When does 35 + 10 NOT equal 45?

[commutator]

So I'm doing some incline bench presses this morning. Need a 45-lb plate, and don't see many free ones. Plenty of 35- and 10-lb plates though. Problem solved, or so I thought.

I was using a weight that is pretty heavy for me, but I had successfully lifted that weight for 4 reps the week before (using 45s), and could have probably squeaked out 1-2 if I had to. This time, rep #4 went down, and stayed on the safety bars (thankfully I was doing inclines instead of flat or decline presses).

Here's the weird thing. I tried a few minutes later using the 45-lb plates (and a spotter) and burned through the 4 reps with no problem again. If anything, it was easier than last week.

Does anyone know what the variance in commercial plate weights is? I'm having a hard time coming up with an explanation other than the combined weight of the 35- and 10-lb plates being more than the 45-lb plate, and I was in a range where 5 lbs or so might make a difference. I realize that there is a slightly different mass distribution, but I can't see how that would have much of an effect on this symmetric, two-handed, vertical motion (yes, I know it's classified as a horizontal push).

This is really bugging me. I think I'm going to have to sneak the plates into the locker room and weigh them when the manager isn't looking.

Cheers,

Commutator

[Rev]

Well I would probably guess that it was your body and not the actual weights. I have had hard warm up sets and then blazed my final heaviest sets many many times before. I can't really explain why, I can make a guess that maybe my body had greater blood flow in to the muscle groups I was using after the building sets, or it was possible I rested longer for the very last set. In fact I did this just yesturday with close grip bench. That's my best guess, good luck.

[commutator]

Originally posted by Rev:
Well I would probably guess that it was your body and not the actual weights. I have had hard warm up sets and then blazed my final heaviest sets many many times before. I can't really explain why, I can make a guess that maybe my body had greater blood flow in to the muscle groups I was using after the building sets, or it was possible I rested longer for the very last set. In fact I did this just yesturday with close grip bench. That's my best guess, good luck.

Rev,

Good suggestion, but I should have added that what I had done up to that set (stretching and warm up sets) was identical to the week before, as well as the same time of day (1st thing in the morning). Thanks for letting me know I'm not the only one though.

[CC dad]

I dont know about plates but we weighed a set of 60lb dumbells at my gym one day and found that one was 61lbs and the other 58lbs.

[OldGuy]

An article on weight of plates.

http://www.ivanko.com/article2.pdf

[Simon.]

Well I posted a reply last night but for some reason it didn't get sent...
You don't need to sneak the plated in to the locker room, you can just do a simple test. Put a 45'er on each side of a bar and balance it on a bench (should be right in the middle but hey i dunno.. :/), then replace one of ther 45'er with a 35 and a 10, and see if it's still balanced.
With a 2 metre long bar, even the slightest different can make it tend to one side or the other...

[Newlife]

Originally posted by OldGuy:
An article on weight of plates.

http://www.ivanko.com/article2.pdf

Great call Oldguy. I was thinking of the same article. This is why all my weights, bars, and collars come from Ivanko. Too much junk on the market and plates vary way too much. And don't even get me started on hole sizing. When someone can't drill a hole the same size from plate to plate, you have to question quality.

I think you were just having an off day. Happens all the time to lifters. Could have been your energy level, the amount of sleep the night prior, water level, stress, or recovery time from the last workout.

[commutator]

Originally posted by Simon Glumcher:
Well I posted a reply last night but for some reason it didn't get sent...
You don't need to sneak the plated in to the locker room, you can just do a simple test. Put a 45'er on each side of a bar and balance it on a bench (should be right in the middle but hey i dunno.. :/), then replace one of ther 45'er with a 35 and a 10, and see if it's still balanced.
With a 2 metre long bar, even the slightest different can make it tend to one side or the other...

Simon,

Thanks for the reply. In the experiment you described though, I would be surprised if there wasn't a difference. The torque that each set of weight applies does depend the distribution of mass, which is a little different for the 45 vs the 35 + 10. If you're balancing the bar on a single point dead center, it would probably tip towards the 35 + 10 side, since that mass will extend out further from the fulcrum than the 45. Balancing on a padded bench (as opposed to an infinitely narrow point) might hide this effect though.

Also, this entire tourque effect would cancel out in the case of a symmetrically loaded bar being held with two hands.

Sorry, one in a while the physicist in me escapes.

Thanks to the others who replied and posted the article.

Cheers,
Commutator

[Phitz]

I'm surprised no one mentioned the old "mind over matter" theory. Or in this case the opposite

I find that my mind makes a connection visually with what I can lift. A bar loaded with more plates just seems to look heavier than one that has less, even though they may be the same weight. That alone tends to trick my brain into thinking it's heavier and, as a result, harder to lift.

I imagine the opposite may be true as well. For example, some people may be able to stack on smaller weights and bench the equivalent of two 45s per side. But then have trouble when they load up two plates because it becomes a bit of a mental block.

Just a theory, but the mind is a significant factor. Of course that's along with all of the other factors people listed above...