But now it's time to turn that frown upside down, says a new study.
According to a report published in the journal Psychology of Sports and Exercise, smiling can help reduce muscle tension and distract joggers from other what they may be feeling in the rest of their body.
After gathering 24 skilled runners, researchers from Ulter University in Northern Ireland asked them to complete four six-minute running blocks with two minute rests in between intervals.
Participants completed their jogs both smiling and frowning. Using a breathing mask, scientists measured energy consumption.
Interestingly while smiling, runners used 2.8 per cent less energy compared to those who frowned.
"The main reason for the 2.8 per cent improvement in running economy, we believe, was that smiling helped participants to relax and reduce muscle tension without deliberately, or conciously trying to relax," says lead author of the study, Noel Brick.
"We know that runners are more efficient when they are relaxed, so this seems the most likely reason."
Who can forget Usain Bolt smiling his way to Olympic gold in record time?
