Metabolic And Mechanical Cost Of Sedentary And Physical Activities In Obese Children And Adolescents

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Author(s):

	Stefano Lazzer
	Stefano Lazzer received a Bachelor in Sport Sciences at the University of Padova, and a Master in Sport Sciences at the University of Grenoble.
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	Grace O’Malley
	Research Lecturer at Royal College of Surgeons in Ireland; Clinical Specialist Physiotherapist in Paediatrics, Temple Street Children’s University Hospital
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	Michel Vermorel
	Michel Vermorel is engineer in Agronomics and has a MSc degree in Nutrition Physiology.
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	Lara Mari
	Department of Medicine, School of Sport Science, University of Udine, Italy.
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	Mattia D’Alleva
	Department of Medicine, School of Sport Science, University of Udine, Italy
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Introduction

Obesity is conventionally defined as a pathological condition arising from a sustained positive energy balance, primarily due to a chronic disparity between energy intake (EI) and energy expenditure (EE).

The daily energy intake can be accurately characterized through both quantitative (caloric value) and qualitative (macronutrient composition) assessments, typically employing dietary record methodologies. Conversely, the precise estimation of total daily energy expenditure (TEE) in free-living conditions presents a significant methodological challenge, necessitating the deployment of qualified personnel and sophisticated technical methods (e.g., Doubly Labeled Water or long-term indirect calorimetry).

TEE is comprised of several interdependent biological and behavioural components:

1. Basal Metabolic Rate (BMR): The energy required to sustain vital functions, extrapolated over a 24 -hour period. This represents the largest fraction of TEE.
2. Thermic Effect of Food (TEF): The energetic cost associated with the digestion, absorption, and assimilation of nutrients (also known as Diet-Induced Thermogenesis).
3. Energy Expenditure for Growth (in pediatric populations) and for tissue repair/healing
4. Thermoregulation: The energy expended to maintain core body However, in developed nations, the impact of cold exposure on TEE is substantially mitigated by adaptations in clothing, housing infrastructure, and heating systems (1).
5. Physical Activity Energy Expenditure (PAEE).

For practical and analytical partitioning, the PAEE component is further subdivided into the energy expenditure associated with sedentary behavior versus actual physical activities (as schematically detailed in Figure 1).

Figure 1. Main components of total daily energy expenditure (TEE) (modified from (2)).

BMR: basal metabolic rate; SMR: sleeping metabolic rate; WMR: wakefulness metabolic rate; TEF: thermic effect of food EE; SA: sedentary activity EE; PA: physical activity EE

MAIN COMPONENTS OF DAILY ENERGY EXPENDITURE

Basal Metabolic Rate

BMR represents the energy expenditure required to sustain fundamental physiologic functions (e.g., cellular activity, organ function, myocardial contractility, muscle tone, and respiration) in an awake individual. Because of the elevated energy demands of the brain and muscle compartments during wakefulness, BMR is approximately 5% higher than the metabolic rate expended during sleep (which reflects the minimum energy level essential for life support).

BMR is typically measured following a 12-hour fast while the subject is at rest in a thermoneutral and quiet environment. This energy expenditure is a continuous 24-hour process and remains relatively stable within an individual over time. BMR constitutes the largest fraction of daily TEE, averaging 60% of TEE. This contribution ranges from 45-50% in highly active subjects to about 70% in sedentary individuals. Consequently, BMR is dependent on the mass and metabolic rate (EE⋅g⁻¹of tissue⋅min⁻¹) of various tissues and organs.

The metabolic rate (MR) of individual tissues and organs exhibits considerable variability. For example, the MR in the digestive tract, liver, brain, heart, and kidney is approximately 10, 15, 20, 30, and 35 times higher, respectively, than that of resting muscle. Conversely, the MR of white adipose tissue is only about one-third of that of resting muscle (3). As a result, while organs account for approximately 7% of body weight (BW), they contribute about 60% to BMR. In contrast, skeletal muscle and adipose tissues constitute 35-40% of BW but contribute only 18-22% and 3-4% to BMR, respectively (4) (Fig. 2).

Figure 2. Contribution of organs and tissues to body weight and basal metabolic rate.

Due to lack of information on organ mass and metabolic rate in individuals, for practical purposes the main significant determinant of BMR is FFM (R² = 0.65-0.80). Fat mass (FM) is a significant determinant only in individuals who are obese (R² < 0.04) (5).

In absolute values, BMR is higher in individuals who are obese compared to those who are lean due to higher levels of Fat free mass (FFM) and FM. However, when adjusted for body composition, BMR is not significantly different suggesting that tissue and organ metabolic rate is not significantly different between those who are obese and those who are lean.

