The Diving Reflex and Long-Distance Swimming
A Physiologic Response to Cold Water Impairs Exercise Tolerance
May 2, 2009
Runners have their “wall”, that point where, after several miles of jogging, glycogen stores are depleted and fatigue comes down like a hammer. Likewise, open-water swimmers have to deal with their own performance barrier: a physiologic peculiarity that results from immersion in cold water and that can end a competitor’s race almost before it begins.
And, just as runners often take measures to overcome their metabolic roadblock, swimmers can minimize the effects of what many call the “diving reflex”.
Putting the Face Into Cold Water Can Slow the Heart Rate
In the strictest sense, a true diving reflex occurs during simultaneous immersion and breath-holding, but the simple act of dunking one’s face in cold water (irrespective of whether a normal breathing pattern is maintained) is sufficient to slow the heart rate, constrict peripheral blood vessels, and shunt blood away from the extremities and toward the core.
In a vigorously exercising athlete, such alterations in the usual circulatory pattern can lead to abrupt fatigue, shortness of breath, muscle cramps, and panic (Paulev P, et al., Facial cold receptors and the survival reflex "diving bradycardia" in man. Jpn J Physiol, 1990; 40(5): 701–12).
Whenever a person’s face is immersed in water colder than 70º F (21º C), sensors around the nose and eyes relay messages via the trigeminal nerve to vagal centers in the brainstem. Stimulation of the vagus nerve then leads to those biological manifestations that constitute the diving reflex.
This response to cold-water immersion does not occur at temperatures above 70º F, nor does it occur when the body alone is immersed in cold water and the face is not. The intensity of the reflex varies among individuals and with water temperature, and it is influenced by ambient air temperatures prior to immersion (Schagatay E, and Holm B., Effects of water and ambient air temperatures on human diving bradycardia. Eur J Appl Phys and Occup Phys, 1996; 73(1–2): 1–6).
Unlike the typical pattern of fatigue that besets runners (which usually begins after a fairly lengthy period of exercise), the diving reflex can begin within seconds following immersion. A well-trained and well-prepared swimmer can attenuate the magnitude of the reflex, and, for most swimmers, its effects are transient. In a sense, one can “swim through it” if the syndrome is recognized and understood.
How a Swimmer Can Prevent or Minimize the Effects of Immersion in Cold Water
- Even elite pool-trained swimmers can be profoundly affected by cold-water immersion. Therefore, a significant portion of any open-water swimmer’s training should take place in cold water.
- Ambient air temperature influences the magnitude of the immersion response: the warmer the air (hence, the face) the more profound the reflex can be.
- Pre-race cooling of the face is helpful for many swimmers: immersing the face in cold water, applying an ice pack to the face, or spending some leisurely time in the water prior to the event will initiate – and hopefully ameliorate – the reflex before strenuous competition begins.
- Applying lanolin or a similar insulating material to the face before immersion is a common tactic.
- Once the event starts, swimmers who feel overwhelmed, panicky, or short of breath should temporarily switch to a less demanding stroke, or even a “drown-proofing” mode, for a short time to allow the circulatory system to stabilize.
- Breath-holding may deepen bradycardia (slowed pulse); swimmers should resist the temptation to hold their breath.
Even well-trained swimmers can be surprised by the relative difficulty of cold-water competition. Recognizing the physiologic changes that accompany facial immersion will make open-water events safer and more enjoyable.
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