Abstract

Introduction
Maintenance of cerebral oxygenation (O2Hb) within a stable range during endurance exercise is thought to
contribute to successful performance (Nielsen & Seifert, 2011). This may be due to the importance of cognitive
processes inherent within the ability to regulate pace (Renfree et al., 2013). Yet cognitive function has been
suggested to be impaired during high intensity exercise (Dietrich & Audiffren, 2011). Using a dual-task
paradigm this study explored the phenomenon of pacing through evaluating the impact of increased cognitive
load at different stages of a cycling time trial (TT) on cerebral O2Hb, pacing and time to completion.

Methods
Twelve well-trained cyclists (31 ± 9 yrs, PPO 352 ± 29 W, VO2peak 57 ± 6 ml⋅kg⋅min-1) performed, in a randomised order, 4 simulated 20-km cycling TTs on separate occasions. These included a control simulated 20-
km TT (TTCON) and 3 experimental conditions in which participants concurrently performed an executive
cognitive task for the duration of the 1st half (TT1stHCL), the 2nd half (TT2ndHCL) and the whole duration of the TT
(TTFullCL). Cerebral O2Hb was assessed at the dorsolateral prefrontal cortex (dLPFC). Blood lactate (BLa), effort (TEA), exertion (P-RPE) and affect (FS) were measured.

Results
Completion time during TTCON (2122s ±378) compared to all experimental conditions was significantly faster;
TT1stHCL (2257s ±382; p<0.01, partial η2=0.93); TT2ndHCL (2205s ±407; p<0.01, partial η2 =0.64); TTFullCL
(2307s ±411; p<0.01, partial η2=0.79). Mean cerebral O2Hb increased in all conditions but did not change
between conditions. Pacing profile was not different between TTCON and TTFullCL. Mean values of BLa, TEA, PRPE
and FS were not different between conditions, even though mean PPO was lower in experimental
conditions. Cognitive performance was impaired in all conditions.

Discussion
Increased cognitive load has a detrimental impact upon endurance cycling performance. Upon an initial increase
there was a plateau, then decline, in cerebral O2Hb during the cycling TT which was not affected by
experimental conditions. This suggests a ceiling in O2Hb delivery to the dLPFC during endurance exercise
performance. Thus, increased cognitive load led to a greater competition of dLPFC O2Hb delivery. For a given
level of power output, TEA, P-RPE and FS increased in the experimental conditions. Therefore increased
cognitive load carries an effortful cost that during self-paced endurance exercise may curtail the selected level of
exercise intensity. During competition athletes should aim to reduce the cognitive load associated with pacing
strategies.

References
Nielsen HB, Seifert T. (2011). J Appl Physiol, 110 (1):292.
Renfree A, Martin L, Micklewright D, et al. (2014). Sports Med, 44(2): 147-58.
Dietrich, A., Audiffren, M. (2011). Neurosci Biobehav Rev, 35, 1305-1325.