The Intuitive Athlete

When I was training seriously the only wearable technology available was a stopwatch. In those pre-GPS days, I would estimate the distance I’d run by using a London A-Z and a ruler. Despite these rudimentary monitoring methods, I seemed to learn to ‘know’ when I was in good shape. Its difficult to explain how I ‘knew’, but there was just a certain feeling in the legs and running just seemed to ‘flow’. It was these feelings that informed decision-making with regards to goal-setting for upcoming races. Somehow, I just seemed to be able to sense if I was in pb shape or not.

It’s not just I who has experienced this phenomenon. In his autobiography, middle distance great Steve Ovett frequently talked of how he could intuitively interpret the signals his body was sending. At one point he says:

“I knew that if that session is achieved in a certain pattern, then it is a case of two plus two makes four… I know from how my body feels after that session that I am ready for a fast run. I can do a session through the woods without the benefit of a watch and still know that I am going well. Instinct… tells me I am in shape for something special”


“I believe part of my talent is an intuitive feeling about when I am ready to race… I know from experience and a certain feeling that I am capable of running really well”


“For many of my races I make what really is a last-minute decision… I do not plan a month in advance: it is almost day to day with me. I have been out on a training run, felt good and got back home to ring round and search for a race.”

This intuitive approach to training also seems relatively common. There are several examples, but my favourite two quotes come from 1988 Olympic 5000m and Multiple World cross country champion John Ngugi of Kenya, and multiple masters world record holder Derek Turnbull of New Zealand. Ngugi said that “when he felt like going fast, he did; and when he didn’t feel like it, he didn’t”, whilst Turnbull claimed “I don’t know about this aerobic business, I don’t train. I just run — when I feel, where I feel, how I feel.”

These anecdotes all sound very nice, but they also sound rather naïve. Surely a more rational ‘scientific’ approach would yield superior results? Just think of all the data on exercise it is now possible to collect to inform training and racing decisions. I’m not so sure. Think of the number of possible training sessions that can be devised as well as the number of ways in which they can be combined. Chess grand-master Gary Kasparov once said:

“The total number of possible different moves in a single game of chess is more than the number of seconds that have elapsed since the big bang created the Universe. Intuition is the defining quality of a great chess player.”

This makes perfect sense – imagine the computing power required to calculate the effects of all possible combinations of training sessions to try and work out what is optimal! However, even given the potential limitations of using a rational data driven approach, it can be hard to believe that basing decisions on whatever ‘feels’ right may be superior. I suspect that this is based on misunderstanding of how intuition is developed. It certainly isn’t just a case of doing whatever you fancy – it is far more subtle that that.

It seems as though intuition essentially relies on a process of pattern recognition and interpretation, a quality that can be developed if certain requirements are met. The most important is experience. This is not entirely surprising, as greater exposure to a situation provides more opportunities to recognise patterns that are important (or unimportant).  The recognition of what is unimportant is probably at least as essential as what is important, especially in the context of potential data overload. This forms the basis for heuristic decision-making whereby an individual ignores most available data and focuses on a few key qualities of their environment to allow them to make ‘fast and frugal’, yet accurate, decisions. To go back to the earlier Steve Ovett quote (“I know from experience and a certain feeling that I am capable of running really well”), this was something he had picked up on. It is necessary to emphasise that when he wrote this, Ovett was an established senior athlete. Earlier in his career he required more specific coaching input from Harry Wilson.

Another key factor, besides experience, contributing to high quality intuition is emotional intelligence (because emotion precedes cognition, facilitating more rapid decision-making). Emotional intelligence represents a set of skills and behaviours which can also be developed though experience and exposure to certain situations.

I am sure that some (most?!) readers will disagree and prefer a more data driven approach (see – However, those who prefer a more intuitive approach should be reassured that this is anything but simplistic and naïve, but rather a sophisticated approach to dealing with large volumes of complex data.

The inherent difficulty in predicting human athletic performance progression

As usual the World Athletics Championships have produced many spectacular performances. From a purely ‘performance’ perspective, the highlights have probably been Sydney McLoughlin’s amazing 400m hurdles world record and Shericka Jackson threatening Florence Griffith Joyner’s ‘untouchable’ long standing 200m time. Every time an athlete produces such an outstanding result, thoughts almost inevitably turn to the question of what time represents the ultimate ‘limit’? So far it seems our predictions have not been particularly successful.

