A microhabitat is a small or localized ecosystem within a larger ecosystem that is sustained and managed by a variety of small populations of plants and animals.
A rotting or decomposing wood is an example of a microhabitat because it provides food, shelter, and opportunities for various plants and species to interact and form an ecosystem. Interactions between biotic and abiotic variables are also present. As stated in the question, there are numerous other features present in this little ecosystem.
Strenuous muscular is just a fancy way to say exercise. As the muscles are used more often the need more oxygen, so that is why your breathing rate increases while doing "exercise".
