The cult of extreme exercise classes can be intimidating, so just steal the best bits and take your high-intensity training anywhere. "CrossFit really broke the old ways of thinking and forced the [functional fitness] dialogue on the fitness world," says kinesiology professor Steven T. Devor, at Ohio State University. But you don't have to join the expensive and borderline cultish classes to get the benefit — much of what they do can be easily re-created in your own workout space. These are the CrossFit principles that will improve any workout, explained here by Zain Elmarouk, of CrossFit 415 in San Francisco.

1. Strive for variety: Don't work out just in the gym — get outside and play, in different ways, to give your body a constantly varied stimulus. Do circuits one day, play a sport the next. Cultivate broad-based fitness that includes endurance, strength, flexibility, power, speed, coordination, and balance, and always vary your movements. If you do nothing but run, you'll become a weak endurance specialist. If you do nothing but lift weights, you'll become an immobile muscle head.

2. Go hard: Too many gym workouts involve aimless, lazy wandering from exercise to exercise. CrossFit showed the mainstream fitness world that better results come from extremely hard work in brief, targeted circuits.

3. Learn body control: Classic gymnastic moves like pull-ups, push-ups, and bar dips teach us to control our bodies in space — without relying on stationary benches and seats — critical for sport and for long-term health.