Influence of Guideline-Based Carbohydrate Intake on Training Adaptations, Health, and Sleep in Female Rugby Athletes: An Exploratory Study

This exploratory study examined the effect of carbohydrate and subsequent energy availability (EA) on training adaptations, health, and sleep metrics across a 7-week preseason in semiprofessional female rugby union athletes. Full food provision on training days (four/week) manipulated carbohydrate intake: 6 versus 3 g·kg-1·day-1 for intervention (n = 7) and CON (n = 6), respectively while standardizing protein intake (>1.2 g·kg-1·day-1). Nontraining days involved ad libitum intake. Quantification of exercise energy expenditure via an individually calibrated wearable device allowed estimation of EA. Strength (three-repetition max squat, bench pull, and bench press), Bronco shuttle time; countermovement jump; biomarkers including iron studies, thyroid function, and cholesterol; sleep metrics; and physique (four-compartment model) were assessed before and after preseason. Training day carbohydrate intake was higher in intervention than CON (6.3 ± 0.2 vs. 3.1 ± 0.2 g·kg-1·day-1, p < .001), resulting in higher EA across the preseason (45.0 ± 5.8 vs. 29.9 ± 5.8 kcal·kg-1 fat-free mass-1·day-1, p < .001). Significant time effects were observed for bench pull (+3.6 kg, p = .024) and bench press (+4.6 kg, p = .011), fat mass (-1.1 kg, p < .001), fat-free mass (+1.2 kg, p = .025), and ferritin (-29 μg/L, p = .009). No significant interaction was observed for training adaptations, physique, or biochemical markers. Greater sleep duration was observed in CON on training nights, F(1, 156.072) = 5.821, p = .017, although other sleep metrics showed limited between-group differences. While increased carbohydrate intake improved EA, it had limited effect on training adaptations, health, or sleep metrics in this small, exploratory cohort.