Hematological and biochemical responses to three doses of caffeine during the CrossFit® workout: a randomized, double-blind, crossover trial

Background This study investigated the effects of three doses of caffeine (CAF) on hematological and biochemical responses during the CrossFit® workout, a protocol known to induce significant physiological fluctuations.Methods In a randomized, double-blind, placebo (PLA)-controlled crossover trial, 26 moderately trained CrossFit® athletes received acute doses of 3, 6, or 9 mgCAF/kgbody mass (BM), or a PLA, 70 min before a 17-min CrossFit® workout.Results While exercise was the predominant driver of hematological changes, with no CAF-specific modulation of blood cell indices, significant treatment × time point interactions were observed solely for glucose concentration. Specifically, MEDIUM (6 mgCAF/kgBM) and HIGH (9 mgCAF/kgBM) CAF doses produced significantly greater post-exercise glucose elevations compared to baseline and PLA visits. Phosphates concentrations increased over time, particularly post-exercise, with no treatment effect retained after excluding baseline visit in the sensitivity analysis. Calcium level dynamics were influenced by temporal factors rather than CAF, and magnesium concentration remained stable.Conclusions These findings suggest that acute CAF ingestion selectively influences post-exercise glucose responses during the CrossFit® workout, whereas hematological variables and most biochemical markers remain unaffected. Significant post-exercise glucose elevations were observed following the 6 and 9 mgCAF/kgBM conditions compared with baseline and PLA visits, while serum mineral concentrations remained largely stable across treatments.Clinical trials registration NCT03822663