Human Limits

Exploring performance and health with Michael J. Joyner, M.D.

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Archive for the ‘Physiology’ Category

A Deep Dive & Risk

Last weekend there was a “60 Minutes” segment on the emerging sport of free diving.  That plus the death of free diver Nicholas Mevoli got me thinking about risk and extreme sports.  When things like this happen sometimes I get calls from the press and almost always my physician colleagues want to know “why anyone would try these things?”  Here are the ideas I cover in response to that question.


The Power of a Subculture

People who attempt to set extreme records or push themselves to the limit are usually part of an extreme and somewhat closed subculture.   Their friends and peer group share an intense interest in an activity and it becomes literally what they eat, breath and dream about.   A question like “how are you today?” from a casual friend or co-worker is frequently answered with something like “pretty good, I did a hard 15 mile run first thing this morning, we will see how the 10 miler this afternoon goes.”  This might be seen as an odd response in the real world, but totally normal in an extreme athletic subculture.


That sort of dialogue is an example from running but similar discussions can be had with those who are really committed to just about anything.   If you have never been part of an extreme athletic subculture three books that describe them in detail are “Muscle”, “Once a Runner”, and the recent the “Secret Race” by Tour de France rider Tyler Hamilton.  So, there is plenty of social reinforcement to “go for it” from the subcultures that people who are committed live in.


My Neurotransmitters Made Me Do It

One of the hallmarks of traditional addiction is the need to use ever more external stimulus to get the same satisfaction from whatever you are addicted too.   Traditional addiction to drugs rewires brain circuitry and neurochemistry to make this happen and there is evidence that gambling can do the same thing to susceptible individuals.  For many a peak and intense athletic experience is sometimes followed by a letdown as the excitement associated with the planning, training, and anticipation of the big event vanish afterward.   The obvious solution to this problem is to find an incremental challenge and start the whole process again.   Parallels with gambling seem appropriate here and when you mix what is happening in the brain with the right subculture it is pretty easy to see how the need to do ever more extreme things happens.


The Environment

A lot of disasters and deaths occur in extreme environments.   Think altitude, diving, hot and cold.  There are tremendous physiological adaptations that can be activated both acutely and in response to training that help us do more or go longer in extreme environments, but when things fail they can fail catastrophically.   There is a quote about bankruptcy from the “Sun Also Rises” by Earnest Hemingway that applies to physiological responses to extreme challenges:


“How did you go bankrupt?  Two ways. Gradually, then suddenly.”


A classic example of this is watching soldiers faint while at attention on a hot day or seeing a patient respond to potentially life threatening blood loss.  If you were to measure the vital signs they would be pretty normal until just before loss of consciousness when there is a sudden drop in blood pressure.  When this happens many of the physiological systems that are compensating for the challenges of not enough blood returning to the heart fail essentially at the same time.  You can tell a similar story about catastrophic physiological failure in response to other severe stresses as well.   So, people feel OK until they don’t and in extreme environments the distance between OK and death is not that far.


You Are On Your Own

Of the people injured in the Boston Marathon bombing essentially everyone who made it to the hospital alive survived.   This is one of the main lessons from military combat casualty care for civilian medicine.  Extreme sports take place in extreme environments distant from the types of comprehensive medical care that make an incredible array of injuries and illnesses survivable especially in young otherwise healthy patients.   Other things that come to mind are the availability (or lack thereof) of specific equipment and logistical support needed to do challenging things in a safer way.   Getting a lot of hardware and a support crew to a remote location is challenging and sometimes there might be a temptation to try to do more with less.


Risk Amplifies

Extreme environments, the limits of physiology, and logistical issues are all risks but they are all amplified by poor judgment.  I like to tell people that taking four 3% risks at the same time doesn’t mean you have a 12% risk of failure.  Instead the risk is more like 3x3x3x3 or 81%.   This is a theoretical example but things really do seem to multiply while doing extreme things in extreme environments.  Time and time again you hear about people choosing to push it just a bit more prior to a disaster.


