At Trimarni Coaching, we believe exceptional coaching begins with understanding the individual. No two athletes are the same. Every athlete brings a unique combination of goals, experience, strengths, challenges, lifestyle demands, and performance aspirations. Our coaching philosophy is built around recognizing those differences and creating a personalized approach that helps each athlete achieve sustainable, meaningful progress.
We coach every athlete as an individual—not as a template. Whether your goal is completing your first triathlon, setting a personal best, qualifying for a World Championship, or simply maintaining a healthy and balanced lifestyle, our programs are designed to fit your life rather than take it over. We believe triathlon should enhance your life, not consume it, and our goal is to help you maximize your performance while maintaining long-term health, enjoyment, and balance.
As coaches and athletes, we bring decades of hands-on endurance sport experience to our athletes. Together, we have completed more than 40 Ironman triathlons and qualified for the Ironman World Championship 10 times. We understand firsthand the physical, mental, and logistical demands of endurance training and racing. More importantly, we know what it takes to prepare athletes of all levels for success, from first-time finishers to highly competitive age-group and professional athletes.
2025 Trimarni Team Results
Our Coaching Team
Marni and Karel lead the coaching program and share primary coaching responsibilities across the Trimarni team.
Assistant coach Joe specializes in workout analysis, training modifications, athlete support, and performance data review. His attention to detail, analytical mindset, and commitment to athlete development make him a valuable resource for our athletes.
Assistant coach Katie - coming soon!
Marni Sumbal, MS, RD, CSSD, LD/N
Marni is a Board Certified Specialist in Sports Dietetics (CSSD), USAT triathlon coach, holds a master of science in exercise physiology, 3x published author, and accomplished endurance athlete. She has held a USAT Coaching certification for almost 20 years. Her athletic achievements include 22 Ironman finishes, 4 extreme triathlon finishes, 6 Ironman World Championship appearances, a 5th-place age-group finish at the 2021 Ironman World Championship in St. George, Overall Female Champion at the 2024 Ironman 70.3 Louisville, and Overall Female Amateur Champion at the 2024 Ironman Chattanooga.
Her expertise uniquely combines exercise science, performance nutrition, and endurance coaching, allowing her to help athletes optimize every aspect of training and racing.
Throughout her coaching career, Marni has guided athletes to first-time Ironman finishes, age-group podiums, World Championship qualifications, and personal best performances. Her extensive background in sports nutrition has helped countless athletes develop confidence through effective fueling strategies, improved dietary habits, and race-day nutrition plans that support peak physical and mental performance.
Karel Sumbal, RETÜL Bike Fit Specialist
Karel brings a unique blend of cycling expertise, triathlon experience, and technical knowledge to the coaching team. As an experienced RETÜL bike fitter and highly skilled bike mechanic, he helps athletes maximize efficiency, comfort, and performance on the bike.
A former Category 1 cyclist who transitioned into triathlon, Karel understands the demands of cycling through the lens of a triathlete. He also understands the difficult that many triathletes experience when learning how to swim as an adult. He excels at helping athletes with technique, efficiency and improved bike execution through smarter decisions regarding gearing, cadence, power management, bike fit, and pacing strategies.
Since becoming a triathlete in 2012, Karel has completed 20 Ironman triathlons, 3 XTRI events, 2 x Breck Epic MTB stage races, Cape Epic, Pisgah Stage Race, Xterra events and several other stage races. He has qualified for and competed at the Ironman World Championship six times.
Katie Colville, degree in Exercise and Sport Science, NASM certified personal trainer
Katie is a 31-time Ironman finisher, eight-time Kona qualifier, and professional triathlete who transitioned to pro racing in 2023. She recently placed 3rd female pro at Ironman Maryland. With a degree in Exercise and Sports Science, nine-plus years of coaching experience, and a decade of strength coaching, she specializes in long-course racing and takes a science-based, holistic approach to athlete development. Her coaching philosophy emphasizes consistent training, strength, flexibility, and self-belief to help athletes reach their potential.
