T Nation

F = MA

Ive been thinking about this a lot lately.

So I understand the force/velocity relation and how optimal force occurs for most people somewhere around 75-85%. But heres a few questions.

1.) If im using 75% 1rm vs. 80% 1rm and focusing on maximal speed during concentric movement, even if the weight is moving slow, is it likely that im producing the same amount of force with the two different weights?

2.) Even with weights around 75% would the force be greatest on the first rep, and drop each rep after that?

3.) If so, then the key to strength wouldn’t be weights near 1rm, but instead would be low reps per set.

4.) How does fatigue play into all of this? Normally if I were doing “heavy weight” maybe 10x3 or even 5x3 using a weight around 85+% the rest breaks are long 3-5 minutes. But if i use say 5x5, i might have shorter rest breaks of 1-2 mins, but isn’t the force likely the same during the set, and since there are more reps, likely more fatigue?

5.) How do muscles that only contract isometrically during a movement play into this? Like grip muscles and core muscles in most lifts. Or, does the greater velocity still transfer greater force to these muscles?

6.) Also, if you were doing an isometric pull, with a weight above your max in say a deadlift, the weight would not be moving, so there would be no acceleration. Wouldn’t that mean by the above equation there is no force. Or is it that gravity is accelerating the weight downward at 9.8 m/s2 and if you exert a certain force, then the weight might only be accelerating at 2 m/s2 downward?

7.) Lastly, im trying to apply this to movements like squats and one-leg squats. The problem i notice, is that im weakest at the bottom, and if I accelerate fully without holding back, i will jump. Since im weaker in the bottom, i have to use lighter weights, but by the top im moving pretty fast, and am much stronger at the top. Are resistance bands the answer to this question?

Thanks for the help guys, and any other info you have would be great.

[quote]dankid wrote:
Ive been thinking about this a lot lately.

So I understand the force/velocity relation and how optimal force occurs for most people somewhere around 75-85%. But heres a few questions.

1.) If im using 75% 1rm vs. 80% 1rm and focusing on maximal speed during concentric movement, even if the weight is moving slow, is it likely that im producing the same amount of force with the two different weights?
[/quote]

That sounds like a reasonable assumption. It would vary by the individual. You are moving more weight at 80%, but will likely be slower. It wouldn’t take much to find out, just a friend with a stopwatch.

It depends what lift you are talking about. Take a lift such as the deadlift, where you start with the concentric, and the 2nd rep could easily be faster, due to the stored energy from the stretch reflex during the eccentric portion of the lift. For something like a bench or squat, the first rep should have the most force, as you will fatigue a little with each rep. This assumes you are moving the weight as fast as you can.

It depends what you consider strength. The key to maximum force production is indeed less weight moved quickly. I think a common misconception is that there is a linear relationship between mass and acceleration. Less force is produced with maximal weights, but the phyiological effects on the body are much different with max weights than with lighter weights and max force.

The key to strenght is dependent on your goals. As an athlete, you are typically concerned with max force, a powerlifter is concerned with max weight. This does not mean that each should only train one way, as there is a huge carryover between training with max force and training with max weights. Hence the need for powerlifters to do speed work and athletes to do max weight work.

You can’t really measure force by the set, you would have to measure it for each rep. If you really want to know, jsut time yourself. Your force production is going to decline throughout each set from rep to rep. When you start set 2, your force production will likely be higher than it was on the last rep of the first set, but lower than the first rep of the first set. If you want to compare how this works with a 5x5 vs. 5x3, you will have to time yourself. There is sure to be a huge variance between individuals, because now you are starting to introduce muscle fiber type into the equation, and to a lesser extent even VO2 max.

Let’s take the DL for example again. The rate at which you lift the weight will not effect the force that your forearms are exerting. They are not moving the weight, they are simply gripping the weight to prevent it from falling. The Force still equals m*a, but to measure it you would need a dynamometer.

Yes, you are exactly right.

[quote]
7.) Lastly, im trying to apply this to movements like squats and one-leg squats. The problem i notice, is that im weakest at the bottom, and if I accelerate fully without holding back, i will jump. Since im weaker in the bottom, i have to use lighter weights, but by the top im moving pretty fast, and am much stronger at the top. Are resistance bands the answer to this question?

Thanks for the help guys, and any other info you have would be great.[/quote]

This is one of the many benefits of resistance bands, chains can also be used for this. You can also just go ahead and jump. Keep in mind, there is nothing wrong with slowing down at the top so that you don’t jump. Deceleration works the same way with regards to force production. It takes a certain force to decelerate your body, too, so this isn’t necessarily a bad thing.

