Step-test-based assessment of cardiorespiratory fitness improvement achieved through isovolume maneuver trial

(1) Objective: We performed a step test to investigate whether isovolume maneuver (IVM) trial is effective in improving cardiorespiratory fitness; (2) Methods: The experiment involved two consecutive step tests in which the IVM was employed between the two tests. The heart rate (HR), breathing rate (BR), instantaneous phase difference (IPD) of thoracoabdominal movement, and physical fitness index (PFI) of the participants were analyzed. We also obtained data on the ascending rate of HR (HRasc), the rate relative to the baseline HR during recovery, and the scores for a modified PFI (mPFI) based on the baseline PFI; (3) Results: We recruited 27 sedentary and healthy college students as participants. The results from the second step-test were compared with the first step-test. The participants' mean HRasc decreased by 30.66 % +/- 32.52 %, their mean BR decreased by 13.08 % +/- 31.90 %, their mean mPFI increased by 30.78 % +/- 38.94 %, and their mean IPD increased by 15.31 % +/- 28.44 %; (4) Conclusions: IVM reduced the participants' BR and HRasc and increased their mPFI and IPD. These findings verify that IVM can effectively improve physical activity performance. Furthermore, an IPD of 39 degrees for implementation of abdominal breathing during exercise is a key threshold that warrants further research.