Aerobic Exercise Part 4
Okay, if you’ve read your way through installments one through three, I’m hoping you’ve learned a valuable lesson; specifically, that there is no point training all of your showy skeletal muscles unless your heart is strong enough to keep them up and running. In fact, when all is said and done, it’s undisputable that the heart must be the strongest muscle of them all. But even though the heart is a muscle like those that adorn your frame, improving its functional capacity is far different than making your biceps more capable of curling your arm. Training the heart and cardiovascular system requires a far different approach.
Exercise physiologists believe that as an intervention, exercise is as valuable as any drug that man has ever made. Consequently, the process of determining an appropriate training protocol is referred to as exercise prescription. Unfortunately, many people who attempt to incorporate exercise into their daily regimen do not understand the precise nature of this process, instead preferring the a-little-bit-of-this-and-some-of-that approach. This is rarely conducive to optimal results and sometimes does more harm than good!
When prescribing exercise, there are two important principles upon which all training programs should be based: These are specificity and overload. Overload means that the only way to improve your body’s capacity with exercise is to force it to operate at a level to which it is unaccustomed. In a practical sense, this means that if you carry an eight-pound briefcase or pocketbook all day, it makes little sense to curl five-pound dumbbells at the gym. But even if you’re operating against a sufficient overload when you work out, it still might not be enough. For example, if you’re looking to train your legs, dusting off the ten-pound dumbbells and performing biceps curls will be of little use. The principle of specificity addresses this because it states that the structural and functional adaptations that can be expected to result from repeat application of an overload will be unique and highly dependent on the particular stressor that is encountered.
Endurance (aerobic) exercise is specific to cardiovascular improvement, so an aerobic overload is required to train your heart. But before a precise prescription of this overload can be formulated, a thorough health screening and cardiovascular assessment must be made. The most recent edition of the American College of Sports Medicine’s Guidelines for Exercise Testing and Prescription states that the main purpose of the initial screening of exercise participants is to identify individuals with medical contraindications to exercise, with clinically significant diseases that mandate a medically supervised program, with increased risk for disease (due, for example, to age, symptoms and/or risk factors) and with other special needs. This is necessary for safety purposes and also to ensure that the program that will be developed will be appropriate for the individual’s specific circumstances. The Physical Activity Readiness Questionnaire (PAR-Q) is a tool that is typically used as a minimal standard for this process.
Once the initial health screening is complete, ACSM’s Guidelines suggests that prospective exercisers should be stratified based on the presence or absence of known cardiovascular, pulmonary and/or metabolic disease, the presence or absence of signs and symptoms suggestive of cardiovascular, pulmonary and/or metabolic disease and the presence or absence of cardiovascular disease risk factors. This classification will affect both the specific aspects of the program that will be prescribed and also any preliminary testing that is performed to assess the participant’s level of fitness. For example, decisions regarding the level of medical examination that is required prior to testing and the need for medical supervision during testing are made according to stratifications of low, moderate or high risk.
The aerobic energy system provides energy during exercise by using oxygen that must be delivered to contracting muscles. Consequently, one way to quantify the functional capacity of this system is to determine the maximal amount of oxygen that the individual can consume (VO2 max). This can be measured directly by having the exerciser work progressively harder (for example, cycling at an increasing work rate or running at an increasing speed and/or incline) during an exercise bout until they cannot continue. Assuming that the person doesn’t quit before they have to, the work rate they achieve at the end of the test will be their maximum one for that form of exercise and the VO2 cost of that work rate can be estimated. A more precise determination can be made in an exercise physiology laboratory where pulmonary gas exchange can be measured directly. This allows for differences in exercise economy (the VO2 cost of work) between different subjects to be accounted for. VO2 max can also be estimated from tests that don’t require a maximal level of exertion (submaximal tests) by determining the subject’s approximately linear relationship between heart rate and work rate during submaximal stages of increasing work. However, this requires extrapolating the line of best fit to the estimated maximal heart rate that the person can achieve, which is variable between individuals. What is more, this variability cannot be accounted for by age alone; therefore, the prediction equation that is typically used for this estimation (220 – age) only provides a rough estimate at best.
This article was originally published in New Living Magazine, which can be accessed on-line at www.newliving.com.
