Physiological, Metabolic, and Mitochondrial Adaptations to a One-Week Endurance Training Camp in Recreational Athletes: An Observational Study.

Endurance training camps are well established in elite sports, but one-week camps for recreational endurance athletes have recently gained popularity despite limited scientific evidence. This study investigated the effects of a one-week endurance training camp on body composition, endurance performance, and markers of metabolic stress and mitochondrial adaptation in recreational athletes. Female and male endurance athletes (≥18 years) participated in a professionally guided one-week endurance training camp. Assessments included body composition, running diagnostics, sleep-quality/recovery-stress questionnaires, nutrition/energy balance diaries, blood profiling, and mitochondrial biogenesis markers. Measurements were conducted before (pre), during (camp), and after the camp (post). A total of 35 participants (18 male/17 female) were included. Body mass and body fat decreased from pre- to post-camp. Lactate concentrations at threshold levels changed, while velocities at fixed lactate concentrations and maximal oxygen uptake did not significantly improve. Post-camp, lactate dehydrogenase, klotho, and vitamin D increased, whereas interferon-γ, kynurenine, cortisol, creatinine, and ferritin decreased. Plasma mitochondrial and nuclear DNA abundance, as well as PGC1-α expression, increased, while vascular endothelial growth factor decreased. A one-week endurance training camp in a holiday-like setting induces measurable physiological, metabolic, and mitochondrial adaptations in recreational athletes and is associated with reduced systemic and psychological stress. However, the concurrent increase in muscle- and cell-stress markers indicates a substantial physiological load.