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Your First Half or Full Marathon, Getting the Body Ready
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In one pass The heart and lungs catch up within weeks while bone and tendon work on a scale of months, so how fast you can add distance depends on the slowest part to adapt.
Educational content, not medical advice — consult a clinician.
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Chapter 1
Ready for a half after three months?
The heart and lungs catch up within weeks while bone and tendon work on a scale of months, so how fast you can add distance depends on the slowest part to adapt. Seven to 10 days into endurance training, the enzymes in the mitochondria (the small structures in cells that produce energy) in your muscles have clearly increased, and a rise in maximal oxygen uptake can be measured within 3 weeks. Yet the core of an adult Achilles tendon is barely renewed for decades, and the tendon training studies pooled in one all lasted at least 8 weeks.
So when you have run for three months, your longest run is 10 kilometers, and you wonder whether you can go straight to a half marathon, the real question is whether your legs have had enough time. No trial has answered it directly; among runners preparing for a half marathon, those whose weekly distance jumped suddenly got injured more in the first few weeks.
This story is for people who have been running for a few months and want to enter their first half or full marathon; the chapters on fuel also apply to long rides.
A step you can take today: count how many weeks are left before the race, then decide whether to enter the half or run a shorter race first.
If you get chest pain or tightness, or faint, while exercising, or become confused or start vomiting after drinking a lot of water, stop and call emergency services now; in the second case, stop drinking water too. See Signs to stop right away.
So when you have run for three months, your longest run is 10 kilometers, and you wonder whether you can go straight to a half marathon, the real question is whether your legs have had enough time. No trial has answered it directly; among runners preparing for a half marathon, those whose weekly distance jumped suddenly got injured more in the first few weeks.
This story is for people who have been running for a few months and want to enter their first half or full marathon; the chapters on fuel also apply to long rides.
A step you can take today: count how many weeks are left before the race, then decide whether to enter the half or run a shorter race first.
If you get chest pain or tightness, or faint, while exercising, or become confused or start vomiting after drinking a lot of water, stop and call emergency services now; in the second case, stop drinking water too. See Signs to stop right away.
Mechanism · What changes in weeks, what takes months
What adapts quickly is the metabolism of the heart, lungs and muscle. Spina 1996 had 12 people cycle for 2 hours a day for 7 or 10 days in a row: the activity of several mitochondrial enzymes in their muscles rose by about 30%, maximal oxygen uptake rose by 9%, and blood lactate was lower at the same power output. The study had no control group. Murias 2010 followed 16 men cycling 3 times a week for 12 weeks: maximal oxygen uptake had already risen within 3 weeks and kept climbing after that.What adapts slowly is the tissue that bears the load. Heinemeier 2013 used the carbon-14 that nuclear tests left in the atmosphere as a label and measured 28 samples of adult Achilles tendon core: it was barely renewed for decades, while the muscle measured alongside kept renewing. The 27 tendon training studies pooled by Bohm 2015 all lasted at least 8 weeks, and studies of 12 weeks or more showed somewhat larger effects, though the difference was not statistically significant.
Bone needs time too. The clinical commentary by Warden 2014 describes bone stress injury (bone damage from repeated loading) as one continuous path: a stress reaction first, which can progress to a stress fracture and finally to a complete fracture; the cause is tiny damage in the bone forming faster than it is cleared. So when a few weeks of running make you feel I can run more now, that signal comes from your heart and lungs. How bone first gets weaker under load and then stronger is covered in Running for Beginners.
Evidence · How fast is too fast
Damsted 2019 followed 261 runners preparing for a half marathon for 14 weeks, recording every run with watch location data: 56 of them (21.5%) got injured. By day 21, runners who had raised their weekly distance by 20% to 60% had more injuries than those who raised it by less than 20%, with a cumulative risk difference of 22.6% (95% 0.9% to 44.3%, a wide range); by days 56 and 98 the difference was no longer significant. It is an observational study: it shows that sudden big jumps and injury go together, and cannot on its own show that those runs caused the injuries.A ready-made numerical rule fares no better. Nielsen 2014 followed 874 novices for a year: those who raised their weekly distance by more than 30% had more distance-related injuries than those who raised it by less than 10%, but the difference did not reach statistical significance ( 1.59, 95% confidence interval 0.96 to 2.66). Buist 2008 randomized 532 novices to a plan that added 10% a week or to a standard plan; injury rates were 20.8% versus 20.3%, almost the same.
Novices get injured more to begin with. In the Videbæk 2015 , novices had 17.8 injuries per 1000 hours of running and recreational runners 7.7, although the studies defined injury and runner type differently. What survives is not a particular percentage but a direction: a tissue bears load relative to what it is already used to, and what to avoid is a sudden big jump.
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Chapter 2
How to build up the distance
A race asks for several hours in a row of bearing your weight and supplying fuel; in training, what comes closest is your longest run of the week, and most of your other running should be easy enough that you can still speak in full sentences. Endurance training increases the mitochondrial enzymes in your muscles, so at the same pace you can use more fat and less glycogen (the body's store of glucose linked into chains), and glycogen is exactly what runs short in the second half (see Zone 2 — mitochondrial training).
Endurance athletes who train a lot do about 80% of their training at low intensity. In a randomized trial of 12 sub-elite runners, the group with more low-intensity time improved more over 10.4 kilometers after 5 months of training. These are all people who train a great deal, so applying this to novices is an inference.
For a first race the goal is to finish with your legs intact, and alternating running and walking is completely fine (see Running for Beginners). Only if you want a faster time do you need to add some quicker sessions; how to set that pace is covered in Lactate threshold.
A step you can take today: lengthen only your longest run of the week, slowly, keep the rest easy, and change one thing at a time.
Endurance athletes who train a lot do about 80% of their training at low intensity. In a randomized trial of 12 sub-elite runners, the group with more low-intensity time improved more over 10.4 kilometers after 5 months of training. These are all people who train a great deal, so applying this to novices is an inference.
