I do a buddy training session for two women (same age), and both women wear heart rate monitors during the session. Both clients have their age, height, weight, gender, and resting heart rate entered in to their HR monitors. At the end of a 30-minute session, Client “A” has burned 475 calories while Client “B” has burned only 320 calories. Client “B” is frustrated because she did the exact same work out as Client “A” and did not burn nearly as many calories. Based on the HR monitor readings, Client “A’s” max HR during the session was higher than Client “B’s.” Does this mean that Client “B” is more fit than Client “A” and that it is going to take more exertion for Client “B” to achieve the same calorie burn as Client “A?” Is Client “B” not working as hard as Client “A,” even though Client “B” feels like she worked as hard as she could during the workout? Could it be possible that both clients are equally fit and one just has a physically bigger heart than the other?