Archive for January, 2014

Aerobic or anaerobic exercise? Which works best?

What’s the real question?

Eventually most of my clients will ask this question… although they don’t frame it in these terms.  The question is usually ‘Why are we working so hard?’

The answer is more than a one sentence answer because to explain what we’re doing I have to go into an explanation of energy systems and the research around what type of exercise works best for weight loss and fitness.  And because clients are here to train I don’t have half an hour to spare to give them a full explanation.  Most people are happy with ‘because it works… wait and see’ but there are people who legitimately need ‘buy in’ to a particular training regime – that is – they have to understand and believe the explanation and hear about the research before they’ll give it a proper shot.

So with that in mind… here we go!  Keep in mind that this is a blog and not a research document and that any simplified explanation of energy systems will by definition omit some important detail, but I’ll do my best.

Input vs Output

In the old days when the research on food and exercise wasn’t so precise we went by this mantra.  Match your output with your input and your weight will remain stable.  But of course whilst this is a good general rule it doesn’t really work like that.  What we know about input is that the type of food you consume is as important as the quantity.  Carbohydrates are used for energy production short term, protein assists in repair and growth of cell tissue, and fats are important for cell function, transport of essential nutrients and nerve and brain function.  So as far as weight control is concerned these days we’ve moved away from consumption of carbohydrates in great quantities as we know that their short processing time in the body means that unless they are used within a few hours they are stored as body fat.  Contrastingly, processing time for protein and fat is longer and we get a few more hours to use these as energy sources before they are stored. That’s very simplified, but in a nutshell, the body metabolizes food differently according to what type of food it is within those categories so we manipulate our input to take advantage of this.

IT turns out that exercise is the same.  In terms of output, the body acts differently according to the type of exercise we do.  In particular we’re talking about intensity.  The body uses three basic energy systems – one is aerobic and the other two anaerobic, and so here is the drum…

The Aerobic Energy System

Most of the time during the day doing our day to day activities we request and are supplied with energy using the cardiovascular system – that is – the sugar produced by your liver and transported through your blood supply to the working muscles is sufficient to supply all of your energy needs there and then.  If you were to walk faster, your body would increase heart and breathing rate and transport more oxygenated blood to your legs to provide the energy required.  If you were to jog or run at a pace that would allow you to have a conversation with someone whilst you were running you would be using this energy system.  It’s our most efficient system as it is constantly in use and can quickly ramp up if requirements increase.  And it will ramp up to a point we call the ‘anaerobic threshold‘ – that is – the point at which you are working so hard that the body can’t produce energy as quickly as you are using it.  This point varies quite a lot from person to person for reasons I’ll explain another time.  During the 80’s, 90s’ and 00’s many training programs revolved around this energy system mostly through a mistaken interpretation of something called the ‘fat burning zone’ by celebrity trainers like Jane Fonda and others, including your average certificate qualified personal trainers.  I’ll do a blog on this another time.  There was a lot of bandwagon jumping because there was a lot of money to be made.  Aerobic sessions are typically longer and require more sessions per week ( five or six) to be truly successful.

These programs have one other major problem… they don’t really work.  I remember many women coming to me and asking ‘why do I have this cellulite on my butt and legs when I’m exercising 90 minutes every day?’  We still see these ‘gym junkies’ at the gym working out for several hours with thin bodies, but no lower body definition – as if the fat has hung onto them.  The fact is it has.  And the excessive aerobic activity is the reason it has.  The body has evolved to work in a way to facilitate survival.  If we were to head back to our hunter gatherer past we would see that humans were either traveling from place to place in search of food, or were actively hunting it.  Whilst traveling from place to place the emphasis is on surviving the trip, so travel would be for several hours or maybe days at a low intensity (in the aerobic zone).  The body has evolved to make attempts to preserve what fat supplies we have in this circumstance to facilitate survival should we not find hunting grounds within a few days.  Research indicates that the body is more likely to break down muscle tissue for energy supply than use stored body fat in situations where food intake is low and aerobic activity is high – the very situation people have put themselves in to ‘lose weight’.  Thus the retention of ‘cellulite’ type fat stores in people who train and eat this way.

