Muscle Augmentation is a Quirk that gives its user the ability to manipulate and amplify their muscles. Muscle fibers can be enlarged to where they can no longer be contained by the skin. This grants its user great strength and defensive durability, as well as enhanced speed and agility.
Muscular is the only wielder of this Quirk where it serves as his lone superpower. He uses Muscle Augmentation to cover his limbs with enhanced muscle fibers that protrude from his skin. He can freely choose the muscle mass he covers with his body to increase his abilities. This grants Muscular immense physical strength and speed. 
When fighting seriously, Muscular can obliterate a large chunk of a cliffside with a single strike. By manipulating the muscles in his legs, Muscular can move at blurring speeds that far outclass Full Cowl at 5%.
The augmented muscles provide Muscular with a high level of protection, and the fibers can act as a shield to absorb attacks. With enough protection, Muscular can even take the impact of special moves as powerful as Izuku Midoriya's 100% Detroit Smash, which is equivalent to the strength of All Might.
Muscular's speed also gives him the option to completely avoid incoming attacks. In order to counter Muscular's enhanced speed, Izuku purposely trapped his hand between muscle fibers so Muscular couldn't avoid his next attack.
All For One gave Wolfram the ability to enlarge his muscles and greatly increase his strength. When activated, Wolfram's muscles don't pop out of his skin, instead, they glow bright red and completely change his appearance. This is similar to how One For All at 100% changes the appearance of All Might and Deku.
Combined with the Quirk Amplification Device, this Quirk gave Wolfram enough raw strength to momentarily overwhelm All Might and turn the tide of their battle. Using this ability, Wolfram was able to injure All Might and compensate for his weakness at close range when manipulating metal.
Hood mainly uses enhanced muscle fibers to support its other Quirks, giving it incredible destructive power. Hood can cover its arms and muscles, transform them into powerful tendrils, and increase their power even more by using it in tandem with another strength enhancement Quirk. 
The brute force of this Quirk has shown to be levels above Muscular's own raw power, and allowed Hood to overwhelm Endeavor. Destroyed muscles can also be regenerated thanks to Hood's healing Quirk.
- Aside from the transferable Quirk One For All, Muscle Augmentation is the second Quirk with the largest number of named users in the series, the first being Super Regeneration.