Will talks about what rep ranges you should be using to get the right force and velocity for your training goals.
High reps, low reps, moderate reps. Which one should I use?! That depends on what kind of adaptation you want to produce in your body. In order to discover what the right rep range or weight works best for a person who is training, some information is needed.
Physics states that maximum force is attained when velocity is small. Likewise, maximum velocity is attained when external resistance is near zero. For instance, a heavy weight will move very slowly. Conversely, when thrown, a light object may move very quickly, but with minimal force.
Force & Velocity
With these laws in place we can deduce that to produce maximal force we must use maximal weight with low velocity. Likewise, to produce maximal speed we must use low external resistance and maximal velocity.
In reality, most sports obviously come somewhere in between these two extremes. But it does give us some training variables. Top weightlifters and powerlifters will commonly use the maximal effort method. In conjunction with this, they will train the squat or deadlift at around 75-85% of their 1 rep maximum.
Why? First, the max effort method trains the strongest muscle fibres to the fullest extent needed in their sport. A maximal effort squat or deadlift will take several seconds to complete, so they will choose exercises with similar movement paths and time under tension (how long the lift is in progress). This method is the only way to push the strongest muscle fibres in the body to the full and to produce maximal force in the movements specific to their training (in this case the squat & deadlift).
Why do they have a separate training session using weights that are 75-85% of a maximal squat or deadlift? (commonly called the dynamic effort method.) Firstly, even a heavy weight needs an element of velocity to move. A lifter only has a short amount of time to complete a lift before the muscles give out. Although a very heavy weight cannot be moved with great velocity, it can move too slowly. This also depends on your own strength levels.
A 100kg squat may be large mass for one person and small mass for another. When lifting maximal and heavy loads the body can only sustain such an effort for a very short amount of time. Thus training to lift a heavy load as fast as possible becomes critical.
As stated before, it is impossible to exert a large amount of force on a object of little mass. So if these athletes were to use a weight that is too light in their dynamic sessions they would neglect the force factor and it would not be of optimal value in lifting heavy weights. If they were to train too heavy on their dynamic sessions they would neglect the element of velocity needed in the movement. But by choosing the correct percentage of a 1 RM a weightlifter can train within the correct part of the force-velocity curve.
This simply means having sufficient velocity and sufficient force in order to achieve the correct training result. Thus by having training sessions dedicated to maximum force and separate sessions dedicated to dynamic movement, a weightlifter/powerlifter learns how to apply the right combination of force & velocity during their lifts.
In part 2: we will look at how different rep ranges affect muscle growth.
References: V. Zatsiorsky “Science and Practice of Strength Training”