by
Nam Nguyen
Over
the summer of 2001 I trained for the Honolulu Marathon in
December. I had never run a marathon
before, and trusted my training and health in the hands of
the "veteran" trainers affiliated with the AIDS
Marathon program. I have heard conflicting stories about
the hazards and benefits of marathon running, mostly passed
by word of mouth, and occasionally backed by the "authoritive" voice
of Runner’s Magazine. This paper allows me to
personally investigate the literature on the effects of intensive
running.
In reviewing the literature, I have come
to appreciate the depth and breadth of material available
on the subject. Obviously, I cannot cover all 139 articles
on BIOSIS alone, but narrowed down the material into six
categories: General Health Needs to think about before embarking
on a training program, Effects on Bone, Effects on Muscles
and more specifically, Effects on Cardiovascular Fitness,
Effects on the Immune System, and a final section on Endorphins
and Mental Health.
Although
there may be conflicting evidence on whether marathon running
in itself is beneficial or overly taxing on the body, those
arguments are assuming that the runner is taking all necessary
precautions to avoid injury, such as stretching and wearing
supportive shoes. A 1993 study by Brooks, et al (1) indicates
that during marathon, trained distance runners rely almost
exclusively on carbohydrates for fuel used during exertion
rather than fat. It may be beneficial, therefore, to load
up on carbohydrates before a race to make sure once has enough
fuel. How much fuel needed is, according to a study by Hill
et al (3), between 6095 and 6550 kcalcenter dotd-1. This
study was done on only one person, using doubly labeled water
technique, which is not without flaws, so obviously much
more research needs to be done, but it is a good benchmark
to start at. It has also been shown that during a race that
serum and urinary magnesium and iron concentrations are decreased
(4), so supplementary metals and minerals may be required
prior and during races so that endurance athletes avoid unnecessary
stress on the body.
Aside from nutritional needs, environment
also plays a role in general health. I’ve already mentioned
stretching and warming up, but injuries can also be prevented
by avoiding certain conditions. After earlier race starting
times had been implemented in 1991 at Grandma’s Marathon
in Duluth, Minnesota, the odds of needing medical assistance
due to heat related illness decreased each year.(5)
It seems that some of the basic things
one needs to do to prepare for a marathon is to prepare for
the energy needed by eating carbohydrates, take care to replenish
metals and minerals, and by running earlier in the morning.
There are various studies on the effects
of strenuous activity such as marathon running on bones.
The articles I concentrated on dealt mainly with the effects
on bone mass density. While a study (6) found that running
positively affects changes in spinal cancellous bone mass
density, another, studying the calcaneus, found no lasting
evidence of structural change following a marathon (7). These
studies cannot be taken to contradict each other, however,
because they concentrate on different bone structures of
the body, which respond and deal with different types and
magnitudes of stresses when a person is running. Although
no conclusion can really be made with just two studies, it
seems that running can be beneficial by increasing bone mass
density, and although it did not do so in the calcaneus,
at least did not affect density adversely.
Other studies concentrated on osteogenic
activities related to marathon running. The logical connection
would be that increased osteogenic activity would lead to
stronger bones while decreased activity would harm them.
Bones are not static structures, constantly forming new cells,
and in the process, breaking down old ones to remain healthy
and adjust to stress loads. It also must be kept in
mind that marathon running is different from light, low-frequency
exercise when dealing with osteogenic activities. Bone formation
and re-absorption decreases with light low-frequency exercise,
but increases after intense physical stress such as marathon
running (8). This suggests that intense exercise increases
overall bone formation, a conclusion that a study of 18 elite
marathon runners in The Marathon World Cup in 1993 agreed
with (9). While it may seem a paradox that light exercise
would decrease osteogenic activities while high intensity
exercise would increase it, the former study only extended
for 5 days after a marathon and the decrease in activity
may be due to a short-term reaction to fatigue. Long-term
strenuous exercise may prompt the body to deal with such
activity with the long term solution of increased osteogenic
capacity, which is what the Marathon World Cup survey concluded.
