skeletal system and the muscular system,
Muscles are attached to the skeleton and work assuming that the skeleton is there; for example, there is no muscle that makes sure you don't bend the middle of your arm, as it's stable because there is a bone in it. Basically, the skeleton is a scaffolding for the muscles.
the skeletal system and the nervous system,
Many nerves run along the skeleton, or even inside the bones, and the bones protect the nerves; for example in the spinal cord
the muscular system and the nervous system.
The Nervous system controls the muscles; it sends the muscles commands
BE nice to your self
you do you
Remember that everyone makes mistakes
Focus on what you can change
Target heart rate is defined as the minimum number of heartbeats in a given amount of time in order to reach the level of exertion necessary for cardiovascular fitness, specific to a person's age, gender, or physical fitness.
On which one? There’s questions here