Postexercise muscle oxygen uptake kinetics in older breast cancer survivors and healthy individuals: Association with myosteatosis.

Reduced cardiorespiratory fitness is common among breast cancer survivors and, although traditionally attributed to cardiac dysfunction, might also be related to peripheral skeletal muscle abnormalities. We examined peak and submaximal plantar-flexion exercise and recovery kinetics for lower-leg oxygen uptake ( V ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ ), blood flow and arteriovenous O2 difference in 35 older, female long-term breast cancer survivors (age, 70 ± 5 years; 14 ± 6 years post-treatment) and 19 age- and sex-matched healthy control subjects using MRI. The calf intermuscular fat to skeletal muscle ratio was evaluated using fat- and water-separated MRI to quantify myosteatosis. No significant differences were found between groups for lower-leg V ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ , blood flow or arteriovenous O2 difference at peak or during submaximal plantar-flexion exercise. Recovery kinetics for these measures were similar between groups (all P > 0.05). No differences were found in calf muscle mass between breast cancer survivors and control subjects. A higher intermuscular fat to skeletal muscle ratio was significantly associated with reduced peak (cycle exercise) pulmonary V ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ (r = -0.37, P = 0.01), lower plantar-flexion power output (r = -0.325, P = 0.012) and delayed muscle V ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ recovery kinetics in both groups (r = -0.325, P = 0.015). Older, female long-term breast cancer survivors have comparable lower-limb skeletal muscle oxidative capacity to control subjects. However, myosteatosis represents a key determinant of exercise performance and recovery kinetics regardless of breast cancer history. Interventions targeting skeletal muscle quality might be effective in improving both submaximal and maximal exercise tolerance and recovery kinetics in older women with or without a breast cancer diagnosis.