Purpose Cardiopulmonary exercise testing (CPET) in preschoolers (4–6 years) represents a challenge. Most studies investigating CPET have been limited to older children (> 8 year). However, knowledge of the performance of small children is essential for evaluating their cardiorespiratory fitness. This study strives to compare a modified Bruce protocol with a new age-appropriate incremental CPET during natural movement running outdoors, using a mobile device. Methods A group of 22 4–6-year-old healthy children was tested indoor on a treadmill (TM) using the modified Bruce protocol. The results were compared with a self-paced incremental running test, using a mobile CPET device in an outdoor park. The speeds were described as (1) slow walking, (2) slow running, (3) regular running, and (4) running with full speed as long as possible. Results Mean exercise time outdoors (6,57 min) was significantly shorter than on the treadmill (11,20 min), $$\dot{V}{O}_{2peak}$$ V ˙ O 2 p e a k (51.1 ml/min/kg vs. 40.1 ml/min/kg), RER (1.1 vs. 0.98) and important CPET parameters such as $$\dot{V}E$$ V ˙ E max, O2pulse, heart rate and breath rate were significantly higher outdoors. The submaximal parameter OUES was comparable between both the tests. Conclusions Testing very young children with a mobile device is a new alternative to treadmill testing. With a significantly shorter test duration, significantly higher values for almost all cardiopulmonary variables can be achieved without losing the ability to determine VT1 and VT2. It avoids common treadmill problems and allows for individualized exercise testing. The aim is to standardize exercise times with individual protocols instead of standardizing protocols with individual exercise times, allowing for better comparability.

Introduction Due to the Corona-lockdowns the closure of sports facilities and schools has led to a decline in physical activity (PA) for months. PA is essential for maintaining cardiopulmonary function assessed by peak oxygen uptake. Since peak oxygen uptake represents the best predictor for mortality and morbidity in children with congenital heart disease the impact of lockdowns on this parameter is vital. Methods We evaluated retrospectively cardiopulmonary exercise data from our patient collective from before lockdown with twin-paired data from during lockdown. The twin-pairing was achieved by matching patients with similar heart disease, age, sex, and test method. Cardiopulmonary exercise testing was achieved on either the treadmill or the bicycle. Results We were able to twin-pair 90 cases (26 twins with heart disease and 19 healthy twins). There was a significant decrease of cardiopulmonary function (V̇O2peak: 35.7±9.8 vs.30.4±10.6) in the heart disease cohort along with a significant decrease in peak oxygen pulse (13.3±4.1 vs. 11.4±4.5), and peak minute ventilation (V ̇E: 83.05±29.08 vs.71,49±24.96). The healthy children improved over the timeframe, but this only reached significance for peak minute ventilation (81.72±25.79 vs.97.94±31.4). Conclusion We observed a significant decline of peak oxygen uptake during lockdown in the group of congenital heart disease (CHD) patients. This involved a loss of cardiac function as well as pulmonary function. This could be explained by limited access to sports facilities and restriction of regular daily movement due to school closure and overprotection. Healthy children improved their pulmonary function. This might be an indication of an improvement of exercise during confinement.

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