The importance of the mode of exercise in the beneficial adaptations of physical exercise for health

It has been widely demonstrated that daily physical activity leads to significant beneficial effects on health, both in prevention^(1,2) and in the treatment of numerous chronic diseases⁽³⁾, regardless of the mode of physical activity. However, in certain situations, choosing a specific exercise mode may be relevant to induce specific health adaptations in individuals. Indeed, performing physical exercise induces a transient stress on the body that triggers an adaptive response, and the repetition of these transient stresses is responsible for the beneficial adaptations associated with chronic exercise. Therefore, it is important to know which structures will be involved, and thus undergo stress, depending on the mode and intensity of the chosen exercise to induce the desired beneficial adaptations.

In this dossier, we will address the characteristics of the different exercise modalities as well as their acute physiological effects, i.e., during the exercise, and chronic effects.

I – The Mode of Exercise

As previously explained, the choice of exercise modality must take into account the desired physiological adaptations as well as the acute physiological changes, particularly depending on the individual’s capabilities. Traditionally, exercises are divided into two main modalities: aerobic exercise and resistance exercise.

Aerobic exercise involves the muscular energy systems that use oxygen, i.e., aerobic metabolism, as well as the cardiovascular system during exercise, and is therefore often associated with endurance exercise where performance is linked to these systems. In contrast, resistance exercise strongly involves the skeletal muscles and the nervous system, and is therefore often associated with exercises requiring a high production of force, such as weightlifting. However, it would be reductive to say that the different exercises performed belong exclusively to one of these categories since the majority of exercises often involve a mix of both modalities. For example, a High-Intensity Interval Training (HIIT) session in a gym might consist of a series of weightlifting exercises interspersed with rest periods, each period lasting between 30 seconds and 2 minutes. Thus, the weightlifting exercises stimulate the muscles and correspond to resistance training, but their duration and intensity strongly stimulate the aerobic and cardiovascular systems. From this, we can refine the exercise conditions based on duration and intensity and describe three major conditions:

• Moderate Intensity Continuous Training (MICT), which are long exercises lasting at least one hour at an intensity at the level of the first ventilatory threshold, corresponding to a point where the individual is able to talk during the exercise while being slightly breathless.
• High-Intensity Interval Training (HIIT), which are shorter exercises during which there is an alternation of high-intensity exercises, close to the maximum, with lower intensity recovery exercises. Generally, these phases last between 30 seconds and 2 minutes depending on the exercises and the individuals.
• Resistance exercises such as weight training (RET) aimed at muscular hypertrophy, which involve either lifting one’s own body weight or lifting weights according to sets interspersed with rest periods. There are different modalities of sets and repetitions depending on the goals, but for example, 3 sets of 12 repetitions interspersed with 1 min 30-2 min of recovery are used for muscle hypertrophy.

II – MICT Exercises

MICT exercises generally correspond to endurance exercises in common language, i.e., long-duration exercises at moderate intensities, often between 55% and 75% of an individual’s maximum intensity.

At the muscular level, the main system involved is the aerobic system, whose role is to produce energy from carbohydrates/fats and oxygen to generate movement. Therefore, it is closely linked to the cardiovascular system, whose role is to deliver oxygen and the nutrients necessary for the skeletal muscles to perform the exercise.

More specifically, skeletal muscle will produce more energy via the aerobic system from carbohydrates, derived from muscle glycogen, and fats, derived from adipose tissue, using oxygen from the ambient air. During exercise, carbohydrates and fats are consumed in different proportions depending on the intensity of the exercise: at low intensity, fats are predominantly used, and as intensity increases, carbohydrates are increasingly utilized. For skeletal muscle to produce this energy, a high supply of fats and oxygen is required, which is ensured by an increase in heart rate and an increase in the diameter of the blood vessels, allowing more blood to flow through the muscles.

Given that these systems are the most involved in this exercise modality, it is also in these systems that we will observe the beneficial effects of the exercise, which are:

• An increase in muscular aerobic systems allowing for greater energy consumption from carbohydrates/fats and oxygen during exercise.
• An increase in cardiac output, which allows for a greater amount of blood to circulate within the body.
• An increase in the density of blood vessels in the skeletal muscle as well as improved function of the blood vessels.

Consequently, this type of exercise is useful for the following objectives:

• An improvement in cardiovascular health and endurance in individuals with chronic diseases, very sedentary individuals looking to get back into sports, or individuals with limited athletic abilities seeking to maintain physical activity.
• A loss of fat mass in sedentary individuals or those with limited athletic capabilities, given the consumption of fats by this type of exercise.
• An increase in the endurance capacity of recreational athletes.

There are two ways an individual can quantify the intensity of exercise:

• The simplest method is based on the talk test, i.e., the individual is able to hold a conversation but it is understood that they are engaging in physical exercise.
• The more precise method involves using a heart rate monitor and working at a heart rate around 60-65% of the maximum heart rate, calculated by 220 minus age.

III – HIIT Exercises

HIIT exercises consist of alternating periods of high-intensity exercise, about 85-95% of maximum heart rate, with periods of rest or low-intensity exercise, and have traditionally been known as interval training. During this type of exercise, the three muscular systems that produce energy will be involved in the exercise. Specifically:

• The anaerobic systems, using phosphocreatine and carbohydrates, and the aerobic system, using carbohydrates, will be utilized to produce maximum energy at the time of exercise and maintain the effort.
• The aerobic system is used to sustain the exercise during the light-intensity phase but also to regenerate phosphocreatine, which will be reused during the intense exercise phases.

