Over the last decade, interval training has been believed to be the best workout for most people. As the go-to fitness routine, interval training improves strength and endurance over moderate-intensity steady-state cardiovascular exercise. Study after study has shown that interval training, particularly high-intensity interval training (HIIT) is the gold standard for rapid results in speed, strength and endurance, be it from running, cycling, weight training or using cardio machines at your gym.