MYOD1 and chronic obstructive pulmonary disease: MyoD protein accumulation during this period was similar between groups while significant increases in Myf5 protein accumulation (p < 0.05) were observed in COPD compared to healthy subjects in our distinct days during differentiation (days 4 (3.2 fold-increase), 5 (3.6 fold-increase), 7 (2.9 fold-increase) and 9 (3.5 fold-increase) (p < 0.05)) (Figure 5B and C, respectively).