Disclaimer: The author is not a qualified medical practitioner or accredited coach. The information provided is not intended as medical advice or to replace advice given by trained medical or allied health professionals or qualified coaches. Content herein does not constitute specific advice to the reader’s circumstance. It is only opinion based on the author’s 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.
‘Life, the biologic chain that holds our parts together, is only as strong as its weakest vital link. When this breaks – no matter which vital link it be – our parts can no longer be held together as a single living being.’ (Hans Selye 1976)1
The Fundamentally Speaking series was meant to fill some gaps in the knowledge content of my previous series for mature distance runners – Main Training Principles and A Practical Philosophy. In my introductory article I gave a commitment to cover a range of topics:
Aerobic threshold;
Anaerobic threshold;
Effect of endurance activity on the heart;
Body composition and weight;
Changes in hormones;
Sleep;
Nutrition;
Arthritis; and
Shoes.
I have covered the first four listed topics and ‘shoes’ in some depth. Upon reviewing the content of past articles, I have also covered on some basis the topics of hormones, sleep, and nutrition. Though I admit these were side discussions and I haven’t given them their own spotlight. The only issue I haven’t really addressed on any level is arthritis.
At this juncture, my preference is to end the Fundamentally Speaking series with some takeaways from my previous articles, and headline issues relating to hormones, sleep, nutrition and arthritis for the reader to consider for their own particular mature running circumstance.
What follows is my attempt to summarise the takeaways and headline issues, as useful points of reference for the ageing distance runner. Both summaries are based on a lived experience melded with evidence-based research.
- Takeaways
1.1 Aerobic Threshold
There is a high level of consensus among ‘the experts’ that aerobic capacity is the major determinant of endurance fitness and simultaneously most affected by ageing.
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
The range of intensity between the two thresholds is called the aerobic training zone.
Aerobic capacity, lactate threshold and economy, in priority order, are the three main components of endurance fitness.5
The ‘big three’ limiters of performance caused by ageing are a decreasing aerobic capacity, increasing body fat and shrinking muscles.6
The progressive reduction of VO2max (driven by decreases in maximal stroke volume, heart rate and arterio-venus O2 difference 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.7
Women may be generally more efficient in their use of oxygen within their bodily system, and their lower VO2max may be partially offset by this level of efficiency.8
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.9
A mature athlete who has a stable and high VO2max 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.10
If you have a consistently high VO2max, to boost your race performance you may 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 returns from improvement in running economy are negligible.
Training in the aerobic training zone remains the default position to stabilise endurance fitness and provide the base for all other training, ala Lydiard. The anaerobic threshold cannot be increased unless considerable improvement is made to a distance runner’s aerobic capacity.
As the years go by, the mature runner tends to drift towards a reduction in volume of training and intensity of continuous runs (often to below the aerobic threshold). This can mean that, by stealth rather than intention, the amount of high intensity training (if maintained) becomes a disproportionately higher percentage of the overall training volume when compared to an open competitor’s program in their prime.
There is some evidence to suggest that for ‘highly trained athletes’ aerobic training effects are lost after three months total abstinence from training.11
There is 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.12
Ultimately, to ensure adequate performance progression, it is vital to maintain a reasonable volume of training and ensure that continuous runs are conducted in the aerobic training zone.
1.2 Anaerobic Threshold
The anaerobic threshold is also known as the inflection point or lactate threshold, and is the uppermost threshold of the aerobic training zone. It is the ‘highest sustained intensity of exercise for which measurement of oxygen uptake can account for the entire energy requirement.’
Anaerobic threshold training will improve a runner’s ability to breakdown and remove lactic acid (and tolerate hydrogen ion buildup), and is conducted at 80-85% of maximal heart rate (MHR).13
Some experts consider the anaerobic threshold a better predictor of endurance performance than VO2max.14
The resting heart rate, maximum heart rate, and the anaerobic threshold, all decrease linearly with age.15 A life trend that is immovable.
There is some evidence that engagement in HIIT by mature athletes = increase in VO2peak (the highest amount of oxygen consumed at peak exercise).
There is plenty of variation in heart rate even for athletes of similar ability, of the same age, so use of heart rate-based training is highly individualistic. Adoption of Perceived Effort may be more in tune with an ageing distance runners training philosophy.
The higher the training intensity above the anaerobic threshold the greater the physiological adaptations. Combining a suitable mix of aerobic and anaerobic training increases the workload for your lactate inflection point and your aerobic capacity.16
Nuance is required to determine the optimal mix of faster work for ageing athletes, having regard to frequency (how often), intensity (how hard), time/volume (how long) and type (what to do?), abbreviated as FITT – as we travel through each decade.
