DAKAR, Senegal — They sprint. They sweat. They squat to the ground and bounce backward. They sit side-by-side and lock arms for group situps. They dig trenches in the sand for stability, to get more out of each push up.

And, then, when the rush-hour traffic really backs up and exhaust fumes pour across this little, sandy triangle of an outdoor gym bordered by a highway and two exit ramps, sometimes the athletes vomit.

“Sports and pollution,” said Joseph Faye, a wrestling coach who was grappling with other young men there on a recent evening, “they don’t go together.”

Increasingly in Dakar, where outdoor exercise is a way of life, the two are colliding.

On any given evening, thousands of runners, wrestlers, soccer players and fitness fanatics take to the beaches and streets for a strenuous workout.