BMR expressed as per kg of FFM is significantly higher in boys than in girls, by 3% and 6% in prepubertal and pubertal subjects, respectively (6). Higher levels of BMR are observed in pubertal children due to higher proportions of skeletal glycolytic fibres (7), higher Na⁺-K⁺ ATPase activity (8), and changes in hormonal status (9).

Collectively, FFM, FM, age, gender, and physical activity explain 70-80% of the variance in BMR (10, 11). The remaining 20-30% may be due to genetic factors or other factors such as differences in gut flora metabolism (12).

The accurate prediction of Basal Metabolic Rate (BMR) in individuals with obesity is crucial for designing effective dietary interventions, as it provides the foundation for determining an appropriate energy deficit. The gold standard for BMR assessment is indirect calorimetry (IC). However, the routine use of IC in clinical settings, whether for diagnostic or prognostic purposes, is limited by its technical complexity, the need for trained personnel, and the high cost of equipment. To address these limitations, several researchers have developed predictive equations to estimate BMR in children and adolescents, based on easily obtainable anthropometric and body composition parameters (13, 14). Equations using anthropometric variables (Equation 1) or body composition parameters (Equation 2) have shown good accuracy in predicting BMR among children and adolescents with obesity (10, 11):

Eq. 1:  BMR = (Gender × 213) – (Age × 28) + (Body Weight × 13) + (Stature × 434) + 355        R² = 0.66, SE = 246 kcal/day

Eq. 2: BMR = (Gender × 217) – (Age × 26) + (FFM × 16) + (FM × 13) + 868   R² = 0.66, SE = 247 kcal/day

where Gender = 1 for males and 0 for females; BMR is expressed in kcal, Age in years, Body Weight in kg, Stature in meters, and FFM and FM in kg.

A recent study (2024) involving 275 children and adolescents (aged 6–18 years; 148 boys and 127 girls) across a spectrum of body mass indices measured BMR via indirect calorimetry and compared the results with 13 existing predictive equations. From this comparison, the authors proposed a new simplified equation using Fat-Free Mass (FFM) as the sole predictor:

BMR = 505.412 + (24.383 × FFM)    R² = 0.65 kcal/day

In another multicenter study including 556 adolescents (mean age ≈ 15 years; 77% female; mean BMI z-score ≈ 3.3; relative BMI at the 95th percentile), BMR was measured using indirect calorimetry and body composition was assessed via DXA. The researchers developed an equation incorporating height, weight, BMI percentile, and gender:

BMR = -2048 + (18.17 × height ) – (2.57 × weight ) + (7.88 × BMIp95) + (189 × gender ).  Kcal/day

This model showed improved predictive accuracy and lower bias compared to 11 previously established formulas, which tended to underestimate BMR in cases of severe obesity (68).

Thermic effect of food

The thermic effect of food (TEF) refers to the increase in energy expenditure that occurs during the processes of eating, digesting, absorbing, and metabolising nutrients. This effect typically lasts for at least five hours after a meal and accounts for roughly 10% of total daily energy intake. The magnitude of TEF depends mainly on the macronutrient composition of the meal and tends to remain relatively consistent within the same individual over time. MR increases are generally lower for fats and carbohydrates, about 3% and 5% of energy intake respectively, over a 3–4-hour period, whereas protein induces a markedly higher thermic response of approximately 20–25%.

Growth

Although children require additional energy to support growth, the contribution of growth to total energy requirements is minimal, except during the first few months of life. Throughout the growth period, energy is deposited in the body primarily as protein and lipids, with energy densities of 5.5 and 9.5 kcal·g⁻¹, respectively. Assuming an energy utilisation efficiency of 50–70% for growth, depending on the proportion of energy stored as lipids, growth contributes only 2–4% of daily energy requirements in adolescents, even during periods of rapid growth (16).

During adolescence, the relative increase in FM is approximately 13% in females, whereas males experience a 4% decrease. On average, adolescent males have 20 kg more FFM than females. These sex-specific changes in body composition during growth account for the substantially higher EE at rest and during physical activity observed in males compared to females of similar total body weight.

Healing

Following injury or surgical procedures increased energy and protein are required by the body to support the immune response and repair. The body makes substrates readily available and in turn, resting energy expenditure rises (17).

Energy expenditure during sedentary and physical activities

Due to their higher body weight, including greater FFM, children and adolescents with obesity exhibit higher total daily TEE, BMR, and sedentary and physical activity energy expenditure compared to non-obese peers (2). However, obese children are known to engage in less physical activity and more sedentary behaviour than age-matched non-obese individuals (18).

Daily EE and the energy expenditure associated with usual sedentary and physical activities were assessed in 50 non-obese and 27 obese adolescents aged 14.0 ± 0.3 y (2). As expected, BMI, FFM, and FM were higher in obese subjects: 34.1 vs 18.8 kg·m⁻², 52.4 vs 39.9 kg, and 43.1 vs 19.7 kg, respectively. On average, the excess weight in obese adolescents consisted of 27% FFM and 73% FM. Energy expenditure during sleep and sedentary activities was 19% higher in obese adolescents compared to non-obese subjects, but these differences were no longer significant after adjustment for body composition.

