Research Blog

Concussions in the NFL lead to Depression

football


Professional football players who suffer from a concussion are more likely to develop long-term mental health episodes such as depression.






The prevalence of concussions in football has significant mental health ramifications. One concussion occurs every 2.44 NFL games. A study published in the American Journal of Sports Medicine looked at correlations between concussion incidences and depression (Nine-Year Risk of Depression Diagnosis Increases With Increasing Self-Reported Concussions in Retired Professional Football Players, 2012.  Zachary Y. Kerr, et al.).

The study used a 2001 General Health Survey sent to the 3,729 members of the NFL Retired Players Association. A second General Health Survey was sent nine years later in 2010. The surveys asked questions regarding the respondents physical and mental health as well as the number of concussions suffered during their professional careers. Those exhibiting depression in the first survey were not used in the study.

Of the players who reported never having a concussion, only 3.0% were diagnosed with depression. Of those who reported suffering from 10 or more concussions, 26.8% were found to suffer from depression. The relationship between number of self-reported concussions and likelihood of suffering from depression was a linear relationship. Those who reported suffering from 3 or more concussions were twice as likely to suffer from depression as those reporting 1-2 concussions over their career and three times more likely than retired professional football players who did not suffer any concussions over their professional career.

Work on depression in US soldiers in Iraq has suggested there may be a link between tauopathies, tau protein deposits in the brain, and depression.  Repeated head impacts elevate tau protein levels causing neural breakdown.  The physical blow to the head could directly cause neuron death or breakage of neuron connections. Lesions in neural tissue could release harmful biochemical agents.

Concussions often go unreported, especially at the amateur level. This study highlights the importance of monitoring the accumulation of concussions. Other studies have found that concussions can lead to negative personality and cognitive changes. Although the dangers of concussions cannot be underscored enough, with regards to this study on concussions in former NFL players there are several limitations. Most significantly, it is likely that there are many lurking variables that this study could not account for. For example, risky behavior that leads to concussions may be favored in those prone to depression. Career-ending concussion accumulation may lead to depression. Nonetheless, the number of concussions suffered is a significant predictor of depression later in life.  

Most likely, a positive relationship between concussions and depression would apply across sports, competition levels as well as to the military and other non-athletic instances.

Playing on Turf increases Injuries in the NFL

football


A recent study found that NFL games played on turf showed significantly higher rates of lower-leg injuries.






Across sports and competition levels, playing surfaces have been switching from natural grass to artificial turf. This has several health ramifications. Some researchers have speculated that the rubber polymers used in artificial turf cause cancer. Although turf's carcinogenic properties have not been proven, a recent study of NFL players showed that the incidence of knee and ankle injuries is significantly higher in games played on turf.

The first NFL stadium to use an artificial playing surface was the Houston Astrodome in 1966. The surface, called AstroTurf, was manufactured by Monsanto and consisted of a padded-carpet over asphalt. In the 1990's infill surfaces became popular and are widespread today. Infill surfaces consist of an interwoven mat of polyethylene fibers filled with rubber particles. The frequency of NFL games played on turf has been increasing over the years as more NFL stadiums adopt turf. The figure below demonstrates this trend over the previous decade.

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Several studies have looked at injury rates in football players based on field surface. A study done in the early 2000s found that ACL injury rates of high school players are higher in games played on turf. However, the same study found college players were more likely to sustain an injury on grass than turf. A recent study looked at several different lower leg injuries in NFL players using extensive data collected by the injury surveillance system maintained by NFL trainers (An Analysis of Specific Lower Extremity Injury Rates on Grass and FieldTurf Playing Surfaces in National Football League Games : 2000-2009 Seasons; 2012. Elliot B. Hershman, et al.). The study used data from NFL seasons from 2000 to 2009.

The aforementioned study looked at several different lower leg injuries in NFL players: knee sprains, MCL and ACL injuries, ankle sprains, inversions and eversions. Although all injury categories demonstrated a higher frequency in turf than grass, MCL (median collateral ligament) injuries and inversions (an ankle sprain where the ankle is twisted inwards) both did not show significance. The injuries that did show significantly higher prevalence on turf were knee sprains, ACL injuries, ankle sprains and eversions. The figure below shows the injury rates in NFL players based on a density ratio of turf over grass injury rates.

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ACL sprains occurred at a rate 67% higher on turf than grass. Eversion ankle sprains occurred at a rate 31% higher on turf than grass. Despite the significantly higher rates of injury on turf, this study was limited because it did not suggest any mechanisms by which turf causes higher lower-leg injury rates nor a means to make artificial surfaces safer.

Aging, Physical Activity and Blood Flow

quadriceps muscle anatomy

Physical activity diminishes age's affect on the reduction of the potent vasodilator NO. Elevated NO in the blood results from or causes a reduction in the amount of dangerous radical oxygen species in the blood.





