Short answers, pulled from the story.
Skeletal muscle comprises about 35% of the human body by weight. By a separate measure cited for healthy young adults, skeletal muscle makes up around 40% of body weight. In Western populations, men have on average around 61% more skeletal muscle than women.
There are more than 600 skeletal muscles in the human body. A single muscle such as the biceps in a young adult male contains around 253,000 muscle fibers, and one ten-centimeter fiber can hold as many as 3,000 nuclei.
The three main fiber types are Type I, Type IIA, and Type IIX. Type I fibers are slow and oxidative, Type IIA fibers are fast and primarily oxidative, and Type IIX fibers are fast and glycolytic. Most human skeletal muscles contain all three types in varying proportions.
Contraction begins when motor neurons release acetylcholine at the neuromuscular junction, depolarizing the muscle fiber. The sarcoplasmic reticulum releases calcium, which binds troponin and shifts tropomyosin, exposing myosin-binding sites on actin so myosin heads can cycle and shorten the muscle. The SERCA pump returns calcium to the sarcoplasmic reticulum to allow relaxation.
Comparing individual muscles is misleading because three factors affect strength at once. By force exerted on an external object, the masseter or jaw muscle is strongest, with the 1992 Guinness Book of Records logging a bite strength of 4337 newtons for 2 seconds. By cross-sectional area the quadriceps femoris or gluteus maximus is usually named, and by weight the myometrial layer of the uterus may be the strongest in the female body.
Yes, skeletal muscle functions as an endocrine organ by secreting myokines, a range of cytokines and peptides that act as signaling molecules in the bloodstream. Interleukin 6 is the most studied myokine, and under different conditions subsets of 654 different proteins appear in the muscle secretome.
Human muscle efficiency has been measured at 18% to 26% in rowing and cycling, the ratio of mechanical work output to total metabolic cost. At rest skeletal muscle consumes 54.4 kilojoules per kilogram per day, more than adipose tissue at 18.8 and bone at 9.6, and muscle contraction produces 85% of the body's heat.