High intensity training that promotes the production of anabolic steroids and burns more calories is more likely to reduce excess flab than long slow distance, and is beneficial for body composition and race results. This is particularly effective when combined with high-load strength training.17
Ideally, an optimal mix will support a progressive overload on your body and ensure adequate recovery. Working out this mix for the mature endurance athlete will depend upon individual capacities, gender and ageing considerations. Though undoubtedly, the shorter the racing distance the greater the need to perform some anaerobic threshold and above training.
Per Peter Reaburn, higher intensity training in zones 5 and 6 should only ever be conducted by ‘healthy ageing athletes who have no cardiac risk factors, a training age of 2-3 years, are not prone to overuse injuries, and who have undertaken an extensive foundation phase.’18
Lactic training is only required in very small doses during key phases of training, prior to peak racing periods.
Running in a more natural environment, often in quiet settings, can assist in the enjoyment of faster sessions.
Alactic sessions or pure speedwork entail bursts of up to 20 seconds at 98-99% maximum effort, with very long rest breaks to enable adequate recovery. With runs of less than 7 seconds there is no lactic acid produced, only starting to accumulate after 10-13 seconds of intense exercise.19 20
Allowing for a period of adaptation, the introduction of alactic sessions or pure speedwork is a useful training strategy to develop an ability to run and relax at top speed.
Introduction of pure speedwork can be challenging, because the neuromuscular adaptation required will be significant, a ‘shock to the system’ as you fire up your fast twitch sprinting fibres.
It is safe to say that at a base level, there is evidence that some form of high intensity interval training contributes to an increase in VO2peak and aerobic capacity for older persons.
For a mature age distance runner, I think it is better to settle on a routine that includes a commitment to regular faster sessions, on some level.
I support a gradual reduction in the use of lactic sessions moving through the M/W40 decade, favouring speed endurance training and anaerobic threshold sessions as an M/W 50 and beyond, complemented by pure speedwork, with just a dash of the anaerobic to hone race performance. With hills and fartlek thrown into the mix to provide a variety of faster sessions and strength-based approaches.
1.3 The Heart and Endurance Exercise
The relationship between heart health and exercise is not a binary equation, it is incredibly nuanced.21
With increasing age there is a progressive decrease in contractility, efficiency and fatigue resistance of the heart and skeletal muscles. There is also a progressive fall in the capacity to deliver oxygen to the myocardium (thick middle layer of the heart) caused by changes in, or disease of, the coronary blood vessels.22
A progressive stiffening of the heart occurs up until the age of 55. Thereafter, it doesn’t get a lot stiffer, instead it starts to shrink.23
Ageing affects the plasticity of the heart and the heart atrophies through inactivity, so continuing to exercise in later years mitigates the stiffening that occurs through ageing and guards against increased deterioration through inactivity.24
Atherosclerosis, commonly known as plaque, is the buildup of fats, cholesterol and other substances in and on artery walls.
The four main things that predispose you to atherosclerosis are a level of dysfunction relating to metabolism, lipoproteins, inflammation, and the endothelium, or a combination thereof.
As a generalisation, in younger individuals, concerns tend to centre on congenital heart conditions. For mature individuals it can revolve moreso around coronary artery disease that develops gradually over many years. This appears to be a proven trend discussed in all the available literature.
Exercised induced cardiac remodelling, known as athlete’s heart, is ‘a physiological response where the heart becomes larger and more efficient than average as a natural response to exercise.’25 This is normal.
Based on substantial research ‘regular physical activity and higher cardio respiratory fitness both delay the development of atherosclerotic cardiovascular disease (CVD) and reduce the incidence of coronary heart disease (CHD) events.’26
Older endurance athletes appear more prone to atrial fibrillation (AF, chaotic rhythm of atria) and calcification (CAC, hardening of the arteries).27
From the experts, it seems that on balance, with increasing age, AF presents a greater relative risk for mature age athletes than CAC.