The Anaerobic Systems

I say systems, because there are two major anaerobic systems within our body that are used according to the intensity of activity.  Our aerobic system works constantly in the background supplying the day to day needs up to the point of intensity we previously called the ‘anaerobic threshold’ (AT).  Above this intensity the energy has to be supplied from another source because our cardiovascular system is unable to pump oxygenated blood through to the working muscles at a rate commensurate with the demand.  If the demand is marginally above the AT we will generally use what’s called the ‘lactic acid’ system.  Energy is supplied via a process within the working muscle that produces energy by using muscle glycogen stored in the muscle.  One of the by products of this system is lactic acid (thus the name) – the chemical that is believed to cause that ‘burning’ feeling in the muscle when you’re near the end of the system’s ability to produce energy (the last 20 seconds of a 400m run for example).  It is limited in it’s ability to produce energy (thus the slow down if you continue at that intensity) and is usually depleted by about one and a half to two minutes.  Hunter-gatherer wise this system is used when actively hunting and chasing food.  The other system kicks in when the intensity is maximal – the ATP-PC system (can’t explain the name here – too involved).  This is the system you would use if you sprinted 100m as fast as you could.  This  is a ‘flight’ system evolved for use to escape danger or to initiate a hunting manouvre that requires full effort.  It is limited in how much energy it supplies and burns out within about 30 seconds for most people.    These systems will replenish quickly during a recovery phase of a training session (i.e. rest between sets) according to a researched formula (later down the page) until the muscle glycogen is depleted.

The advantage of these anaerobic systems for weight loss is that they are very expensive for the body.  Unlike the aerobic system, the energy required is not ‘steady state’.  The body uses more energy than it can produce at the time and builds up an energy deficit that has to be repaid during recovery.  The production of energy without oxygen is very inefficient and uses more calories both in the production of the energy itself and in the repair and replenishment of the body to it’s resting state.  Muscle glycogen, for example, is a physiological imperative- that is – the body has evolved to fast track the replenishment should it be required for more ‘hunting’.  Typically it does so from recent food consumption, but where carbohydrate consumption is not sufficient, it draws on fat stores for this replenishment.  So rather than encouraging fat to stay on the body it uses your fat stores to replenish muscle glycogen it can’t replenish from your food consumption.  So if you’re restricting your diet in terms of carbs, this is how that works.

Effect in Metabolism

Your ‘metabolism’  is the rate at which your body works.  During exercise your metabolic rate increases, and as you recover it slows down.  The higher your metabolic rate, the more calories you are using.  Many weight loss products aim to increase your metabolism to assist the weight loss process.  The whole purpose of using anaerobic activity to assist in weight loss is that it’s effect on metabolism is far far greater than an aerobic activity.  An aerobic system is a closed system in that, as previously explained, energy is requested and supplied in full at the time.  There is no requirement for the body to produce energy beyond the time period of the activity.  The opposite is true of anaerobic activity.  The body must produce the energy on demand, but then must also replenish and repair what’s been used – and it does this during rest.  So your caloric output is made up of what you use during the activity PLUS what your body does afterwards to return to your normal resting rate.

And this is the crunch…  Research indicates that an aerobic session will elevate your metabolism for approximately 20 minutes after the activity if you are exercising below the anaerobic threshold, whereas a high intensity (90% of maximum) anaerobic session will elevate your metabolism for up to three or four hours.  That’s right.  You get three or four hours of increased caloric consumption by doing nothing more after your intense workout.  So if you run for 90 minutes (why would you?) below your anaerobic threshold, your rate increases for total of  110 minutes.  A 45 minute intense training session will have your rate increase up for up to 285 minutes.

That’s why we’re working so hard.


In summary, the most efficient and effective training session for weight loss is one where you work at 90% of your maximum effort for as long as your muscle glycogen stores will last.


How does my training program assist this?

So if you’re training with me for weight loss, how does the formula I use meet the above criteria?

The formula I use is to complete three pairs of superset weight activities followed by a high intensity interval training session (HIIT) usually on a spin bike.

More specifically I use multi muscle group exercises in non-synergistic target muscle group pairs mostly using free weight dumbbells, swiss balls and body weight activities.  These are done for 3 x 8 sets with 1 minute recovery and with fast concentric and slow eccentric movements.  The HIIT session is designed to complete the depletion of muscle glycogen supplies to the clients’ tolerance and fitness levels.