For a first race the goal is to finish with your legs intact, and alternating running and walking is completely fine (see Running for Beginners). Only if you want a faster time do you need to add some quicker sessions; how to set that pace is covered in Lactate threshold.
A step you can take today: lengthen only your longest run of the week, slowly, keep the rest easy, and change one thing at a time.
Evidence · Why most running should be easy
The Seiler 2010 review pulled together training records of national and international endurance athletes: they trained 10 to 13 times a week, with about 80% of sessions at low intensity (blood lactate around 2 millimoles per liter) and about 20% dominated by high-intensity work, such as intervals near 90% of maximal oxygen uptake. The review adds that in athletes who are already well trained, there is no convincing evidence that putting more weight on high-intensity intervals brings long-term gains. This describes how athletes train; it is not a trial.Esteve-Lanao 2007 was a small randomized trial: 12 sub-elite runners trained for about 5 months, one group spending 80.5% of training time at low intensity and the other 66.8%, with the high-intensity share kept similar. Afterward, in a simulated 10.4-kilometer cross-country race, the group with more low-intensity work was 157 seconds faster and the other group 121.5 seconds faster, a significant difference. The authors' conclusion comes with a condition: the amount of high-intensity training still has to be sufficient.
As for the mechanism, the Spina 1996 abstract notes that endurance training increases mitochondrial enzymes, and one result is less reliance on carbohydrate and more use of fat, which improves endurance. The basis for the talk test (still being able to speak in full sentences means you are below the lactate threshold) is covered in Zone 2 — mitochondrial training; none of these studies were done in novices.
Chapter 3
What hitting the wall is
Hitting the wall means the glycogen in your legs is nearly used up: fat cannot supply the energy this pace needs fast enough, so you are forced to slow down. The faster you run, the more the muscles rely on glycogen, and the fewer fatty acids they can get from the blood. In endurance events lasting more than about 90 minutes, exhaustion usually arrives together with very low muscle glycogen.
A second line runs through the brain. Glycogen in the liver keeps blood sugar up; once blood sugar falls, the commands the brain sends to the muscles weaken. In a small study, people who cycled for 3 hours drinking only water saw their blood sugar fall, their maximal leg force drop, and the nervous system's activation of the muscle decline.
A study that analyzed more than 4 million marathon records found, judging by late-race pace, that about 28% of men and 17% of women hit the wall, mostly after the 20-mile mark (about 32 kilometers). Whether to worry in a half marathon depends on time, not distance: in moderate-intensity runs of 60 to 90 minutes, a fair amount of glycogen usually remains in the legs.
A step you can take today: run the first half of the race at the pace you have practiced, and do not let the crowd pull you faster.
A second line runs through the brain. Glycogen in the liver keeps blood sugar up; once blood sugar falls, the commands the brain sends to the muscles weaken. In a small study, people who cycled for 3 hours drinking only water saw their blood sugar fall, their maximal leg force drop, and the nervous system's activation of the muscle decline.
A study that analyzed more than 4 million marathon records found, judging by late-race pace, that about 28% of men and 17% of women hit the wall, mostly after the 20-mile mark (about 32 kilometers). Whether to worry in a half marathon depends on time, not distance: in moderate-intensity runs of 60 to 90 minutes, a fair amount of glycogen usually remains in the legs.
A step you can take today: run the first half of the race at the pace you have practiced, and do not let the crowd pull you faster.
Evidence · What glycogen and blood sugar each cover
The Hawley 1997 review separates two situations. In moderate-intensity running or cycling of 60 to 90 minutes, storing extra glycogen before the start brings no benefit, because plenty is still left in the muscles at the end. In endurance events lasting more than 90 minutes, exhaustion usually coincides with very low muscle glycogen (about 25 millimoles per kilogram of wet muscle), and starting with more glycogen can postpone fatigue by about 20%. The authors conclude that once glycogen is used up, burning more blood sugar cannot fill the gap.Why going faster means relying more on glycogen was measured by Romijn 1993 with isotope tracers in 5 trained people: as intensity rose from 25% to 65% to 85% of maximal oxygen uptake, muscle glycogen oxidation rose with it, while fewer fatty acids entered the blood.
For the blood sugar line, Coyle 1986 tested 7 endurance cyclists riding to exhaustion at 71% of maximal oxygen uptake. With a placebo drink they were exhausted after 3.02 hours, and before that their blood sugar fell to 2.5 millimoles per liter; with a sugar drink their blood sugar held, they rode about 1 hour longer (4.02 hours), and their muscle glycogen use over the first 3 hours was the same both times. Nybo 2003 had 8 trained men cycle for 3 hours: without sugar, blood sugar fell from 4.5 to 3.0 millimoles per liter and the average force of a sustained maximal knee extension was 197 newtons, compared with 222 newtons with sugar (248 newtons before the ride), and nerve activation was also lower in the no-sugar ride. Both are small cycling studies.
Smyth 2021 used race records, taking a sustained marked late-race slowdown as a stand-in for hitting the wall. This is inferred from pacing; nobody measured glycogen.
Chapter 4
Do you need gels on the run?
In a run of about an hour, your glycogen still holds out, and eating sugar along the way works mainly through your mouth and brain; in longer runs, sugar eaten on the way keeps your blood sugar up and pushes back the moment you run out of strength. In one study, cyclists drinking only a placebo could not keep going after about 3 hours, and their blood sugar fell before they stopped; in the ride where they drank a sugar drink along the way, they lasted about 1 hour longer.
What happens if you eat nothing is the two lines described in What hitting the wall is: glycogen runs out and blood sugar falls. But eating more is not always better. Sugar first has to pass through the transporters (proteins that carry sugar into cells) on the cells of the small intestine, and that door has a ceiling; the excess stays in the gut and can cause bloating and diarrhea (see The gut during exercise).
The gut can be trained, too. In a randomized trial of 25 runners, eating sugary gels or food repeatedly while running over two weeks cut gut symptoms by about 60%.
