Home A column by Michael Beisty The Mature Distance Runner: Fundamentally Speaking Part One : The Aerobic Threshold

The Mature Distance Runner: Fundamentally Speaking Part One : The Aerobic Threshold

August 1, 2024

Disclaimer: Content herein does not constitute specific advice for the reader’s circumstances. It is only an opinion based on my perspective that others may learn from. Anyone of any age who engages in running should be in tune with their body and seek medical advice before embarking on any intensive activity (including changes to said activity) that may unduly extend them. This is critical should the aspiring athlete have underlying medical conditions and/or ongoing health issues requiring medication.

‘One obvious explanation for the decline in running performance after the age of 30-32 years is the gradual decline in the capacity to consume oxygen during exhaustive exercise (aerobic capacity).’ (David L Costill, PhD, 1979)¹

In this article, I attempt to provide information in a simple fashion and minimize overly technical descriptions of physiological processes. To assist those who want a very high level of detail, I point you to the references/sources listed at the end of the article.

1. Introductory Information

Aerobic threshold is a sometimes misunderstood concept. And it seems to me that aerobic capacity can tend to be discounted by mature competitors who aspire to high-performance standards. This article attempts to shine a light on the value of aerobic threshold training, what it entails and where it sits in the quantity versus quality equation.

2. Stripping It Back

Firstly, what is a threshold in exercise training terms? Threshold is a level of effort that causes a physiological adaptation within the body and improvement in performance.²

The two main training thresholds are aerobic, when lactate first comes on the scene rising in the blood above normal resting levels, and anaerobic (also known as the inflection point or lactate threshold), where blood lactate increases rapidly, at a rate in excess of the body’s ability to remove it.³ Aerobic threshold is also described as ‘the uppermost limit of exercise when the production of energy starts to become dominated by anaerobic glycolysis (sugars) rather than the oxidation (aerobic in nature) of fats.’⁴

Taking from a range of sources, in practical terms, your aerobic threshold is steady-state (not slow) running that can be maintained for extended periods (hours if required), where your breathing is not labored.

The range of intensity between the two thresholds is called the aerobic training zone. Training at higher intensities within this zone will deliver greater levels of physiological adaptation, increase aerobic capacity, and subsequently result in a higher aerobic threshold level, where running remains ‘comfortable’ but stretching at faster speeds as fitness improves. However, the reality for the mature endurance athlete is that the physiology of ageing – most notably, a reduction in VO₂max and maximal heart rate, a decrease in blood volume pumped per heartbeat, loss of muscle mass, a reduction in the number and effectiveness of aerobic enzymes, and a decrease in total blood volume ⁵ – dampens the outcome in absolute terms.

3. VO₂max

VO₂max is universally accepted as the key measure of a person’s maximum aerobic power. It ‘represents the maximum amount of oxygen that can be removed from circulating blood and used by the working tissues during a specified period’ of exercise.⁶ This process is expressed by the formula of:

VO₂max = mLO₂/kg/min, which is millilitres of oxygen/kg of body weight/minute.

While your aerobic threshold (or lower lactate threshold) can be held for hours, running at 100% VO₂max is only possible for 5 to 8 minutes before anaerobic glycolysis ⁷ takes effect – and the ‘big bear’ arrives.

The effect of aerobic threshold training is to increase a runner’s aerobic capacity, measured by VO₂max. Training is typically conducted at 65-70% of the maximal heart rate (MHR). Though an accurate measure requires laboratory testing, in simple terms the MHR can be determined by running to exhaustion. Whereas, anaerobic threshold training will improve a runner’s anaerobic capacity, the ability to breakdown and remove lactic acid (and tolerate hydrogen ion buildup), and is conducted at 80-85% of MHR.⁸

4. Oxygen and Mitochondria

The cardiovascular system plays a significant role within the human body. Simply put, ‘the arteries carry bright red oxygenated blood from the heart to the various tissues of the body. Veins then carry the bluish deoxygenated blood back to the heart, which then pumps it through the lungs for a fresh supply of oxygen.’^{9 10}

Telford describes the two most significant limitations of aerobic power as the mitochondria, and the speed at which the body can deliver oxygen to the mitochondria.¹¹ Mitochondria are organelles, a membrane bound structure found within a cell. They are universally described as the powerhouses of the cell. Located next to muscle filaments, their main function is to produce the energy required to power muscle contraction, a process of oxidative phosphorylation. The latter is the final biomechanical pathway in the production of adenosine triphosphate (ATP). As Noakes states¹² ‘ATP is the form in which energy is used in the body – it is the body’s energy currency.’

Source: The Body, author: Alan E. Nourse, published 1969 by Time-Life Books.

