[quote]5.0 wrote:
JJ wrote:
When a very heavy load is lifted, one has to try to lift it as fast as possible. Due to something called the size principle - which dictates which motor units are used and in which order - when max power/speed is used to contract a muscle, the most motor units are employed - and this means the max amount of fibre contracts.
So conversely, if a load is very light, like a cup of tea (i AM a Brit y’know), then the speed is not fast, so as not to use alot of muscle units, which would result in you smashing the cup into your jaw.
I don’t understand this. What does the speed of the lift have to do with using more motor units, as you say, versus just having to lift a heavier weight? Wouldn’t just the sheer weight of something that’s very heavy employ more motor units, just because it’s heavier? Thus the logic of lifting very heavy while ‘on’, not lifting fast.
If I can do 20 pull-ups at a dead hang, slow with proper form, my body is going to benefit multitudes more from that, rather than cranking out 20 pull-ups as fast as I can. [/quote]
OK…
muscle contracts by the spinal cord and brain sending electric messages down pathways to motor units, these are attached to musclefibres which then contract.
There are type I, Type IIa and IIb. This goes the same in a sense for the motor units too.
If you lift a weight slowly, mostly the units that contract the Type I fibres contract… this is one of the reasons that when you lift slowly, you cannot lift heavy.
When you lift fast and explosively, more FAST twich fibres are used (which have the biggest potential for growth due to their size).
If you lift a cup, then maybe 1% of your motor units are ‘firing’.
If you lift a ME weight, then you are using as many of your motor.muscle units as possible… so maybe 80%.
The first fibres to be used in ANY movement ever, are the slow twitch, and as things get heavier and heavier, the fibres used are larger and larger - this is the size principle - that fibres are activated in order of size.
When you lift a ME weight, the actual weight doesnt move fast - cause it is fookin heavy, but you are trying to lift it fast arent you? I know for a fact you aint doing super slow with ME loads!
So while is isnt the speed of which the actual weight moves, it is the speed of which you try to move it that will 1) activate more muscle leading to greater strength and size gains, and 2) activate the last fibres to be used, the highly hypertrophy-able fast twich type IIb fibres.
Also, when we train a-la bodybuilding in the 8-12 rep range (apparently!), we are not using the majority of fast twitch finres UNLESS…
Unless we 1) try to move the weight as fast as possible on the concentric (lower nice and slow)and 2) work to failure.
As a muscle fatigues it uses more and more motor units to complete the reps, and is one of the reasons training to true failure is difficult and very painful! So with a weight that i will fail with on rep 12, by 8 most of the slow twitch are fatigued and more IIa are being used, then by 10, 11 and 12… i am recruiting the largest fibres, IIb to finally exhaust that muscle totally.
I will say that this is the beginnings of more advanced physiology, and while it isnt necessary to know, there are very important points here - my body has changed alot now i understand the ‘size principle’ better…
Last point,
[quote]
If I can do 20 pull-ups at a dead hang, slow with proper form, my body is going to benefit multitudes more from that, rather than cranking out 20 pull-ups as fast as I can. [/quote]
You are confusing fast with sloppy. If you can do 20 full ROM reps from a dead hang… great. But if you did the reps with an explosive concentric, controlled eccentric (as in the first example) and full ROM - you would be able to complete the same 20 reps, but with added resistance! This is due to the fact you are recruiting more muscle fibres on the concentric - which directly provides more strength, AND a better growth response, all things being equal (ROM, rest, tempo)
JJ