Why hire a personal trainer or pay for a monthly gym membership when you can enlist artificial intelligence (AI) to create a free exercise programme that will get you into shape? Millions of people are now relying on fitness advice at their fingertips in the form of AI-generated workouts in a global AI fitness and wellness market recently valued at £7.3 billion.

It’s an industry that is becoming more refined by the month, with a booming number of AI personal coaching paid-for apps such as Aaptiv, FitnessAI and Fitbod providing training programmes based on your detailed goals and fitness levels, and customising each session from feedback about how you felt and performed in your previous workout. Many of them can be synced with fitness trackers for even more tailored advice. But it is the free AI platform ChatGPT that is among the most popular, with a growing number of people asking the chatbot for free fitness advice. So can we really rely on AI to get us into shape?

When researchers from the University of Connecticut and other institutions asked ChatGPT to provide workout recommendations for specific groups, including those with hypertension, type 2 diabetes and osteoporosis, they found the advice often didn’t reflect standard medical guidelines. In 53 per cent of cases the recommendation was to seek a doctor’s approval before exercising, which the scientists said was unnecessary and might deter people from being active. In their verdict of the findings, which were published in JMIR Medical Education last year, the scientists said that consumers and health professionals should be cautious about relying solely on AI for exercise recommendations.

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Ash James, director of practice and development at the Chartered Society of Physiotherapy (CSP), agrees that AI should be seen as a tool to support not replace personal trainers and qualified medical practitioners. “AI tools such as ChatGPT are trained on massive datasets from the internet, books and academic literature, but they do not ‘know’ facts or have clinical judgment in the way a fitness or healthcare professional does,” James says. “They work by predicting what text is likely to come next based on patterns in the data they were trained on and, while they can be very useful, they sometimes need human input.” In other words, the advice should ideally be interpreted and fleshed out by real-life experts.

So what happened when I put ChatGPT to the test? Here’s what I found:

Can AI help you to get shapely arms?

Can ChatGPT deliver a programme for shapely and strong biceps and triceps for those of us that want arms like Michelle Obama? I’ve interviewed enough personal trainers to know that weights are essential to transform the shape of arms and that endless triceps dips alone are not going to combat bingo wings. What’s needed is a mix of movements to prompt the calorie burn needed for arms to become leaner: progressively heavy weights and commitment to arm-specific routines on three to four days a week.

So what did ChatGPT suggest when I asked how quickly I could change my arms as a 56-year-old weight-training novice (which I am not)? Encouragingly, the response was realistic — I could, I was told, expect to get stronger in three to four weeks, see noticeable definition within eight weeks, but for “Michelle Obama-level arms” I would need to work at it for at least three months “depending on how much you need to reduce fat covering them”.

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ChatGPT prescribed a 12-week plan that was not at all comprehensive — it suggested twice-a-week light weights initially — although the exercise range was good. What it lacks, of course, is the ability to check and correct poor form that might lead to injuries. For that you need the human touch and a personal trainer to observe at the gym. Once you’ve mastered the moves, the AI routine can be followed, but you’d need to ramp up the weights more than it suggests as you progress.

Treat AI marathon training plans with caution

Standard training programmes for marathon runners are 16 weeks in duration. If you have entered a spring marathon, such as London, this means you can start a plan in January and be ready to toe the line in April. The more running you have done beforehand the better, but even beginners can follow a get-you-round schedule to complete the 26.2-mile event in about four months.

In terms of basics, the AI plans don’t differ much to those provided in online programmes or apps, all incorporating the basics of easy, steady and longer runs with gradual progression of miles over the weeks.

As a qualified running coach, my concern with the AI plan when I asked for a programme for a complete beginner is in the detail (or lack of it). I was alarmed to find that AI provides six-week marathon plans for beginners, albeit with the proviso that they are “aggressive” and that ideally you need longer to prepare. Running too far or too quickly too early on is a fast route to overuse injuries such as shin splints, which will hamper your progress before you really get started. If you haven’t run before, it’s best to start with a run/walk combo for time rather than distance, which wasn’t recommended by AI — even when I prompted it with appropriate fitness level and goals for a novice.

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Some of the terminology — taper, light speed, tempo — might also be baffling for newcomers to running. If you are an experienced runner who can adapt sessions set by algorithms as required and listen to your body to make sure it is coping, then AI plans are fine. But it is worth joining a club or enlisting a human coach to provide added insight if you are unsure if you are ready for a ramp up in running load.

Can AI help you to become more flexible?

