A radioactive isotope is an unstable element, which can stabilize itself by emitting alpha,beta or gamma rays.
Sit-ups are the muscle strengthening activity. Running and jumping are both cardio, and stretching just warms up the muscles.
Your functions and blood are all moving by the force of gravity, so when everything is raised or lowered(moving your arm), your pulse wave changes. This can also result from subtlty in higher blood pressure, when activity occures. Just as your pulse waves changes in the rest of your body when excersising, you will have a slight change in pulse when simply moved your arm up and down, you're gettin' that blood pumping! ;)
Hope this helps :)