A step you can take today: start practicing eating a little sugary food during your longer runs. Gels, sports drinks or solid food all work; do not save the first time for race day.
What happens if you eat nothing is the two lines described in What hitting the wall is: glycogen runs out and blood sugar falls. But eating more is not always better. Sugar first has to pass through the transporters (proteins that carry sugar into cells) on the cells of the small intestine, and that door has a ceiling; the excess stays in the gut and can cause bloating and diarrhea (see The gut during exercise).
The gut can be trained, too. In a randomized trial of 25 runners, eating sugary gels or food repeatedly while running over two weeks cut gut symptoms by about 60%.
A step you can take today: start practicing eating a little sugary food during your longer runs. Gels, sports drinks or solid food all work; do not save the first time for race day.
Numbers · How long you run changes how you fuel
Sports nutrition consensus sorts fueling by duration. Burke 2011 writes that in sustained high-intensity exercise of about 1 hour, small amounts of carbohydrate, even just rinsing the mouth and spitting it out, improve performance through the central nervous system; for longer events, 30–60 grams an hour is an appropriate target; events over 2.5 hours may benefit from up to 90 grams an hour, which takes products that mix several kinds of carbohydrate to absorb that much. Jeukendrup 2014 adds that a single kind of sugar can be burned at up to about 60 grams an hour, which is the advice for exercise of 2 to 3 hours; for ultra-endurance events it is about 90 grams, which has to be a mix of sugars that use different transporters so the sugar does not build up in the gut; the form can be liquid, semisolid or solid.These numbers are ceilings for athletes, not everyone's ration. Jeukendrup 2014 states that when absolute intensity is low and carbohydrate is burned slowly, the advice may need to be adjusted downward, which is exactly the situation of a slow recreational runner. The author of that review worked at the time at the research institute of a sports drink company.
The effect grows with duration. The systematic review by Stellingwerff 2014 included 61 randomized studies with a water-only control (679 people), and 82% saw a statistically significant improvement in performance; the longer the exercise, the larger the percentage gain. In exercise of about 1 hour, what works is sugar touching the mouth and stimulating the brain's reward areas, and the type and amount hardly matter; beyond 2 hours, when muscle glycogen runs short, what works is delivering and burning a lot of sugar.
Evidence · How the gut gets trained
Costa 2017 first gave 25 endurance runners a test: 2 hours of running at 60% of maximal oxygen uptake, eating a gel disc with 30 grams of carbohydrate every 20 minutes, then a 1-hour distance run. They were then randomized to three groups that, over two weeks, repeatedly ate sugary gel discs, sugary food or a placebo while running, and were tested again. In the gel-disc and food groups, gut symptoms fell by 60% and 63%, and the distance test improved by 5.2% and 4.3%; the placebo group dropped by 2.1%. The gel-disc group also left less sugar unabsorbed and had higher blood sugar.Cox 2010 had 16 trained cyclists or triathletes train for 28 days, one group taking carbohydrate during training and the other not, with the same total energy. In the carbohydrate group, the outside glucose burned during 100 minutes of steady cycling rose from 54.6 to 63.6 grams, with no change in the other group; but both groups improved their performance by about 6%, with no difference between them.
A 2014 review of gut problems during exercise says that 30%–50% of athletes have had gut discomfort during exercise, mostly mild and harmless, and that practicing fueling in training can lower that risk. Whether the small intestine's transporters actually multiply as a result, Jeukendrup 2017 states that the human evidence is limited, so this is not written as a program for training your gut wider.
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Chapter 5
Eating and drinking around race day
Try nothing new on race day: your gut is used only to the way you have practiced eating, and a new food, gel or drink can turn into stomach trouble halfway through. Between 30% and 50% of athletes have had gut discomfort during exercise, and a review concludes that practicing your fueling in training lowers that risk.
Whether to eat extra carbohydrate beforehand depends on how long you will be running, not on whether it is a full or a half marathon. In events over about 90 minutes, starting with more glycogen postpones exhaustion; in moderate-intensity runs of 60 to 90 minutes, the extra glycogen goes unused. Eating somewhat more starchy food for a few days before the race is enough to raise glycogen, without starving first and then flooding (see Glycogen supercompensation).
Drink according to thirst. Drinking more than you lose through sweat, breathing and urine dilutes the sodium in your blood, which is called exercise-associated hyponatremia; at one marathon it was more common in people who took more than 4 hours to finish. How to protect yourself in hot weather is covered in Exercising in the Heat.
A step you can take today: before one of your long runs, try out the food you plan to eat the night before the race and on race morning.
Whether to eat extra carbohydrate beforehand depends on how long you will be running, not on whether it is a full or a half marathon. In events over about 90 minutes, starting with more glycogen postpones exhaustion; in moderate-intensity runs of 60 to 90 minutes, the extra glycogen goes unused. Eating somewhat more starchy food for a few days before the race is enough to raise glycogen, without starving first and then flooding (see Glycogen supercompensation).
Drink according to thirst. Drinking more than you lose through sweat, breathing and urine dilutes the sodium in your blood, which is called exercise-associated hyponatremia; at one marathon it was more common in people who took more than 4 hours to finish. How to protect yourself in hot weather is covered in Exercising in the Heat.
A step you can take today: before one of your long runs, try out the food you plan to eat the night before the race and on race morning.
Evidence · Who carbohydrate loading helps
The Hawley 1997 review says that in moderate-intensity running or cycling of 60 to 90 minutes, extra glycogen at the start brings no benefit; in events over 90 minutes it can postpone fatigue by about 20%; and in events where you cover a set distance as fast as you can, high-carbohydrate diets have been reported to improve performance by 2%–3%.That you do not need to starve first and then flood comes from Sherman 1981. Trained runners compared three ways of eating: the classic low-carbohydrate then high-carbohydrate, a milder normal eating then high-carbohydrate, and normal eating throughout. Muscle biopsies on day 7 showed glycogen of 207, 203 and 159 millimoles per kilogram of wet muscle, so the first two were almost equally high. Yet in the 20.9-kilometer run that followed, the two high-glycogen ways of eating were not faster. That distance is close to a half marathon, but the participants were trained runners; for someone who takes more than 90 minutes to finish a half, eating extra carbohydrate beforehand may help by the time boundary above, and neither that case nor longer races that truly run glycogen down to empty were measured in this study.
