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Bulletin #52 – Endurance Performance, Part 2

Scientific BackgroundLast month I explained the conceptsof VO2 max and the lactate threshold. Theseare simply scientific ways of measuring car-diovascular fitness. Briefly, VO2 max is thebody’s maximum rate of oxygen consump-tion (1,2). This determines the maximal in-tensity of aerobic exercise which you cansustain. The lactate threshold is the percent-age of VO2 max at which lactic acid first ap-pears as a waste product in the blood (1,2).Lactic acid is a byproduct of anaerobicmetabolism when glucose is broken downwithout oxygen. Thus the terms “lactatethreshold” or “anaerobic threshold” areoften used interchangeably. This repre-sents the rate of energy production whichcan be sustained aerobically before theanaerobic pathways kick in.These concepts may sound com-plicated but a simple example will make themclear. Let’s take a sedentary person whohasn’t exercised in years and put him on atraining program. Initially he can only ridethe stationary bike for 20 minutes at low in-tensity because he’s so out of shape. Aftersix months of consistent training he can ridefor 20 minutes at high intensity. He has justincreased his VO2 max, his maximal level ofsustainable exercise.

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At the beginning of histraining program if he tried to peddle againsthigh resistance, after a few minutes his thighswould begin to burn and ache from lacticacid accumulation. After six months of train-ing he can peddle for 20 minutes against highresistance with no thigh pain. He has justincreased his lactate threshold.An aerobic exercise training pro-gram will increase both VO2 max and anaero-bic threshold. What does this mean? Themeaning of an increase in VO2 max is prettyobvious: it means you can exercise harder.An increase in anaerobic threshold meansthat you can exercise at a higher percentageof your maximal ability before anaerobic me-tabolism begins to contribute to energy pro-duction. So not only can a trained athleteexercise harder, he can exercise more effi-ciently. He can exercise at a higher percent-age of his maximal ability before the lacticacid burn begins to set in.

That implies hecan maintain a higher percentage of his maxi-mal output for a longer time before reachingfatigue. So now you can see that VO2 maxand anaerobic threshold describe somewhat different aspects of endurance performance.Another fundamental concept we need tounderstand is the respiratory quotient (RQ).This is defined as the ratio of carbon dioxideproduced to oxygen consumed during en-ergy production (1,2). What does this haveto do with anything? It has everything todo with fat loss and body composition.Respiratory quotient is measured by ana-lyzing the amount of oxygen a personextracts from the air and the amount ofcarbon dioxide he exhales into the atmo-sphere as he breathes. We can learn somevery interesting things using this tech-nique. It turns out that if a person is burn-ing pure carbohydrate as his energysource the respiratory quotient is 1.0. Ifhe is burning fat as his fuel source therespiratory quotient is 0.7. This differencecomes from the fact that the carbon at-oms  in carbohydrate molecules are al-ready partially oxidized (the carbon at-oms are bound to oxygen in the sugarmolecule).

In fatty acids the carbon at-oms are bound to hydrogen, and are said tobe “reduced” (the chemical opposite of oxi-dized). It makes sense then that fat shouldcontain more calories per gram than sugar,because in sugar the carbon atoms are al-ready partially oxidized before you eat it. Ina fatty acid molecule the carbon atoms arenot oxidized at all, so when they are burnedinside cells more energy is released per car-bon atom than for glucose. Also, since thecarbohydrate molecule already containssome oxygen atoms built into it, it takes fewermolecules of oxygen to complete its oxida-tion than for a fat molecule. This is the rea-son burning fat as your fuel source resultsin a different respiratory quotient than burn-ing carbs. A typical mixed diet containingprotein, carbs, and some fat results in a RQaround 0.8.Whew! So what does this have todo with bodybuilding and fat loss? By mea-suring the RQ of people while they are exer-cising we can determine the fuel substratewhich is being used. At rest and during sleepmostly fat is used as the body’s fuel source.During low intensity exercise, such as walk-ing or low intensity biking, still mostly fat isused.