Energy expenditure during treadmill walking at identical speeds, measured using whole-body calorimeters, was 81% higher in obese adolescents relative to non-obese peers. After adjustment for body weight, EE remained 25% higher (P < 0.001), likely reflecting the increased difficulty of walking in severely obese subjects (19–21).

In free-living conditions, DEE was 2.26 MJ higher in obese adolescents compared to non-obese adolescents (P < 0.001) (Fig. 3). After adjustment for body composition, EE during sleep, sedentary activities, and total daily EE were not significantly different between groups; however, energy expenditure associated with physical activities was 61% lower in obese adolescents (P < 0.001), despite the higher energy cost of such activities. In fact, obese adolescents spent 47 min·d⁻¹ more in light physical activities (slow walking and housework) and 53 min·d⁻¹ less in moderate physical activities (normal-speed walking and recreational activities) than non-obese subjects (22).

Figure 3. Least-squares mean (± SE) energy expenditure (EE) of and time devoted to the main activities by non-obese (–; n = 50) and obese (–; n = 27) adolescents in free-living conditions. Significant effects of obesity: *P < 0.05, ***P < 0.001.

Significant effects of obesity: *P < 0.05, ***P < 0.001.

The inter-individual variability in EE was high and gender dependent in obese adolescents. After adjustment for differences in FFM, it averaged ± 10.1 % in boys and ± 12.4 % in girls for EE during sedentary activities in standardized conditions (whole-body calorimeter). Similarly, after adjustment for body weight, the inter- individual variability in EE during walking at 5 km ⋅h^-1 on a treadmill was ± 21.3 % in boys and ± 12.9 % in girls (22), which suggests differences in walking efficiency.

Effects of reduction of obesity on energy expenditure

The primary objectives of weight reduction programmes are: 1) to decrease FM to mitigate metabolic disorders that predispose obese adolescents to complications and severe morbidities, including hypertension, cardiovascular disease, and diabetes; 2) to enhance motor skills, physical capacities, enjoyment, and motivation to engage in physical activity; 3) to preserve or increase FFM to support TEE and facilitate long-term weight regulation; and 4) to modify dietary habits and behaviours to improve energy balance. All programmes should also aim to enhance overall well-being, promote social integration, and support psychological development, as these factors are essential for achieving sustainable long-term outcomes. Severe energy restrictions in adolescents resulted in significant decreases in FM and FFM (23), which may slow down growth and induce reductions in energy expenditure, favouring subsequent body weight regain. On the contrary, physical training, without energy restriction preserved FFM or allowed increases in FFM, physical capacities and energy expenditures, but with a lower reduction in FM (24, 25). Weight reduction programs offer the possibility to combine medical, psychological and physical therapy, nutritional education and dietetic follow- up, and adapted progressive physical training.

A study following this model was conducted with 26 obese adolescents (12 boys and 14 girls), aged 12 – 16 years, over a 9-months period. Body weight loss averaged 18.4 kg (- 20 %) in boys, including 18.0 kg FM (- 51 %) but only 0.4 kg FFM (- 0.7 %). Mean BMI decrease was 8.1 and 6.3 kg/m² (s.e.m.: 0.38 kg.m^-2) in boys and girls respectively. Body weight loss averaged 15.6 kg (- 17 %), including 12.5 kg FM (- 31 %) and 3.2 kg FFM (- 6%). EE was affected by weight loss. BMR, sleeping EE, and sedentary EE were significantly lower at the end of the 9-month weight reduction program, both in absolute values (- 8.3, -14.0, and -14.0%, respectively; p< 0.001) and after adjustment for FFM (-6.3, -12.6, and -11.7%, respectively; p<0.001). The energy cost of walking at the same speeds also decreased significantly (-24% and -22% in boys and girls, respectively), even after adjustment for BW (-17.6% in boys; p<0.004). As a consequence, with the same activity program, daily EE was significantly lower (11.67 vs. 13.96 MJ/d; p<0.001) after the weight reduction period, even after adjustment for FFM (11.84 vs. 13.76 MJ/d; p<0.001) (26).

The weight reduction program, also resulted in a continuous increase in walking speed during the 9 – month period: +2.9 km.h^-1 in boys and +1.8 km.h^-1 in girls. The working capacity of arms and legs was increased threefold. Cardiovascular capacities improved: heart rate decreased 11-18 beats per minute (bpm) during sleep and sedentary activities, and 20-25 bpm during walking at 4-5 and 6 km.h^-1 (Fig. 3, (26)).

