Crocodile
Part I

By Dr. Lonnie Lowery

Interestingly, serious weight lifters share in such power - at least to a degree. The amazing anaerobic processes that enable a big croc to eat even other predators also drive power athletes.

But there is a price. Want to find out what I'm talking about? Let's take a whirlwind tour of a discipline called "comparative physiology". (I promise to keep the focus on athletes and come to some practical conclusions.)

By learning about extreme species, we can actually improve our own performance. There's a validated link between knowledge and success, so why not study the extremes of what nature has to offer? Before traveling to the fringes of evolutionary specialization, however, we'll begin with hum drum humans.

When it comes to raw physicality, we humans don't look like much compared to other species. No claws. No fangs. No poison. We don't even measure-up on muscle mass or strength compared to, say, mountain gorillas or even horses. Our muscles are the focus of this article, so let's look closer at what little we have. Average (sedentary) human adults and children possess about 50/50 fast- versus slow-twitch muscle fibers.(1, 3) That's neither here nor there regarding performance.

People typically have just a moderate amount of glycolytic capacity (for power) and a modest number of mitochondria - the "aerobic powerhouses" of cells (for endurance). At first glance, an alien observer may well conclude that we're just not much across the board. Making conclusions from first glances, however, is a bad policy - as we'll find out later.

But before we examine how the seeming mediocrity of humankind can actually become its strength, let's review some biological extremes.

Birds, at one end of the muscle performance spectrum, generally shame us on the endurance scale. Imagine contracting your pecs repeatedly for thousands of reps. Birds do. They avoid fatigue thanks to the freakish mitochondrial density and capillarization present in their flight muscles.(4, 7, 14) All those slow-twitch, highly aerobic, well-supplied muscle fibers are an evolutionary adaptation that has been meticulously crafted over eons. Imagine feeling almost zero fatigue after countless contractions. Amazing.

When it comes to size, strength and power, however, modern birds are just not built to compete.

Small, slow-twitch, Type I muscle fibers and oxidative processes like the tricarboxylic acid (TCA) cycle are limited in how quickly they can ramp-up to meet a challenge. (Although aerobic systems do contribute sooner during exercise than once thought; there is no exclusive, sequential shift from one energy system to another as many believe.) But there's more to avian slowness than this.

Maybe we're "flying off course" with all this talk of intramuscular metabolism.

Why? Because provision of oxygen-rich blood becomes another limiting factor, regardless of what's going on inside a specialized muscle - at least for we humans. That is, a hugely-proliferated cellular "furnace" (mitochondrial matrix) only goes so far when the supply of oxygen depends on multiple other factors. No furnace or flame is going to burn too brightly when put under a glass, pinching off its air.

Similarly, we humans could use extra "ductwork" (blood vessels) in this regard, even beyond what we can create via endurance training. (By the way… for you brainy muscle geeks who care, mitochondria don't exist as individual bean-shaped units like many folks think but rather as an inter-connected matrix like I mentioned.)

But let's get back to the croc, shall we?

Crocodiles differ dramatically from birds and even humans.

Far from being aerobic machines, these creatures often rely on comparatively inefficient anaerobic metabolism. Here's a nifty quote: "…reptiles outstrip their aerobic capacities with any exercise more intense than a slow walk" (2). Niiice! This reminds me of my brother, The Yeti, back when we were singularly power training and perhaps getting too big, too fast. Have you ever seen a seemingly fit man grab his knees and pant helplessly after climbing a single flight of stairs? Now THAT'S training specificity!

Unfortunately for crocs, providing huge quantities of energy (ATP) without "burning" a substrate like carbs or fats in the TCA and electron transport system (within their mitochondria) is rough. And yet nature has found a way.

First, of course, is the creatine-ATP system.

There's nothing like "raw energy", even if it does only last a few seconds. Then there's an increasing contribution of energy from direct breakdown of carbohydrate. By investing two ATP early in this process, it's possible to generate four ATP by the "end" of anaerobic glycolysis.

It's a worthwhile investment: two in, four out.

But there's a much more fascinating aspect to anaerobic glycolysis (and glycogenolysis). Oxygen be damned, anaerobic energy production can still ramp-up several fold.(8, 19, 20) Need energy right now to catch that meal? YOU GOT IT. Need to out-sprint and out-muscle any other beast? YOU GOT IT. Coupled with that full-bore ability to use creatine phosphate and rifle through (hydrolyze) ATP, you're now the true king of the jungle.

But now the rub. After their freakish displays of power, crocodiles lie around panting all day.(2,13) The lactic acid build-up in their bloodstreams would reportedly kill a human. Wow. And all those hydrogen ions flying off the individual steps in glycolysis create muscle-burning, metabolism-stopping acidity that keeps the blinding effort extremely brief. It's the price of power.

Some of us, however, choose power - whatever the cost.