For what to eat the night before and on race morning, this site found no trial that gives specific foods or amounts, so only the principle is given here: eat what you have practiced with, a little more starchy food, and do not try anything new at that point.
Safety · Why drinking too much is dangerous
The third international consensus on exercise-associated hyponatremia (Hew-Butler 2015) states that the single most important risk factor is persistently drinking more water, sports drink or other hypotonic fluid than you lose through sweat, breathing and urine; all sports drinks are hypotonic, so drinking too much of them is not protective either. Drinking to thirst limits overdrinking while also preventing excessive dehydration, and when fluid intake is excessive, extra salt cannot prevent hyponatremia.Almond 2005 took blood from 488 runners at the finish of the 2002 Boston Marathon: 13% had hyponatremia and 0.6% had it to a critical degree. In a multivariable analysis it was linked to weight gain during the race, a finishing time over 4 hours, and a body mass index () that was too high or too low; whether people drank sports drinks or plain water was not linked to it. This is an observational study.
So do not deliberately drink extra before the race, and drink to thirst during it; if you weigh more after the run than at the start, you drank too much. In hot weather you sweat more and the risk of heat illness rises too; how to prepare and what to do in an emergency are covered in Exercising in the Heat.
Chapter 6
Signs to stop right away
In a long run, some kinds of discomfort are not tiredness but your body raising the alarm; if they appear, stop, and do not push on just to finish. This site does not diagnose.
Sudden chest pain or tightness during or after exercise, or fainting during exercise: call emergency services now.Marked breathlessness, a racing heart or feeling about to faint during exercise: stop at once and do not push through; if the symptoms do not settle, seek medical care right away.During or after a long run, confusion, vomiting or seizures on top of headache and nausea, when you have been drinking all along: it may be low blood sodium from drinking too much, which is an emergency. Stop drinking water and call emergency services now; at a race, get to the nearest medical station.Someone in hot weather who becomes confused, behaves strangely or collapses: treat it as an emergency, cool them on the spot right away, and call emergency services at the same time.Pinpoint pain in one spot on a bone that hurts sharply when pressed, gets worse the more you run, or even wakes you at night: suspect a stress fracture, stop running, and see a doctor.
A step you can take today: if you have known heart disease, or have had chest pain, unexplained breathlessness or fainting during exertion, see a doctor for an assessment before you enter.
Sudden chest pain or tightness during or after exercise, or fainting during exercise: call emergency services now.Marked breathlessness, a racing heart or feeling about to faint during exercise: stop at once and do not push through; if the symptoms do not settle, seek medical care right away.During or after a long run, confusion, vomiting or seizures on top of headache and nausea, when you have been drinking all along: it may be low blood sodium from drinking too much, which is an emergency. Stop drinking water and call emergency services now; at a race, get to the nearest medical station.Someone in hot weather who becomes confused, behaves strangely or collapses: treat it as an emergency, cool them on the spot right away, and call emergency services at the same time.Pinpoint pain in one spot on a bone that hurts sharply when pressed, gets worse the more you run, or even wakes you at night: suspect a stress fracture, stop running, and see a doctor.
A step you can take today: if you have known heart disease, or have had chest pain, unexplained breathlessness or fainting during exertion, see a doctor for an assessment before you enter.
Red flag · Why these signs cannot wait
Cardiac arrest during a race is rare, but it happens. Kim 2012 counted US marathons and half marathons from 2000 to 2010: among 10.9 million participants, 59 had a cardiac arrest, about 0.54 per 100,000; the rate was 1.01 per 100,000 in full marathons and 0.27 in half marathons, and higher in men than in women; 42 of the 59 (71%) could not be saved. The causes were mostly hypertrophic cardiomyopathy or coronary atherosclerosis, and prompt cardiopulmonary resuscitation by a bystander was among the strongest predictors of survival. The American College of Sports Medicine consensus on pre-exercise screening notes that exercise-related cardiovascular events are often preceded by warning symptoms, so once chest pain, chest tightness or fainting appears, do not keep going to the finish.The early headache and nausea of hyponatremia are easily mistaken for dehydration, and pouring in more water then makes it worse; having drunk all along, and weighing more rather than less, are the clues that tell it apart (Hew-Butler 2015 · Almond 2005). Heatstroke is a core temperature that is too high plus a change in mental state, and cooling comes before transport (NATA 2015).
Bone stress injury is a path that can keep going downhill: a stress reaction first, which can progress to a stress fracture and finally to a complete fracture, typically showing up as local bone pain and tenderness (Warden 2014). So pinpoint bone pain is not an ache you can run through; the earlier you stop and see a doctor, the shorter that path.