Superset weight training

The Exercises

The exercises are chosen to maximise whole body use.  The more muscle groups used in the activity, the more muscle glycogen is used and the more energy therefore expended.  I incorporate large muscle groups such as quads, hamstrings, gluteals etc as much as possible because they require more energy expenditure because of their size.  Dumbbells are used because they require the use of the upper body when doing lower body activities and they engage core muscles more often than not because control of the dumbbells is essential during most of the activities.  The exercise pairings maximise workload by switching the emphasis from one area of the body (and thus bloodflow) to another whilst recovery of the other group takes place.

Sets and Reps

Research indicates that for beginners, 8 reps is the best compromise between maximal effort and time in contraction.  By the time we get to 6 or 7 reps the fatigue sets it and the last couple of reps are difficult.  After three sets of 8 reps most people are significantly depleted of muscle glycogen in the working muscles.  If they can continue either more reps or sets, then the weight is increased.


To enable the correct number of reps and sets to be performed according to the research, we set the weight such that the participant can complete 8, maybe 9 but not 10 reps.  This ensures fatigue at a level which encourages the optimum depletion of muscle glycogen at the end of the session.


Weight sessions are mostly done using the ATP-PC energy system.  This system works maximally for about 30 seconds after which it tails off.  Research indicates that one minute 30 seconds ( a one to three work/rest ratio) will allow recovery (not replenishment that’s a different thing) of the system sufficient to repeat the activity.  As stated above, after three sets significant depletion of muscle glucogen will have taken place.  I allow one minute between supersets which equates to one minute 30 seconds between sets of the same exercise if the set takes 30 seconds to complete.

Fast concentric slow eccentric

Strength gains are at or slower than the speed of contraction.  For functional use, any strength gains have to be developed at a normal speed, so we do the pushing phase of the exercise at a fast speed.  This also contributes to energy consumption during the session and maximises replenishment requirements.  Endurance gains are directly proportionate to the amount of time the muscle spends in contraction.  By doing the return phase of the exercise at half the pushing phase time we maximise endurance gains and again contribute to increased energy use.  This method makes the activity significantly harder using more energy and requiring greater post exercise replenishment thus contributing to the amount of time of metabolic rate increase post exercise.


High Intensity Interval Training

We finish off the session with some interval training (these days called HIIT, but of course if it’s not high intensity it’s not interval training!).  The purpose of this is to work towards as maximal depletion of muscle glycogen as the participant can manage.  The weight session does most of the work, but usually the larger muscle groups in the legs / gluteal area  have the most residual muscle glycogen and so we work there.  In the past I have tried boxing activities or kettlebell interval sessions but quite often the upper body has been mostly depleted during the weights session and the activity can not be performed as intensely as it should be.  Working the legs, with the spin bike or running (which is my personal preference) ensures the maximal depletion, and therefore maximal replenishment requirements and maximises the time in post exercise metabolic rate increase.

I like to switch things around between ATP-PC and lactic acid interval training to retain the shock factor to the body and thus continually initiate a training effect.  I use 1:3 work rest ratio for a 30 second 9/10 effort  and a 1:1 for an 7-8/10 effort one minute work period.  As participants become more experienced I generally introduce random reps with the appropriate 1:3, 1:2 or 1:1 work rest ratio.


Of course, every four to six weeks depending on how we’ve been going, I change the whole program.  Normally clients will alternate two sessions for this period, after which I’ll use another program.  I have designed my programs to gradually become more difficult as clients progress from one to another.  The result is usually a lighthearted complaint about ‘this program being worse than the last one’.



There is quite a bit of sports science in the above information, and you could still get a good grasp of what I’m on about by skim reading those parts.  The essential information is that modern training sessions work utilising anaerobic energy systems as much as possible, seeking to deplete muscle glycogen through activities that work at about 90% of maximum effort.  This maximises energy use and increases the demands on the body after exercise in terms of repair and recovery.  A well participated session will increase your metabolism for hours after you finish.  Contrast with that the old fashioned aerobic training sessions where metabolism is only increased for short periods after you stop exercising.

The sessions I run for clients are aimed at taking advantage of the research which shows this.  A superset weights session with as heavy weights as you can manage for the correct number of reps and sets done with the correct timing will maximise this muscle glycogen depletion.  Finishing you off with a high intensity interval training session completes the depletion process to the clients’ fitness levels both mentally and physically.

I hope that makes it clearer… feel free to discuss!