These are intense but brief workouts designed to stimulate your fat - burning, muscle building hormones in as little time as possible. (busymanfitness.com)
It is a lot harder for women to increase muscle size through weight - training than men, simply because they don't have enough muscle building hormones in their body. (womenshealthandfitness.com.au)
As you already probably know, testosterone is one of the most important muscle building hormones produced in the body. (fitnessandpower.com)