Obesity condition is strongly correlated with joint and muscle problems favoring an increased risk of physical disability [13]. Jensen et al. [13] observed that the relationship between obesity and functional impairment extended in longitudinal follow-up to men and women at a BMI of 35 or greater. It is also important to notice that total fat mass is the body component more strongly associated with increased risk of disability than body fat distribution [14]. Studies have pointed out the relationship between pain and body weight showing that body weight is significantly related with knee, hip, and back pain in older population [15] and with neck and back pain in general population [16]. The prevalence of significant musculoskeletal pain in obese subjects results in a significant negative relationship between obesity and health-related quality of life [17]. These data demonstrate that pain is a strong covariate of obesity, and, therefore, this should be considered in the design and development of obesity treatments. Excess of body fat could cause abnormal posture, both in dynamic [18] and static conditions [19]. This abnormal posture limits the normal joints’ physiological range of motion and consequently enhances the risk of musculoskeletal overload [20]. Moreover, increased forces across the joints play a fundamental role in the negative relationship between obesity and weight-bearing joints (back, knees, ankle, and hip), compared to non-weight-bearing joints (shoulder/neck and upper extremities). Therefore, the effects of weight on joints depend on the body regions that are involved. In support of this relation, Shiri et al. [21] analyzed the effects of overweight and obesity on sciatica. The author affirmed that both overweight and obesity conditions are associated with an increasing risk in hospitalization for sciatica and with an increasing risk of surgery for lumbar disk herniation. The increased mechanical loads on knees and the decrease in lower limb flexibility could justify the high incidence of knee osteoarthritis [22] and skeletal alteration in obese subjects [23]. Obesity is also strongly correlated with muscle problems. In fact, a specific feature of obesity called “sarcopenic obesity” has recently become of interest for researchers [24, 25]. This condition emerges when obese subjects have inadequate muscle mass compared to their body size. The imbalance between obesity and muscle function, either defined by small muscle mass or poor muscle strength, is associated with risk of disability. The sarcopenic obesity condition could depend on different factors. First, fat mass increases with the age, whereas muscle mass and strength tend to decline progressively after the age of 40 years. In support of these trends, Droyvold et al. [26] showed that during approximately 10 years, body weight increased in all age groups below 70 years, while Evans et al. [27] analyzed the causes that lead to a loss of skeletal muscle mass during aging. Second, a sedentary lifestyle, typical of obese subjects, speeds on the decrease of skeletal muscle mass and the gain of fat mass. Moreover, more causes of sarcopenic obesity were evaluated such as inflammation, insulin resistance, malnutrition, etc. [24].

Cardiorespiratory fitness, defined as the ability of the body to transport and use oxygen, depends on the integration of cardiac, pulmonary, and musculoskeletal systems. Fitness professionals should be aware that overweight and obese subjects could be poorly conditioned since the aerobic capacity of these subjects has been shown to be low, and in some instances, critically low [28]. De Souza et al. [29] reported that aerobic capacity of severe obese subjects (44 ≤ BMI ≤ 54.8 kg/m²) ranged from 16.1 to 34.7 ml·min⁻¹kg⁻¹. The poor aerobic capacity must be taken into consideration when determining exercise intensity in deconditioned subjects. Among the parameters to be considered in the exercise program for obese population, intensity has received special attention [10]. Cardiopulmonary exercise test allows the fitness professionals to assess the right intensity of training program. Intensity rate could be described in both absolute and relative terms. Relative terms take into account the exercise capacity of the subjects to perform the activity, while absolute terms only consider the demands of the activity. Cardiopulmonary exercise test provides important data to prescribe the appropriate exercise intensity for overweight and obese subjects in both relative and absolute terms. Commonly, exercise intensity is based on measured, or estimated, peak oxygen uptake (V˙O_2peak) or maximum heart rate (HR_max) [30]. However, when a workload is quantified only in relation to V˙O_2peak or HR_max, it can result in different metabolic requirements between subjects. Therefore these variables should be used with caution when prescribing exercise, due to the lower cardiorespiratory fitness of overweight and obese subjects [10].

An alternative approach is to define the exercise intensity in relation to validated physiological break point such as the aerobic/anaerobic threshold. The aerobic threshold marks the upper limit of an almost exclusively aerobic metabolism that permits exercise lasting for ten of minutes at a lactate level of approximately 2 mmol·l⁻¹. The individual aerobic threshold (AerT) represents in general a mild to moderate exercise intensity (31). For these reasons, during the last years, AerT has been used more frequently [31] to prescribe exercise intensity, and it has also been applied in obese population with comorbidity [32]. Considering that the obese population is characterized by a low cardiorespiratory fitness, it can be very important to use threshold concept when exercise intensity has to be chosen. The procedures to determine the AerT [10] during an incremental exercise testing may include protocols based on of blood lactate measurements or on gas exchange analysis. The determination of AerT through gas exchange analysis is a noninvasive practice, and this deserves a special consideration for a simple intensity exercise prescription in overweight and obese subjects. There are different protocols to assess this parameter as described by Emerenziani et al. [10]. One of the suitable methods is the determination of the optimal respiratory efficiency by plotting the ventilatory equivalent (V˙E/V˙O₂) as a function of V˙O₂ in order to identify the point during exercise where this curve has its minimum value.