In the present study, obese individuals did not present a statistically significant difference in the gluteus medius strength, compared to non-obese individuals (p > 0.05). However, when these values were normalized in relation to body weight, there was a significant difference (p < 0.05) between groups, which indicates that obese individuals have a relative gluteus medius weakness, when compared to normal weight individuals.
The absolute strength values were 292.0 N for RGM, and 290.7 N for LGM in the control group. In the obese group, the values were 256.2 N and 261.1 N, respectively. In a literature review, Benfica et al. [42] describes hip abductor muscle strength values, in individuals between 50 and 59 years old, as being 208.12 N for dominant limb and 203.27 N for non-dominant limb in women, and 305.97 N for dominant limb and 298.49 N for non-dominant limb in men. In the present study, this variation in the measurements can be explained by the age differences between the analyzed samples, gender variations, and differences related to the measurement technique. The age range of the participants (from 20 to 60 years old) was chosen since it constitutes an economically active group, in which any movement disorder can cause great functional and work impact. Also, people over 60 may have reduced muscle mass and function [43]. It is worth noting that the sample used in the present study consisted predominantly of women (92%) for reasons of convenience, and that the abductor muscle strength varies between genders. Women have lower abductor muscle strength, which corresponds to a greater risk of developing musculoskeletal pathologies [44].
Some authors suggest that the antigravity muscles of obese individuals have greater absolute force [45-48]. Increased muscle strength is a beneficial adaptation to obesity, with excess body weight acting as a chronic training stimulus for daily activities [48]. Several studies report increased knee extension strength in obese individuals, with values varying from 10 to 30% higher when compared to normal weight individuals [49]. Due to gait changes, obesity can cause mechanical adaptations that favor the use of the strongest muscles and minimize the use of the weakest muscles. Gait analysis in obese individuals shows a shorter stride length with a strategy of higher quadriceps overload and decreased hamstring activation [10,50].
Regarding the gluteus medius, Lerner et al. [13] reported that obese individuals have greater absolute strength during gait and correlated this with increased BMI. This data was not confirmed by the gluteus medius strength analysis performed in the present study, since there was no difference in the isometric strength values between groups tested (p > 0.05). Apparently, obesity results in larger and lower quality muscles, which have the same absolute strength and power as smaller muscles in thin individuals [51]. Analysis using nuclear magnetic resonance suggests that the gluteal musculature presents an increase in fat infiltrate with an increase in BMI [52]. Although obesity increases muscle mass in a short term in young individuals, lipid infiltration in skeletal muscle can reduce the incorporation of amino acids into muscle proteins in the course of time, with a decrease in total muscle mass [20]. Possibly, the long-term effect of obesity on muscle tissue overlaps this weight stimulus on antigravity muscles and culminates in muscle loss over the years [18].
Even though they seem to have greater absolute strength, obese individuals have less relative strength in some muscles, such as the quadriceps [53,54]. Lafortuna et al. [55] also corroborate these data when they evaluated the lower limb muscle strength through leg press exercise. Compared with normal weight individuals, obese individuals were stronger, but when the values were related to their muscle mass, this difference disappeared. When Lerner et al. [13] normalized the strength of gluteal musculature by weight, there was no relevant difference between obese and normal weight groups. Regarding muscle mass, they also reported that obese individuals required greater strength of gluteal musculature for a normal gait. This fact is relevant, since it suggests that obese individuals need greater strength in this muscle group, becoming more susceptible to fatigue. Thus, it is expected that overweight individuals have greater muscle strength to maintain proper body balance while standing or walking. This fact was not proven in the present study. When normalized in relation to body weight, obese individuals had relative weakness of gluteus medius musculatures (p < 0.05). It can be concluded that using the strength variable alone does not seem to be an adequate option to assess the abductor musculature, since more than half of the world’s population is overweight and these strength values can be overestimated [56,57].
The determination of the force required by abductor muscles to body balance in a standing position depends on two variables: pelvic anatomy and body weight [59]. In the present study, since there was a pairing in relation to gender, age, and height, it is considered that there was a similarity in the pelvic anatomy between the pairs. Since the examination was performed by a single examiner, weight was the only relevant variable that could interfere with the sample strength.
When the statistical analysis of the factor loads was performed, it was possible to differentiate two distinct groups for all gluteus medius force variables, regardless of normalization with weight. This indicates that both the absolute strength values and those related to weight were different, constituting two distinct groups: the obese group and the normal weight group or control.
Obese individuals generally struggle to move their body mass. A lack of strength, observed specifically in sarcopenic obesity, culminates in functional adaptations and imbalance, predisposing to injuries [12,60]. The gluteal strength of obese individuals is a relevant factor since these two variables are independently associated with musculoskeletal system alterations [23-30,61]. According to new scientific evidence, muscle strength is inversely and independently associated with all-cause mortality [62].
The present study has some limitations. First, the sample size was small. Therefore, further studies are needed to generalize the results found. Second, the sample was predominantly composed of women (92%). Although it does not interfere in the conclusions, since they were paired samples, it can represent a bias because men have greater strength than women and may not present similar results. Further studies are needed to prove if there are morphological and functional changes in obese gluteal muscles that may justify gait imbalances and associations with musculoskeletal disorders.