Most fitness enthusiasts would have an idea of what CrossFit is about: High-intensity movements that range from jumping on boxes to flipping tyres and climbing ropes.

Founded by former gymnast Greg Glassman in 2000, the fitness programme optimises physical competence in 10 disciplines: Cardiovascular and respiratory endurance, stamina, strength, flexibility, power, speed, coordination, agility, balance and accuracy.

Workouts are varied and unpredictable. One moment it's burpees, the next you may be doing deadlifts. The following day, it's a completely different workout targeting other areas of fitness.

As Glassman said: "Five or six days per week, mix these elements in as many combinations and patterns as creativity will allow. Routine is the enemy. Keep workouts short and intense. Regularly learn and play new sports."

Not surprisingly, it has become a hit among the millennials with short attention spans; there is no danger of workout boredom.

It is also effective, because it recruits many more muscles than a normal gym training session. Although it sounds intimidating for beginners, once you put yourself through the exercises, it is definitely fun and liberating.

During an introductory CrossFit session by Reebok, instructors had participants doing three sets of four basic moves, circuit style - medicine ball squats, box jumps, rowing and burpees.

"The beauty of CrossFit is its versatility. You can scale everything to your activity and interest. If you don't like lifting heavy weights, you can do gymnastics and bodyweight movements," says Andreas Gloor, Reebok sports marketing manager.

Yet, with explosive plyometric moves like box jumps and squat jumps, CrossFit may seem like a risky sport. Common injury areas are the heels (from jumps) and shoulders (from weightlifting). A recent study in the Journal of Strength and Conditioning Research found the CrossFit injury rate to be comparable to that of gymnastics and Olympic weightlifting.

Put simply, CrossFit is not the safest workout, but it's not the most dangerous either. To play safe, don't attempt to do something beyond what your coach recommends.

Exercises can be customised to your abilities and injuries.

Said Gloor: "The movements may be set for the class, but the weights will be different. If you don't feel good using a weight, go without. If you can't do box jumps because of knee problems, you can do step-ups."

Though CrossFit is frequently practised by people in physically demanding roles like policemen, military professionals and athletes, it has attracted an increasing number of exercise beginners over the years.

Said Gloor: "I see people from all walks of life: sedentary office workers, people looking to lose weight and get fitter, mothers who want to shed post-pregnancy fat. There are as many women as men doing CrossFit."

There is a strong emphasis on community. It's not uncommon to see CrossFitters become close friends and hang out outside their box, the CrossFit term for a gym.

"For most of us, we want to feel better about ourselves and move in a supportive environment. And CrossFit provides that," Gloor said.

CrossFitters have a culture of high-fiving each other after a workout, It is bonding through shared pain.

• This article first appeared in www.shape.com.sg