Running Low: A Seasonal Analysis of Micronutrient Deficiencies on External-Load Measures in Elite Female Rugby League Players.

UNLABELLED: 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.