Movement and the balance between work and recovery

Physical activity is arguably one of the most powerful biological tools for protecting longevity ever studied in preventive medicine. While a sedentary lifestyle acts slowly like a metabolic brake capable of progressively compromising the body's functioning, movement produces the opposite effect: it reactivates physiological systems, improves cardiovascular efficiency, optimizes energy metabolism, and increases the body's ability to adapt to the biological stresses of aging. It is not simply a matter of "burning calories"; every movement generates a cascade of cellular signals involving muscles, blood vessels, the brain, the immune system, and glucose metabolism.

One of the most surprising aspects to emerge from recent research is that the benefits of physical activity begin much earlier than previously thought. For many years, the dominant message was that only high levels of exercise could produce significant health benefits. New evidence shows, however, that the human body responds positively even to small increases in daily movement. It is as if the organism were biologically "programmed" to benefit from any amount of activity compared to complete immobility.

One of the largest meta-analyses available on the subject has shown that simply increasing the number of daily steps is associated with a progressive reduction in cardiovascular mortality and all-cause mortality. Analyzing over 226,000 participants, the authors observed that every increase of 1,000 steps per day reduced total mortality by 15%, while every increase of 500 steps was associated with a 7% reduction in cardiovascular mortality. Even more interesting is the fact that the benefits began to appear at around 4,000 daily steps, a threshold much lower than the famous "10,000 steps" goal (Banach et al., 2023) [8].

This finding has profound physiological and clinical implications. It means that the human body seems to respond primarily to the transition from inactivity to movement, even when the latter is relatively modest. In sedentary individuals, in fact, even small increases in locomotor activity can improve insulin sensitivity, endothelial function, lipid metabolism, and cardiorespiratory capacity. This is a fundamental concept because it makes prevention much more accessible: one does not need to suddenly become an athlete to achieve significant survival benefits.

A subsequent meta-analysis published in the Journal of the American College of Cardiology further refined these results, showing that measurable benefits on mortality appear at around 2,500 daily steps. Compared to subjects who accumulated about 2,000 steps per day, reaching about 2,517 steps was already associated with a significant reduction in total mortality, while about 2,735 steps reduced cardiovascular risk. The authors also identified an optimal range between approximately 7,000 and 9,000 daily steps, beyond which the benefits tended to progressively stabilize (Stens et al., 2023) [9].

These results challenge the idea that there is a universal "magic" threshold valid for everyone. In reality, the relationship between physical activity and health appears much more like a continuous curve: every increase in movement produces additional advantages, especially in the most sedentary subjects. From a biological perspective, this phenomenon can be explained by considering that movement acts simultaneously on numerous physiological systems. Walking increases glucose consumption by skeletal muscle, improves insulin sensitivity, stimulates circulation, reduces inflammation, and improves mitochondrial function.

A particularly interesting aspect concerns the fact that it is not just the quantity of movement that counts, but also its intensity. A large prospective study of over 403,000 US adults showed that, for the same total volume of physical activity, a higher proportion of vigorous exercise is associated with an additional reduction in mortality. Subjects in whom over 50–75% of total physical activity consisted of vigorous exercise showed a 17% reduction in mortality compared to those who performed only moderate activity (Wang et al., 2021) [10].

This phenomenon is likely linked to the specific biological adaptations induced by intense activity. Vigorous exercise produces more marked increases in VO₂max (the maximum amount of oxygen your body can consume in one minute during intense physical activity), improves mitochondrial function more significantly, increases muscle mass, and leads to a more powerful improvement in cardiovascular and metabolic function. In practice, intense activity seems to "train" the body's ability to produce energy and adapt to physiological stresses more deeply.

However, one of the most important messages to emerge from recent research is that even light activity exerts significant protective effects. A meta-analysis based on accelerometric measurements showed that low-intensity activities, such as walking slowly, doing household chores, or simply moving more often throughout the day, significantly reduce the risk of mortality. Compared to subjects who performed less than 3 hours of light activity per day, those who accumulated over 7 hours per day showed a 44% reduction in the risk of death (Ku et al., 2020) [11].

This finding is extremely important, especially for the elderly, frail subjects, or people with physical limitations who cannot perform intense activities. The human body seems to benefit from any form of movement. Even activities considered "too light" according to old exercise paradigms still produce metabolic, cardiovascular, and anti-inflammatory improvements.

