The Hidden Role of Muscle Fat
When we think of performance decline, especially in clients with type 2 diabetes, we may chalk it up to age, poor recovery or not enough training. But what if we’re missing the real culprit?
A recent study published in the Journal of Cachexia, Sarcopenia and Muscle (Kim et al., 2025) reveals that muscle fat infiltration, what’s technically known as myosteatosis, could be silently undermining strength and endurance in clients who seem to be doing everything right.
And here’s the kicker, this isn’t just about older adults. This is happening in diabetic clients of all ages, including athletes.
Muscle Fat. The Stuff No One Sees
When it comes to muscle mass, we’ve been conditioned to think in terms of size. Bigger muscles mean better performance. But this is not necessarily.
The study by Kim et al. breaks muscle composition into three parts:
- NAMA (Normal-Attenuation Muscle Area): Lean, fat-free, functional muscle.
- LAMA (Low-Attenuation Muscle Area): Muscle infiltrated with fat. Think marbled steak.
- IMAT (Inter/Intra-Muscular Adipose Tissue): Fat in and around the muscle fibres.
While your client’s total muscle mass might look solid, if that muscle is laced with fat, it’s going to function more like an old engine full of sludge.
This explains why some diabetic athletes can maintain decent muscle size and still struggle with explosive movement, fatigue, or slower recovery.
Diabetes and Myosteatosis. A Perfect Storm
The study looked at 1,440 adults, nearly half with diabetes. Even after adjusting for age, participants with diabetes consistently had:
- More LAMA and IMAT
- Lower NAMA (lean muscle)
- Worse results in grip strength, gait speed and walking endurance
Even when muscle mass was equal or higher, the function wasn’t. Diabetic participants showed worse performance across the board.
So what’s going on?
Diabetes leads to chronic inflammation, reduced insulin sensitivity in muscle tissue, impaired blood flow and changes in how muscle regenerates. Fat infiltrates muscle fibres more easily and the body struggles to repair or rebuild lean tissue effectively.
The result is your diabetic client might be putting in the work, but still losing power, speed and stamina.
Traditional Training Falls Short
Now for the part that really challenges conventional thinking. The researchers found that regular exercise improved muscle quality (↑ NAMA, ↓ LAMA) in non-diabetic participants, but not in diabetics.
That’s huge.
It means that your usual approach of more resistance training, more cardio, more consistency etc., may not deliver the same results for your diabetic clients. It’s not that exercise doesn’t help at all, but it’s less effective at reducing the fat that’s clogging up the muscle tissue.
For strength & conditioning coaches and personal trainers who train diabetic clients, this needs to be a wake-up call. We can’t just prescribe the same programme to everyone and expect the same outcome.
How to Adapt Programming
The research makes it clear. Improving strength and performance in diabetic clients isn’t as simple as lifting heavier or training more often. When fat has crept into muscle tissue, the muscle doesn’t work the way it should. Therefore, training needs to shift from building more muscle to building better muscle. And here are some suggestions on how to do just that.
1. Shift the Goalpost from Size to Function
Muscle size doesn’t always tell you how well the muscle is actually working. The study showed that even when diabetic participants had similar or greater muscle mass, they still performed worse. That’s because the quality of that muscle was compromised by fat infiltration.
That’s why it’s essential to focus on function-first assessments. Instead of relying on circumferences or max lifts alone, integrate tools that reflect real-world muscle function, such as:
- Grip strength tests – one of the most reliable predictors of overall strength and even mortality. It’s easy to implement and can flag functional decline early.
- Gait speed or timed walks – valuable for assessing coordination, neuromuscular control and lower-body output. Slower walking speed was a clear marker of reduced performance in the study.
- Sit-to-stand or chair rise tests – simple, yet powerful indicators of functional lower-limb strength and endurance.
These functional assessments help you spot underlying muscle inefficiency that won’t show up on a tape measure or in a training log.
2. Incorporate More Power & Neuromuscular Work
Fat-laced muscle doesn’t fire the way it should. Myosteatosis affects the muscle’s ability to produce force quickly and in coordination with the rest of the body. That’s why it’s not just about strength. It’s neuromuscular efficiency which becomes a top priority.
To combat this, build in exercises that challenge explosive output, reflexive control and fibre recruitment:
- Explosive lifts (with control) – medicine ball slams, jump squats, kettlebell swings. These movements encourage fast-twitch fibre activation, which tends to atrophy faster in those with diabetes.
- Agility drills – ladder work, directional changes, cone patterns. These retrain motor units, sharpen coordination and improve dynamic stability.
