (P=0.009) compared to control test 2, post 20% MVC and 100% MVC tests, and relative peak force was lower at all intensities compared to all other tests (P<0.001). Absolute and relative peak force was most accurate at 50% MVC (-12.06 N and -2.42%, respectively). Prior fatiguing isometric exercise did not affect the subsequent perceptual response range. In conclusion, isometric force was most accurate at 25% MVC but under-produced (perceptually overestimated) during higher contraction intensities preceding a maximal voluntary contraction (100% MVC). The ability to match absolute force with target contraction intensities was most accurate at 50% MVC during all five experimental conditions and poor at opposite ends of the force domain. Furthermore, prior fatiguing isometric exercise did not have an effect on the subsequent perceptual response range.

Adult↗

PubMed2005

Long-latency afferent inhibition during selective finger movement.

Stimulation of a peripheral nerve of a hand at rest modulates excitability in the motor cortex and, in particular, leads to inhibition when applied at an interval of approximately 200 ms (long-latency afferent inhibition; LAI). Surround inhibition (SI) is the process that inhibits neighboring muscles not involved in a particular task. The neuronal mechanisms of SI are not known, and it is possible that LAI might contribute to it. Using transcranial magnetic stimulation (TMS) with and without movement of the index finger, the motor-evoked potentials (MEPs) were measured of two functionally distinct target muscles of the hand (abductor digiti minimi muscle = ADM, 1st dorsal interosseus muscle = FDI). Electrical stimulation was applied 180 ms before TMS to either the fifth finger or the index finger. Both homotopic and heterotopic finger stimulation resulted in LAI without movement. With index finger movement, motor output further decreased with homo- and heterotopic stimulation in the ADM. In the moving FDI, however, there was no change with either homo- or heterotopic stimulation. Additionally, in the unstimulated movement trials, LAI increased with the amount of unintentional co-activation that occurred despite attempts to maintain the ADM at rest. However, with finger stimulation added, there were almost no increased MEPs despite co-activation. These findings suggest that LAI increases during movement and can enhance SI.

Adult↗

PubMed2005

Variability in exercise capacity and metabolic response during endurance exercise after a low carbohydrate diet.

The impact of altered blood glucose concentrations on exercise metabolism and performance after a low carbohydrate (CHO) diet was investigated. In random order, 1 wk apart, 9 trained men underwent euglycemic (CI) or placebo (PI) clamps, while performing up to 150 min of cycling at 70% VO2(max), after 48 h on a low CHO diet. The range in improvement in endurance capacity with glucose infusion was large (28 +/- 26%, P < 0.05). Fifty-six percent of subjects in CI failed to complete 150 min of exercise despite maintenance of euglycemia, while only 2 subjects in PI completed 150 min of exercise, despite being hypoglycemic. Total CHO oxidation remained similar between trials. Despite longer exercise times in CI, similar amounts of muscle glycogen were used to PI. Maintenance of euglycemia in the CHO-depleted state might have an ergogenic effect, however, the effect is highly variable between individuals and independent of changes in CHO oxidation.

Adult↗

PubMed2005

Effect of distance feedback on pacing strategy and perceived exertion during cycling.

PURPOSE: The aim of this study was to investigate whether providing incorrect distance feedback would alter pacing strategies, perceived exertion, and heart rate during 20-km cycling time trials (TT). METHODS: Well-trained cyclists (N=15) performed a peak power output (PPO) test, familiarization trial, and four 20-km cycling TT during which they were provided with only distance feedback using 1-km distance splits. For the control trial, subjects received accurate feedback at each kilometer split. In the increase trial, they received inaccurate feedback at 0.775 km for the first kilometer split with the distance increasing by 25 m each subsequent split up to 1.25 km in the final kilometer split. For the decrease trial, inaccurate feedback was provided at 1.25 km for the first kilometer split with the distance decreasing by 25 m each subsequent split up to 0.775 km in the final split. For the random trial, distance splits were randomized. RESULTS: No significant differences were found in the finishing times between trials. Pacing strategies were unaltered as suggested by similar power output profiles during all trials. RPE scores were also similar for all trials. However, average heart rate varied significantly between trials (P<0.05). CONCLUSIONS: These results suggest that exercise performance, pacing strategy, and RPE during a 20-km cycling TT are not altered by incorrect distance feedback. The data supported the existence of a pacing strategy that is set before exercise and that is unaffected by external distance feedback.

Adaptation, Physiological↗

PubMed2004

Voluntary running distance is negatively correlated with striatal dopamine release in untrained rats.

