The quantification of daily carbohydrate periodization among endurance athletes during 12 weeks of self-selected training: presentation of a novel Carbohydrate Periodization Index

BackgroundContemporary sports nutrition guidelines recognize that endurance athletes should periodize their daily carbohydrate (CHO) intake according to the demands of their training and competitive schedule. However, objective assessments of the dietary CHO periodization practices adopted by endurance athletes during prolonged training periods are not readily available. ObjectivesTo objectively assess the magnitude of the CHO periodization practices adopted by endurance athletes via the formulation of a novel CHO Periodization Index (CPI). The CPI is proposed to represent a single metric to quantify how tightly an athletes CHO intake is matched with training load, the magnitude of adjustment, and how frequently these adjustments occur. MethodsSelf-selected training and dietary intake was reported daily by 55 endurance athletes (61.8% male) for 12 weeks (representing a total of 4,395 days of dietary assessments). Calculations were made for correlations between daily CHO intake and training load (product of session rating of perceived exertion and duration), CHO monotony (mean daily CHO intake divided by SD), CHO range (highest minus lowest single-day intake), and the CPI (correlation * range / monotony). Sub-group analysis was also performed to examine differences in CPI, frequency of fasted training sessions, and weekly training volume based on competitive level, habitual diet, and sex. ResultsMean participant daily CHO intake was 3.9 {+/-} 1.5 (range 1.2 to 7.2) g/kg, with the highest single-day intake being 17.6 g/kg. Mean CHO range was 6.6 {+/-} 3.1 (range 2.0 to 15.2) g/kg. Carbohydrate monotony values ranged from 1.0 to 6.0. Pearson correlations between training load and daily CHO intake ranged from -0.34 to 0.87. Mean CPI was 1.0 {+/-} 1.2 (range - 1.2 to 5.6) and was higher among the highest-level athletes. ConclusionEndurance athletes do not readily adjust daily CHO intake according to the demands of training. Furthermore, the CPI represents a promising tool that that can be used by researchers, coaches, and athletes to quantify CHO periodization practices and compare within and between individuals. Key PointsO_LIIt is recommended that endurance athletes adjust their daily carbohydrate intake according to variations in exercise volume and intensity, but there is limited knowledge of how this is being applied by athletes, and limited methods for quantifying or assessing the variations in intake. C_LIO_LIWe introduce a novel Carbohydrate Periodization Index (CPI), a single metric to capture how tightly an athletes carbohydrate intake is adjusted based on training load, the magnitude of adjustment, and how frequently these adjustments occur. C_LIO_LIData demonstrate that many endurance athletes do not follow recommended practices of adjustment in daily carbohydrate intake, or if they do, the magnitude of adjustment is small relative to changes in training volume and/or intensity. C_LI