Board Thread:Questions and Answers/@comment-118.211.8.204-20150302141811/@comment-3250527-20150908104837

You forget the fact that, in the virtual world, it is not your muscles doing work, it is your brain; your neurons. Through stimulation of the brain, you can release greater "thought power", or "imagination" to control your avatar.

Looking back at the anime in Episode 15 (because I hate quoting from the light novel, unless it's for specific, nitty-gritty details, and Kirito had just finished two months worth of physical rehabilitation, he picks up Sugu's shinai, claiming that it was light. Sugu immediately denied him, saying that "timber bamboo... [is] pretty heavy".

And, mind you, this is only two-months worth of physical rehab. Suguha has been training in Kendo ever since she was a child (judging from the portrayal of her younger self, likely since elementary school days), and she still calls the shinai "heavy". Kirito's muscles are actually (likely) crying with pain; however, his brain doesn't register the pain since it is used to the weight of 50+kg heavy swords. One in each hand, to boot. It's kind of similar to adrenaline rushes, where people miraculously gain incredible amount of strength in a dire situation.

But, back to Yuuki and Kirito. True, both of them have immersed themselves in the Virtual Reality, Yuuki for longer than Kirito. However, it doesn't just stop there; Yuuki is actually connected to a machine (Medicuboid) with a higher processing power than the AmuSphere. This is like comparing a desktop computer to a tablet or laptop PC; the former is more powerful than the latter. So, while Kirito may be physically stronger than Yuuki, Yuuki is mentally stronger than Kirito, since the mind is actually what matters most in ALO. On top of that, Kirito is likely more knowledgable than Yuuki, who was surprised at Kirito's display of Spell Blast (Youtube mirror). Not to mention Bullet Deflect, and all the other Outside System Skills he has demonstrated throughout the series.

Finally, for Excaliber, just remember Kirito's battle with Eugene. Demonic Sword Gram lost to a store-bought great sword and Leafa's sword. With Excaliber not having revealed its special abilities, it's best to just call it as "having very high parameters", which then Yuuki will rather respond to dodges and sidesteps to preserve her weapon's Durability.