That is simply a hypothesis of mine, and more research should
be done in this area to further understand the effects of
marathon running and running in general.
There is no doubt that running a marathon
is a taxing experience, and many people are studying the
effects of fatigue on the muscles. These studies fall into
those looking at oxidative damage produced or due to metabolism
within muscles which produces energy and inflammatory reactions.
It is an easy assumption to make that all markers of oxidative
damage indicate harmful effects, but in viewing the material,
it should be kept in mind that oxidants are found naturally
in the body, used mainly by the immune system to keep us
healthy. An increased expression of inducible nitric oxide
synthase during running exercise seems related to inflammatory
response, but whether it is an immunoregulatory response
or a cell-damaging reaction is not known (10). An analysis
of 8-hydroxydeoxygualnosine levels, an indicator of oxidative
DNA damage, of super-marathon runners during a four day race
saw significant increases for the first three days and then
a significant decrease on the fourth day. A super-marathon
is on a completely different intensity and endurance level
than a marathon, and so the results of the study, that extreme
physical exercise causes oxidative DNA damage to well trained
athletes may not apply entirely to marathon runners, but
is something that cannot be ignored. Unfortunately I do not
have an article dealing with marathons, but that would be
interesting to look into. The good side however, is that
this study also concluded that "repeated extreme exercise-induced
oxidative stress does not propagate an increase of urinary
8-OHdG, but rather causes an adaptation leading to normalization
of oxidative DNA damages" (11). This opinion, that intensive
regular exercise leads to a normalization of oxidative DNA
damage may have support in inflammatory reactions. A study
focusing on C-reactive protein as an indicator of inflammatory
reaction found that the decrease of CRP after training "suggests
that intensive regular exercise has a systemic anti-inflammatory
effect"(12). In general, resting correlates with a decline
in radicals, although some runners did not experience a decrease
even eight days after a race (13).
I can personally attest to swelling and
inflammation after a marathon! It is a comforting thought
that the body can adjust to the levels of exercise and that
training will reduce inflammation (I can attest to that too).
However, the literature on oxidative damage, especially in
the context of oxidative DNA damage, which may be carcinogenic,
is also something to worry about. This is another topic where
the research is far from being done.
EFFECT ON CARDIAC FITNESS
Although the heart can be generally counted
as muscle, being one of the hardest working muscles in the
body, I thought it best to put it in a category of its own.
The heart is a handful in itself. (Yes, bad pun intended.)
The literature in this area falls mainly into two categories:
that trying to see if there is a protective cardiovascular
action of exercise and that of seeing the risks on the cardiovascular
system from intense endurance exercise. In well-conditioned,
middle-aged runners, cardiovascular risk factors are related
to degree of fitness, measured by marathon finishing times
(14). People who finish slower are more likely to have a
cardiac event. A study involving middle-aged male marathon
runners observing prothrombotic markers noticed that fibronolytic
activity doubled within four hours after competition, and
noted that persistence of procoagulant effects "may
trigger acute cardiac events associated with strenuous exercise" (15).
While prothrombotic markers may be an indicator of potential
cardiac infarction, it is often hard to discern whether or
not a runner is at risk. Indicators such as myoglobin and
serum creatine kinase MB isoenyme levels are used as indicators
for risk of myocardial infarction, but lack specificity in
trained runners and should be interpreted with caution (16).
On the other hand, an analysis of relative
risks associated with underlying cardiovascular disease and
intense endurance running found that the risk of sudden cardiac
death in runners with potentially lethal cardiac disease
was only 1 in 50,000. It is as little as 1/100th the annual
overall risk associated with living, either with or without
heart disease (17). The article even goes further to conclude
that routine screening for cardiovascular disease in long-distance
runners may not be justifiable. Risks for athletes who have
undetected cardiac disease are a distinct category, although
it is helpful to know that if they, who do have disease,
run such low risks, at least according to a study, then the
risks for healthy individuals may not be that high either.