From a physiological point of view, the reason is intuitive: skeletal muscle does not rigidly distinguish between "training" and "daily movement." Every muscle contraction represents a metabolic stimulus. Even light movements increase energy expenditure, improve glucose clearance, promote venous return, and counteract the deleterious effects of prolonged sedentary behavior.

The evidence becomes even more relevant in the elderly population. A massive prospective study of nearly 147,000 subjects over 60 showed that high levels of physical activity are associated with a drastic reduction in the risk of cerebrovascular disease and total mortality. Maximum benefits were observed in subjects who accumulated about 2,000–2,500 MET-minutes per week of total physical activity (a standardized unit of measurement used to quantify the total volume of physical activity performed). In particular, all-cause mortality was reduced by approximately 48% in the most active subjects.

Physical activity in the elderly seems to simultaneously counteract multiple mechanisms of biological aging: sarcopenia, chronic inflammation, insulin resistance, vascular deterioration, and loss of functional autonomy. It is as if movement were able to slow down numerous "biological clocks" of aging simultaneously (Yang et al., 2024) [12].

An extremely interesting aspect is that the benefit of physical activity does not decrease with age. On the contrary, it tends to become even more important. An aggregated analysis of over 2 million individuals from four international mega-cohorts demonstrated that the protective effect of physical activity remains stable throughout adult life and appears even more pronounced in the elderly. The authors observed that, while other protective factors such as non-smoking, optimal body weight, or absence of hypertension tend to lose some of their impact with advancing age, physical activity maintains a strong association with survival (Martinez-Gomez et al., 2024) [13].

This phenomenon likely depends on the fact that physical exercise acts simultaneously on many biological systems: cardiovascular, muscular, metabolic, respiratory, immune, and neuroendocrine. Furthermore, since the absolute risk of mortality increases with age, even a similar relative reduction produces much larger absolute benefits in the elderly.

The most recent accelerometric evidence also shows that movement maintains protective effects even in frail subjects. A longitudinal study from the UK Biobank observed that frail individuals with low levels of physical activity had the highest risk of mortality, while any increase in activity, whether moderate-to-vigorous or light, was associated with a significant reduction in risk. Conversely, high levels of sedentary behavior drastically increased the risk of death and reduced life expectancy (Yang et al., 2025) [14].

One of the most encouraging aspects to emerge from these studies is that even relatively small amounts of moderate-to-vigorous activity seem sufficient to partially compensate for the negative effects of sedentary behavior. An individual analysis of four large prospective cohorts showed that prolonged sedentary behavior increased the risk of mortality primarily in subjects who performed less than 22 minutes per day of moderate-to-vigorous activity. In more active subjects, however, the association between sedentary behavior and mortality was greatly attenuated or even absent (Sagelv et al., 2023) [15].

A further particularly important element concerns the fact that the greatest relative benefits seem to occur precisely in the most sedentary and inactive subjects. A prospective study of over 109,000 Chinese adults showed that just 75 minutes of physical activity per week was associated with a significant reduction in mortality. In the elderly, the dose-response curve took on a typical "L" shape: the greatest advantage was observed when moving from complete inactivity to modest levels of movement (Wang et al., 2025) [16].

From a biological point of view, this phenomenon is perfectly consistent with human physiology. A completely sedentary organism is, in fact, in a state of severe metabolic and cardiovascular dysfunction. When even small levels of movement are reintroduced, the relative physiological improvement is enormous. It is a bit like slowly turning on a system that has been off for too long: even minimal reactivation produces immediately relevant effects.

Overall, all this evidence converges toward an extremely clear message: movement is one of the most powerful determinants of human survival. There is arguably no single drug capable of simultaneously influencing so many biological systems with such an extensive impact on longevity. Physical activity improves glucose metabolism, cardiovascular function, brain health, immune function, hormonal balance, and functional capacity. At the same time, it counteracts chronic inflammation, sarcopenia, insulin resistance, and vascular deterioration.

