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«BOOK OF ABSTRACTS Edited by: Loland, S., Bø, K., Fasting, K., Hallén, J., Ommundsen, Y., Roberts, G., Tsolakidis, E. Hosted by: The Norwegian ...»

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Experiments in humans clearly show the great ability of skeletal muscle to regenerate after loading or injury or both. Satellite cells in human skeletal muscle enter proliferation in response to light and heavy resistance training or endurance exercises both in young and old individuals. Enhancement of satellite cell pool in response to training is another health benefit of exercise. The proliferative capacity of skeletal muscle is influenced by the length of DNA sequences located at the end of chromosomes called telomeres. A dramatic shortening of telomeres is associated with a reduction in tissue regenerative potential. Rather than considering skeletal muscle as a stable tissue in term of regenerative events, muscle biologists start to learn that under harmful circumstances an abnormal shortening of telomeres might occur and that when training is properly performed the telomere length can be positively regulated. No doubt that new mechanisms relating the effects of exercise on the regenerative capacity of skeletal muscle and the regulation of telomere length will emerge in the near future.

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14:00 - 15:30 Oral presentations OP-PH03 Physiology 3

INFLUENCE OF EXERCISE VARIATION ON THE RETENTION OF A PACING STRATEGY

MAUGER, A., JONES, A., WILLIAMS, C.A.

EXETER UNIVERSITY

Background: In competitions where time to completion is the measure of success, pacing strategy exerts an important influence on performance. The Theory of Teleoanticipation and the Central Governor Model, proposes that a pacing strategy is set in a feedforward manner, based on distance or duration, prior to the onset of an exercise bout. Prior experience of an exercise bout allows the construction of a pacing schema, which is utilised for subsequent, similar bouts of exercise. During exercise, distance or time remaining is judged by an ‘internal clock’ that is located in the brain. It is proposed that this timing mechanism works in a scalar fashion, using relative rather than absolute quantities. Despite the apparent importance of the scalar clock to the maintenance of a pacing strategy, knowledge in this area is presently limited.

Aims: To establish whether the introduction of an exercise bout of different distance, in the absence of distance feedback, would affect the retention of the pacing schema stored from a prior exercise bout. Furthermore, to identify whether the internal clock has an ability to calibrate to absolute distance, and whether this mechanism is disrupted by an exercise requiring a different pacing strategy.

Methods: Sixteen highly-trained male cyclists were randomly split into a control (CON) or experimental group (EXP) and completed four time trials (TT) of two different distances (2x4 km and 2x6 km) in varying orders, separated by 17 minutes. The participants in the CON group completed both distances in a sequential order (i.e. half performed 4 km, 4 km, 6 km, 6 km, and the other half performed 6 km, 6 km, 4 km, 4 km). The EXP group completed both distances in a variable order (i.e. half performed 4 km, 6 km, 4 km, 6 km, and the other half performed 6 km, 4 km, 6 km, 4 km). During each TT, power output, VO2 and heart rate were recorded. Participants in both groups were asked to call out their RPE for every km they thought they had completed.

Results: No significant differences were found between or within groups for completion time or PO (p 0.05). The CON group showed a significant improvement in their estimation of distance completed in both the 4 km (24.6 ± 18.2 % vs. 8.2 ± 5.5 %) and 6 km (15.2 ± 7 % vs.

8.6 ± 3 %) distances (t7 = 2.791, t7 = 3.118, p 0.05). No significant differences in distance estimation were observed in the EXP for either of the TT distances (p 0.05).

Conclusion: The primary finding of this study is that participants who did not receive an exercise interruption displayed a significant improvement in their judgement of distance completed, despite no improvement in completion time. This suggests that a learned pacing schema is robust and not negatively affected by subsequent pacing variation and can be retrieved when required. The internal clock shows an ability to be calibrated to absolute distance, although this does not improve performance.

UNRAVELLING THE MECHANISMS OF EARLY-MORNING CEREBRAL EVENTS: THE IMPORTANCE OF DIURNAL VARIATION IN ORTHOSTATIC TOLERANCE

LEWIS, N.C.S., LUCAS, S.J.E., GRANT, E.J.M., ATKINSON, G., JONES, H., AINSLIE, P.N.

