Jaime Arellano: 5 STARS


The gym with high quality students ....ppl get impress by a big gym and forget about quality ..by choosing underground Ur choosing quality ...the Athletes at underground are the most in shape and well prepare athletes from any gym ....the cardio and kettle bell workouts are unique and impressive ...and the fighters and martial artist are top of the line !!!

Very well equipped gym with a very knowledgeable sensei. .. the perfect place to Lear and train all forms of mix martial arts and boxing. ..also a great place just to workout and keep in shape with great trainers and training partners that make you feel like at home since the 1st class.. and the prices are a steal

David Roesner: 5 STARS


 I have trained in countless gyms across the country, that includes Weight Lifting gyms, Boxing Gyms, Mixed Martial Arts, boot camp training and Aerobics. MMA Underground brings all those to the table and is the place I call Home. Wide range of equipment that you can not find anywhere else. Great trainers that will teach and motivate you. If your trying to loose weight, or learn how to fight, or gain some muscle, or just get back in shape, Underground is the gym for you.  

Jared Keck: 5 STARS


 A great place to train with a great Sensei who loves to teach.

Oscar will teach you if you are willing to learn not only Martial Arts but also how the live to Warrior Lifestyle.

As someone who is a little older (47) with no martial arts experience I was a little intimated walking in. Oscar put me right as ease. He cares about his fighters. Your training partners in many ways become family.

If you are just looking for a great workout he has that everyday also 

Kathy Pletz: 5 STARS


I started training here in 2008. I lost 50 pounds and have kept the weight off. For being 56 years old I even got my waist back! The kettle bell training and strength training is an all body workout and muscle strengthening. I also love the fact that it is a 30 minute workout for me and it would be awesome all people who are short on time. Oscar Sensi is wonderful and so are all the people who go there, it is a family who really cares about one another.

MMA Underground is the best! 

Joshua House: 5 STARS



I trained here for about a year and a half. Unlike larger gyms, training was very personal and the sensei was constantly reviewing techniques and movements during drills. If students had questions in the middle of a drill, he would demonstrate proper technique again and again until everyone had a clear understanding.

There is a high emphasis on conditioning and technique, and it shows. Several fighters that have trained at MMA Underground have participated in and won several fights.

In training, fighters are mixed among weight classes as there is also an emphasis on real-world fighting and self-defense. Light fighters get great experience rolling with heavier fighters.

10/10 would train here again if I lived in the area and I highly recommend it for newcomers and veterans alike.

Tonia Slain: 5 STARS


MMA Underground is a highly respectable gym carrying a variety of workouts for all levels with a supportive environment to push everyone in a direction of total wellness. Oscar and Dylan know how to push your limits through encouragement and presenting challenges appropriate to your level. Highly recommended!

Cheryl Cangiolosi: 5 STARS


I have been working out with Dylan at MMA Underground for 6 months now. Every class is fun, challenging and one of the hardest workouts I have ever done. It is a family environment and everyone pushes each other to stay motivated. I highly recommend them!

Liz Murray: 5 STARS


I've tried several gyms and could never find a place that I felt like I could fit in or be comfortable or get motivated to achieve what I wanted. MMA Underground is hands down the best experience I've ever had in a gym. Oscar is a wonderful instructor with an extensive martial arts background. The environment he fosters within MMA Underground makes everyone feel welcome and important. They offer several different classes, all which are excellent workouts. Whether you want to compete, become a professional fighter, tone up, or just pick up a new hobby Oscar and the team at MMA Underground can help you achieve your fitness goals. There is even a kids class for young ones to learn mixed martial arts, I have a 7 year old daughter and she absolutely loves it just as much as I do. This gym is positively AMAZING!

Sarah Quigel: 5 STARS


I have taken classes at MMA Underground over the past 6 years and love it! I have never had better results from any other workout before-- the 30 minute strength training (Kettlebells, circuits, kick boxing, etc) is always a challenge. Oscar, the owner/instructor, is always coming up with new ideas to keep the workouts fresh, fun, and tough!

This gym is for everyone -- whether you are just looking for a good workout or fighter training of all levels. I started with no experience and always felt welcome & encouraged to improve/get stronger. MMA Underground is an excellent value, a great atmosphere, and I would recommend it to anyone (and have)

Ralph Davis: 5 STARS


Not only a great gym to be a part of, but a great family. The workouts (before the MMA classes) are fantastic and put me in the best shape of my life and can be suited for any person with any level of endurance. The head trainer, Oscar, has been around martial arts and physical training his whole life and truly knows a great deal. The learning and training environment is geared towards any level of experience and can be tailored to train you for competition (golden gloves, boxing matches, NAGA, cage matches, submission wrestling, etc). I played competitive athletics throughout high school, D1 collegiate rugby, and ran a marathon and the years training here have by far the best sports and one of the best life experiences I have had.

