A muscle biopsy obtained from a healthy volunteer consists mainly of myoglobin-rich, glycogen-poor fibers with many mitochondria. Which of the following is the most likely biopsy site?

Question

A muscle biopsy obtained from a healthy volunteer consists mainly of myoglobin-rich, glycogen-poor fibers with many mitochondria.  Which of the following is the most likely biopsy site?

Quizplus · Accepted Answer

11ec160b_3d02_8812_9249_7b65998e2683_MD0001_00 The body's muscles are composed of 2 main fiber types: slow twitch (Type I) and fast twitch (Type II). Type I fibers perform actions requiring low-level sustained force (eg, postural maintenance) and function primarily via aerobic metabolism, meaning they have high myoglobin (oxygen storage) and mitochondrial (aerobic respiration) concentrations. The soleus muscle of the lower leg and paraspinal muscles of the back are postural muscles predominantly composed of Type I fibers. Type II fibers are specialized for generating rapid forceful movements and they fatigue quickly. These fibers derive ATP energy mainly via glycogenolysis and subsequent anaerobic glycolysis. Muscles that maneuver the upper extremities (Choices A, B, C, and E) are primarily geared toward rapid forceful movements and are more likely to have a higher percentage of Type II than Type I muscle fibers. Educational objective: Postural skeletal muscles such as the soleus and paraspinal muscles contain predominantly Type I, slow twitch muscle fibers that derive ATP primarily via oxidative (aerobic) metabolism. __________ References: Exercise-induced skeletal muscle remodeling and metabolic adaptation: redox signaling and role of autophagy. (http://www.ncbi.nlm.nih.gov/pubmed/24450966)

A Muscle Biopsy Obtained from a Healthy Volunteer Consists Mainly