As professional in-home and virtual personal trainers, we pride ourselves on helping our clients understand some of the basic science behind our exercise programs. For instance, it’s important to understand that not all muscles work the same way. 

The body is made up of different types of muscle fibres: slow twitch (Type 1) and fast twitch (Type 2). Each plays a unique role in how we move, train, and perform. In this post, we’ll discuss the difference between these fibres and how our team uses their strengths to tailor workouts more effectively.

THE BASICS OF MUSCLE FIBRES

Skeletal muscle fibres differ in how they produce energy, how quickly they contract, and how resistant they are to fatigue. Slow twitch fibres are designed for endurance: they contract more slowly but can sustain activity for long periods. 

On the other hand, fast twitch fibres contract quickly and powerfully but fatigue much sooner. If you’ve ever wondered why some people naturally excel at marathons while others shine in sprints, the answer often lies in the balance of slow and fast twitch fibres in their muscles. While genetics play a big role, training can influence how efficiently your body uses both types.

SLOW TWITCH

Slow twitch muscle fibres are built for stamina, “[utilizing] energy more slowly than fast-twitch muscle fibers. But that doesn’t mean they’re second best. In fact, slow-twitch muscles are actually used first and more often in everyday activities” (Cleveland Clinic, 2024). They rely primarily on oxygen to generate energy through aerobic metabolism, which makes them incredibly efficient at sustaining long-duration activities like distance running. These fibres are smaller, rich in blood supply, and packed with mitochondria: the energy-producing powerhouses of the cell. When you engage in lower-intensity, steady-state exercises, your slow twitch fibres are doing most of the work. For our clients who enjoy endurance-based workouts or want to improve their cardiovascular health, slow twitch training is key. 

FAST TWITCH

Fast twitch muscle fibres are designed for quick, explosive movements. They produce energy anaerobically, meaning they can generate force without relying on oxygen, but only for short bursts. “Fast-twitch fibers generally produce the same amount of force per contraction as slow muscles, but they get their name because they are able to fire more rapidly. These fibres come into play during activities like sprinting, jumping, or heavy lifting” (Very Well Fit, 2024). 

There are two sub-types of fast twitch fibres: Type 2a and Type 2b. Type 2a fibres have some endurance capabilities and can use both aerobic and anaerobic energy systems. Type 2b fibres are pure power producers, firing rapidly and with great force but tiring quickly. Training your fast twitch fibres means focusing on higher-intensity movements found in HIIT or plyometrics. Our in-home personal trainers in Toronto, Collingwood, London, Hamilton, and Ottawa, (and virtual personal trainers everywhere) use these methods to help clients increase strength and muscle tone efficiently, even in a small workout space.

MUSCLE FIBRE DEVELOPMENT

While genetics determine your natural muscle fibre ratio, your training style influences how each fibre type develops and performs. Endurance training enhances the efficiency and oxygen capacity of slow twitch fibres. On the other hand, strength and power training stimulates fast twitch fibres to grow in size and strength. Many people benefit from a balance of both. A well-rounded fitness program should challenge your muscles in various ways, as mixing cardio and resistance training ensures both fibre types are activated. 

WHAT’S RIGHT FOR YOU?

If your goal is to run longer distances or boost endurance, slow twitch-focused workouts like steady-state cardio, bodyweight circuits, or yoga can help. If you want to build strength or improve explosive performance, fast twitch-targeting exercises should take priority. That said, both fibre types are essential for overall fitness. 

Even endurance athletes need some fast twitch power to handle inclines and sprints, while strength athletes benefit from slow twitch endurance to sustain longer training sessions. The right mix depends on your individual goals, fitness level, and body composition.

Understanding the science behind muscle fibres is only the first step. Applying that knowledge to your workouts takes professional guidance and consistency. Our in-home and virtual personal trainers design programs that strategically target both fibre types through varied intensity, duration, and recovery periods. For example, we might pair resistance training days that stimulate fast twitch fibres with recovery runs or mobility sessions that develop slow twitch endurance. This approach improves performance and prevents injury while building a body that’s strong, resilient, and adaptable.

FINAL THOUGHTS

Both slow and fast twitch muscle fibres are essential to how your body moves, performs, and adapts to exercise. Understanding how they work — and how to train them — can transform your fitness. Whether your goal is to build strength, improve endurance, or simply stay active, a balanced program that challenges both fibre types will help you get there more efficiently.

At Nielsen Fitness, our  trainers work with clients to build customized programs that bring out the best of both worlds: the stamina of slow twitch endurance and the explosive power of fast twitch strength. With the right training plan, you can achieve a stronger, more capable body, no matter your starting point. Contact us today to learn more!