In the early 1950’s the big question in the athletics world was whether or not it was possible to run a mile in less than 4 minutes. Despite doctors at the time saying attempting such a feat would be fatal (allegedly – I have read this in several places but never been able to find any contemporary evidence), athletes from around the globe made multiple attempts before Roger Bannister finally achieved it at Oxford in May 1954. Having demonstrated that 4 minutes did not represent an impenetrable barrier, 7 more men achieved the same feat in the following 12 months. Nowadays sub 4 minute miles are relatively commonplace, even amongst high school athletes, and in 1998 Daniel Komen ran 2 miles in less than 8 minutes, and Joshua Cheptegei’s recent 5000m WR isn’t ‘that’ far away from being equivalent to 3 miles in 12 minutes. Clearly then, ‘expert’ predictions were miles off…

A number of attempts have been made to predict future WR progressions. The most basic have used linear regression using previous WR performances and extrapolated into the future. These methods have produced some eyebrow raising results. For example, in a short communication to Nature (, Tatem et al. (2004) predicted that by the year 2156, males and females would have equal 100m WR’s of 8.079s! There are obvious problems inherent in attempting to use linear methods to make such predictions. Firstly, if you take things to their logical conclusion, then at some point in the distant future, athletes will be running negative times (i.e. finishing before the gun is fired). Intuitively, it also seems implausible that records would improve in a linear manner – as records get more and more difficult to beat you would expect them to advance by progressively smaller increments. What also needs to be considered is the ‘quality’ of the data included in the analysis. As time has passed, track and field has transitioned from a predominantly European activity performed in University’s to a truly global sport meaning that the available talent ‘pool’ has increased massively. This effect has also likely been far greater for females than males given the limited opportunities for female participation until relatively recently, meaning the rate of improvement for females has been greater (and hence if you extrapolate far enough into the future, females will surpass males).

A more sophisticated analysis was used by Nevill & Whyte (2005) (  who found a ‘flattened S’ shaped curve better fitted existing WR data in male and female middle- and long-distance running events. This produced the far more sensible predictions detailed below (WR’s at time of publication on left, ‘ultimate’ predictions in bold on right):

Distance(m)Time (m:s)Speed (m:s)Time (m:s)Speed (m:s)

However, even here we have a problem in that although the model predicts male WR’s to carry on improving, it predicts that the female 1500m limit has already been achieved. Undoubtedly this prediction is influenced by the performances of Soviet block athletes in the 1980’s and ‘Ma’s Family Army’ in 1993, all of whom have been implicated in doping scandals.

Of course, the problem with attempting to model WR performance progression is that it only takes one extreme performance to invalidate the model.   Consider the men’s 200m WR which was set at 19.72s by Pietro Mennea in 1979 and which remained unbroken for 17 years until Michael Johnson ran 19.32s at the Atlanta Olympics, reducing the longstanding record by 2% in one go ( If this single performance is incorporated into the model, it will have a substantial influence on all future predictions.

A further issue complicating attempts to predict future performance progression is the number of variables influencing performance. Its not as though performances over the last 100 or so years have been achieved by a static population of genetically identical athletes operating in the same environment. Larger populations are now active in the sport, training programs and sports medicine (and unfortunately drugs) have evolved substantially, and track surfaces and footwear have both improved considerably since Roger Bannister broke the 4-minute barrier on a track resembling a ploughed field wearing what looked like a pair of stout brogues. It is modelling the technological advancements which represents perhaps the greatest challenge. No-one knows what these advances will be, or how big their impact will be until they exist. If someone did know what the future technology would be, then someone would almost certainly already be using it.

So… predicting the ultimate levels of human performance is an extremely difficult task. The only thing I am confident of is that we will continue to be surprised by how quickly people run and will continue to argue about the legitimacy of technological developments.

The core training principles of specificity and overload

The physiology underpinning endurance performance is fascinating, and I am as ‘guilty’ as anyone of nerding out over the intricacies of muscle fibres, metabolism, mitochondria, fuels, training zones and the like. However, I also think that sometimes its too easy to get bogged down in the minutiae and lose sight of the big picture which for many people is the goal of going faster in competition (whilst remaining healthy – something else I feel is often overlooked).

Training is in principle a simple activity, in that you apply a stress to the body, allow it to recover, and the body responds by adapting so that, if faced with the same stressor again, it can deal with it more easily. What the endurance athlete is attempting to do is apply repeated stressors followed by appropriate recoveries so that, in the long term, there is a gradual increase in physiological resources that provide the athlete with more options during competition (the option of ‘sitting’ on Jacob Ingebrigtsen throughout a mile race is not available to me because I lack the required physiological resources!).

