Returning to life on the line after two months off made some workers feel sore.
"Your body tends to heal" during time away, Sokol said. "Going through the wear and tear on your body again, it's kind of like you're a new hire."
But in today's world, that leads to new worries: Is my headache or muscle stiffness an early symptom of the virus? Or just normal aches and pains associated with hard labor?
"It's just the fear of the unknown, of not being able to see the virus," Ferguson said. "We get here, we're working, we're sweating, our body temperature is fluctuating. We don't know what we're coming in contact with because we don't see it."
That can lead to some uncertainty on how to answer the daily health survey. A worker at the Ford Chicago plant posted on the UAW local's Facebook page, wondering whether she should report every minor issue and risk being barred from working or enter the plant and risk spreading an illness.
Asymptomatic carriers of COVID-19 remain a threat, punctuated by the Ford plant shutdowns last week. In both cases, workers had passed temperature scans and were on the line before feeling sick.
"Anything can happen," Ferguson said. "I'm realistic about all of this. Nothing can prevent you from getting sick. They can put precautions into place ... but it doesn't guarantee it."
UAW President Rory Gamble said the automakers "have more protocols in place than if you were to drop in at your local hospital" but that rapid testing and, eventually, a vaccine are needed to truly ease worker concerns.
"The first couple days were better than expected," Gamble told WWJ-AM radio in Detroit. "We expected some glitches along the way. We feel we have a pretty solid system in place; we just really have to tighten up controls on the application of it."Before she returned to work last week, Arlene Williams, a 49-year-old machine operator at GM's Romulus Powertrain plant, was concerned that the coronavirus curve wasn't flattening enough in Michigan.
Workers in her machining area are spread several yards apart, and requirements to use hand sanitizer and wear a mask and safety goggles soothed her worries a bit. But with all that's still unknown about the virus and how it can spread, she was wary of being back on the job.
"If we had our choice to come back, would we? No," Williams said. "But everybody has a job to do."