I Am All For It

Based on the observations above you might think I oppose people taking on extreme challenges in fact I am all for it.  Back in 2011 when Diana Niad was attempting to swim from Cuba to Florida I commented to PBS that questions about “why” do it


“miss the point, at some level, you’ve got to admire anybody who wants to test the limits of human potential in general, and her own limits, in specific…It’s a good thing we’re not all average.”


That having been said, I just want people to understand what they are getting into and avoid getting sucked up by their subculture and neurochemistry into challenges they are not prepared for in truly unforgiving environments.

A View on Blood Doping

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Elite Octogenarians!

A number of recent posts have focused on what might be called the “geopolitics” of healthcare and the Federal budget in the United States and offered analysis and ideas about how things like sin taxes and insurance plans might incent healthier behavior.   Today I want to get back to human performance and elite athletes, topics that were covered in detail last summer during the Olympics.   The twist here is that I want to talk about elite 80 year old endurance athletes.

In an amazing scientific paper, scientists from Ball State University in Indiana, along with collaborators in Sweden, found 9 elite cross-country skiers (including an Olympic Champion) who had remained highly physically active and trained throughout life.   On average these individuals had VO2  max values of 38 ml/kg/min.  This is a value similar to that seen in sedentary men in their teens and twenties.   It is also a value about 80% higher than the values seen in sedentary 80 year olds.   VO2 max is a marker of the ability of the heart and lungs to deliver oxygen to exercising muscles and also the ability of the muscles to use oxygen.   A simple analogy is that VO2 max somewhat similar to a measure of horse power for a car.   With more horse power you can do more!

Below is a figure from the paper.   The key point is that a VO2 max value of about 15 is required to be functionally independent and that the untrained octogenarians were likely drifting downward toward that value, while the athletes had plenty of reserve and extra capacity.    Another key point that my colleague Jill Barnes and I made in an editorial on this paper is that while the high values in the athlete’s likely had a component of “natural ability” or “genetics”, it should be possible for highly active regular guys in their late 70s and 80s to have VO2 max in the high 20s or lower 30s, or about twice the value needed to remain independent.

This paper raises a lot of questions about things like what kept these men motivated to stay so active throughout life.  It will also be interesting to see what the data in older women looks like as more women participate in endurance sports throughout life.    While there is no fountain of youth, the data in these older elite athletes is just another example of what lifelong exercise can do.



Exercise and Brain Size

A few weeks ago I pointed out that age associated cognitive impairment and Alzheimer’s disease shared many risk factors with cardiovascular disease.    The brain shrinks as it ages and it shrinks faster in people with cognitive impairment and Alzheimer’s disease.   There are also other subtle structural changes associated with aging and cognitive decline.   A recent paper in the journal Neurology reported on how physical activity affects brain volume in almost 700 people in their 70s who were studied in England.

“A higher level of physical activity was associated with higher fractional anisotropy (a marker of brain structural integrity), larger gray and normal appearing white matter volumes, less atrophy, and lower white matter lesion load.  The physical activity associations with atrophy, gray matter, and white matter lesion remained significant after adjustment for covariates, including age, social class, and health status…..”


Conclusions: In this large, narrow-age sample of adults in their 70s, physical activity was associated with less atrophy and white matter lesion.  Its role as a potential neuroprotective factor is supported; however, the direction of causation is unclear from this observational study. “

The paper goes on to discuss factors that might be responsible for the positive effects of physical activity on brain size and function.  There is evidence that exercise stimulates the growth of new brain cells and improves connections between brain cells, so no major surprises here.