[quote]dankid wrote:
Ive been thinking about this a lot lately.

So I understand the force/velocity relation and how optimal force occurs for most people somewhere around 75-85%. But heres a few questions.

1.) If im using 75% 1rm vs. 80% 1rm and focusing on maximal speed during concentric movement, even if the weight is moving slow, is it likely that im producing the same amount of force with the two different weights?
[/quote]
according to louie simmons the force peaks at around 55-60% 1RM. Dont know if thats right but it is what he says he got from some Soviet weightlifters. So probably there is a greater force at 75 than 80.

Makes sense to me.

I think the “key to strength” is effort in+progress(meaning heavier weights at same reps). that said, speed work, I have found, is very helpful for increasing strength.

[quote]
4.) How does fatigue play into all of this? Normally if I were doing “heavy weight” maybe 10x3 or even 5x3 using a weight around 85+% the rest breaks are long 3-5 minutes. But if i use say 5x5, i might have shorter rest breaks of 1-2 mins, but isn’t the force likely the same during the set, and since there are more reps, likely more fatigue?
[/quote] If you are lifting x pounds it only takes x(the same x) pounds of force to keep it going. It takes greater than x pounds of force to cause a positive(lifting) acceloration. SO if you are lifting it as fast as you can, then you are applying as much force as you can, and are applying more force than you would with a slow tempo. However when you fatique yourself you probably cant produce as much force as you could before, which would cause the speed to slow down. So if your lifting speed slows down then you are producing less force, but if you are still pushing as fast as you can you are still creating a maximum muscle tension in a fatiqued state.

If you are doing the lift as fast as possible then you would probably be straining all the muslces involved to the largest degree you could,but for a decreased length of time. From my own experience doing speed deadlifts my lats were weak and when i did speed pulls it made my lats feel like they were going to explode, even though i was only using about 50% 1RM weight. Even a max pull didnt strain my lats like that.

If you cant pull hard enough to Impart greater acceloration than 1G upward then you are still applying all the force you can, it just isnt enough to move it. If the bar is on the ground is gravity imparting 1G downward on it, even if it is not moving?

You could try that or chains. You could also try getting stronger at the bottom. You could also hang some weight off a chain so once you get to your strongest point(or a little before) you get a little bit more load, but it could be a shock so dont just max out on that right away, see how it goes first, and dont be afraid to think it is stupid because it may be.

Thanks for the replies. Two questions still.

The forearm question. Isnt the force at your forearms still dependant on acceleration. Because although the forearms aren’t lifting the weight, they are connecting the weight, and the prime movers. I read something about the grip force of olympic lifters during a snatch. I think its isometric or eccentric strength though.

Also, your last comment. How does decelerating at the top of a movement increase force. Wouldn’t muscle spindles or the golgi tendon inhibit muscle activation to prevent your joint from overextending too fast?

Once again thank you.

[quote]tedro wrote:
dankid wrote:
5.) How do muscles that only contract isometrically during a movement play into this? Like grip muscles and core muscles in most lifts. Or, does the greater velocity still transfer greater force to these muscles?

Let’s take the DL for example again. The rate at which you lift the weight will not effect the force that your forearms are exerting. They are not moving the weight, they are simply gripping the weight to prevent it from falling. The Force still equals m*a, but to measure it you would need a dynamometer.
[/quote]

I think lifting a weight faster will cause your hands to exert more force on the bar. For every action there is an equal but opposite reaction, I think Louie Simmons said that(j/k). Seriously though, if more force is being put on the bar(it is moving faster) then the bar is applying more force on your hands. It isnt as hard to grip because you arent holding onto it for as long is all.

You’re first point was not accurate, maximum power usually occurs somewhere around 75-80% depending on the person and the movement, not force.

The effect of gravitational force in an isometric was already covered.

The forearm question is an interesting point because it brings up internal and external work. We’re almost always doing more internal work than external because we have to account for things like stabilization and posture. Who knows?

Just train progressively, eat a lot and don’t get hurt. Everything else isn’t terribly important. Interesting, but not terribly important.

[quote]dankid wrote:

Also, your last comment. How does decelerating at the top of a movement increase force. Wouldn’t muscle spindles or the golgi tendon inhibit muscle activation to prevent your joint from overextending too fast?

