How to Get Carrie Underwood's Toned Legs - Straight from the Star's Trainer

09/29/2014 at 03:16 PM ET

Zach Harrison

As a former U.S. Marine, Erin Oprea is dedicated to fitness. Now a Nashville-based personal trainer with clients like Carrie Underwood, she uses her expertise to help those with busy lives stay fit. Visit her site Oprea Personal Fitness or follow her on Twitter @OpreaFitness. Then come back to PEOPLE.com every Monday to master a new workout move.

I love the sun and refuse to believe the summer is over. Which means that I’m happy we’ve continued to have warm weather here in Nashville. I’ll continue to wear my short-shorts for every last ray!

And shorts (or skirts) mean you have to keep those legs toned. This variation on a traditional lunge will both give you a leg workout and help stabilize your core by making you balance.

Add this super-charged lunge into your workout this week.

Zach Harrison (2)

Lunge, Kick & Hold

1. Stand on your right leg and lunge back on your left making sure you drop your back knee straight down.

2. Return to the standing position on your right leg while extending your left leg straight out, hold it up for 2 seconds and push through you left heel while flexing your quad.

3. Repeat 12 to 15 times then switch legs. Try and do it 3 rounds.

I love the burning feeling that comes during the leg extension hold. Not only will you tone your legs, but you’ll also get an added core workout from balancing on one leg while holding the kicking position. On top of toning my legs I get an added core workout from one-legged balancing while holding that squeeze in the kicking position.

[Editor's note: We're so excited to welcome Erin to the ranks as a PEOPLE.com blogger. Come back every Monday for an easy exercise that you can master every Monday. And if you have trouble spots you need help with, let us and Erin know in the comments.]