Figure 4. Relationship between heart rate (HR, bpm) and energy expenditure (EE, kJ min^-1) as measured by whole-body calorimetry, before (- – -) and after (⎯⎯) the weight-reduction program (mean values of all subjects) (26).

During the 4-month period following the weight reduction program, 12 of the 26 adolescents maintained their body weight, while 10 others gained 6.6 kg body weight, including 5.8 kg FFM (27).

The results of this study confirm and demonstrate that a multidisciplinary weight reduction program in a specialized institution induces numerous beneficial effects in obese adolescents, but reductions in EE were observed, especially during sleep and sedentary activities (which account for about 80 % daily EE). These phenomena contribute to the frequent FM and body weight regains after a weight reduction program.

In addition, for adolescents who are obese and limited in their functional capacity by impaired exercise performance, it is optimal to devise a form of physical activity which promotes considerable EE. This should ideally promote substantial fat oxidation with the minimal subjective perception of effort and exercise intensity, which could ultimately allow a better tolerance and adherence to physical activity protocols. Previous studies, suggest that adolescents who are obese exhibited maximal fat oxidation rates at 41% V’O2max, which corresponded to 58% HRmax (28). Similarly, walking entails the advantages of enhancing fat utilization over cycling at an intensity requiring similar EE (29). It should be noted however, that in children who are obese, walking and jogging may be associated with joint pain and as such, non-weight bearing activity (e.g. cycling or walking in a swimming pool) may be initially preferable.

The study by D’Alleva et al. (2021) assessed the effects of a 9-month multidisciplinary weight reduction programme, followed by a 4-month follow-up, on 26 obese adolescents. The protocol, which included nutritional, behavioural, and physical activity interventions, led to an average reduction in body weight of 18% and fat mass of 40%, with a significant improvement in body composition. Simultaneously, the energy cost of walking (ml · kg⁻¹ · m⁻¹) decreased by approximately 20%, indicating greater locomotor efficiency and lower energy expenditure per metre travelled, particularly due to the reduction in trunk fat mass. During the 4 -month follow-up, a slight increase in weight and walking energy cost was observed, although both remained below baseline values. This suggests that, despite partial weight regain after the end of treatment, some metabolic and functional benefits are maintained over time, highlighting the importance of support and maintenance strategies after the intensive phase of the intervention (66).

Physical activity ratio for various sedentary and physical activities

Professionals caring for children and adolescents who are obese require information on the type, energy cost, and duration of their usual physical activities to prescribe appropriate individual dietary treatments and activity guidelines.

In clinical practice, the questionnaire is the most common method used to estimate the physical activity level of subjects (30). From this, sedentary and physical activity recalls can be converted to daily energy expenditure using the factorial method with previously determined metabolic equivalents (MET) (31). It should be noted that the Compendium values were obtained mainly from studies in normal-weight adults, and the authors defined the MET as the ratio of work metabolic rate to a standard resting metabolic rate of 1.0 kcal·kg⁻¹·h⁻¹ (4.184 kJ·kg⁻¹·h⁻¹).

On the basis of previous studies (2, 32, 33), the measured energy cost of walking at 3.5 km⋅h^-1was on average 16% higher than the predicted MET EE (31). In addition, for all physical activities, including walking or body movements, considered in this study, the EE were on average 15-35% higher than that predicted by MET (31).

These data suggest the use of the appropriate Physical Activity Ratios (PARs) values (PAR = EE of activity (kcal⋅min-1) / BMR (kcal⋅min-1)) to determine daily energy expenditure by the factorial method in adolescents who are obese. These PARs values (2, 32, 33) allow more precision in the estimation of daily energy expenditure of obese who are obese when using the factorial method (Fig. 5).

Figure 5. Physical activity ratios (PAR) corresponding to various sedentary and physical activities (modified from (2, 32, 33)

All values are mean ± SD; PAR: Physical activity ratio = PAR = EE of activity (kcal⋅min^-1) / BMR (kcal⋅min^-1).

Estimation of total daily energy expenditure

TEE of subjects is often evaluated from subjects’ diaries or recalls during the previous weeks (26). The activities reported are then evaluated for frequency, duration, and intensity to evaluate mean daily energy expenditure (kcal). The latter can be calculated by using the following equation:

TEE =

where N corresponds to the number of activities, BMR is expressed in kcal⋅min-1, PAR (Table 1) is a dimensionless measure, and duration of activity in min.

On this basis, a boy (14 y, body weight 93 kg, height 1.62 m) has a predicted basal metabolic rate of 1.46 (kcal⋅min^-1). If he sleeps for 540 min (PAR: 0.93), dresses for 60 min (PAR: 2.05), eats for 120 min (PAR: 1.75), stays at school for 420 min (PAR: 1.65), watches television for 180 min (PAR: 1.57), walks for 60 min (PAR: 5.46) and cycles for 60 min (PAR: 3.75), his daily energy expenditure can be estimated to 3441 kcal⋅day^-1.

