T Nation

More Speed =/= Less Force


#1

kso I have been doing some desultory researches over the past week on biomechanics of weightlifting, and I have come across many different people including articles on this website stating "more speed = less force needed" which I believe is VERY misguiding.
Don't get me wrong, I understand training speed in powerlifting allows one to shorten the distance between FMax and limit strength (helps recruit more motor unit faster) which makes hitting that PR easier, but I don't think that means less force is needed like people often say. In fact, from basic calculation F=Mass x Accleration, we can see that if acceleration(velocity/speed) increases while mass remains the same, doesn't that mean More Speed = More Force exerted?
Also, in relativity, it is common knowledge that the relativistic mass(mr) is equal to the invariant mass(m0) at zero velocity.
mr = m0 /sqrt(1 - v2/c2)
Therefore to quote Stephan Hawking "Because of the equivalence of energy and mass, the energy which an object has due to its motion will add to its mass"
Just my opinion, I am doing a science fair project on examining accomodating resistance and I just need to be sure of this.


#2

I'm not very edumacated in physics or biomechanics, I'd like links to the articles you are referring to.

Without seeing those, theres a number of different things that could be goin on here.

1) People misuse physics terms all the time. You even kinda did it yourself, F=mass x acceleration. Acceleration =! Speed. Acceleration=Velocity/Time.

2) People use math/physics to describe things a bit different, or from different perspectives that sometimes don't make a damn bit of sense, imo. For instance, maybe someone said this because at the top of a "speed lift" you are actually decelerating, thus less force.

3)Some people can't lift relatively heavy weights fast, and the reduction in weight is enough that the overal force is actually lower.


#3

http://www.T-Nation.com/free_online_article/sports_body_training_performance/accommodating_resistance

"...if you lift a weight with, the less force is needed to complete... "

http://www.T-Nation.com/free_online_article/sports_body_training_performance/continuum_training

Four lines under "The Contraction Speed Continnum"

Plus some forum posts and comments I see over the internet.

1) my bad for doing that, I thought it would make it easier to understand when I say "acceleration increases" since acceleration already meant increase in speed.

I figured they probably used the term so to avoid complicated explanation. People like me would actually believe those things but luckily I was interested enuf to do a little research.


#4

I'm not an expert on physics, but I know a little bit, so I'll chip in.

You could nitpick this a million ways, yes acceleration =/= speed, and yes the bar decelerates at lockout, but these details are not important in this situation.

I don't understand what your question is though? Or is this just a general discussion? If so, what about it do you wanna discuss?


#5

What does =/= mean or represent?


#6

ROFLMAO you can't compare quantum physics to Newtonian mechanics.

The two are sooooooooo different. For example; it's possible for an electron to be in two places at once. It's even possible for an electron from your body to be inside a wall. Are you going to find the same set of Ivanko plates in two places at once, much less inside a wall? Probably not.

The few equations you'd be looking at if we're talking about weight lifting are;

PE = mgh
KE = .5mv^2
and
F = ma

You could get into more complicated formulas but these are the three that you'll derive everything else from.

You could get momentum in there as well (p = mv) but that's not needed in the general scheme of things unless you're talking about movement from dead-stop (paused).

There is absolutely NO need to get into relativity with speeds this slow and masses this large. You won't take relativistic principles into account until said object reaches ~3.0*10^7 m/s. Needless to say, neither of us are going to be breaking the sound barrier while benching anytime soon. Or ever, for that matter.

I get where you're coming from, but you're complicating this way too much. Skip the relativity and stick to Newtonian mechanics. Relativity just isn't applicable here.

If you want to calculate the amount of force being exerted on a bar then you'll need to videotape yourself. Determine average bar acceleration on both lifts (the max effort and the speed lift) by plotting a series of data points over time based on the position of the bar vs. time. Calcuate said accelerations. Compare these to the weights being moved in terms of force output in relation to mass and you should be able to find some sort of relationship or at least come to a conclusion. This should be done using quite a few samples if you're serious about this science fair project.

Perform an actual experiment and then compare the results. Determine this for yourself. Empirical evidence and data is crucial, imo. Make sure you're accelerating the bar as quickly as possible (assuming you try to do this) in both lifts to get a relatively accurate comparison.

-To above, acceleration does decrease/increase. It's called "jerk" (change in acceleration).


#7

it's supposed to represent an equals sign with a dash through it, meaning that it doesn't equal ____

e.g. - 2 =/= 3 (barring significantly large values of 2, lolll)


#8

Well, I first came across the Strength Curve & Force Velocity Curve few days ago while trying to find a science fair project on biomechanic.This made me think of Chains/Bands and how they can possibly change the curves. As I did more research, I see people advocating for speed training by stating more speed =/= less force. At first I believed they were correct but then, as I tried to make my own strength curve graph, I realized thats impossible. This thread is barely pointing out to a small misconception.


#9

I understand your point but i wasn't comparing them two. I was just using them to explain my point that more speed doesn't mean less force like many believes. I probably gone overboard with my explanation but I was pretty impressed how two different things can have such similiarity.


#10

Oh ok. Well I look at it like this, if someone benches 400 pounds at a speed of 1 (made up for example) and benches 200 pounds at a speed of 2, force is the same. If they can bench 200 pounds at a speed higher then 2, then there is more force.

This only is going to work to a point though. You won't bench 10% of your max more then ten times as fast, for example.


#11

In no way, shape, or form does speed = acceleration. They are two completely different things. Speed =/= velocity, however.

CS


#12

but speed = |velocity|, so it's not as if they're not interrelated


#13

Acceleration/deceleration is that rate of change in speed. It is the velocity over time squared when expressed as math.


#14

Youre missing the entire point of strength training. Increasing any one variable in any equation regarding force/speed/acceleration for maximal lifting in order to explain maximal strength does not make any sense. Do your project on optimal training application and not on 'more speed=less force' because this is not ture in real life.


#15

I know, that's why I said that. Were using =/= to mean "is not equal to"

Speed and velocity are not the same thing.


#16

Yep, exactly as I expected. The first link, when the word "force" is used, its not in a strict physics definition. Like you say, probly to simplify it.

The second link, this quote is relevant: "higher the velocity of contraction, the less force you can produce". So we are talking about how much force the lifter is applying, not the force of the weights themselves. Aka, people can't life maximal/near-maximal weights quickly, so it is therefore a natural "weakness". Weaknesses are something we like to train, and that's why Dave Tate knows what he's talking about here, even if its not strict/clear physics-wise.

Also, as usual: What STB said, lol


#17

Is speed like mph and velocity like mph due north?

Another way to phrase the question:

Is speed the how fast and the velocity how fast and the direction?


#18

yep!


#19

What he means: If you blast through your sticking point you won't need to push as hard during the lockout as you would have had to if you grinded through your sticking point.

Which makes perfect sense. You just have to read what he said. Physics gets abused all the time in weight lifting articles.
And everyone abuses F=ma
the resulting force = ma = the force exerted by the lifter minus the weight of the bar. (mg)
So the force exerted by the lifter is m(a+g)