A risk not worth taking: iPods and thunderstorms [R].

Runners are well accustomed to maintaining training schedules, often braving foul weather to keep their workouts on track. Let's face it, if we skipped a workout every time it rained, at the very least we'd fail to meet training goals--whether they be race-oriented or for general fitness--and at the worst-case end of the spectrum, we wouldn't be accurately described as regular runners at all. Those without indoor treadmill access or home cross-training machines, pools and gymnasium equipment are simply out of luck when the weather changes, and so these runners don their best raingear, caps, and wicking underlayers to hit the streets whenever necessary.

Be that as it may, it is never wise to keep a workout scheduled on a day when thunderstorms are likely. Risk of injury goes up when severe winds, poor automobile visibility, darkness, puddling and other hazards abound. If the weather report foretells of thunder and lightning, there are obvious reasons to stay home. Nevertheless, on occasion some runners may throw caution to the wind, as it were, and hit the outdoors in these conditions, perhaps some even with regularity. But now there is an added risk for users of personal audio devices who run in summer thunderstorm conditions. While incidents are so far rare, they have such severe consequences that they warrant our full attention.

At least one case has now been reported that shows it's possible for personal audio devices to redirect current from a lightning strike through the body--and because of the position of the metal earphones, this means directly through the head. This can happen whether the person is directly struck by lightning or not. Furthermore, sweat exacerbates the problem, serving as an additional conductor, and therefore puts lightning conditions, outdoor exercise, and personal audio entertainment as a potentially life-threatening combination to be utterly avoided.

In July, a 37-year-old man was brought to an emergency room in Vancouver after jogging in a thunderstorm while listening to his iPod, when a nearby tree was struck by lightning. Witnesses reported that he was thrown approximately eight feet away from the tree.

The patient was admitted with second-degree burns on his chest and left leg. In addition, two linear burns extended along the front of his chest and up his neck to the sides of his face, terminating in "substantial burns" in the openings of both ear canals. This burn pattern turns out to describe the exact path his earphone cords fell across his chest, up his neck and into his ears at the time of the lightning strike. Both of his ear drums were ruptured, and he had a severe conductive hearing deficit. He also had sustained a fracture in his lower jawbone, and suffered bilateral dislocations of the joints there, as well as fractures to the bones of his inner ear. The doctors reset the man's jaw and repaired his ear drum perforations with a surgical procedure known as perichondrial grafting.

This chilling scenario, in which a person is not directly struck by lightning but rather lightning jumps from a nearby object to the person, is the far more common one and presents many additional hazards. Known as a side flash, this phenomenon can result in blunt trauma injury due to a forceful muscle contraction that actually projects the victim some distance. For runners with personal audio devices, however, there is an added danger. Because of the ordinarily high resistance of skin, lightning is often conducted over the outside of the body during a side flash (an effect known as a flashover); however, sweat and metallic objects in contact with the skin can disrupt the flashover, leading to the internal flow of current. Although the use of a device such as an iPod or an MP3 player may not increase the chances of actually being struck by lightning, the combination of sweat and metal earphones may direct the current to, and through, the runner's head. This is precisely what occurred when the runner in Vancouver was struck.

In this patient's case, the mandibular fractures were probably caused by muscle contraction, since there were no external signs of injury to the man's face. The perforations of the ear drums likely occurred as a result of the sudden heating and expansion of air around the current, leading to pressure waves. Perforations are commonly seen in patients who have been struck by lightning, although the injuries this runner suffered to the inner ear bones are unusually rare.

The potential for permanent hearing loss due to prolonged use at high decibel levels of personal stereo equipment, including not just iPods but portable CD and MP3 players, has been well documented in health research. The added risk of injury to runners for whom hearing traffic, cyclists and other runners has been limited contributes to the widespread discouragement and oftentimes outright ban on them in races and even some parks. Now, the recent awareness of this additional, albeit uncommon, hazard is another strike against the regular use of these devices during your outdoor workouts.

(N. Engl. J. Med., 2007, Vol. 357, No. 2, pp. 198-199)