european college of sport science

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
OP-PH03 Physiology 3
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 VARIA-
TION 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 -
10 mmHg, until pre-syncope. Pre-syncope was terminated on participants’ request due to subjective symptoms associated with fainting,
or when systolic BP reduced to 0.05).
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.
100 14 TH
ANNUAL CONGRESS OF THE EUROPEAN COLLEGE OF SPORT SCIENCE