Insulin resistance represents one of the main pathophysiological hubs underlying modern metabolic diseases. It is a condition in which peripheral tissues, particularly skeletal muscle, the liver, and adipose tissue, become progressively less sensitive to the action of insulin. To maintain normal glycemia levels, the pancreas is therefore forced to produce increasingly larger quantities of the hormone, establishing a state of chronic hyperinsulinemia that often precedes the onset of type 2 diabetes by many years.

In recent decades, it has become increasingly clear that physical activity represents one of the most powerful physiological tools to counteract this process. Exercise does not act solely by increasing energy expenditure; it profoundly modifies cellular metabolism, improving the tissues' ability to use glucose, reducing chronic inflammation, and restoring insulin sensitivity.

One of the most relevant aspects emerging from modern research is that sedentary behavior itself seems to represent an autonomous metabolic factor capable of promoting insulin resistance, even independently of levels of moderate-to-vigorous physical activity. A study published in the Journal of Behavioral Medicine showed that time spent sitting is directly associated with increases in insulin, HOMA-IR (a blood test that measures insulin sensitivity and estimates insulin resistance), leptin, and TNF-α (a pro-inflammatory cytokine produced mainly by macrophages), as well as a reduction in the adiponectin/leptin ratio (adipose tissue hormones that participate in the regulation of metabolism and energy balance), which is considered an important indicator of cardiometabolic risk. In particular, time spent in front of screens during leisure time was associated with a worsening of insulinemia and HOMA-IR even after adjustment for age, sex, moderate-to-vigorous physical activity, and body fat percentage (Coughlin et al., 2024) [17].

This data suggests a fundamental concept: it is not enough to "work out" for a few hours a week if the rest of the day is spent almost entirely in a sedentary position. Muscle is, in fact, the main organ responsible for peripheral glucose uptake. When movement is drastically reduced, muscle glucose utilization also decreases, and the insulin response progressively worsens.

Metabolic alterations induced by sedentary behavior can appear surprisingly quickly. A study published in Diabetologia demonstrated that just 14 days of a drastic reduction in physical activity are sufficient to significantly reduce systemic and muscle insulin sensitivity, increase liver fat, worsen the lipid profile, and reduce cardiorespiratory capacity. Participants reduced their habitual activity by an average of over 10,000 steps per day, simultaneously increasing sedentary time by approximately 223 minutes per day (Bowden Davies et al., 2018) [18].

The effect of exercise on insulin sensitivity appears particularly evident in sedentary obese subjects: a study comparing high-intensity interval training (AIT) and non-linear resistance training (NRT) showed that both strategies significantly improved HOMA-IR and reduced fasting insulin after just 12 weeks. Reductions in insulin resistance reached approximately 48.5% in the NRT group and 40.8% in the AIT group.

The authors observed that these improvements occurred independently of significant changes in body weight, suggesting that exercise exerts direct metabolic effects on insulin-dependent tissues. The main mechanisms involved include increased expression of GLUT-4, improvement in post-receptor insulin signaling, an increase in glycogen synthase (an enzyme that promotes the formation of glycogen reserves), and an increase in metabolically active muscle mass (Nikseresht et al., 2014) [19].

Even relatively simple protocols seem to produce relevant benefits. A randomized clinical trial published in Sports Medicine Open demonstrated that 16 weeks of combined aerobic and resistance training significantly reduce fasting insulin and HOMA-IR in sedentary obese adults, regardless of whether the training was periodized or not. A particularly interesting aspect is that metabolic benefits were also observed with moderate-intensity and relatively low-frequency weekly protocols (Streb et al., 2021) [20].

The evidence becomes even more robust in meta-analyses. A systematic review published in Scientific Reports analyzed 24 randomized controlled trials on sedentary non-diabetic adults, demonstrating that combined training significantly reduces glycemia, fasting insulin, HOMA-IR, TNF-α, and C-reactive protein. In particular, fasting insulin showed a very marked reduction, while HOMA-IR decreased significantly.

According to the authors, the synergistic effect of combined training depends on the complementary action of aerobic and resistance exercise. Aerobic training improves lipid oxidation, mitochondrial function, and glucose uptake, while resistance training increases muscle mass and the expression of GLUT-4 transporters. The increase in muscle mass likely represents one of the most important mechanisms through which exercise improves insulin sensitivity (Silva et al., 2024) [21].