After a decade or so working with fellow exercise physiologists, I've become accustomed to occasional ribbing about my poor aerobic capacity (VO2max). My reply takes one of two forms. One may sound too aggressive and the other too vain, but here they are:

A.) "Would you rather have a hummingbird or a crocodile on your side in a fight?" …ahh, food for thought… or
B.) "In case you haven't noticed, no one can see your VO2max."

Building massive and powerful muscles has both survival and social implications. Of course, I never begrudge runners, swimmers or cyclists for their friendly taunts because we both know that I could pin-down and devour a half-dozen of them at will. Even if it did require a half-hour to recover. So much for keeping this discussion limited to animals, eh?

So, there's your brief "sprint" through several facts to set the stage. I hope I've whet your appetite; I have to rest and recover now. Stay tuned for Part II on how to become the crocodile.

About The Author

Dr. Lonnie Lowery is an exercise physiologist, nutrition professor and former competitive bodybuilder living in the Midwest. Although there is a waiting period, Dr. Lowery does accept a minimal number of phone consultations set up through Staley Training. He can be reached at lonnie@staleytraining.com.

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References / Further Reading:

1.	Bell, R., et al. Muscle fiber types and morphometric analysis of skeletal muscle in six-year-old children. Med Sci Sports 1980; 12:28.
2.	Bennett, A. Exercise performance of reptiles. Adv Vet Sci Comp Med. 1994;38B:113-38.
3.	Dudley, G., et al. Muscle fiber composition and blood ammonia levels after intense exercise in humans. J Appl Physiol 1983; 54: 582.
4.	Dudley, R. Limits to human locomotor performance: phylogenetic origins and comparative perspectives. J Exp Biol. 2001; 204(Pt 18):3235-40.
5.	Essen-Gustavsson B, and Tesch, PA. Glycogen and triglyceride utilization in relation to muscle metabolic characteristics in men performing heavy-resistance exercise. Eur J Appl Physiol Occup Physiol. 1990;61(1-2):5-10.
6.	Fry, A., et al. Catecholamine responses to short-term high-intensity resistance exercise overtraining. J Appl Physiol. 1994; 77(2): 941-6.
7.	Harrison J. and Roberts, S. Flight respiration and energetics. Annu Rev Physiol. 2000; 62:179-205.
8.	Hultman, E. and Spriet, L. Skeletal muscle metabolism, contraction force and glycogen utilization during prolonged electrical stimulation in humans. J Physiol. 1986 May;374:493-501.
9.	Keizer, H., et al. Influence of liquid and solid meals on muscle glycogen resynthesis, plasma fuel hormone response, and maximal physical working capacity. Int J Sports Med. 1987 Apr;8(2):99-104.
10.	Kellmann, M. (Ed.). Enhancing recovery. Human Kinetics: Champaign, IL; 2002.
11.	Kentta, G., and Hansen, P., Overtraining and recovery. A conceptual model. Sports Med. 1998; 26(1):1-16.
12.	Komi, P. (Ed.). Strength and power in sport. Blackwell Science: Oxford; 1992.
13.	Lehninger, A., et al. Principles of Biochemistry. Irving Place, New York: Worth Publishers 1993; 417.
14.	Mathieu-Costello, O., et al. Structural basis for oxygen delivery: muscle capillaries and manifolds in tuna red muscle. Comp Biochem Physiol A Physiol. 1996;113(1):25-31.
15.	Parkhouse W. and McKenzie, D. Possible contribution of skeletal muscle buffers to enhanced anaerobic performance: a brief review. Med Sci Sports Exerc. 1984 Aug;16(4):328-38.
16.	Raja, G. Repeated bouts of high-intensity exercise and muscle glycogen sparing in the rat. J Exp Biol. 2003; 206(Pt 13):2159-66.
17.	Robergs, R. ASEP National Mtg., 2002.
18.	Shi X. and Gisolfi, C. Fluid and carbohydrate replacement during intermittent exercise. Sports Med. 1998 Mar;25(3):157-72.
19.	Spriet, L. Anaerobic metabolism in human skeletal muscle during short-term, intense activity. Can J Physiol Pharmacol. 1992 Jan;70(1):157-65.
20.	Spriet, L., et al. Anaerobic energy release in skeletal muscle during electrical stimulation in men. J Appl Physiol. 1987 Feb;62(2):611-5.
21.	Tesch, P.A. and Larsson, L. Muscle hypertrophy in bodybuilders. Eur J Appl Physiol 1982; 49: 301.
22.	Thorstensson, A. Muscle strength, fiber types and enzyme activities in man. Acta Physiol Scan 1976; (Suppl): 443.
23.	Williams, M., et al. Effects of recovery beverages on glycogen restoration and endurance exercise performance. J Strength Cond Res. 2003 Feb;17(1):12-9.

 

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