One of the primary goals of cardiovascular exercise is to enhance the aerobic capability of the athlete, senior, youth, or adult. Enhancing aerobic capabilities through a regular exercise program allows formerly sedentary individuals to improve their activities of daily living and allows athletes to reach their full potential. Once they establish a certain level of fitness, many individuals find that they reach a plateau in terms of the progress and benefits that they receive from their exercise routines. Adding interval training to any workout program further increases the aerobic capacity of the individual and leads to greater gains in speed, endurance, and overall fitness levels.
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Aerobic or cardiovascular conditioning or fitness refers to the ability of the respiratory and circulatory systems to provide adequate oxygen to working muscles during the course of activity. In the body, the respiratory system (i.e., the lungs, trachea, and nose) draws in oxygen and releases carbon dioxide. The circulatory system (i.e., the heart, veins and arteries) pumps blood through the lungs allowing for the exchange of oxygen to the blood and the release of carbon dioxide. Once the exchange takes place in the lungs, the respiratory system then disperses the oxygenated blood throughout the body to provide fuel for working muscles. This process occurs in everyone, regardless of your fitness level, to do even activities of daily living, such as walking to your car, taking the stairs, or cleaning the house, or to race a competitor to the finish line.
Defining VO2 Max
VO2 max is the total capacity of the body to transfer oxygen to the muscles. As an individual increases their aerobic fitness level, they maximize the capability of the body to supply and utilize oxygen during activity, and thereby their endurance levels. Aerobic conditioning increases VO2 max by increasing the volume of blood the heart can output, or cardiac output, while enhancing the ability of the muscular system to extract oxygen from blood.
Who Can Benefit?
The fitness and genetics of the individual using an aerobic fitness program will determine the initial benefits that they receive. According to Scott Powers, coauthor of the book "Exercise Physiology, Theory and Application to Fitness and Performance," sedentary individuals who begin doing an aerobic conditioning program three to five times per week, for 20 to 60 minutes, at an intensity level between 50% to 85% VO2 max, are likely to see gains in their maximal aerobic capacity in the range of 15% to 50% in just two to three months. Conditioned and long-time exercisers will not see the same VO2 max gains as the sedentary individual. Rather, individuals who have a higher VO2 max at the start of an exercise program, due to either genetics or previous training, will see gains of just 2% to 3% under the same training program.
How to be Successful with Interval Training
To achieve the maximal benefits of interval training, it is critical that an individual achieve what is known as the "Overload Principle." Simply stated, the overload principle results when the body responds to an excessive stressor, such as interval training, that pushes the body beyond the current normal physiological limits. The stressors in interval training are the volume, intensity, and duration of the training. When beginning an interval training program, begin with fewer total repetitions and sets of intervals. As training and aerobic fitness improves, slowly increase the total number of intervals and sets.
Overloading the Body for Aerobic Conditioning
You can overload the body through interval training in one of two ways: either by increasing the total amount of time a body is placed under stress, or by increasing the intensity of the interval. The length and intensity of the interval is dependent upon the goals of the individual. Longer work intervals, at approximately 85% of VO2 max or maximum heart rate, cause greater gains in aerobic endurance. Shorter, high-intensity bouts, those completed at approximately 85% to 100% max of VO2 or heart rate, increase the overall speed and power of the athlete.
Types of Interval Training Programs
Most interval training programs focus on either time/distance or the intensity for the single work session. In one example, for someone just beginning an interval training program, a typical session would be 30 seconds of intense work effort (85% to 100% VO2 max), followed by a recovery period at 65% or less of VO2 max of between 30 to 90 seconds. This session is repeated from four to six times to complete one set.
For the more advanced individual looking to improve overall aerobic endurance, a single interval repetition may be 400 to 1600 meters performed at 80% to 85% of VO2 max with recovery intervals of at least the same distance and or time of the actual interval. Progress both types of training slowly by adding more repetitions to the set before adding additional time or distances to the training.
Recovery Is Critical
The key to being successful with interval training successful is to make sure that you get adequate amounts of rest/recovery during and after these sessions. By not including recovery sessions, the risk for developing "overtraining syndrome" and being unable to physically or mentally continue to train or exercise dramatically rises. The intensity and work of the interval is such that it takes longer for the body to recover from an interval session than a regular lower intensity training session. Typical training programs recommend that individuals have at a minimum two recovery days in between interval training sessions to allow the body time to repair and prepare itself for another session.