So… what does an athlete with aspirations of beating Ingebrigsten need to do? We can discuss VO2 max, LT, anaerobic power etc, but ‘all’ that is required is the ability to run 4 laps of a track in a little under 56s each. This means the athlete needs to be able to generate sufficient forces to run quickly enough and must be able to supply energy at the required rate for long enough to cover the distance at this speed. These requirements should underpin all training decisions if the goal is performance and not just a nice training diary or some impressive lab results.

Everyone knows, and it is intuitively obvious, that the response to training is specific (you wouldn’t train for the 100m by running 2 hours slowly) and this applies to mechanics, muscle recruitment and metabolism. The reason why our 100m sprinter wouldn’t benefit from long slow runs is that they recruit different muscle fibres and use different energy systems to those used in competition. Therefore, if we take what I call a ‘proper’ race, the 1500m, then it would seem the most beneficial training sessions in terms of their transferability to the race situation would involve prolonged running at race speed. Lots of sessions are possible but let’s say that the ability to run 3x1000m with good (8-10 minute) recoveries correlates very well with race ability, then it would be logical to conclude that being able to run this session faster would result in improved race ability.

The key question is how to improve the ability to run this session faster. The easiest approach is to simply try and run it as fast as possible in every hard training session, however, I suggest this approach is doomed to failure. In reality you would soon see a plateau in performance due to fatigue (this session is HARD!) and also due to failure to adhere to one of the other key principles of training – OVERLOAD. How can this be if the sessions are so hard? Well, ‘hard’ as the sessions are, they are not sufficiently fast to improve basic ‘speed’ or sufficiently long to improve ‘endurance’.

In order to overload these abilities, I need to sacrifice some degree of specificity. On the ‘speed’ side I could run e.g. 4x400m at ~800m race speed to make 1500m pace easier. In turn I could run some very fast 60/100’s to improve my 800m pace, and then do some weight training or plyometrics to improve my sprinting. What you can hopefully see though is the trend that as the degree of overload in the speed / force direction is increased, the activities get less specific to the target event.

The same principles hold true in the ‘endurance’ direction – the ability to maintain the required speed can be enhanced through sessions such as 8x1000m, 30 minutes fast continuous runs, 1-hour moderate runs, 2-hour slow runs etc. Again – greater overload requires some sacrifice of specificity.

What this suggests is that although the ability to do high quality specific training is crucial, you need to work from the extreme ends of the spectrum if you aim to maximise performance ability. The difficult part is in deciding how much emphasis to place on each end. This will vary depending on individual athlete characteristics, but its probably not too controversial to suggest more work is usually required at the ‘endurance’ end than the ‘speed’ end. Concentrate on just one (or even both) of the ends though, and you may end up with a ‘fit’ athlete who may not necessarily be able to utilise those abilities to actually race quickly.

Beware of ‘neomania’

Sport being the competitive activity that it is encourages innovation as competitors seek marginal gains that may give them an edge over their rivals.  This inevitably leads to the production of new technologies and techniques that are enthusiastically adopted by athletes and coaches. Certainly not all (there will always be Luddites), but a good proportion of sport practitioners seem to display elements of neomania, or a craving for new things. I used to be a bit like this myself in that, although I’ve certainly never been a technophile, the assumption was that new is always better or improved.

However, when you have been around long enough (or read enough), it becomes clear that what goes around comes around and there isn’t much new under the sun. In fact, in many domains technology and practices haven’t changed for a VERY long time (think wheels or cooking utensils). If we think of standard sports and exercise practices, then lifting heavy weights or covering long distances on foot at easy efforts have been used for centuries and continue to be used to this day.

What we are seeing here is the Lindy Effect ( which suggests that the future life expectancy’ of a technology or idea is directly proportional to their current age. Whatever has survived a long time already is likely to survive a long time into the future. Obviously this doesn’t apply to individual organisms or else you would expect an 80 year old grandparent to have more remaining years of life than their 10 year old grandchild, and it doesn’t apply in every single case (even the wheel was new once). However, it remains a useful heuristic as anything that has survived the ultimate test of time must have some important qualities. Wheels, knives and forks, the music of Mozart, long duration exercise and lifting weights have all demonstrated their value through their longevity, but its easy to think of things which didn’t – Betamax and VHS video recorders, the Sony Walkman, the inexplicable musical popularity of Jive Bunny and the Master Mixers, and the Sinclair C5 all had their 15 minutes of fame before going the way of the Dodo. Just since I started in athletics, I can think of several shoes technologies that have come and gone (Reebok ERS/ Pump / Hexalite, Brooks Hydraflow, Adidas Torsion, ASICS split tongue, Vibrams etc). Vibrams were a particularly interesting development as their rationale was to recreate barefoot running, thereby undoing the perceived negative impact of current shoe technology. At the moment everyone is wearing some version of the new ‘super shoes’ – this will probably change although I am confident that in 100 years people will still be wearing some kind of shoe to run in (shoes being another very old technology).

