Pulmonary V̇O₂ on-kinetics and walking net V̇O₂ associate with fatigue and mood disturbance in postmenopausal women

Postmenopausal women often experience fatigue and mood disturbance both of which interfere with quality-of-life. Since greater physical function aids psychosocial well-being, we hypothesized the acute cardiopulmonary responses during walking may reveal important factors linked to fatigue and mood disturbance. In this cross-sectional study, women of similar body mass index (BMI) aged 55-75 y were dichotomized to mid-life (55-65 y; 83.4 ± 8.4 kg/m²; n = 14) or older (≥65 y; 81.8 ± 10.4 kg/m²; n = 11) groups. A 6-minute walk test was used to estimate peak aerobic capacity (V̇O_2peak). A treadmill task coupled with indirect calorimetry measured mean response time (MRT) - representing the duration to reach 63 % of steady-state net oxygen uptake (V̇O₂). Average daily fatigue and fatigue interference were measured with the Fatigue Symptom Inventory. General mood disturbance was measured with the Profile of Mood States (POMS) questionnaire. Age-group differences were not detected in fatigue ratings, MRT, or walking net V̇O₂. However, older women had lower aerobic capacity (p = 0.002, ES = 1.39) and greater disturbance in the POMS Depression-Dejection subscale (p = 0.042, ES = 0.41). Among all participants, and independent of V̇O_2peak, MRT correlated with average daily fatigue (r = 0.500, p = 0.015), fatigue interference (r = 0.421, p = 0.046), and POMS total mood disturbance (r_s = 0.437, p = 0.037). Regression modeling revealed MRT and walking net V̇O₂ jointly explained 55 % (R = 0.744, p < 0.001) of the variance in average daily fatigue. In conclusion, MRT and walking net V̇O₂ may serve as important points of intervention to alleviate fatigue and mood disturbance in postmenopausal women.