Does anybody understand why some of the numbers are so out of proportion with the length of time spent in the study? They say they lost 0.2-0.3kg of muscle mass

Does anybody understand why some of the numbers are so out of proportion with the length of time spent in the study? They say they lost 0.2-0.3kg of muscle mass in the lower half of the body. But that's a very large change; when you exercise and train properly, the maximum amount of muscle you get is like 0.5kg/month (the study's reduction in activity was two weeks long), and when you gain weight some fraction is always muscle (they didn't gain weight but they gained fat mass and lost muscle mass, IIUC from Table 2). I remember reading that when you start/stop exercising, your muscles retain a different amount of water depending on how much work they typically do. So is what they got an actual change in body composition? When they report lowered VO2max of 2.2ml/min/kg, that's ±4.7 according to Table 2. Isn't 2.2ml/min/kg an improbably large change for two weeks, compared to how quickly your VO2max will improve if you, e.g., start running? And why is the SD on that so large?