Exercise Physiology

The Science of Performance

Power Running^sm

Part 4: Metabolic Fitness

Have you ever conducted a really intense workout, say an all out 5k race, and experienced nausea and/or distress as a result?  Perhaps you have seen other athletes at the end of a workout or race hunched over from nausea or fatigue, obviously under considerable distress.  I remember watching Bob Kempainen at the 1996 Olympic Marathon trials.  Bob was leading in the final miles of the race when, without even breaking stride, he vomited several times.  Not only did he not break stride while vomiting, he then pulled away from his competition and ended up winning the race.  I remember marveling at his ability to withstand the intense nausea and discomfort he was certainly experiencing and yet not even slow his pace! 

Running is not the only activity that can cause this level of distress.  Arnold Schwarzenegger, upon completing his first high intensity Nautilus workout is quoted as saying, “I’ve had times during workouts when I’ve had difficulty standing up.  This is the first time I’ve had difficulty laying down.”  In his inimitable style, Arnold was referring to metabolic fitness. 

Metabolic fitness refers to the ability of the body’s systems to withstand intense efforts and the fatigue that accompanies it.  The concept of metabolic conditioning was first suggested in the 1970s by Arthur Jones, the inventor of Nautilus weight training machines.  Jones described metabolic conditioning as the ability to perform high intensity muscular work for a prolonged period of time.  He used the term in conjunction with high intensity strength training, but I submit that his description can be applied to any activity where the athlete is working at very high levels of intensity, just like Bob Kempainen in the marathon trials.  Arthur coined the term metabolic conditioning and applied it to weight training; I use the term metabolic fitness as a way of applying the concept to any high intensity activity.

High intensity workouts and races place an incredible amount of stress on the body.  The systems most affected by high intensity are the musculoskeletal, respiratory, and circulatory systems.  As you conduct a high intensity workout the pH balance in your muscles drop contributing to your sense of fatigue.  Muscle fibers become increasingly fatigued, making it increasingly harder to maintain a set work rate.  Respiratory rate increases dramatically.  Breathing becomes labored, increasing your sense of distress, general discomfort, and widespread fatigue.  Your circulatory system kicks into high gear, with your heart rate increasing as the intensity of the workout increases.  Blood flow to inactive muscle tissue and less active tissues, such as liver, kidneys, and digestive system, is instead diverted to the exercising muscles.  This can lead to the nausea and gastrointestinal distress often experienced by athletes.  Body temperature begins to rise, causing blood flow to be diverted from your warmer core to the surface of your skin as your body works to keep core temperature from rising too high.  The rising core temperature contributes to the stress being experienced.  High ambient temperatures, like those found in summer, make it much more difficult for the body to maintain its core temperature.  If dehydration sets in, it makes your circulatory system work all the harder, in addition to making it even more difficult to control core body temperature.  All of these processes and others are occurring simultaneously during a high intensity workout or race, making it increasingly difficult for you to maintain your level of effort.

Note that fatigue is a component of metabolic fitness, not a separate entity.  Typically, fatigue has been the term used by coaches and physiologists to describe some of the effects high intensity has on the body.  Unfortunately, the term fatigue is too limited to describe all of the bodily functions being affected during a high intensity workout.  Metabolic fitness is a more complete term for describing all the various effects that high intensity has on the body.  Metabolic fitness includes but is not limited to the following factors: muscle glycogen levels, blood glucose level, muscle pH levels, body temperature, circulation, respiration, and hydration level.  All of these factors are components of metabolic fitness and have an effect on fitness level.  Metabolic fitness describes the body in its entirety and its capability to handle the demands of a particular activity.

We also make a distinction between metabolic fatigue and muscular fatigue.  Metabolic fitness refers only to effects that are transitory, to effects that dissipate with or shortly after the cessation of work.  Effects such as core temperature, respiration rate, glycogen levels, etc. are properly described by the term metabolic fitness.  Metabolic fitness does not refer to the long term effects muscle fibers experience as a result of particularly hard workouts and races, nor does it explain short-term muscle fatigue from brief, high intensity work.  

Maximizing Metabolic Fitness

Metabolic fitness directly affects your power output.  Remember that our formula for power is muscle contractility + metabolic fitness.  Metabolic fitness plays a major role in determining the percentage of maximum capability you will be able to maintain for a set distance (which is just another way of saying power output).  For example, if your metabolic fitness is low, you might be able to maintain a pace of just 75% of maximum for 5K.  As your metabolic conditioning improves, you might then be able to maintain a pace of 82% of maximum for the same 5K distance.  As your metabolic fitness improves you will be able to run at increasing closer percentages to maximum for any distance.  Indeed, studies on elite runners have shown that the biggest difference in performance amongst elites is the ability to maintain a work load closer to the maximum.¹

If you want to perform at your absolute best, you must maximize your metabolic fitness.  You must train in an appropriate manner so as to minimize the effects of intensity on the body.  Like all other physiological functions, the body adapts specifically to the stress that is placed on it.  The best method for improving metabolic conditioning is high intensity workouts.  Speed work obviously fits the bill but, considering the principle of specificity, even better are workouts conducted at or near the distance you are going to be competing, run at or near race pace, and under the same environmental conditions as the race will be held at.

I recommend one race specific workout per week.  As an example, if you are training for a 10K, then you would run a weekly 6 - 7 miler, on similar terrain as the upcoming race, and run at a pace similar to your planned race pace.  As your metabolic fitness improves, your pace for this workout will quicken also. 

The combination of one speed workout (recommended in part 2 of this series) and one race specific workout each week will help you maximize metabolic fitness, allowing you to reach new levels of performance.

Till next time keep on running.

Reference:

1.  Coetzer P, Noakes TD, Sanders B, Lambert MI, Bosch AN, Wiggins T, Dennis SC., Superior fatigue resistance of elite black South African distance runners. J Appl Physiol. 1993 Oct;75(4):1822-7.