Why does t-p interval shorten during exercise?

Answer 1

P through to end of T is the time in which the electrical events occur in the heart, which take a certain amount of time to complete

While the T-p interval is the rest time between an therefore has the most flexiblilty can can increase or decrease depending on the bodys needs

Therefore when the heart rate needs to be increased, as in the case of excercise, this time can be shortened when the heart rate increases to supply the oxygen demands of the body.