Metabolism of Non-steady State Work & Sport

Endurance sports such as running and cycling performed in a steady state condition have been thoroughly investigated over the years largely because they could be studied in the laboratory. However, much of work and sport occurs intermittently under non-steady state metabolic conditions. Only recently has portable equipment assessing oxygen uptake been available to study the metabolism of non-steady state activities performed outside laboratory conditions such as basketball, volleyball, tennis, and the martial arts. Dr. Kris E. Berg, professor and director of the Exercise Physiology Lab at the University of Nebraska at Omaha, discussed the implications of his research on physical conditioning, nutritional support and exercise adherence at the recent 2008 AAHPERD Conference in Fort Worth, Texas.

Commonly, cardio-vascular fitness is measured by the volume of oxygen one can consume while exercising at maximum capacity. "VO2 max is the maximum amount of oxygen in millilitres, one can use in one minute per kilogram of body weight. Those who are fit have higher VO2 max values and can exercise more intensely than those who are not as well conditioned. Numerous studies have shown that one can increase VO2 max by working out at an intensity that raises the heart rate to between 65 and 85% of its maximum for at least 20 minutes three to five times a week." (Brian Mac) Typically, these same studies have been based on time-motion analysis and heart rate data and have not taken into account the fluid relationship between heart rate and oxygen uptake in the context of sport, or non-steady state activities.

Often, the calculation of VO2 energy expenditure of various sports is effectively a laboratory estimation based on distance travelled. What this doesn't take into account is the energy cost of continual changes of velocity and direction, or the cost of acceleration and decceleration. Neither does it factor in elements like temperature, emotional state and hormonal effects. With recent advances in technology, Dr. Kris Berg has been able to generate accurate data for studying the VO2 and energy expenditure values for tennis, racquetball, basketball and martial arts. What he discovered is that the mean VO2 values for these activities is very similar to those for steady state modes of exercise (i.e. endurance sports). Many of these activities meet the current aerobic exercise guidelines for aerobic fitness - even when the heart rate has NOT been elevated for a steady 20 minutes. Apparently, short bursts of intense activity interspersed with periods of rest are the key. Numerous speed bursts are supplied mostly by phosphagens in the body. Phosphagen synthesis is largely dependent on oxidative metabolism. Consequently, high intensity bursts of activity elevate the uptake of oxygen considerably - even when the heart rate is not continuously raised.

This has important implications for physical conditioning in general. Where previously medical and fitness professionals recommended only endurance type activities such as running and cycling for cardio-vascular fitness, they can now recommend other activities and be assured that guidelines for aerobic fitness will still be met! People who prefer a more social atmosphere for fitness, or who prefer playing sports to the solitary pursuit of running, for example, will enjoy the fact that they can play their favourite sport a few times a week and improve their cardiovascular fitness at the same time. In terms of athletic conditioning, activity specific interval training can be used to improve aerobic fitness within the context of the sport; by including more frequent, short bursts of intense activity. The emphasis is still very much on getting out and getting active, but the range of activities that will improve cardio-vascular fitness is obviously much wider than researchers have credited in the past. So enjoy - get out and play!!

(This information is based on an Alliance Scholar Lecture by Dr. Kris E. Berg at the American Alliance for Health, Physical Education, Recreation & Dance (AAHPERD) Convention April 10, 2008 in Fort Worth, Texas.)