Enhanced energy availability has limited impact on training adaptations across a pre-season in female rugby union athletes

Aim
This single-blinded, controlled dietary intervention examined the influence of enhanced energy availability (EA) on training adaptations across a 7-week pre-season in female rugby union athletes.

Introduction
Athletes often fail to upregulate energy and carbohydrate (CHO) intake to match training demands, potentially leaving them vulnerable to problematic low EA1. Current sports nutrition guidelines recommend 6-10g CHO·kg-1·d-1 on heavy training days2 yet typical reported intakes are 3-4g CHO·kg-1·d-1.1
Observational studies (4-12 weeks) suggest female athletes who fail to increase energy intake to accommodate increased needs throughout intensive training blocks (where exercise energy expenditure (EEE) is increased to 1200-1400kcal·d-1) fail to adapt to the training stimulus3,4. This remains to be verified by interventional studies as controlling for EA becomes more challenging over time5.

Methods
13 female rugby athletes were allocated to intervention (INT, n=7) or control (CON, n=6). Both groups were supplied with full food provision on all training days but were blinded to the intervention (see Figure 1).
Training load consisted of 4 squad sessions per week, including field and resistance training.
EEE was estimated using Actiheart wearables with individual HR-VO2 algorithms derived from a treadmill graded exercise test.
Comparisons between INT and CON for change in training adaptations were explored using linear effect mixed modelling (time, group and interaction (group*time) effects).

Results
Training day energy and CHO intakes were higher in INT than CON (3092±230 vs 2474±225kcal·d-1, p=0.006; 6.3±0.2 v 3.1±0.2g·kg-1·d-1, p <0.001).
Self-reported non-training CHO and protein intakes remained higher in INT (3.3±0.8 v 2.2±0.7g·kg-1·d-1, p=0.007; 1.8±0.4 vs 1.3±0.4g·kg-1·d-1, p=0.026) with no differences in energy or fat intake between groups.
EEE per session was lower for INT than CON (554±100 vs 661±128kcal, p<0.001), however there was no statistical difference when expressed relative to FFM.
EA on training days, non-training days and collectively across the 7 weeks was higher for INT than CON (47.3±2.6 vs 27.5±3.0kcal·kg-1·FFM-1·d-1, p<0.001; 43.6±5.0 vs 33.3±9.2kcal·kg-1·FFM-1·d-1, p=0.026; 45.6±3.7 vs 30.5±5.5kcal·kg FFM-1·d-1, p<0.001).
The model revealed a significant time effect for 3RM bench pull (F[1,10] = 7.047, p = 0.024; increase 4.5kg (0.7-8.3kg)) and bench press (F[1,10] = 9.671, p = 0.011; increase 5.1kg (1.4-8.7kg)) over the 7 weeks.
There were no significant time, group or interaction effects for any other fitness metrics (see Figure 2).

Conclusions
This is the first intervention study in which blinded dietary control has been applied over more than several days.
Implications of altered (problematic) EA were not evident in this small group of high-calibre female rugby athletes which may be explained by the length of time and severity of the EA applied.
Despite differences in EA status, female rugby athletes improved upper body strength over a 7-week pre-season period. However, the training load (as inferred by EEE) may have been an insufficient stimulus to enable changes in high-intensity running capacity and lower body strength and jump performance, and with that, the implications of problematic low energy availability.