It is even suggested that marathon running does not adversely
affect the hearts of healthy individuals, regardless of training
levels (18). Even more promising is that the formation of
cyclic guanosine monophosphate, a potential indicator of
cardiovascular fitness, increased with training in runners
(19). This may be responsible for some protective cardiovascular
actions of exercise. It must be noted that the range of articles
reviewed dealt with many different indicators, and different
types of subjects. Some concentrated on middle-aged men,
some concentrated on trained athletes while others took a
range of less trained to well trained athletes, others included
women in their studies, while some excluded them. None had
very large sample sizes, except perhaps the analysis of risks
in running for people with cardiac disease. The results are
varied and cannot really be compared to each other, but can
provide a general overview of the issues involved with cardiac
health and running.
As
more often than not, all systems are related to each other,
and it is hard to completely separate each system. The effects
of running on the immune system is distinctly related to
inflammatory response and muscle tissue, but the articles
reviewed in this category are more solely related to immune
cells and the effects of exercise upon them while still keeping
in mind their relation to inflammatory response. It would
seem from the literature that the immune system is put on
overtime due to running. Marathon runners seem to maintain
or even enhance their intestinal immunoglobulin producing
cells shortly after running. This may reflect stress-induced
hormonal influence or an immune response to an elevated influx
of antigens (20). Cortisol levels are elevated relative to
controls three hours after intense running, which may cause
the increase of immune cell production and neutrophil/lymphocyte
ratios increase after running as well (21) although lymphocyte
proliferative response was decreased in comparison to controls.
The decreased lymphocyte proliferative response may be due
to leucocytosis that was stress dependent and correlates
with increased serum cortisol levels (22). It would seem
that immediately after running, the immune system is in high
gear, for whatever reason, but is then suppressed by the
addition of cortisol. Cortisol reduces swelling. Articles
such as the one dealing with immunoglobulin producing cells
may also indicate a heightened ability to deal with microbiological
invaders, suggesting a stronger immune system as a result
of exercise, but this is conjecture on my part. Of all the
articles, I feel least able to understand and interpret the
ones dealing with immunity because it is not an area where
I have done much studying.
Everyone has heard of a runner’s
high, and the soothing effects of running. Some articles
seem to give a scientific basis to these feelings of contentment,
exhilaration, and well-being (not to mention sudden absence
of tiredness or pain!) associated with running. Incremental
exhausting and prolonged exhausting endurance exercise such
as marathon running induced an increase of similar magnitude
in beta-endorphin and adrenocorticotropic concentration (23).
Along with beta-endorphin, it also increases hermophin-7
as well (24). It is interesting to note that beta-endorphins
and hermophins are endogenous opioids found in the body,
producing similar effects of exogenous opiates, such as analgesia
and reduction of anxiety. This effect is shown to be similar
in males and females, although female have higher baselines
of beta-endorphin and adrenocorticotropic concentrations
so while their levels rise to the same concentrations as
that of males, there is less of an overall increase (25).
Unlike most areas covered in this paper, there was found
no conflicting evidence for the increase of endorphins in
the system during running. This is not a statement that they
do not exist, just that I did not find any, which was unusual
enough to note. The soothing effects of running can be strongly
asserted in the scientific literature as well as the colloquial
one. To test the long-term effects of such an activity, a
study followed fifteen marathon runners for twenty-nine years
and tested them on several psychological variables such as
tension, depression, anger, fatigue and confusion. The study
concluded that a lifetime of regular physical activity is
associated with desirable physical and mental health (26).
Although the sample size is small and not all runners are
male or started running since high school, but it is an encouraging
thought nevertheless that it may apply to a more general
population.
Running a marathon is no small task. Even
walking once would almost seem harder. There are many aspects
involved in participating in one, and like any other sport,
it seems to come with its associated risks and benefits.
The effects on mental well-being seem very positive, while
having varying degrees of beneficial effects on the heart
and bones. The most stress due to running seems to be taken
up, not surprisingly, by the immune system and the muscles.
However, hopefully paying attention to the energetic, nutritional,
and mineral requirements, as well as paying attention to
environmental effects of such a race would alleviate the
negative effects of running 26.2 miles in a day.
—copyright © 2002, Nam Nguyen
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