The physiology of a "stiff" muscle

What is happening in a muscle that is “stiff”? That is, it’s not especially sore but the range and speed of motion seems to be limited. This usually happens after exercising it in a way that it’s not used to, or overuse. Like your back when you wake up after shoveling two feet of snow the day before, or if you spend 4 hours raking leaves.

Is it a low level of pain such that your brain subconsciously and autonomically limits the range of motion? Is is that the fibers become shortened and inflexible temporarily? If so why? Is it fatigued muscle fibers that cannot fully respond until they recover?

I have never studied muscle biology so if you are an expert in this area please try to discuss in layman’s terms.

As I understand it, physical exertion beyond normal will cause some damage to muscle fibres, hence the soreness. The damage causes causes the muscles to repair themselves, only a little stronger. This is why you need to push yourself, feel the pain, to get appreciably stronger/fitter.

And your body temperature drops. Muscles are very sensitive to temperature hence the need to warm-up before a hard/intense bout of exercise or violent movement.

I would also imagine the injured muscles “tense up” to prevent movement and further injury.

Yes, I’m familiar with muscle soreness but I’m talking about something that *seems *a little different than soreness. It is a temporary feeling of a loss of flexibility. Feels like what the tin man looked like just as Dorothy applied the first drops of oil.

In their introduction to their recent review article on delayed onset muscle soreness (DOMS), the authors state:

“Even though the exact cause of DOMS remains unclear, several studies have suggested that DOMS is triggered by a sequence of various biochemical changes after muscle damage rather than a single event of damage (Armstrong et al., 1984; Close et al., 2005; Smith et al., 1991).”

Similarly, the authors of this older review article write:

“The mechanisms, treatment strategies, and impact (of DOMS) on athletic performance remain uncertain, despite the high incidence of DOMS”.

So, looks like the answer to your question may not be known.