At the other extreme, during very highintensity exercise such as weight lifting thepredominant fuel source is carbohydrate.And at moderate exercise intensity a mixtureof fat and carbs is used for fuel. If you thinkabout the biochemical pathways of energyproduction this makes perfect sense. Highintensity exercise like weight lifting is prima-rily fueled by the anaerobic pathway. This isbecause the muscle’s demand for energy isso high that oxygen cannot be supplied tothe muscle fast enough to keep up with thedemand, so the muscle has to turn to anaero-bic metabolism. Anaerobic metabolism cansupply rapid bursts of energy very quickly,but cannot be sustained for a very long time.This is why you can ride the bike for hoursbut can only do squats for about a minutebefore you fatigue. The body can use car-bohydrate as a fuel for anaerobic energy pro-duction (glucose is converted to pyruvatein the glycolytic pathway and pyruvate issubsequently converted to lactate). How-ever, there is no such thing as anaerobic fatmetabolism. Fat requires oxygen to be con-verted to usable energy. Simply put, youcan’t burn fat fast enough to keep up withthe rigorous energy demands of intenseweight lifting, so you have to use carbs.

Onthe other hand, the oxidation of fat makesthe perfect energy source for lower inten-sity exercise such as walking.Many people use this rationale toadvocate low intensity exercise (such aswalking) as the ultimate exercise for fat loss.At first thought, this makes good sense. It istrue that during low intensity exercise ahigher percentage of the energy expendedis derived from fat. The problem is that dur-ing low intensity exercise you burn very fewcalories, so even if almost all of the caloriesare derived from fat, that’s still not much fatloss. During moderate intensity aerobic ex-ercise, such as jogging or a brisk bike rideagainst moderate resistance, a higher per-centage of the calories you burn come fromcarbs, but you burn so many more total calo-ries that the overall result is still greaterfat loss. So it’s not just the percentage ofenergy derived from fat that’s important,but also how many total fat calories youburn. If you do your aerobics at moder-ate to high intensity you will burn morecarbs along with the fat, but you’ll endup burning a greater amount of fat in thelong run because you expend more calo-ries.To put this in perspective, don’t letme leave you with the wrong message.Walking is a great exercise for fat loss,it’s just that you’ll have to walk for hourseveryday to see really noticeable results.I’m not against walking, I just don’t thinkit’s the best choice for serious fat loss.Just as there are plateaus you encounterwhile gaining muscle, you will also hit pla-teaus during fat loss.

Probably the best wayto stimulate accelerated fat loss is to increasethe intensity of your aerobics. In your ownexperience, who’s leaner – the guy who walksthree miles a day or the guy who runs threemiles a day? The runners I know are leanerthan the walkers. I’ve worked with a lot ofbodybuilders who could never really get intocontest shape until they started running.Last month I talked about some ofthe metabolic adaptations that occur as aresult of endurance training. One is an in-crease in the vascular supply to muscles.The harder the muscles are forced to work,the more blood they need. Another impor-tant adaptation is an increase in the fat-burn-ing capacity of muscle cells. Endurance train-ing causes an increase in the cellular contentof mitochondria and enzymes responsible forburning fat. I don’t think you get much of ametabolic adaptation to low intensity exercise.Sure, you can burn fat if you walk longenough, but you really won’t increase yourcapillary density or beef up your fat-burningenzyme pathways significantly unless youtrain hard. The concept of intensity applies toendurance training just like it does to resis-tance training. If you want to see a big changein your body you have to force it to adapt byproviding an intense training stimulus.  

If you still don’t believe me, justtry it. It won’t cost you anything and youhave nothing to lose. Try doing low inten-sity aerobics for a month (walking) and mea-sure your body composition before and af-ter. Then do moderate to high intensity aero-bics for a month (jogging or fairly strenuousbiking) and again measure your body com-position. You’ll see. I’ve done this kind ofthing with competitive bodybuilders abouta zillion times, so I know what will happen.Practical ApplicationsHow do we put this all together toget the best results? Do moderate to highintensity aerobics for 30 to 60 continuousminutes a minimum of three days a week,and seven days a week is better. You shouldbe breathing hard and sweating. Remember,fat metabolism requires oxygen. If you’re notbreathing hard you’re not consuming muchoxygen and so you can’t be burning muchfat. It’s not that complicated. What aboutheart rate? If you want to measure heart rate,that’s fine. Probably between 70-85% of yourtheoretical maximum heart rate is a good goalto both burn fat and accrue the metabolicadaptations of endurance training (increasedcapillary density and increased fat-burningmachinery). Your theoretical maximum heartrate is 220 minus your age.