Joe Nagy, Ironman University Certified
Joe approaches training and racing with a methodical and analytical mindset. Over the years, he has dedicated himself to researching, testing, and refining every aspect of performance across swimming, cycling, running, strength training, and recovery. His expertise now spans both macro-level optimization—such as coaching strategy and bike fit—and micro-level refinements, including tire pressure, chain lubrication, and other equipment details that can influence race-day outcomes. Joe has a marathon PR of 2:53.09, has qualified for the Boston Marathon two times, qualified for the 70.3 World Championship three times and has finished the 5-stage Oregon Trail Gravel Grinder and Paris Roubaix Challenge Cycling event.
MISSION
We provide personalized coaching for athletes of all abilities, specializing in endurance sports. Our integrated approach combines science-based training, sports nutrition, and individualized guidance to help athletes build fitness, develop skills, and reach their performance goals. We believe the best results come from prioritizing health, supporting mental well-being, stretching the comfort zone and finding enjoyment in the process. Our philosophy is simple: health first, performance second — building stronger, more resilient athletes through a sustainable approach to training and lifelong athletic development.
VISION
We strive to create a positive, supportive, and inclusive environment where athletes of all abilities can thrive. Whether your passion is triathlon, XTERRA, mountain biking, gravel cycling, or extreme triathlon, our goal is to keep the journey enjoyable, rewarding, and sustainable. Through personalized guidance and expert coaching, we help athletes build fitness, pursue meaningful goals, develop confidence, and discover their full potential both in sport and in life.
CORE VALUES
Protecting mental and physical health
Trust and loyalty
Communication
Long term development
Education
Collaboration
Patience
Integrity
Discipline and commitment
Individual Coaching
Our Individual Coaching Program is designed for athletes seeking a highly personalized coaching experience with ongoing support, education, accountability, and expert guidance. Every training plan is customized to your goals, experience level, race schedule, lifestyle, and performance objectives.
We are passionate about the athlete development process and committed to providing a high level of personalized support, communication and education. Our coaching extends far beyond simply prescribing workouts. Every workout is designed with attention to:
Endurance development through building durability, efficiency and resilience
Strength training and mobility integration
Daily and race-specific nutrition
Terrain management, tactics and race execution
Structured periodized training
Mental and physical health
Injury prevention
Long-term athletic progression
Bike fit, gear and equipment
Our mission is to help athletes become the strongest, most resilient version of themselves through purposeful training so they can arrive at the start line confident in their preparation and ready to perform at their best.
Thank you for considering Trimarni coaching.
What to Expect as a Trimarni Coached Athlete
Customized Workouts
Training delivered every 1–2 weeks
Periodized training built around your annual race schedule submitted each December
Unlimited training modifications based on changes in fitness, racing, work, weather, family, travel, or life circumstances
Individualized training adjustments made as needed throughout the season
Recommend Training Tools
GPS watch with advanced heart rate features
Heart rate monitor
Bike power meter (strongly encouraged for optimal bike training and race execution)
Coach Support
Weekly workout feedback and communication
Communication through Training Peaks, email, phone, FaceTime, or Zoom
We believe great coaching extends far beyond writing workouts.
Testing
Performance Testing
Fitness testing conducted when appropriate
Training zones established and updated as fitness progresses
Detailed feedback provided following testing sessions
Strength, Recovery & Injury Prevention
A strong athlete is a durable athlete.
Strength training integrated into your annual plan
Access to the ECFIT strength training app at a discounted rate
Programming developed by renowned endurance strength coach Erin Carson
As needed mobility and strength support by coach Katie
Ongoing focus on recovery, mobility, and long-term athletic development
Sport Nutrition Support
Nutrition is a critical component of endurance performance. Throughout the season, athletes receive education and guidance on:
Daily nutrition habits
Performance nutrition
Training and race-day fueling
Hydration strategies
Race execution nutrition plans
Nutrition-related questions and feedback as needed
Fully personalized daily and sport nutrition consultations are available separately with Marni and are not included in the monthly coaching fee.
