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The future of fitness: How AI coaches are changing the way we exercise

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The future of fitness: How AI coaches are changing the way we exercise

Fitness and health apps have been promising “smart coaches” and “personalised training plans” for years. But, to date, most programmes have been like online shopping recommendations, with exercises broadly matching your demographic profile and performance level.

However, the rapid advances in real-time image recognition, generative AI and natural language processing are bringing an AI coach worthy of the name within our grasp. And not just for high-tech gyms like Lumin, but also for people working out at home or in the park. Peloton, for example, films how you exercise and provides feedback in real time. Google has also announced AI-powered personalised fitness and health advice for its Fitbit range.

HYROX pro athlete Jake Dearden putting in the work on an indoor bike

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© Baptiste Fauchille/Red Bull Content Pool

Market analysts think the AI fitness market could be worth close to $35b USD by 2030. But how close are we to that future? Which company is training up the supertrainer? And how will that change the way we exercise, sweat and track our progress? And what do we need to know about this new world?

Harnessing AI’s potential to make personalised training available to all

Lucy Charles-Barclay prepares for training in London, England, on July 14, 2021.

Most fitness apps give generic exercise suggestions

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Confidence Udegbue has the perfect CV for designing an AI coach. The Vice President of Product at fitness app Freeletics studied electrical and computer engineering and teaches fitness classes in his free time. His broad shoulders, muscular biceps and infectious spirit are a dead giveaway: this guy knows what he’s talking about.

“In the gym, I can see immediately when someone I’m teaching is making a mistake,” says Udegbue. “But that expertise is hard to scale.” Freeletics is trying to solve that problem with AI. The app has been using a predictive algorithm since 2019 to suggest workouts based on demographic data and self-assessed fitness levels. This means that a 39-year-old man who has been training for two years and is at level 63 in the app won’t receive the same instructions as a 25-year-old beginner.

Freeletics uses AI-based motion analysis powered by models like those from Google’s MediaPipe framework, which includes BlazePose – the successor to the earlier PoseNet model. The models provide a skeletal muscle database that can replicate all types of exercises, for which Freeletics sports scientists then define the movements. That way, the system can assess whether that squat you just did went low enough.

Can an AI coach give useful real-time workout feedback?

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One of the most revered sabre fencers in the world, Olga Kharlan, checks her phone during training

World-class sabre fencer Olga Kharlan checks her phone

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In 2024, Freeletics introduced the Coach+ feature – an AI-powered chatbot with Freeletics expertise and access to anonymised data from over 59m user journeys. Users can ask the virtual coach questions like, “How can I build muscle mass?” or “I feel weak – how can I motivate myself?”

Freeletics is currently testing a version that will allow the app to see you work out. As of April, users have been able to record themselves exercising on their smartphones. “AI counts the reps and gives direct feedback,” Udegbue says. That is particularly helpful because even experienced athletes do not always perform pistol squats or burpees correctly.

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Democratising the personal coach experience

Max Verstappen of Oracle Red Bull Racing stretches before a F1 Grand Prix

Max Verstappen warming up before a F1 race

© Getty Images / Red Bull Content Pool

A personal coach was long the preserve of Hollywood actors, top models and CEOs – a highly competent service provider, always available whenever a slot opened up in their client’s busy schedule. They know their clients’ allergies, preferences and weak spots. They always know how to set the pace. Sometimes they’re pushy, sometimes they go easy. They are a mix of therapist, personal assistant and best friend – open 24/7, all major credit cards accepted.

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In the soccer world, the manager is often called “boss” – a figure of respect who takes care of the players both on and off the field. A good coach can tell when something is off in a movement – when the person’s mind is elsewhere, or they’re lacking energy. Anyone who has had that person in their life knows that a good coach is worth their weight in gold, which is why there are coaches for everything – careers, relationships, nutrition – and why the idea of a personalised fitness coach is so appealing.

AI has no body or talent. It doesn’t know what it feels like for sweat to run down the skin or for muscles to cramp or for adrenaline to rush through the veins. But it does recognise patterns and make predictions that we humans can use increasingly often and, in the best-case scenario, find out more about ourselves in the process.

How AI will allow us to ‘chat with our body’

Mutaz Barshim powers through a workout in the gym

High-jump star Mutaz Barshim lifting heavy

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© Diaa Amer/Red Bull Content Pool

Mirrors show you how you see yourself. But the Magic AI Mirror promises that you will like what you see if you follow the exercises and tips on the reflective screen. Behind the glass surface is an AI coach who steers your workouts in real time.

