The goal of this randomized crossover trial is to compare the results of a stationary and a mobile ergospirometry system in 20 healthy endurance trained participants. The main question it aims to answer is to investigate the differences in VO2-measurements between the mobile K5 and the stationary Quark ergospirometry system.

Participants will do a maximal ramp test followed by a sub maximal step test with 6 stages on two different days.

20 endurance trained men and/or women will be recruited. A screening will be done before starting with the test protocol on the treadmill to ensure the suitability of the participants. The test protocol includes two parts. The first part is a maximal ramp test (+0.6km/h each minute until exhaustion). The second part includes a step test with 6 sub maximal stages - each lasting 5 minutes - at 50%, 55%, 60%, 70%, 75% and 80% of the maximal velocity achieved in the first part. There will be a short break between the ramp and the step test. The stationary and the mobile system are tested on 2 separate days with a break of 1-3 days in between. On the second day, procedure will be exactly the same for the participants.

Inclusion Criteria:

• endurance trained (minimum two times endurance training per week)
• healthy as assessed by the physical-activity-readiness-questionnaire (PAR-Q)
• adequately informed and consent confirmed per signature

Exclusion Criteria:

• Pregnancy based on anamnesis
• acute illness, injury, infection, etc., which would impact the measurements

healthy endurance trained male or female older than 18 years