european college of sport science

Thursday, June 25th, 2009
NON-LINEAR INCREASE IN RPE DURING CONSTANT LOAD EXERCISE TO VOLITIONAL EXHAUSTION
RENFREE, A., GURNEY, T.
UNIVERSITY OF WORCESTER
It has been proposed that during constant load exercise to exhaustion, the increase in RPE throughout is linear and that termination
usually occurs prior to attainment of the highest possible RPE score (Noakes 2004). This suggests that the rate of increase in RPE during
constant load exercise, in addition to the highest RPE that can be sustained, determines the duration that a constant workload can be
maintained for. This study models the increase in RPE during constant load exercise to exhaustion at supra lactate threshold intensity
using both the Borg Category (C20) and Category-Ratio (CR10) scales.
Ten recreationally active male participants performed an incremental exercise test on an electronically braked cycle ergometer to allow
visual identification of the workload that coincided with the lactate threshold (LT). Participants then performed two trials to volitional exhaustion
at a workload 60W above LT. RPE was recorded at 60s intervals using either the C20 or CR10 scale. Participants were familiarised
with the scales in advance, and the order was randomised. For both scales, RPE data was subsequently scaled as a percentage of
total exercise duration for each participant.
Total exercise duration was similar regardless of whether participants reported RPE using the C20 (16.7+5.3min) or CR10 (17.1+8.1min)
scales (P>0.05). During every individual trial, participants reported achieving maximum possible RPE regardless of the scale used. When
reporting RPE using C20, termination coincided with achievement of maximal RPE in 30% of participants. When reporting RPE using CR10,
on no occasion did termination coincide with achievement of a maximal RPE. As a group, participants spent 17+14.2 % of total exercise
duration at maximal RPE when using the C20 scale, and 21 +12.0% when using the CR10 scale.
These results suggest that in recreationally active participants, the rate of increase in RPE during constant load exercise is not linear and
that termination does not always coincide with attainment of the highest possible values. Therefore, regardless of the RPE scale used, the
findings of this study disagree with the contention of Noakes (2004) that RPE is the real determinant of the fatigue point during prolonged
sub maximal exercise at a fixed work rate. It is possible, however, that the observed relationship between RPE and termination of exercise
may depend to some extent on the training status and experience of participants in these studies.
Reference
Noakes, T. D. (2004) Linear relationship between the perception of effort and the duration of constant load exercise that remains, J Appl.
Physiol. (96) 1571-1573.
TASK FAILURE DURING HIGH-INTENSITY EXERCISE IS ASSOCIATED WITH A CRITICAL REDUCTION IN TISSUE OXY-
GENATION
BISHOP, D., BORTOLOTTI, S., FERRI, A.
UNIVERSITÀ DEGLI STUDI DI VERONA
Introduction: Task failure is an important feature of performance, ageing and many diseases. Three popular models suggest that task
failure may be due to: a) a failure of skeletal muscle motor unit recruitment (1); b) depletion of a fixed, critical, muscle energy store (2); or c)
a critical reduction in tissue oxygenation (3). The purpose of this study was to assess the hypothesis that task failure during high-intensity,
whole-body exercise may be associated with a critical reduction in tissue oxygenation.
Methods: Six well-trained cyclists (VO2max: 67.6 +/- 6.3 mL/kg/min) performed an incremental test to exhaustion on a cycle ergometer.
They then performed a familiarisation session, followed by, in a random order, constant-load exercise tests at 100, 110 and 120% of
VO2max until task failure. During these trials, near-infrared spectroscopy (NIRS) was used to monitor changes in the concentration
(μM) of oxygenated haemoglobin (Hb) and myoglobin (Mb) (delta[02Hb]), deoxygenated Hb+Mb (delta [HHb]) in the right vastus
lateralis muscle and the frontal cerebral cortex. Oxygen uptake (VO2) and rating of perceived exertion (RPE) were also monitored during
all 3 trials. The study had ethics approval and all subjects signed a statement of informed consent prior to the study.
Results: At task failure, there was no significant difference between the three conditions for delta[HHb] (40 +/- 5 vs 39 +/- 8 vs 37 +/- 7
μM; P>0.05), delta[02Hb] (23 +/- 5 vs 26 +/- 6 vs 22 +/- 3 μM; P>0.05), VO2 (67.6 +/- 4.5 vs 67.4 +/- 3.8 vs 64.7 +/- 4.1
mL/kg/min) or RPE (20 vs 20 vs 20; P>0.05). There were also no significant differences between trials for cerebral oxygenation levels.
Discussion: Our delta[02Hb] and delta[HHb] values, for both the right vastus lateralis muscle and the frontal cerebral cortex, are similar to
those previously reported in the literature (3). We report for the first time however, that task failure during 3 different exercise intensities
occurred at similar tissue oxygen (and oxygen consumption) levels. While further research is required, our results raise the possibility that
task failure during high-intensity exercise (at sea level) may be associated with an inability to further increase the rate of aerobic energy
supply.
References
1. Davis, J. M. and S. P. Bailey. Med Sci Sports Exerc. 29:45-57, 1997.
2. Monod, H. and J. Scherrer. Ergonomics. 8:329-338, 1965.
3. Subudhi, A. W., A. C. Dimmen, and R. C. Roach. J Appl Physiol. 103:177-183, 2007.
CARBOHYDRATE SUPPLEMENTATION PREVENT PROTEIN METABOLISM IN A LONG DISTANCE MOUNTAIN BIKE
TREADMILL
MOTA, M.P., SOARES, J., TEIXEIRA, R., JOÃO, P.
UNIVERSIDADE DE TRÁS-OS-MONTES E ALTO DOURO
Introduction: As a consequence of its intensity and duration, Mountain Bike (MTB) can induce an increase in serum urea concentration as
the final product of protein metabolism. This may be explained by the significant reduction in muscle glycogen with the duration of the
event. In order to prevent muscle glycogen depletion and afterward protein metabolism, we searched if carbohydrate ingestion during a
long distance MTB treadmill can prevent protein metabolism.
Methods: Ten male athletes aged between 15 and 46 yrs took part in this study (average=32±8.7 yrs). All the subjects performed a 59.14
km MTB treadmill in 5.71 hours (±0.76) during which a carbohydrate supplementation (glucose concentration of 0,7g/Kg/h) was given to
each athlete and heart rate was monitored through Polar S625X.
Results/Discussion: Bearing in mind heart rate data, our results revealed that the MTB treadmill was performed with an average intensity
of 82.4%. Although relative values of serum urea concentration were significantly increased (15.55%; p=0,012) at the end of the MTB
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