Spasticity is usually caused by central nervous system injuries, such as brain injuries or spinal cord injuries. Spasticity is a little different from stiffness.
One of the hardest moments during quarantine for me was when my apartment building announced its gym was closing to prevent the spread of coronavirus. As the outside gyms closed all around the city in the weeks prior, I felt grateful that the one in my building was open. The gym was the lasting lifeline to my sanity, and to have that yanked away from me, I felt lost.
Exploration for an infant means discovering anything about that environment. If that infant needs an opportunity to be brought to them, that's okay. Let an infant explore through their senses, whether it's touch, or smell, or taste, or sight, or hearing.