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References · 28
- Spina, R. J., Chi, M. M., Hopkins, M. G., Nemeth, P. M., Lowry, O. H., & Holloszy, J. O. (1996). Mitochondrial enzymes increase in muscle in response to 7-10 days of cycle exercise. Journal of Applied Physiology, 80(6), 2250-2254. Background in the abstract: endurance training raises mitochondrial enzyme activity, and 'one consequence of this adaptation is that there is a decreased reliance on carbohydrate utilization with a concomitant increase in fat utilization, resulting in an improvement in endurance capacity.' Twelve subjects (6 men, 6 women) cycled 2 h/day at 60-70% of peak oxygen uptake for 7 (n = 5) or 10 days (n = 7), with no separate control group. Peak oxygen uptake rose 9% (2.97 to 3.24 L/min), blood lactate was lower at the same absolute work rates, and citrate synthase, beta-hydroxyacyl-CoA dehydrogenase, mitochondrial thiolase and carnitine acetyltransferase rose by approximately 30%. Conclusion: 'in humans, as in rats, the adaptive increase in mitochondrial enzymes in skeletal muscle occurs fairly rapidly in response to exercise training'; the results give no support for the claim that it is delayed for more than 2 weeks (abstract, PMID 8806937). 10.1152/jappl.1996.80.6.2250
- Murias, J. M., Kowalchuk, J. M., & Paterson, D. H. (2010). Time course and mechanisms of adaptations in cardiorespiratory fitness with endurance training in older and young men. Journal of Applied Physiology, 108(3), 621-627. Eight older (68 years) and 8 young (23 years) men cycled three times a week for 45 min at about 70% of maximal oxygen uptake for 12 weeks, tested every 3 weeks. 'VO2max increased within 3 wk with further increases observed posttraining in both O (+31%) and Y (+18%)'; maximal cardiac output and stroke volume were higher after 3 weeks with further increases after 9 weeks. Early adaptations (first 3 weeks) relied mainly on a widened arterial-venous oxygen difference (about 66%), later ones on greater maximal cardiac output. Conclusion: with short-term training both groups significantly increased VO2max, but the share explained by cardiac output and oxygen extraction followed a different pattern by age (abstract, PMID 20056848). 10.1152/japplphysiol.01152.2009
- Heinemeier, K. M., Schjerling, P., Heinemeier, J., Magnusson, S. P., & Kjaer, M. (2013). Lack of tissue renewal in human adult Achilles tendon is revealed by nuclear bomb 14C. The FASEB Journal, 27(5), 2074–2079. Bomb-pulse 14C in 28 forensic Achilles tendon core samples and 4 muscle samples: the tendon core retained 14C levels matching the atmosphere several decades before sampling, showing very limited tissue turnover, while muscle showed continuous turnover (abstract, PMID 23401563). 10.1096/fj.12-225599
- Bohm, S., Mersmann, F., & Arampatzis, A. (2015). Human tendon adaptation in response to mechanical loading: a systematic review and meta-analysis of exercise intervention studies on healthy adults. Sports Medicine - Open, 1(1), 7. 27 studies (37 interventions of at least 8 weeks, 264 healthy adults aged 18-50, Achilles or patellar tendon): stiffness SMD 0.70, Young's modulus SMD 0.69, cross-sectional area SMD 0.24, all significant. Stiffness adaptation depended on loading intensity but not on contraction type; 'Although not significantly different, SMD was higher for interventions with longer duration (≥12 weeks).' Conclusion: 'tendons are highly responsive to diverse loading regimens. However, the data strongly suggests that loading magnitude in particular plays a key role for tendon adaptation in contrast to muscle contraction type' (abstract, PMID 27747846). 10.1186/s40798-015-0009-9
- Damsted, C., Parner, E. T., Sørensen, H., Malisoux, L., Hulme, A., & Nielsen, R. Ø. (2019). The association between changes in weekly running distance and running-related injury: preparing for a half marathon. Journal of Orthopaedic & Sports Physical Therapy, 49(4), 230-238. Prospective cohort of 261 healthy runners preparing for a half marathon, followed for 14 weeks with GPS-recorded running. 56 participants (21.5%) sustained a running-related injury. Twenty-one days in, significantly more runners were injured when they increased weekly running distance by 20% to 60% than by less than 20% (cumulative risk difference 22.6%, 95% CI 0.9% to 44.3%, P = .041); no significant difference was found after 56 and 98 days, and the running schedule followed did not modify the association. Conclusion: 'Significantly more runners were injured 21 days into the study period when they increased their weekly running distances by 20% to 60% compared with those who increased their distances by less than 20%' (abstract, PMID 30526231). 10.2519/jospt.2019.8541
- Hew-Butler, T., Rosner, M. H., Fowkes-Godek, S., Dugas, J. P., Hoffman, M. D., Lewis, D. P., Maughan, R. J., Miller, K. C., Montain, S. J., Rehrer, N. J., Roberts, W. O., Rogers, I. R., Siegel, A. J., Stuempfle, K. J., Winger, J. M., & Verbalis, J. G. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clinical Journal of Sport Medicine, 25(4), 303–320. Full text read 2026-09-24 (simultaneous BJSM publication, 49(22), 1432, via a Wayback snapshot of 10 October 2024; PubMed has no abstract, PMID 26102445): the single most important risk factor is sustained excessive intake of water, sports drinks or other hypotonic fluids beyond sweat, respiratory and renal losses; all sports drinks are hypotonic (sodium about 10-38 mmol/L), so overdrinking them is not protective. Using thirst to guide drinking should limit overdrinking while preventing excessive dehydration (Grade 1C); earlier advice to drink before thirst was meant for high sweat rates; fluid deficits up to about 3% of body mass are tolerated in cool to temperate conditions. Sodium supplements cannot prevent EAH when fluid intake is excessive (Grade 1C). Treatment: symptom severity, not the sodium value, guides therapy (Grade 1A); restrict hypotonic and isotonic fluids until urinating; severe EAH with encephalopathy gets an immediate 100 mL bolus of 3% NaCl, repeated up to twice (about 10-min intervals) if there is no improvement, without waiting for a lab value (Grade 1B); IV hypotonic fluids, lactated Ringer's or normal saline are contraindicated in confirmed dilutional EAH. Travel and meals for the panel were funded by CrossFit, Inc. 10.1097/JSM.0000000000000221
