Changes of sEMG Characteristics and Rated Perceived Exertion (RPE) Scale with Weight-Bearing Walking at Acute Hypobaric Hypoxia Environment

In recent years, the popularity of high-altitude mountain climbing and hiking has soared. To mitigate muscle and bone damage, as well as human errors resulting from physical exhaustion, we investigated the perceived exertion and muscle fatigue during weighted hiking in acute hypobaric hypoxia environments. Eight subjects participated in this study, carrying a 15 kg backpack and walking on a treadmill at 2.5 km/h for 30 min in hypobaric chambers simulating altitudes of 40 m, 3500 m, and 4500 m, at a temperature of 24.2 ± 1.6 °C. Subjects reported their perceived exertion using the modified Borg CR10 RPE scale every 10 min, while surface electromyography (sEMG) data was collected from various muscle groups. Analysis revealed significant increases in RPE scores over time, with marked differences between 40 m and 4500 m, and between 3500 m and 4500 m. At 4500 m, the median frequency (MF) of the erector spinae muscle decreased significantly, while the biceps femoris exhibited initial activation followed by fatigue. Conversely, the biceps brachii and gastrocnemius muscles showed increased activation with exercise duration. This study offers insights into the physiological changes, fatigue progression, and safety considerations for weighted hikers in acute hypoxic environments.