The Role of Aerobic Fitness in High Intensity Efforts, Part I

by Thomas Kurz

“Aerobic training causes harmful changes in skeletal muscle fiber type, hormonal secretions and force output characteristics. The fastest, most powerful muscle fibers become slower and more resistant to fatigue. . . . Aerobic exercise also produces the catabolic hormone cortisol, which is antagonistic to anabolic hormones such as the human growth hormone and testosterone. . . . A fighter may have a 20-30 second flurry, rest for 10-15 seconds and so on. . . . People confuse being out of breath as a need for more aerobic conditioning. . . . Fighters and forms competitors depend on sharp, crisp techniques. Aerobic training hurts these athletes even more than contact fighters.” (“The Problem with Aerobic Training.” by Charles I. Staley, B.Sc., MSS [Vice President of Program Development for the International Sports Sciences Association] in M. A. Training, Vol. XXV, No. 3, May 1998, p. 24.)

The above statements are full of misconceptions and inaccuracies. The fallacy of some of them is plain to see while others are not as obviously wrong, but state-of-the-art exercise physiology and sports methodology research dispels them all.

How training affects the skeletal muscle fibers and hormonal secretions depends on many factors, not just on whether exercises are aerobic or anaerobic. Consider a sport that requires aerobic and anaerobic energy as well as a great jumping ability–basketball. Basketball is a sport with an energy cost per minute similar to boxing (McArdle, Katch, and Katch 1991), perhaps the most popular form of fighting. Agility and jumping ability are more obviously displayed in basketball than in boxing. All the running and dribbling players do in basketball’s 20-minute periods, mostly aerobic activities, does not keep them from jumping high. How come? It is a matter of how much of various exercises, including aerobic, they do.

So much for the detrimental effects of aerobic exercise on muscle fibers and force output characteristics….

There is research that shows that endurance athletes (long distance runners, for example) have a greater percentage of slow twitch muscle fibers. But these athletes were studied after many years of doing nearly exclusively exhaustive long-distance endurance training! (Also, they were selected for long-distance running because they likely had predispositions for it, such as a greater percentage of slow twitch fibers.) The effects of long-term, exclusively aerobic endurance training consisting of prolonged workouts on muscle fibers are not the same as the effects of performing aerobic exercises as a part of a mixed training. Fitts and Widrick (1996) show that endurance exercise improves the speed of slow twitch fibers but prolonged daily endurance workouts depress peak force and peak power.

The situation is similar with hormonal secretions—a lot depends on the duration of the workout, on the intensity of exercises, on an athlete’s gender, and training level, and on the duration in months of the training program. Here’s a good rule of thumb: the longer and the more fatiguing the workout, the more it raises the concentration of cortisol in the blood. Another way of putting this rule: The greater the buildup of lactic acid, the greater the concentration of cortisol in the blood (Kraemer et al 1989). Blood lactate concentrations also correlate with an increase of serum growth hormone (Baechle 1994, Hakkinen and Pakrinen 1993). Here are examples.

• One hour of anaerobic exercise at 110% VO2max done in 2-minute periods elevated levels of cortisol in the blood during an 8-hour recovery period while one hour of aerobic exercise at 65% of VO2max did not (Hackney, Premo, and McMurray 1995).

• Eight sets of 10 repetitions maximum (10RM) leg-press with 1-minute rests between sets increased cortisol concentration in plasma while the same workout performed with 3-minute rest breaks did not, because the shorter rest breaks caused a greater lactic acid buildup (Kraemer et al 1996).

• Four sets of 10 repetitions maximum (10RM) squats with 90-second rests between sets significantly raised levels of lactate and cortisol, growth hormone, both total and free testosterone, and adrenocorticotropic hormone (Kraemer et al 1998a). Twenty sets of 1RM squats with 3-minute rests between sets increased slightly the serum concentration of growth hormone but did not significantly increase concentrations of cortisol and testosterone while 10 sets of 10RM did increase the concentration of cortisol as well as growth hormone and testosterone. The 10 sets of 10RM were more fatiguing than 20 sets of 1 repetitions with heavier weight (Hakkinen and Pakrinen 1993).

Knowing all this, you need to note that concentrations of hormones in the blood do not indicate the effects of these hormones on cells (Baechle 1994). Remember that blood lactate concentrations correlate with both cortisol and with growth hormone—the exercise protocols that produce the greatest cortisol responses also produce the greatest growth hormone response (Baechle 1994). Exercises that increase levels of lactate also increase levels of testosterone in blood in males (Kraemer et al 1998a, Kraemer et al 1998b, Baechle 1994). Baechle (1994) writes: “While chronic high levels of cortisol may have adverse effects, acute increases may be a part of a larger remodeling process in muscle tissue.” He also points out that using cortisol levels and the testosterone-cortisol ratio “has met with only limited success” in control of strength and power training, probably because of the “multiple roles” of these and other hormones, as well as complex interrelationships among hormones, their receptors in cells, and various exercises (Baechle 1994).

Click here to read “The Role of Aerobic Fitness in High Intensity Efforts, Part II.”

References

Baechle, T. R. 1994. Essentials of Strength Training and Conditioning. Champaign, IL: Human Kinetics.

Fitts, R. H. and Widrick, J. J. 1996. “Muscle mechanics: adaptations with exercise training.” Exercise and Sport Sciences Reviews 24: 427-473.

Hackney A. C., Premo, M. C., McMurray, R. G. 1995. “Influence of aerobic versus anaerobic exercise on the relationship between reproductive hormones in men.” Journal of Sports Sciences 13, no. 4: 305-311.

Hakkinen, K. and Pakrinen A. 1993. “Acute hormonal response to two different fatiguing heavy-resistance protocols in male athletes.” Journal of Applied Physiology 74, no. 2: 882-887.

Kraemer, W. J. et al. 1989. “Training responses of plasma beta-endorphin, adrenocorticotropin, and cortisol.” Medicine and Science in Sports and Exercise 21, no. 2: 146-153.

Kraemer, W. J. et al. 1996. “The effects of plasma cortisol elevation on total and differential leukocyte counts in response to heavy-resistance exercise.” European Journal of Applied Physiology and Occupational Physiology 73, no. 1-2: 93-97.

Kraemer, W. J. et al. 1998a. “Acute hormonal responses to heavy resistance exercise in younger and older men.” European Journal of Applied Physiology and Occupational Physiology 77, no. 3: 206-211.

Kraemer, W. J. et al. 1998b. “The effects of short-term resistance training on endocrine function in men and women.” European Journal of Applied Physiology and Occupational Physiology 78, no. 1: 69-76.

McArdle, W. D., Katch, F. I., and Katch, V. L. 1991. Exercise Physiology: Energy, Nutrition, and Human Performance. Philadelphia: Lea & Febiger.

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