The paper also mentions that exercise may also improve blood flow to the brain.  The figure below is from a study done in my lab by Dr. Jill Barnes.   It shows using a measurement called CVCi, that the ability of the brain blood vessels to relax and vasodilate (usually a good thing) in response to CO2 is lower in healthy 60 somethings vs 20 somethings.  In both age groups a drug called indomethacin reduced the vasodilation in response to CO2.  Blood flow at rest was also lower in the older subjects, or as Dr. Barnes put it:

“Young adults demonstrated greater MCAv (index of blood flow) 55 ± 6 vs. 39 ± 5 cm/s and MCAv reactivity 1.67 ± 0.20 vs. 1.09 ± 0.19 cm·s to hypercapnia (CO2) compared with older adults.”



The next figure I want to show you is from a study on aging and brain blood flow in trained and untrained male subjects.



The authors commented that:

This ∼17% difference between trained and sedentary men amounted to an approximate 10 year reduction in MCAv (blood flow) ‘age’ and was robust to between-group differences in BMI and blood pressure. Regular aerobic-endurance exercise is associated with higher MCAv in men aged 18–79 years.


Summary:  Exercise and physical activity do good things for your brain as you age.  They help you grow new cells and they keep blood flow to the brain high.   One idea is that blood flow is higher because the brain remains bigger in those who are active as they age.   The other interesting thing to note is the “10 year” anti-aging effects of exercise on blood flow.    That number, or perhaps an even higher one, seems to be pretty consistent for the anti-aging effects of exercise on many elements of our physiology.


3 Weeks = 30 Years!

Last week I had the opportunity to attend the “Integrative Biology of Exercise” conference sponsored by the American Physiological Society.   During an excellent talk on how exercise training can modify the changes in heart function with age, Dr. Ben Levine showed classic data from a study done in the middle 1960s known as the Dallas Bed Rest Study.

In this study 5 healthy young men did nothing but bed rest for three weeks while detailed measurements of their cardiovascular function and exercise capacity were measured.    Not surprisingly, cardiac function declined and exercise capacity fell dramatically with bed rest.   The figure below shows what happened to VO2 max which is considered the gold standard measurement of exercise capacity after bed rest.



What is even more interesting about this figure is that when the same subjects were studied 30 years after the original bed rest study, their VO2 max fell more with just three weeks of bed rest than with 30 years of aging.   Below is a video link of Dr. Levine talking about his work on related topics.


 If video does not load, click here.


Another interesting video on the topic of inactivity comes from Dr. Bente Pedersen of the University of Copenhagen.    Her team has conducted an incredible study showing that just two weeks of minimal physical activity can put previously health young men on the path to what might be described as pre-diabetes.    In the video below she discusses these findings and also concepts related to the fit vs. fat topic covered a few posts ago.


If video does not load, click here.


These are terrific talks by scientific leaders who are my friends and colleagues.  One of the great things about the electronic environment is that presentations by such outstanding investigators are available to us all.


Too Much Exercise?

Today’s post was stimulated by an e-mail exchange with Amby Burfoot of Runner’s World on reports over the past few months suggesting that lifelong intensive exercise training might be “bad” and actually increase the risk of heart problems.  The idea is that during exercise adrenaline and related hormones cause the heart to beat faster and harder.  Do this day after day for years and the thinking goes that areas of micro damage might occur.  In addition to leading to small areas of heart damage, there might also be a buildup of calcium in the blood vessels that supply the heart.  So what is the evidence to support these ideas?


First, after extremely prolonged and intense exercise like a marathon or ironman triathlon the pumping ability of the heart can be reduced by a few percent for a few days and there can be a rise in blood levels of substances released from the heart.  However, the pumping function of the heart returns to normal within a week and there is no evidence of long term heart damage.   The blood levels of substances released from the heart also return to normal.  The other tricky thing here is that the skeletal muscles of highly trained athletes undergo biochemical changes that make them more like heart muscle.  The wear and tear on skeletal muscles during a competitive event can then cause a rise in the blood levels of so-called cardiac markers that are in fact released from skeletal muscle and set off all kinds of false alarms about heart damage.