So… any implications for the sport and exercise practitioner? I think they are obvious – don’t let your enthusiasm for the shiny and new distract you from the dusty old techniques that have withstood the test of time. Anything that has been around for a long time has survived for a reason.

Where did it all go wrong?

At one point in the late 1990’s I was a relatively fast runner who felt indestructible. I was fit, motivated, trained very hard, recovered well and felt good. Now I am a very slow runner who cant string together a few days of training, is always sore and tired, struggles to walk downstairs in the morning,and often just cant be arsed. Obviously this transition didn’t happen overnight, but as I huffed and puffed around the woods the other day trying to recover from a bout with Covid, I couldn’t help wondering – ‘where did it all go wrong?’

This is obviously not a simple question to answer. First of all there is the biological component to consider. As you age your physical capacities diminish. Training can delay this process to a certain extent, but in the end Mother Nature wins and the slide begins. However, I reckon my own ‘peak’ occurred at only 24/5, relatively young compared to many top athletes. The problem is that you never really know when things are as good as they are going to get until after they have gone. By 27 though I certainly felt ‘different’ in that there was a subjective sensation of loss of ‘bounce’ in the legs along with lingering fatigue and soreness.

So why was I ‘done’ by 27 whilst others run well into their 40’s and beyond? Its important to remember that each time you train you are inflicting some degree of damage which in turn stimulates recovery and adaptation. Perhaps muscle is only capable of a limited number of repair cycles before it can no longer adapt? It would certainly seem unlikely that there is a limitless capacity for adaptation. Some damage does not stimulate adaptation at all and is simply injurious. Lots of little injuries add up until eventually the big end goes and you find yourself out of action for a while and inevitably experience de-training as a result.

Now, although I have absolutely no data to support this (when I have time I’ll investigate), I have a hunch that all runners can expect to improve for a number of years on taking up training before a plateau in performance, regardless of their age on starting. I started young so was ‘done’ young. I am also not aware of any of my competitors as juniors who are still very competitive in the masters ranks. Conversely, the fastest masters appear to be relative newcomers to the sport.

What about the mental side? Speaking personally again, although in hindsight I was past my peak at 27 I definitely didn’t accept it at the time and looked for various strategies to maintain performance. More mileage, elaborate track sessions, short hills, yoga, strength training, supplements – none had any effect. My mental approach changed slightly too in that I would tell myself I wasn’t quite in shape ‘yet’ and would set slightly more conservative goals for competition. Inevitably I’d fail to even achieve these so would avoid competition to focus on getting in some good training. After a while this continuous failure to achieve goals resulted in loss of motivation meaning I would begin to question the value in driving 4 hours to a race at the weekend.

Its also notable that my decline coincided with beginning full time work. Until that point it had been possible to avoid the real world through continuing in study or else working part time selling surfboards, a lifestyle that made it possible to make a planned track session the focus of the day. Now though it had to come after a full days work and a commute, and was usually performed alone. Fitness slipped further, and performances and motivation soon followed. This all came to a head one day when I stepped off the track 100m into a planned session of 8x600m and then followed a prolonged break of several years.

Eventually the desire to make a competitive comeback returned but did not last long – squeezing in training around full-time work and two kids to run much slower than before held no attraction. These days it is fear of what might happen if I stop exercising altogether that gets me out the door.

So, ‘where did it all go wrong?’ is a difficult to answer. Like most things in sport it emerges from the interaction of physiological. psychological and environmental factors.

The futile search for the optimal training method

I originally became interested in sport science because as an obsessive athlete I really wanted to know how I could run faster. Surely a thorough understanding of how the body works and adapts to exercise would allow me to ‘work out’ the optimal way to train? In essence I was working under the assumption that the ‘recipe’ was out there awaiting discovery. Now I am less convinced – in fact I’m pretty confident it’s not.

In searching for the perfect training program, there are lots of things that need to be optimised. At the level of the individual session alone, consideration needs to be given to intensity, volume, recovery periods, time of day, nutritional status, mood, motivation, and probably a whole host of other factors. The magic of training doesn’t exist solely in the details of a single session though, and how they are put together is likely more important. This means we need to consider overall periodisation strategies, recovery between and sequencing of sessions, rate of progression, and again a whole host of additional factors.

