The recommended 60 minutes of moderate-to-vigorous-intensity physical activity  is only being met by a minority of children today. Even though it is well known that physical activity can lead to a multitude of benefits and reduction of risk factors , most children spend their time with sedentary activities . Cardiorespiratory fitness can be estimated by measuring during an incremental step test . This parameter which is negatively associated with morbidity, and mortality from all causes and especially from cardiovascular disease and cancer , can be improved by physical activity  and HIIT in particular .
Trampoline jumping is a widely used physical activity in children. Therefore trampoline jumping represents an ideal means for promoting physical activity in children. In order to evaluate its intensity during different jumping modalities we investigated slow endurance jumping over a period of five minutes with high-intensity jumping over a period of two minutes.
Eligibility of trampoline jumping for MICT and HIIT
Interestingly during the endurance interval was already higher than at VT1 even though the heart rate was comparable, indicating that the heart rate is not an accurate tool for estimating cardiopulmonary function. The same observation was made for at VT2 which was comparable to both high-intensity intervals but the mean heart rate was significantly lower during the first high-intensity interval and only rose to comparable values during the second high-intensity interval. Slow trampoline jumping could therefore be an adequate tool for moderate-intensity continuous training in children as it can be performed close to at VT1. However, the children stated that they were bored during the slow jumping and felt no tiredness afterwards. The vigorous jumping was much more enjoyable according to their accounts and was performed with -values at VT2, thus representing high-intensity interval training.
As the mean achieved during the second high-intensity interval was not significantly lower than from the incremental step test, and the maximum recorded during the trampoline test was significantly higher, the children were not only able to achieve peak oxygen uptake or even more during vigorous trampoline jumping but were also able to sustain this high intensity for a duration of two minutes as can be seen in the exemplary data represented in figure 1. These findings suggest that a true can be achieved during trampoline jumping by kids.
Two previous studies have investigated the cardiopulmonary effects of trampolining [22, 23]. The maximum recorded during vigorous jumping was around 40 ml kg-1 min-1 in healthy, adult males [23, 22] , which is significantly lower than the maximum recorded in our study (55.6 ml kg-1 min-1). Children tend to achieve higher -values than adults during cardiopulmonary exercise tests , which can explain this discrepancy. Also in these previous studies, -values during vigorous trampolining did not differ significantly from vigorous running on the treadmill [22, 23], whereas the children in our study achieved significantly higher values during jumping than running. A possible explanation for this difference could be the higher fun factor of the trampoline in a young age-group. The children were maybe more willing to fully exhaust themselves on the trampoline than while running outdoors. Comparable test protocols are needed to evaluate this finding further.
Cardiac and pulmonary contribution during trampoline jumping
The cardiac output, indirectly measured through the O2-pulse, was comparable during both high-intensity intervals and at during the outdoor test. Interestingly, the minute ventilation was significantly lower during both high-intensity intervals than at during the outdoor test, but the maximum value during trampoline jumping and incremental step test was comparable. This indicates that peak O2-pulse was reached by the children during the trampoline test, they were able to maintain this high cardiac output for the full duration of the high-intensity interval. On the other hand peak reached during trampoline jumping and outdoor running was comparable, but could not be maintained over a timeframe of two minutes either as a consequence of rising too slowly or of being too difficult to keep up.
This study has several limitations. First of all the number of participants is small and more significant differences might have become apparent with a higher number of children. There was no evaluation of the power realized during the trampoline jumping as the determination of metabolic equivalents for trampoline jumping is not established yet.