Those who do a lot of endurance activity are more prone to AF and atrial flutter (caught up in an electric circuit, 5 times per second, ongoing cycle).28
Those at greatest risk of AF are those who do very little and those who do a lot of exercise.29
According to some studies, every 10 years of heavy exercise your risk of AF and flutter increases by 16% and 40%, respectively.30
For lifelong endurance athletes, whose extent of exercise is typically 10 to 20 folds greater than the minimum recommendations for exercise of the average person, there appears to be a threshold beyond which the benefits of exercise are lost.31
‘Middle-aged endurance athletes are at a five-fold increased risk of AF compared with sedentary counterparts……..Extrinsic contributing factors include male sex, tall stature, and the volume and intensity of exercise.’32
To reduce the long-term risk of AF or other cardiac complications, Reaburn’s advice for ‘older’ mature athletes is to cease long threshold training. Instead, he opts for regular low-moderate training, and threshold or high intensity interval training (HIIT) only once per week.33
Although 20-30% of the average population go through life with whistle clean arteries, generally, arteries become more calcified with age.34
Calcification is more common in men than women.35
Calcification is more prevalent in those doing a high percentage of very vigorous exercise.36
Though high intensity activity is good for the body, VO2 max and performance, to lower the risk of calcification mature athletes also need to engage in a significant amount of low intensity exercise.37
‘While fitness can provide a relative insurance policy against the risk of heart attack, reducing the odds against it, it can’t guarantee you will never have a heart attack, and heart attacks are common. However, the fitter you are, for any degree of calcium you have (measured by a CAC score) your risk of heart attack is lower.’38
‘An exercise paradox exists, whereby if you are a runner, overall, you will have less risk of heart attack but if you are going to have a heart attack it is more likely to occur while running. You exercise regularly so that every bout of exercise is less of a relative risk. But exercise is a risk activity that you then do regularly to make yourself lower risk. This milieu of what goes on in exercise may go some way to explaining the scarring in arteries, heart muscle and atrium that can cause a problem for some people. Ultimately it is a transient greater risk. All of this doesn’t mean the running or endurance activity kills a person. In fact, but for the running, death may have occurred earlier. Or it may not have. There is no real way of knowing.’39
1.4 Body Composition and Weight
The three most significant changes to body composition through ageing are an increase in unwanted body fat, a loss of skeletal muscle mass and a decrease in bone density and bone strength.
Strategies that increase the resting metabolism rate and the afterburn effect can reduce the negative effects of these changes to a mature runner’s body composition.
Four key activities to improve body composition and manage racing weight are: nutrition including the type and optimal timing of food consumption for recovery and muscle building, strength training (primarily heavy free weights), adequate aerobic running combined with small bouts of targeted high intensity exercise, and sufficient sleep.
Depending upon your starting point, improvements in your power to weight ratio for racing performance may require additional activity in the fields of muscular development, weight loss, weight gain, or fat loss.
Body composition is influenced more by diet and nutrition than exercise or genetics.
A person who is serious about their health would not engage in alcohol consumption on any level.
Any reduction in fat has to occur as a result of a healthy sustainable weight loss.
The optimal weight for you, of your age, for your racing distance, should be a ‘level representing maximum strength with minimum extra baggage.’40
There is no magic formula to achieve an ‘ideal’ body composition, only a balanced diet that is right for you, at your age and state of fitness, that can be found through trial and error.
1.5 Shoes
It has been stated by authoritative sources that there is no ideal biomechanical running action, just as there is no such thing as the ideal shoe, only a shoe that best suits an individuals’ specific biomechanics.
There is some value for a mature runner to persist with minimalist athletic footwear, as much as practicable, on varied terrain, to retain a degree of sensory awareness and enhance proprioception.
Benefits of the carbon fibre plated shoes are less evident as we progress through each decade, and the ageing process takes hold.
Carbon fibre plated shoes may be a risky proposition for some mature runners as they can either change biomechanics, or not be a good fit to existing biomechanics, in both instances increasing the potential for injury.
For the ageing runner into their sixties and beyond, changes in the feet demands some consideration of additional support and cushioning.
- Headline Issues
Within this summary I have listed some points of reference for the other topics to be investigated by the reader for their own particular ageing circumstance.
Some may accuse me of laziness in short circuiting these topics, but the reader may find more value in following their own research path. Should the reader want to accept this personal challenge I have distilled each topic into a very small number of general discussion/reference points to assist. They are by no means exhaustive, as each topic is complex in its own way. So here we go.
2.1 Changes in Hormones
As we age, our hormones change, requiring a reconsideration of how we adapt our training to maximise performance. Hormones are the critical factor that provides biological stability, anchoring our race performances throughout our life.
Although changes in hormones gradually occur from the late thirties, the major changes in men and women tend to occur from around 50 years of age onwards.
