Posted: April 4, 2024 at 12:34 pm
Following up on Monday’s email, this one will have a little more info on your fast twitch fibers and high-threshold motor units.
Muscle fibers don’t really contract individually. They are bundled together and the entire bundle contracts as a group. These groups are often referred to as “motor units” since they all fire together when given the signal from your nervous system.
Let’s say you do a mellow activity like walking – your body only recruits the bare minimum number of motor units, and as you might remember from the last email it prioritizes the slow-twitch fibers to save energy.
If you want to train your fast twitch fibers & high threshold motor units then you need sufficient demands: either heavy weights or high speed movements (or a hybrid of them).
So, in order to train them you need to do things like heavy deadlifts, heavy squats, heavy presses, or fast movements like box jumps, agility ladders, medicine ball throws, or sprints.
These high threshold motor units are essentially responsible for two important athletic qualities: strength & power (yes, this is overly simplified).
Strength is the ability to lift something heavy, usually for a small number of repetitions, and due to the heavy weight the movements are slow.
Power has a speed component to it – either the ability to move an object quickly (maybe a medicine ball or a kettlebell) or to move your own body quickly, such as rapidly repositioning yourself to NOT fall if you trip on a curb or a stair.
If you only train with heavy weights all the time and never do any power training, your ability to move quickly will likely deteriorate. In fact, without training it, power is the athletic quality that we lose the fastest as we age – up to 8-10% PER YEAR over age 40. Some of the best minds in health & fitness are now touting power training as the most important quality to train in order to stay high functioning and healthy as you age.
I like to think about it like heavy strength training helping you build up more potential and capacity in your high threshold motor units, and actual power training (kettlebell swings, box jumps, medicine ball throws, and so on) are what helps you realize those gains.
So, in summary, keep lifting heavy, and consider adding in some power work as well.
-Tony