MECHANICAL COST OF WALKING AND RUNNING

It has been suggested that children with obesity experience a higher mechanical cost during standing and walking. In particular, greater loading of the lower limb joints has been observed compared with normal- weight peers, and this persistent overload may predispose them to altered gait mechanics and pathological locomotor patterns (34).

Human locomotion can be described by two main gaits, walking and running, both characterized by alternating stance and swing phases but differing in timing and muscle activation patterns. During walking, one foot is always in contact with the ground, while in running both feet leave the ground during the flight phase. The stance phase is longer in walking, whereas swing duration increases in running.

The total mechanical work (W_TOT)required to maintain motion is given by:

𝑊𝑇𝑂𝑇 = 𝑊𝐼𝑁𝑇 + 𝑊𝐸𝑋𝑇

where:

𝑊_𝐸𝑋𝑇= work needed to move the center of mass,

𝑊_𝐼𝑁𝑇= work required to accelerate the body segments relative to the center of mass (34, 35).

𝑊_𝐼𝑁𝑇 increases with speed, stride frequency, and limb mass (36), typically accounting for 25–40% of 𝑊_𝑇𝑂𝑇.

Figure 6. Comparisons of walking and running mechanics (modified from Bramble and Lieberman (38)).

1. Kinematics of walking (left) and running (right). During walking, the centre of mass is lowest near toe-off (TO) and highest at mid-stance (MS) where the leg is relatively straight. During running, the head and centre of mass are highest during the aerial phase and lowest at MS, when the hip, knee and ankle are flexed; the trunk is also more inclined and the elbow more flexed.
2. Biomechanical contrasts between human gaits. During walking, an inverted pendulum mechanism exchanges forward kinetic energy (EK) for gravitational potential energy (EP) between heelstrike (HS) and MS; the exchange is reversed between MS and TO. During running, a mass-spring mechanism causes EP and EK to be in phase, with both energies declining rapidly to minima between footstrike (FS) and MS. Leg tendons and ligaments partially convert decreases in EP and EK to elastic energy (EEL) during the first half of the stance, which is subsequently released through recoil between MS and TO.

Walking mechanics are often modelled as an inverted pendulum, in which potential energy (𝐸_𝑃 = 𝑚 ⋅ 𝑔 ⋅ℎ) and kinetic energy (𝐸_𝐾 = 1/2⋅ 𝑚 ⋅ 𝑣²) oscillate in opposite phase, allowing partial energy exchange and minimizing the total mechanical work:

𝑊_𝐸𝑋𝑇 = Δ𝐸_𝑃 + Δ𝐸_𝐾

The efficiency of this energy recovery (𝜂) is defined as:

𝑊𝑇𝑂𝑇

𝜂 =  𝐸𝐸  × 100

and can reach up to 60% depending on stride length and walking speed (41, 42).

Conversely, in running, 𝐸_𝑃 and 𝐸_𝐾 vary in phase, and elastic energy (𝐸_𝐸𝐿) stored in tendons mainly the Achilles tendon plays a key role in energy return (43, 44). During the stance phase, part of the total energy is stored as 𝐸_𝐸𝐿 through tendon stretch and then released during recoil to power the next step.

Recent findings by Fernandez-Menendez et al. (2020) highlight how excess body mass alters these energy exchanges. Children with obesity show a reduced ability to recover energy during walking and impaired elastic recoil during running. Increased segmental inertia and altered tendon stiffness reduce the conversion of kinetic and potential energy into elastic energy, causing greater 𝑊_𝐸𝑋𝑇 and lower mechanical efficiency. These adaptations elevate the energy cost of locomotion (Cw) and may increase fatigue during prolonged activities. Such evidence underscores the need to consider mechanical inefficiency and excessive lower limb loading in paediatric obesity to prevent long-term musculoskeletal alterations.

Figure 7. Relative internal translational mechanical work of the lower limbs

(A), upper limbs (B), and head and trunk segment (C). Relative internal rotational mechanical work of the lower limbs (D), upper limbs (E), and head and trunk segment (F). The dashed lines with open symbols correspond to the obese group (O; n 11 except for 6 km h^-1 n 6 because 5 participants were not able to complete this walking condition) and the solid lines with solid symbols correspond to the lean group (L; n 13). The values are presented as means SD. †Significant difference (P 0.05) between groups (Fernandez-Menendez et al., 2020).

Effects of obesity on mechanical cost of walking and running

In individuals with obesity, body mass distribution differs from that of non-obese subjects, with thigh dimensions disproportionately increased relative to the rest of the body. Although external mechanical work (W_EXT) during walking was higher in obese adolescents, adjustment for body weight revealed no significant differences between obese and non-obese participants. Consequently, walking efficiency (η) was, on average, 23% lower in obese adolescents, with the difference decreasing from 30% to 20% as walking speed increased (21).