Secreted by the endocrine system, ‘hormones are chemical messengers within your body that govern all aspects of your biological function.’41 Hormones are transported via your bloodstream, targeting cells within your muscles, organs, glands, bones, cartilage and other tissues, affecting reactions within those cells.
In practical effect, hormones play a part in regulating sleep, optimising bone health, maintaining metabolic function, appetite control and adaptation to training.42 43
Hormones can have a cascading effect, triggering the release of other hormones, or alternatively, an inhibiting effect on their secretion.44
In simple terms, running is primarily a catabolic exercise (breaks down muscle), whereas strength and resistance training is anabolic, releasing hormones that build muscle and enhance recovery. It is well known that running generates exercise related hormones such as adrenaline (epinephrine), which stimulates the release of glucagon. As effort is increased additional hormonal responses come into play to ensure muscles are adequately fuelled.45
Magill et al46 identify the three types of hormones as:
Steroids, derived from cholesterol, which include cortisol, estrogen and testosterone;
Proteins and peptides, created from chains of amino acids, which include insulin and human growth hormone (HGH or GH); and
Amines, derived from the amino acid tyrosine, and includes epinephrine, norepinephrine and the thyroid hormones of thyroxin (T4) and triiodothyronine (T3).
It is well established that the proper functioning of hormones assists your body to achieve and maintain homeostasis. In other words, a state of equilibrium.
There are some major hormonal changes that occur with ageing47:
- Anabolic hormone decline is significant for men and women. In particular, women experience a much greater reduction in growth hormones that build muscle and bone.
- Women are significantly affected by menopause (at the average age of 51) and reduction in estradile (subset of estrogen). At the same age men experience a relatively minor reduction in testosterone.
- Hormonal imbalances can occur over time, for example that relates to the thyroid gland that affects metabolic rate, especially for peri and menopausal women. As a result, women are more prone to autoimmune conditions and body composition changes that generate increased visceral fat etc
- Vitamin D deficiency is commonplace and often overlooked, and may require supplementation.
Regardless of age, the two main factors for release of growth hormone/anabolic stimuli are exercise and sleep/recovery.
In terms of racing performance critical issues for the mature distance runner to consider are48:
- There is a substantial evidence base that the quality of training is more important than quantity in supporting the production of growth hormones.
- To provide requisite anabolic stimulus, ideally, HIIT/interval training should be conducted regularly and strength training at least three times per week.
- Sleep before midnight is when the peak production of anabolic hormones occurs.
2.2 Sleep
As we age, the ability to sleep can become more difficult, yet the need for sleep does not decrease. This is especially so for a high performing mature distance runner, as the physiological adaptation to training occurs during sleep and from other recovery strategies.49
Sleep is the essential ingredient for full and fast recovery, yet often the first to suffer when balancing busy lives with exercise commitments.
Patel et al50 advise that the circadian rhythm regulates the sleep cycle, which is driven by the suprachiasmatic nucleus (SCN) of the brain’s hippothalamus. It also regulates the nocturnal release of adrenocorticotropic hormone (ACTH), norepinephrine (NE) and melatonin, the two former promoting wakefulness and the latter preparing you for sleep. While it is obvious that human beings need sleep to maintain good health, and there is a suggestion that sleep restores the natural balance among neuronal centres, the physiological functions of sleep remain subject to ongoing scientific research.
Friel51 and Patel et al52 describe in some detail the phases of sleep as rapid eye movement (REM) and nonrapid eye movement (NREM), the latter divided into another three stages, labelled as N1, N2 and N3. The body moves through the N1, N2, N3 and REM phases as a full cycle of 90 minutes, up to six times during a full night’s sleep. N3 or ‘slow-wave sleep’ (SWS) is where the brain’s electrical activity lessens. Slow wave occurs in the early stages of sleep and REM largely in the later part of the night’s sleep cycle. N3 and REM have the greatest influence on recovery, by release of a range of growth (estrogen and testosterone), and other hormones, that aid recovery. Interruption of this ongoing sleep pattern or reductions in total time spent sleeping will adversely affect cellular recovery from exercise as well as general wellbeing.
As Patel notes, the most significant change in sleep associated with ageing is a progressive reduction in SWS.53
Combined with good quality sleep of up to ten hours per night (no less than six is my rule of thumb), for the mature athlete, at least one rest day per week is recommended.54
Digesting protein before going to bed is beneficial to assist in muscle repair, and is also a precursor to the creation of melatonin for a good quality sleep.55
2.3 Nutrition
If I had to distil nutrition down to one critical issue that affects performance I would concentrate on the mix of carbohydrates and protein. It is all too easy to reduce carbs as a short cut to potential weight loss. However, complex carbohydrates are the key fuel for quality exercise and strength training, so you do this at your peril.
