Background: In order to counteract fatigue, physical activity (PA) is recommended for all stages of cancer. However, only few advanced cancer patients (ACP) are physically active. Quantitative data with high numbers of ACP reporting barriers to PA are missing. This study aimed to identify barriers to PA in ACP with tiredness/weakness and investigate their motivation towards it.

Methods: Outpatients with metastatic cancer receiving cancer care at a German Cancer Center reporting moderate/severe tiredness/weakness during self-assessment (MIDOS II) were enrolled. We assessed Fatigue-(FACF-F) and Depression (PHQ8) Scores, demographics, cancer-specific parameters, motivation for PA, physical, psychological and social barriers.

Results: 141 of 440 eligible patients (32.0%) with different diagnoses agreed to participate. Patients frequently reported "I feel weakened due to my tumor therapy" (n = 108; 76.6%), physical symptoms (tiredness, weakness, dyspnea, joint-problems, pain, nausea [n = 107; 75.9%]) and fatigue (n = 99; 70.2%) as barriers to PA. However, no significant group differences regarding these barriers were found between physically active and inactive patients. Social barriers were rarely chosen. Motivated patients were 5.6 times more likely to be physically active (p < 0.001), also motivation turned out to be the strongest predictor for a physically active behavior (β = 1.044; p = 0.005). Motivated attitude towards PA was predicted by fatigue (β = - 2.301; p = 0.008), clinically relevant depression (β = - 1.390, p = 0.039), knowledge about PA and quality of life (QoL) (β = 0.929; p = 0.002), PA before diagnosis (β = 0.688; p = 0.005 and Interest in exercise program (β = 0.635; p = 0.008).

Conclusion: "I feel weakened due to my tumor therapy" is the most reported barrier to PA among both, physically and inactive patients. Motivation for PA is the strongest predictor of performing PA. Interest in PA, knowledge about PA/QoL and PA before diagnosis are main predictors of a motivated attitude. Absence/presence of social barriers did not associate with motivation, fatigue and depression proved to be a negative predictor. Programs including information, motivational counseling and individualized training should be offered for ACP to overcome barriers and reduce fatigue.