During this type of exercise, the aerobic system is highly activated, which implies a very high oxygen demand at the muscular level, and in response, the cardiovascular system will therefore be heavily involved. Thus, despite the differences in intensities and durations, the beneficial effects on muscular metabolism and the cardiovascular system will be similar between MICT and HIIT exercises:

• An increase in muscular aerobic systems allowing for greater energy consumption from carbohydrates/fats and oxygen during the exercise.
• An increase in cardiac output, which allows for a greater amount of blood to circulate within the body.
• An increase in the density of blood vessels in the skeletal muscle as well as improved function of the blood vessels.

In addition to more specific endurance adaptations, it has also been shown that HIIT exercises can induce muscular hypertrophy⁽⁴⁾ and that a combined RET and HIIT training can achieve similar results to low-intensity RET exercise while allowing for endurance adaptations⁽⁵⁾. Therefore, this exercise can be recommended for:

• Improvement of performance in athletic individuals with a reduced training volume.
• Improvement of cardiovascular health in individuals who have no contraindications to practicing high-intensity sports activities and who have limited time available for practice.
• Improvement of capacity and cardiovascular health in individuals engaged in weight training who want to maintain their muscle mass.
• Loss of fat mass in individuals who have no contraindications to practicing sports and have limited time available for practice.

Generally, the exercise modalities in HIIT are⁽⁴⁾:

	Repetitions	Exercise (duration, intensity)	Rest
REHIT	2-3	20 sec, maximum sprint	2-3 min
Tabata	7-8	20 sec, maximum sprint	10 sec
Wingate	4-10	30 sec, maximum sprint	4 min
Gibala	10	60 sec, above 90% of HRmax	60 sec
Norvégien	4	4 min, 85-95% of maximal HR	3 min

These modalities are diverse and can therefore be adapted to the individual and their capabilities to avoid inducing excessive fatigue.

IV – RET Exercises

Resistance exercises include weight training with external weights or body weight, i.e., exercises during which the musculoskeletal system will lift an external load or body weight. Therefore, the most involved physiological systems are:

• The skeletal muscular system, more specifically, the skeletal muscles that are involved in the weight training movement performed.
• The central nervous system, which is responsible for initiating the movement and recruiting the skeletal muscles, thus influencing the amount of force produced.

During this type of exercise, the action of moving a load causes an increase in the tension applied to the muscle, which constitutes a stress for it and thus the main stimulus for adaptations to this type of exercise. In response, the cellular pathways responsible for protein synthesis are activated in order to increase the number of myofibrils⁽⁶⁾, the structures responsible for muscle contraction, and thus the force produced by the muscle. Furthermore, this type of exercise is also responsible for the production of hormones, such as IGF-1, which also stimulate protein synthesis at the muscular level⁽⁷⁾. Consequently, this type of exercise must also be accompanied by an adapted protein intake to maximize muscle hypertrophy⁽⁸⁾, the doses of which are described in this dossier (Protein Intake in Sports Practice | Aminogram). The performance of these movements is also accompanied by a significant exchange of nerve messages between the skeletal muscles and the central nervous system, which can modify the functioning of the latter⁽⁹⁾. The beneficial adaptations to this type of exercise are therefore:

• An increase in skeletal muscle mass allowing for better functional capacity in individuals.
• An improvement in proprioceptive abilities, i.e., the ability to sense and evaluate the position of the body in space, as well as motor coordination.

Given these benefits, this type of exercise can be recommended for:

• Individuals with chronic pathologies presenting significant cardiovascular limitations with the goal of increasing or maintaining their skeletal muscle mass and thus their functional capacity.
• Sedentary individuals or those engaging in recreational sports activities aiming to increase their skeletal muscle mass for health and/or aesthetic purposes.
• Athletic individuals looking to improve their muscle mass and/or enhance a specific sports quality related to their sporting activity, such as speed of movement or maximum strength.

Depending on the goals of the individuals, several resistance exercise modalities exist, which are organized in the form of repetitions grouped into sets spaced by rest periods depending on the load lifted: below 60% of the maximum (low load) or above 60% of the maximum (high load). It has been shown that both conditions allow for muscle hypertrophy, but only the “high load” condition allows for an increase in an individual’s maximum strength (10). Traditionally, weight training exercises are divided as follows:

• For strength gain, between 3 and 5 sets of 4-5 repetitions close to the maximum (80-90%) interspersed with 1 min 30 sec-2 min of rest.
• For muscle hypertrophy, between 3 and 5 sets of 10-12 repetitions between 70% and 80% of the maximum, depending on the level of training, interspersed with 1 min-1 min 30 sec of rest. It is also possible to perform this type of exercise with lower loads in the case of individuals who have difficulties lifting heavy weights.

Conclusion

As described in this dossier, the different exercise modalities involve specific physiological structures and result in specific beneficial adaptations for each of them. Therefore, it is important to know the characteristics of these modalities in order to advise individuals in the most suitable way based on the beneficial adaptations sought as well as the goals and physical capabilities of each individual.

References

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