Race Planning & Execution
Our goal is to ensure every athlete arrives at the start line confident, prepared, and ready to perform.
Athletes receive:
Course-specific strategies and tactics
Education on pacing, fueling, and race execution
Pre-race and post-race chat, if/as needed
Post-race data review and performance feedback
Race result recognition in the weekly team newsletter
Additional Athlete Benefits
Discounts on Trimarni camps and events
Discounts with over 20 team partners
Team races and pre-race pizza party
Team races - video race recon and tips
Team & Community
Access to a supportive and knowledgeable athlete community
Ongoing education, motivation, and accountability from coaches and teammates
Coach Support
Education
Weekly team newsletter
Team updates and athlete highlights
Educational Google Drive
Monthly Zoom chats
Access to the private Trimarni Coaching Facebook community
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$300/month
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We are committed to building long-term athlete-coach relationships because meaningful athletic development takes time.
While we encourage athletes to commit to at least one year of coaching, we understand that life circumstances can change unexpectedly. If situations arise that prevent you from continuing coaching, we will always work with you and never expect you to pay for services you are unable to use.
Coaching is an investment in your performance, health, and long-term success. Our role extends far beyond creating workouts—we provide training guidance, communication, education, race strategy, nutrition support, bike expertise, accountability, and ongoing athlete development throughout the year.
If our monthly coaching fee presents a financial challenge, we still encourage you to apply and share your circumstances in your coaching application.
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Applications Open Once Per Year
Enrollment for one-on-one Trimarni Coaching opens annually in October for the upcoming season.
Because coaching spots are limited, priority is given to current athletes and returning team members. We encourage interested athletes to apply during the enrollment period to secure consideration for the upcoming year. If you missed the application period, send us an email.
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If individualized coaching is not the right fit at this time, you can still become part of the Trimarni community through one of our training plans and team membership options.
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We are so excited that you are excited. We open our coaching application in mid October (for 2 weeks) and we encourage you to apply during that time frame. To be one of the first to apply, be sure to follow us on social media, subscribe to our newsletter and send us an email letting us know that you are very interested. If you missed the timeframe for applying, send us an email to see if we have an opening.
Coaching iNvestment
Your Questions, Answered
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We design training around your life, not the other way around. Every plan is built to fit within the realities of your work, family, travel, and personal commitments, while still ensuring your key races are properly prioritized so you can build, peak, and perform at the right time.
Our focus is on long-term athlete development. We closely monitor your progression throughout the season, providing ongoing feedback and adjustments to help you train effectively, stay consistent, and continue improving. Our goal is to optimize your performance while supporting your overall health, balance, and enjoyment of the sport.
We are committed to being accessible and responsive throughout your training journey. Athletes can reach us whenever needed via email, text, phone, FaceTime, or Skype. Coaching is not a distant service—it is an ongoing relationship built on communication, trust, and support. We value long-term partnerships and are invested in both your immediate goals and your broader athletic progression over time.
Our coaching is best suited for athletes who:
Want a close, collaborative coach-athlete relationship with ongoing communication and individualized attention
Value consistent feedback, accountability, education, and structured performance monitoring
Are highly motivated and willing to invest in their training and development to reach their potential in triathlon
Struggle with consistency and benefit from a highly individualized, adaptable training approach
Have experienced overtraining or unhealthy coaching environments in the past and are seeking a more balanced, sustainable approach
Prioritize both health and performance, and want a training process that supports both long-term wellbeing and race-day success
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Yes.
While running and cycling are core components of triathlon, off-road and adventure-based racing place different demands on the body. These events require distinct skills, strength profiles, terrain-specific fitness, and tailored fueling strategies. Our off road coaching is designed to bridge that gap—helping athletes adapt their triathlon fitness to perform confidently across a wider range of endurance challenges.With a combined 40 Ironman finishes between Marni and Karel, including 9 Ironman World Championship appearances, Cape Epic experience, a combined 6 XTRI finishes along with numerous different off road and cycling adventures, we bring extensive experience in “adventure” racing. That experience allows us to guide athletes not only in traditional triathlon, but also in transitioning successfully into off-road racing, trail running, gravel cycling, stage racing, and other multi-sport adventures.