If I am looking for ‘scientific’ solutions to these issues I can look for two types of evidence – experimental studies or case studies of successful athletes (its interesting you never see case studies of unsuccessful athletes; maybe they are doing the same as the successful ones?).

Experimental studies can be very useful as they are able to demonstrate the superiority of one type of session over another. However, care must be exercised. Take the example of this very nice study by Ronnestad et al demonstrating the superiority of short over long interval training in improving aerobic power ( Looking at the overall results there appears a clear ‘win’ for the short intervals. However, there are varying responses by individual participants. Take this figure showing pre- and post-intervention 5-min all out power output:

For the participant in the LI group who started with the second highest power output, the intervention has been highly effective. However, for the athlete who started slightly above him its been a disaster. So the overall message to take from the study is that short intervals are ‘probably’ better for most people except for the few for whom they aren’t. How do you know if you are one of the few? I have no idea! Try them and see what happens.

One other comment about this study – it was 10 weeks long and participants were highly trained. Will the apparent superiority of short intervals persist if the training is continued beyond 10 weeks? Would you get the same results in less well-trained participants? Dunno on both counts…

As for case studies or descriptive studies, these are my favourite papers to read, and I find them fascinating. They are very useful as they allow identification of common themes – if there is some common theme present in the training of all elite athletes then this is probably important. However, there are still issues to consider when interpreting these. Take some of the excellent studies describing the training performed by the great Kenyan athletes.  All vey interesting, but how applicable are they to the athletes I work with who are not Kenyan, are not born and raised at altitude, and have not been running 10km to and from school each day since the age of 6? Perhaps the foundations of the Kenyan success lie elsewhere and are not based in some perfect training programme? Just because Eliud Kipchoge benefits from a weekly long fast run, it does not necessarily follow that you or I will (or even Kipchoges’ training partners). What may be of more interest from a training perspective is what these athletes did in the distant past to get them to the position where they can benefit from such training. (

If we consider performance a biopsychosocial emergent phenomenon (as we should), then it is clear that science is limited in its ability to provide all the answers to the ‘how should I train?’ question (I always emphasise to my students just how hard sport science is – people are ‘messy’ and operate in messy environments). Trying to implement a truly evidence-based program is next to impossible –the best we can do is evidence ‘informed’. There will always be a role for the subjective and the ‘art’ in coaching.

(Basic) exercise physiology for endurance coaches Part 3 – adaptations

This is (probably) the final post in a short series about (basic) exercise physiology for endurance coaches. Part 1 addressed force production, part 2 addressed energy, and this part addresses adaptations to training. This is a vast topic, so for simplicity I will only be addressing key principles relevant primarily to endurance athletes.

How training ‘works’

Training is a stress that damages the body, meaning you are not as fit immediately after a session as you were before it. However, it is during the recovery that the magic happens. This is when your body adapts by building more of the protein structures that were most stressed in the exercise bout. This could include enzymes, contractile proteins (actin and myosin – see part 1) or sites of aerobic metabolism (i.e. mitochondria in the muscle cell). The key here is that the adaptations are specific to the stresses imposed, so don’t do a series of short sprints with long recoveries (predominantly anaerobic) and expect to improve aerobically. Remember the diagram showing muscle recruitment and force generation in Part 1? That is very relevant here too – do nothing but very slow runs and you only train a small fraction of your fibre population, leaving the rest effectively untrained (unless you exercise for long enough to fatigue these fibres thereby ‘forcing’ more fibres to contribute).

Energy system adaptations

I am going to base the remainder of this post around the energy systems explained in part 2. As this is aimed at endurance coaches, I will largely ignore the PCr system because of its rather limited contribution. However, you should be aware that there are a host of muscular, neural, endocrine and metabolic adaptations to short sprint training that can all contribute to increased power output and speed.

The aerobic system

This system contributes the majority of the energy for all events from 800m onwards with its relative contribution increasing along with distance. There are numerous adaptations to training that mean quite substantial improvements in aerobic power (rate of energy production) and capacity (amount of energy produced) can be achieved.

