Elaysian is a low gravity planet. Compared to Earth the gravity is so low that if one would simply jump you would be airborne.
Eylasians are a low gravity species which means that their physique and neural motor cortex is adapted to cope with a low gravity. When exposed to 1G gravity environments they need physical support to function. This support varies from wearing an external skeleton with intergrated servomotor's which help supporting the persons own skeleton although this only helps for short periodes of time. For longer physical support other forms of support are needed like a old Earth wheeldriven wheelchair or an anti-grav unit.
A medical treatment was developed by Doctor Julian Bashir based on earlier neural muscular adaptation research by Nathaniel Terros. By elevating the neural output to the brains motor cortex via neural analeptic transmitters he inproved his theory and made this treatment possible. The drawback of this treatment is that if started no exposure to low gravity environments is adviced because this would confuse the persons body and motor cortex. When finished the person can move naturally in 1G as if they where in their low gravity environment. A side-effect of this treatment is that once finished it is not possible to reverse it.
Only a handfull of Elaysians ever left the planet. One of those people was Melora Pazlar who became the first Eylasian to enter Starfleet. (DS9:"Melora")