The mechanical pattern of walking also differs between obese and non-obese adolescents. Specifically, obese individuals exhibit greater mediolateral displacement of the centre of mass, associated with increased step width, particularly at lower walking speeds—likely reflecting reduced postural stability. This altered gait pattern did not result in higher external work (W_EXT) in the study. The elevated net energy cost of walking in obese adolescents may be partially attributable to increased step-to-step transition cost, i.e., the internal work occurring during the double-support phase, associated with a wider gait.

Gushue et al. (45) proposed that overweight children exhibit altered knee joint kinematics due to higher peak knee adduction moments (73–100% greater than those of normal-weight children). The authors suggested that gait adaptations may increase medial compartment loading of the lower limbs and contribute to the development of varus or valgus deformities and osteoarthritic degeneration. This hypothesis was supported by Davids et al. (46), who demonstrated that the dynamic gait deviations observed in obese children result in pathological compressive forces in the medial compartment of the knee. Excessive joint loading across the medial tibiofemoral compartment is believed to play a key role in the pathogenesis of articular injury and knee osteoarthritis (47, 48, 49, 50). Similarly, increased shearing forces at the hip and a reduced femoral neck anteversion angle may predispose to the development of slipped upper femoral epiphysis (51, 52).

It is therefore reasonable to assert that excess adiposity increases the energetic cost of movement and contributes to biomechanical inefficiency and postural instability. McGraw and colleagues (2000) and Colné et al. (20, 53) found that obese individuals spent significantly longer in the double-support phase of gait compared to their lean counterparts. Obesity was also associated with greater postural sway and a slower preferred gait cadence compared with normal-weight participants. Postural instability in the mediolateral plane is primarily corrected through stabilising responses occurring around the hip (20). These compensatory responses can contribute to a slower gait progression, as reported by Colné et al. (20, 53).

Additionally, the external work (W_EXT) and the net energy cost of running and efficiency (η) in obese and normal- weight adolescents and adults running at 8 km h^-1(Taboga et al.2012) were independent of body mass of the subjects. Elastic tissues of obese subjects seem to adapt (e.g. by thickening) to the increased mass of the body, thus maintaining their ability to store elastic energy, at least at 2.2 ms^-1 speed, at the same level as in the lean subjects.

The 2019 Molino-Garcia review analysed the walking patterns of overweight and obese children and adolescents, comparing them with those of individuals of normal weight to determine whether these alterations may contribute to the development of musculoskeletal disorders. Overweight and obese boys exhibit greater movement of the pelvis in the transverse plane, increased internal rotation of the hip, and higher moments at the hip due to flexion, extension, and abduction (with corresponding mechanical powers of generation and absorption). They also show greater movement and moments of adduction and abduction at the knee, with increased absorption and generation of power in that area. All these compensatory mechanisms increase the workload on the lower limb joints and may therefore lead to the early onset of musculoskeletal problems. (70)

Another study in 2000 analysed differences in gait and postural stability between obese and non-obese prepubescent boys. Ten obese boys and ten normal-weight boys were examined at three walking cadences. Full vision, darkness, and visual confusion conditions were used to accentuate differences in static postural stability. Dual position differences suggest reduced dynamic stability in obese boys. The greater areas of oscillation in the medial-lateral direction in obese boys, and the absence of significant frequency measures, suggest that the instability observed in obese boys is caused by overweight rather than underlying postural instability. (71)

Lerner et al. ( 2014) found that as BF% increases, there is a reduction in the knee bending angles in the initial position, an increase in the range of motion of pelvic obliquity, a decrease in the relative demand for VAS, but an increase in the relative demand for GMED and SOL. This suggests that changes in the relative strength requirements of lower extremity muscles during walking may alter walking mechanics in children as BF% increases. The authors recommend activities to strengthen the hip abductors and plantar flexors to normalise long-term gait, reduce fatigue of these essential muscles, and lower short-term risk (72).

Effects of reduction of obesity on mechanical cost of walking

After a 3-month multidisciplinary weight reduction program, adolescents who were obese lost on average 6 % of body mass, 15 % of FM without significant changes in lean body mass (54). After weight loss, the net metabolic cost of walking at 1.25 m⋅s^-1, decreased in association with the biomechanical parameters of walking: stride length increased by 3.5 %; lateral leg swing and the variation of the medio-lateral kinetic energy decreased by 18 % and variation in potential energy by 6 %. Consequently, the net energy cost of walking, adjusted for body mass, decreased by 9 %, whereas the external work (W_EXT) did not vary significantly.