Magill makes the point that increasing your oxygen supply and your ability to use that supply, will increase your energy production, and therefore result in faster race times.¹³ And the best way to achieve an increase in oxygen supply is by improving the transportation of oxygen to the mitochondria, which in turn increases the size of the mitochondria. The best way of feeding your mitochondria is by the creation of more capillaries, which deliver oxygen to the muscle fibres themselves.

As Martin and Coe put it, ‘Part of the process of getting fit through training at the cellular level involves an increase in both the size and number of mitochondria, together with their fuel-metabolizing enzymes, so that the maximal energy producing capacity of the trained muscle can increase.’¹⁴

5. Some Historical Context

Many years ago, Frank Horwill, instigator and a founding member of the British Miler’s Club, published a brief article in Athletics Weekly titled ‘Aerobic Running: A Closer Look.’¹⁵ Its purpose was to review the current state of knowledge about aerobic running. Horwill drew upon the work of the eminent British physiologist and biophysicist, A. V. Hill.

Hill, a Nobel Prize winner in 1922, developed the muscle contraction model. He was responsible for the quantification of total oxygen requirements for each running event and their conversion into aerobic and anaerobic ratios as follows: 200 metres: 5% aerobic 95% anaerobic, 400: 27/73%, 800: 33/67%, 1500: 50/50%, 3000: 60/40%, 5000: 80/20%, 10000: 90/10%, marathon: 99/1%. Horwill noted that it was being argued that the bulk of a person’s training pattern, for each event, should reflect these ratios.

Based on current day information, the ratios calculated by Hill are not totally accurate and don’t allow for gender differences. However, turning his mind to their practical application, Horwill devised tentative definitions for different types of aerobic work that could be applied to a largely aerobic training program:

Pure aerobic running: jogging

Aerobic running: steady state running, 2-3 minutes per mile slower than best mile

Fast aerobic running: at the runner’s best 5000 metres pace

Speed aerobic running: at the runner’s best 3000 metres pace

Intermediate aerobic running: at the runner’s best 10000 metres pace.

By way of example, using a 4 minutes 1500 metre runner wanting to train for 10000 metres, Horwill calculated the relative training speeds as follows:

Pure aerobic: speed per 400, 2 minutes

Aerobic: 90 seconds

Fast aerobic: 70.5 seconds

Intermediate aerobic: 72 seconds

Speed aerobic: 69 seconds

Anaerobic: 63 seconds

I’d suggest this is a useful approach to consider for your own training as a mature runner, doing the necessary calculations based on your own 1500 metres performance levels. Certainly, examining my own training program, based on age grade equivalents, the bulk of my quality sessions would fall within the fast aerobic to speed aerobic range.

Though I cannot lay my hands on the articles, I can clearly recall an insightful exchange between Dick Telford and Ron Clarke in an Australian magazine in the 1980s that is relevant to this discussion. Ron respectfully took Dick to task for some comments Dick made in an article about the Australian system of distance running with an inference that in his heyday Ron ran much of his continuous runs at a relatively easy pace. Ron highlighted that his regular training runs were anything but easy, and that he ran at a much faster pace, one that stretched him, which delivered a progressive performance improvement. I’d take this to mean that Ron was performing much of his continuous running into the higher ranges of his aerobic training zone, and at times approaching Horwill’s definition of intermediate aerobic speeds.

Similarly, Lydiard’s system relied on a period of base training over long distances, pushing the boundaries of the aerobic threshold. Granted there was allowance for some slower recovery, and shorter, supplementary runs throughout the Lydiard program but by and large it was building the base through faster aerobic continuous distance runs. Unfortunately, in some circles, his training methods were erroneously described as 100 miles per week of long slow distance (LSD).

Ron Clarke (left) and Harald Norpoth(right) racing in 1967. Both could be described as successful products of two different systems of aerobic training. Source: International Athletics Annual 1968.

The founder of LSD was Ernst van Aaken, M D. LSD was part of his system of training that he described as the endurance training method. He developed his methods as an opposing system to interval training that became prominent in the 1950s. Central to this method was ‘to continuously increase oxygen uptake capacity by long daily endurance exercise at moderate pace.’¹⁶ Van Aaken stated there were more similarities than differences to Lydiard’s program. However, one major difference was the adoption of ‘slow jogging and more frequent rest breaks’ when running the longest distances, with a stated preference that heart beat not exceed 130 beats per minute (bpm).¹⁷ The bulk of his distance running program sat in the range of 120-150 bpm.¹⁸

Interestingly, van Aaken felt that the notoriously fast kicks of some of his proteges, such as Harald Norpoth, came from their huge aerobic engines developed by many hours of long slow distance running, rather than the faster work they also engaged in.¹⁹ Unfortunately, his training methods became known mainly for this component. However, if you read his books, apart from some very long runs, you will see that a range of ‘other’ long continuous running, tempo runs and pace work at lower intensities was done by his athletes, never exceeding 180 bpm. ^{20 21} Sharpeners and alactic sessions were also included, where there was no oxygen debt or lactic acid involved. Though very long runs were a cornerstone of his methods, these days, we would likely view the ‘other’ work as key to his athlete’s success rather than focus solely on the longest runs.

