And when you're resting between work intervals or after your workout, slow everything down by using diaphragmatic breathing, aka "belly breathing". Take slow inhales through your nose as you feel your belly expand, then let your belly fall as you gradually exhale through your mouth. This can help you reset in less time. If that doesn't give you much relief, know that the smothered feeling is just that, a feeling. "When we exhale normally, air leaves in a fairly linear direction, so we are sure that we have exhaled", says Rossi. "But in a mask, air also goes out through the sides and travels over our face, which can make us feel claustrophobic". Even when you're on the treadmill or stationary bike or doing some other steady-state activity, don't be afraid to slow down for an active-recovery break if you feel light-headed or dizzy. That could be a sign that you've subconsciously changed your normal breathing pattern because the mask feels "different", says Rossi. Anyone who's ever done more than stand in a surgical or cotton mask knows that exercising in one can feel a bit stifling, to say the least. But the reason isn't that you're being deprived of oxygen. It's that when you're breaking a sweat while wearing a mask, the mask traps some of the heat your body is trying to lose as your core temperature increases. This could prevent your body from efficiently cooling itself, says Christopher Lundstrom, PhD, a lecturer on sport and exercise science at the University of Minnesota. You are unlikely to overheat just from wearing a mask, but your brain will sense that increase in temperature and cause you to slow down, he says. Your workout might subsequently feel harder, which is totally OK, he adds, as long as you pay attention to your body and don't push too hard in hot and/or humid conditions.