How is force typically graded in skeletal muscle, and what does the all-or-none principle imply for an individual muscle fiber when activated?

• A. Force is graded by recruitment of more motor units; individual fibers contract fully when activated
• B. Force is graded by increasing firing rate in a single motor unit only; fibers contract partially
• C. Force is graded by alternating contraction of motor units; each fiber contracts partially
• D. Force is graded by recruiting fewer motor units; individual fibers contract partially when activated

Answer: (A)