Americans hit the gym in search of bigger arms, massive chests and smaller waists, but many don't know that gyms are hotbeds for germs.
ABC News conducted a test to find out just how many germs people could encounter when working out.
Dr. Philip Tierno, a microbiologist, said that the large number of people, exposed skin, and sweat present at gyms could be perfect for spreading infections.
"You're not using that one machine exclusively for yourself," Tierno said. "You're leaving that machine, and someone else follows you and your germs that you leave behind. Eighty percent of all infectious disease is transmitted by contact."
Tierno said that if a sick person used a machine, the person who used it next and then touched their eyes or mouth could get sick.
ABC News staffers took swabs to almost every piece of gym equipment they used and brought the samples to Tierno's lab at New York University Hospital.
Tierno found the germs staph aureus, klebsiella, enterobacter and E. coli, which can cause various ailments.
Tierno said the highest risk areas at the gym were machines used by "multiple people in quick sequence, such as dumbbells, seats where people may bike, or where people may sit down to lift weights."
For example, on a lateral pull-down machine, ABC News found bacillus, which comes from the soil.
It most likely came from someone's shoes. On an exercise bike, ABC News found sarcinia, candida specie, staphylococcus epi and diptheroids.
The worst place of all was the shower floor.
"Unfortunately, germs do survive in the shower, on walls, and on the floor," Tierno said. "I found it in hordes -- unbelievable quantities. We use the word 'innumerable.' Innumerable."
According to Tierno, E. coli and many of the other germs found by ABC News won't necessarily make you sick.
"You wear your little slippers, and you're OK," Tierno said. "But just as easily as those nonpathogenic germs touch those surfaces, we can have more pathogenic forms touch them. That's the point."