Table 2. Characteristics of muscle force and breath-holding challenge.

Characteristics
Muscle force
Handgrip strength (kg)	28.6 ± 3.7
Quadriceps strength (kg)	29.3 ± 6.6
Breath-holding parameter
Threshold time of dyspnea (sec)	20.4 ± 7.4
Breath-holding time (sec)	34.5 ± 13.3
Highest Borg dyspnea during breath-holding	5.9 ± 1.9
Dyspnea reserve time (DRT), (sec)	14.8 ± 7.4
50% threshold time of dyspnea (sec)	10.19 ± 3.7
50% DRT point (sec)	27.5 ± 10.0
Lowest SpO2 during breath-holding (%)	90.3 ± 3.5

Data are presented as mean ± SD. Dyspnea reserve time (DRT) was calculated by subtracting the threshold time of dyspnea from total breath-holding time. The 50% DRT point was calculated as sum of the threshold time of dyspnea and 50% DRT of each subject.