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The Effects of Running a Marathon on Memory

nyc-marathonRegular exercise is known to have many advantages.  In addition to the obvious physical benefits such as reducing the risks of heart disease and obesity, it can also benefit the brain.  Regular aerobic exercise releases endorphins, a naturally occurring opiate, to improve an athlete’s mood.  It also increases cognitive function in healthy adults, including improved working memory and executive functioning (Guiney & Machado, 2013).   Marathon running, however, is above and beyond typical regular aerobic exercise; it is considered the ultimate test of fitness.   The marathon always concludes the Olympic games, seeming to symbolize the pinnacle of athleticism. But to complete a marathon, runners put their bodies through the ringer.  They run more mileage than the human body was probably ever designed to run, all in preparation for the 26.2-mile race.  Though regular exercise has positive effects on both the body and the mind, could running a marathon actually be too much exercise?  Beyond sore muscles, marathon runners often experience tendonitis, torn muscles and ligaments, sprains, stress fractures, shin splints, and other injuries.  But might there also be negative cognitive effects of running a marathon?

A study by Teal S. Eich and Janet Metcalfe (2009) from Columbia University investigated the effects of running a marathon on explicit and implicit memory. Implicit memory is knowledge from previously learned skills, such as using language or riding a bike, whereas explicit memory involves the conscious recollection of a specific moment in the past, such as recalling where you spent Thanksgiving last year.  The researchers tested these aspects of cognition because explicit memory deficits have been linked to high levels of cortisol in men (Schwegler et al., 2010), which occur in high-stress situations such as extreme physical activity.  So potentially, they hypothesized, running a marathon might severely impair explicit memory.

Additionally, they wondered about marathon running’s effects on implicit memory, because individuals with brain damage and amnesia show deficits in explicit memory while maintaining implicit memory.  So might marathon running make an individual show a similar cognitive state as an individual with brain damage?

Eich and Metcalfe tested a group of marathon runners with explicit and implicit memory tasks immediately after running a marathon.  They also tested a control group of marathon runners 1-3 days before running a marathon, in order to control for fitness, socioeconomic status, or other factors that might differ between people who run marathons and those who do not.  Results of the study showed that immediately after completing a marathon, athletes have simultaneously heightened implicit memory, but impaired explicit memory.

The cognitive effects of running a marathon are somewhat similar to having damage to your hippocampus, the area of the brain where long-term memories are formed; for both situations, implicit and explicit memories dissociate.  It is almost as if such strenuous exercise creates temporary brain damage.

It is understandable that explicit memory is diminished, because the stresses of a marathon likely deplete the body and brain of much of its resources and energy.  Oddly, though, not only does implicit memory not decrease; it actually increases.  It is not entirely clear why this phenomenon occurs.  Why would athletic stress hinder one’s ability to recall what happened yesterday, but increase one’s ability to ride a bike?  Perhaps there is an evolutionary, survival-based backing behind this phenomenon.   For example, heightened implicit memory after strenuous exercise, such as running from a carnivorous animal, might be an adaptation that helped primitive mankind’s survival.  While most explicit cognitive resources might have been exhausted in order to avoid becoming something’s dinner, implicit memory might be all that remains, and therefore become more important.  Yet, survival processing has been shown to increase explicit memory but have no effect on implicit memory (Tse & Altarriba, 2010).

Running 26.2 miles is not a simple or natural task, and unsurprisingly alters brain function.  Does the fact that it temporarily diminishes explicit memory and dissociates explicit and implicit memories mean that such rigorous activity as actually bad for you?  Before such conclusive statements can be made against marathon running, more research needs to be conducted.  For example, how long do the deficits in explicit memory last?  Does running multiple marathons increase the deficit? And are these deficits significant enough to impair one’s daily life?  Still, the likelihood that the consequences of marathon running outweigh the benefits seems slim.

 

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References

Eich, T. S., Metcalfe, J. (2009). Effects of the stress of marathon running on implicit and explicit memory.  Psychonomic Bulletin & Review, 16 (3), 475-479. doi:10.3758/PBR.16.3.475

Guiney, H., & Machado, L. (2013). Benefits of regular aerobic exercise for executive functioning in healthy populations.  Psychonomic Bulletin & Review, 20(1), 73-86. doi:http://dx.doi.org/10.3758/s13423-012-0345-4

Schwegler, K., Ettlin, D., Buser, I., Klaghofer, R., Goetzmann, L., Buddeberg, C., . . . de Quervain, D. J.. (2010). Cortisol reduces recall of explicit contextual pain memory in healthy young men. Psychoneuroendocrinology, 35(8), 1270-1273. doi:http://dx.doi.org/10.1016/j.psyneuen.2010.02.011

Tse, C., & Altarriba, J. (2010). Does survival processing enhance implicit memory? Memory & Cognition, 38(8), 1110-1121. doi:http://dx.doi.org/10.3758/MC.38.8.1110

  1. May 19th, 2013 at 22:34 | #1

    I feel this makes a lot of evolutionary sense as well. When engaging in continuous strenuous physical activity way would there be a need to remember what’s going on. As mankind was evolving running was a simple mode of transportation, and as such map needed to be formed during the process. From my experience during travel I am generally using implicit memory of direction, rather than constantly think about the next turn.

  2. xzhao
    May 18th, 2013 at 21:51 | #2

    It’d be interesting to pinpoint the exact cutoff between when the amount of exercise is beneficial versus no longer beneficial. For instance, for people who work out in order to relieve stress due to exams, how much is actually good for their situation and how much would push them too far?

    In addition, it’d be interesting to see what tasks the researchers gave the runners to test their explicit memory and how they manipulated effects of transience and forgetting in general. Also, information is maintained better when you’ve been constantly studying it, so when you exercise for long periods of time you remove yourself from that information and focus on other things. Is this a contradicting factor that was considered? If not, it’d be interesting to see what that may imply as well.

  3. May 13th, 2013 at 16:20 | #3

    Another further study that would be interesting to look at would be if other strenuous activities have similar cognitive effects. For example, do explicit and implicit memory performances change after 100-mile bike rides or triathlons?

    Also, Iron Man competitions require running a marathon, IN ADDITION to cycling 112 miles and swimming 2.4 miles. Would explicit memory be even lower, while implicit memory is even higher, or is there a cap on how much physical activity can affect memory?

  4. May 10th, 2013 at 10:05 | #4

    This is a really interesting study! As a distance runner myself it is interesting to hear about how long runs can effect the brain. I wonder if there is a difference between well-trained marathon runners versus beginners? Perhaps runners that have a lot of experience have also trained their brains to minimize negative cognitive impacts as they are well prepared for their race. On the other hand, perhaps these runners have the greatest effects on explicit memory as they also have higher milage. It would also be interesting to see whether the findings are replicated for long-distance runners who don’t compete–is it the race that impairs their explicit memory? Or the running itself? Finally, what can be done to mitigate these negative impacts?

  5. May 4th, 2013 at 11:17 | #5

    This is a really fascinating study about the effects that rigorous exercise can have on cognitive function. I wonder how much of the explicit memory deficits can be attributed to the emotions associated with completing the 26.2 mile course. For marathoners, reaching the finish is a huge accomplishment that can bring a runners high or extreme frustration depending on performance. I think that intensely emotional situations lend themselves to poor focus on many cognitive tests regardless of the situation. I believe it would be beneficial to conduct similar studies after races of varying lengths from sprints up to 100 mile ultra races to determine whether it is simply physical exhaustion or really deficits in nutritional stores that can cause the impairments.

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