Growl goes even deeper into movement detection. The start-up has developed an exercise boxing bag that captures every movement with 3D cameras and Lidar (light detection and ranging) technology. AI corrects your posture or encourages you when your energy decreases.

Whoop’s fitness trackers combine biometric data with generative AI. If you’re wondering when you got your best sleep, you’ll get a precise answer: “On July 14, because the allergy season was over and you didn’t drink alcohol.” You can chat with your body.

Freeletics is also banking on predictive AI. “Soon the system will recognise that user X has had an increased resting heart rate for days, so I won’t suggest high-intensity exercises,” says Udegbue.

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The vision all companies are working on is a multimodal coach: AI that unlocks information – biometrics, genetics, video, training history – and conveys it intuitively to the user. But a perfect coach is more than just an algorithm. Researchers are working on reinforcement learning systems that set individual step goals that are challenging but achievable, and adapt whenever progress has been made.

The power of human and AI combined

Adriano de Souza in seen during the video recording of Se Prepara series in Florianopolis, Brazil, on April 30, 2019.

Training is possible anywhere

© Marcelo Maragni/Red Bull Content Pool

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“We will not be able to deliver on the promise of absolute personalisation for the mass market,” Eskofier says. But before you lose hope, you should know what he means by personalisation.

His laboratory supports, among other people, Sebastian Steudtner, the big wave surfer and world record holder. To do this, they measured his body in an MRI scanner, carried out psychological assessments, calculated strength curves and even fitted his surfboard and wetsuit with sensors.

Eskofier’s team created Steudtner’s digital twin. By the time the project concluded in May 2025, their AI system could already discuss with a real coach what angle Steudtner should surf a 100-foot wave at, and whether he’d be strong enough to do it.

The one thing AI will never change in fitness training

Constantin Popovici of Romania stretches at the athletes' area during the training day of the final stop of the Red Bull Cliff Diving World Series in Boston, USA, on September 18, 2025.

No equipment, no excuses – embrace the simplicity of pure movement

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“We can’t offer that service to millions of people,” Eskofier says. “But these systems can still create real added value.” He believes AI coaches are a good base: “AI can take over data processing and routine personalisation, while real coaches can focus on mentoring.”

AI coaches are getting smarter all the time, too, which is why it’s important to know what they can and can’t do. Limited data sets can lead to bias if too few women or people of below-average height are represented in the data.

“No matter how good the technology gets, one thing will never change,” says Udegbue. “A coach can only make you better if you want to be better yourself, too.” It’s all in your hands.

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Why 21-15-9 Might be the Smartest Workout Format in Fitness – and How to Use it to Drive Muscle Growth

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Why 21-15-9 Might be the Smartest Workout Format in Fitness – and How to Use it to Drive Muscle Growth

CrossFit means a lot of things to a lot of people – because it’s made up of a lot of things.

Since the rise of the fitness giant, countless brands, events and training methods have sprung up around it – not claiming to be CrossFit, but looking suspiciously CrossFit-esque.

There are, however, a handful of things that are uniquely CrossFit: the ‘Girls’ benchmark workouts. The Hero WODs and, of course, its signature rep schemes.

Chief among them is ’21-15-9′.

The 21-15-9 rep scheme may just be the single most CrossFit thing in existence. But what exactly is it? Where did it come from? And why might it actually be better at building muscle in a hurry than its conditioning roots would have you believe?

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Let’s have a look.

What Is 21-15-9?

If you’ve never encountered it before, the format couldn’t be simpler. Choose two exercises (occasionally more) and perform 21 reps of each, then 15 reps of each, then nine reps of each, completing the entire workout as quickly as possible – with good form.

Probably the best-known example is ‘Fran’: 21 thrusters and pull-ups, followed by 15 of each, then nine. On paper it doesn’t look especially intimidating. In practice, it’s one of the most feared benchmark workouts in fitness.

Where Did it Come From?

Unlike many modern training methods, 21-15-9 didn’t come out of a study. It came from the gym floor.

CrossFit founder Greg Glassman has explained that the format emerged through years of coaching and experimentation in the 1990s. Rather than chasing a perfect sets-and-reps prescription, he was looking for a workout that allowed athletes to maintain a high power output from start to finish.

