With this perk and 10 Strength, you can carry up to 300 lbs. before becoming overencumbered.
In Fallout: New Vegas with the add-on Honest Hearts, this perk allows you to bring 100 lbs. of equipment with you through a dialog check with Jed Masterson.
In Fallout: New Vegas with the add-on Lonesome Road, when combined with a Strength of 10, Burden to Bear, the NCR Courier duster and the Hoarder trait, you can achieve a carrying weight of 400 pounds.
“What are you, part pack mule? Though those favoring heavier weapons and armor are likely to take this perk on general principle, it's also hugely beneficial to scavengers; spend more time in the wilderness gathering loot to sell or trade! Carry a greater complement of killing equipment! And at higher levels, have some way of easily maneuvering back to safety without dropping your ill-gotten gains.”— Fallout 4 Vault Dweller's Survival Guide description
With rank 3 of this perk, running while overencumbered consumes AP similarly to sprinting. Because of this, increased Endurance also lowers the AP drain just like it would for sprinting.
Rank 3 of the Moving Target perk also takes effect with the ability granted by rank 3 of this perk, reducing the AP drain of running while overencumbered. It also combines with rank 5 of this perk multiplicatively, further reducing (but not negating) the AP drain.
On Survival Mode, Rank 4 will negate damage taken from being overencumbered.
A bug with rank 3 will use your Fusion Core energy, Since it still drains AP. This will quickly use up any Fusion Core energy from your suit but only when moving. as mentioned above Moving Target and Rank 5 of Strong Back will reduce the AP drain. But you can never negate AP drain on moving thus will still continually drain your Cores while moving.
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