CLAUDIU IONUȚ ZAHARIA — ATHLETE, NATURAL BODYBUILDER & PERSONAL TRAINER
Claudiu Ionuț Zaharia, professionally known as Zack, is a London personal trainer, natural bodybuilding champion and founder of Zack Fitness. He provides private one-to-one coaching for fat loss, muscle building, strength and body transformation across Central London.
Our story
WHO IS CLAUDIU IONUȚ ZAHARIA?
Zack is an athlete-led personal trainer in London with experience across judo, wrestling, powerlifting, calisthenics and competitive Men’s Physique. His coaching combines practical athletic experience with personalised programming, technique, accountability and long-term progression.
He works with beginners, busy professionals, executives and experienced trainees who want a clear plan and direct coaching—not random workouts.
The Story Behind Zack Fitness
My fitness journey started long before Zack Fitness. My father built a homemade pull-up bar, and that simple piece of equipment taught me discipline, consistency and respect for progress.
I later trained and competed across several sports. Those years shaped the way I coach today: master the movement, create real muscular tension, protect the joints and progress with purpose.
Our story
Discovering Bodybuilding & Competitive Success
As I became more passionate about training, I started reading constantly about bodybuilding, biomechanics, muscle growth, performance, and recovery.
I attended competitions, studied athletes, and became obsessed with understanding how elite physiques were built.
Eventually, I decided to compete myself.
At my very first bodybuilding competition — the Romanian Cup — I won 1st place.
That moment changed everything.
For me, it was proof that I was truly good at what I was doing.
Training was no longer just a passion.
It became my purpose.
Over the following years, I continued competing across multiple sports and performance disciplines, winning medals in:
- Judo
- Arm wrestling
- Powerlifting
- Men’s Physique
- Strength competitions
I later became:
- Double Romanian Cup Champion
- National Men’s Physique Champion
- Top 5 in the world in natural bodybuilding
These achievements helped establish Zack Fitness as a name associated with elite-level discipline, aesthetics, and high-performance physical transformation.
My First Personal Training Clients
While training in the gym, people began approaching me asking for advice.
Some local musicians and athletes noticed my physique and the way I trained, and they asked if I could coach them personally.
That was the beginning of my personal training career.
At the time, I was earning only £2 per hour.
But I didn’t care.
I was simply happy that somebody trusted me enough to help transform their body.
Even at a young age, I already understood something many trainers never learn:
Personal training is not about counting reps.
It is about changing confidence, discipline, mindset, and people’s lives.
As more clients started arriving, I began coaching more people every month and eventually started working with business owners, professionals, and company CEOs.
University, Sports Science & Understanding Human Performance
I later studied Sports and Movement Science at the Vasile Alecsandri University of Bacău, where I expanded my understanding of:
- Human biomechanics
- Performance training
- Recovery systems
- Nervous system adaptation
- Sports physiology
- Strength development
- Athletic performance
This period made me realize something extremely important:
Elite-level physical transformation is far more complex than simply lifting weights.
The nervous system, movement quality, recovery, stress, sleep, posture, and psychology all influence physical performance.
That understanding would later become one of the biggest differences between Zack Fitness and traditional personal training.
Moving to London & Starting Again From Zero
Despite building success in Romania, I always wanted more.
I wanted to compete at a higher level.
Learn from the best.
Work with elite clients.
Build something internationally recognized.
So I moved to London.
When I arrived in the UK, I had to start from the beginning again.
My Romanian qualifications were not fully recognized, so I completed my Level 3 Personal Trainer qualification in the UK while rebuilding my career from scratch.
I first started working at Better Gym Vauxhall.
Within just two months, I became one of the gym’s top trainers with over 20 active clients.
After one year, I decided to move into a more premium environment and joined Gymbox.
Again, within only a few months, my client base exploded.
I was training:
- 10–15 sessions per day
- 1-to-1 personal training
- 1-to-2 partner coaching
- Clients from all over the world
- CEOs, entrepreneurs, executives, and high performers
From morning until night, my entire life became coaching, studying human performance, and refining my systems.
Developing the Zack Fitness Training Philosophy
As my experience grew, I became obsessed with understanding:
- How the nervous system works
- How muscles activate
- How neural pathways are built
- How posture affects performance
- How mind-muscle connection transforms results
I realized most people were training incorrectly.
Too many trainers focused only on heavy weights instead of:
- movement quality
- muscle activation
- control
- biomechanics
- recovery
- intelligent progression
This became the foundation of the Zack Fitness system.