Second, no one is sure exactly what finding calcium in the coronary arteries means in asymptomatic people especially older athletes.   Also, case reports in a few people are hard to interpret and in more controlled studies it appears that the coronary arteries of lifelong ultramarathon runners are a bit bigger than those of non-runners and can also dilate more.   The figure below shows this data, and bigger coronary arteries that relax more are almost certainly a very good thing.


Third, there is some data in animal models that areas of micro damage caused by prolonged intense exercise make the heart more susceptible to dangerous irregular heartbeats.  However, in these studies aversive stimuli (tail shock) were used to get the animals to run so there is the added issue of “mental stress” in addition to exercise.   Also, the animals were doing a training regimen that was truly heroic in terms of both daily duration and intensity and how this translates to what even the most fanatical human might do over 10 or 20 years is unclear.   In other animal models, exercise training tends to protect the heart from irregular beats.


Fourth, when detailed research and data collection is done on who dies during exercise a couple of patterns emerge.  Young people who die suddenly typically have congenital problems with the electrical system in their hearts or defective coronary arteries.   Middle aged and older people typically have evidence of heart disease that in many cases probably started before they became fit or started to train.   There are also cases of heart problems in athletes likely related to acute inflammation of the heart perhaps associated with a viral illness.   However, marathon running as a whole appears to be very safe.


Fifth, all the news is not positive.  There is some evidence that lifelong training is associated with a condition known as lone atrial fibrillation.   However, the data are only suggestive and much bigger and better controlled studies are required on this topic.   This condition while bothersome is typically not life threatening and can be treated.


Perspective:  Over the last few months I have been making the case that one of the biggest public health and ultimately medical problems out there is inactivity.   Is there a cardiac risk associated with being super fit and training a whole lot?  To the extent there is comprehensive and well controlled data the answer appears to be no.  It does appear that in terms of health there are diminishing returns and that people who train “a whole lot” (say more than an hour almost every day) are not  better off than people who just do “a lot” (30-60 minutes most days).  However, people who do a whole lot of training are probably doing it for reasons other than health that include things like a need to compete, a need for time alone, or the need for some sort of big challenge in life.  Not exercising enough is extremely common and dangerous.  By contrast, a life time of exercising “too much” is extremely rare and the evidence to suggest it does long term harm to the heart is pretty speculative.





Live Long and Prosper!

For the last month or so I have been focused on the twin problems of inactivity and obesity.   Today I want to turn the tables on these problems and ask what we know about people who live a long time and remain independent.

It turns out a lot is known about who makes it into their later 80s, 90s or 100.   In other words who lives a long time and remains independent and engaged in life   One of the first people to study this topic was Dr. Lester Breslow who died earlier this year at age 97.   His obituary in the Lancet pointed out that he was a pioneer in public health showing that:


“45-year-olds who adopted six healthy habits—exercise, non-smoking, weight control, adequate sleep, moderation in alcohol use, and breakfasting well—lived longer than people with three or fewer healthy habits.”


Midlife fitness is also important because it reduces the burden of chronic disease as people age and limits the slow drift into disability and functional limitations seen in many older people.    So if you want to be a vigorous older person, be a vigorous middle-aged person.

One of the most interesting studies on this topic comes from the Honolulu Heart Project that has followed about 8,000 Japanese American males born in the early 1900s.  The study started in the middle 60s and has found that only a couple of factors explain who lives a long time and who remains healthy.  Recently the more than 2,000 men who are still alive were studied and it was found that:


“Compared with people who died at the age of ≤79 years, centenarians belonged 2.5 times more often to the highest third of grip strength in midlife, were never smokers, had participated in physical activity outside work, and had a long-lived mother (≥80) Associations for nonagenarians (90 year olds) and octogenarians (80 year olds) were parallel, but weaker.  Statistical modeling showed that mother’s longevity and offspring’s grip strength operated through the same or overlapping pathway to longevity. High midlife grip strength and long-lived mother may indicate resilience to aging, which, combined with healthy lifestyle, increases the probability of extreme longevity.”