LIVERPOOL JOHN MOORES UNIVERSITY, AND THE UNIVERSITY OF OTAGO

Introduction: The most common form of syncope is explained by vasovagal mechanisms. Hypotension during pre-syncope is probably precipitated by sympathetic nervous system withdrawal (Mosqueda-Garcia et al., 1997) but loss of consciousness is caused by cerebral hypoperfusion. The risk of neurally-mediated syncope peaks in the morning (van Dijk et al., 2007), coinciding with the time of resuming upright posture and the beginning of physical activity. It is critical that the relative importance of orthostatic- and exercise-related challenges are unravelled to gain an understanding of why cerebral ischemia events peak in the morning. This study is the first to examine the extent to which orthostatic-induced reductions in blood pressure (BP) and cerebral blood flow may differ with time of day. It was hypothesised that orthostatic tolerance is impaired in the morning due to a diurnal failure to maintain BP and thus cerebral hypoperfusion.





Methods: Nine male and six female participants aged 27±5 yrs (mean±SD) completed two trials starting at 06:00 h and 16:00 h. Continuous beat-to-beat measurements of cerebral blood flow velocity (CBFv; transcranial Doppler), BP (Finometer), heart rate (HR), and end-tidal PCO2 were obtained during 15 min of supine rest and during 60° head-up tilt with lower body negative pressure in 5-min increments of mmHg, until pre-syncope. Pre-syncope was terminated on participants’ request due to subjective symptoms associated with fainting, or when systolic BP reduced to 80 mmHg for more than 10 s. Data were analysed using paired t-tests and reported as mean±SD.

Results: During supine baseline, mean BP was 5±1mmHg higher, and CBFv was 7±3 cm/s lower in the morning compared with the afternoon (P0.05). Baseline measurements of HR and end-tidal PCO2 did not differ between times of day (P0.05). Time to pre-syncope occurred faster in the morning (1634±633 s) than in the afternoon (1988±475 s) with the 95% confidence limits for the mean difference between times of day being 25 to 684 s (P=0.04). Despite the diurnal variation at baseline, mean BP, CBFv, HR and end-tidal PCO2 at presyncope did not differ significantly between times of day (P0.05).

Discussion: A marked reduction in orthostatic tolerance is evident in the early morning, resulting in an earlier onset of pre-syncope.

Although the sequence of haemodynamic adjustments is similar between the two times of day, the adjustments are accelerated in the early morning, presumably via impairment in the bar reflex control of BP at this time of day. This study shows that postural changes independent of an exercise effect can increase the risk of vasovagal syncope in the morning in young, healthy and physically-fit people.

References Mosqueda-Garcia R, Furlan R, Fernandez-Violante R, Desail T, Snell M, Jarai Z, Ananthram V, Robertson RM, Robertson D. (1997). J Clin Invest, 99, 2736-2744.

van Dijk N, Boer MC, Santo TD, Grovale N, Aerts AJJ, Boersma L, Wieling W. (2007). Europace, 9, 823-82.

14 ANNUAL CONGRESS OF THE EUROPEAN COLLEGE OF SPORT SCIENCE

TH Wednesday, June 24th, 2009

THE EFFECT OF BICARBONATE INFUSION IN CEREBRAL METABOLISM DURING MAXIMAL EXERCISE

VOLIANITIS, S., RASMUSSEN, P., SEIFERT, T., SECHER, N.H.

AALBORG UNIVERSITY

Exercise lowers the cerebral metabolic ratio of O2 to carbohydrates (glucose + ½ lactate). Metabolic acidosis increases cerebral lactate uptake and exacerbates the cerebral metabolic ratio in vitro. However, the influence of pH on cerebral lactate uptake and the cerebral metabolic ratio during exercise in humans is not known.

