Walking net O2 rises with advancing age in older women: where to go from here?

Abstract

Walking net O2 tends to increase with advancing age; however, factors contributing to this relationship have not been widely described. The implications of such findings could inform targeted strategies to promote independent mobility in older adults. Herein, we evaluated the relationship between net O2 and age at two submaximal workloads while exploring potential moderators of this relationship. Secondary analyses were performed on 35 older (65 ± 3years) women who completed a battery of physical assessments including fixed-speed, non-graded and graded (+ 2.5%) treadmill walking with indirect calorimetry to determine net O2. Maximal oxygen uptake ( O2max), knee extensor maximal isometric voluntary contraction (MVC), peak rate of torque development (RTD), and plantar flexor range-of-motion (PFROM) were also measured. Bivariate correlations showed non-graded (r = 0.403, p = 0.017) and graded (r = 0.413, p = 0.014) net O2 were positively related to age. Notably, these relationships strengthened after adjusting for O2max. Regression modeling showed age, RTD:MVC ratio (composite of muscle performance), and PFROM together explained 49% and 34% of the variance in non-graded and graded net O2, respectively. Further analyses suggested knee extensor MVC moderates the relationship between non-graded net O2 and age, accounting for 9% of the variance [ΔR2 = 0.090, F (1,31) = 4.13, p = 0.05]. These data support the premise that, in older women, walking net O2 rises with advancing age, and additionally, the RTD:MVC ratio and PFROM are independent correlates of non-graded net O2. Exercise interventions with a high degree of training specificity including explosive, velocity-based elements may promote independent mobility in older women.