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I generally do normal biceps curls using dumbbells of 10 kilograms on each hand. With that I am able to do 20 curls with each hand at a stretch( I am a beginner).

However I tried today lifting a rod with 10 kilogram on each side (i.e.total 20 kilograms) . I initially thought that lifting a rod with 20 kg (10 kg on each side) with both hands(through the same distance) will be very similar to lifting 2 dumbbells of 10 kg each (one in each hand ,together) through the same distance.

A barbell is similar in principle to 2 dumbbells joined together. So I thought that i would be able to do the same number of repetitions . But I could do only 10 at a stretch. Can someone explain me why the difference? Is there some valid general reason, or was it a fault with my body(maybe tiredness or something which I thought i wasnt))?

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    I think you forgot to factor in the weight of the barbell (rod) in this situation. – Alex L Dec 5 '15 at 18:36
  • Oh thanks. Now I see. Can you estimate how much a general barbell weighs? – Qwerty Dec 5 '15 at 19:39
  • You should also consider that if the bar is getting thiker that the weight you will be able to lift decreases because of the fact that a part of your strength goes into your forearms holding the bar :-) – mitro Dec 5 '15 at 20:48
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    Most Olympic bars are 45 or 30 pounds (20 or 13.5 kg), but can be lighter if they are fairly short or cambered (or standard bars). Your best option is to weigh yourself and then again with the bar to find the weight. Another option is to compare the barbell with pre-marked dumbbells until you find the correct weight. – Alex L Dec 6 '15 at 15:01
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    Because you mentioned "10kg on each side", you're probably using a barbell. However, if you're using a bar with a preset weight on it, then the weight written on the bar is the total weight. – Yousend May 16 '16 at 13:17
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The additional weight could be due to a number of factors:

  • You have ignored the weight of the bar. A Olympic barbell is 20kg (sometimes 13.5kg). A Ez bar (cambered) is usually 7.5kg.
  • A thicker bar means your forearms are working harder to hold the weight.

Stand on a pair of scales with either weights and then work out what the difference is.

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