Typically aerobic fitness is measured as the highest oxygen consumption achieved by a subject on a treadmill or cycle ergometer. Figure 46.8 shows that O2 uptake increases with leg power output to the limit of uptake at VO2max. This power output by the legs represents a direct measure of aerobic exercise performance that can be related to the muscle properties governing the demand and supply of ATP. Our focus is on how these muscle properties determine aerobic leg performance; specifically, how muscles generate and use ATP in power production and how the changes in muscle properties with age affect muscle power production.
Rowers, treadmills, bikes, and cross-country skiers are all effective if you use them. There is some suggestion that some individuals are more inclined to exercise at home with equipment than at the gym or a class. The activity you choose is a personal choice and it varies for everyone, and so you need to experiment until you find what works best for you. Some individuals prefer to go to the gym while others are perfectly content to work out at home on their own equipment in front of their TV. TV can make the time pass quickly, and so can your favorite movie, music, scholarly courses taught by professors, or books on tape (see resources for online vendors). Finding something that will distract you might just make that 30-minute workout bearable, and believe it or not you might even look forward to it! After all, it could be the only 30 minutes in your day that you have all to yourself. Indulge! Aerobic exercise videos and DVDs are also effective if you use them! They are convenient if you prefer to work out at home instead of taking a class at a studio or a gym, and there are hundreds to choose from. I suggest that you check out Collage Video (http://www.CollageVideo.com), or give them a call and ask for a recommendation. Also check if your local library rents exercise videos on tape or DVD. And by the way, there are videos for all types of activity; from weight training, to tai-chi, to stretching. Check out all the possibilities to add flexibility and strength-building to your cardio workout.

Here’s what’s happening in your body when you’re running and walking: “Muscle action that propels you from point A to B requires the utilization of a thing called ATP,” explains Janet Hamilton, an exercise physiologist and running coach with RunningStrong. “Your body stores only a limited amount of ATP (enough for only a few seconds of activity), so it needs to replenish that supply, and it does so by metabolizing your stored fuels (glycogen and fat). The process of making useable energy (ATP) from stored fuel (glycogen and fat) is dependent on how much you need and how quickly you need it.” So the more intense the activity, the greater the demand for fuel—and since walking is less intense and demanding than running, it doesn’t demand that ATP be produced at the same rate. 

The same goes for intensity, too: Hiking or climbing stairs can actually bring your walking METs burn up to running levels. “Greater muscle forces are required to move faster to accelerate the body up and down, move the limbs faster, and work against gravity,” says Hunter. “Running or walking uphill requires a greater energy, just like lifting weights upwards. It’s as if our body is the weight that we must move to greater heights, so the greater the slope, the greater the energy requirement.”
When you slap your foot on the ground like some undifferentiated plate of meat, it negates all your ability to use the muscles at the back of your body, and loads all the work on to your hip flexors. Feet have the same structure as hands – tarsals, metatarsals, phalanges. We should experience the same articulation, the same wriggling and precision, the same fine motor-skilled attention to the detail of the exterior world, but we don’t: it’s more of a slap, slap, slap, or at best, a pad, pad, pad.
4. It eases joint pain. Several studies have found that walking reduces arthritis-related pain, and that walking five to six miles a week can even prevent arthritis from forming in the first place. Walking protects the joints — especially the knees and hips, which are most susceptible to osteoarthritis — by lubricating them and strengthening the muscles that support them.
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