The number of muscles in our body varies from around 640 to 850. We have 3 types of muscles in our body: skeletal, visceral, and cardiac. The skeletal muscles are voluntary, while the visceral muscles are involuntary. There are no exact number of muscles in our body because there are different opinions of what constitutes a distinct muscle.

Sources: The American Medical Association Encyclopedia of Medicine, pp. 703-6; Brandreth, Gyles. Your Vital Statistics, p. 17; Cody, John. Visualizing Muscles, p. 5.

Every hair follicle on our body has it's own individual muscle. We have about 5 million of those. Each is controlled individually. There have been documented cases of hairs moving in patterns from people that are hallucinating under the effects of snake bites, hinting at the fact the brain can control each of those muscles individually.  2 billion capillaries. Each capillary has a precapillary sphincter before branching off. Those are muscles as well.

The 600-800 answer , though being valid in a context , originates from the skeletal muscle answer , which used to be the general answer in the days before microscopes were common tools. Later other muscles got added , up to a point , but by now it's not a general answer anymore.

It's better to just specify "skeletal muscles" , especially in the question , since that's generally the answer that's being sought.

The general answer though .. "How many muscles do we have?" .. is a whole whole lot .