Anastasia Sfakiotis: 5 STARS


Best place to workout in Crystal Lake..Oscar is the best!!!He is very patient,friendly and knowledgable...I would recommend to everyone to visit that place you have nothing to loose only earn and learn a lot about Martial Arts.:)


Salvador Mendoza: 5 STARS


This is a great place to learn & practice Martial Arts, Oscar Sensei & his team of coaches will teach you to develop your skills to become a true warrior in an environment that will make you feel like family....Come & have tons of fun!!!!

Marta Garcia: 5 STARS


I don't personally get to train at MMA underground because I live over an hour away however my brother trains there. I couldn't be happier with MMA underground I have seen such a positive transformation not only physically but emotionally in my brother. MMA underground is made up of some of the best people I know. Sensei Oscar is one of the most genuine caring guys you could ever meet. He will give you the shirt off his back or the swift kick in the butt to motivate you if that's what is needed. I like to go there to visit and watch my brother train and I am always welcomed with open arms. They really are like a family there. All the people that train there push and motive each other to succeed in whatever goal they have set. I highly recommend trying it out!


Maria Perez-Schaley: 5 STARS


I am so GRATEFUL to have found this dojo. Sensei Oscar is an amazing teacher. He also is a wonderful example of a man who incorporates not only his teachings but his thoughts of who a truly good person is. I have personally seen awesome transformations of the MMA fighters who train there. My son goes to this facility to train. He has gained not only muscle and weight loss but has become more confident. He is more focused and on a good track. I myself have taken some classes there. It was so much fun and you feel amazing. It brings out something very cool in you. I hope to be able to join someday once I get some medical issues out of the way. It is a honor to train there. Also an honor to know Oscar and become part of the MMA Underground family.    

Dawn Meade: 5 STARS


Amazing place. Great people. Oscar has made a friendly, family oriented environment. 

Jeanne Meister: 5 STARS


I have been taking various cardio boxing/kettlebell classes for the last two years. From the moment I began working out at MMA Underground, I knew it was where I needed to be. Oscar and his staff bring a multitude of experience to this gym. Whether you are just looking for a great cardio burn and strengthening to various forms of fighting, you will find it here. As a woman, I have not only physically strengthened, but mentally strengthened. It's an empowering feeling and I highly recommend it! 

Lori D'anza: 5 STARS


What's something exciting your business offers? Say it here.  

Excellent place! From beginners to highly experienced, they make all feel welcome, no matter what level you are at.

Jimmy Merino: 5 STARS


Mixed martial arts has been around forever! I always worried about my son getting picked on because he's a small dude like his daddy! He learned enough to protect himself and I sleep better at night knowing he is capable of handling his own! Thanks to his teacher for taking the time with my son Chris Merino and teaching him it’s not the size of the dog in the fight, It’s the size of the fight in the dog!

Emily Kunash: 5 STARS


Love the staff. The workout I get at Underground is incredible.

Balage Srinivasan: 5 STARS


The instructors are extremely knowledgeable, highly motivated, and awesome people to be around. I've never been in a gym with a better vibe, ever. 

Keren Marie York: 5 STARS


This place became like family, and has made me the person I am today!! Don't know where I would be without MMA underground 

Jessica Vilmin: 5 STARS


One of the best gyms I've ever been to. One hour quickly turns to four, and it begins to feel like a second home! Every day is a new challenge! If I didn't move so far away I'd be back again.

Judith Wolf-Dentro: 5 STARS


Wish I could've gone again today!!!! Such a intense workout that after two days of going morning and night, I had to take a break! Lol love the place! I love the instructors! I'm completely addicted to this place and will always keep coming back for more!

Jennifer Brotemarkle Silber: 5 STARS


I just started a week ago and already I feel so much better! My results are both physically and emotionally/mentally noticeable. Huge stress release, much needed in my life right now. I have been impressed by the friendly and helpful staff and members. The workouts have been amazing! I LOVE working out again!!!

Marco Leyva: 5 STARS


When I came to this place I had no idea how to fight, however with the great people here I was able to learn a lot. MMA underground not only helped prepare me for my final wrestling season, but gave me the confidence to trust in my abilities. I highly recommend this gym to anyone who wants to learn to fight while still having a great time doing it.

Samantha Fetzner-Dayton: 5 STARS


I spent several months in classes at MMA Underground and was impressed with both Oscar and Dylan's coaching! I felt like I learned a substantial amount and was so inspired I bought myself equipment for home- both kettlebell and boxing! I highly recommend this place for it's classes! Top notch and never a dull moment! 

