Bad vibes for inline skaters.

Neuromotor functions are sometimes temporarily impaired in people following sessions of inline skating. The sensations most commonly reported are numbness, difficulty controlling movements and an inability to precisely detect foot position. A study held at the University of Quebec recently determined that it is the constant vibrations caused by the wheels' contact with the pavement that causes this.

The researchers asked six men and four women, all recreational skaters, to skate on a 200-meter outdoor stretch of pavement for 35 minutes. The vibrations during skating were recorded and the skaters were then measured for various motor function ability, including maximal force, reflex and ability to detect ankle angle changes. A series of measurements revealed that the skate vibrations had indeed been transmitted to the lower limbs of the skaters. Each of the motor functions was diminished; indeed, reflex dropped by nearly 35% and remained depressed for more than 30 minutes after inline skating. The researchers controlled for other factors that might influence motor function such as the pressure of the skate's boot on the foot. For this they had each skater wear the boots at rest for 30 minutes.

Immediately after a bout of inline skating, impaired balance and the control and execution of simple motor tasks are concerns. But the long-term cumulative effects of exposure to the vibrations associated with inline skating are not known. To help determine what they may be, it is useful to look at studies of hand tool operators.

A 1978 study found that long-term exposure to vibrations can lead to Raynaud's phenomenon, which is characterized by sporadic interruptions of blood flow. There is a sudden whitening of the extremity followed by a painful, throbbing return of blood flow. If long-term exposure to vibrations continues, eventually burning replaces normal feeling. Permanent sensation loss and damage to muscles can occur. There is reduced strength, joint pain and often chronic tingling. The International Conference on Hand-Arm Vibration cited one study in which, of 100 hand tool workers, 80% had swelling and wasting of the nerves in the hand. Among these workers it is the most frequent reason given for changing jobs.

The International Organization for Standardization's standard for vibrating hand tools predicts that the amplitude of the vibrations the skaters were exposed to in the Canadian study, if increased to two hours per day, could result in stage one of Raynaud's phenomenon in 30% of the skaters in just three years.

Some skaters report that a switch to a skate with a carbon fiber rack reduces vibration. Until inline skate design focuses on eliminating the transmission of vibration to the lower limbs, the U.K. Health & Safety Executive lists frequent breaks and moderation in the activities that cause these vibrations as the main ways the risks can be minimized. Perhaps skating should not be the only form of daily exercise you allow yourself. And keeping the lower extremities warm-both during and after skating--is one way to regulate blood flow.

(Med. & Sci. in Sports & Exerc., 2002, Vol. 34, No. 12, pp. 2037-2044; U.K. Health & Safety Executive information Sheet, www.hse.gov.uk; Report of the 8th Int'l Conf. On Hand-Arm Vibration, Umea, Sweden, 1998, pp. 155-165; Scandinavian Journal of Work, Environment & Health, 1978, Vol. 4, No. 5, pp. 159-166)