PURPOSE: To evaluate the influence of pH on cerebral metabolism during maximal exercise. METHODS: Sodium bicarbonate (Bic, 1 M;

350-500 ml) or an equal volume of saline (Sal; 1 M) was infused intravenously at a constant rate during a ’2,000-m’ maximal ergometer row in six male oarsmen (23 ± 2 yrs). Comparisons between the two conditions were made using two-way ANOVA with repeated measures. RESULTS: During the Sal trial, pH decreased from 7.41 ± 0.01 at rest to 7.02 ± 0.02 but only to 7.36 ± 0.02 (P 0.05) during the Bic trial. Arterial lactate increased to 21.4 ± 0.8 mM (mean ± SEM) and 32.7 ± 2.3 mM during the Sal and Bic trials, respectively. The arterialjugular venous (a-v) lactate difference increased from -0.03 ± 0.01 mM at rest to 3.2 ± 0.9 mM (P 0.05) and 3.4 ± 1.4 mM (P 0.05) following the Sal and Bic trials, respectively. The cerebral metabolic ratio decreased equally during the Sal and Bic trials from 5.8 ± 0.6 at rest to 1.7 ± 0.1 and 1.8 ± 0.2, respectively.

CONCLUSION: The enlarged blood-buffering capacity after infusion of Bic attenuated the metabolic acidosis but did not affect the cerebral lactate uptake or the cerebral metabolic ratio during maximal exercise.

EFFECTS OF PRIOR EXHAUSTIVE LEG OR ARM EXERCISE ON SUBSEQUENT PERFORMANCE, POWER AND EMG ACTIVITY

IN A DIFFERENT MUSCLE GROUP

GABE BELTRAMI, F., DE GROOT, R., RAUCH, L., TUCKER, R., RAE, D.E., NOAKES, T.D.

UNIVERSITY OF CAPETOWN

Introduction: A prior bout of exhaustive exercise is known to result in early exhaustion being reached during a subsequent bout of maximal exercise. Much of the research to date has examined peripheral factors for this phenomenon. Therefore, the aim of this study was to investigate the contribution of central regulation on the performance of maximal exercise preceded by a bout of exhaustive exercise using a different muscle group.

Methods: Ten healthy men (5 well-trained cyclists and 5 well-trained canoeists) were recruited for this study and all completed two exercise trials. In trial 1, subjects performed an incremental leg ergometry test to exhaustion (LEG A), followed 15 minutes later by an incremental arm ergometry test to exhaustion (ARM B). In trial 2, the order was reversed (ARM A followed 15 minutes later by LEG B). The two trials were separated by at least 3 days and the order in which the subjects performed the trials was randomised. Time to exhaustion (TE), power output (PO), heart rate (HR), rating of perceived exertion (RPE), oxygen consumption (VO2), ventilation rate (VE), plasma lactate (LA) and electromyography (EMG) of two lower (rectus femoris and vastus lateralis) and two upper limb (triceps and biceps) muscles were measured during all trials.

Results: During the A trials, subjects reached exhaustion faster and at a higher PO during legs compared to arms. While HR and RPE were similar in the leg and arm tests at exhaustion, VO2 (p = 0.018) and VE (p = 0.008) were lower in the arm test. Performance during ARM B was unaffected by prior LEG A. However, prior ARM A significantly reduced TE (p = 0.011) and peak PO (p = 0.011) during subsequent LEG B. There were no changes in maximal VO2, HR, RPE, VE and LA between trials A and B of each muscle group. LA was higher at the beginning of LEG B (p 0.001) and ARM B (p = 0.001) exercise compared to their respective A trials. Prior LEG A affected subsequent ARM B HR for the first 40% of the trial. During LEG B, however, HR differed only at the start and 20% of the test. EMG increased linearly during all the trials and maximal EMG activity measured during the tests was only 55% of previous MVC. RPE rose linearly during all tests, regardless of different levels of LA and HR. None of the measured physiological/neuromuscular variables measured showed a plateau at exhaustion.

Conclusion: Prior arm exercise reduced peak power output during a subsequent bout of exhaustive leg exercise without altering the physiological or EMG variables measured in this study. In contrast, prior leg exercise did not alter peak power output during subsequent arm exercise. These results suggest that during the tests RPE was set in anticipation, being independent of the amount of muscle mass activated, HR or LA. These data are difficult to interpret according to traditional peripheral models of exercise fatigue and deserves further investigations.

IMPACT OF TRAINING STATUS ON MAXIMAL OXYGEN UPTAKE CRITERIA ATTAINMENT DURING CYCLING

CHRISTIE, C.

RHODES UNIVERSITY



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