The decrease in the net energy cost of walking were correlated with the decreases in body weight, FM and percent of gynoid mass, but not with the lateral leg swing after weight loss. The main determinant was the decrease in body weight, which in turn reduced the leg muscle work required to raise and accelerate the centre of mass as well as to support body weight and maintain body equilibrium (55) during walking.

Indeed, as vertical motions allow a pendulum-like exchange between potential and kinetic energy, weight- reduced individuals could reduce the potential energy available (hence vertical motions) because of the decrease in medio-lateral kinetic energy fluctuations. The reduction in FM in the gynoid region, independently of the decrease in total body FM, is related to the decrease in net cost of walking (55).

Reductions in hip and knee moments proportional to weight loss have also been observed following bariatric procedures (56).

Thivel’s 2025 study aims to evaluate the cost of walking (Cw) after weight gain at different speeds. The net cost of walking (subtracting basal metabolism) shows no significant differences with simulated weight gain. This leads to the conclusion that, contrary to expectations, an acute increase in weight does not result in an extra cost of walking in this population (73).

Practical Applications

High cardiorespiratory fitness during childhood and adolescence has been associated with a lower percentage of body fat and a healthier cardiovascular profile (57, 58), while childhood adiposity is associated with an unfavourable lipid profile (59). Studies of the available evidence (60) indicated that increased physical activity and decreased sedentary behaviour protect against weight gain in childhood and adolescence.

From a public health perspective, the focus should be on preventing of weight gain and regain after weight loss (61, 62). Physical activity is recognized as a major component of the management of overweight or obesity. The importance or magnitude of the beneficial effects of physical activity in this context differs according to the outcome examined. Physical activity appears essential for weight maintenance after diet-induced weight loss, rather than for weight loss per se. It is also important for the preservation of fat-free mass during weight loss. Physical activity has beneficial effects on fitness and reducing obesity-related complications, such as cardiovascular diseases and diabetes. Most data suggest that total volume of physical activity, rather than its intensity, is important for managing weight.

Amount of physical activity needed to prevent obesity

There is no definite consensus on the amount of physical activity required to prevent weight gain at the population level, and the shape of the dozen the amount is not clear. This is a complex issue, especially in view of the difficulty of matching energy intake with energy expenditure in times of readily available food and low levels of habitual physical activity (61, 62).

The U.S. Department of Health and Human Services 2008 Physical Activity Guidelines for Americans (63) recommend that children and teens be physically active for at least 60 minutes on most, if not all, days, including:

Aerobic: Most of the 60 or more minutes a day should be either moderate- or vigorous-intensity aerobic physical activity (running, hopping, skipping, jumping rope, swimming, dancing, and bicycling are all examples of aerobic activities), and should include vigorous-intensity physical activity at least 3 days a week. Aerobic activities increase cardiorespiratory fitness.

Muscle-strengthening: As part of their 60 or more minutes of daily physical activity, children and adolescents should include muscle-strengthening physical activity on at least 3 days of the week. Muscle- strengthening activities can be unstructured and part of play, such as playing on playground equipment, climbing trees, and playing tug-of-war. Or these activities can be structured, such as lifting weights or working with resistance bands.

Bone-strengthening: As part of their 60 or more minutes of daily physical activity, children and adolescents should include bone-strengthening physical activity on at least 3 days of the week. Produce a force on the bones that promotes bone growth and strength. This force is commonly produced by impact with the ground. Running, jumping rope, basketball, tennis, and hopscotch are all examples of bone strengthening activities.

It is important to encourage young people to participate in physical activities that are appropriate for their age, that are enjoyable, and that offer variety.

Amount of physical activity needed to weight loss

The amount of physical activity needed to weight loss is related to negative balance between daily energy intake and daily energy expenditure. EI can be calculated as 1.2 or 1.3 times basal metabolic rate (32). While, energy expenditure can be calculated as suggested previously. As well as physical activity must to consider the following suggestions:

Endurance Exercise

Frequency:

For moderate-intensity activities, it is recommended to accumulate up to 60 min·day⁻¹ in bouts of at least 15 min each, or at least 20–30 min·day⁻¹ of vigorous-intensity activity, or an equivalent combination of both. Within this framework, the Combined training (COMB) offers an effective alternative by medium duration of exercise (~36 min per session) with higher volume of low intensity training and lower volume at high intensity. This structure allows for a higher training frequency while maintaining overall manageable workloads, promoting consistency and adherence, key factors in long-term weight management and aerobic adaptations (74).

