Cardiorespiratory fitness is the most important variable related to health and a strong predictor of mortality. However, it is rarely used in clinics due to costs, specialized equipment, space needs, and the requirements of expert staff such as an exercise physiologist, physician, or other health professional. This work aims to validate and test the reliability of a submaximal step test to estimate VO₂max of 8-to 16-year-old pediatric populations as a simple and low-cost tool for clinical practice. A cross-sectional study included 242 children and adolescents (42.1% girls) aged 8–16. Cardiorespiratory fitness was determined by a maximal incremental test on a treadmill until exhaustion. The step test entailed maintaining a steady pace of 22 steps per minute for 3 min (60 bpm), with the heart rate being recorded at the end of the test. Nutritional status was computed through BMI z-score. A multiple linear regression model validated the step test and developed a new equation to predict VO₂max, including the third-minute heart rate, weight, and height. The reliability among predicted and measured VO₂max was assessed by Bland-Altman analysis. The mean age was 12.5 ± 2.6; 51.6% were overweight or obese. The cardiorespiratory fitness measured as VO₂max was 35.01 ± 0.58 ml·min-¹·kg⁻¹. A robust correlation was observed between the predicted VO₂max from the step test and the measured VO₂max (r = 0.86, p < 0.001). Bland-Altman analysis indicated statistical concordance between predicted and measured VO₂max. Our findings indicate that the step test protocol is valid and reliable for estimating VO₂max in children and adolescents. Furthermore, the predictive equation is suitable for application among children aged 8–16.

Weekend cyclists are individuals who engage in vigorous physical activity only on weekends, as opposed to those who exercise regularly during the week. Research suggests that concentrating physical training on one or two days may benefit heart health and metabolism, similar to exercising regularly. However, it remains unclear whether weekend cyclists exhibit similar adaptations in metabolic, performance, and muscle oxygenation markers. The aim of this study is to compare cardiorespiratory fitness, body composition, cardiometabolic risk markers, muscle strength, and muscle oxygenation between cyclists who concentrated training on weekends and cyclists who distributed training across three or more days per week. In this study, we used an analytical, observational, non-experimental design that recruited 28 cyclists, divided into weekend cyclists (n = 14) and regular cyclists (n = 14). Body composition, blood tests, lower body strength, aerobic capacity, and muscle oxygen saturation were assessed. Results: Weekend cyclists exhibited lower VO₂max (36.7 ± 3.9 vs. 48.9 ± 6.3 mL·kg⁻¹·min⁻¹), lower knee extension strength (3.16 ± 0.57 vs. 4.42 ± 0.83 Nm·kg⁻¹), and reduced ΔSmO₂ responses during exercise compared with regular cyclists (all p < 0.05). In addition, weekend cyclists presented higher body fat percentage (25.9 ± 3.8 vs. 17.2 ± 4.2%), greater waist circumference (90.5 ± 4.3 vs. 83.6 ± 5.1 cm), and lower HDL cholesterol levels (54.2 ± 8.4 vs. 64.1 ± 11.0 mg/dL). In conclusion, weekend cyclists have lower cardiorespiratory fitness, muscular strength, and reduced ΔSmO₂ responses during incremental exercise, along with higher levels of visceral fat and triglycerides, compared to those who train three or more days a week. The distribution and frequency of training within their workout plans were associated with differences in cardiorespiratory fitness and cardiometabolic markers.