About Us


Tom Clifford

Elite Athlete
Professional Endurance Sport Coach
Founder, Without Limits

Founder of the highly successful Without Limits Coaching Program and Without Limits Apparel Brand, Tom Clifford is an elite endurance athlete by any measure. As a competitive athlete in college and beyond, Tom knew how important group training was for motivation. After developing a number of innovative structured running programs and group practices, endurance athletes of all levels became aware of his expertise, and Without Limits Coaching was born. Tom’s ongoing success in coaching has paralleled his continued athletic performance, achieving elite status as an endurance coach and becoming highly sought out for his innovative and motivational training plans.

1 Mile 4:09
3000m 8:22
5k 14:39
8K 24:52
10K 30:52
15K 47:50
13.1 1:08:21
26.2 2:27
70.3 4:02:52
140.6 9:57:00
  • Captain – Eastern Michigan University Cross Country/Track
  • USA Triathlon All American
  • IRONMAN 70.3 North Carolina Champion 2017 4:02:52
  • Top 20 men at NYC Marathon 2013
  • Top 70 men at Boston Marathon 2014
  • Top Amateur at Steelhead 70.3 2012
  • 3rd Age Division WORLD 70.3 Championships Clearwater, FL
  • USATF Level 2 Certified Coach Specializing in Endurance
  • USA Triathlon Certified Coach
  • Coached over 40 athletes to the Boston Marathon
  • Coached 4 female athletes to the “A” Standard Olympic Marathon Trials
  • Coached 3 athletes to their USA Triathlon Pro-Card License
  • Coached 14 athletes to a sub 5 hour 70.3
  • Coached Kona Qualifiers



Scott W. Tunis, MD FACS

Board Certified Physician and Surgeon
Principal Investigator Vitamin Clinical Trials
Multiple Patent Holder

As an actively practicing Board Certified Ophthalmologist / Eye Physician and Surgeon with over 30 years experience, Dr. Scott Tunis is a multi-patent holding, nationally honored, and highly respected member of the eye surgery community. With a special interest and expertise in the beneficial effects of vitamins, anti-oxidants and micro-nutrients, Dr. Tunis was the Author and Principal Investigator of an NIH protocol compliant, prospective, placebo-controlled, double-blind, human clinical trial testing the efficacy of anti-oxidants in slowing the rate of cataract formation: “The Post-Vitrectomy Lenstatin Study”: A Prospective Randomized Double Blind Human Clinical Trial Testing the Efficacy of Lenstatin in Inhibiting Cataract Formation and Progression After Pars Plana Vitrectomy. A lifelong recreational runner, Dr. Tunis ran his first marathon at age 60. At age 63, and exactly 12 months after total knee replacement surgery he completed his first post-surgical half marathon. Through his participation in the runners’ community, it became apparent to Dr. Tunis that endurance athletes desired a daily vitamin formula which was targeted to meet their specific goals of improving daily health, optimizing endurance and promoting recovery. Read the Study.


Board Certified,  American Board of Ophthalmology
Fellow,  American Academy of Ophthalmology
Fellow,  American College of Surgeons
Member, American Society of Cataract and Refractive Surgery
Consumer’s Research Council, America’s Top Ophthalmologists
2010 – 2016 Premier Surgeon – USA Top Innovators in Premium IOL Surgery
Holder of Two United States Patents: 5549614 and 5556400
Performed over 50,000 Eye Surgical Procedures


Diana Davis, BS RDN LDN CDE

BS Nutrition and Dietetics
Registered Dietitian and Nutritionist

With a B.S. in Nutrition and Dietetics, over 30 years’ experience in counseling patients in wellness and diet, and a special interest in optimizing nutrition for peak performance, Diana brings a wealth of practical expertise to the collaborative formulation of Runners Essentials Daily Vitamin Formula. Diana is also an accomplished endurance athlete with a full understanding of the nutritional requirements and specific needs of athletes desiring to maximize their physical performance through scientifically based and natural dietary supplementation.


B.S. Nutrition and Dietetics Miami University 1982
Registered Dietitian and Nutritionist since 1983
Certified Diabetes Educator since 2005
Program Manager Diabetes Self-Management Training Program 2006 – 2018
Program Director Weight Management 2008 – 2017
  • Started running at Age 50
  • Completed her first half-marathon in 2012
  • Qualified for the Boston Marathon with a 4:03:06 at age 58