Remember from part 2 that aerobic metabolism is far more efficient that anaerobic metabolism provided oxygen is available to accept pyruvic acid at the end of glycolysis. Any adaptations which improve the ability to get more oxygen from the atmosphere to the muscles is therefore likely beneficial, and there are a number that do just this. Oxygen is transported from the lungs to the muscles via the blood in combination with haemoglobin in the red blood cells, and there are a number of training adaptations that facilitate this process:

  • The left ventricle of the heart increases in size meaning more blood is ejected per ‘beat’ (i.e stroke volume increases). This means more oxygenated blood can be delivered to the tissues per minute (cardiac output).
  • Blood plasma (the fluid component) increases meaning blood can flow more easily through the vessels (and also assists in thermoregulation).
  • Red blood cell production is increased meaning more oxygen can be transported in the blood.
  • More capillaries (the finest branches of the blood vessels where gaseous exchange occurs) are formed around individual muscle fibres. This allows more rapid gaseous exchange to occur as it reduces the distances it must travel over and increases the available surface area.

All of the above adaptations to aerobic training (sometimes called central adaptations) increase delivery of oxygen to the muscles. Further adaptations (peripheral) occur inside the muscle that allow it to be utilised more effectively when it arrives. This list is by no means exhaustive, but these include:

  • Increased number of mitochondria (remember the Krebs cycle and electron transport chain from part 2? This is where this all occurs). More mitochondria (the ‘powerhouses’ of the cell) mean more rapid ATP resynthesis.
  • Increased activity and concentration of aerobic enzymes within the mitochondria. I’m not sure this is a perfect analogy, but if the mitochondria are the powerhouses, then this suggests the ‘workers’ are more numerous and better skilled meaning everything runs more efficiently.
  • Related to above – specifically greater concentration and activity of enzymes involved in fat metabolism meaning you can better access the vast energy reserves we all have stored as fat.

So… as simple as I can make it, but hopefully sufficient as a summary of the physiological adaptations to endurance training that can lead to improvements in both the power and the capacity of the aerobic energy system.

Anaerobic glycolysis

So far the aerobic system sounds great and you may be wondering why you even need to train the anaerobic system. The answer is that anaerobic metabolism can supplement the energy produced aerobically thereby allowing you to (temporarily) run faster (although the aerobic system is ‘slow’ this is a relative term. I once put a class of 1st year sport and exercise science students on a treadmill at world record marathon pace. The longest anybody hung on before they were swinging from the safety harness was 53s -you can imagine how much better Eliud Kipchoge is at delivering and using oxygen).

Glycolysis is a simple enzyme mediated series of reactions, so do some high intensity training and you get increases in the concentration and activity of the key rate limiting enzymes and hopefully a corresponding increase in anaerobic power.

There is a bit more to it though – remember from part 2 that anaerobic glycolysis results in a drop in pH due to an accumulation of H+ ions, and that this has negative consequences for energy production and muscular force generation? In an attempt to minimise the impact of this the body responds to high intensity training by producing more chemical ‘buffers’ which can neutralise the acid. The most important of these is bicarbonate (HCO3) which combines with H+ to form carbonic acid (H2CO3) in the blood. When this reaches the lungs it breaks down to form H2O and CO2 which is exhaled (which is why the inability to hold a proper conversation during exercise is a sign you are producing increasing amounts of energy via glycolysis).

So – this concludes my series on (basic) exercise physiology for endurance coaches. Your task is to use it to inform the design of training programs that are appropriate to your athletes’ event specialism and stage of career development. I am not going to write a specific post on ‘how’ to train because I am not wed to any specific method / system. I believe there are multiple ways of achieving the desired goals provided core principles are adhered to. However, some of the articles on this site do address a few of these.

(Basic) exercise physiology for endurance coaches Part 2 – energy

My previous post (Part 1 – explained how faster running speeds are achieved by recruiting greater proportions of the available muscle mass in order to produce greater ground reaction forces. It concluded by saying that greater muscle mass recruitment also resulted in increased rate of energy use and therefore the ability to supply energy at the required rate and in large enough quantities is a major limiting factor in running performance. This part explains where the energy comes from.

The only usable source of energy for muscular work in the body is a molecule called Adenosine Tri-Phoshate (ATP). This is used in the forming and movement of the cross bridges between actin and myosin filaments as described in part 1. More force therefore means more cross bridges which therefore means more rapid ATP use. Each ATP molecule consists of an adenosine group and three phosphate groups and the chemical energy ultimately used in muscular force generation is stored in the bond between the second and third phosphate groups. In the presence of a specific enzyme (ATPase) this bond is broken, the energy is liberated, and you are left with adenosine di-phosphate and a free phosphate. Simple!