- NHS. (2026). Heart attack: symptoms. Symptoms can include chest pain that may feel like crushing or squeezing on the chest and may spread to the arm, neck and jaw; feeling short of breath; feeling or being sick; feeling like indigestion; sweating; and pale, blue or grey skin. Call 999 for chest pain that feels tight or like squeezing, or that spreads to the arms, neck or jaw, with severe difficulty breathing, or if someone becomes unresponsive. A heart attack needs emergency treatment in hospital (page last reviewed 31 March 2026). www.nhs.uk/conditions/heart-attack/symptoms
- NHS. (2026). Fainting (page last reviewed 17 August 2026). Fainting is when you pass out for a short time; it is not usually serious, but anyone who has fainted should see a GP to find out what might have caused it. Causes can include standing up too quickly (which could be a sign of low blood pressure), not eating or drinking enough, being too hot, being very upset or in severe pain, heart problems, and taking drugs or drinking too much alcohol. Call 999 if someone is not breathing, cannot be woken up within 1 minute, has not fully recovered or has difficulty with speech or movement, has chest pain or a pounding, fluttering or irregular heartbeat (palpitations), has seriously hurt themselves before or after fainting, is shaking or jerking (a seizure), fainted while exercising, or fainted while lying down; do not drive yourself to A&E. If you feel about to faint: lie down with your legs raised, or if you cannot, sit with your head lowered between your knees; drink some water; cross your legs while standing up or rock up and down on your toes; clench your fists. If you see someone faint: check whether they respond by gently shaking their shoulders and asking loudly; if not, shout for help and tilt back the head and lift the chin; listen for breathing for at least 10 seconds; if they are breathing normally, lay them on their back and raise their legs (on their side if pregnant, especially over 28 weeks); they usually wake up within 30 seconds. www.nhs.uk/conditions/fainting
- Seiler, S. (2010). What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance, 5(3), 276-291. Review: descriptive studies of nationally or internationally competitive endurance athletes training 10 to 13 times per week 'seem to converge on a typical intensity distribution in which about 80% of training sessions are performed at low intensity (2 mM blood lactate), with about 20% dominated by periods of high-intensity work, such as interval training at approx. 90% VO2max.' Training-intensification studies in already well-trained athletes 'do not provide any convincing evidence that a greater emphasis on high-intensity interval training in this highly trained athlete population gives long-term performance gains.' The predominance of low-intensity, long-duration training combined with fewer highly intensive bouts may be complementary (abstract, PMID 20861519). 10.1123/ijspp.5.3.276
- Esteve-Lanao, J., Foster, C., Seiler, S., & Lucia, A. (2007). Impact of training intensity distribution on performance in endurance athletes. Journal of Strength and Conditioning Research, 21(3), 943-949. Twelve sub-elite endurance runners (mostly 5,000-m and cross-country specialists) were randomly assigned to two heart-rate-controlled programs for about 5 months. Share of training time in zone 1 (below the ventilatory threshold) and zone 2: 80.5% and 11.8% in the Z1 group versus 66.8% and 24.7% in the Z2 group, with high-intensity time kept similar. The improvement in a simulated 10.4-km cross-country race was significantly greater in Z1 (-157 s) than in Z2 (-121.5 s). Conclusion: the results support 'the value of a relatively large percentage of low-intensity training over a long period (approximately 5 months), provided that the contribution of high-intensity training remains sufficient' (abstract, PMID 17685689). 10.1519/R-19725.1
- Reed, J. L., & Pipe, A. L. (2014). The talk test: a useful tool for prescribing and monitoring exercise intensity. Current Opinion in Cardiology, 29(5), 475-480. 'In healthy adults and patients with cardiovascular disease, comfortable speech is likely possible (equivocal or last positive talk test stage) when exercise intensity is below the ventilatory or lactate threshold, and not likely possible (negative talk test stage) when exercise intensity exceeds the ventilatory or lactate threshold.' The talk test has been consistent across walking, jogging, cycling, elliptical trainer and stair stepper, and may not be practical for high-intensity interval training. Summary: it 'is a valid, reliable, practical and inexpensive tool for prescribing and monitoring exercise intensity in competitive athletes, healthy active adults and patients with cardiovascular disease' (abstract, PMID 25010379). 10.1097/HCO.0000000000000097
- Hawley, J. A., Schabort, E. J., Noakes, T. D., & Dennis, S. C. (1997). Carbohydrate-loading and exercise performance: an update. Sports Medicine, 24(2), 73-81. Review: little or no effect of raising pre-exercise muscle glycogen above normal resting values on a single exhaustive bout of high-intensity exercise lasting less than 5 minutes, 'nor is there any benefit of increasing starting muscle glycogen content on moderate-intensity running or cycling lasting 60 to 90 minutes', because substantial glycogen remains in the working muscles at the end. 'However, elevated starting muscle glycogen content will postpone fatigue by approximately 20% in endurance events lasting more than 90 minutes. During this type of exercise, exhaustion usually coincides with critically low (25 mmol/kg wet weight) muscle glycogen contents, suggesting the supply of energy from glycogen utilisation cannot be replaced by an increased oxidation of blood glucose.' In set-distance events, high-carbohydrate diets have been reported to improve performance by 2 to 3% (abstract, PMID 9291549). 10.2165/00007256-199724020-00001
- Romijn, J. A., Coyle, E. F., Sidossis, L. S., Gastaldelli, A., Horowitz, J. F., Endert, E., & Wolfe, R. R. (1993). Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration. American Journal of Physiology, 265(3 Pt 1), E380-E391. Stable isotope tracers and indirect calorimetry in five trained subjects at 25, 65 and 85% of maximal oxygen consumption. 'Plasma glucose tissue uptake and muscle glycogen oxidation increased in relation to exercise intensity. In contrast, peripheral lipolysis was stimulated maximally at the lowest exercise intensity, and fatty acid release into plasma decreased with increasing exercise intensity.' During 2 h at 65% of maximal oxygen consumption, oxidation of plasma-derived substrates rose over time while muscle glycogen and triglyceride oxidation fell. Conclusion: carbohydrate availability is regulated directly in relation to exercise intensity, while lipid regulation seems more complex (abstract, PMID 8214047). 10.1152/ajpendo.1993.265.3.E380