If training with comparatively heavy loads of volume, intensity and strength, a mature distance runner needs to ensure adequate consumption of carbohydrates is maintained. In tandem with this, increased protein consumption (ideally at mealtime) will assist to build muscle and bone health.
2.4 Arthritis
While the two main types of arthritis that occur with ageing are osteoarthritis (OA) and rheumatoid arthritis (RA), the former is more closely associated with athletic and sports endeavours. OA generally relates to wear and tear on joint cartilage and RA is an autoimmune disease that causes inflammation of the joint linings. OA is typically gradual onset that occurs in weight bearing joints. RA is rapid onset attacking small, symmetrical joints (knuckles, feet, wrists). Treatment of OA relies heavily on pain management whereas RA relies on immune-suppression drugs. RA is less age related, and can strike at any time as a cause of systemic inflammation.56
Certainly, I have some of both, as do many others, but the thing that has really affected my ability to run and compete has been OA of both knees and the left hip. RA (hands) has affected my capacity for weight lifting at various times (but has not stopped me).
There are many myths about OA and running, the most prominent being that running causes arthritis in the knee and hip joints. While a case can be made that excessive volume can marginally increase the risk of knee and hip OA, as a general tenet OA is not caused by running.57
It is now well established that running may actually protect the joints and contribute to the development of increased bone density. That being said, many ageing distance runners blame the onset of arthritis for their declines in performance or decision to totally withdraw from endurance sports competition, especially as they enter their seventh decade of life. They give up the ghost. Having been through it myself, I know it does require discipline and some perseverance to continue running, or ‘rehab’ yourself, even with only a mild form of OA in hips and knees.
And let’s be clear, OA is not curable. It cannot be fixed. But in many instances it can be managed and mitigated by appropriate lifestyle decisions, and consideration of training loads. While I know OA can be debilitating, I have been fortunate in overcoming this affliction through appropriate planning and patience in my approach, without the need to resort to surgical intervention. At different times I have not been able to run for months and have suffered setbacks. But gradually, through the strategies of seeking physio assistance, adopting strengthening regimes, listening to my body and managing through the pain and inevitable re-sets that occur, I have been able to compete again.
So, what I would say to the mature distance runner suffering from OA, is do not give up the ghost, do not abandon your aspiration to continue competing, and do not gravitate to surgery in haste. In the first instance, give your body a chance to rehabilitate itself, with your help, and the assistance of allied health professionals and general practitioners. Thoroughly investigate your options.
Now, of course, if it really is a lost cause, and you can’t achieve a level of rehabilitation back to what you consider is your reasonable competitive level, and/or the pain remains extreme, maybe that’s when intervention such as ‘replacement’ surgery is required. It has to be a personal decision guided by medical advice. Whilst it is not easy sitting on the sidelines, I have used a rule of thumb of persevering for at least one year with rehab, knowing that as you get older things just take that bit longer to right themselves.
- Author’s Note
This article brings to a close the Fundamentally Speaking series. I trust that topic content was not too dry and readers gained some additional understanding of the ageing process as it relates to their own performance.
In all that I have written, my intent was to couch the topics of discussion within my lived experience in the hope that it provides some relevance to the reader’s particular circumstance. But I am no expert, just someone who has a passion for writing, and running, and is willing to share my perspectives, thoughts and personal knowledge.
In the final analysis, there are no right and wrong approaches. Just your own.
In my book, Hans Selye’s quote say’s it all. Hopefully, through all of the information I have provided in this series, and others, the reader is able to juggle factors affecting life’s biologic chain, addressing the weakest vital links as they arise to maintain a long and competitive endurance existence.
And that, dear reader, is a wrap.
