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I'm not talking about training with weights so that when you run without them you're muscles are used to pushing more weight so with less weight it'll be easier, I'm talking about while actually holding them.

So this question arose when I decided to carry some light weights (1kg) as I went for a fast jog: I noticed how easy it was to run faster while holding the weights which got me thinking.

I figure that it would allow you to run faster for the same sort of reasons that we swing our arms in the first place but now it's just multipled somewhat. Running with weights in your hands will allow you to conserve angular momentum far better which means you should be able to move your legs at a faster rate, ie. some more of the work is being done by the arms. Moving your left arm back will contribute to moving your right arm forward, so the more momentum that is in your arm the easier it should be correct? obviously this only works with light weights as if the weight slows down your arm movements you may actually lose momentum. Are my conclusions correct?

I also guess that this will also tire out your legs more as you are pushing around more weight.

Does this all mean that sprinters should train their arms a lot in order to run faster with the higher mass causing more momentum with each swing of the arms? Does this also mean that training with weights is somewhat pointless (overall) as your core will be doing less work?

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The physics of this can be boiled down to Newton's 3rd law;

For every action, there is an equal and opposite reaction.

This is the physical law which dictates that if I push you, you automatically push me back. The reason why you fall and I don't, is that my stance was more balanced (I was leaning into into it because I was ready for it, as the perpetrator), and I absorbed the recoil. This is the same thing that happens when firing a gun. The bullet is pushed forward, but the gun is equally pushed back. But the gun is blunt and not sharp, meaning you don't get harmed holding on to it because the impact is spread out over a larger surface area. But to the point...!

For your example, let's focus on the weight in your left hand. When you push this weight forward, it will push you backwards with an equal amount of force. This means you'll spend slightly more energy accelerating.

When the weight is pushed all the way forward, it has to stop for a moment, before it returns. You will then start pulling the weight backward, but the weight will also pull you forward. This is where you get the feeling of being assisted.

But whatever force you exert in order to move the weight, is mirrored onto you. So when the weight is pulled all the way back again, and you start to push it forward, it will push you back, making this part of the motion detrimental to your forward momentum.

Now, for the case of both weights, it's exactly the same, but alternating (because when you push one weight, you pull the other weight). In other words, this all adds up to 0 total assistance gained from the weights.

But this does not mean that running with weights is pointless, because the energy you spent running is moderated by the weight of your body, and whatever else you're moving (clothes, backpack etc). So if you're holding some extra weight, that's more energy spent per step.

Quick tip; the benefits of extra weight is more beneficial when doing uphill cardio, because the energy spent gaining altitude is directly, and linearly dependent on the mass (weight) of your body and baggage.

So in conclusion, carrying weights while running is indeed beneficial, but it does not assist you in any way. At the end of the day, the assistance you get from the momentum of the weight, is momentum you spent energy starting in the first place. The feeling of being assisted there, is simply you reaping what you sowed!

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    I think the OP was correct to consider angular momentum. Heavier weights = more resistance to the rotation caused by the lower body. Arm swing does cancel forward and backward, but scarboroughtrack.com/sprintingmechanics.pdf points out that the arms are synchronized going up and down. Weights would make this positive contribution to your vertical propulsion weaker. – Noumenon May 9 '15 at 15:47
  • I think in a simplified way you're correct, but it's far too oversimplified to properly address the question. Simplifying to this degree would also make swings impossible. I think this question would've been better on the physics site, any way I can move it? – Aequitas May 9 '15 at 21:19
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Weight negatively impacts running economy, period. Those weights you are carrying are gobbling up extra oxygen with every mile.

However, flailing arms, and arms held too high, also contribute to poor running economy. The weights are helping to keep your arms in a better position, and keep them from moving around too much, so you are getting a taste of what it feels like to have better running form.

A smoother, more controlled form feels more efficient and faster, but in this case this is almost certainly a false sense, more than offset by the effects of the extra weight, especially since you are carrying it at your extremities.

This intuition is corroborated by the paper "Factors affecting running economy in trained distance runners":

Carrying mass distally increases the aerobic demand of running to a greater extent than carrying mass closer to the centre of mass. [P. 469, par 3].

(The above claim is referenced, in turn, to some other publication: some 1994 paper on body-mass-modified running economy and step length in middle-distance and long-distance elite males.)

However, it is not clear that holding the weights is actually all that "distal". If your hands stay close to your hips, the weights are not that far from your center of mass, in fact.

One way to be sure would be to have you do this on a treadmill while you run at a predetermined pace, and breathe into a device which measures oxygen uptake: then compare with weights and without.

Here is the thing: you can improve your running form so that your arms are in a better position and don't move excessively, without carrying weights. Running economy is improved by putting in the miles, week after week, at a decent training pace, by doing interval training, hill work, and also resistance training.

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I asked this question a year ago and it got blocked/edited/removed for being a dangerous?? Anyways I put some more thought into it (but just know Im not mechanically inclined :))

I figured out on my own after reading some books on running form, or at least an idea of why not to do this:

  • The energy lost due to carrying weight like the two other answers said.

  • The weights seem to spread out my stride while slowing down my cadence.

  • A similar gain in stride seemed to come from leaning forward and extending my arms out a little more.

  • A book and other sources that say arms are only for counter weights to remain balanced.

  • As I ran with weights I always ended up bringing them closer to my body to be able to continue to carry them, but without weights you can extend your arms out more and have the same effect as carrying weights to some point.

Lastly I started looking at cadence and stride length to target those super fast times the pros do, and I found out that you are airborne for a good proportion of the time while running. Hard to notice this duration of time in the air, but I believe it now and carrying weights would reduce this airtime. I dont think there is any added momentum for carrying weights since each weight is counter balancing the other one. The extra oxygen used to swing the weights are taking oxygen away from your legs, so you heart rate is probably higher for lower rates of speed. Actually Kaz's answer is pretty good. Last thing, a higher cadence with a longer stride and a slight lean gives me the same feeling as when I was carrying weights. I hope my experiences will help.

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I run with weights almost every day. They do not make me run faster. The opposite is true. They make me run slower, even when I'm not carrying them. A very distinct benefit however, is that the weight helps me avoid injury from running. It's counterintuitive, but is true and can be explained mathematically.

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