Physiological Responses to CrossFit Training: Evaluation of Aerobic Endurance through Cardiopulmonary Exercise Testing

Background. CrossFit is a high-intensity training method involving varied functional movements that is potentially effective for improving aerobic endurance. Objectives. This study used a mixed-methods approach to evaluate the effects of a structured CrossFit programme on cardiorespiratory fitness, combining objective measurements with the athletes’ subjective perceptions. Materials and Methods. A total of 80 regular exercisers (aged 20–35) were divided into an experimental group (CrossFit) and a control group (weight training). A quantitative assessment was conducted using cardiopulmonary exercise testing (CPET) at two time points (T0 and T1, after 12 weeks), analysing VO₂ max, ventilatory threshold and heart rate response to submaximal loads. In parallel, semi-structured interviews were conducted at the end of the intervention and analysed using thematic analysis. Results. The results showed greater improvements in the CrossFit group than in the control group, with an average increase in VO₂ max of +8.2% vs. +1.9%, an increase in ventilatory threshold of +6.4% vs. +1.1%, and a reduction in heart rate at the same load of −3.7% vs. −0.9%, respectively. Conclusions. The interviews confirmed better fatigue management, more efficient breathing, and the transfer of benefits to daily activities. Therefore, the findings indicate that a 12-week CrossFit programme appears to promote significant cardiorespiratory adaptations, consistent with the athletes’ perceptions.