In the context of training and performance, understanding and managing intensity is crucial: it represents one of the key factors in optimizing training load, promoting physiological adaptations, and avoiding overtraining . In
sports performance, every improvement is a response to a training stimulus. The human body possesses an extraordinary capacity for adaptation, but this is only effective if the stimulus is proportionate to the individual's capabilities .
This is why proper load management—that is, the overall amount of stress the body is subjected to during training—is so important.
The training load is made up of three fundamental variables:
- Volume : total amount of work performed (e.g. duration, repetitions, distance);
- Frequency : how many times the training is done in a given period;
- Intensity : difficulty of the effort.
Factors that influence intensity
Intensity is highly subjective. For this reason, it's important to measure and monitor it using objective parameters, such as:
- Heart rate
- Power (e.g. watts in running or cycling)
- Pace or speed
- Load lifted
- Muscle saturation/oxygenation
Among these, the most used parameter is heart rate , due to its practicality, accessibility and good level of reliability.
Energy mechanisms and energy production systems
Depending on the intensity and duration of the effort, the body activates different energy systems to produce the energy needed for muscle contraction:
- Prolonged efforts at low-moderate intensity: the body uses mainly the aerobic system , obtaining energy from fats and carbohydrates.
- Short, high-intensity efforts (e.g. sprints or maximal lifting): the anaerobic alactic system is activated , which relies on creatine phosphate as an immediate energy reserve.
Knowledge of these systems is essential to building an effective and personalized training plan.
Practical applications in different sports
Load modulation varies depending on specific objectives and the type of discipline.
For example:
- Marathon or granfondo : focus on volume and frequency to develop aerobic fitness. The intensity is targeted and focused on pace.
- Speed disciplines (e.g., 100m sprint): Intensity is key. Therefore, volume and frequency must be carefully balanced to avoid overload and optimize performance.
The “220-age” formula and the limits of standard models
One of the most common formulas for estimating maximum heart rate ( HRmax ) is the classic "220-age" formula. However, this is an approximation with no scientific basis.
It doesn't take into account key factors such as:
- Training level
- Health status
- Type of exercise (swimming, running, cycling, etc.)
- Biological differences (gender, ethnicity)
- Dominance of one metabolic system
Using a non-personalized HRmax can lead to significant errors in defining intensity zones, or to the risk of overtraining or ineffectiveness of the training stimulus.
Distribution of energy substrates in the Intensity Zones
Each zone corresponds to a specific level of intensity, and is reflected in the energy substrates used by the body.
As exercise intensity increases, the body changes its energy strategies . At low intensities, it primarily uses fat as an energy source, ideal for long, moderate efforts. Gradually, as the effort intensifies, the contribution of carbohydrates increases, which are quicker to utilize but have limited reserves.
This shift also leads to increased lactic acid production. When the anaerobic threshold is exceeded, the body enters a phase of rapidly increasing fatigue . At higher levels, maximum oxygen consumption is reached, representing the limit of aerobic capacity.
Understanding these steps is essential for effective and sustainable training.
Zone 2 Training:
|
Training Zone Variability
Zones based on standardized models and default settings of cardio instruments have significant margins of error, due to:
- Individual differences
- Current form
- Type of sport practiced
In endurance athletes, Zones 1 and 2 can be very broad; in less trained or power-oriented individuals, there is a more rapid transition to higher zones, with early carbohydrate activation and early lactate production.
The suggested ranges may therefore be too general.
The Importance of Laboratory Tests
The “ gold standard ” in performance evaluation is the VO2max test , performed in the laboratory using a metabolimeter, usually on a treadmill or cycle ergometer.
This test allows you to:
- directly measure metabolic zones
- accurately identify the anaerobic threshold
- determine the transition points between the predominant use of fat and the increase in carbohydrate consumption as intensity increases
- identify the point at which significant lactic acid accumulation begins.
Thanks to these measurements, it is possible to customize the intensity of the training with extreme accuracy, optimizing the stimuli and improving the effectiveness of the training load.
Load management through a nutritional strategy
The intensity and duration of training significantly influence energy and nutritional needs. Therefore, nutrition and training can work synergistically , mutually enhancing their effects if well-planned. A proper nutritional strategy can prepare the body to better sustain an effort, allowing for an increase in intensity or volume, for example, by modulating carbohydrate intake in the pre-, during-, and post-activity phases.
Pre (before the activity)
The pre-workout phase is crucial for optimizing performance and reducing the risk of premature fatigue. A proper nutritional strategy requires the availability of readily available energy , particularly in the form of easily digestible carbohydrates, especially when the expected effort is medium-high intensity or long-duration.
Consuming low-to-moderate glycemic index carbohydrates approximately 1.5-3 hours before activity promotes a gradual release of energy and helps stabilize blood sugar levels. In some situations, such as early morning or short-duration workouts, a small snack close to activity (30-60 minutes before) may be helpful . This snack contains simple carbohydrates and a minimal amount of protein or fat, so as not to slow down digestion.
The pre-race strategy can be tailored to the objective: during certain periods, carbohydrate intake can be intentionally limited to stimulate adaptation. In other periods, however, maximum energy availability should be prioritized, such as before high-intensity workouts or races.
Hydration is another key element: arriving well hydrated at the start of the activity is essential to maintain performance, especially in unfavorable environmental conditions (heat, humidity, altitude) .
During (during the activity)
During sports performance, careful planning of hydration and supplementation, especially of carbohydrates , is essential, which affect the perception of effort, the management of fatigue and the ability to maintain the desired intensity.
Indicatively:
- for moderate intensity activities ( Z1-Z2 ), at least 30 g of carbohydrates/hour are recommended ;
- for more intense and prolonged efforts ( Z3 ), you can go up to 60 g/hour ;
- In case of very long or maximal sessions ( Z4-Z5 ), you can get up to 90 g/hour , using specific carbohydrate mixes with a 2:1 ratio between glucose and fructose.
It is not necessary to fully compensate for the caloric expenditure during exercise, but buffering energy losses helps maintain performance and delay the onset of fatigue.
After (after the activity)
In the immediate post-workout period, the primary goal is to restore energy reserves , especially during heavy training. During this phase, the so-called "glycemic window" opens, a period of approximately 30-60 minutes in which the body shows increased sensitivity to insulin and a marked efficiency in reabsorbing glucose. This makes replenishing muscle and liver glycogen particularly beneficial.
Scientific guidelines suggest a targeted carbohydrate intake (from 0.7 to a maximum of 1.5 grams per kg of body weight ) within the first two hours after activity to optimize the metabolic response, promote recovery , and help prevent fatigue during intense or short-term training phases.
To aid muscle recovery, it is important to consume a source of protein , whey or vegetable , depending on your preference.
Good training!
Bibliography:
- Robergs RA, Landwehr R. The surprising history of the "HRmax=220-age" equation. J Exerc Physiol Online. 2002;5(2):1-10.
- 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 (2nd 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
PLEASE NOTE : The information provided is for informational purposes only and does not replace the advice of your doctor or healthcare provider. The information is intended for healthy individuals: any diet or exercise program must be supervised by a qualified professional before beginning it, in accordance with Italian law. Enervit SpA assumes no liability, as the information is for informational purposes only, and interested parties should consult their healthcare provider before undertaking any diet or exercise program.