- Eccentric work – slow, controlled negatives during lifts e.g. 3–5 second lowering phases, reinforce tissue resilience and stimulate high levels of muscle tension, which is essential for improving muscle fibre quality.
This type of training isn’t just useful for athletes. It’s critical for diabetic clients who may have compromised motor control due to subtle nerve or fibre degradation.
3. Prescribe HIIT with Care
We know that High-Intensity Interval Training can dramatically improve insulin sensitivity and stimulate muscle adaptation, but the study showed that in diabetic individuals, exercise didn’t improve muscle quality (NAMA) as effectively as it did in non-diabetics.
So while HIIT can still be useful, you’ll need to tailor it more carefully:
- Use shorter bursts and longer recovery periods to prevent excessive fatigue or poor form, which can blunt benefits.
- Start at a lower intensity to build tolerance and avoid overloading metabolically impaired muscle tissue.
- Track blood glucose responses pre- and post-workout, especially in clients on medication, to ensure sessions are safe and effective.
Combining these methods with mobility, resistance work and coordination drills gives your client a well-rounded approach that targets more than just VO₂ max or calorie burn.
These strategies are explored in depth in our strength & conditioning coach course, which covers how metabolic factors, like insulin resistance and inflammation, impact performance and programme design.
Don’t Ignore Nutrition
Improving muscle quality in diabetics isn’t just about what they do in the gym. Nutrition matters. A lot.
Fat infiltration in muscle is worsened by poor dietary patterns, oxidative stress and low-quality protein intake. Encourage your clients to:
- Eat more antioxidant-rich foods such as berries, leafy greens and nuts
- Use high-quality protein, especially leucine-rich sources such as check breast, lean beef, tuna, eggs and whey protein
- Consider BCAA supplementation, which may support lean muscle maintenance
This is where combining training knowledge with the nutrition coach course gives you a much stronger edge as a coach. If you understand both sides of the coin, being training and nutrition, you’re better equipped to support change.
Why It’s Important
You might be thinking, “I don’t train diabetic clients.” But here’s the thing, you probably do and don’t know it.
Many clients are prediabetic, undiagnosed or managing diabetes privately. And even beyond diabetes, muscle quality matters for general performance, injury risk, recovery and metabolic health.
Whether you’re working with athletes, casual gym-goers or clients with obesity, recognising that not all muscle is equal is critical.
The insights from this research also tie directly into the obesity & diabetes management course, where you’ll learn to spot these issues and build more tailored strategies for your clients.
As we’ve discussed, in fitness we’ve long focused on size, reps and personal bests, but the game is changing. For diabetic athletes and everyday clients alike, muscle quality is the missing piece of the puzzle.
Training isn’t just about building muscle, it’s about building the right kind of muscle. Fat-free, functional, resilient tissue that performs under pressure and supports long-term health.
So if your client isn’t progressing the way you’d expect, don’t just push harder.
Look deeper.
Reference
Kim, J.A., Shin, C., Jung, I., et al. (2025). Impact of Muscle Quality on Muscle Strength and Physical Performance Beyond Muscle Mass or Diabetes Status. Journal of Cachexia, Sarcopenia and Muscle, 16:e13760. Click here to review the full research study.
The Course That Goes Beyond Reps and Sets
If you’re working with clients who have type 2 diabetes or obesity, understanding muscle quality could completely change how you train them. A 2025 study published in the Journal of Cachexia, Sarcopenia and Muscle found that even when muscle mass was similar, diabetic participants had significantly worse muscle function due to fat infiltration. This is known as myosteatosis. In fact, regular exercise improved muscle quality in non-diabetics but had little effect in diabetic individuals unless training was specifically adapted. That’s why the TRAINFITNESS Level 4 Obesity & Diabetes Management course goes beyond the basics, giving you the knowledge to programme more effectively, reduce risk factors and improve real-world outcomes for your clients. If you want to help clients improve not just how they look, but how their muscles actually work, this course is essential.
Level 4 Obesity & Diabetes Management Course – Distance Study
Build a Career Helping Clients Eat, Train and Live Better
If you’re starting out in the fitness industry and want to specialise in nutrition as well as training, the Nutrition & Exercise Specialist and Master Diplomas™ are the perfect fit. With rates of type 2 diabetes and obesity continuing to rise, clients are no longer just looking for workouts, they need qualified professionals who understand how nutrition and exercise work together to support real health change. These diplomas give you the skills to design effective training plans and provide targeted nutritional advice, including how to work safely and successfully with diabetic clients. Whether your goal is to coach individuals one-on-one or build a long-term career supporting people with complex health needs, this is where it starts.
Nutrition & Exercise Specialist/Master – Distance Study, In-Person & Live-Virtual
