This study investigates the association between the triglyceride-glucose (TyG) index and impaired cardiovascular fitness (CVF) in a non-diabetic young population. Using data from the National Health and Nutrition Examination Survey (NHANES) (1999–2004), the researchers analyzed 3364 participants who completed CVF examinations. Impaired CVF was defined as low and moderate CVF levels based on estimated maximal oxygen consumption (Vo2max). The TyG index was calculated using the formula Ln[TG(mg/dL) × FPG(mg/dL)/2]. The results showed a significant association between the TyG index and impaired CVF, with a dose-response relationship observed. Multivariable logistical regression analysis revealed that a 1-unit increase in the TyG index was associated with an increased odds ratio (OR) for impaired CVF (OR, 1.46; 95% CI 1.13–1.90). Additionally, a significant interaction between sex and the TyG index for impaired CVF was found in individuals under 20 years old (p = 0.027). The study concluded that higher TyG index values are associated with an increased likelihood of impaired CVF in non-diabetic young individuals, and sex may play a role in this relationship, with males being more susceptible to impaired CVF under similar TyG index conditions.This study investigates the association between the triglyceride-glucose (TyG) index and impaired cardiovascular fitness (CVF) in a non-diabetic young population. Using data from the National Health and Nutrition Examination Survey (NHANES) (1999–2004), the researchers analyzed 3364 participants who completed CVF examinations. Impaired CVF was defined as low and moderate CVF levels based on estimated maximal oxygen consumption (Vo2max). The TyG index was calculated using the formula Ln[TG(mg/dL) × FPG(mg/dL)/2]. The results showed a significant association between the TyG index and impaired CVF, with a dose-response relationship observed. Multivariable logistical regression analysis revealed that a 1-unit increase in the TyG index was associated with an increased odds ratio (OR) for impaired CVF (OR, 1.46; 95% CI 1.13–1.90). Additionally, a significant interaction between sex and the TyG index for impaired CVF was found in individuals under 20 years old (p = 0.027). The study concluded that higher TyG index values are associated with an increased likelihood of impaired CVF in non-diabetic young individuals, and sex may play a role in this relationship, with males being more susceptible to impaired CVF under similar TyG index conditions.