Your resting heart rate is an indicator of your fitness level because it directly determines how hard your heart is working at rest and during certain aerobic exercises. The human body's heart can only beat at a maximum of 220 beats per minute but this varies through age. Knowing one's maximum and resting heart could help you in determining the appropriate aerobic exercises that you can engage in.
The best time to measure resting heart rate is when you first wake up in the morning when you are very still in bed because any sudden movements (e.g. light walk) would cause the heart to beat fast.
There is t an app for everything, my advise in to see a real councilor
When you flex your muscles you are contracting them. When your muscle fibers gain tension through Actin and Myosin crossbridge cycling they may shorten due to the tension. This is called muscle contraction
Genetics are an undeniable factor in how easy it will be for some people to pack on size
