Last month I left you ready to startyour last set of the belt squat workout —the dreaded 100 rep set. This set pushes bothaerobic and anaerobic energy producingsystems in their absolute limits. It elicits andadaptive response in your cardiovascularsystem to strengthen your heart and in-crease capillary density in muscle. This in-creases cardiovascular reserve and anaero-bic threshold and improve nutrient and oxy-gen delivery to the muscle.A cell contains enough ATP tosupply energy to last for about two seconds(1). So you would use this up during yourfirst rep. Obviously you have to immediatelyand constantly replenish you ATP supply.Within about 1.2 seconds of maximum con-traction, 80% of the ATP is being derivedfrom CP — creatine phosphate (1). CP is theother phosphagen compound, along withATP, which supplies energy very rapidly. Thephosphagen system is always the first en-ergy pathway called into action. Since themachinery of the cell needs ATP for power,it begins by using ATP, and then other en-ergy sources are used to replenish the ATP.CP acts like a buffer to maintain relativelyuniform levels of ATP within the cell. As ATPis broken down to release his energy, one ofits phosphate groups is split off to form amolecule of ADP (adenosine diphosphate)and a free phosphate group. CP is able todonate its phosphate group to the newlyformed ADP to regenerate ATP. The phos-phagen system able to supply energy in rapidbursts, immediately on demand, but it doesn’tlast very long (about six seconds at maximalpower output).
This is why a typical set withheavy weights doesn’t last very long — yourun low on ATP and can’t make it fast enoughto continue.Within 2.5 seconds of maximal con-traction, 50% of ATP is being supplied bythe lactic acid system, also known as theglycolytic pathway (1). Anaerobic glycoly-sis is the pathway used to make ATP fromcarbohydrates in the absence of oxygen.This is the second energy producing sys-tem called into play and is used to meet short-term energy de-mands. When the in-tensity of exercise istoo great and thebody can’t supplyoxygen fast enough,carbs can be par-tially broken down toyield energy withoutoxygen. The advan-tage is this is a veryrapid way to pro-duce energy, but thedisadvantage is thatit’s not as efficient asaerobic energy pro-duction.After sixseconds of maximalcontraction CP lev-els have fallen toaround 65% of theirresting level andpower output beginsto decline. Continuing beyond six secondsof maximal contraction, ATP and CP levelsbegin to fall and lactic acid begins to accu-mulate. These factors severely hinder poweroutput (1). So we can see that after just afew reps we’re using both of our anaerobicpathways: the phosphagen system and thelactic acid system.Back to our belt squats: during thesecond 20 reps you will need some help. ATPlevels may be depleted by as much as 60%of initial values (1). CP levels are nearly ex-hausted after about 40 seconds of maximalintensity exercise (1). At this point glycoly-sis is going full speed, but is unable to gen-erate enough ATP to keep up with the de-mand.
Lactic acid production is maximal dur-ing exercise of intensity that can be main-tained for 1-3 minutes. So one minute intothe set lactic acid levels are soaring and yourmuscles are burning like crazy.The third energy producing sys-tem — the aerobic pathway — begins to kickin after about 20 seconds into the set, andbecomes the major energy producer afterabout 90 seconds (see figure). Notice thatthere is considerable overlap, with all threeenergy systems being utilized at the sametime. It’s not like you use up one energysource, turn off that system, then turn onthe next system. They all blend in together,with different systems playing the major roledepending on the intensity and duration ofthe exercise. If we were talking about lowintensity exercise like walking instead ofbelt squats, the aerobic system could pro-duce energy fast enough to fuel the ac-tivity, and the lactic acid system wouldnever be called in.The aerobic pathway is able to sup-ply energy for long-term demands — evenfor hours. Activities like weight lifting drawmainly from the phosphagen and lactic acidsystems, while things like running and bik-ing are fueled mostly by the aerobic system.The advantage of the aerobic system is thatit can supply energy for a very long periodof time, but the disadvantage is that it can-not produce energy very quickly. For weightlifting you need to supply a tremendous amount of energy immediately, but for en-durance activities you need a lower energylevel for a longer period of time.In the aerobic pathway, carbohy-drates and fat are burned — combined withoxygen — to release energy.
