SPORT
Intensity Zones in Sports Practice
Definition and Management of Training Load
Intensity Zones in Sports Practice
Definition and Management of Training Load
by Francesco Chiappero
In the context of training and performance, understanding and knowing how to manage intensity is fundamental. Intensity is one of the key factors to optimize training load, promote physiological adaptations, and prevent overtraining.
Every improvement in performance is a response to a training stimulus. The human body has an extraordinary ability to adapt, but this is only effective if the stimulus is adjusted to the individual’s capacities.
This is why proper load management is so important — that is, the total amount of stress to which the body is subjected during training.
The training load is composed of three main variables:
- Volume: total amount of work performed (e.g., duration, repetitions, distance);
- Frequency: how often training occurs within a given period;
- Intensity: the difficulty of the effort.
Factors That Influence Intensity
Intensity is highly subjective, so it is essential to measure and monitor it through objective parameters such as:
- Heart rate
- Power (for example, watts in cycling or running)
- Pace or speed
- Weight lifted
- Muscle oxygen saturation
Of all these, the most used is heart rate, due to its practicality, accessibility, and acceptable reliability.
Energy Systems and Energy Production
Depending on the intensity and duration of the effort, the body activates different energy systems to produce the energy necessary for muscle contraction:
- Prolonged efforts of low to moderate intensity: the aerobic system is mainly used, which obtains energy from fats and carbohydrates.
- Short and intense efforts (such as sprints or maximum lifts): the alactic anaerobic system is activated, which uses phosphocreatine as an immediate energy source.
Knowing these systems is essential to plan effective and personalized training.
Practical Applications in Different Disciplines
Load modulation varies depending on the goals and type of discipline:
- Marathon or gran fondo: the focus is on volume and frequency, to develop aerobic efficiency. Intensity is moderate and regulated by pace.
- Explosive disciplines (such as the 100 meters): the central element is intensity, so volume and frequency must be carefully adjusted to avoid overload and optimize performance.
The "220 - Age" Formula and Its Limitations
A widely used formula to estimate maximum heart rate (HRmax) is the classic “220 minus age.” However, it is an estimate without scientific basis. It does not consider key factors such as:
- Training level
- Health status
- Type of activity (swimming, cycling, running…)
- Biological differences (sex, ethnicity)
- Dominance of a metabolic system
Using a non-personalized HRmax can lead to significant errors when defining intensity zones, increasing the risk of overtraining or rendering the stimulus ineffective.
Distribution of Energy Substrates According to Intensity
Each intensity zone corresponds to a different level of energy substrate usage.
As exercise intensity increases, the body changes its energy strategy. At low intensity, it mainly uses fats, ideal for long and moderate efforts.
With increasing effort, the body relies more and more on carbohydrates, which are faster to use but limited in quantity.
This shift also leads to an increase in lactic acid production. Once the anaerobic threshold is exceeded, fatigue increases rapidly. At the highest levels, maximum oxygen consumption is reached, reflecting the limit of aerobic capacity.
Understanding these phases is essential for effective and sustainable training.
Training in Zone 2: A Long-Term Strategy.
More and more athletes are training in Zone 2 to develop aerobic base and improve metabolic efficiency. This intensity zone is strategic to promote lasting adaptations:
Zone 2 work is especially useful during base phases, active recovery, and with a view to sports longevity. |
Variability of Training Zones
Training zones based on standard models or default device settings show significant margins of error due to:
- Individual differences
- Current fitness level
- Type of sport practiced
In endurance athletes, Zones 1 and 2 can be wide. In less trained individuals or those with a more anaerobic profile, the shift to higher zones is faster, with early activation of carbohydrates and earlier lactate production.
Default ranges may be too generic.
The Importance of Laboratory Testing
The gold standard for evaluating performance is the VO₂max test, performed in a laboratory with a metabolic analyzer, usually on a treadmill or cycle ergometer.
This test allows to:
- Directly measure metabolic zones
- Precisely identify the anaerobic threshold
- Detect the transition point from predominant fat usage to carbohydrate usage as intensity increases
- Determine when significant lactic acid accumulation begins
With this data, training intensity can be personalized with great precision, optimizing stimuli and improving load efficiency.
Load Management Through Nutritional Strategy
Training intensity and duration significantly influence energy and nutritional needs. Proper planning of diet and training allows both to work in synergy, enhancing their effects.
A good nutritional strategy can prepare the body to tolerate greater intensity or volume, adjusting, for example, carbohydrate intake before, during, and after exercise.
Before Training
The pre-training phase is key to optimizing performance and preventing early fatigue. Available energy is needed, especially in the form of easily digestible carbohydrates, particularly if a medium-high intensity or long-duration session is expected.
Consuming low or medium glycemic index carbohydrates between 1.5 and 3 hours before provides a gradual energy release and stabilizes blood glucose. In short or very early sessions, a small snack 30–60 minutes before, with simple carbohydrates and a minimal amount of protein or fat, can be useful.
Depending on the goals, the pre-training strategy can vary:
- In some periods, carbohydrate intake may be intentionally reduced to generate adaptations.
- In others, maximum energy availability is prioritized, for example before a competition.
Hydration is also key: starting exercise well-hydrated is essential, especially in unfavorable environmental conditions (heat, humidity, altitude).
During Training
During effort, proper hydration and carbohydrate intake help control perceived exertion, fatigue, and maintain the desired intensity.
In general:
- Zone 1–2: at least 30 g of carbohydrates per hour
- Zone 3: 60 g/hour
- Long or intense efforts (Z4–Z5): up to 90 g/hour, using specific blends with a 2:1 ratio of glucose and fructose
It is not necessary to fully compensate for calorie expenditure during exercise, but cushioning the energy deficit helps maintain performance and delay fatigue.
After Training
In the immediate post-training phase, the main goal is to recover energy reserves, especially after intense loads. During this phase, the so-called “glycemic window” opens, lasting about 30–60 minutes, during which the body is more insulin-sensitive and more efficient at absorbing glucose.
Scientific recommendations suggest consuming between 0.7 and 1.5 g of carbohydrates per kg of body weight in the first 2 hours to optimize glycogen resynthesis and promote recovery.
To repair muscle tissue, it is important to include a source of protein (whey or plant-based, according to preference).
Happy training and ride strong!
Bibliography:
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- Ivy, J. L. (2004). Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Medicine, 34(7), 435–458.
- Rodriguez, N. R., DiMarco, N. M., & Langley, S. (2009). Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise, 41(3), 709–731
- Jeukendrup, A., & Gleeson, M. (2009). Sport Nutrition: An Introduction to Energy Production and Performance (2ª ed.). Human Kinetics., 145.
- Karsten, B., Jobson, S.A., Hopker, J. et al. Validity and reliability of critical power field testing. Eur J Appl Physiol 115, 197–204 (2015). https://doi.org/10.1007/s00421-014-3001-z
IMPORTANT NOTICE: the information provided is for informational purposes only and does not replace the advice of your physician or a qualified healthcare professional. The content is intended for healthy individuals: any dietary regimen or physical activity must be supervised by a qualified professional, as required by Italian law. Enervit S.p.A. assumes no responsibility, as the information is purely educational. Anyone wishing to begin a nutritional or physical activity program should first consult with their trusted specialist.