title: Cerebrovascular responses during rowing: Do circadian rhythms explain morning and afternoon performance differences?
abstract: The purpose of this study was to characterize cerebrovascular responses to rowing exercise, investigating whether their diurnal variation might explain performance differences across a day. Twelve male rowers completed incremental rowing exercise and a 2000-m ergometer time trial at 07:00 h and 16:00 h, 1 week apart, while middle cerebral artery velocity (MCAv), cerebral (prefrontal), and muscular (vastus lateralis) tissue oxygenation and hemoglobin volume (via near-infrared spectroscopy), heart rate, and pressure of end-tidal CO2 (PET CO2) were recorded. MCAv was 20-25% above resting levels (68 ± 12 cm/s) during submaximal and maximal exercise intensities, despite PET CO2 being reduced during maximal efforts (down ∼ 0.5-0.8 kPa); thus revealing a different perfusion profile to the inverted-U observed in other exercise modes. The afternoon time trial was 3.4 s faster (95% confidence interval 0.9-5.8 s) and mean power output 3.2% higher (337 vs 347 W; P = 0.04), in conjunction with similar exercise-induced elevations in MCAv (P = 0.60) and reductions in cerebral oxygenation (TOI) (P = 0.12). At the muscle, afternoon trials involved similar oxygen extraction (HHb volume and TOI) albeit from a relatively lower total Hb volume (P < 0.01). In conclusion, rowing performance was better in the afternoon, but not in conjunction with differences in MCAv or exercise-induced differences in cerebral oxygenation.
authors.affiliation: School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand.|Nuffield Department of Clinical Neuroscience, University of Oxford, Oxford, UK.
authors.forename: O K
authors.initials: OK
authors.lastname: Faull
authors.affiliation: School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand.
authors.forename: J D
authors.initials: JD
authors.lastname: Cotter
authors.affiliation: Department of Physiology, University of Otago, Dunedin, New Zealand.|School of Sport, Exercise & Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK.
authors.forename: S J E
authors.initials: SJ
authors.lastname: Lucas
mesh_terms: D000293:Adolescent; D054874:Athletic Performance / Q000502:physiology*; D001783:Blood Flow Velocity; D002940:Circadian Rhythm / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006339:Heart Rate; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism*; D017397:Prefrontal Cortex / Q000378:metabolism; D052097:Quadriceps Muscle / Q000378:metabolism; D013997:Time Factors; D055815:Young Adult
chemical_list: D006454:Hemoglobins; D010100:Oxygen
keywords: Cerebral blood flow; circadian rhythms; hypocapnia; rowing performance