Contrary to popular belief, the longsword was an extremely efficient weapon if crafted and used correctly. But just how much strength would a swordsman need to successfully use such a sword? This all depends on two very important factors.
The first being the blacksmith's experience level. A longsword is a double-edged, two handed weapon weighing upwards of five pounds. Crafting such a sword took a certain amount expertise and craftsmanship to assure the balance was as close to perfect as possible. If this was done effectively whilst the sword was being made, the amount of strength needed to handle the sword would be dramatically decreased. A fantastic example of this, is the claymore. The claymore is a form of longsword deriving from 13th century Scotland. Although this weapon was over 55 inches in average length, it was said to have exceptional balance and durability. This blade was used by the Highland Scots for over 250 years. But, just how strong were these soldiers in order to be able to wield the such a longsword?
Well, another factor which goes into the strength needed to wield a claymore was technique. The longsword needed to be held with two hands. There were no exceptions to this rule, as wielding the blade with one hand was practically impossible. Just simply holding a balanced longsword was not necessarily a difficult task to perform. However, swinging a longsword took some skill and strength.
But how much strength exactly? If the right technique was used, even some weaker soldiers could swing a longsword hard enough to pierce certain armors. But If a swordsman wanted to do serious damage to opponents they would have to train for years. The longsword was highly regarded as a symbol of strength and power. One of the largest longswords on record was called the 'fuilteach-mhuirt'. It weighed just over 22 pounds whilst being over 88 inches long. This sword could not have been easily wielded by an average person. The person in which the 'fuilteach-mhuirt' belonged to was likely over 200 pounds and extremely strong. The owner was said to be a member of Clan Maxwell. Clan Maxwell was an Armigerous clan residing in the lowlands of Scotland.
Overall, the longsword was, and will always be, an extremely powerful sword. It was widely feared in most battles for its devastating strikes. If an experienced blacksmith created the blade to be finely balanced, it could be very easily controlled. It didn't take an extreme amount of strength to just simply use the sword. But to use it at its full potential the wielder would have to train for years and be extremely strong. Especially if the blade was bigger and heavier than the average blade.