About Keri


I've always been into health and fitness, but really struggled with the "all or nothing" and "more is better" mindset, which messed up my hormones and really ruined my relationship with food and exercise for a very long time.

Luckily for me, getting pregnant with my twin boys (via IFV after years of infertility issues) was the point at which I finally started to listen to my body. I learned how to balance my hormones through diet and exercise and in doing so I got better results than I ever did following restrictive diets and exercising hours and hours a week.

My mission is to help as many women as I possibly can develop their own version of "The LEAN Life", which is my acronym for a Lifestyle of Efficient exercise and Automated Nutrition. As a working mom, I don’t have the time or the desire to stress over food and exercise but I DO want to feel great in my clothes, have the energy to keep up with my VERY active boys, continue to repair my relationship with food and take care of my hormonal health which is super important to me now that I'm in my 40s.

Keri's Education & Experience


Master's in Applied Exercise Science with a concentration in Strength and Conditioning - Springfield College - 2002

Bachelor's in Exercise Science with a concentration in Human Performance and Fitness - UMass Boston - 2000


Certified Health Mindset Coach 2021

StrongFirst Bodyweight Instructor (SFB) May 2016

StrongFirst Level 1 Kettlebell Instructor (SFG) August 2015

Functional Movement Systems (FMS) - May 2015

Original Strength - April 2015

Metabolic Effect Hormonal Fat Loss Nutrition Consultant - 2014

Certified Strength and Conditioning Specialist - National Academy of Sports Medicine - 2002



Balance Body University - Pilates Reformer, Mat and Barre - 2010


Strength Coach - Mike Boyle Strength and Conditioning - 1999-2003

Director of Personal Training - Master Trainer - Fitness Unlimited - 2003 -  2010

Owner - Keri Mantie Personal Training - 2011 - Present


Boston University Strength and Conditioning - Fall 1999

University of Tulsa Strength and Conditioning - Summer 2001

The College of the Holy Cross Strength and Conditioning - Spring 2002