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Every year, millions of sports-related concussions occur around the world. A concussion is the most common form of mild traumatic brain injury (mTBI). When a concussion takes place, the brain is set in motion and hits the cranium. In fact, the injury can be twofold as the brain might bounce off the cranium and hit another side of the cranium. Meanwhile, the nerve cells in the brain become overstretched and blood vessels burst. The result is a temporary loss of brain function that potentially generates a sudden increase in brain temperature. The resulting biochemical processes impact the brain’s metabolism and lead to cell destruction.


The concept of ”sub-concussive repetitive head impact” has gained massive attention as it has become evident that repeated head collisions cause serious neurodegenerative pathology such as Chronic Traumatic Encephalopathy (CTE), a disease commonly found in the brain of deceased athletes whom have participated in contact-, combat-, or collision sports.

Among the ever increasing discoveries from studies in this field, two conducted at Cleveland Clinic (Marchi, et al., 2013) and Purdue University (Talavage, et al., 2014) highlight the effect that repetitive head collisions may have on the blood-brain barrier and on cognitive outcome.

The Cleveland Clinic study, published in the journal PLoS One in 2013, emphasized that the blood-brain barrier becomes damaged by the accumulation of head collisions over time. The study at Purdue University concluded that a concussion can be considered the result of multiple hits, rather than just a single isolated incident.


The brain consumes oxygen and glucose to generate energy (metabolism). The brain’s metabolic demand increases and decreases by approximately 6–10% for each °C change in body temperature. An individual’s body temperature strongly influences the temperature of the brain, as the brain composes 1,5% of the body weight yet receives 20% of the blood which the heart pumps out. Physical activity can elevate the body temperature from 36-37 °C up to 38.5–41 °C, thus increasing the temperature of the brain. At elevated temperatures, the brain’s metabolic demand is increased. Research shows that elevated body temperature (hyperthermia) causes worse cognitive outcome in several types of brain injury. In fact, as little as 0,5 °C increase in brain temperature can lead to worse cognitive outcome. A concussion causes temporary brain dysfunction. Insufficient oxygen and glucose could therefore quickly lead to tissue damage and brain cell destruction.

Concussions and repetitive head impact can cause axonal injury (injury to nerve fibers) in the white matter tracts of the brain. This in turn impacts the Central Nervous System (CNS) and causes disturbance in the regulation of cerebral blood flow. White matter tracts affect learning and coordinate communication and connectivity between different regions of the brain. Damage to the brain connectivity is a critical factor in the development of cognitive impairment. Axonal injury can also lead to a change in an individual’s pace, mood, and behavior.

Axonal injury and white matter tracts

  • A sport-related concussion (SRC) often happens when the athlete has exercise induced hyperthermia, thus having an increased risk of serious and long-term brain damage as well as poorer cognitive results.

  • Elevated brain temperature causes worse outcomes in several types of head trauma

  • Brain cooling reduces the brain’s demand for oxygen and glucose, thus reducing the risk of tissue damage and cell destruction.

  • Cooling leads to reduced accumulation of blood fluid (edema) inside the brain and decreased intracranial pressure (ICP) in severe TBI.

  • ​Glucose enters the brain through the blood-brain barrier. Physical activity increases the demand for glucose, implicating the destructive effects of compromised blood-brain barrier. Thus, brain cooling after sessions of repeated head collisions may potentially be an effective treatment method.

  • Cooling to normal temperature (normothermic) may prevent or limit the long term cognitive deficits caused by hyperthermia. By cooling athletes that are prone to encounter repetitive head collisions, PolarCool aims to relieve initial symptoms such as dizziness, nausea, concentration and memory difficulties.

  • The time from injury to start of cooling has proven to be critical, which makes the portable PolarCap® System ideal as it enables on-site acute treatment after head trauma in the world of sports and recreational activities.

Cooling as treatment of concussive and sub-concussive brain injury

Multiple mechanisms can explain the beneficial effects of cooling as treatment for concussive brain injury:

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