Once again thank you.[/quote]

Your overthinking, just get stronger at the bottom and slow down at the top or jump for now.

[quote]dankid wrote:

1.) If im using 75% 1rm vs. 80% 1rm and focusing on maximal speed during concentric movement, even if the weight is moving slow, is it likely that im producing the same amount of force with the two different weights?

[/quote]

In the Russian Weightlifting Text “Managing the Training of Weightlifters” They recommend using weights of 80-95% (depending on the athlete) to develop speed-strength. Loui Simmons in his articles about the dynamic method has stated that in DE Bench Workouts even though a lifter might only be moving 225lbs of bar weight, they can be generating forces above 400lbs.

You can produce the same amount of force with different weights. Depending on your efforts, you can even produce more force with a lighter weight than you would with a heavy weight (going balls out with 135 but going easy with 225).

Sub-maximal weights are great for reps and great for teaching the body to generate force. But Heavy, near-maximal weights will stress the body more and cause more radical adaptations of the CNS, Muscles, etc. And you can’t be certain how much force you’re creating. But you can be more certain when you use heavy weights.

[quote]dankid wrote:
Also, your last comment. How does decelerating at the top of a movement increase force. Wouldn’t muscle spindles or the golgi tendon inhibit muscle activation to prevent your joint from overextending too fast?

Once again thank you.[/quote]

Yes, this deceleration force is going to be minimal in the grand scheme of things, I probably shouldn’t have included it. While the golgi tendons will inhibit muscle activation, it is also fully possible that you are moving at a rate fast enough to require the activation of the antagonist muscles to slow you down.

Just to clarify a few things:

Many times velocity and acceleration are confused. Velocity is the rate of change of position. If a bar is moving at a constant velocity, no matter how fast, the net force on it is zero. Acceleration is the rate of change of velocity.

Yes F=ma however that is net force. That means F=ma= (force you apply to the bar) - (mass of bar x acceleration due gravity)

If the net force is zero (i.e. bar is moving at constant velocity or not moving), then the force being applied to the bar is equal to the weight of the bar.

[quote]Scrotus wrote:
tedro wrote:
dankid wrote:
5.) How do muscles that only contract isometrically during a movement play into this? Like grip muscles and core muscles in most lifts. Or, does the greater velocity still transfer greater force to these muscles?

Let’s take the DL for example again. The rate at which you lift the weight will not effect the force that your forearms are exerting. They are not moving the weight, they are simply gripping the weight to prevent it from falling. The Force still equals m*a, but to measure it you would need a dynamometer.

I think lifting a weight faster will cause your hands to exert more force on the bar. For every action there is an equal but opposite reaction, I think Louie Simmons said that(j/k). Seriously though, if more force is being put on the bar(it is moving faster) then the bar is applying more force on your hands. It isnt as hard to grip because you arent holding onto it for as long is all. [/quote]

Hopefully this answer’s dankid’s question.

The faster you lift the weight, the greater the force required to hold onto the bar, this is what Louie was alluding to. However, lifting fast does not affect the force that your forearms are exerting. Your forearms are exerting a force against the bar, that when coupled with the coefficient of friction between the bar and your hands acts against the force of gravity. Creating greater force at your hips has no effect on how much force you are producing at your forearms.

I think some people are getting force and power confused. Force=(mass)x(acceleration), but power=(force X distance)/time.

[quote]tedro wrote:
Creating greater force at your hips has no effect on how much force you are producing at your forearms.[/quote]

Are you sure about this? I understand the friction part of it, but there has to be a change in force.

If your pulling 400lbs and have a slow acceleration, but are squeezing the bar are hard as you can, then your forearms (grip) is producing forces near your isometric maximum.

But if your doing a 200lb clean, your accelerating very fast, and the GRF at your feet would be transfered through your ankles,knees,hips,spine,shoulders,elbows,wrists, and into the hands. Because of inertia, the greater the acceleration, the greater the GRF, and the greater the reaction force the bar has on your hands.

Is this correct?

Also, as for power / force, i understand the scientific differences between the two, but what does this mean for training. I think i read that max power is around 50% 1rm, while max force is around 75% 1rm. Isn’t the goal of strength training to produce a large muscular tension, which would be at the max force?

Ive also heard some authors on here, stating that power is the key, to getting strong and big.

Whats the deal, and why do they call it powerlifting? Olympic lifting results in greater power doesn’t it?

Thanks again.