This study examined the relationship between voluntary running distance and glutamate- and K+-stimulated dopamine release in the striatum (nucleus accumbens and caudate-putamen) of male Long-Evans rats. Twenty-one rats were housed individually in cages with attached running-wheels for 1 week. There was a 19-fold variability between rats in voluntary running distances over this period (range = 2.3-44.6 km). The average distance completed during the week was 16 +/- 2.8 km. There was a strong positive correlation between the running distances completed during the first 24 h (day 1) and the last 24 h. Certain rats were therefore inclined to run from the start. The average daily running distance (2.4 +/- 0.4 km per day) was negatively correlated with the weight of the rat (r = -0.82). Glutamate-stimulated release of dopamine was not a significant predictor of voluntary running distance. However, the average daily running distance was negatively correlated with K+-stimulated dopamine release in the nucleus accumbens core and caudate-putamen but not the nucleus accumbens shell. The present findings suggest that decreased depolarization-induced release of striatal dopamine may be a predictor of hyperactivity. The results show, in a normal population of Long-Evans rats, that there are, at the end of the continuum, rats that display some of the neurochemical and behavioral characteristics of a rat model for attention-deficit hyperactivity disorder.

Analysis of Variance↗

PubMed2004

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 microg/4 microL 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.

Animals↗

PubMed2004

Anticipatory pacing strategies during supramaximal exercise lasting longer than 30 s.

PURPOSE: This study assessed whether pacing strategies are adopted during supramaximal exercise bouts lasting longer than 30 s. METHODS: Eight healthy males performed six Wingate anaerobic tests (WAnT). Subjects were informed that they were performing four 30-s WAnT, a 33-s, and a 36-s WAnT. However, they actually completed two trials of 30, 33, and 36 s each. Temporal feedback in the deception trials was manipulated so that subjects were unaware of the time discrepancy. Power output was determined from the angular displacement of the flywheel. The peak power (PPI), mean power (MPI), and fatigue (FI) indices were calculated for each trial. RESULTS: Power output was similar for all trials up to 30 s. However, at 36 s, the power output was significantly lower in the 36-s deception trial compared with the 36-s informed trial (392 +/- 32 W vs 470 +/- 88 W) (P < 0.001). The MPI was significantly lower in the 36-s trials (714 +/- 76 W and 713 +/- 78 W) compared with the 30-s trials (745 +/- 65 W and 764 +/- 82 W) although they were not different at 30 s (764 +/- 83 W and 755 +/- 79 W). The significant reduction in FI was greatest in the 36-s deception trial. CONCLUSIONS: The significant reduction in power output in the last 6 s of the 36-s deception trial, but not in the 36-s informed trial, indicates the presence of a preprogrammed 30-s "end point" based on the anticipated exercise duration from previous experience. The similarity in pacing strategy suggests that the pacing strategy is centrally regulated.

Adult↗

PubMed2004

Regulation of pacing strategies during successive 4-km time trials.

PURPOSE: Athletes adopt a pacing strategy to delay fatigue and optimize athletic performance. However, many current theories of the regulation of muscle function during exercise do not adequately explain all observed features of such pacing strategies. We studied power output, oxygen consumption, and muscle recruitment strategies during successive 4-km cycling time trials to determine whether alterations in muscle recruitment by the central nervous system could explain the observed pacing strategies. METHODS: Seven highly trained cyclists performed three consecutive 4-km time trial intervals, each separated by 17 min. Subjects were instructed to perform each trial in the fastest time possible but were given no feedback other than distance covered. Integrated electromyographic (iEMG) readings were measured at peak power output anti from 90 s before the end of each trial. RESULTS: Subjects attained VO2 values similar to their VO2(peak) in each interval. Time taken to complete the first and third intervals was similar. Peak power output was highest in the first interval, but average power output, oxygen consumption, heart rate, and postexercise plasma lactate concentrations were not different between intervals. Power output and iEMG activity rose similarly during the final 60 s in all intervals but was not different between trials. CONCLUSION: The increase in power output and the parallel upward trend in iEMG at the end of each interval indicate that the iEMG changes "tracked" the power output changes dynamically and that therefore the observed pacing strategies were not regulated by peripheral mechanisms. Rather, these findings are compatible with the action of a centrally regulated mechanism that alters the number of motor units that are recruited and de-recruited during exercise based upon peripheral feedback or anticipatory feed-forward.

Adaptation, Physiological↗

PubMed2004

Deception and perceived exertion during high-intensity running bouts.

This investigation examined the overall and localized perceived exertion responses to repeated bouts of submaximal, high-intensity running when subjects were deceived. Well-trained male and female n = 40) runners were randomly assigned to four groups who completed three 1680-m bouts of running at 80-86% peak treadmill running speed. The two experimental groups, Expected Similar and Expected Increase, were deceived of the actual run intensities while the two control groups, Control Increase and Control Similar, were informed of the actual protocol. After each run, ratings of perceived exertion (RPE) were taken for the whole body, chest, legs, head, and other areas. No significant differences were found in overall RPE between deceived and control groups. However, there was a tendency for the Expected Increase group, deceived into believing the intensity would be higher than they were subsequently made to run, to experience an attenuated increase in RPE between runs compared to the control group (Control Increase) who were honestly informed. For all groups, legs and chest were given consistently higher localized exertion scores than the head and other areas. It appears that a precise system of afferent feedback mediates the overall perceived exertion response during high-intensity running, and psychological intervention that alters pre-exercise expectations has minimal feedforward effect on exertion ratings taken postexercise.