ATP                    ADP + P + ENERGY

This all looks great, but there is one small problem. You probably have a total of less than 100g stored in your entire body – enough to sustain about 2 seconds of high intensity exercise before it runs out and you are left as a rigid corpse! To prevent this unfortunate scenario you need to somehow stick the ADP and P back together again as quickly as you are breaking it down. Fortunately, the body has three ways it can do this:

The Phosphocreatine system (AKA the ATP-Pc system, the PCr system depending on what book you read)

Stored within your muscle cells you have a high energy phosphate molecule called phosphocreatine (PCr). In a very simple process, PCr is broken apart by an enzyme called Creatine Kinase (CK) to release energy which is used to recombine ADP and P to produce more ATP.

PCr                P  +  Cr   +  ENERGY

                                 ADP  +  P                  ATP

On paper this looks great. The simplicity of the process means it can resynthesise ATP very rapidly (it is POWERFULL) meaning it can fuel very high exercise intensities, and it produces no harmful by-products. The problem is that the quantity of PCr stored within the muscles is relatively small. Precise numbers vary depending on what you read, but after somewhere in the region of 8-15 seconds of high intensity exercise, muscle stores are almost empty. Although the system is very powerful, it therefore has a low CAPACITY for ATP resynthesis. After about 100m of flat out running this system is therefore ‘done’ and if you want to carry on running quickly you have to get the energy for continued ATP resynthesis from somewhere else.

Intramuscular PCr stores will eventually be replenished, but after maximal intensity exercise it takes in the region of three minutes for this to occur. Therefore, if you are wanting to maintain quality during things such as maximal speed sessions, be generous with the recovery!

Anaerobic Glycolysis (AKA the Lactic Acid system).

The next method we can use to generate energy for ATP resynthesis is through anaerobic glycolysis which involves metabolism of carbohydrate (some readers may have been wondering where ‘food energy’ comes into play). Although more complex (and therefore slower / less powerful) than the PCr system, glycolysis is still+ a relatively simple process:

Glucose or glycogen is converted to an intermediary (glucose-6-phosphate) which then undergoes a series of 12 enzyme mediated reactions until eventually pyruvic acid emerges at the end. What happens to the pyruvic acid depends on whether or not oxygen is available (more on that later), but for now we will assume its not in which case it is converted to lactic acid.

It is during the conversion of glucose-6-phosphate to pyruvic acid that sufficient energy is produces to resynthesise 3 molecules of ATP. However, although the conversion of glycogen to glucose-6-phosphate is ‘free’, the conversion of glucose ‘costs’ 1ATP. Therefore, you get either 2 or 3 molecules of ATP per molecule of carbohydrate depending on whether you start from glucose or glycogen.

There is a problem with this system though, and that is the production of lactic acid. As soon as this is produced it dissociated into a lactate ion and a Hydrogen ion (H+). The lactate itself is likely not a problem and is taken off and metabolised elsewhere in the body. The H+ are a problem though because as they accumulate the intracellular environment becomes more acidic (the pH drops). The issue here is that enzymes (in particular the magnificently named phosphofructokinase – the key rate limiting enzyme in glycolysis) are very sensitive to changes in pH. As pH drops, the activity of the enzymes is reduced meaning that effectively the waste products of glycolysis slow the rate of glycolysis!

H+ accumulation has one other unfortunate side effect in that they block the formation of cross bridges between actin and myosin (see part 1) meaning force production is compromised.

So… anaerobic glycolysis is a relatively simple allowing generation of energy relatively quickly. However, its by products have negative consequences for continued exercise performance (and its use also ‘burns’ through carbohydrate stores quickly). The rate of H+ accumulation depends on how quickly you run, but the middle distance (800m and 1500m) events produce the lowest post-exercise pH values. If you want to complete even longer races you need to find yet another sources of energy, which brings us to…

Aerobic (oxidative) metabolism.

Recall the fate of pyruvic acid in glycolysis – if there is no oxygen available it is converted to lactic acid and you end up with 2 or 3 molecules of ATP from each molecule of carbohydrate. What happens if oxygen is available? This is where things get interesting (and complicated!). The following is therefore a massive oversimplification, but hopefully sufficient to illustrate the key points:

In the presence of oxygen, pyruvic acid is converted to acetyl-coenzyme A and enters the Krebs cycle (more on ‘where’ this actually happens later). This involves a whole series of chemical reactions which result in the production of sufficient energy to resynthesise 2 molecules of ATP and further intermediaries which enter the electron transport chain which itself pumps out energy for resynthesis of 34 molecules of ATP, carbon dioxide and water (I said it was a massive oversimplification!). The key point here is that while anaerobic glycolysis results in resynthesis of 2 or 3 molecules of ATP per molecule of carbohydrate, aerobic metabolism can result in 38 or 39 molecules of ATP per molecule of carbohydrate – it is waaaaaaaay more efficient! Furthermore, because the by-products are benign, as long as you are running aerobically you can go for hours fuelling yourself in this way (until your glycogen stores are depleted).