In parallel, a large systematic review on overweight and obese adults confirmed that physical activity significantly reduces insulin resistance and intrahepatic fat, with particularly marked effects in subjects affected by type 2 diabetes. High-intensity protocols seemed to produce the greatest benefits thanks to higher recruitment of glycolytic fibers (muscle fibers specialized in the rapid production of energy for intense activities), greater peripheral glucose uptake, and better metabolic flexibility (Battista et al., 2021) [22].

A particularly important aspect is that many of these improvements occur even in the absence of significant weight loss. This point is crucial because it demonstrates that the metabolic benefits of physical activity do not depend exclusively on weight loss. Movement, in fact, exerts direct effects on muscle, liver, and adipose biology.

These effects are evident as early as adolescence. A study published in the Journal of Clinical Endocrinology & Metabolism showed that 12 weeks of moderate aerobic exercise significantly improve both peripheral and hepatic insulin sensitivity in sedentary normal-weight and obese adolescents, even in the complete absence of weight loss. In obese subjects, peripheral insulin sensitivity actually increased by 59%, while hepatic sensitivity improved by 23% (van der Heijden et al., 2009) [23].

These results are particularly relevant because they demonstrate that the improvement of insulin sensitivity can occur very early, already during adolescence. Furthermore, the fact that the benefits manifest even without weight loss suggests that exercise acts directly on the intracellular pathways of insulin signaling.

Pediatric meta-analyses further confirm these data. A systematic review including 28 controlled studies demonstrated that physical activity significantly reduces glycemia, insulin, HOMA-IR, IL-6, CRP, and leptin in overweight or obese children and adolescents, while simultaneously increasing adiponectin levels (Li et al., 2024) [24]. Another meta-analysis published in JAMA Pediatrics highlighted that the most effective approaches are HIIT combined with resistance training and concurrent training. The authors also observed a non-linear dose-response relationship: clinically significant benefits appeared with as little as 900–1200 MET-minutes per week, equivalent to 2–3 weekly 60-minute sessions of moderate-to-vigorous activity. This means that even relatively moderate amounts of exercise can produce important improvements in insulin resistance (García-Hermoso et al., 2023) [25].

A further meta-analysis published in Frontiers in Endocrinology confirmed that aerobic exercise and combined training significantly improve glycemia, insulinemia, HOMA-IR, and body weight in overweight or obese children and adolescents. According to the authors, physical activity simultaneously counteracts numerous pathophysiological mechanisms involved in insulin resistance: oxidative stress, mitochondrial dysfunction, accumulation of free fatty acids, and production of pro-inflammatory cytokines (Kazeminasab et al., 2023) [26].

Overall, all this evidence converges toward an extremely clear conclusion: movement represents one of the most powerful physiological regulators of human insulin sensitivity. Physical activity improves the muscle's ability to use glucose, reduces visceral and liver fat, modulates systemic inflammation, and improves mitochondrial function.

In parallel, sedentary behavior exerts the opposite effect: it rapidly reduces insulin sensitivity, increases adipose accumulation, and progressively favors metabolic dysfunction. Even more importantly, these processes seem to begin very early and are at least partially reversible through the restoration of regular movement.

Exercise, therefore, does not act only as a tool to "burn calories," but as a true biological modulator of glucose metabolism. Every muscle contraction represents a metabolic signal capable of improving the insulin response and counteracting the mechanisms underlying modern metabolic diseases.

Physical activity is one of the most effective tools humans have to preserve health and prevent numerous chronic diseases. Unlike a drug, which generally acts on a specific biological target, physical exercise produces a coordinated response that involves virtually every organ and tissue in the body. Muscles, liver, adipose tissue, the cardiovascular system, the brain, and even the immune system modify their functioning in response to movement, progressively adapting to become more efficient. In fact, every training session represents a stimulus that induces the body to consume energy, activate specific molecular programs, and subsequently rebuild itself in a slightly better condition than the previous one. It is precisely the constant repetition of these adaptations that determines, over time, the benefits we all know: greater strength, better endurance, improved glycemia control, reduction of body fat, and a lower risk of developing numerous metabolic diseases.