It’s important to remember that triathletes are, by definition, multisport athletes. However, adapting training appropriately is key. For example, removing swimming entirely in preparation for a trail running event is rarely optimal for overall durability, aerobic fitness, and recovery capacity. Instead, we help athletes intelligently adjust their training while maintaining the aerobic balance that supports long-term performance and injury prevention.
Our coaching approach is grounded in both experience and current exercise science. We stay up to date with evolving research, training methodologies, and endurance sport trends to ensure athletes receive modern, effective, and safe preparation for their events.
Above all, we are fully committed to supporting your athletic journey—whether on roads, trails, gravel, or mountains. Our goal is to help you train smart, stay healthy, and perform at your best across every environment you choose to explore.
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Absolutely. We believe in developing athletes across all experience and fitness levels. What matters most to us is motivation, consistency, and a genuine commitment to growth.
We have extensive experience coaching triathletes from complete beginners to high-performing age-group athletes, and we focus on building the full athlete—not just fitness. That includes swim, bike, and run development, nutrition habits, daily lifestyle routines, race strategy, and practical fueling approaches that support both training and racing.
Our goal is to help you become a more capable, efficient, and resilient athlete through smart, sustainable progress. And it’s important to remember that “fast” is always relative in endurance sport. Success in triathlon isn’t defined solely by speed—it’s built on consistency, health, durability, and mental strength over time.
When those elements come together, performance naturally follows.
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We’re grateful that you’re considering Trimarni Coaching to support your athletic journey. Over the years, we’ve had the privilege of working with athletes who have reached meaningful new levels in their performance through consistent effort, trust in the process, and a long-term commitment to improvement.
Our athletes have achieved a wide range of goals, from completing their first sprint, Olympic, Half, or Full distance triathlon, to earning personal bests, stepping onto podiums, and qualifying for the Ironman World Championship. While each journey is unique, the common thread is steady progress built through structured training and sustained dedication.
We don’t take your trust lightly. At the same time, we also recognize that if you’re exploring structured coaching, you are already taking an important step toward achieving your goals. That willingness to invest in your training, habits, and lifestyle is often what sets successful athletes apart.
Before committing to one-on-one coaching, you may find it valuable to consider joining our team membership and follow a Trimarni training plan as a way to experience our coaching philosophy, community, and education while you continue building toward your long-term goals
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Anyone is welcome to attend a Trimarni group or private training camp; however, Trimarni athletes and team members receive preferred pricing as part of their membership benefits.
Our private camps are an ideal option for athletes seeking individualized attention and a highly personalized training experience. Hosted in Greenville, South Carolina, our private “train-cation” setting offers a unique opportunity to train in a scenic, bike-friendly environment near the mountains, where we can directly address your specific needs and training goals. With quiet roads, varied terrain, and beautiful surroundings, it is an excellent location to focus on meaningful performance development.
Private coaching camps are particularly effective for athletes who may have specific limiters impacting consistency or preventing progress to the next level. These camps provide focused, one-on-one coaching designed to identify weaknesses, improve efficiency, and build confidence across swim, bike, and run disciplines. All experience levels are welcome, and sessions can be tailored to emphasize cycling development when appropriate, taking full advantage of the surrounding terrain and Coach Karel’s background as a cyclist-turned-triathlete.
Our group camps provide a balanced blend of structured training, skill development, education, and community. Athletes can expect a supportive and motivating environment that fosters improvement, connection, and enjoyment. Participants consistently leave camp with improved fitness, greater confidence, practical knowledge, and lasting relationships with fellow athletes.
Retül bike fits are available at both group and private Greenville camps for an additional fee, offered at a discounted rate for camp participants and Trimarni athletes.
Get in Touch
If you are interested in a training plan or individual coaching, we would love to hear from you.