Many physiology studies have shown that reactive oxygen species increase in humans with age. Reactive oxygen species have been impacted in the age-related deterioration of the brain. Fortunately, physical activity has been shown to decrease the concentration of reactive oxygen species. The role that physical activity has on preventing Alzheimer's Disease through reactive oxygen species reduction was discussed in a previous post on ExerciseMed.org. The focus here is the effect that physical activity has on the concentration of reactive oxygen species in the skeletal muscle.

Nitric oxide (NO) is a key regulator of vasodilation in blood vessels feeding the skeletal muscles. When reactive oxygen species are present, nitric oxide gets catabolized. One of the reasons antioxidants are so popular in the health food industry is because, as their name suggests, antioxidants eliminate reactive oxygen species. Older sedentary humans should show the greatest increase in NO following treatment with antioxidants because antioxidants are more prevalent in older patients who abstain from physical activity. One recent Danish study tested this hypothesis by treating subjects with the antioxidant N-acetylcysteine (Lifelong physical activity prevents an age-related reduction in arterial and skeletal muscle nitric oxide bioavailability in humans, 2012.  Michael Nyberg, et al.).

The study placed 8 subjects into each group: a sedentary youth group (mean age: 23), a sedentary older group (mean age: 66) and a physically active older group (mean age: 62). The subjects performed knee extensions for the exercise variable. The study found that the sedentary youth group had the highest concentration of NO metabolites, NOx. The physically active older group, although lower than the youth group, had a higher concentration of NOx in muscle tissue than the sedentary older group. When the older sedentary group was provided with antioxidant N-acetylcysteine (NAC) their NOx levels rose to the active older group with out antioxidants (Control, CON). Both older groups saw a significant increase in NOx concentration, suggesting that NO was compromised by radical oxygen species. At 45% of maximum power output only the older sedentary group saw increases in muscle interstitial NOx concentration following injection of antioxidant NAC. The results can be seen in the figure below.

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Figure 1. Muscle interstitial NOx at rest and during 12 W and 45% Wmax without and with infusion of NAC
Exercise was performed at the same absolute workload of 12 watts and at a relative workload corresponding to 45% Wmax without (CON) or with (NAC) infusion of N-acetylcysteine in young sedentary, older sedentary and older active subjects.  †Significantly different from young sedentary within same condition, P < 0.05; ∗significantly different from control conditions,  P < 0.05; #significantly different from rest within same condition, P < 0.05. 

The older active group showed no decrease in NO2 in their arteries when treated with antioxidant NAC. The young and old sedentary groups both saw increases in arterial NO2 (as shown in the figure below only the older sedentary group saw a significant increase in arterial NO2). This means that only the older active group was able to contain the radical oxygen species.  

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Figure 2. Plasma NO2− and NOx at rest without and with infusion of NAC
Femoral arterial blood samples collected during rest without (CON) or with (NAC) infusion of N-acetylcysteine in young sedentary, older sedentary and older active subjects. ∗Significantly different from control conditions, P<0.05 

Although antioxidants increased the amount of NO in the blood, the blood flow to the legs did not increase following antioxidant administration. The increase in NO concentration did not cause an increase in leg muscle blood flow. This result is surprising because NO is known to be a potent vasodilator. Thus, exercise-induced hyperemia (increased blood flow) must occur through a pathway other than NO in the legs.

Figure 3. Leg haemodynamics at rest and during 12 W and 45% Wmax
Exercise and rest without (CON) or with (NAC) antioxidant in young sedentary, older sedentary and older active subjects. †Significantly different from young sedentary within same condition; #significantly different from rest, ‡significantly different from older sedentary within same condition.

This study showed that one mechanism by which NO is increased in physically active elders is through a decrease in radical oxygen species. Another mechanism is an increase in Nitric Oxide Synthase (NOS), a protein that synthesizes NO. The physically active older subjects were found to have a significantly higher amount of endothelial NOS and neural NOS. The authors suggest that the elevated amount of NOS in active older subjects could act as a radical oxygen species scavenger. The increase in NO production may compensate for the age-related increase in radical oxygen species.

In conclusion, the discussed study found that physical activity decreased age's affect on nitric oxide (NO) decline in the blood. NO is a vasodilator, it opens up blood vessels. The concentration of radical oxygen species was lower in the physically active older subjects than the sedentary older active subjects. The older active subjects had the highest amount of nitric oxide synthase (NOS).  Since radical oxygen species decrease NO concentration, NO concentration may be elevated in the physically active because the combined effects of lower radical oxygen species and higher NOS. Another possibility is that NO scavenges radical oxygen species. This means that the low concentration of radical oxygen species is the product, rather than the cause, of high NO levels in the blood. In addition, nitric oxide was found to play no role in hyperemia during physical activity. Regardless, physical activity is important for maintaining vascular health by maintaining nitric oxide levels with aging.

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