Body Cooling and Sleep in Athletes
When athletes obtain optimal sleep, their mood, fatigue, mental and physical performance, recovery, and cognition improve while their risk of injury decreases. However, incorporating sleep as part of an athlete’s training regimen is often overlooked. Additionally, obtaining sufficient sleep can be difficult as athletes travel to tournaments — especially if it involves traveling across time zones. The change in time disrupts an athlete’s circadian rhythm, which can contribute to sleepiness and fatigue, and negatively impact an athlete’s performance. A recent study by the American Academy of Sleep Medicine (AASM) demonstrated that baseball players’ performance decreased as the season progressed due to frequent travel (i.e., disruptions in the sleep-wake schedule). Improving sleep could potentially improve performance and prevent injury in athletes, and in recent years, scientists have used partial body and whole-body cooling as a way to do this. Some results have been promising.
In sports medicine, the use of cool temperatures as a therapy, such as to relieve inﬂammation and reduce muscle soreness, has traditionally involved applying ice packs to the effected part of the body or submerging one’s body in a cold-water bath. Greater pain relief could presumably be accomplished by using extremely cold temperatures. With this in mind, in the 1970s, rheumatologist Toshima Yamauchi in Japan was the first to use the technique of whole-body cryotherapy (from the Greek kryos meaning “cold” plus therapy) to relieve pain in people with arthritis. He found that this technique resulted in
more relief than ice baths, and the technique was soon adopted by athletes to relieve pain and soreness.
Cryotherapy involves exposing the body to extremely cold temperatures of -148°F to -220°F (-100°C to 140°C) for two to five minutes. During the extreme cooling, blood vessels on the surface of the skin contract, thereby reducing blood ﬂow to inﬂamed areas. On leaving the cryotherapy chamber, vessels very quickly expand (which brings more oxygenated blood to injured tissues) and levels of anti-inﬂammatory substances increase, which may decrease pain and soreness.
In cryotherapy, cold temperature exposure takes place in a cryotherapy chamber. The chamber can be a vertical, cylindrical tank that surrounds the whole body, except for the head (i.e., an open cryotherapy chamber), for partial body cooling or a tank that a person can fully walk into (i.e., closed cryotherapy chamber) for whole-body cooling.
In an open cryotherapy chamber, liquid nitrogen (-220°F/130°C) is sprayed into the chamber via ports. The liquid nitrogen quickly vaporizes because the human body is substantially hotter. However, because the vapor is at subzero temperatures, the body is surrounded in a cold nitrogen fog. In a closed cryotherapy chamber, liquid nitrogen is not sprayed into the chamber. Oxygenated air within the chamber is instead cooled by other means to a temperature of -148°F to -220°F (-100°C to -140°C).
A closed cryotherapy chamber provides uniform cooling over the skin because a person’s whole body is exposed to the cold air. In an open cryotherapy chamber, the lower extremities tend to be colder than the upper extremities because nitrogen vapor escapes around the head, which is exposed to ambient room temperature. While in a cryotherapy chamber, a person wears minimal clothing — socks, gloves and underwear — and in the closed chamber, a headband and mask — to protect the ears, nose and mouth from frostbite.