This is a prettycrude way to do it however because howyour heart rate responds to exercise dependson your level of training.Do your aerobic exercise for at least30 minutes per session. It takes a while toliberate fatty acids from adipose tissue andreally start burning much fat. You probablydon’t burn much fat until about 15 minutesor so into the exercise session. Do your aero-bics on an empty stomach. First thing in themorning before breakfast is a great time. Thenyour glycogen levels are somewhat depletedfrom your overnight fast and insulin levelsare low. Since insulin blocks fat metabolism,aerobic exercise right after eating carbs is abad idea. No carb drinks before or duringyour aerobics. Another good time to do youraerobics is right after weight training. Theweight training depletes your glycogen lev-els so your body will be forced to burn fatinstead of carbs. Also, weight training in-creases catecholamine levels (epinephrineand norepinephrine) which stimulate fat me-tabolism. So you’ll start burning fat rightfrom the start of your aerobic exercise ses-sion that way.The particular type of exercise youdo doesn’t matter. Running, rowing, biking,stair climbing, skiing, in-line skating, and aero-bics classes are all okay. Pick something youlike and can stick with. I suggest mixing it upfor variety. Just make sure you are breathinghard and try to work up a sweat. One tech-nique to help keep the intensity up is circuitaerobics.

Five minutes on the stair climber, fiveminutes on the treadmill, five minutes on thebike, and five minutes on the rowing machine,then repeat the circuit.So we’ve covered the type of exercise,the training intensity, the trainingduration, the training frequency, andthe timing of the training session. Ican’t close without talking a littleabout nutrition. There are four keypoints I’d like to make. First, don’t cut calo-ries too much. If you are faithful to the dietas outlined in the Nutrition Manual, youprobably won’t have to cut calories at all. Ifyou eat according to the diet, do your weighttraining, and do your aerobics, you will au-tomatically get lean without having to cutcalories. If you do need to reduce calories,do so very modestly. Ten percent below yourmaintenance requirement is plenty. If youreduce calories too drastically you will losemuscle, and thereby decrease your metabolicrate and your ability to burn fat. Remember,muscle is the engine that burns fat. Main-taining muscle mass is a priority. Second,eat a low fat diet. The aerobics program asdescribed here is designed to maximize fatburning. If you don’t eat any fat in your diet,then the fat you burn during your aerobicshas to come from stored body fat. If youhave much fat in your diet then when youexercise you’ll simply burn the fat you justate. You’ll be spinning your wheels andwon’t get leaner. If you burn fat during exer-cise, but don’t eat fat, then you’ll have tolose body fat. It’s that simple. Third, getplenty of protein.

This is key to preservingmuscle mass while losing fat. During aero-bic exercise, especially at high intensity,some of the fuel is derived from amino acids.This can result in muscle loss if you’re notcareful. I’ve had very good results using ascoop of Hi-Protein powder before aerobics.This supplies very little carbohydrate anddoes not raise insulin levels significantly. TheHi-Protein increases the blood levels of aminoEndurance Performance, Part IIacids, so that any aminos which are oxidizedduring the exercise session are derived fromthe protein powder instead of being ex-tracted from muscle tissue. Here’s the strat-egy: if you exercise in the morning, get upand have a cup of coffee and a scoop of Hi-Protein powder, then do your aerobics. If youdo your cardio work after weight training,then have a scoop of Hi-Protein between theweight training and the aerobics. This willprevent any loss of muscle tissue and willnot inhibit fat metabolism. Fourth, followyour body composition. All serious body-builders follow their percent body fat andlean body mass. You have to in order to knowwhat’s going on with your body composi-tion. Scale weight is just not enough. TheBody-Stat Kit is an invaluable tool in thisregard. It includes a detailed manual that ex-plains how to modify your diet and exerciseto keep things moving in the right direction,and discusses specific problems commonlyencountered while dieting for contests.Parrillo Performance. We’re here to show youhow.


1. McArdle WD, Katch FI, and Katch VL.Exercise Physiology: Energy, Nutrition, andHuman Performance. Lea & Febiger, Phila-delphia, 1991.

2. Wilmore JH and Costill DL. Physiology ofExercise and Sport. Human Kinetics,Champaign, IL, 1994.

2018-03-13T11:10:36+00:00 June 1st, 2009|Technical Supplement Bulletins|

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