The all-or-none law of muscle contraction refers to a maximum contraction or no contraction of a ............

Explanation

**Step-by-Step Solution:**

1. **Understanding the All-or-None Law**: The all-or-none law of muscle contraction is a principle that describes how muscle fibers respond to stimuli. It states that a muscle fiber will either contract fully or not at all when stimulated.

2. **Threshold Potential**: For a muscle fiber to contract, the stimulus must exceed a certain level known as the threshold potential. If the stimulus is below this threshold, the muscle fiber will not contract.

3. **Response to Stimulus**: When the stimulus exceeds the threshold potential, the muscle fiber will respond with maximum contraction. If the stimulus does not exceed this threshold, there will be no contraction.

...