Brain oxygenation declines in elite Kenyan runners during a maximal interval training session.
OBJECTIVE
The purpose of this study was to characterise the cerebral oxygenation (Cox) response during a high-intensity interval training session in Kenyan runners, and to examine any relationship with running performance.


METHODS
15 Kenyan runners completed a 5-km time trial (TT) and a Fatigue Training Test on a treadmill (repeated running bouts of 1-km at a pace 5% faster than their mean 5-km TT pace with a 30-s recovery until exhaustion). Changes in Cox were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxy-haemoglobin (Δ[O2Hb] and Δ[HHb]), tissue oxygenation index (TOI), and total hemoglobin index (nTHI).


RESULTS
The number of 1-km repetitions achieved by the participants was 5.5 ± 1.2 repetitions at a mean pace of 20.5 ± 0.7 km h-1. Δ[O2Hb] measured at the end of each running repetition declined progressively over the course of the trial (p = 0.01, ES = 4.59). Δ[HHb] increased during each running bout until the end of the Fatigue Training Test (p < 0.001; ES = 6.0). TOI decreased significantly from the beginning of the test (p = 0.013, ES = 1.83), whereas nTHI remained stable (ES = 0.08). The Cox decline in the Fatigue Training Test was negatively correlated with the speed at which the test was completed (p = 0.017; r = -0.61), suggesting that the best performers were able to defend their Cox better than those of lower running ability.


CONCLUSIONS
In conclusion, this study suggests that elite Kenyan runners cannot defend cerebral oxygenation when forced to exercise to their physiological limits. This emphasises the critical importance of pacing in their racing success.
Department of Physical Education and Sport, Faculty of Physical Activity and Sport Sciences, University of the Basque Country UPV/EHU, Portal de Lasarte 71, 01007, Vitoria-Gasteiz, Spain. jordan.santos@ehu.eus.|UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Cape Town, South Africa. jordan.santos@ehu.eus.
Jordan
http://orcid.org/0000-0001-9467-525X
J
Santos-Concejero
Department of Kinesiology, University Laval, Quebec, Canada.
F
F
Billaut
Department of Sport Science, University of Stellenbosch, Stellenbosch, South Africa.
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L
Grobler
Department of Physiology, European University of Madrid, Madrid, Spain.
J
J
Oliván
UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Cape Town, South Africa.
T D
TD
Noakes
UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Cape Town, South Africa.|School of Medicine, University of the Free State, Bloemfontein, South Africa.
R
R
Tucker
D000328:Adult; D056352:Athletes; D001921:Brain / Q000378:metabolism*; D000072696:High-Intensity Interval Training / Q000009:adverse effects*; D006801:Humans; D007630:Kenya; D010101:Oxygen Consumption; D012420:Running / Q000502:physiology*
African runners; HIIT; Near-infrared spectroscopy; Oxy-hemoglobin; Performance