You might be able to classify my commitment to exercise in the past as "dabbling." I would occasionally get on a kick where I would run after school each day or sign up for yoga classes, but eventually—usually sometime in Week 2—something else would capture my time or my attention and my exercise plan would move to the back burner (or completely off the stove).

Lately, however, everywhere I turn, I see articles, Web sites, or television shows about the importance of adolescents getting enough exercise and the health risks associated with a lack of regular physical activity. Once again, I made the decision to start an exercise routine, but this time, I promised myself that I would do it right. I conducted the research, I consulted my physician, and now it's official: I'm hooked on exercise.

Don't get me wrong; the first few days were anything but easy and I was sure that exercise was cutting into other valuable activities. After all, I had a stack of library books calling my name and scores of recorded television shows to watch. Nonetheless, I exercised. Now, a solid three months into my exercise journey, my body feels and looks stronger, healthier, and more toned, my mind is clearer and more focused, and I'm ready to share what I've learned.

The Elements of Physical Fitness
While swimming, pumping iron, and stretching do wonders for your body, individually they are not enough to keep you in superb physical condition. A trip to the doctor taught me that true physical fitness comes from a combination of three different elements: endurance, strength, and flexibility. Endurance is the ability to engage in aerobic activity for a sustained amount of time. In plain English, that means performing an activity that gets your heart pumping faster and your lungs breathing harder for about thirty to sixty minutes at a time. Such activities include swimming, running, or bicycling. My personal favorite is hiking up a wooded mountain near my house with my trusty dog, Blitz. Other workouts pale in comparison to a brisk hike on a beautiful fall day. Strength refers to how strong your muscles are. Exercises that improve strength include weight training (with supervision and proper instruction, of course), push-ups, stomach crunches, and pull-ups, all of which work and tone your muscles. Flexibility is the ability to easily bend, stretch, and move your muscles and joints. Exercises such as yoga and pilates improve flexibility. By combining exercises that tested my endurance, strength, and flexibility into my daily workouts, I saw and felt better, faster results.

The Benefits of Physical Fitness
Since I started—and stayed committed to—my new exercise routine, the number of benefits I have experienced has been astonishing. My body feels stronger and healthier. I can do everyday tasks with more efficiency because my endurance, strength, and flexibility have all improved. Exercise has also helped to improve my overall mood. Whenever I feel stressed or depressed, I exercise, and it seems like I sweat out those negative feelings. Exercise allows my body to burn pent-up energy, so I sleep more soundly at night, which helps to improve my focus and concentration throughout the day. Finally, and perhaps most importantly, I've learned that exercising is fun. I have developed ways to incorporate all kinds of activities into my workouts such as dancing, kickboxing, and, of course, playing with Blitz.

Exercise used to feel like a chore, but now when I miss a workout, I feel like I've missed out on an important part of my day.
Which statement from the text gives evidence to support the writer's thesis that physical exercise is worthwhile?