For more on how to produce significant results by understanding how the body adapts to high-intensity exercise and how to identify key neuro-endocrine responses, view ACE fitness expert Pete McCall's recorded one-hour webinar.
Metabolic conditioning has become a popular and, in some cases, an almost over-used phrase in the fitness industry. From highly popular DVD-based exercise programs promoted on late-night infomercials to the recent commercialization of the "sport of fitness" emphasizing high-intensity Crossfit exercise programs, touting metabolic conditioning as the best form of exercise has become a popular marketing technique. On one hand, this recent trend toward high-intensity training is a good thing because more challenging workouts DO expend more energy and produce sought-after results such as weight-loss or lean-muscle gain. On the other hand, however, when applied incorrectly or too often, high-intensity exercise can potentially have devastating consequences, including injury or even death.
Metabolism refers to the human body's process of converting food into fuel, allowing the muscles to perform work. Adenosine triphosphate (ATP) is the chemical responsible for fueling muscular contractions and is derived from the macronutrients: carbohydrates, fat and (occasionally) protein. The body can produce ATP immediately without the presence of oxygen to fuel high-intensity activity or use oxygen to generate ATP for lower-intensity activities over an extended period of time.
Generally speaking, the intensity of physical activity determines the rate of ATP production and consumption. There are three primary energy pathways in the body that convert macronutrients into ATP: immediate, intermediate and long-term. High-intensity activities utilize the immediate energy pathway to produce ATP, low-intensity activities produce ATP from the long-term pathway, and moderate-intensity activities employ the intermediate energy pathway. The amount of available fuel and oxygen will determine which pathway is engaged to produce energy.
My former colleague Doug Hatten, a New York City-based Fitness Educator, describes the difference between the energy pathways by using the analogy of attempting to catch a bus. If you notice that the bus is at your stop, but you're still a block away, you sprint to catch the bus—this immediate need for energy uses stored ATP-CP to fuel the activity. As the bus pulls away without you, you slow your running to a fast jog hoping to catch the bus at the next stop—the intermediate pathway produces ATP via glycolysis to fuel this activity. Once you realize that even a fast jog won't help you catch the bus, you slow down to a walk—energy for this low-intensity activity is produced from the long-term energy pathway where free fatty acids are converted to ATP through mitochondrial respiration.
So, what exactly is metabolic conditioning? What does that mean? Do you realize that simply sitting at your desk is actually a form of metabolic conditioning? Right now, your body is metabolizing free fatty acids into ATP to fuel mitochondrial respiration. However, by sitting there you are not challenging your body to produce ATP rapidly, so there is no increase in energy expenditure or adaptation to a specific exercise intensity.
Metabolic conditioning is often used to describe exercise programs utilizing the immediate and intermediate energy pathways, which can be achieved with a variety of different modes of exercise. The type of exercise is not important; rather, the intensity and duration of an exercise is the determining factor influencing which energy pathway is called to action.
Designing an exercise program is based on manipulating specific variables that affect the body's adaptation to an exercise stimulus. These include exercise selection, intensity, repetitions, sets, rest interval and time under tension. Simply changing one or two of the variables can involve different energy pathways and increase the metabolic demand. For example, when teaching an exercise program designed to help a new client develop core strength, the first couple of workouts could allow for 30- to 45-second rest intervals between each exercise. As the client’s fitness level improves, simply reducing the rest interval between each exercise to 10 or 15 seconds, or removing between-exercise rest intervals all together (creating a circuit of exercises), would greatly increase the demand for energy, thus making the workout more metabolically challenging. If, in this example, you were to use bodyweight exercises, resting between each exercise would allow the long-term energy pathway (mitochondrial respiration) to be the dominant supply of ATP. However, removing the rest interval and having the client do a circuit would increase the work-rate and use the intermediate energy pathway (glycolysis) to fuel the muscular work. When using circuit-training, it is important to allow sufficient rest between entire circuits to allow a client to recover and prepare for the next circuit.
Metabolic conditioning does not have to mean gut-busting workouts that leave clients reaching for the trashcan. Challenging your clients to work a little harder and minimizing the rest intervals can create an effective metabolic demand and increase energy expenditure during a workout. Simply changing a couple of variables, such as using heavier resistance to increase the intensity, adding more repetitions or additional exercises to a circuit or doing more sets during a training session, can create an additional metabolic challenge for your clients.
Take your favorite total-body exercise program or use a favorite piece of equipment such as a TRX Suspension Trainer and make it more metabolically challenging for your client by progressing from incorporating rest intervals between each exercise to doing all exercises back-to-back in a circuit format. Just be sure your client doesn't have any existing health issues before increasing the intensity of an exercise program to make it more demanding. Then start having fun manipulating the variables and watching your clients sweat!