Jariya WaisayaratArpa PornpetchprachaMana Rochanawutanonจริยา ไวศยารัทธ์อาภา พรเพชรประชามานะ โรจนวุฒนนท์Mahidol University. Faculty of Medicine Ramathibodi Hospital. Department of Pathology2022-10-102022-10-102022-10-102011Ramathibodi Medical Journal. Vol. 34, No. 4 (Oct-Dec 2011), 190-1980125-3611 (Print)2651-0561 (Online)https://repository.li.mahidol.ac.th/handle/20.500.14594/79840Objectives: To present normative data on muscle fiber type proportion and mean fiber size of the biceps brachii and vastus lateralis muscles in non-skeletal muscle disease Thai population. Methods: Muscle samples for each of the left biceps brachii (n = 20) and the left vastus lateralis (n = 20) muscle were taken from 20 cadavers (14 males and 6 females) within 18 to 36 hours after sudden accidental death or who had died after a short acute illness without evidence of neuromuscular disease. Three fiber types (type I, type IIA, and type IIB) were classified using myofibrillar ATPase histochemistry. Fiber type proportion and the lesser diameter of muscle fiber type I, type IIA and type IIB was measured. The mean lesser diameter of each fibers was analyzed statistically comparing between males and females, between age group less than 50 years old (< 50 yrs) and age group 50 years old more (³ 50 yrs), and between biceps brachii and vastus lateralis muscles. Results: The fiber type percentage of biceps brachii and vastus lateralis muscle showed predominance of type II fiber and on significance differences between type IIA, and type IIB proportions. There were no significant difference in the percentage of each type between males and females. The mean lesser fiber diameter of biceps of biceps brachii and vastus lateralis muscles in our study was in normal range established by previous standard reference. Type I fiber were larger than type II fibers, and type IIA fibers were larger than type IIB fibers in males and females. In vastus lateralis muscle, age group less than 50 years old (< 50 yrs) had larger fibers size than age group 50 years old more (³ 50 yrs) in all type of muscle fibers. Conclusion: There were no gender difference in the fiber size and fiber proportion in our study. The mean lesser fiber diameter of type I, type IIA and type IIB in non-skeletal muscle disease Thai population was with the interval established from the data published by previously standard reference. Aging had influence on muscle fiber by decrease fiber size in all three types in vastus lateralis muscle.engMahidol UniversitySkeletal muscleThai populationCadaveric casesOriginal ArticleDepartment of Pathology Faculty of Medicine Ramathibodi Hospital Mahidol University