Those who have tried the HIT (Heavy Duty) weight training method will note strength improvements, but experience relatively disappointing muscle mass gains, a fact which perplexes many. Certain programs offer excessive volume, while others focus on insufficient workload (like HIT), and both are counterproductive to building muscle mass. The proper cycle of sets, reps, rest periods, and grips are necessary to not only consistently add muscle mass, but also to avoid overtraining, and HIT, by design, does not provide sufficient overload or intensity (even though, by name, the concept implies pure intensity) to stimulate consistent muscle growth. In fact, the only lifter HIT (Heavy Duty) workout techniques will benefit is one who is either a novice to weight training or who is returning from an extended vacation (and thus is unaccustomed to stress, and will soon plateau with HIT), or an advanced lifter who is overtrained (and benefits from a reduction in stress, but who also soon experiences a dreaded muscle mass plateau).
For both the beginner (or one who returns from an extended vacation) and overtrained athlete, HIT will only provide results for a limited time, and then muscular progress quickly tapers off. Insufficient volume and improper rep speed are the two main reasons why HIT (Heavy Duty) is one of the most ineffective muscle building techniques currently available, yet low volume weight training routines do tend to enhance strength, which offers bodybuilders false hope that they will also soon build muscle mass.
Contrary to popular belief, the two goals (strength and muscle mass) do not directly correlate, and are achieved using different weight training methods. Routines focusing on excessive volume must be avoided, but a lack of sufficient overload is an equally sizable roadblock to building muscle mass (evidenced by the disappointing muscle gains that result from the Heavy Duty approach). A constantly changing number of sets is best, but only when cycled properly, and combined with proper grips, rest periods, and rep speed. Also, a potent bodybuilding diet plan is just as important as proper weight training principles, and is one of the main reasons why so few build significant muscle mass despite consistent effort in the gym.
Remember, whether you wish to produce small or significant improvements in muscle mass, the principles are identical. I have achieved tremendous success (over 60 lbs of muscle mass gained), and am teaching men and women around the world how to build muscle mass naturally and tone their body through my MuscleNOW bodybuilding program, without supplements or steroids.