6 weeks of fartlek-style endurance training does not alter physiological responses to mild cold exposure but attenuates the cold-induced plasma noradrenaline response: A randomized, matched control trial
Alexander Braunsperger, Lara Becker, David P. Camargo, Sidney Radsak, Magdalena Paintner, Dimitrios Kossenakis et al. · Journal of Clinical & Translational Endocrinology · 2026
Background and aims: Rodent studies suggest that endurance training may promote the browning of white adipose tissue and enhances adipose tissue thermogenesis during cold exposure. However, it remains unclear whether endurance training leads to similar adaptations in humans. The
Aim: of this study was therefore to find out whether six weeks of intensive, fartlek-style cycle endurance training alters responses to cold exposure, specifically cold-induced changes of oxygen uptake, plasma noradrenaline concentrations and the effect of conditioned serum on markers of adipocyte browning in culture.
Methods: and
Results: Twenty-four healthy, untrained participants completed a six-week fartlek-style cycling intervention (3 sessions/week) or control period. We estimated cold-induced adaptive thermogenesis before and after the intervention by indirect calorimetry during 60 min of mild cold exposure at 18 °C. Endurance training increased on average the VO₂max by 5 ml/kg/min (95% CI 1 to 8; p = 0.010), maximal power output by 19 W (95% CI 5 to 33; p = 0.011), and power at the 4 mmol/l lactate threshold by 30 W (95% CI 18 to 43; p < 0.001). However, training did not alter cold-induced oxygen uptake, carbon dioxide production, energy expenditure, supraclavicular skin temperature, or mean skin temperature compared with controls. In an exploratory analysis, the cold-induced increase in plasma noradrenaline was attenuated after endurance training (−176 pg/ml, 95% CI -337 to −14; p = 0.035), whereas the exercise-induced noradrenaline response was unchanged. Cold- or exercise-conditioned serum did not alter UCP1 mRNA expression in beige adipocytes.
Conclusion: Six weeks of fartlek-style endurance training increased cardiorespiratory and metabolic fitness but had little effect on the response to cold exposure with no evidence for adipose tissue browning based on the conducted serum incubation experiment.