I’ve been lifting weights at home for a few years now, but recently I’ve found myself stuck in a rut. If anything, my routine has become a humdrum habit, without a clear goal and sense of progression to keep me motivated. Ten exercises, three sets, eight reps, 30 minutes. I’ve run through it so often that I could do it in my sleep.
I’m a true tech lover, so of course I got artificial intelligence (AI) to help me out. Apple has just launched its revamped Siri AI and I’ve been playing around with its early beta edition, so I was curious to know if its new skills extended to solid fitness advice — and if they did, how they held up against the ever-popular ChatGPT.
To find out, I asked each chatbot to dream up a workout routine that could revitalize my fitness habits. After working through both plans and tapping a professional personal trainer for their insights, I was left with the impression that only one of the two workout plans was worth sticking with.
The setup
To start with, I put together a prompt that I then fed into both AIs. The goal was to briefly explain my physical state and outline the kind of workout I was after, noting any constraints such as time and location (I work out at home).
Here’s the prompt I used:
“I am a 36-year-old man in good physical shape who exercises regularly. Create a three-day overall workout plan for me with the goals of hypertrophy and building muscle. The workout will be done in a small home office using dumbbells as the only equipment. It can include calisthenics as well as weighted exercises and should aim to cover different areas of the body. Ensure it lasts no longer than 45 minutes. Explain how often each workout session should be repeated over the course of a week and when rest days should take place, if required.”
I didn’t add any subsequent follow-up messages, as I wanted to know what each AI could come up with given the kind of information that a regular user might provide.
The new challenger: Siri AI
At its Worldwide Developers Conference (WWDC) in June, Apple made a big song and dance of its new Siri AI virtual assistant, a new foundational model based on Google’s Gemini LLM.
When given my workout prompt, Siri AI put together a plan that included a “push” day focusing on my chest, shoulders and triceps; a “pull” day centered on my back, biceps and rear delts; then a final “legs and core” day. It offered a workout schedule and suggested that each session would take around 45 minutes, with three sets of 8-12 reps and a rest of 60-90 seconds between each set.
“Focus on controlled movements and progressive overload by gradually increasing the weight of your dumbbells or the difficulty of your calisthenics,” it advised. Each exercise was accompanied by a short explanation of how to perform it, which was a welcome touch.
Putting Siri’s action plan into practice, it was obvious that my old self-made workout plan wasn't pushing me hard enough, as the first day’s workout left me feeling like I’d worked harder than I had for months. Off to a good start, I thought.
But Siri’s plan came up well short of 45 minutes, with most days’ efforts lasting a mere 25 minutes. And aside from the lack of warm up, there was also no word on how to complement the exercises with targeted nutritional intake. That’s a serious oversight in its workout regimen, especially for beginners.
To help me better understand the plans from both Siri AI and ChatGPT, I asked personal trainer and fitness coach Scott Laidler for his opinion. Speaking of Siri’s effort, Laidler said that it had a few things going for it.
“Siri’s is simple which means there is little to misinterpret,” said Laidler, adding that “the equipment substitutions are sensible for the office environment.”
While Siri recommends upping the weight as you get stronger, it doesn’t say “what to do once this plan hits diminishing returns, which is months away, not years,” according to Laidler. While it sounds like an open-ended plan, “it’s really only built for a defined window,” Laidler warned, which could “lead to frustration unless you knew to come back to the table and ask for a new plan several times per year.”
That’s a problem inherent in the responses from both Siri and ChatGPT.
The class leader: ChatGPT
While Siri AI’s workout plan was concise, ChatGPT was much longer. It explained what the priorities of the workout were and gave some basic advice, such as aiming to finish with one or two reps in reserve as a guidance on how much weight to use. It then listed a weekly schedule before laying out a simple warm up to perform each session.
Each exercise was listed, with varying numbers of sets and reps, followed by a note on which muscle groups were being targeted. Unlike Siri, there was no explanation of how to perform each exercise, which feels like an oversight with potential for injury. That was a clear win for Siri AI.
At the end, ChatGPT included a “progression” section explaining how to push yourself further, a guide on recovery and nutritional intake, then an explanation of “why this split works.” Taken together, it was a detailed workout plan, if a rather verbose one.
According to Laidler, ChatGPT’s plan was “the better program by some margin.” Siri “applies a flat ‘three sets of 8-12’ to every exercise, with each muscle group trained once a week,” Laidler noted. ChatGPT, on the other hand, “hits most muscle groups twice across the week, varies the sets per exercise, includes a warm up, and gives real progression logic. On paper it’s the more sophisticated plan.”
ChatGPT “is closer to what the literature would see as optimal for the stated goal of gaining muscle,” Laidler stated. “Reps in reserve (RIR) offers a way for the user to keep a reasonable distance from failure, which de-risks the plan especially when training alone.”
OpenAI’s LLM has a trick up its sleeve, too: it can analyze your form based on uploaded videos. I asked it to judge my Romanian deadlift form and it gave me an 8.5 out of ten, giving pointers on what I did well and what could be improved. I wouldn’t take this advice over that of a human expert, but compared to Siri AI — which can’t do any of this at all — it’s another point to ChatGPT.
The overall picture
Despite their individual strengths, Laidler warned that neither Siri AI nor ChatGPT had created an optimal workout plan. As he pointed out, “It doesn’t appear that the LLM has asked follow up questions that may have helped customize the plan a little more.”
This highlights a problem with using AI for personal fitness. While a personal trainer would naturally ask these questions straight away, an AI chatbot won’t necessarily propose them unless prompted. Without a more detailed knowledge of your personal situation, you could end up with a sub-par workout routine that’s not well-suited to your circumstances.
So, if you’re going to use AI to sketch out a fitness plan, make sure to add as much detail in your prompt as possible. Ask it to pose follow-up questions to ensure it has as all the information it needs, and come back to it regularly. Don’t just stick to the plan it gives you and repeat it ad infinitum or you’ll end up like I did: languishing, with your progress grinding to a frustrating halt.
Of course, as Laidler pointed out, the problem with doing this — telling the LLM your injury history, what feels like a hard set, your workout preferences, and more — means that “you need to already know what a well-built program looks like to comprehensively prompt for one.” And if that’s the case, do you even need an AI to help you in the first place?
If you do want to go ahead with an AI fitness coach, ChatGPT is a better bet than Siri AI for now, as it includes more varied sets and targets more muscle groups. Neither is perfect, but Apple has plenty of work to do if it wants to match ChatGPT’s take on fitness advice.
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