Later, all heart rate data were averaged at 10 s intervals In or

Later, all heart rate data were averaged at 10 s intervals. In order to establish a reference #Transmembrane Transporters inhibitor randurls[1|1|,|CHEM1|]# for heart rate, we identified three zones of physical exertion based on the VT and the RCP: zone I, below to the VT; zone II, between VT and RCP; and zone III, above RCP. In addition, to estimate the total work load of exercise performed by subjects we used the training impulse (TRIMP) method by Foster et al. [22]. To calculate TRIMP, the score for each heart rate zone was computed by multiplying the accumulated duration in this zone by a multiplier for this particular phase, e.g. 1 min in zone I was given score of 1 TRIMP (1 × 1), 1 min in zone

II was given a score of 2 TRIMP (1 × 2), and 1 min in zone III was given a score of 3 TRIMP (1 × 3). The total

TRIMP score was obtained by summating the results of the three zones [(min of zone I HR [< VT] × 1) + (min of zone II HR [> VT - < RCP] × 2) + (min of zone III HR [> RCP] × 3)]. To estimate energy expenditure during the race, the individually derived linear relationship between heart rate and VO2 was used to estimate the oxygen cost during the work efforts (r2 = 0.988 ± 0.005). Two different individualized equations were established: 1) a linear regression equation for racing time which was derived from data during the incremental exercise test. We used an energy equivalent of oxygen based on the mean intensity during racing time (i.e. the non-protein energy equivalent corresponding to mean heart rate during the work efforts). This value was, on average, 0.02 MJ/LO2 (4.970 ± 0.048 kcal/LO2), corresponding to a RER of 0.941 ± 0.057 [23]. 2) A single exponential

equation best fitted to VO2 and heart rate was taken during the recovery period of the cycle ergometer test (r2 = 0.912 ± 0.015). An energy equivalent of 0.02 MJ/LO2 (4.825 kcal/LO2) was used, assuming a RER of 0.82 [23]. The rationale for much our approach was that athletes performed bouts of exercise in which the heart rate-VO2 relationship can be assumed to be linear, interspersed with periods of recovery and rest, during which the heart rate-VO2 relationship becomes nonlinear [24]. Statistical analyses Data are presented as individual values and means ± SD. A non-parametric Wilcoxon test was used to compare the energy balance and changes in body mass and exercise intensity during the event. In addition, differences between nutritional data during the first (1900 h – 0700 h) and the second (0700 h – 1900 h) 12 hour period were assessed. The main nutritional variables (i.e. energy, carbohydrates, proteins, fats, fluid, sodium and caffeine) were correlated to speed and distance completed in absolute (i.e. km; km/h) and relative (i.e. % of decrease of distance and speed) values using Spearman’s rank correlation analysis.

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