1.1 What is "HIT"?
The acronym "HIT" stands for High Intensity Training.
HIT in extremely basic form means organizing your workouts so that they are:
Hard - as hard as possible in good form.
Brief - 1-3 sets of a few basic exercises performed in an hour or less.
Infrequent - No more than three times per week, often times two, or even one.
Safe - HIT is intended to be an extremely productive protocol, but also one that stresses safety. One of the fundamental goals of strength training is to act as injury preventative.
That is the essence of HIT. There is nothing complex or "magical". HIT has been used successfully for decades by many trainees without the acronym, "HIT".
It must be noted that High Intensity Training is not a set of principles etched in stone. It is a disciplined style of training which is based on the two universally known factors affecting muscular growth - Overload and Progression.
Repetitions should be done in a controlled fashion so that continuous tension is placed on the muscles. Some use a 2 second count for the concentric (lifting) phase while others use a 20 second count. The key is performing quality repetitions to a point of volitional fatigue.
One set is productive, although some high intensity advocates sometimes choose to perform more than one set. Some people may require additional sets. As a general rule, with of course some exceptions, one set performed in a high intensity manner will provide all the stimulation you need for muscular hypertrophy (growth).
The following is a quote from Dr. Ken Leistner which provides a good synopsis of what High Intensity Training is all about.
"High-intensity training is going all-out, not almost all out. It is taking one set to one's absolute limit, not almost to the limit. It is using whatever equipment that is available, not just a machine or group of machines. It is not the words of two or three men, but a commitment to work as hard as possible while in the gym without socializing, resting excessively between sets, or falling prey to the 'this isn't going to work so I'll copy the star' attitude".
When an exercise is performed in the described high intensity manner, one set usually gives your body optimum strength stimulation. Multiple sets of the same exercise are simply not necessary.
Dorian Yates' (1992-97 Mr. Olympia) trainer, Mike Mentzer, recommends the following:
"Train intensely, train briefly, and train infrequently - it's valid and will work for everyone."
A quote from Mike Mentzer about the "copying the star" mindset so prevalent in "muscle mags" and gyms:
" . . . it is a mistake to point to the 'apparent' success of a couple dozen top title winners as indubitable proof that a certain training approach is efficacious. If one were to look back through the course of their bodybuilding careers and calculate the hours, months and years of wasted effort resulting from their blind, non-theoretical volume approach, one would have to question whether their achievements could properly be termed successful at all." Mike Mentzer, IronMan Magazine, March 1994.