Question

Red muscle fibres are present in

• A. Extensors of backs
• B. Flight muscle of birds
• C. Athletes of marathon race
• D. All of the above

Answer 1

The correct option is D All of the above

Three major types of skeletal muscle fibers have been identified in vertebrates: slow-oxidative, fast-oxidative, and fast-glycolytic. Slow-oxidative fibers are specialized for endurance activities such as swimming, running long distances like the marathon, or maintaining posture. They contract slowly and fatigue slowly. These fibers require a steady supply of oxygen. They derive most of their energy from aerobic respiration and are rich in mitochondria and capillaries. Slow-oxidative fibers are rich in myoglobin, a red pigment similar to hemoglobin in red blood cells, which stores oxygen. Myoglobin enhances rapid diffusion of oxygen from blood into muscles during strenuous muscle exertion. Because of the myoglobin, slow-oxidative fibers are red. Birds that fly have red breast muscles specialized to support sustained activity. In humans, the proportions of slow-oxidative and fast-oxidative fibers vary among individuals and from muscle to muscle in the same person.

Hence the correct option is D.