What are three examples of Beowulf's superhuman strength throughout the story?
During the battle with Grendel's mother, there are numerous comments made by the poet to the effect that Beowulf is "wigena strengest": the strongest man. He is also described as "trusting to strength," in the knowledge that he is not at the same disadvantage as another mortal man in his battle against this supernatural being, however fearsome Grendel's mother may be. So, we know that the poet does set considerable store by Beowulf's great strength. As indicated in the previous answers, we also see this strength at play in Beowulf's fight with Grendel and in his furious manhandling of Grendel's head.
However, there is also cause to question how far Beowulf's belief in his own strength may be overstated. The idea of "ofermod" (over-ambition) in Beowulf has been the subject of much scholarship. At the end of the poem, Beowulf takes on the dragon on his own, but ultimately his belief in his own strength is insufficient to save him. In part, we are led to believe that this is because of his great age, and not a reflection on his bravery, but others have pointed to some of Beowulf's earlier boasts and questioned the truthfulness of them. Beowulf is strong, but is he truly superhumanly so? Early in the poem, Beowulf describes to Unferth how he held his breath for the entire duration of a swim beneath the ocean and a battle against several fierce seamonsters—perhaps another example of superhuman strength, but equally perhaps an expression of ofermod, or a typical meadhall boast that stretches the truth.
The instances showing Beowulf's superhuman strength are regularly expounded upon by the poet, who not only describes the feat, but mentions how no other single man could complete the task. The first of these that appears in the text is in the Beowulf's battle with Grendel. The other Geats leap to Beowulf's aid, but their weapons are useless against Grendel's tough hide and devious spells that "blunted every mortal man's blade." Be that as it may, Beowulf still managed to rip Grendel's arm off at the shoulder - and Beowulf used only his hands and beastly strength.
The second example I would mention is the giant-forged sword in Grendel's mother's lair. The poem describes this sword as "so massive that no ordinary man could lift its carved and decorated length." Not only does Beowulf manage to lift it from its hanging place on the wall, he also manages to swing it hard enough to cut off Grendel's mother's head with it.
Last, but certainly not least, is the presentation of Grendel's head to Hrothgar and the Danes. After killing the mother, Beowulf was still filled with rage. He went after the body of the already deceased Grendel and cut off its head with the giant-forged sword. It took four men to carry the head on spears back to Herot, but when they arrived, Beowulf single-handedly tossed the head down on the table in front of the Danes who had so recently deserted him.
Beowulf is stated to have defeated five great giants and led them to their imprisonment. The idea that a human being is able to defeat five giants demonstrates that Beowulf is no ordinary human being. Beowulf also exhibits superhuman strength, because it is stated that he fought monsters in the ocean and eliminated them one after the other. Beowulf’s adventures are stated during his introduction to Hrothgar when he went to face Grendel.
The fight with Grendel’s mother is another exemplary demonstration of superhuman strength. Beowulf is stated to have stayed underwater for hours fighting Grendel’s mother. Man is naturally not adapted to staying underwater for long periods of time without any form of underwater breathing technology. Thus, the story of Beowulf staying underwater for hours shows superhuman abilities.
In his last battle, Beowulf fights a dragon. He is old at the time, but his youthful vigor has not left him, as seen in his vicious fight against the dragon. In a show of superhuman strength, Beowulf decides to face the dragon with only a sword and a shield. He manages to defend himself from the dragon’s attacks, but he gets injured. Wiglaf, one of his soldiers, joins the battle and helps Beowulf defeat the dragon.