This was addressed in a second fitness test: Each participant had to perform a three-minute ramp protocol on a rowing ergometer starting at 25 watts. Strain was increased by 25-watt steps to a minimum of 75

watts and a maximum of 125 watts. Stroke frequency had to be kept constant at between 30-40/min. As the seat of the custom-made rowing machine was not movable, all force had to be recruited from the upper part of the body. Between the cycling and the rowing ergometry tests, all participants were allowed to recover for at least two hours. Full recovery was verified by repeated lactate measurements until two consecutive measurements had returned to the individual’s baseline values. Ergospirometry Ergospirometric measurements Inhibitors,research,lifescience,medical were performed with a mobile breath-by-breath ergospirometry device (Cortex Metamax 3 B™, Cortex Biophysik, Leipzig, Germany), combined with a chest-belt heart rate meter (Polar T 41™, Polar Electro, Inhibitors,research,lifescience,medical Büttelborn, Germany) during the endurance tests.

We recorded respiratory rate, respiratory minute volume, oxygen consumption, carbon dioxide production and HR. All parameters were transmitted to a Windows™ based PC and recorded using MetaSoft 3.3™ software (Cortex Biophysik, Leipzig, Germany). As PWC170 is a validated, standard, cycling-based parameter of physical fitness, we aimed to determine a corresponding fitness parameter evaluated during rowing exercises. Therefore, correlations for ergospirometric parameters measured Inhibitors,research,lifescience,medical during rowing with Inhibitors,research,lifescience,medical the individual PWC170 were calculated. Part II: External chest compression Two days after part I, the participants performed two nine-minute sequences of ECC. We chose nine-minute sequences because this is approximately the average time that a first responder has to give ECC during out-of-hospital resuscitation prior to the arrival of professional healthcare providers at the scene [15,16]. Using a computer-generated randomization list, participants were randomly assigned to Inhibitors,research,lifescience,medical start ECC with a CVR of either 15:2 or 30:2, followed by a CVR of

30:2 or 15:2 in a crossover manner. Between the two ECC sequences, all participants were allowed to recover for at least 90 minutes. Full recovery was verified by repeated lactate measurements until two consecutive measurements had returned to the individual’s baseline values. ECC was performed on a standard ALS ALK inhibitor manikin (ResusciAnne™, Bumetanide Laerdal Medical, Stavanger, Norway) placed on the floor with a linear force-depth relationship (32.5 kg 38 mm, 44 kg 51 mm, see Figure ​Figure1).1). The quality of the ECC, determined by the compression depth and rate was measured and recorded by a PC-based automated skill reporting system (SkillMaster™ Reporting System, Laerdal Medical, Stavanger, Norway). In a brief pre-trial test, all participants were initially reminded to use the correct compression site (centre of the chest), rate (100 min-1) and depth (4-5 cm), but no corrective feedback was given during the course of the trial.