Introduction
There is renewed interest in understanding sex differences and similarities in skeletal muscle (SM) and body composition.1–5 On the one hand, SM is now known to be important in many physiological and disease processes.6–12 On the other hand, sports performance differences between male and female athletes have attracted new attention in recent years because of the inclusion of transgender athletes in female competitions.13
There are known sex differences in SM and body composition.2 Males have higher muscle mass than females in absolute terms and relative to body mass, and this difference is greater in the upper body.14 15 Females have a higher percentage of body fat than males of the same body mass index (BMI) and tend to accumulate more subcutaneous adipose tissue (SAT) around the hip, while males around the trunk and abdomen.16 Less is known regarding sex differences in intramuscular fat (IMF). Using Dixon MRI and computational tools, we have previously shown that the IMF of gluteus maximus (GMAX) is associated with different levels of physical activity and that females had higher levels of IMF in the gluteal muscles.17 18
In this work, we focus on sex differences in recreational cyclists, as cycling is one of the sports that has gained more popularity as a means to stay fit and active among middle-aged adults.19–21 Although traditionally dominated by males, nowadays, this trend has changed, and females have closed the gap in participation and performance.22–25 The performance gap seems to have reached a plateau, and the sex differences are now probably due to biological reasons,26 in particular VO2max27 28 and musculoskeletal factors. Consequently, it is important to understand if there are sex differences in muscle mass and composition between equally trained cyclists.
The aim of this study is twofold: to quantitatively evaluate if there are muscle mass differences between male and female recreational cyclists; and to compare muscle quality and body composition in the pelvis region between two well-matched groups of fit and healthy male and female adults, which is relevant to study public health and SM related diseases. To achieve this, we recruited well-trained recreational cyclists who underwent Dixon MRI and computed the IMF content, muscle mass, lean muscle mass of the gluteal muscles and the SAT volume of the pelvis.