Adult↗

PubMed2003

Athletes with exercise-associated fatigue have abnormally short muscle DNA telomeres.

INTRODUCTION/PURPOSE: Although the beneficial health effects of regular moderate exercise are well established, there is substantial evidence that the heavy training and racing carried out by endurance athletes can cause skeletal muscle damage. This damage is repaired by satellite cells that can undergo a finite number of cell divisions. In this study, we have compared a marker of skeletal muscle regeneration of athletes with exercise-associated chronic fatigue, a condition labeled the "fatigued athlete myopathic syndrome" (FAMS), with healthy asymptomatic age- and mileage-matched control endurance athletes. METHODS: Muscle biopsies of the vastus lateralis were obtained from 13 patients diagnosed with FAMS and from 13 healthy control subjects. DNA was extracted from the muscle samples and their telomeric restriction fragment (TRF) or telomere lengths were measured by Southern blot analysis. RESULTS: All 13 symptomatic athletes reported a progressive decline in athletic performance, decreased ability to tolerate high mileage training, and excessive muscular fatigue during exercise. The minimum value of TRF lengths (4.0 +/- 1.8 kb) measured on the DNA from vastus lateralis biopsies from these athletes were significantly shorter than those from 13 age- and mileage-matched control athletes (5.4 +/- 0.6 kb, P < 0.05). Three of the FAMS patients had extremely short telomeres (1.0 +/- 0.3 kb). The minimum TRF lengths of the remaining 10 symptomatic athletes (4.9 +/- 0.5 kb, P < 0.05) were also significantly shorter that those of the control athletes. CONCLUSION: These findings suggest that skeletal muscle from symptomatic athletes with FAMS show extensive regeneration which most probably results from more frequent bouts of satellite cell proliferation in response to recurrent training- and racing-induced muscle injury.

Adult↗

PubMed2003

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.

Awareness↗

PubMed2002

Agonist-antagonist common drive during fatiguing knee extension efforts using surface electromyography.

AIM: This study examined the electromyographic (EMG) activity of knee extensor agonists and a knee extensor antagonist muscle during fatiguing isometric extensions across a range of force levels. METHODS: Five female subjects performed isometric knee extensions at 25%, 50%, 75% and 100% of their maximal voluntary contraction (MVC) with the knee flexed to 75 degrees. Surface EMG (SEMG) was recorded with bipolar electrodes from the vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF) and biceps femoris (BF) and the root-mean-squared (RMS) amplitude and the percentage frequency compression of these recordings were calculated. Commonality and cross talk between recordings were also examined. RESULTS: Cross talk between recordings was deemed negligible despite significant levels of commonality between the agonist and antagonist SEMG, which was attributed to common drive. SEMG RMS amplitude increased significantly for all muscles during the 25%, 50%, 75% MVC knee extensions until task failure, and decreased significantly for 100% MVC. The frequency spectrum of the SEMG compressed significantly for all muscles and % MVC levels. The VM, VL and BF SEMG recordings responded similarly to fatigue. The RF's frequency spectrum compressed to a significantly higher degree. CONCLUSIONS: The VM, VL, RF, and BF fatigue in parallel, with high similarity between VM, VL and BF, giving support to the concept of a shared agonist-antagonist motoneuron pool.

Adult↗

PubMed2002

Changes in oxygen consumption during and after a downhill run in masters long-distance runners.

OBJECTIVE: To determine whether oxygen consumption during submaximal running increases in proportion to years of accumulated training and racing in masters runners after a bout of downhill running. SETTING: University of Cape Town, Sports Science Institute of South Africa. PARTICIPANTS: Seventeen male masters distance runners (45-55 years) with a range of training (3,536 km to 79,320 km) and racing (205 km to 12,218 km) experience. INTERVENTION: A 40-minute continuous treadmill run, at 70% of peak treadmill running speed, consisting of two horizontal runs of 10 minutes each, separated by a 20-minute downhill (-10%) run. MAIN OUTCOME MEASURES: Heart rate and oxygen consumption were measured continuously during the run. Data were analyzed to identify correlations between the end of the first horizontal section (minute 10) and the first minute of the second horizontal run (minute 31). Delta values were related to current training mileage (km/wk), total accumulated racing distance (km), and total accumulated training distance (km). RESULTS: There were significant changes in both heart rate (p < 0.001) and oxygen consumption (p < 0.001) over time during the 40-minute run. There were no significant relationships between the change in oxygen consumption (delta) between minute 10 and minute 31 and total accumulated training mileage, total accumulated racing mileage, and current training. CONCLUSIONS: The results of this study suggest either that submaximal oxygen consumption is not a sensitive marker of changes in neuromuscular activity or that the downhill protocol did not impose a sufficient eccentric stress for the subjects.

Age Factors↗