Clearly we can’t pick our mothers, but we can chose not to smoke and to remain physically active.   Studies of the Seventh Day Adventists in California who have incorporated the ideas outlined above also live long lives and remain independent into old age.  The slide below show that Adventist men live about 7-8 years longer than other men in California, for women it was about 4-5 years.  About 70% of Adventists men make to age 80 but only 40% of the male population as a whole makes it to age 80.


Summary:  Dr. Breslow was right a few simple behaviors can have a big impact on both how long we live and how well we live.


Interval Walking Training

In several recent posts I have focused on physical activity and health and also the link between obesity and inactivity.  Not a lot of good news if you look at the population statistics, but good news if you think about just how protective exercise and physical activity are both in terms of obesity and also general health.  So, what to do about it?

Perhaps the easiest, cheapest and most convenient form of exercise for most people, especially middle aged (40-65) and older (>65) people is simply walking.   One of the best and most effective ways to get the most out of your walking is to do something called Interval Walking Training (IWT).    This program was developed in the Japan by my close friend and colleague Hiroshi Nose, and his research team to help thousands of people get into better shape.

The idea is to use the same principles that elite endurance athletes and Olympians do when you go for a walk.   To get in the best shape possible the elites do work outs that include multiple 3-5 minute efforts that are nearly all out followed by 2-3 minutes of recovery several times or more per week.   Both scientific studies and practical experience suggests that this is a key to getting in the best possible shape.   It also gives you incredible “bang for the buck” in terms of time, and what works for the elite athletes can work for us all.

The IWT program consists of 5 or more sets of 3 minutes of low-intensity walking followed by fast walking for 3 minutes four or five times per week.    Low intensity walking should be a bit faster than a stroll (40% effort) and higher intensity walking should be at greater than 70% of maximum effort.  Hiroshi’s team has used this approach in a number of their studies and they use heart rate monitors and tracking devices called accelerometers to set and measure exercise intensity.

The figure below is one that shows a typical heart rate response and calorie consumption pattern with this type of training in one of the subjects in Japan.  It was sent to me by Dr. Shizue Masuki and the data was collected by Dr. Ken Miyagawa, they are both key members of the Nose team.  Hiroshi had the following comments about the data:

“As shown in the figure, HR increases to ~130 beats/min during fast walking, but decreases during slow walking, This slow walking or recovery period is important because it motivates a subject to walk at high intensity again. Moreover, because the interval walking training was performed in a hot environment (atmospheric temperature=32 C, RH=60%), HR level increases with increasing body temperature, which makes it difficult to estimate walking intensity from HR accurately. Therefore, it is important to monitor walking intensity with a tri-axial accelerometer.”


Does this work?  To quote one of the early papers on IWT:

“In the IWT group, isometric knee extension increased by 13%, isometric knee flexion by 17%, peak aerobic capacity for cycling by 8%, and peak aerobic capacity for walking by 9%, all of which were significantly greater than the increases observed in the moderate-intensity continuous walking training group. Moreover, the reduction in resting systolic blood pressure was higher for the high-intensity interval walking training group.”

Below is a figure from a collaborative study that we did with the team from Japan.  It shows what happens to selected inactivity associated risk factors when 26 previously sedentary people (average age 54) followed the program about four days per week for three months.   The people with the worst initial values for HbA1c (a diabetes related marker), HDL cholesterol, LDL cholesterol and glucose showed the biggest improvements with IWT.  We also found big increases in exercise capacity and reductions in blood pressure.  So, it worked!


In an article in the New York Times on what the best form of exercise Professor Nose put what IWT can do for people in laymen’s terms.


“Physical fitness — maximal aerobic power and thigh muscle strength — increased by about 20 percent which is sure to make you feel about 10 years younger than before training…….symptoms of lifestyle-related diseases (hypertension, hyperglycemia and obesity) decreased by about 20 percent, and depression scores dropped by half.”


I am closing with a shot of a beautiful park in Matsumoto, Japan where the Nose team is located and where many of the subjects he studies do their walking.