Yoshikazu Yamaji

(1) Background: Reduced lung function in early adulthood is associated with future risks to health outcomes that have not been fully explored by gender. We investigated gender-specific relationships between lung function and extrapulmonary variables, assessing their potential as screening markers for respiratory dysfunction in young adults. (2) Methods: The participants were 151 medical students. Clinical data, handgrip strength (HS); body composition parameters such as skeletal muscle mass index (SMI), whole-body phase angle (WBPhA), and bone mineral content (BMC); and pulmonary function variables, vital capacity (VC), forced VC (FVC), and forced expiratory volume in one second (FEV1), were measured. (3) Results: FEV1 was significantly correlated with BMI, SMI, WBPhA, BMC, and both left and right HS (p < 0.0001, respectively) across all participants. According to gender, FEV1 had the strongest positive association with left HS in males (p < 0.0001) and BMC in females (p < 0.0001). The area under the curve for detecting the bottom quartile of FEV1 was 0.705 (cut-off 41.0 kg, sensitivity 91%) for left HS in males and 0.742 (cut-off 2.11 kg, sensitivity 81%) for BMC in females. (4) Conclusions: Gender-specific relationships between intrapulmonary and extrapulmonary factors such as left HS and BMC could be useful for screening suspected respiratory dysfunction in early adulthood.