Does anybody know what this is on my underwear ? should i be worried ?

I believe it's a color dye from pants or a shirt that must have gotten wet and stained your clothes. You should take a shower to get rid of any dyes that are on your body - if you see a rash see the doctors. To get rid of the stain, use bleach and dip the clothing in wet water and let it air dry.

It's probably just dye cuz it's white and was washed with colored clothes in the washing machine

Ican only answer your first question, a machine is like a human body because it's a little similar. they both almost work like the same.

The average resting heart rate (hrrest) for a 34 year old is 73 beats per minute2. 34 year old males average heart rates of 71 bpm while females average slightly higher at 76 bpm2. the normal resting heart rate range for all adults and children 10 and over is between 60 and 100 beats per minute3. 90% of 34 year olds resting pulses fall within the range of 54 to 92 bpm. in general, an adult's resting heart rate will be lower for those in better athletic condition.