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The thinking is surprisingly elegant. You begin with 21 reps while fresh. By the time you reach the set of 15, your ability to produce force has already fallen. By the final nine, you’re significantly more fatigued – but the workload has dropped by almost the same amount.

Instead of grinding through increasingly miserable sets of the same length, the workout ‘meets you where you are’, reducing the work required as your capacity declines. The result is a workout that encourages you to keep moving instead of standing around trying to recover.

The numbers themselves are also remarkably practical. Forty-five total reps per movement provides plenty of training volume without turning the session into an endurance slog, while every set divides neatly into thirds if you need to break it up.

(Although I’ve got to be honest, I’m a 20-15-10-5 man myself, just for the sake of round numbers.)

Why Does it Work So Well?

Although there isn’t research showing that 21-15-9 is somehow the magic formula, there are obvious reasons why it consistently produces brutally effective workouts.

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Descending reps help maintain intensity. As fatigue accumulates, reducing the target allows movement quality, bar speed and overall work rate to stay higher than they would if you simply repeated the same number of reps over and over.

It also tends to land in a physiological sweet spot. Most 21-15-9 workouts take between three and eight minutes, depending on the movements and the athlete. That’s long enough to create a serious cardiovascular challenge while still requiring meaningful force production throughout. You’re taxing your anaerobic systems hard while relying on your aerobic system to help you recover just enough to keep going.

Finally, there’s the psychological trick. The hardest-looking part comes first. Once you’ve survived the opening 21, every remaining round appears more manageable. ‘Only 15 left.’ Then, ‘Just nine.’ In reality, you’re becoming more fatigued with every rep, but the shrinking target keeps you attacking the workout instead of pacing too conservatively.

Why it Might be Surprisingly Good for Building Muscle

Perhaps the biggest misconception about 21-15-9 is that it’s ‘just cardio with weights’.

Choose the right load and something interesting happens. Very few athletes complete every round unbroken. Instead, the workout naturally evolves into a series of short, broken sets separated by only a few seconds of rest.

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Your 21 might become 11-5-5. Your 15 becomes 8-4-3. Your final nine might stay unbroken – or become 5-4.

In effect, you’ve accidentally turned the workout into a form of rest-pause training.

Those brief pauses allow just enough recovery to squeeze out more high-quality repetitions before fatigue catches up again. By the latter stages of each mini-set, you’re repeatedly working very close to failure, recruiting the high-threshold motor units with the greatest potential for muscle growth.

It’s a similar principle to rest-pause training, myo-reps and cluster sets: all methods used to accumulate hypertrophy-friendly volume while keeping the load relatively heavy and the rest periods brutally short.

You’re basically speed-running a large number of hard, growth-stimulating reps in a very small window of time. Could this help explain why elite CrossFit athletes often carry an impressive amount of muscle despite spending relatively little time performing traditional bodybuilding splits?

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It’s certainly plausible, although the ‘elite’ part often selects for athletes with the greatest muscle-building potential.

Much of their training isn’t simply conditioning. It’s high-density resistance training performed under accumulating fatigue, with only fleeting recovery between efforts. In other words, they’re often doing something bodybuilders have deliberately programmed for decades: packing a lot of hard work into a very short period of time.

That’s not to say 21-15-9 is superior to a well-designed hypertrophy programme. If your sole goal is building muscle, there are more efficient ways to do it.

But if you’re looking for a workout that develops fitness, tests your mettle and still provides a meaningful stimulus for strength and size, it’s easy to see why this deceptively simple rep scheme has remained one of CrossFit’s defining fingerprints for more than 20 years.

Best Bodyweight 21-15-9 Workout: ‘JT’

If you’re looking for an interesting twist on the 21-15-9 format, look no further than Hero WOD ‘JT’, which concentrates the muscle-building potential of the format into a brutal upper-body workout.

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Created in honour of Petty Officer 1st Class Jeff Taylor, who was killed in Afghanistan in 2006, the workout strips away barbells altogether and relies solely on three bodyweight movements:

21-15-9 reps of:

Don’t let the lack of equipment fool you. The volume – 45 reps of each movement, 135 reps in total – combined with the descending rep scheme makes this a brutal upper-body test, hammering the shoulders, chest and triceps while demanding serious muscular endurance.

Better still, it perfectly demonstrates one of the biggest strengths of 21-15-9. As fatigue mounts and the sets naturally fragment, the workout begins to resemble one giant rest-pause set, allowing you to accumulate a huge number of hard, near-failure reps in less than 10 minutes.

