Is there a problem when a four-year-old girl frequently walks on the tips of her toes? She has no known medical conditions.
- T.T., Jerusalem
Prof. Yoram Nevo, head of pediatric neurology at Hadassah-University Medical Center in Jerusalem, comments:
I see quite a lot of such cases. This is habitual behavior - and quite common at this age. It occurs in boys and girls, and almost always passes with time. In many of these cases, the child doesn't go only on tiptoes but walks normally at other times. The phenomenon most commonly does not continue beyond the age of six or seven years. Even though this is usually a transient phenomenon, the pediatrician should be consulted. In rare cases, an orthopedic problem involving the Achilles tendon or a neurological problem of the lower limbs should be excluded. It is not the result of psychological or psychiatric problems.
When one buys a new cellphone, it generally includes a leaflet that talks about the amount of radiation it emits. I recently bought a GPS location-finder. This operates (as far as I understand) by bouncing radio waves off four different satellites constantly in order to fix your location and see how it is changing. Satellites are a lot further away than cellphone antennas, so presumably it takes a lot more energy to reach them.
The devices are installed close to our brains in the car or are carried close to our bodies if we're out hiking. Yet there was no mention of radiation in the printed material that came with it, and I don't recall ever reading about it in the paper or on the Internet. Do you know of any research about the dangers of GPS radiation?
- B.S., by e-mail
Michael Peleg, a communications systems engineer and expert on non-ionizing radiation, replies:
The GPS consumer equipment such as that installed in mobile phones and used for navigation, location and timekeeping does not transmit any signals. It operates by receiving the signals from the satellites and analyzing them. The satellites transmit their accurately coordinated signals all the time, but their power density on earth is extremely weak and is of no concern.
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