To understand how training exerts such profound effects, it is necessary to observe what happens inside the muscle cell the moment contraction begins. Every movement requires energy in the form of ATP, the body's main "energy currency." During exercise, ATP consumption increases rapidly, and consequently, the concentration of its degraded forms, particularly AMP and ADP, rises. This change is immediately sensed by a protein called AMPK (AMP-activated protein kinase), which is now considered the body's primary energy sensor. When energy availability decreases, AMPK goes into action just as a power plant manager would during a sudden increase in energy demand: it temporarily interrupts all non-essential activities and directs resources toward processes capable of rapidly producing new ATP (Jørgensen et al., 2006) [27]; (Richter and Ruderman, 2009) [28].

The activation of AMPK is arguably the most important molecular event induced by physical exercise. This is not a response limited exclusively to skeletal muscle, but a mechanism that simultaneously affects various metabolically active tissues. In the muscle, it rapidly increases glucose uptake through the translocation of GLUT4 transporters to the cell membrane, increases the use of fatty acids as fuel, improves mitochondrial efficiency, and temporarily reduces all processes that require high energy consumption. In parallel, in the liver, it promotes lipid oxidation, limits the synthesis of new fats, and helps maintain stable glycemia during exertion. Adipose tissue also responds to AMPK activation by increasing lipid mobilization and progressively reducing lipotoxicity (cellular damage caused by the excessive accumulation of fats and lipid derivatives), while at the brain level, exercise indirectly improves leptin and insulin sensitivity, contributing to the control of appetite and energy balance (Richter and Ruderman, 2009) [28].

This response can be interpreted as a sophisticated energy-saving program. If, during a power outage, a house automatically turns off non-essential appliances to keep only the essential ones running, in the same way, AMPK temporarily suspends all cellular processes that are most costly from an energy standpoint to focus resources on the production of ATP necessary for muscle contraction. These processes also include protein synthesis, one of the most biologically expensive mechanisms, as it requires enormous amounts of ATP, GTP, amino acids, ribosomes, and messenger RNA. During exertion, therefore, the muscle does not invest energy in building new proteins but concentrates every resource on the immediate production of energy (Jørgensen et al., 2006) [27].

For many years, this phenomenon was misinterpreted as a possible limitation of strength training. In reality, it represents exactly the opposite: an elegant study conducted using serial biopsies of the vastus lateralis muscle (a large muscle on the outer part of the thigh) in healthy volunteers showed that, immediately after a resistance training session, the activity of the AMPKα2 isoform increases by about 75%, while muscle protein synthesis temporarily decreases. Simultaneously, a reduction in the phosphorylation of the 4E-BP1 protein—one of the main regulators of the initiation of messenger RNA translation—is observed, resulting in a slowdown in the production of new proteins. This behavior does not represent a contradiction to the hypertrophic effects of training, but constitutes a refined energy conservation strategy: while the muscle is engaged in exertion, every molecule of ATP must be prioritized for contraction (Dreyer et al., 2006) [29].

The same study highlighted an extremely interesting aspect: the reduction in protein synthesis does not depend on a complete "shutdown" of the mTOR pathway, but rather on a much more sophisticated regulation. Although the phosphorylation of the 4E-BP1 protein decreases significantly during exercise, the phosphorylation of mTOR does not undergo equally marked variations. This suggests that the control of protein synthesis is not entrusted to a single on/off switch, but to a complex network of parallel regulations involving proteins such as TSC2 and other intracellular targets. This has profoundly changed the traditional view of the relationship between AMPK and mTOR, demonstrating that the two pathways are not simply antagonistic, but collaborate dynamically to adapt metabolism to the different phases of training (Dreyer et al., 2006) [29].

In fact, as soon as the exertion ends, the metabolic scenario changes rapidly. With the progressive restoration of energy reserves, AMPK activity decreases, and anabolic signals mediated by AKT and mTOR begin to increase. In this phase, the muscle shifts from energy conservation to the reconstruction of structures damaged during exercise, vigorously reactivating protein synthesis and laying the biological foundations for hypertrophy. It is therefore precisely the alternation between an initial phase of energy saving and a subsequent phase of reconstruction that explains how training manages to simultaneously improve metabolism and increase muscle mass and strength (Dreyer et al., 2006) [29]; (Mingzheng and You, 2025) [30].

