What does muscle stiffness come from?

Dehydration: 1.Can be from dehydration, 2.Calcium, magnisium or other electrolyte deficiency, 3. Can be from inflammation, or resulted from an injury, suggesting, drink plenty of fluid, before and after sports, supplementing calcium and magnisium, icing after running, etc.

NS Controls Muscles: Complex: only heart muscle contracts without brain/nervous commands, though ~110 BPM & constantly adjusted from brain split-second. All other muscles only contract after neurotransmitters are released at muscle membrane. Thus ns always plays a dominant role, along with blood supply, electrolytes, hydration, (all regulated by brain), metabolic products remaining in muscle after exercise/injury etc.