I hear everyone talking about the importance of a high intensity workout. Does this mean not much rest between sets, a lot of sets, low reps or what?
Intensity is correctly defined as the percentage of momentary muscular ability that is being exerted during an exercise. For example the first rep is by far the easiest and therefore is low in intensity. However the final rep will require an all out effort, ie. 100% of its momentary ability or 100% intensity. It is this rep that is the most productive rep of the set as it responsible for triggering the growth mechanism.
To me , intensity is putting a 100 pound plate strapped to a dip belt between my legs and doing wide grip dips to failure for 2-3 sets till I feel the steam pouring off my body and the sweat leaking out of me like a firemain rupture. Weighted dips are maybe even superior to bench press for gargantuan chest and arms. It is especially motivating if pretty girls are watching you, cause anytime you put 100 pounds of weight between your legs and do 8-10 reps of deep dips you will attract attention especially if you already weigh 260 pounds and your doing it with superior form. Hoorah.
Intensity is just the percentage of your 1 rep. max. being lifted. Similarly, volume for an exercise is just sets x reps. So a high intensity workout is just working out with a weight that is closer to your one rep. max than would be typically used.
Intenisty is properly defined as: Inroad/Time.
Thats it. Simple. The degree of inroad (muscular fatigue) you can achieve as compared or divided by the time it takes you to achieve it.
For example: a 40% muscular inroad achieved over 90 seconds is more intense than a 40% inroad achieved over 120 seconds.