136 Chapter 6: Training for Endurance Table 6.17. Common Lacing Techniques Used with Running Shoes Runner’s Loop (secures heel and prevents toes from sliding forward) Window Lacing (alleviates pressure points on the top of the foot) Reef Knot (holds laces more securely) When to Replace Your Running Shoes Researchers recommend that running shoes be replaced after accumulating between 350-500 miles (Cook et al., 1985). While walking is not as hard on shoes as running, it is still unlikely they are able to provide adequate support and cushioning after 500 miles. Individuals who average 30 minutes per day of walking (or 3-4 hours per week) should consider replacing their shoes every six months. Individuals who average 60 minutes per day of walking (or 7-8 hours per week) should consider replacing their shoes every three months. In addition to mileage, body weight is another important factor to consider. The more an individual weighs, the faster the support and cushioning will wear out. Individuals weighing over 200 pounds may want to consider replacing their shoe even more often than the aforementioned recommendations. Summary • Cardiovascular fitness is the ability of the heart, lungs, and organs to consume, transport, and utilize oxygen. • There are three basic energy systems simultaneously at work during exercise: the phosphagen, glycolytic, and oxidative systems. They are used to replenish levels of adenosine triphosphate (ATP), the energy used to power muscle contractions. • VO2max is the maximum amount of oxygen that the body can take in and utilize in
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