[quote]tedro wrote:
Scrotus wrote:
tedro wrote:
dankid wrote:
5.) How do muscles that only contract isometrically during a movement play into this? Like grip muscles and core muscles in most lifts. Or, does the greater velocity still transfer greater force to these muscles?

Let’s take the DL for example again. The rate at which you lift the weight will not effect the force that your forearms are exerting. They are not moving the weight, they are simply gripping the weight to prevent it from falling. The Force still equals m*a, but to measure it you would need a dynamometer.

I think lifting a weight faster will cause your hands to exert more force on the bar. For every action there is an equal but opposite reaction, I think Louie Simmons said that(j/k). Seriously though, if more force is being put on the bar(it is moving faster) then the bar is applying more force on your hands. It isnt as hard to grip because you arent holding onto it for as long is all.

Hopefully this answer’s dankid’s question.

The faster you lift the weight, the greater the force required to hold onto the bar, this is what Louie was alluding to. However, lifting fast does not affect the force that your forearms are exerting. Your forearms are exerting a force against the bar, that when coupled with the coefficient of friction between the bar and your hands acts against the force of gravity. Creating greater force at your hips has no effect on how much force you are producing at your forearms.[/quote]

I was just joking about louie saying that, because I say Louie says this or that on every training post I make, or it seems that way to me. anyways the part about every action having an equal but opposite reaction is basic physics. One of Newtons laws I think but I dont remember/not sure on account of I havent taken a physics course in like 5 or six years.

If a greater force in the downward direction was negated by friction then you could hold onto an infinite amount of weight as long as you didnt rip your hands off. Grip would be a non issue for everyone, which is not the case. Unless I am completely missunderstanding what you are saying.
It isnt going to be that hard on your grip to pull 275 in half a second but with over 2x the force, as it would be to pull 550 in 4 seconds(still as fast as possible), which is why your grip might give out on a max lift but not a speed lift.

Also if you are not accelorating the bar the whole way up then you might have a force peak at the beginning of a pull and have it drop off to just holding it as you approach lockout.
Isn’t power also Force*time?

Power=strengthspeed or
Power=force
(distance/time)

Same thing.

Alright, I think I’ve figured out the confusion about the forearms/grip.

This is kind of an interesting question. I think dankid is thinking of your hands more as hooks. Therefore, the faster the bar accelerates, the greater the force on your hands.

I am considering the hands more as a gripper, where they are exerting the same force on either side of the bar and the movement of the bar is irrelevant.

Either way, the forearms are going to be maximally (or close to it) contracted the whole time, and what we really should be looking at is the force that the muscles and tendons exert on the bones of the hands and fingers. In this case, the force of the muscles on the bones will not be affected by the acceleration of the hips.

I hope this clears it up, this has become an interesting discussion. Feel free to ask more questions, you are really making me think.

[quote]dankid wrote:
Also, as for power / force, i understand the scientific differences between the two, but what does this mean for training. I think i read that max power is around 50% 1rm, while max force is around 75% 1rm. Isn’t the goal of strength training to produce a large muscular tension, which would be at the max force?

Ive also heard some authors on here, stating that power is the key, to getting strong and big.

Whats the deal, and why do they call it powerlifting? Olympic lifting results in greater power doesn’t it?

Thanks again.

[/quote]

You make a good arguement as to why “powerlifting” is an oxymoron, but that’s about it. The relevancy to your comments on max power and max force is questionable.

I think the bottom line is that there is a place for training for max force, max power, max muscle contraction, and max weights. No one is a substitute for the other, but they all carryover well.

I wish I had my “science and practice of strength training” with me, i would be able to quote it.

I believe they stated something like olympic power lifters were tested for maximal grip strength and could exert 200N of force per hand. But when doing a snatch near maximum, the forearms are exerting something way higher, like 500N ea.

I think it has to do with eccentric strength though.

I do believe that the speed of the hips will affect the grip force required.

Max force=max effort. The most force you are able to produce is the most weight you are able to lift. Max power is dynamic effort. That’s where the percents come in.

[quote]dankid wrote:
I wish I had my “science and practice of strength training” with me, i would be able to quote it.

I believe they stated something like olympic power lifters were tested for maximal grip strength and could exert 200N of force per hand. But when doing a snatch near maximum, the forearms are exerting something way higher, like 500N ea.

I think it has to do with eccentric strength though.

I do believe that the speed of the hips will affect the grip force required.[/quote]

Yes, it will affect the grip force required, I said this earlier. It will not affect the maximum force that the forearms are capable of producing.