In aerobic and anaerobic training, intensity is measured by the percentage of maximum heart rate achieved or the speed in relation to the distance. Volume is measured by distance traveled times the number of reps if multiple repetitions are performed. Frequency is how often the exercise is performed.
Interval training is a method used to increase the anaerobic threshold, which is the point at which the muscles switch over to anaerobic glycolysis to produce energy. It is also the point at which the amount of carbon dioxide produced equals the amount of oxygen consumed. If the anaerobic threshold is raised, the speed at which one can function aerobically is increased and time of aerobic events is reduced. That can be the difference between a respectable marathon time of 3 hour and an Olympic medal finish under 2 hours and 10 minutes. It is generally stated that aerobic exercise should generally be done at 70-85% of age adjusted maximum heart rate. Maximum Heart rate is often calculated at 220-age for women or 205-1/2 age for men. The Karvonen formula uses a percentage of the difference between the age-adjusted maximum heart rate and the resting heart rate to determine the level of intensity. That percentage is added to the resting heart rate to determine the target heart rate. This is fine for 98 percent of the population. However, there are elite athletes who have a higher maximum heart rate because they are genetically able to generate higher maximum heart rates. That may be part of the reason they become elite. A treadmill or stationary cycle ergometer test where respiration gases are measured is the most accurate method of determining both maximum heart rate, which doesn't change from training and the anaerobic threshold, which does. The anaerobic threshold will increase with the proper type of training. The extent to which it can improve is genetically pre-determined.
The factors that go into producing the ability to run, swim or ride a bicycle farther and faster are both fixed due to genetics and changeable due to performance factors. Aerobic capacity is only part of the equation. Genetic factors that cannot be changed include: lengths of limbs, muscle insertion points on the bones, percentage of slow-twitch versus fast twitch muscle fibers, total number of muscle fibers, body build (somatype) and height.
Genetic factors that can be influenced by training and lifestyle include; lung capacity, size of the heart, size of left ventricle, size of arteries; quantity of red blood cells and hemoglobin in the blood, total blood volume, ability to dissipate heat, quantity of fat-burning enzymes in the muscles, balance of strength and flexibility between muscle groups, glycogen storage capacity of muscles and liver, strength of Type I muscle fibers, efficiency of muscle fiber recruitment, and an efficient gait. Training can more easily influence other factors that are not genetically based and knowledge including: mental attitude of perseverance, use of strategy, proper attire, previous injuries, proper conditioning and shoes for weather and road conditions.
Interval training, which varies between short periods of high intensity training with longer periods of low to medium intensity, is a very efficient way to increase anaerobic threshold. An example would be a marathon runner who alternates bouts of running at a 400 meter race pace for one minute with four minutes of marathon pace speeds. This will increase the marathoner's overall speed and allow for the ability to "kick" at the end of a close race. Interval training should be performed on one or two days per week. Off days should be scheduled as needed. Some days should be purely long, slow distances; other days can include intervals. Some days could be intermediate distances at intermediate. One day per week could use another form of aerobic training, especially in the off-season.
Besides increasing aerobic capacity and anaerobic threshold one can increase performance with development of strength endurance in the muscles used in running. That is achieved by performing strength training for the slow-twitch muscle fibers. Start with loads in the neighborhood of 40-60% of one repetition maximum or 12-40 reps. Increase the amount of weight performed with this number of reps. Some strength work (up to 80% of 1 rep max) should be performed as part of the program. That type of resistance training should be performed for one or two mesocycles per macrocycle.
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