Does Supplementation Affect Swimming Performance in Endurance-Trained Males? A Randomized Placebo-Controlled Crossover Study.

: (COL) is recognized for its unique composition and potential ergogenic and immunological benefits. Unlike mature milk, COL is rich in immunoglobulins, lactoferrin, and various growth factors, making it one of the most potent natural immune stimulants. The purpose of this study was to evaluate the effects of 12-weeks of COL supplementation on swimming-specific performance (SSP) and exercise adaptations in endurance-trained male athletes. Twenty-eight male triathletes and swimmers (age: 31.1 ± 10.2 years; body mass: 81.9 ± 9.0 kg; height: 1.82 ± 0.06 m) participated in a randomized, double-blind, placebo (PLA)-controlled crossover study and received 25 g∙day of COL or PLA for 12 weeks. The study assessed the effects of COL on SSP (8 × 100 m performed at various intensities) and exercise adaptations [heart rate (HR) and blood lactate concentrations ([])]. Four main study visits were conducted-before and after COL ( and ) and PLA ( and ) supplementation. : COL had no significant effect on SSP. Still, the total time of the SSP test was about ~3.04 s shorter after COL supplementation, and ~7.13 s longer after PLA supplementation. Neither COL nor PLA supplementation affected HR during the SSP test. Post-exercise blood [] was significantly reduced after both COL and PLA supplementation. The analysis of SSP results in the consecutive study visits revealed possible existence of the practice effect. : and high-quality milk protein (PLA) seem to be comparably effective in evoking exercise adaptation in endurance-trained male athletes. Long-term crossover supplementation protocols in athletes must consider the impact of possible practice effect when interpreting the outcomes related to exercise performance, but not biochemical or physiological markers of exercise adaptation.