The rate of en-ergy production by this pathway is limitedby your vascular supply (which limits oxy-gen delivery) and by the size and number ofmitochondria inside cells. Mitochondria areorganelles in cells where aerobic metabolismis carried out. Notably, fat can only be usedfor energy via the aerobic pathway. Fat can-not undergo anaerobic glycolysis, as cancarbs. Therefore, aerobic activity is the onlyway to burn fat. This is another reason tomake aerobic exercise a part of your program,in addition to strengthening your heart andblood vessels.Now, back to our set: after 50 repsthe phosphagen system is long gone, andthe glycolysis is pretty much shot too. Youhave continued to expend energy faster thanyour cells can replace it, and consequentlybuild up an “oxygen debt.” This describes asituation we are all familiar with. You knowhow you breathe real hard for a few minutesafter a set? This extra oxygen is being usedto replenish the ATP, CP and glycogen youspend anaerobically during the exercise. Theoxygen debt is the difference between theamount oxygen actually consumed and theamount that would have been consumed ifthe exercise had been fueled entirely aerobi-cally from the beginning (2). By the time theoxygen debt builds up to 3-4 liters of oxy-gen, you enter a severe level of ATP deple-tion. Exercise will only continue on a “payas you go” basis wherein ATP is being con-tinually replenished by aerobic metabolism(2). Power output decreases and your heartand lungs are working at absolute maximum.You will be sweating profusely.
All energysystems are either maxed out or have alreadyfailed.By 60 reps you will beg to quit. Atthis point you will be beyond positive fail-ure and it will be difficult even to resist theweight on the way down. From here on outyour life is in the spotter’s hands. By 70 repsyou get that adrenaline rush that comes fromthe fear of eminent death. By 80 reps youcan’t feel your legs anymore and your mindenters a strange trance-like state. You kindof lose touch for a while. You probably won’thave much energy left to groan or screamand your body gets limp. By 90 reps you’rejust along for the ride, with the spotters do-ing almost all the work.The universal reaction after thisexperience is to lay down on the floor. Somepeople have to throw up. Loss of conscious-ness may occur as the result of acute meta-bolic acidosis — the lactic acid builds upand acidifies the blood. This corrects itselfin a few minutes after you blow off somecarbon dioxide. Most people lie down forfive minutes or so before pulling themselvesover to a bench. You’ll be breathing hardand sweating for about 20 minutes after this.One other energy system deserves mention,but probably doesn’t play much of a role inbelt squats. That’s the glucose-alanine cycle(2). During long term aerobic exercise afterblood glucose and glycogen are depleted,the body begins to break down muscle tis-sue into free amino acids.
The amino groupsare removed from the amino acids and addedto pyruvate to form alanine. Alanine is trans-ported by the bloodstream to the liver whereit can be converted to glucose. The glucoseis carried back to the muscle to be used asfuel (2). In addition, the branched chainamino acids (BCAA’s) leucine, isoleucineand valine can be used directly as fuel bythe muscles. So in ultra-endurance activities,such as a marathon, muscle is actually bro-ken down and used as fuel. This is one rea-son why endurance athletes have smallmuscles and one reason why bodybuildersdon’t run marathons. Amino acids may sup-ply 15% of energy used in endurance activi-ties (2).In summary, we find that the beltsquat boosts energy producing capabilitiesof the entire body. Cardiovascular reserveand anaerobic threshold are increased.Training at this level of intensity carries overinto your other exercises and allows you toperform them more intensely also. Belt squatstax all three major energy producing systemsat maximal levels. While ultra-endurance ac-tivities like marathon running are counter-productive for bodybuilders, a certainamount of high intensity aerobic exerciseseems to allow increased muscular growth.This may result from increased vascular sup-ply to muscles which may stimulate growthby providing increased nutrient delivery (1-3).Everybody has a dream. Every-body wants to get to that next level. That’swhat Parrillo Performance is all about.
1. Hatfield FC. Hardcore Bodybuilding — AScientific Approach. Contemporary Books,Inc., Chicago, 1991.
2. McArdle WD, Katch FI, and Katch VL.Exercise Physiology — Energy, Nutrition,and Human Performance. Lea & Feiberger,Malvern PA, 1991.
3. Lieber RL. Skeletal Muscle Structure andFunction. Williams and Wilkins, Baltimore,1992.