Iron and vitamin D are essential for physiological mechanisms underpinning physical capacities characterizing team-sport performance. Yet, the impact of iron deficiency on physical capacities beyond endurance is not clear. Purpose: The purpose of this study was to assess variations in seasonal micronutrient concentrations and how iron deficiency impacts external-load measures in elite female rugby league players. Methods: Iron and vitamin D status were measured in 28 players (age 24 [4] y, body mass 76 [11] kg) across 3 time points of the 17-week National Rugby League Women`s season. Physical demands were evaluated using external-load measures (eg, total distance, PlayerLoad) for training and competition. Linear mixed-effects models were employed to assess the effect of change in serum ferritin concentration on external-load measures. Effect sizes with 95% CIs were calculated to interpret the magnitude of difference in change in indices and performance outcomes between iron-deficient and iron-sufficient players. Results: Iron-deficiency prevalence ranged from 26% to 57% across the season, and <22% of players were vitamin D deficient at each time point. Weak to strong positive associations (R2 = .3-.6) were observed between all external-load measures and moderating variables (serum ferritin, week, position, and athlete). However, these associations were largely attributable to the contribution of week and position. Differences in load measures between iron-deficient and iron-sufficient players were mostly trivial to small. Conclusions: Iron status of elite female rugby league players had little effect on most workload measures within this cohort. However, longitudinal monitoring is warranted to identify how external-load measures are affected individually in response to fluctuations in serum ferritin.
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