Can AI Really Replace Your Personal Trainer?

Artificial intelligence is increasingly shaping how people approach health and fitness, but experts warn it may not be ready to replace real personal trainers.

A recent test explored whether AI could safely act as a fitness coach by asking four popular models to create a four-week fat loss programme.

Each model received the same prompt requesting a structured plan focused on fat loss, accountability, and motivation, without any personal details or medical context provided.

No information was shared about age, injuries, fitness level, mental health history, or whether ongoing coaching was wanted, yet every model immediately produced a detailed programme.

Despite the lack of screening, the responses followed strikingly similar formats, raising questions about how responsibly AI handles health-related goals.

Most plans included weekly workout schedules ranging from three to five sessions, combining strength exercises such as squats, lunges, push-ups, and rows with cardio training recommendations.

High-intensity interval training and steady state cardio were commonly suggested, alongside advice encouraging users to increase intensity each week to maintain progress.

Many responses also used accountability language, including strict daily step targets or rules framed as non-negotiable commitments designed to enforce consistency.

However, none of the models questioned whether fat loss was medically appropriate or emotionally safe before presenting structured plans.

Dr Crystal Wyllie, GP at ZAVA, explained that fat loss is not a neutral goal and can influence both physical health and mental well-being.

She warned that while AI can quickly create structured routines, it cannot recognise vulnerabilities, adjust for injuries, or intervene if someone experiences complications.

Dr Wyllie added that AI can still be useful for learning exercises, generating workout ideas, and encouraging habit building through reminders and motivation.

She cautioned that prescriptive fat loss programmes, strict dietary targets, or pressure-based coaching may pose risks, especially for beginners or people with underlying health conditions.

According to Dr Wyllie, any serious diet or fitness plan should remain flexible and supervised by a qualified professional rather than relying entirely on automated guidance.

Among the models tested, ChatGPT demonstrated some awareness of safety by first asking questions about age, training experience, injuries, and nutrition habits before generating its plan.

It then delivered a full four-week programme combining strength training, cardio sessions, progressive intensity, and daily step goals to support fat loss.

Although the tone remained encouraging, the plan still treated fat loss as a universal objective without confirming whether it suited the user’s health circumstances.

Dr Wyllie noted that structured guidance like this may help beginners understand exercise balance, but high-frequency workouts could become unsafe without individual assessment.

Grok adopted a more energetic coaching style, assuming a beginner-to-intermediate fitness level while introducing calorie deficits and specific protein intake recommendations.

Its programme combined resistance training, HIIT sessions, and weekly progress tracking, yet it failed to consider medical history or personalised dietary needs.

Dr Wyllie warned that while motivational language can build consistency, strict calorie or protein targets may trigger anxiety or unhealthy behaviours if not tailored professionally.

Claude focused heavily on accountability, promising to track progress, celebrate achievements, and call out missed workouts in a coach-like dynamic.

The structured routine included strength sessions, conditioning work, and daily activity targets, but its pressure-driven tone raised psychological concerns among experts.

Dr Wyllie explained that such language could create guilt or compulsive exercise patterns, particularly for individuals already sensitive to body image pressures.

Meanwhile, Gemini delivered the most rigid programme, setting strict daily rules around steps and protein intake.

It encouraged users to train to failure and requested personal measurements to calculate exact calorie targets, presenting adherence as mandatory rather than adaptable.

Dr Wyllie cautioned that inflexible routines may increase injury risk and burnout, stressing that safe exercise depends on listening to one’s body and adapting when necessary.

The findings highlight how AI can inspire workouts and provide structure, yet doctors believe human oversight remains essential when health, nutrition, and mental well-being are involved.

As AI tools grow more accessible, experts urge users to treat them as supportive guides rather than replacements for qualified trainers or medical professionals.