What Does “Science-Backed” Truly Mean?

For Instructors who may not know you – who are you, what does your team do, and what does “science-backed” really mean at Les Mills?

Bryce: I am the Head of Research for Les Mills and have been involved with the company for over 30 years, originally starting as a physiotherapist. My team’s role is to ensure that every workout is effective and safe. “Science-backed” isn't just a buzzword; it means we obsess about the details, so our partners and participants don’t have to. It also involves partnering with researchers at top universities such as Penn State and Iowa State University to conduct research related to the effects of exercise and psychological factors such as motivation.

Is Les Mills unique in this approach, and what advantage does this give Les Mills Instructors?

Bryce: Yes, the extent of our testing and research is unique. The advantage for Instructors is confidence. In an era of misinformation, you can be confident that the program you are delivering is effective and safe. We constantly test, iterate, and revise programs before they are released. We effectively act as the "fence at the top of the cliff" regarding injury prevention and results, rather than the ambulance at the bottom.

When a new program or release is first conceptualized, how do your team and the creatives work together?

Bryce: It is a collaborative process. We work with the creative team to ensure the choreography is safe and appropriate for the group we are targeting. The creatives work in teams to test and iterate. My team reviews the choreography to ensure it meets safety guidelines and delivers the intended training effect. Science ensures the structure works, while creativity ensures it’s an experience people love.

How do you design and test programs so they work for all fitness levels?

Bryce: We focus on "autonomy" and "inclusivity." Research shows that beginners often feel intimidated and dislike being challenged too early. Therefore, we ensure there are low-complexity, low-intensity options that deliver a training effect appropriate for someone new to fitness. For advanced participants, we ensure the intensity can be scaled up (like high-impact options). The goal is to allow everyone to find their own level within the same class.

Is there a fine line between overexertion and healthy ‘pushing yourself further’?

Bryce: The first thing to remind ourselves is that the vast majority of adults aren’t meeting the exercise guidelines of 150 minutes of moderate-to-vigorous exercise per week, a couple of strength sessions, and some core/flexibility work. In my view, that’s our biggest priority.

Recovery is really important, but in light of the above, I think it's recovery from life (stress and anxiety) that’s key, rather than the physiological effects of exercise.

In saying that, though, we know from previous research that our Instructors are a high-volume training group. In that case, they need to be mindful of using recovery strategies (one complete day off per week) to keep them at their best, particularly when they’re adding high-intensity sessions into their weekly routine.

How do biomechanics influence choreography, and what safeguards are in place?

Bryce: We review every release to ensure moves are biomechanically sound for the general population. For example, in BODYPUMP™, we don’t squat below 90 degrees of hip and knee flexion. This ensures we are maximizing muscle load while minimizing joint stress. We also sign off on the cueing and coaching in every release to ensure the Instructor has the tools to keep everyone safe.

Can you share examples of times when science or testing led to changes in choreography?

Bryce: In LES MILLS SPRINT™, we found that if there are too many speed tracks in succession, or if the cadence of a track is too low, heart rate testing shows a drop in intensity. We then advise changing the track order to maximize the HIIT response.

How do you scientifically measure enjoyment, and why is “fun” so important?

Bryce: Some of our research has looked at “enjoyment” and “intention to return” via surveys. Intrinsic motivation – essentially enjoyment – is a critical predictor of long-term adherence. If people don’t enjoy aspects of their workout experience (e.g., the Instructor, the music, or the group), it becomes much harder to make it a habit. Our research shows that when people feel connected and enjoy the experience, their exertion levels actually increase, sometimes without them even realizing it feels harder.

Does science influence program formats (for example, 30 vs. 55 minutes)?

Bryce: Yes. For example, the 45-minute format in BODYPUMP, incorporating the lunge–shoulder track and the bicep–tricep track, was designed to enable the shorter version to have a similar calorie output to the longer one, due to the integrated style of the tracks.

Why is there no cooldown stretch in LES MILLS GRIT™?

Bryce: We felt that the core track provided enough recovery to bring the heart rate down after the peaks in the working tracks. Our goal in HIIT classes is to spend 20 of the 30 minutes above 85% of max heart rate. This maximizes the “bang for your buck” in 30 minutes – meaning that’s all you need to do for that day.

Have you noticed a shift away from ‘extreme’ workouts toward a more holistic approach?

Bryce: Absolutely. We’re seeing a massive shift from "fitness" (aesthetics, calorie burn) to "wellness" (longevity, mental health). People want to move to feel good and live longer, not to get shredded. Removing calorie counts aligns with this – focusing on the quality of the movement and its health benefits (like cardiovascular health and strength) rather than just energy expenditure.

How is the science behind releases translated into Instructor education?

Bryce: We integrate the "why" into Instructor education so they can explain it to their members. When an Instructor understands why we use the ranges of motion we use in a squat, for example, they coach it with more conviction. It elevates them from just "showing moves" to "coaching with purpose."

How is fitness science evolving at Les Mills?

Bryce: The science moves with the trends. With each new development comes a new opportunity. For example, we are currently looking at the effects of breathwork in the Les Mills Yoga™ series on performance in recreational runners.

We wouldn’t have even thought about that 18 months ago.

That’s the fun bit – there's always more to explore.