ILS means 'Imaginary Lat Syndrome'. You usually see teenagers infected with this after a workout or after their first serving of cell-tech and nitro-tech.
It can be transmitted by dillusional men as well. You can tell when someone is sickened by it...they walk around like they are so swollen and gigantic their arms stick out 4 feet from their sides and usually hold their breath until they turn purple and pretend like its such a burden to be so galactically enormous they have a mean looking agressive sour-puss on their face and pretend like they are in chronic pain.
You can usually see them at corporate chain gyms on Monday nights...around 6:30pm-9pm. Some have tribal tattoos going around their arm.