High temperatures and humidity raise your body temperature, says Rock Positano, DPM, director of the Non-surgical Foot and Ankle Service at the Hospital for Special Surgery in New York City. In turn, your blood vessels dilate to improve circulation, which causes slight swelling in your arms, hands, legs, and feet. Blood flow also increases to these areas any time you stand, walk, or run thanks to gravity and a heightened core temp.
The severity of this effect will differ from one person to the next. But since your feet will always be bigger later in the day, you’re best off getting fitted for sneakers in the afternoon, Positano says.
If you do so in the morning, your pair will be snug during p.m. workouts. Tight shoes compress your feet and increase your risk of injury in those muscles, tendons, and ligaments, Positano explains.
The bottom line:
Whether you’re going to the store or testing a pair you bought online, try your shoes on around 3 p.m. (when it’s hottest) or right after work. The only exception: If you exclusively exercise in the morning, that’s when you should test for fit.