The importance of this temporal regulation has been further confirmed by the most recent research dedicated to muscle aging. Today we know that AMPK and mTOR do not function as two systems constantly in competition, but as two conductors who intervene at different moments of the same biological concert. During exercise, AMPK prevails, favoring ATP production, the mobilization of energy substrates, the activation of autophagy, and the improvement of mitochondrial function. Once the session is over, when energy availability is restored and adequate nutrients are present, the physiological activation of mTOR prevails instead, promoting protein synthesis, muscle fiber remodeling, and functional recovery. This orderly succession allows the muscle to adapt without compromising either energy balance or growth capacity (Mingzheng & You, 2025) [30].

The importance of this molecular cascade was also confirmed by a randomized study that compared six weeks of functional resistance training and traditional resistance training in sedentary young men. Although the two protocols used different intensities, both resulted in a significant increase in lean mass, strength, power, and muscle endurance. Functional training, characterized by lower loads and a high number of repetitions, also favored a greater reduction in fat mass, likely due to a higher overall energy cost. Traditional training, performed at higher intensities, resulted in a more marked activation of AMPK (Zuo et al., 2023) [31].

The effectiveness of training becomes even more evident when analyzed in the context of aging. Over the years, skeletal muscle develops progressive anabolic resistance and reduced insulin sensitivity, accompanied by a decrease in mitochondrial function, the accumulation of intramuscular lipids, an increase in oxidative stress, and a loss of the ability to adapt rapidly to energy demands. However, physical exercise represents the most powerful physiological intervention capable of restoring this balance. During aerobic activity, AMPK activation prevails, while in the recovery phase, the physiological activation of mTOR promotes protein synthesis and the maintenance of muscle mass. The integration of aerobic training and resistance training is currently the most effective strategy to simultaneously counteract insulin resistance and sarcopenia (Mingzheng and You, 2025) [30].

In recent years, a further mechanism through which physical activity protects muscle has emerged: the regulation of autophagy. During muscle contraction, the increase in the AMP/ATP ratio activates AMPK, which physiologically inhibits mTORC1 through TSC2. This action reactivates the autophagy-lysosome system, allowing the cell to eliminate damaged mitochondria, aggregated proteins, and lipid droplets accumulated over time. Through so-called lipophagy (degradation of fats stored within the cell), intracellular lipid deposits are also degraded, further improving insulin sensitivity and reducing metabolic inflammation (Zhang et al., 2026) [32].

These observations have been further strengthened by recent experimental studies that have identified the AMPK pathway as one of the main mechanisms through which exercise also protects muscle from ferroptosis, a particular form of cell death characterized by iron accumulation and intense lipid peroxidation. In animal models of sarcopenic obesity induced by a high-fat diet, aerobic training reduced lipid accumulation in the muscle, improved strength, normalized iron metabolism, increased antioxidant defenses, and reactivated AMPK phosphorylation (Ru et al., 2026) [33].

Further confirmation of the centrality of these metabolic pathways comes from studies on human aging. In elderly men, a significant reduction in the activity of the AMPK pathway and mTOR signaling has been observed compared to young subjects, indicating that with age, both the mechanisms responsible for energy production and those involved in protein synthesis are attenuated. This suggests that the benefits of training do not depend on a chronic and permanent activation of metabolic pathways, but on the constant repetition of the stimuli induced by each session, which over time translate into an improvement in muscle function and a slowing of the decline associated with age (Li et al., 2012) [34].

Taken together, these findings profoundly change the way we interpret training. Physical exercise is not simply a means to burn calories, but a biological stimulus capable of reprogramming cellular metabolism. Each session activates an orderly sequence of events: initially, AMPK preserves energy balance by increasing ATP availability and temporarily suspending the most expensive processes through the inhibition of mTOR; subsequently, through the reduction of AMPK and the reactivation of mTOR, the programs for repair, mitochondrial biogenesis, autophagy, and protein synthesis are activated, making the muscle more efficient, stronger, and metabolically more flexible. It is precisely the constant repetition of this cycle of consumption, recovery, and adaptation that explains why training is currently one of the most effective tools for improving insulin sensitivity, preventing obesity, countering sarcopenia, and reducing the risk of the main chronic diseases associated with aging.