6. A Master’s Translation

In summary, there is a high level of consensus among exercise physiologists, academics and research scientists, and authoritative coaches, that aerobic capacity is the major determinant of endurance fitness and simultaneously most affected by ageing. It is also clear that aerobic capacity, lactate threshold and economy, in priority order, are the three main components of endurance fitness.²² When cross referenced against the ‘big three’ limiters of performance caused by ageing – decreasing aerobic capacity, increasing body fat and shrinking muscles ²³ – and having regard to your own level of adaptation to training, it becomes evident where you may need to target your training to maximise performance.

Friel ²⁴ explains that there are two main sub-systems of aerobic capacity – oxygen delivery to the muscles (involving lungs, heart, blood, arteries and capillaries) and oxygen uptake (muscles capture the oxygen as it flows past in the capillaries and use it to produce energy). A deterioration in oxygen delivery is considered to be the major determinant of any decline in aerobic capacity. In particular, for mature athletes a reduced stroke volume (the amount of blood pumped by each heart beat) and reduction in maximum heart rate are the major contributors to this decline.

Friel ²⁵ further explains that stroke volume is largely contingent on the size and contractility of the left ventricle of the heart. If, through a lack of activity, the left ventricle is rarely challenged to pump a lot of blood per beat, then size and contractility may be lost, thereby reducing aerobic capacity. Something that seems more common in men.

Results of a study published in 2007²⁶ also support the notion that the progressive reduction of VO₂max (driven by decreases in maximal stroke volume, heart rate and arterio-venus O₂difference or the amount of blood taken up by the tissues) is the primary cause of the decline in performance of endurance athletes as they age, followed by reductions in lactate threshold. Notably, exercise economy did not change with age.

6.1 Women

It is useful to compare men to women.²⁷A study of 75 competitive runners (37 men and 38 women) examined the relationship between lactate threshold (LT) expressed as a percentage of VO₂max and running velocity at lactate threshold (LT_V). Other relationships examined were the extent to which VO₂max, the oxygen cost of running (C_R) and maximal aerobic speed (MAS) determined running velocity. To quote the results of this study, ‘Lactate threshold did not correlate with LT_V. The product of MAS and LT correlated strongly with LT_V. There were no differences between elite, national and recreational runners regarding LT, but female runners had higher LT than the male runners. Female runners at the same relative performance level had lower velocity and VO₂max, but better C_Rthan male runners.’

Of note the women’s VO₂max was 21% lower than the men but their oxygen cost of running was 9% better than the men.’ As a layperson I interpret this to mean that women may be generally more efficient in their use of oxygen within their bodily system, and that their lower VO₂max may be partially offset by this level of efficiency. Resulting in higher performance levels than would otherwise be the case because of a lower VO₂max.

6.2 Physiological Adaptation

Friel ²⁸ reminds us that training in the aerobic training zone and use of frequent longer steady-state aerobic-threshold workouts are key to physiological adaptation, the most notable being more efficient use of fat for fuel: drawing upon fat stores and not affecting glycogen uptake. A range of other adaptations also result from aerobic threshold training: increased capillaries, more delivery pathways for blood, oxygen and fuel, adaptation of slow twitch (and fast twitch) muscles to enable greater levels of fatigue resistance. Apart from an increase in aerobic enzyme production, that assist in the production of energy from oxygen and fat, aerobic threshold workouts also create more of the hormone erythropoietin (EPO) that increases red blood cell production and delivers more oxygen carrying capacity to the muscles.

6.3 Implications for Training

There is evidence that improvements in aerobic capacity arise from combining aerobic and anaerobic training as a means to increase the workload for your lactate inflection point.²⁹ In 2021 an extensive scoping review of research of mature adults was completed. This review captured 69 studies conducted since 2009, with a participant mean age of 65 and over (men and women), across a range of exercise modalities. This review suggested that some types of high intensity interval training may deliver better aerobic outcomes than traditional endurance training described as moderate intensity continuous training (MCT).³⁰

This is where it can get confusing. The mature endurance athlete may misconstrue this to mean that higher volumes of anaerobic work as a percentage of total volume of running will deliver better performance outcomes. In my experience, this view is certainly prevalent in mainstream middle distance running spheres, and an approach that has proven to be unsustainable. What I like to call a perceived shortcut to nowhere, as your body’s eventually runs itself down, and out.