Jessica Taylor: 5 STARS


I love this place! Great people, great work out! There are a lot of different options for exercise at different times in differs days which helps with a crazy schedule. They even have classes for kids. 

Rafael Arellano: 5 STARS


MMA Underground is a great place to lose weight & learn MMA, Thank you Oscar for your dedication & hard work!!


Piotr Masnica: 5 STARS


MMA Underground has changed my life for the better. The trainers and students are absolutely amazing. Anyone is willing to help you out and help improve your weaknesses. If you want to become a great fighter quickly this is the place to train at. It has helped me become more humble and calm in many situations. If I could rate this place any better I would.

Neil Cangiolosi: 5 STARS


Great place to workout. The teachers are all excellent and very friendly.

Meigan Pollack: 5 STARS


I love this place. I certainly feel challenged while I'm working out and so fantastic when I leave. It keeps my mind engaged and absolutely engages my body as well. The staff is wonderful and I really have a great time while I'm working out. Thanks guys you are the best.

Susan Tillich-Gerber: 5 STARS


MMA UNDERGROUND is the best place to workout. Lots of variety from boxing to Kettle Balls and much much more. Love Oscar and Dylan. Very knowledgeable trainers. Lots of great people to workout with. They encourage each other and keep me motivated.  

Sharon Massie Whitaker: 5 STARS


Love this place! Great instructors!

Zach Benkert: 5 STARS


This gym is best the place to train in Mchenry County. Whether you are looking to get into the sport of MMA, or just looking to better your physical fitness, MMA Underground has you covered. You can learn and grow as an athlete in a comfortable, stress free environment where everyone there is looking to help you better yourself. Oscar knows what he is doing and always takes care of everyone at his gym. I have made some great friends at this gym and I know that if you take the time to stop by, you will too. 

Jon Alfaro: 5 STARS


I went to MMA underground in it's early days. It changed my life. Oscar made a huge impact on me as a trainer/coach and friend. Amazing gym. Prepare to be transformed.

Chi Sheibley: 5 STARS


Not only have I become more physically and mentally stronger here, but training with Oscar has allowed me to become more focused in life as well as put me on a strong path towards a professional career in MMA. I would highly recommend this gym to anyone looking to become a stronger and stress free person in every aspect in your life!

Hugo Morales: 5 stars


As an avid practitioner of martial arts for over 20 years and being in out of many gyms I've studied in my technique was cleaned up in here, the lineage goes back to Kimura, it's friendly and inviting here I'd recommend it for your a confidence and good health

Karen Sheibley: 5 stars


I didn't know when I started how much I would like this place...I'm so grateful for MMA Underground and for Oscar. It is a place that makes you feel like family and challenges you to do your best. I don't know if it has helped me more physically or mentally but I am so glad I'm here. Thank you to our daughter who brought us in and thank you to Oscar for sharing his knowledge and expertise.

Zarik A Khimani: 5 stars


Treated like family.

Vic F Rodriguez: 5 STARS


Don’t know where I would be without this place and Oscar 

Dylan Kowalski: 5 STARS


My life has gotten better in every way since I started training here. Would recommend to anyone.

Salvador Moreno: 5 STARS


The best teacher 

Chace Davis: 5 STARS


A great place to train, work out, improve fighting skills and become a better person. I trained for some years a while back and go back every chance I get just to say hi, catch up and even learn something. I've been through 20 years of school, earning my medical doctorate and now finishing training at a prestigious hospital and I can say my time spent at MMA underground was foundational to the learning habits and discipline that have carried me to where I am. Even if I'm not paying dues, I always feel like a member. Highly recommended. 

Nate Aleo: 5 STARS


Underground has been my safe haven for the last 2 and a half years of my life. Before the gym I felt unfulfilled with my life, and that I needed to do something more besides work and hang out with my friends. I had tried mixed martial arts previously at another gym and quit the same week. They didn't take the time to teach me and just made me hit a bag. I regretted the decision of quitting and found this place a couple years later when I moved to Lake in the Hills. In the beginning it was hard because I was out of shape, but coach Dylan Kowalski and head coach Oscar Olivares have been there to push me through all of it. Including all of my training partners who are more than friends but are family we are one. Fast forward to today I'm having success in my fights and currently on a winning streak. I would recommend this gym to anyone who wants to pursue being a fighter, or just training to stay in shape and live a healthy lifestyle.  

John Pletz: 5 STARS


Sensei Oscar is a phenomenal teacher. If you want to learn true mixed martial arts, this is where you go.