Strong Back/Lionheart

Strong Back is a perk in Fallout, Fallout 2, Fallout 3, Fallout: New Vegas, Fallout 4, Fallout Tactics, J.E. Sawyer's Fallout Role-Playing Game and Lionheart.

Fallout, Fallout 2, Fallout Tactics and J.E. Sawyer's RPG
With each rank of this Perk, the player character can carry an additional 50 lbs. of equipment, for a total of 150 with all ranks.

The perk is a convenience and largely useless. The existence of party members means the only moment where carrying capacity becomes a problem is random encounters and even those are repeatable.

Fallout 3 and Fallout: New Vegas
Adds +50 to carrying capacity. With 10 Strength and this perk the carry weight is set at 300, while Burden to Bear raises it beyond that limit, up to 400 poundswhen combined with a Strength of 10, Burden to Bear, the NCR Courier duster and the Hoarder trait.

Again, the perk is largely a convenience, rather than an obligation. The only story impact it has is in Honest Hearts, where it permits the player to bring an additional 100 lbs of equipment through a speech check with Jed Masterson.

Fallout 4
Compared to previous games, Strong Back is a viable option:
 * Rank 1 adds +25 to carry weight.
 * Rank 2 adds another +25 to carry weight.
 * Rank 3 permits running while overloaded (costs Action Points).
 * Rank 4 permits fast travel. On Survival difficulty, the fourth rank instead eliminates damage from overencumbrance.
 * Rank 5, added by Far Harbor, halves the AP consumption rate while running overencumbered.

Lionheart
With each rank of this Perk, the player can carry an additional 50 lbs. of equipment (150 with all three ranks).