Have you ever wondered what's actually happening in your muscles during training? Or why coaches emphasize training in specific zones? Let's break down the science of training zones and why they matter for your performance.

When you exercise, your muscles need oxygen to produce energy. How much oxygen your muscles use versus how much they receive creates different training stimuli and signals for adaptations. Think of it like a car - you have different gears for different situations. Your muscles also have different "gears" or zones that create specific adaptations.

What's Happening in Your Muscles?

At lower intensity (below your first threshold), your muscles receive more oxygen than they need. This creates conditions for building more mitochondria and developing a stronger aerobic system by creating more capillaries that allow for more oxygenated blood to be delivered to your muscles. Through these adaptations, your muscles become more efficient at using fat for fuel, which is crucial for endurance performance.

As intensity increases above first threshold but below second threshold, oxygen supply and demand reach a balance point. This zone challenges your body's ability to deliver and use oxygen effectively. Exercising in this zone relies more on the use of carbohydrates for fuel, which can result in the production of more lactate within the muscle. Exercising at these intensities helps to improve your carbohydrate and lactate processing ability.

At high intensities (above second threshold), your muscles require more oxygen than your body can deliver. This creates a powerful stimulus for adaptation (large adaptation signals for increasing mitochondrial and cardiovascular function) but also accumulates fatigue VERY quickly. Training in this zone enhances your body's ability to perform at higher intensities, but it requires careful dosing and recovery following the hard sessions.

Why Individual Training Zones Matter?

This might come as a surprise but these training zones and what intensity they occur at are highly individual and can change daily based on factors like:

• Recovery status
• Fueling and hydration
• Environmental conditions
• Overall fitness level
• Previous training stress

Training in the wrong zones can lead to:

• Insufficient training stimulus
• Excessive fatigue
• Plateaued performance
• Increased injury risk

This is why generic training zones based on age or perceived effort often fall short. Your muscles tell a unique story about how they're responding to exercise, and understanding this response is key to optimizing your training.

Limitations of Training Intensity Zones

Training intensity zones are useful tools for structuring workouts, but they come with important limitations that athletes and coaches should understand. Rather than having clear-cut boundaries, training zones represent gradual transitions in how your body responds to exercise. Think of them more like a color gradient than distinct boxes - there's no exact moment where aerobic training becomes threshold training. Even within a single training session, your zones can shift based on factors like fatigue, hydration, temperature, and accumulated training stress. This is why relying solely on static heart rate or power zones can be misleading. Your "second threshold" on a hot day after a poor night's sleep will be different from your threshold when you're fresh and well-rested in ideal conditions. This is where real-time physiological monitoring with tools like muscle oxygen saturation becomes valuable - it shows you how your body is actually responding to the training stress in that moment, rather than relying on predetermined numbers that may no longer be appropriate for your current state.

The Power of Precision

The solution to training by your individualized training zones comes from measuring/monitoring your physiology and more specifically your muscle oxygen physiology. By monitoring muscle oxygen saturation (SmO2), you can identify your individual training zones and adjust them on a daily basis. This allows you to:

• Train at the right intensity for your desired adaptation
• Adjust training based on daily readiness
• Maximize training effectiveness
• Reduce unnecessary fatigue

Using physiologically-based training zones takes the guesswork out of training intensity and puts you on the path to reaching your full potential. Don't leave your training to chance - get the data you need to train smarter, not just harder.

Ready to use individualized training intensities to optimize your training? Download our free "Training and Racing with Moxy" ebook to learn how to identify your unique physiological training zones and how to change your training intensities on a daily basis.