Objective: Mask plays an important role in preventing infectious respiratory diseases. The influence of wearing masks in physical exercise on the human body needs to be studied. The purpose of this study is to explore the influence of wearing surgical masks on the cardiopulmonary function of healthy people during exercise.Methods: The physiological responses of 71 healthy subjects (35 men and 36 women, age 27.77 ± 7.76 years) to exercises with and without surgical masks (mask-on and mask-off) were analyzed. Cardiopulmonary function and metabolic reaction were measured by the cardiopulmonary exercise test (CPET). All tests were carried out in random sequence and should be completed in 1 week.Results: The CPETs with the mask-on condition were performed undesirably (p < 0.05), and the Borg scale was higher than the mask-off (p < 0.001). Rest oxygen uptake (V.O2) and carbon dioxide production (V.CO2) with the mask-on condition were lower than mask-off (p < 0.01), which were more obvious at peak exercise (V.O2peak: 1454.8 ± 418.9 vs. 1628.6 ± 447.2 ml/min, p < 0.001; V.CO2peak: 1873.0 ± 578.7 vs. 2169.9 ± 627.8 ml/min, p = 0.005), and the anaerobic threshold (AT) brought forward (p < 0.001). At different stages of CPET with the mask-on condition, inspiratory and expiratory time (Te) was longer (p < 0.05), and respiratory frequency (Rf) and minute ventilation (V.E) were shorter than mask-off, especially at peak exercise (Rfpeak: 33.8 ± 7.98 vs. 37.91 ± 6.72 b/min, p < 0.001; V.Epeak: 55.07 ± 17.28 vs. 66.46 ± 17.93 l/min, p < 0.001). VT was significantly lower than mask-off just at peak exercise (1.66 ± 0.45 vs. 1.79 ± 0.5 l, p < 0.001). End-tidal oxygen partial pressure (PetO2), end-tidal carbon dioxide partial pressure (PetCO2), oxygen ventilation equivalent (V.E/V.O2), and carbon dioxide ventilation equivalent (V.E/V.CO2) with mask-on, which reflected pulmonary ventilation efficiency, were significantly different from mask-off at different stages of CPET (p < 0.05), but no significant difference in percutaneous oxygen saturation (SpO2) was found. Differences in oxygen pulse (V.O2/HR), oxygen uptake efficiency slope (OUES), work efficiency (△V.O2/△W), peak heart rate (HR), and peak systolic blood pressure (BP) existed between two conditions (p < 0.05).Conclusion: Wearing surgical masks during aerobic exercise showed certain negative impacts on cardiopulmonary function, especially during high-intensity exercise in healthy young subjects. These results provide an important recommendation for wearing a mask at a pandemic during exercises of varying intensity. Future research should focus on the response of wearing masks in patients with related cardiopulmonary diseases.

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Introduction: To date, the anti-gravity treadmill (AlterG), as a representative method of Lower body positive pressure (LBPP) treadmills, has been rarely reported for knee osteoarthritis (KOA) rehabilitation. The purpose of this case study was to setup the clinical protocol example for AlterG intervention on KOA and evaluate treatment effectiveness by 3D gait analysis combined with free EMG to explore the kinematic gait parameter changes. Patient concerns: A 65-year-old female patient (BMI = 26, mild obesity) undergoing “more than 7 years of KOA.” The activity of the right knee joint was obviously limited and she suffered from severe pain over the past month. Diagnosis: Due to the patient's symptoms and radiographic findings, she was diagnosed with acute attack of KOA. Interventions: The patient has performed clinical function evaluation and gait analysis combined at pretreatment, post-treatment, and 4 months follow-up assessment. AlterG training was performed 6 days/week for 2 weeks, with up to 30 min of training per session. The training protocol included two major parts, walking and squatting in AlterG. Outcomes: After 2 weeks of AlterG intervention, the 10-m walking test (10 MWT) and Timed-up-and-go (TUG) test improved significantly post-treatment, whereas the Visual Analog Scale (VAS) score decreased post-treatment. The Modified Barthel Index improved post-treatment and the patient restored basic community walk after treatment. The temporal parameter results showed that stride length (%height), mean velocity (%height), and cadence gradually increased before treatment, after treatment, and at 4-month follow-up. The right range of motion (ROM) of knee flexion-extension were gradually increased. Meanwhile, the synchronized EMG data showed that the RMS (root means square) values of the rectus femoris, semitendinosus, and biceps femoris at post-treatment were improved to different degrees than at pretreatment. Conclusion: We found that for this patient with KOA, AlterG relieved pain, and was also effective at improving spatio-temporal parameters, knee flexion/extension gait pattern, and corresponding muscle strength, thereby restoring certain community activities.