However, Friel provides a useful insight that a mature athlete who has a stable and high VO₂max, is clearly less limited by aerobic capacity. And could benefit by introducing a combination of aerobic capacity intervals and sub lactate threshold sessions as an optimal approach to boost the lactate threshold and further increase VO₂max.³¹ While this would improve endurance fitness, it would also result in the ability to train in a higher range of the aerobic training zone for continuous runs and prevent the burnout that inevitably comes with excessive anaerobic work (my interpretation).

Alternatively, if you have a consistently high VO₂max, to boost your race performance you may actually need to pay some extra attention to lactate threshold training (anaerobic) or running economy. However, there are limits on the returns from anaerobic training and as indicated earlier, the returns from improvement in running economy are negligible.

It has been cited that elite athletes can only improve VO₂max by about 15 percent with intensive training.³² Clearly, the greater gains arise from aerobic capacity. To my way of thinking, training in the aerobic training zone remains the default position to stabilise endurance fitness and provide the base for all other training, ala Lydiard.

6.3.1 The Mature Age Drift

The mature runner tends to drift towards a reduction in volume of training and intensity of continuous runs (often to below the aerobic threshold), as the years go by. This can mean that the amount of high intensity training (if maintained) can easily become a disproportionately higher percentage of the overall training volume when compared to an open competitor’s program in their prime. I would argue that this is the subliminal effect of a natural tendency to give in to the ageing process (‘run less but run fast if I can’), rather than any deliberate intent to increase the percentage of high intensity sessions per se.

Although many studies point to the maintenance of, or at least, lesser deterioration in aerobic capacity by maintaining anaerobic sessions, as volume decreases year on year, I’d argue that such an approach is sub-optimal, and risks continued performance progression/mitigation as we age. All things being equal, if a mature racer can maintain the physical and psychological commitment required, I contend that volume needs to be maintained at a ‘reasonable’ level. My personal rule of thumb for a reasonable volume is to convert the miles run from my younger days to kilometres in my mature years. For instance, 100 miles per week in my twenties is equivalent to 100 kilometres per week in my early to mid-sixties, and 80 miles per week is equivalent to 80 kilometres per week, and so on.

While maintaining a reasonable volume, to ensure adequate performance progression, it is vital that continuous runs are conducted in the aerobic training zone. Some have argued that slow longer runs may assist in the development of a base level of endurance health but would not contribute significantly to high end aerobic capacity necessary for solid racing performance. While long very slow running can play a legitimate supporting role in the cardiovascular adaptations of a well-performed distance runner (certainly it can do no harm), there are many who express the view that running very slow only helps you to run slow, and may actually inhibit your ability to run faster. Given ageing factors, this would be moreso for a mature aged distance runner.

While the effect of reduced training frequency (say from six to two sessions per week) can be mitigated by the maintenance of high intensity, there is some evidence to suggest that for ‘highly trained athletes’ aerobic training effects are lost after three months total abstinence from training.³³ There is also a view that continuation of high intensity sessions (typically anaerobic) throughout a mature endurance athlete’s career may be an ‘aerobic capacity preserver’, substantially mitigating the decline in Vo₂max.³⁴

While leaving a detailed examination of the anaerobic threshold to my next article, its pertinent to note that my Soft Quality Program (SQP) for the over sixties cohort is about centring training efforts primarily in the aerobic training zone, volume being in the range of 80 to 110km pw depending on time of year and racing commitments. Into my sixties my higher intensity sessions have reduced in frequency, with the inclusion of speed endurance sessions, or aerobic intervals (sub threshold anaerobic sessions rather than anaerobic lactic) at 5000 metres to 3000 metres pace, complemented by pure speedwork (alactic) – in a mix of hill work, fartlek, rhythm interval sessions and short reps. I have retained anaerobic sessions, on a very limited basis, when compared to my fifties. And while I do like to train largely within the aerobic training zone, some of my long runs are slower, enabling more effective recovery, as I deal with the reality of ageing.

7. Concluding Comments

The purpose of this article was to highlight the significance of aerobic threshold training as the main determinant of endurance fitness, and therefore race performance outcomes, something that can be lost on the mature distance running cohort in their advancing years. The temptation to run shorter and easier continuous runs is understandable given it takes us longer to complete our daily runs. The ageing process can also throw up challenges to maintaining a reasonable volume of sessions in the aerobic training zone.

The ‘use it or lose it’ mantra is ever present in justifying an over-emphasis on above anaerobic threshold, high intensity training. However, a mature runner will reap significant benefits, mitigating reduction in performance and achieving sustainable outcomes by conducting major portions of their training in the aerobic training zone. After all, the anaerobic threshold cannot be increased unless considerable improvement is made to a distance runner’s aerobic capacity. It is a law of exercise physiology that is irrefutable.

Of course, it would be farcical to say that high intensity training is of no value to a mature competitor, or should not be included on some basis in a well-balanced program, a topic that will be the subject of my next article about the anaerobic threshold.

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