It gets even better, because you can also ‘pump fats into the aerobic system. I won’t go into the complex biochemistry, but (depending on the type of fat being metabolised) you can get hundreds of molecules of ATP per molecule of fat. Even very lean athletes have enough energy stored as fat to run hundreds of miles – ‘something else’ will stop you long before you run out of fat!

If there is a ‘problem’ with the aerobic system then its with its sheer complexity, not just biochemically but you need to get oxygen from the atmosphere to the muscle cell. This means that although this system has by far the highest capacity for ATP resynthesis, it is the least powerful and is incapable of generating the exercise intensities that can be fuelled by the anaerobic systems.


A ‘homework’ task for anybody still reading who would like to test their understanding:

Can you use the information presented in parts 1 and 2 to explain why the men’s marathon world record is not 68 minutes (as it would be if Usain Bolt could maintain his 100m speed for another 26 and a bit miles)?

(Basic) exercise physiology for endurance coaches Part 1

Recently I had a chat with a very good coach who wanted to pick my brains on the physiology of endurance training. It was a very interesting conversation, and he clearly knew his stuff when it came to different training methodologies, practical organisation, psychology, tactics etc. However, he admitted that he knew ‘nothing’ about the physiology.   I suspected this was a slight exaggeration, but after a bit of digging it became clear that nothing meant NOTHING. This came as a bit of a surprise as he has had a lot of success as a coach (or perhaps physiological knowledge is overrated?!). Going through a few concepts with a pen on the back of an envelope was an interesting exercise for both of us as it helped clarify what we are trying to achieve through training. Rather than just leave things on the back of an envelope, I have therefore tidied things up a bit in a format aimed at a similar audience – coaches with no background in exercise physiology. No unnecessary technical terminology, no academic references etc. Nothing will be ‘new’ to anyone who has previously studied sport science at UG level, but it may serve as a reminder of the ‘big picture’.

How do you run faster?

The primary means of running faster is by applying more muscular force in the direction of the ground. According to Newton’s Law (“for every action there is an equal and opposite reaction”) the ground ‘pushes’ back and propels you along the track. The harder you ‘push’ the harder the world pushes back and the faster you go (assuming efficiency of technique – beyond the scope of this piece). In order to run any distance quickly then, you need to be able to push hard enough (generate enough force) and to continue doing so for the required duration. Immediately then, two potential mechanisms for performance enhancement are evident – you can develop the ability to push harder/ more forcefully through becoming stronger, or you can develop your endurance so that you can maintain any given level of force for longer.

How do you develop force?

Your muscles are made up of many muscle fibres, which in turn contain many thin protein filaments (actin & myosin) which interact to cause a shortening of the muscle fibre when an impulse from the nervous system arrives. This interaction involves the formation of cross bridges between the actin and myosin filaments which have the effect of shifting the actin and producing a shortening of the fibre as a whole (I am aware this is a gross oversimplification(!) but hopefully sufficient for illustrative purposes. For more detail see the ‘Sliding Filament Theory’). This is important, because the formation of cross bridges requires ENERGY to occur (more on that later).

How is force production controlled?

You cannot ‘sort of’ bring about contraction in an individual muscle fibre, it is either ON or OFF. The way you change the force an entire muscle produces then is through varying the number of fibres recruited. This is illustrated by the figure below:

As you can see, when producing low force (as when running slowly), then only a small proportion of the available muscle fibre ‘pool’ is recruited / used.  As you produce greater and greater forces so that you run faster and faster this is achieved through recruiting more and more fibres until you are running as fast as possible when most are recruited (more on slow and fast twitch later, but ST are recruited at low intensities and the FT do not come in until later).

The key thing to take away from this is that more active muscle fibres means more cross bridges between actin and myosin are being formed. Now, this is a good thing because more cross bridges mean more forces. BUT recall that cross bridges also require energy. This means that when producing low forces (or running slowly), rate of energy use is low. When producing high forces (running quickly), you are using energy much more quickly because you are creating many more cross bridges. From an endurance runner’s perspective, this means you can be exceptionally muscularly strong (able to produce high forces) but this is potentially of limited value to you if you cannot supply energy quickly enough to sustain work at this intensity (less of a concern if you are a sprinter).

So… in summary so far, to improve as an endurance runner we need to increase the rate at which we can supply energy (and in some cases the amount we can supply) for the fuelling of muscular work. By doing so you can create more cross bridges, generate more ground reaction forces and go faster for longer.