One thing that you learn in a Physiology of Exercise class is that the body adapts to the stress placed on it. Depending on the level of fitness you desire the workout you participate in will determine how fit you are. One thing to remember is that the level of fitness can vary. How fit you want to be is up to you. The point of this is that you do not have to keep improving all the time. Once you reach the desired level of fitness for your everyday activities you just have to stay active enough to maintain that level of fitness.
I had a friend that ran at a pace of 10 minutes per mile. He had a loop in his back yard that he ran for 30 minutes. He was so consistent in that pace that he did not have to count the laps it took to run three miles. He knew when he ran for 30 minutes he had covered three miles. The problem he had was that in the beginning his pulse rate became slower as he achieved a higher level of fitness. Then after a short time the pulse rate increased. He wondered why his pulse rate would go from slow to fast and slow again. The point of adapting to the stress placed on the body caused this change in his pulse rate. As he ran and improved from low level fitness to a higher level of fitness he was placing his body under a stress. Once his body reached that level of fitness and the stress did not change, the 10 minute mile was no longer a stress, and the pulse rate increased. In order to keep the pulse rate at a slower rate he had to put in a workout that was above that steady level of exercise. He could take a day or two and walk faster, or further, and the pulse rate would remain at steady level.
Here in central Texas it is easy to put in a run, or walk, that increases the stress level of a workout. They call this area “the hill country” for a reason. You can find all shapes, sizes, and lengths of hills almost anywhere you run. When a race director mentions that the course is flat it means that the hills are gentle and not hard. If the race is “hilly” you will find a couple of challenging hills along the route.
