Research Blog

Memory Loss, Anxiety Reduction in Middle-Aged Running Mice

Running is shown by one study to increase memory, reduce anxiety, raise stability via increased brains levels of neurotrophic factor BDNF.  

Running has been shown by several studies to increase neurogenesis (proliferation of new neurons) in the brain, specifically the dentate gyrus in the hippocampus. A decrease in neurogenesis later in life has been linked with memory loss.  

A recent study looked at the affects of 6 months of running on neurogenesis and chemistry of brain sections as well as behaviors dependent on brain function (Running throughout Middle-Age Improves Memory function, Hippocampal Neurogenesis, and BDNF Levels in Female C57BI/6J Mice, 2012; Michael W. Marlatt, et al.).

The mice were tested for behavioral changes after one month and six months of voluntary running-wheel training. Many behavioral changes were significant only after six months of training. For example, the running mice were significantly better at the Morris water maze after six months of training, but not after one month of training. How does the water maze work?  Mice were placed in a water bath with a target. After finding the target they were placed back in the water bath at a later date. The mice were tracked with a video camera and the amount of time in the target quadrant was recorded. After six months of training the running mice showed significantly more preference for the target quadrant. This suggests that these middle aged running mice had a greater memory retention.

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Time spent in quadrants in the Morris water maze.  Only the 6 month running mice spent significantly more time in the target quadrant.  

To test for anxiety, mice were placed in an open field an observed. The ratio of time spent in the center of the field to the periphery of the wall was calculated.  Mice that spent more time in the center of the field would be expected to have less anxiety, while mice that spent time hiding along the wall would have more anxiety. The running mice were found to spend more time in the center of the field than their control counterparts at both one month and six months of voluntary exercise training. This supports previous studies showing that running reduces stress and anxiety.

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Falls on a rotarod after 15 seconds in running mice (dark grey) and resting mice (light grey).

The running mice were found to be stronger and better balanced. This was tested with a rotarod. Mice spent 15 seconds on the rotarod and the number of falls were recorded.  The running mice fell about a fifth as much as the control mice as the figure above demonstrates.  

The researchers then looked at brain sections of the hippocampus to explain the behavioral differences. BrdU (an agent that gets incorporated into the DNA of new nuclei) was used to look for new neurons. Running mice had significantly higher levels of BrdU in the dentate gyrus of the hippocampus. In addition, DCX, a neural marker, was found to be slightly higher after 6 months of voluntary exercise training.  Finally, neurotrophin factor BDNF was measured. BDNF aids in keeping neurons healthy. The running mice had significantly higher levels of BDNF.

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The dentate gyrus with DCX and DAPI immunochemistry.

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A Running mice showed increased levels of neurogenesis marker BrdU B BrdU co-localized with NeuN neural marker C DCX in D neurons D DCX in type C neurons

In conclusion, this study found that six months of voluntary running raised memory retention, decreased anxiety and increased stability in middle aged mice. The hippocampus was found to have increased levels of neurogenesis, BDNF and DCX.

The Physiology of Icing Sore Muscles

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Meb Keflezighi (right, winning the 2009 NYC marathon) credits much of his success to icing.

About a year ago I met Meb Keflezighi, one of the greatest American marathon runners of all-time, while training at Mammoth Mountain in California. Since then the 37 year-old stud has had a very successful season culminating in a fourth place finish at the 2012 London Olympics. During our meeting he stressed the importance of icing on his success. Therefore, I was not too surprised that Meb emphasized his devotion to icing during media interviews after winning the 2012 American Olympic marathon trials. Meb is unquestioably one of the world's most elite marathon runners. However, the question reains: What part has icing played on Meb's running career?

Although studies looking at the effects of icing, or cryotherapy, have had somewhat conflicting results, most studies have found icing following exercise-induced muscle damage to be beneficial. The extent of muscle damage peaks between 24 and 72 hours following strenuous exercise. Exercise-induced muscle damage includes sarcolemma disruption, fragmentation of the sarcoplasmic reticulum, lesions of the plasma membrane cytoskeletal damage and swollen mitochondria. Outside the muscle fiber there may be swelling due to an increase in blood flow and capillary permeability.  

One study looked at the multi-day effects of icing on exercise-induced muscle damage (Effects of cold water immersion on the symptoms of exercise-induced muscle damage, 1999, Roger Eston and Daniel Peters). The study used 15 female subjects and endurance exercised their biceps. The cryotherapy group submerged their exercised arm into a tub of 15 degrees Celsius  water for 15 minutes. This treatment was administered immediately after the bout of exercise and every 12 hours thereafter for 3 days.

