In a relationship, there are benefits or rewards for both partners. They each gain something from eachother by being together,
The second sentence would be the correct replacement for the sentence
Cardiorespiratory endurance is a measurement of how well your heart, lungs and muscles work together to keep your body active over an extended period of time. Exercisers can improve cardiorespiratory endurance by participating in a program of regular aerobic exercise.
Hindus is my guess. The religion of Hinduism believes in reincarnation, the belief that souls are born and reborn many times, each time in a new body.
