Examples of enhanced strength

Jessica effectively takes care of Linderman's thugs.
(Genesis)

Jessica exposes her mother bear side to Linderman's henchman.
(Collision)

Jessica leaves a mess in her wake after killing Ernie, the high roller, and the lowlife...

...and hurls D.L. across the room.
(Better Halves)

Jessica rips the door off a safe...

...threatens to tear the money launderer in half, a threat she later carries out...

...overpowering the three men, then buries them in the desert.
(Stolen Time)

Jessica threatens her father.
(Six Months Ago)

Jessica's anger causes her to close her car door a little too hard...

...kicks D.L. in the chest...

...and accidentally throws Micah against some rocks.
(Fallout)

Niki catches a baton...

...and is surprised after she breaks it in half...

...Jessica breaks a guard's nose.
(Godsend)

Jessica snaps the chains on her cuffs to attack Dr. Witherson...

...leaving her barely conscious on the floor.
(Distractions)

Jessica sneaks up behind Matt after freeing herself from Matt's restraints...

...throws Matt Parkman out a window...

...and folds Aron Malsky in half.
(Run!)

Niki lunges at an agent...

...and pole-dances to defeat another.
(Walls, Part 2)

Jessica throws Linderman across his office.
(Landslide)

Niki punches Candice...

...and is amazed by her strength...

...then forcefully opens a locked door...

...and finds Micah inside...

...she also breaks a doorknob to hinder Linderman's security guards.
(How to Stop an Exploding Man)

Niki swings a parking meter at Sylar...

...hits hims...

...and he falls to the floor...

...then Peter punches Sylar...

...and eventually leaves him bloodied.
(How to Stop an Exploding Man)

Peter forcefully sends McSorley's son into a wall of Wandering Rocks.
(Lizards)

In the Company hospital, Niki throws Mohinder aside ...

... before holding Bob aloft and choking him.
(Fight or Flight)

Niki punches Mohinder.
(Fight or Flight)

Niki bashes down a door...

...and makes her way into Bob's office.
(Out of Time)

Knox leaves a hole through the German's chest and the wall behind him.
(One of Us, One of Them)

Knox feels Peter's fear, then chokes and lifts him off of the ground. (One of Us, One of Them)

Knox "breathes in" Noah Gray's fear...

...and uses it to knock Gabriel into the child.
(I Am Become Death)

Peter easily breaks Sylar's neck.
(Angels and Monsters)

Knox takes in Adam's fear...

...until he can overpower Adam.
(Dying of the Light)

Michael Fitzgerald charges towards Sylar.
(Viewpoints)