The study results show that creatine kinase activity, a predictor of muscle damage, was lower in the cryotherapy treated group two and three days after the bout of exercise. The graph below shows these results.

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Eston and Peters also showed that the arm circumference and tenderness were not significantly affected. However, arm strength returned to baseline much faster in the cryotherapy group. This is of particular interest to athletes who often are expected to complete consecutive workouts in a 72 hour timeframe.  The difference was significant: after 72 hours the control group had a mean isometric strength that was 86% of baseline while the cryotherapy group had a mean isometric strength that was 111% of baseline.

A more recent study on the subject of icing measured blood flow, temperature and muscle endurance in cryotherapy treated and control groups (Changes in Blood Flow, Temperature and Muscle Endurance in Association with Cryotherapy, 2009, Masahiro Utsunomiya, et al.). In this Japanese study three groups were established: resting group (10 minute rest), 2-minute cooling group (2 minute icing and 8 minutes of rest) and 10-minute cooling group (10 minutes of icing).  Endurance was significantly boosted by icing. After ten minutes of rest the resting group performed at 59.2% of the initial test, the 2-minute cooling group 73.1% of initial test and the 10-minute cooling group 80.7% of the initial test. This suggests that the effects of icing are immediate.  Decreases in deep part temperature and tissue circulating volume were also observed as duration of icing increased.

The authors suggested that the cooling decreased oxygen consumption and cellular metabolism. This would potentially increase muscle endurance.  However,  an EMG signal processed with Fast Fourier Transformation saw no significant differences between the groups during the second bout of training. The authors hypothesized that the lack of significance means differences in endurance could have been the result of lowering myogenic pain instead of an increase in physiological fatigue.

The Running Mechanics of Elite African and Caucasian Marathoners

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The mechanics of the perfect running form we should all strive for...

An interesting video comparing the running mechanics of some of the fastest African and Caucasian marathon runners including Ryan Hall and Meb. This video offers suggestions for enhancing performance and preventing injuries. Brought to  you by Somax Performance Institute, a renowned sports science center just north of San Francisco.  Enjoy!


Despite Increased Participation, Marathon Mortality Remains Constant

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Marathon participation has been growing swiftly over the last decade. Despite the increase in participants (including "ridiculously photogenic guy" 10k finisher to the right), mortality rate has not increased and average finish time has improved.

The marathon has seen tremendous growth in participation over the last decade. As the figure below shows, the number of marathon participants has soared from 299,000 participants in 2000 to 475,000 in 2009. This growth has been ruled in part by an increase in awareness of the benefits of running, many of which have been reported on this site. Despite the health benefits, one study found that 90% of marathon participants reported suffering a musculoskeletal or other participation-related injury prior to or during the marathon (Mortality Among Marathon Runners in the United States, 2000-2009. Published 2012. Simon C. Mathews, et al). In addition, the media has reported on several high-profile marathon deaths.

It might be supposed that given the increase in participants, mortality rate in marathon participants might rise due to a greater proportion of unqualified runners.  A recent study found this not to be the case. In fact, not only have mortality rates remained constant over the last decade (as the figure below depicts), but average finish time has slightly decreased.

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The rate of mortality remains slightly higher in males than females. The median age of mortality was 41.5 years old. The average distance completed before death was 22.5 miles. The most common cause of death among participants 45 years or older was myocardial infarction or coronary atherosclerosis (a heart attack). For younger participants the most common cause of death was cardiac arrest. Interestingly, participants who died within 24 hours of completing the marathon had an average finish time below the average of all marathon finishers. This suggests that physical fitness does not predict risk of marathon mortality, although it may be a sign of overexertion.  

In conclusion, mortality rates in marathon finishers remains very low. Over the last decade there was 0.75 deaths per 100,000 finishers.  By comparison, motor vehicle fatalities represent 11.2 deaths per a population of 100,000.  Only 28 deaths of marathon participants during or in the 24 hours following their race have been reported in the last decade. This is an indication of the rarity of marathon fatalities, and also the limits of drawing demographic conclusions on the basis of such a small sample size. Marathon mortalities prevalence in the media is the result of several high profile incidents. Overall marathon running is safe regardless of age or physical fitness.

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