The most important factor in improving cardiorespiratory fitness (cardio or CR) is training intensity. Changes in CR fitness are directly related to the “hardness” of an aerobic exercise. The higher the energy expended per unit of time, the greater the intensity of the exercise, the greater the effect on cardiorespiratory fitness. You need to know how "hard" it is to determine if an aerobic exercise like running produces a CR training effect or if it's just to burn a few calories. Heart rate during work or exercise is a great indicator of how hard you're exerting. Only by tracking your heart rate during a workout can you be sure that the intensity is sufficient to improve your CR fitness level. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get an original essay In other words, your ability to monitor your heart rate is the most important key to success in CR training. Training Heart Rate (THR) = Desired training intensity. THR is the heart rate you need to train at to get a training effect. The US Army's fitness gurus gave us two methods for determining THR. The first method, percentage of maximum heart rate (%MHR), is simpler to use, while the second method, percentage of heart rate reserve (%HRR), is more accurate. With this method, THR is calculated using the estimated maximum heart rate. You can estimate your maximum heart rate (MHR) by subtracting your age from 220. So, a 20 year old person would have an estimated maximum heart rate (MHR) of 200 beats per minute (220 - 20 = 200). A person who is out of shape should exercise at 70 percent of their MHR; if in relatively good shape, at 80 percent MHR; and, if in excellent shape, at 90 percent MHR. Examples: A 20 year old in good physical condition would have a THR of 160 beats per minute (BPM). 220 - 20 = 200 *.80 = 160 BPM. A 30-year-old man in good physical condition would have a THR of 152 beats per minute (BPM). 220 - 30 = 190 *.80 = 152 BPM. A 40-year-old person in poor physical condition would have a THR of 126 beats per minute (BPM). 220 - 40 = 180 *.70 = 126 BPM. %HRR methodA more accurate way to calculate THR is the %HRR method. The 60-90% HRR range is the THR range in which people should exercise to improve their CR fitness level. If you know your general CR fitness level, you can determine what HRR percentage is a good starting point for you. For example, a person in excellent physical condition might start at 85 percent of their HRR; if in fairly good shape, at 70 percent HRR; and, if in poor shape, at 60 percent HRR. Most CR workouts should be performed with a heart rate between 70 and 75 percent HRR to achieve or maintain an adequate fitness level. A person who has achieved a high fitness level may benefit more from working at a higher HRR percentage, particularly if they cannot find more than 20 minutes of CR exercise. Exercising at an HRR percentage below 60 does not give the heart, muscles and lungs an adequate training stimulus. Exercising at more than 90 percent can be dangerous. Before anyone begins aerobic training, they need to know their THR (the heart rate at which they should.