Intensity:

On a 0–10 scale for perceived exertion, 5–6 represents moderate intensity and 7–8 vigorous intensity. In adolescents, maximal fat oxidation (Fatmax) occurs at around 50% V̇O₂peak (~65% HRmax, ~130 bpm), typically corresponding to brisk walking at 5 km·h⁻¹ (29). Conversely, short high-intensity bouts (30–60 s) at 100% V̇O₂peak are effective in enhancing aerobic power and metabolic efficiency (64). The COMB integrates both intensities within the same session, combining a high intensity component (~17% of total time), consisting of three 2-minute repetitions at 95% V̇O₂peak, with a moderate intensity component (~83% of total time, ~30 minutes at 60% V̇O₂peak). This polarized intensity distribution maximizes cardiovascular and metabolic adaptations by targeting multiple energy systems while minimizing perceived exertion and fatigue accumulation (74).

Duration:

For moderate-intensity exercise, at least 45 min·day⁻¹ of continuous activity is recommended, while vigorous- intensity work can be performed in shorter sessions, provided weekly energy expenditure remains sufficient. The COMB protocol optimizes training duration by alternating intensity domains within ~36 minutes per session, providing similar or superior physiological benefits to longer continuous protocols. This time-efficient structure improves adherence and reduces psychological fatigue, while still eliciting substantial improvements in V̇O₂peak, fat oxidation, and body composition (74).

Type:

Any activity that minimizes orthopaedic stress and allows for sustained engagement can be utilized. Walking and running are the most common, while stationary cycling is advantageous for individuals with limited tolerance for weight-bearing and activities. In the context of COMB training, modality selection should ensure a smooth transition between the HIIT and MICT components, facilitating both neuromuscular efficiency and metabolic flexibility. For instance, cycling or treadmill running can easily accommodate rapid shifts in intensity, ensuring consistent workload control and minimizing injury risk (74).

Means of promoting physical activity

A 2025 review analyses a large sample of studies to investigate the effect of wearable devices on daily physical activity, including comparisons with a control group that does not wear them. The review shows that children and adolescents who use a sports tracker take a significantly higher number of steps per day than those who do not. However, there is no evidence of an increase in moderate or vigorous physical activity. Wearing these devices could therefore promote more walking among children and adolescents (76).

Amount of physical activity needed to preventing weight regain

While consensus is lacking on the amount of physical activity needed to prevent weight regain, there is an indication that children and adolescents would need 60 or more minutes of daily of physical activity needed to prevent weight regain, there intense activity, to avoid regaining weight (65, 66). This physical activity also can be done in smaller chunks of time over the day. Engage in more than 1 h of daily physical activity promoting walking or cycling to school, suggesting activities that involve parents or friends and promote even small amounts of moderate to vigorous activities. Particularly promote enjoyable and fun activities. As well, discourage sedentary behaviour remain a simple way to increase physical activity.

Conclusion

TEE, BMR, and EE associated with various physical and sedentary activities are significantly higher in obese adolescents than in their normal-weight peers. However, after adjustment for FFM) o BW, only walking shows significant differences between the groups.

The mechanical pattern of walking differs between obese and normal-weight adolescents. In particular, obese subjects exhibit a greater mediolateral shift of the centre of mass, associated with an increase in stride length, especially at lower speeds, probably due to reduced postural stability.

The higher net energy cost of walking in obese subjects can be partly explained by the increased cost of step-to- step transition, that is, the internal work that occurs during the double support phase, related to a wider gait.

Increased energy costs and greater joint load may predispose the developing musculoskeletal system of obese children and adolescents to injury and growth alterations. In addition, these factors may negatively affect interest in, or predisposition towards, physical activity.

Children with obesity spend more time in light physical activities but much less time in moderate-intensity or sporting activities than normal-weight subjects. Energy expenditure related to sports activities did not differ significantly, suggesting that obese adolescents participate in less intense activities. Consequently, energy expenditure from moderate and sporting activities in obese subjects represented only 20% and 25%, respectively, of that observed in their normal-weight peers.

A multidisciplinary weight reduction programme produces numerous benefits but also leads to a decrease in energy expenditure during sleep and sedentary activities. These reductions are attributable not only to the loss of FM and FFM, but probably also to a decrease in the size and metabolism of metabolically active organs resulting from the energy deficit. These phenomena may explain the frequent reacquisition of fat mass and body weight after the end of the programme.

It is therefore essential that adolescents scrupulously follow dietary recommendations and engage in moderate daily physical activity to maintain the benefits obtained from weight reduction. In addition, the prescription of age-appropriate physical activities that are enjoyable and capable of promoting high lipid oxidation is recommended, as they are more tolerable and may improve adherence to exercise programmes. Wearing a step- tracking device could encourage young people and teenagers to be more active.

Previous studies have shown that obese adolescents reach maximum fat oxidation at approximately 41% of VO₂max, corresponding to 58% of maximum heart rate (HRmax). It has also been observed that walking promotes greater lipid utilisation than cycling for the same energy expenditure, although weight-bearing activities may initially be uncomfortable for individuals with severe obesity.

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