- Nybo, L. (2003). CNS fatigue and prolonged exercise: effect of glucose supplementation. Medicine and Science in Sports and Exercise, 35(4), 589-594. Eight endurance-trained men did 3 h of cycling, randomized to be with or without glucose supplementation, and then a 2-min sustained maximal knee extension with twitch interpolation. Without glucose, blood glucose fell from 4.5 to 3.0 mM; with glucose it was maintained. Average force was 248 N at baseline, 222 N in the glucose trial and 197 N in the placebo trial, and in the placebo trial the lower force came with reduced central nervous system activation. Conclusion: 'Exercise-induced hypoglycemia attenuates CNS activation during a sustained maximal muscle contraction, whereas central activation appears to be unaffected by 3 h of moderately intense exercise in endurance-trained athletes when euglycemia is maintained by carbohydrate ingestion' (abstract, PMID 12673141). 10.1249/01.MSS.0000058433.85789.66
- Smyth, B. (2021). How recreational marathon runners hit the wall: a large-scale data analysis of late-race pacing collapse in the marathon. PLOS ONE, 16(5), e0251513. Hitting the wall 'refers to the iconic hazard of the marathon distance, in which runners experience a significant slowing of pace late in the race, typically after the 20-mile mark, and usually because of a depletion of the body's energy stores.' Using pacing data from more than 4 million race records, a pacing-based definition (a sustained late-race slowdown) was used as a proxy: 28% of male and 17% of female runners hit the wall; when they did, males slowed more than females (relative slowdown 0.40 vs 0.37) and over longer distances (10.7 km vs 9.6 km), small effect sizes. Slowdowns were more frequent in the 3 years around a recent personal best (36% vs 23%) (abstract, PMID 34010308). 10.1371/journal.pone.0251513
- Stellingwerff, T., & Cox, G. R. (2014). Systematic review: carbohydrate supplementation on exercise performance or capacity of varying durations. Applied Physiology, Nutrition, and Metabolism, 39(9), 998-1011. Sixty-one randomized, placebo (water-only) controlled performance studies (n = 679): 82% showed statistically significant performance benefits and 18% no change. There was a significant correlation between longer total exercise time and a larger percent performance gain with carbohydrate. In short exercise (about 1 h), oral exposure to carbohydrate stimulating reward centres of the brain provides a central mechanism, and 'the type and (or) amount of CHO and its ability to be absorbed and oxidized appear completely irrelevant'; in longer exercise (over 2 h), where muscle glycogen is stressed, the main mechanism is high rates of carbohydrate delivery and oxidation. Multiple transportable carbohydrates are beneficial in prolonged exercise, but recommendations should be tailored to each athlete's tolerance (abstract, PMID 24951297). 10.1139/apnm-2014-0027
- Burke, L. M., Hawley, J. A., Wong, S. H., & Jeukendrup, A. E. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(Suppl 1), S17-S27. Consensus review: carbohydrate availability is raised by eating carbohydrate in the hours or days before a session, during exercise and in recovery. 'Carbohydrate intake during exercise should be scaled according to the characteristics of the event. During sustained high-intensity sports lasting ~1 h, small amounts of carbohydrate, including even mouth-rinsing, enhance performance via central nervous system effects. While 30-60 g · h(-1) is an appropriate target for sports of longer duration, events >2.5 h may benefit from higher intakes of up to 90 g · h(-1). Products containing special blends of different carbohydrates may maximize absorption of carbohydrate at such high rates' (abstract, PMID 21660838). 10.1080/02640414.2011.585473
- Coyle, E. F., Coggan, A. R., Hemmert, M. K., & Ivy, J. L. (1986). Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. Journal of Applied Physiology, 61(1), 165-172. Seven endurance-trained cyclists exercised to fatigue at 71% of maximal oxygen consumption twice, once drinking a flavored-water placebo and once a glucose polymer solution. With placebo, fatigue came after 3.02 h and was preceded by a fall in plasma glucose to 2.5 mM; when fed carbohydrate, plasma glucose was maintained (4.2-5.2 mM) and they exercised for an additional hour (4.02 h). The pattern of muscle glycogen use did not differ over the first 3 h, and the extra hour was done with little reliance on muscle glycogen. Conclusion: when fed carbohydrate, highly trained endurance athletes can oxidize carbohydrate at relatively high rates from sources other than muscle glycogen late in prolonged strenuous exercise, 'and that this postpones fatigue' (abstract, PMID 3525502). 10.1152/jappl.1986.61.1.165
- Jeukendrup, A. E. (2010). Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Current Opinion in Clinical Nutrition and Metabolic Care, 13(4), 452-457. Narrative review: the ceiling on exogenous carbohydrate oxidation sits in intestinal absorption, most likely saturation of carbohydrate transporters. Glucose alone had been taken as peaking near 1 g/min; combining carbohydrates that use different intestinal transporters (glucose plus fructose) raised measured exogenous oxidation to 1.75 g/min. The paper's own limit: this combination, ingested at high rates, is discussed for endurance work lasting 3 hours or more — not a universal feeding table. 10.1097/MCO.0b013e328339de9f
- Costa, R. J. S., Miall, A., Khoo, A., Rauch, C., Snipe, R., Camões-Costa, V., & Gibson, P. (2017). Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Applied Physiology, Nutrition, and Metabolism, 42(5), 547-557. Twenty-five endurance runners did a gut-challenge trial (2 h running at 60% of maximal oxygen uptake while taking 30 g carbohydrate gel-discs every 20 min, then a 1-h distance test), were randomly assigned to 2 weeks of repeated gut-challenge with carbohydrate gel-discs, carbohydrate food or placebo, and repeated the trial. Gastrointestinal symptoms fell by 60% with gel-discs and 63% with food, more than with placebo; the distance test improved by 5.2% and 4.3% but not with placebo (-2.1%); gel-discs also reduced malabsorption (breath hydrogen) and raised blood glucose; oxidation rates did not differ. Conclusion: 'Two weeks of gut-training with CHO-S and CHO-F improved gastrointestinal symptoms and running performance compared with PLA' (abstract, PMID 28177715). 10.1139/apnm-2016-0453
