There’s a reason we list gender and sex as separate topics in the title.  That’s because, unlike what you might think, it’s not as simple as XX and XY chromosomes leading to male and female bodies which makes men and women. It’s biology–which is  a notoriously complicated mess. It’s psychology–even more complicated! And it’s society all wrapped together.  

Welcome to a very special edition of the SciRunner podcast featuring our first guest Tessa Fisher.  Probably the world’s only queer, trans astrobiologist, the Arizona State University PhD student and avid runner helps Katie and Nigel explore the science and sociology behind gender and running.  It’s a long one.  So long that we’re actually splitting it into two episodes!  Stay tuned for part 2 where we discuss running and transition.

What did we find?

On average, men run faster than women, and the difference seems to be more due to testosterone levels than different body characteristics (e.g. body fat). Sex lies on a spectrum, and the world’s experts on the topic report 20+ ways that someone can be somewhere between male and female. You can have XY chromosomes, have high testosterone levels, but be so insensitive to the effects that your external anatomy is completely female. This makes it hard to define gender categories in runners.  In addition, the effects of endogenous (self-produced) testosterone on female running performance aren’t well understood, and don’t seem to have much of an effect.

Science discussed:

Position statement about sex and gender by the American Physiological Society

Male runners are about 14% faster than female runners

Body fat only explains about third of the difference in speed difference between men and women

Male greyhounds only run about 0.7% faster than female greyhounds

Overview of testosterone effects on running performance

Review of gender and running–hematocrit and testosterone.

Review of how sex is a spectrum

Article talking about how there is no single biological criterion for sex

Testosterone levels in female athletes vs. non-athletes

Height and Y chromosomes in female athletes

Olympic policies have led to medically unnecessary treatment of high testosterone in women

The history of gender testing in the Olympics & the IAAF concluding testosterone wasn’t important

Historical intersex conditions and women runners





First it starts with a 5K. Next thing you know your child has moved onto a 10K, then a half marathon, then even a full marathon. Spending hours every week feeding this disgusting habit. And by disgusting I mean nipple chafing and foot blisters.  

Why do people run? In our last episode we talked about the health benefits of running, which I’m pretty certain a lot of people probably run for that reason, maybe even exclusively, or at least get started for health reasons — but MAYBE lots of people also run because… well… they get high.

What do we conclude?

It seems pretty clear that you can get high from running.  Now, whether this is relatively mild changes in pain perception, or slightly elevated mood following running, or getting outright blitzed mid-run seems to vary between runners, but it’s good to know at least the mild form is repeatable!  We still don’t really know the mechanisms–there might be endorphins, but that’s a hard thing to be sure of.  Endocannabinoids seem like a pretty likely candidate too, but the case is far from settled!  The best evidence we have suggests that a 30 minute run at 70-80% of your maximum heart rate (not too fast!) seems to make most runners feel good.  

Smoking pot recreationally before running doesn’t seem to have the negative effects you might think it does–since it’s a bronchodilator. But since it also increases heart rate, it doesn’t seem like it would be helpful to smoke up pre race (maybe just for a training run). Whether or not pot is a performance enhancing drug is still being sorted out, but there’s no blaring sign that you *shouldn’t* occasionally smoke up before running if it’s legal in your jurisdiction.  Just take ‘er easy.

Studies mentioned in this episode:

Getting the runner’s high is pretty common

Old definition of the runner’s high as a “transcendental” experience

New definition of runner’s high

The runner’s high as a placebo response

People who think the runner’s high is a myth

Blood plasma levels of endorphins increase after exercise

More endorphin studies

Yet more endorphin studies!

And more!

PET study showing possible endorphins in the brain

Naloxone doesn’t block the mood effects of therunner’s high

Naloxone does seem to block some of the pain relieving effects

Review suggests the endorphin hypothesis has little evidence

A review of the endocannabinoid system

First evidence of endocannabinoid release in runners

Review of exercise and the endocannabinoid system

Optimal running dose for endocannabinoid release

Running in adolescence reduces cannabinoid receptors in rats

Knocking out cannabinoid receptors decreases wheel running in mice

Blocking cannabinoid receptors decreases running in mice

Exercise addition and endocannabinoids

Review of cannabis and sports

Judgement impairment following cannabis use

Cannabis use doesn’t always decrease reaction time

Old Canadian studies on pot use and cycling

Cannabis decreases grip strength

Review of cardiovascular effects of cannabis

Cannabis use increases heart rate

Cannabis is a bronchodilator

Potential use of cannabis as an anti inflammatory drug 

Review of effects of cannabis on exercise performance

Cannabis smoking doesn’t decrease lung function

Cannabis smoking doesn’t seem to have negative lung effects





Every six months or so, headlines proclaiming the doom of people who like to run seem to pop up like little schadenfreude sundaes.  People love to tell runners that all their hard work is likely causing more harm than good, and after the deaths of celebrities like Jim Fixx, Micah True, and even poor old Pheidippides (he of Marathon fame), it is a little scary to contemplate. But how good is the science behind this idea?  Are you really likely to die mid-run?

TL:DR version?

Exercise, any exercise at all, is generally good for you.  It will increase your lifespan, reduce your risk of diabetes, reduce excess weight, and more.  Most people don’t get near enough.  Do some people die during marathons?  Yes, but it’s unclear whether marathons actually elevate your risk of early death–those people had underlying structural abnormalities or atherosclerosis already.  And the clinical significance of any kind of heart damage marker following extreme exercise is unclear–long distance athletes live longer than sedentary or even moderately active people, so it doesn’t appear that these markers mean anything in this population.


  1. What is the right amount of exercise for maximizing lifespan?  “I have no idea — though my answer for 99.99% percent of people would be “More than what you’re doing right now.” — Alex Hutchinson, science writer
  2. Remember Jim Fixx–lots of running won’t fix a bad diet
  3. If you’re feeling weird, talk to you doctor! Some cases of hypertrophic cardiomyopathy and athersclerosis can have symptoms like heartburn, tightness in the chest and arms.

Studies mentioned in the episode:

Pheidippides probably didn’t die

The rate of cardiac arrest in marathons is 1/184,000 participants

Atherosclerotic heart disease tends to be the cause of death during marathons

Marathons prevent deaths from traffic accidents

Cardiovascular disease is the leading cause of death worldwide

Even small amounts of running massively decrease your risk of death from heart disease

Among runners, those who run more need fewer diabetes and cholesterol-lowering drugs

Similarly, more intense running reduces diabetes and cholesterol drug use

Student athletes have fewer heart attacks than the general population

Most people are less active than they think they are

Copenhagen heart health study about risks of strenuous jogging

O’Keefe softens his stance, says 5-6 days of running/wk for total of less than 5 hours is probably ok

Running helps prevent diabetes, high blood pressure, and cardiovascular disease

Marathon runners have higher rates of markers of heart damage

Recreational Boston Marathon runners have elevated markers of heart damage following the race

Ironmans do not cause increases in heart damage markers

Recreational Berlin Marathon runners have elevated markers, but no indication of actual heart damage

Elevated heart damage markers following exercise likely are not meaningful

Cardiac arrhythmias are reduced following marathons

Alex Hutchinson attacks the “running too much” myth


Cover photo by mebrett is licensed under CC BY 2.0


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