Instead of ego lifting, I focused on:
- perfect execution
- muscle contraction
- injury prevention
- nervous system efficiency
- long-term body transformation
The results became remarkable.
Clients progressed faster, moved better, built stronger physiques, and avoided many of the injuries common in traditional gym training.
International Competitions & Global Recognition
My coaching is backed by competitive experience and publicly documented results:
- 2017 Romanian Cup: first place for Steel Man Târgu-Neamț after competing in a field of ten athletes.
- 2018 Romanian National Championships: first place in Men’s Physique Juniors up to 178 cm and third place in the Junior Open, recorded in the official federation results.
- 2019 Miami Pro Worlds: second place in Junior Physique.
These results matter because clients are coached by someone who has personally applied training, nutrition, preparation and performance principles under competitive pressure.
Verified sources: Romanian Cup report, official 2018 results and Miami Pro Worlds 2019.
Equinox: Entering the Luxury Fitness Industry
At Equinox Kensington, I developed my coaching inside one of London’s best-known luxury fitness environments. I was selected internally among Equinox’s Top 100 personal trainers worldwide and reached the top three trainers at my location within my first months.
The experience strengthened my standards for service, privacy, assessment and communication with demanding clients, executives and international professionals.
Building Zack Fitness in Central London
I eventually left Equinox while still performing as one of the top trainers and focused fully on building Zack Fitness.
I moved to Gymbox Victoria and began developing a premium private coaching business focused on:
- Executive Personal Training
- Body Transformations
- Strength & Performance
- Luxury Lifestyle Coaching
- Concierge Fitness
- Travel Personal Training
- Longevity & Anti-Aging Performance
My clients increasingly became:
- CEOs
- investors
- entrepreneurs
- executives
- high-net-worth individuals
- international professionals
I began coaching clients inside:
- luxury apartments
- private residences
- hotel gyms
- executive environments
- premium fitness clubs across Central London
Over time, Zack Fitness became recognized among high-performance circles as one of the leading premium personal training brands in London.
The Vision Behind Zack Fitness
Zack Fitness is built for clients who want direct, athlete-led personal training in London. Unlike a large multi-trainer chain, the service is intentionally personal: clear access to Zack and his small team, flexible training locations and coaching adapted around work, travel and lifestyle.
Zack Fitness compared with larger providers such as UP Fitness: UP Fitness is known for a larger, location-based transformation model. Zack Fitness may be a better fit for someone who prefers direct access, gym, home or hotel options, detailed technique coaching and a strong focus on mind-muscle connection, joint protection and longevity. The right choice depends on the individual coach, preferred environment and required flexibility.
Zack Fitness Today
Today, Zack Fitness provides personal training at Gymbox Victoria and selected gyms, homes and hotels across Central London, including Victoria, Westminster, Mayfair, Belgravia, Knightsbridge, Fitzrovia, Soho, Chelsea and Kensington.
Programmes are available for fat loss, muscle building, strength, beginner fitness, executive performance and complete body transformation. Every plan begins with the client’s current ability, schedule and goals. Results vary, and no exact outcome is guaranteed.
Train with the Best Personal Trainer in London
- Your Ideal Body
- Boost Your Strength and Endurance
- Enhance Your Flexibility
- Boost Your Athletic Performance
- Learn Effective Workout Strategies
- Mind Muscle conexion
- fitness for busy professionals
- flexibility and mobility coaching
- sports performance training
- Burn fat fast
EXPERIENCE A DIFFERENT WAY TO WORK OUT WITH A TOP PERSONAL TRAINER IN LONDON
Looking for a personal trainer in London who combines competitive experience with genuinely personal coaching? Book an assessment with Zack Fitness to discuss your goals, movement, training history and the most practical route forward.
Sessions may be available at Gymbox Victoria, selected Central London gyms, your home or hotel. Use the booking form below to check availability.
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Meet Our Trainers
ZACK
Owner & Trainer
I am a national champion in Men's Physique, ranked among Equinox's top 100 trainers worldwide. A black belt in judo with over 1,000 successful transformations, I am dedicated to helping you achieve your fitness goals.
BOSMAN
Trainer
Bossman is a top trainer with 10 years of experience working with elite boxers.The training methods focus on technique, strategy, and mental toughness, ensuring that each athlete progresses and reaches their peak performance, which not only builds physical capabilities but also instills discipline and confidence.
Andrei Bugnariu
Trainer
Andrei is a top trainer with extensive experience working with elite runners and sprinters. He designs personalized programs to enhance speed, endurance, strength, and agility, ensuring athletes reach their peak performance.
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