Feeling a little queasy when you’re on the StepMill and streaming Homeland on your smartphone? Experts say many of us are starting to develop digital motion sickness, or “cybersickness.” Motion-sickness symptoms (nausea, headaches, dizziness) are more likely to strike if you’re on a motorized device like a treadmill or elliptical because both the machine and you are moving, explains Thomas Stoffregen, Ph.D., a professor of kinesiology at the University of Minnesota. “This forces your postural-control actions to be compensatory, and compensatory control is more likely to lead to instability,” he says. (Consider how you’re more likely to feel nauseated if you’re a passenger in a car than if you’re the driver.) Researchers also note that cybersickness symptoms affect women more than men, possibly due to subtle differences in our balance and body sway. Bottom line: If you’re prone to motion sickness, stick with tunes instead of video during your cardio.