When celebrity trainer Anna Kaiser calls and invites you to do a 5-day intensive workshop with her that mimics the exact workout she does on her famous clients, you don't say no. At least I don't say no. Because Kaiser, founder of AKT In Motion, is one of the most motivating, positive, brilliant minds in the fitness industry. And she kicks major ass. This worked out perfectly since I was in the mood for a major ass-kicking.

So I said a resounding YES and shortly after found myself waiting patiently inside her Nomad studio one Monday morning a few weeks ago for day numero uno of the aforementioned workshop. On the agenda: 5 days of intensive classes, all led by Kaiser, that would give me a taste of the full scope of the concept behind her workout. (Her method, by the way, is an exercise routine rooted in functional movement combining circuit training with HIIT, strength, toning, dance cardio, Pilates, and yoga.) Oh, and PS, Kelly Ripa, Karlie Kloss, Shakira, and other beautiful bods in Hollywood all call her on the reg to whip them into shape.

Day 1: Happy Hour, her signature dance cardio class (below). We start with a warm up before we start rocking out to a beast of a playlist that gets us through an hour + of sweat drenching cardio. Anna (who by the way just had a baby), is working harder than any other person in the room, as revealed by all of our heart rate monitors that are displayed on a screen at the front of the studio. Her energy is palpable, and I leave the class feeling incredibly inspired and excited for the week of classes ahead of me.

Day 2: I leap out of bed in the morning without hesitation (this is rare. Unheard of, actually) and make my way to the studio for Sweat Dream, a cardio-strength combo class using resistance bands hung from the ceiling. This class is no joke. By the end of the hour I can barely move my arms. But just like yesterday, Anna's energy gets me through it, no problemo.

VIDEO: How to Get Toned Arms Like Kelly Ripa

Day 3: I wake up this morning extremely sore, as anticipated. But I feel great. Today's class is called Tone, which consists of 45 minutes of total body toning followed by 15 minutes of foam rolling and deep stretching. This is actually the perfect day for this class because I am in desperate need of stretching. I am 10 minutes late which puts me in a state of panic the whole subway ride uptown, but I finally make it. Bonus: My heart rate is already through the roof and I'm sweating, and I haven't even started the workout. The first 45 minutes are a challenge (think Pilates and barre-inspired strength moves) but it's the cool down that really throws me over the edge. Yes, the cool down. We work our fatigued muscles out on the torture device known as the foam roller and suddenly I've never been so desperate to get back to toning. It hurts. BAD. The best kind of pain that is so brutal yet you know is doing your body so much good. By the time 15 minutes has ended I feel like I just had a 90-minute massage. I leave class and head immediately to Paragon Sports to pick up a foam roller for my apartment. I've used it every day, ever since. It's changed my life.

Day 4: Due to the aforementioned foam rolling, I feel pretty good. I am sore from head to toe but oddly also feel refreshed and renewed. I head to day 4 of class, known as 4Play. (4 exercises x 4 circuits, done through a combination of HIIT intervals and functional strength training, using weights, bands, balls, and anything else you can think of). This. Is. Hard. SO hard. I think about quitting, but then I look over at bright-eyed bushy-tailed Anna, and I instantly erase that thought from memory. As a plow through a series of weighted squats, I ponder how it is that she is pouring sweat and exerting more energy than all of us, yet doesn't look tired in the least bit. Then I think about how she has a newborn at home and begin to wonder how many hours of sleep she got last night (Two? Three, maybe?) I decide to squat lower and suck it up because I literally have zero excuses not to.

Day 5: The last day of the workshop! One would think I would be thrilled to be done with this journey of torture, but in actuality, I woke up this morning feeling sad. For the entire week, I committed to something that was doing my body, mind, and soul an incredible amount of good. I started each morning with one of the most positive, upbeat, inspiring woman I know. I tested my body to its limit. And I feel incredible. I go to class (a combination mixer of all of AKT's offerings) and give it my all. I collapse into a sweaty fetal position on my mat at the end.

What did I do after? Go directly to the spa? Throw my gym shoes in the trash on the way out the door? No. I immediately went to the front desk and signed up for a double class for the next morning. Crazy? Yes. True story? Double yes.

I've been addicted ever since. And my body has never felt better. Karlie, I understand your obsession.

For more information about AKT In Motion, aktinmotion.com.