No, they just respond more slowly. That study had people doing four hours of exercise a week. That is not very much. A lot of people would exceed that in one tr

No, they just respond more slowly. That study had people doing four hours of exercise a week. That is not very much. A lot of people would exceed that in one training session (e.g. someone training for an endurance event like a triathlon). Furthermore, there are more facets to fitness than endurance. Strength, flexibility, balance, and so on are all important to fitness, whether you define fitness in terms of quality of life or athletic achievement.