Can dairy beverages promote post-exercise recovery in young female athletes? A crossover study on milk and kefir.

This study assessed the effect of milk and kefir on post-exercise recovery in young female athletes. Using a crossover design, 16 participants (14.2 ± 1.9 years) completed three high-intensity cycling sessions. Each session was followed by ingestion of water, milk or kefir (∼250 ml), with recovery outcomes assessed pre-exercise, post-exercise and post-beverage (∼90 min post-ingestion), including physical (mean power output, MPO) and cognitive performance (Stroop, Go/No-Go), heart rate variability (Ln-rMSSD), acute fluid balance (body mass), muscle soreness and perceived fatigue. Overall, recovery profiles for physical and cognitive performance, Ln-rMSSD and body mass did not differ significantly across beverages (time × beverage interactions: p > 0.05). Conversely, muscle soreness and perceived fatigue improved from post-exercise to post-beverage after water and kefir (p ≤ 0.024, r = 0.47-0.59), but not after milk (p ≥ 0.075, r = 0.40-0.42). Despite the absence of significant differences, effect size (ES) analysis indicated small pre-exercise-to-post-beverage changes in MPO for milk and kefir (ES = 0.48-0.49) compared with moderate decreases following water (ES = 1.07). Similarly, post-exercise-to-post-beverage MPO increased largely after milk and kefir (ES = 1.29-1.30), but only moderately after water (ES = 0.62). Body mass decreased moderately from pre-exercise to post-beverage with water (ES = 0.65), with trivial-to-small differences observed for milk (ES = 0.37) and kefir (ES = 0.18), while perceptual recovery appeared overall more favorable with water than milk and kefir. In conclusion, although milk and kefir showed potential benefits for physical performance and fluid balance, these findings should be interpreted cautiously due to the lack of statistical significance. Conversely, the slightly better perceptual recovery observed with water likely reflects normal variability in subjective ratings rather than true physiological differences.