explain what an internal influence is and provide two examples

It is basically how you feel about yourself , an example would be emotions, intentions, personality

It’s about how you feel about yourself, and how it effects you.
Ex:
If you have depression your heart is directly effected by what you’re brain is telling you to feel. If someone calls you a bad name / you feel badly about your body, your heart will feel heavy.
Ex 2:
Going on a run..
When you run you automatically feel like a whole new person. Any exercise done right makes you feel like you’ve accomplished something, making your body and emotions feel completed in some way.

Musculoskeletal or gastrointestinal

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)