- Jeukendrup, A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 44(Suppl 1), S25-S33. Review proposing guidelines scaled to the duration and intensity of exercise: 'during exercise lasting approximately 1 h in duration, a mouth rinse or small amounts of carbohydrate can result in a performance benefit. A single carbohydrate source can be oxidized at rates up to approximately 60 g/h and this is the recommendation for exercise that is more prolonged (2-3 h). For ultra-endurance events, the recommendation is higher at approximately 90 g/h.' At such high rates the carbohydrate must be multiple transportable carbohydrates to prevent accumulation in the intestine. The source may be liquid, semisolid or solid, and 'the recommendations may need to be adjusted downward when the absolute exercise intensity is low and thus carbohydrate oxidation rates are also low.' The advice is independent of body weight and training status. Author affiliation: Gatorade Sports Science Institute (abstract, PMID 24791914). 10.1007/s40279-014-0148-z
- de Oliveira, E. P., Burini, R. C., & Jeukendrup, A. (2014). Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Medicine, 44(Suppl 1), S79-S85. Review: 'Generally, studies suggest that 30-50% of athletes experience such complaints. Most gastrointestinal symptoms during exercise are mild and of no risk to health, but hemorrhagic gastritis, hematochezia, and ischemic bowel can present serious medical challenges.' Causes are physiological, mechanical or nutritional; reduced mesenteric blood flow during intense exercise, especially when hypohydrated, is believed to be a main contributor. 'Nutritional training and appropriate nutrition choices can reduce the risk of gastrointestinal discomfort during exercise'; evidence for other proposed interventions is still lacking (abstract, PMID 24791919). 10.1007/s40279-014-0153-2
- Sherman, W. M., Costill, D. L., Fink, W. J., & Miller, J. M. (1981). Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. International Journal of Sports Medicine, 2(2), 114-118. Three 6-day regimens in trained runners: classic low-then-high carbohydrate, mixed-then-high, and mixed throughout. Muscle glycogen on day 7 reached 207, 203, and 159 mmol glucosyl units/kg wet tissue. The 20.9 km performance run was not faster after the two high-glycogen regimens. The paper's own three conclusions: glycogen can be raised with a moderate exercise-diet regimen; starting glycogen changes how much is used; carbohydrate loading did not help this 20.9 km run. 10.1055/s-2008-1034594
- Almond, C. S., et al. (2005). Hyponatremia among runners in the Boston Marathon. The New England Journal of Medicine, 352(15), 1550–1556. 2002 Boston Marathon: 766 enrolled, 488 gave a usable finish-line sample. Hyponatraemia (serum sodium <= 135 mmol/L) in 13%, critical (<= 120 mmol/L) in 0.6%. On multivariate analysis it was associated with weight gain (OR 4.2), racing time > 4:00 h (OR 7.4) and BMI extremes; female sex, the composition of fluids ingested (sports drink vs water) and NSAID use were not (abstract, PMID 15829535). 10.1056/NEJMoa043901
- NHS. (2026). Heart palpitations. Heartbeat feels racing, irregular with skipped or extra beats, pounding or fluttering, in the chest, neck or throat; lasts seconds, minutes or longer; usually harmless. Common causes: strenuous exercise, lack of sleep, stress and anxiety, medicines, alcohol, caffeine, nicotine and recreational drugs; sometimes menopause or pregnancy; can be caused by iron deficiency anaemia, an overactive thyroid, an arrhythmia or other heart problems. See a GP if they keep coming back or happen more often, last longer than a few minutes, you have a heart condition, or there is a history of heart problems in your family. Call 999 or go to A&E if palpitations do not go away or come with chest pain, shortness of breath, feeling faint or fainting; if these symptoms have stopped, ask for an urgent GP appointment. Do not drive to A&E. Avoiding triggers such as stress, smoking, caffeine and alcohol can help when no condition is the cause; an ECG helps find the cause (page last reviewed 17 March 2026). www.nhs.uk/symptoms/heart-palpitations
- Casa, D. J., DeMartini, J. K., Bergeron, M. F., Csillan, D., Eichner, E. R., Lopez, R. M., Ferrara, M. S., Miller, K. C., O'Connor, F., Sawka, M. N., & Yeargin, S. W. (2015). National Athletic Trainers' Association position statement: Exertional heat illnesses. Journal of Athletic Training, 50(9), 986-1000. 10.4085/1062-6050-50.9.07
- Warden, S. J., Davis, I. S., & Fredericson, M. (2014). Management and prevention of bone stress injuries in long-distance runners. Journal of Orthopaedic & Sports Physical Therapy, 44(10), 749-765. Clinical commentary (level of evidence 5): 'Bone stress injury (BSI) represents the inability of bone to withstand repetitive loading, which results in structural fatigue and localized bone pain and tenderness. A BSI occurs along a pathology continuum that begins with a stress reaction, which can progress to a stress fracture and, ultimately, a complete bone fracture.' 'A BSI results from disruption of the homeostasis between microdamage formation and its removal'; the load applied to bone is the more modifiable side, through training-program design, reducing impact forces (running softer or with a higher stride rate) and strengthening local muscles such as the calf for tibial BSIs. Most BSIs heal after a period of modified loading and a progressive return to running, but they tend to recur (abstract, PMID 25103133). 10.2519/jospt.2014.5334
- Riebe, D., Franklin, B. A., Thompson, P. D., Garber, C. E., Whitfield, G. P., Magal, M., & Pescatello, L. S. (2015). Updating ACSM's recommendations for exercise preparticipation health screening. Medicine & Science in Sports & Exercise, 47(11), 2473-2479. ACSM roundtable: 'there is considerable evidence that exercise is safe for most people and has many associated health and fitness benefits; exercise-related cardiovascular events are often preceded by warning signs/symptoms; and the cardiovascular risks associated with exercise lessen as individuals become more physically active/fit.' The new screening model rests on current activity level, the presence of signs or symptoms or known cardiovascular, metabolic or renal disease, and the desired exercise intensity (abstract, PMID 26473759). 10.1249/MSS.0000000000000664