Weegy: Basic Muscle Physiology: Muscles consist of individual muscle fibers (cells) connected in bundles. Muscle fibers are made up of smaller protein structures called myofibrils. Proper strength training causes individual fibers to increase the number of [ myofibrils, resulting in hypertrophy. Inactivity can reverse this process, resulting in atrophy. target=_blank rel='nofollow'>https://docs.google.com/viewer?a=v&q=cache:pgbXf1GB-GAJ:' target=_blank rel='nofollow'>www.abac.edu/Health/Fahey9e/PDF3/Chapter_04_3per.PDF+&hl=en&pid=bl&srcid=ADGEEShKfiTZ3GkzHmi1P-cBqtqqYqsmGgDyTNJPE6gPghGiVzroM6NYB-iUtNkovvVMgxffq2oy2j_3Wz4cDdWL0O9vcX2phfsT7ZuA1BJFSThlm9NEQCJrzjiPkL9mPcYChdux8kgC&sig=AHIEtbRsZG3Z1A-JmnmxKqU0Fx_T4Ec8Vg ] (More)

Weegy: Factors Affecting Flexibility * Heredity * Age * Gender * Mode and level of activity * Internal Tissue Temperature * Injury (scar tissue, altered bony structure) * Pain (increases muscle spasm). (More)