Background: The harmonious development of gross motor skills (GMSs) is vital for children, fostering their physical, cognitive, and socio-emotional growth. This study aimed to achieve three primary objectives: (1) to establish standardized reference values for all GMS tests conducted; (2) to examine the impact of overweight and obesity on factors influencing the development of GMSs and cardiorespiratory fitness (CRF); and (3) to investigate the relationship between GMSs and CRF levels and body image dissatisfaction among Canadian children from the province of Québec. Methods: The study encompassed 3144 children aged 6 to 12 years (1535 boys and 1609 girls) recruited from 24 elementary schools situated in five urban areas. Anthropometric measurements included body mass, body height, and body mass index (BMI). Physical performance was assessed using a maximal aerobic power test and 12 GMS tests, which comprised two segmental speed tests, four agility tests, two static balance tests, one simple reaction time test, and three coordination tests. Body perception and body image dissatisfaction were evaluated using a silhouette scale featuring two sets of nine drawings depicting a spectrum of body shapes ranging from very thin to obese. Results: Standardized normative values were established for each GMS test. GMSs demonstrated continuous improvement throughout childhood, albeit with a deceleration in progress during later developmental stages. At comparable age, boys generally outperformed girls on tests demanding greater strength, speed, or endurance, whereas girls exhibited superior performance in balance and hand–foot coordination tasks (p ≤ 0.05). However, segmental speed remained equivalent between sexes (p > 0.05). GMS and CRF were significantly influenced by obesity status. Children with a normal BMI demonstrated superior performance compared to their overweight or obese counterparts, particularly in tests requiring body mass displacement (p ≤ 0.05). Conversely, socioeconomic status exhibited no significant impact on body perception in boys (p = 0.106), but it was a notable factor among 6–8-year-old girls from lower socioeconomic backgrounds (p = 0.045). Conclusions: Obesity status is linked to diminished GMS performance, especially in tasks involving body mass movement. These findings underscore the importance of early intervention strategies to encourage an active lifestyle and promote a healthy body composition in children.

Background: The obesity epidemic among adolescents significantly impacts not only their physical health but also various psychological factors, including their perception of body image. Thus, this study pursued three main objectives: (1) to update the reference standard values for all the physical fitness tests performed; (2) to examine the impact of overweight and obesity on factors influencing physical fitness in adolescents; and (3) to determine the relationship between the physical fitness level and the body image dissatisfaction among a population of French-Canadian adolescents. Methods: A total of 1862 adolescents aged 12 to 17 (1008 boys and 854 girls) participated in this study. Data were collected from 12 French-language high-schools from different socioeconomic backgrounds and spread across four regions of the province of Québec, Canada. Anthropometric measures (body mass, body height, body mass index (BMI), waist circumference, waist-to-height ratio) and fitness tests (aerobic power, anaerobic power, muscle endurance, muscular power, flexibility) were conducted. To assess adolescents’ body perception, a silhouette scale was used. Results: Standardized normative values were established for each fitness test (Lambda Mu Sigma; LMS method). In boys, performance generally improved with age, except for the V-test and sit-ups, which remained stable, and VO₂peak, which declined during adolescence in both genders (unpaired t-test and Cohen’s d effect size). In girls, only the vertical jump and 30 m sprint improved with age, while the other tests stabilized by age 13. Fitness level was significantly influenced by obesity status. Boys and girls with a normal BMI performed better than those who were overweight or obese (ANOVA = p < 0.001 and effect size F). Girls appeared to be less affected by obesity status, with differences between overweight and obese groups rarely being significant (p > 0.05). Fitness level was also linked to body satisfaction, with satisfied adolescents generally achieving better scores than dissatisfied ones, even among those with a typical BMI. Socioeconomic status did not impact body image perception in boys (p = 0.351). In contrast, girls from lower socioeconomic backgrounds exhibited significantly more negative perceptions (p = 0.002) than their peers from more affluent families. Conclusions: Obesity status is strongly associated with poorer performance on fitness tests. Conversely, higher levels of physical fitness are linked to improved body image satisfaction. This positive relationship between fitness and body image holds true even for individuals with a healthy body weight (typical BMI).