The purpose of this study was to conduct an exploratory analysis of the START examining the effects of resistance exercise training (RET) and aerobic exercise training (AET) on sarcopenia, dynapenia, and associated quality of life (QoL) changes in breast cancer (BC) patients receiving adjuvant chemotherapy. Participants were randomized to usual care (UC) (n = 70), AET (n = 64), or RET (n = 66) for the duration of chemotherapy. Measures of sarcopenia [skeletal muscle index (SMI)] and dynapenia [upper extremity (UE) and lower extremity (LE) muscle dysfunction (MD)] were normalized relative to age-/sex-based clinical cut-points. QoL was assessed by the Functional Assessment of Cancer Therapy-Anemia (FACT-An) scales. At baseline, 25.5 % of BC patients were sarcopenic and 54.5 % were dynapenic with both conditions associated with poorer QoL. ANCOVAs showed significant differences favoring RET over UC for SMI (0.32 kg/m(2); p = 0.017), UE-MD (0.12 kg/kg; p < 0.001), and LE-MD (0.27 kg/kg; p < 0.001). Chi-square analyses revealed significant effects of RET, compared to UC/AET combined, on reversing sarcopenia (p = 0.039) and dynapenia (p = 0.019). The reversal of sarcopenia was associated with clinically relevant improvements in the FACT-An (11.7 points [95 % confidence interval (CI) -4.2 to 27.6]), the Trial Outcome Index-Anemia (10.0 points [95 % CI -4.0 to 24.1]), and fatigue (5.3 points [95 % CI -1.5 to 12.1]).
Early-stage BC patients initiating adjuvant chemotherapy have higher than expected rates of sarcopenia and dynapenia which are associated with poorer QoL. RET during adjuvant chemotherapy resulted in the reversal of both sarcopenia and dynapenia; however, only the reversal of sarcopenia was associated with clinically meaningful improvements in QoL.