Back in 2003, Forbes ranked squash as the number-one healthiest sport after taking calorie burn, cardio endurance, muscular strengthmuscular endurance, flexibility, and injury risk into consideration. The World Squash Federation (WSF) & Professional Squash Association (PSA) also dubs it one of the toughest racquet sports.

For those who are not yet familiar with the sport, Here’s what you need to know:

Squash is relatively similar to tennis in that you use a racquet (smaller than the one used in tennis) to hit a ball back and forth with your opponent. Like tennis, you can play in singles or doubles. However, there’s no net between you and the other player; you stand next to each other in a small, walled-in court. The idea is to hit the ball against the front wall of the court until one of the players fails to return it. Each time you return the ball, you get a point-but there’s a catch. The ball can bounce against any of the surrounding walls too, but it must bounce against the front wall for it to score a point. A full squash match is usually made up of five sets (11 points each) and a game can last from 40 minutes to an hour.