If your goal is building an impressive upper body while developing serious work capacity, there are few bodyweight workouts that deliver quite so much bang for your buck, making ‘JT’ one of my personal favourites.

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fitness magazine cover featuring a muscular man with kettlebells

If there’s one thing Kori Sampson knows, it’s how to optimise your body composition for performance. To tap into his knowledge as an elite athlete and coach, we asked him to create a 4-week plan to help you move faster, recover quicker and keep pushing when the fatigue sets in – all while improving your muscle-to-fat ratio.

Ready to build muscle, burn fat and come out the other side looking, feeling and performing better? Click here to get 14 days of free access to the plan via the Men’s Health app.


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10 minutes of swimming might not sound worth it – but I tried it for 2 weeks and found the benefits of a quick dip

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10 minutes of swimming might not sound worth it – but I tried it for 2 weeks and found the benefits of a quick dip

The concept of ‘exercise snacking’ has never been more popular. Not only is it convenient and accessible, but there is solid scientific evidence that short bursts of physical activity can yield real benefits for our health. But can a swimming workout be an effective ‘exercise snack’?

A study published in the European Heart Journal found that just 15 to 20 minutes of vigorous physical activity a week (almost as low as two minutes a day) was enough to significantly lower the risk of heart disease, cancer and early death. The study defined vigorous activity as any exercise that leaves you out of breath and raises your heart rate, including swimming.

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The Fitness Secrets of Wimbledon’s Top Tennis Pros

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The Fitness Secrets of Wimbledon’s Top Tennis Pros

While many of us are far from becoming top-ranked athletes, there’s plenty to learn from the pros when it comes to optimising our health and fitness. From Janik Sinnner’s muscle-building techniques to Novak Djokovic’s devotion to longevity, dig into these tennis pros’ secrets for peak performance.

Joris Verwijst/BSR Agency//Getty Images

CARLOS ALCARAZ

Fitness Game Changer:

Sand Footwork Drills

Any pro tennis player has to play with agility, but Alcaraz can move. To do so at a high level, the 21-year-old performs lateral movement drills in the sand, teaching his feet to drive up from an unstable surface. This can help prevent ankle injuries and build strength in his calves and shin muscles.

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jannik sinner

Jose Breton/Pics Action/NurPhoto//Getty Images

JANNIK SINNER

Fitness Game Changer:

Landmine Rotations

Sinner has historically lacked the physical prowess of his competitors, so the 23-year-old has gone all in on strength and mobility work. He does landmine rotational exercises such as the hollow body landmine press, which builds upper-body power.

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novak djokavic

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NOVAK DJOKOVIC

Fitness Game Changer:

Devotion to Longevity

He’s been around this long for a reason. Djokovic, 37, eliminated gluten and dairy from his diet, started practising mindfulness techniques like conscious breathing and visualisation, and even brought a hyperbaric chamber to the 2019 US Open.

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ben shelton

Cameron Spencer//Getty Images

BEN SHELTON

Fitness Game Changer:

Explosive Strength Moves

Known for his consistently fast serves, Shelton, 22, relies on single-leg training, using dumbbells to do lateral lunges, step-ups, and even Bulgarian split squats. He focuses on exploding upward on every rep so he’s ready to attack the ball on each serve.

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frances tiafoe

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FRANCES TIAFOE

Fitness Game Changer:

Overcoming Isometrics

Tiafoe spent last off-season doing overcoming isometrics: exercises that force the 27-year-old to hold a position against a load he can’t move. This aids in boosting power and strength and can improve joint health.


fitness magazine cover featuring a muscular man with kettlebells

If there’s one thing Kori Sampson knows, it’s how to optimise your body composition for performance. To tap into his knowledge as an elite athlete and coach, we asked him to create a 4-week plan to help you move faster, recover quicker and keep pushing when the fatigue sets in – all while improving your muscle-to-fat ratio.

Ready to build muscle, burn fat and come out the other side looking, feeling and performing better? Click here to get 14 days of free access to the plan via the Men’s Health app.

Lettermark

Andrew Gutman, NASM-CPT is a journalist with a decade of experience covering fitness and nutrition. His work has been published in Men’s Health, Men’s Journal, Muscle & Fitness, and Gear Patrol. Outside of writing, Andrew trains in Brazilian Jiu-Jitsu, helps coach his gym’s kickboxing team, and enjoys reading and cooking. 

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