References
1 Selye, H, The Stress of Life (revised edition), 1976, originally published 1956, p432
2 Training Thresholds, PDEHPE.NET, 2022:
3 What is aerobic threshold: an athlete’s guide?, 18 July 2017, updated 7 February 2023: https://www.polar.com/blog/understand-aerobic-threshold/
4 Breese, J, What Is The Aerobic Threshold: The Ultimate Guide, Strength Matters, 1 July 2023: https://strengthmatters.com/what-is-the-aerobic-threshold/
5 Friel, J, Fast after 50, 2015, p68
6 Friel, 2015, pp81-82
7 Tanaka, H & Seals, D, Endurance exercise performance in Masters athletes: age-associated changes and underlying physiological mechanisms, The Journal of Physiology, 23 August 2007: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2375571/
8 Stoa, M et al, Factors Influencing Running Velocity at Lactate Threshold in Male and Female Runners at Different Levels of Performance, Frontiers in Physiology, 4 November 2020:https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2020.585267/full
9 PDEHPE.NET, 2022
10 Friel, 2015, p122, p160
11 Fee, E, The Complete Guide to Running: How to become a champion, from 9 to 90, 2005, p26
12 Friel, 2015, p111
13 PDEHPE.NET, 2022
14 Reaburn, P, The Masters Athlete, 2009, p73
15 Janssen, P, Lactate Threshold Training, 2001, p42
16 PDEHPE.NET, 2022
17 Friel, 2015, p254
18 Reaburn, 2009, p96
19 Fee, 2005, p157
20 Livingstone, K, Healthy Intelligent Training, 2009, p63
21 Interview by Dr Glenn McConell with Dr Andre La Gerche, The heart and exercise: Should middle-aged men pull on lycra? Inside Exercise, Number 69, October 2023: https://www.youtube.com/watch?v=bvMUAse5mls
22 Noakes, T, The Lore of Running, 2003, p41-42
23 10 Interview by Dr Glenn McConell with Dr Benjamin Levine, Can extreme exercise damage the heart? Inside Exercise, Number 8, 31 July 2022: https://www.youtube.com/watch?v=WlppG5olndQ
24 Levine, 2022
25 5 Things Athletes Should Know About Their Hearts, Medstar Health, 9 February 2021: https://www.medstarhealth.org/blog/athletes-heart
26 Franklin, et al, Exercise-Related Acute Cardiovascular Events and Potential Deleterious Adaptations Following Long-Term Exercise Training: Placing the Risks into Perspective–An Update. A Scientific Statement from the American Heart Association, Circulation, 31 March 2020: https://www.ahajournals.org/doi/10.1161/CIR.0000000000000749
27 Interview by Simon Willis with Dr Peter Clarkson, How hard to train? A cardiologist on heart health for older athletes, 19 February 2024: https://www.youtube.com/watch?v=olg90Dq9ay8
28 Clarkson, 2024
29 Clarkson, 2024
30 Clarkson, 2024
31 Parry-Williams et al, The heart of the ageing endurance athlete: the role of chronic coronary stress, European Heart Journal, 22 March 2021: https://academic.oup.com/eurheartj/article/42/28/2737/6179516?login=false
32 Parry-Williams et al, 2021
33 Interview with Peter Reaburn, Maximising Health & Performance of the Masters Athlete, Episode 215, The Physical Performance Show, posted by Runners Tribe 1 June 2020: https://www.runnerstribe.com/podcasts/maximising-health-performance-of-the-masters-athlete/
34 La Gerche, 2023
35 Clarkson, 2024
36 Clarkson, 2024
37 Clarkson, 2024
38 La Gerche, 2023
39 La Gerche, 2023
40 Henderson, J, editor, The Runner’s Diet, Runner’s World Booklet of the Month No. 14, 1972, p72
41 Magill, P, Schwartz, T & Breyer, M, Build Your Running Body, 2014, p222
42 McGregor, R, Running and Hormone Health: Everything You Need to Know, Runner’s World Newsletter, 9 December 2023
43 Interview by Coach Parry with Nicky Keay, The Hidden Hormone Mistakes Runners Over 50 Make Every Day, 21 July 2025: https://www.youtube.com/watch?v=9OscvmUMtVU
44 Magill et al, 2014, p222
45 Magill et al, 2014, p222
46 Magill et al, 2014, p222
47 Keay, 2025
48 Keay, 2025
49 Keay, 2025
50 Patel, A, Reddy, V, Shumway, K, Araujo, J, Physiology, Sleep Stages, National Library of Medicine, National Center for Biotechnology Information, 26 January 2024:
https://www.ncbi.nlm.nih.gov/books/NBK526132/#article-29141.s1
51 Friel, 2015, pp207-208
52 Patel et al, 2024
53 Patel et al, 2024
54 Keay, 2025
55 Keay, 2025
56 This paragraph is a summation of general information freely available from multiple medical sources on the internet, 2025
57 Shmerling, H, Does Running Cause Arthritis? Harvard Health Publishing, 26 April, 2023
https://www.health.harvard.edu/blog/does-running-cause-arthritis-202304262930