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))?