Under the guise of being a 39-year-old man who can’t touch my toes and hates yoga, I asked AI for a plan to become more flexible. It correctly informed me that it’s not unusual to be unable to touch my toes and that it’s likely that my lower back, hips and calves, not just my hamstring muscles, need some attention. It plotted a good mix of dynamic stretches (leg swings and hip circles) and loaded stretches such as weighted Romanian deadlifts, finishing with some static holds to improve general flexibility. Targeted strength training is key to improving mobility, so it was good to see it included. However, ChatGPT’s recommendation to “grease the groove” by aiming to touch my toes gently several times a day is questionable. Toe-touching is widely regarded as a measure of flexibility and physical health, but many experts say it shouldn’t be — and that it should not be a fitness goal in itself. Some hypermobile but unfit people can touch their toes, while many elite athletes can’t, and forcing the movement could cause damage.

Just had a baby? Postpartum exercise plans offer sound advice

It’s not easy to find reliable postpartum fitness plans, so I posed as a 36-year-old new mum who gave birth three weeks ago and told ChatGPT that I want to be back in shape in three months. The NHS advice is to start gentle activity as soon as you feel up to it after a straightforward birth but to wait until your six-week postnatal check (possibly longer if you had a caesarean) before starting any high-impact activity. The response was impressive. It advised against rushing back into intense workouts too early as it could lead to risky issues such as diastasis recti (abdominal muscle separation), pelvic floor dysfunction or prolonged bleeding.

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Instead it suggested a gentle healing plan of walking, Kegel contractions and specifically to avoid crunches, planks or any jumping and pounding until cleared by your doctor. From six weeks after giving birth, and with medical clearance, there was a neat and progressive plan of walking, flexibility, core and pelvic work and some light resistance training. Pretty much gold-standard advice.

Will AI help in losing the paunch?

In middle-aged and older men, the appearance of the dreaded paunch is usually down to a combination of poor diet, lack of exercise and declining testosterone levels, which work together to deposit body fat around the middle. What advice would AI give to a 58-year-old man who has never been to a gym and wants to blast his belly fat in six weeks? It makes no bones about what is needed — strength training, cardio and diet changes — and correctly points out that you can’t spot reduce fat around the middle and will need to lose overall body fat for your paunch to shrink. Beyond that, though, the plan it provides is insufficient for meaningful changes.

A primary goal should be to increase cardio — running, cycling, swimming or power walking — to an hour most days over the six weeks, although ChatGPT suggests 20-40 minutes on three to four days a week with no increases in volume as you get fitter. Deadlifts and squats are key exercises with good personal trainers because they use larger muscle groups and therefore burn more calories, yet they didn’t feature in the AI workout regimen, which instead included options such as wall press-ups and water bottle rows. These would have little impact when it comes to shifting stubborn belly fat and you’d need to work much harder for results in the time frame.

Don’t trust AI advice for rehab from acute injuries

I asked ChatGPT to recommend treatment for an imaginary sprained ankle incurred when running. On this, it let me down. Its recommendation was to follow the Rice — rest, ice, compression, elevation — protocol, which has been considered outdated by the CSP and medical organisations since 2019 after the publication of compelling research published in the British Journal of Sports Medicine. AI also suggested using over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen to relieve swelling, which goes against NHS advice to avoid such medication for 48-72 hours after the injury has occurred. This is based on evidence that, if taken too soon, NSAIDs slow down the healing process by disrupting the body’s natural inflammatory response, which is a key part of tissue regeneration and healing. What the CSP and others suggest instead is the Peace (protection, elevation, avoid anti-inflammatories, compression, education) protocol, which encourages early and progressive return to activity. A big fail for AI.

You can’t rely (entirely) on AI for motivation

AI can provide you with basic prescriptive workouts and long-term plans. It delivers sound advice for some injury and rehab issues. What it can’t do is give meaningful encouragement or comfort on an off day and so will never replace the human interaction of a trainer or cycling/running buddy.

A friend tells me that Athlete Intelligence on Strava, which uses generative AI to analyse data from previous activities to create post-workout summaries, often informs him he is slower than usual on his ride or his relative effort is lower than usual even when it is evidently not the case.

When I begged ChatGPT to provide motivation for a workout it told me, “Motivation is unreliable — it’s like a cat: sometimes affectionate, sometimes hiding under the bed. What you need is momentum.” What? When I probed with more specifics it did fire back with one of my favourite strategies, “Tell yourself you’ll just do ten minutes. If you still hate it after that, you’re allowed to stop. (Spoiler: you probably won’t.)”

Maybe it can read my mind after all?