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Objectives To determine whether objectively measured intermittent moderate-intensity physical activity (IMPA) and light-intensity physical activity (LIPA) are associated with cardiorespiratory fitness (CRF) in adults.Design Cross-sectional.Setting Community-based setting.Participants Participants included 289 (75% female) adults with overweight or obesity (body mass index 32.7±5.0 kg/m 2 (mean±SD)).Main outcome measures Objective measures of all physical activity variables were obtained using a hip-worn accelerometer. CRF was assessed directly during a maximal graded treadmill test using indirect calorimetry.Results Participants accumulated 14±9 min/day of IMPA and 278±71 min/day of LIPA. The average intensity of IMPA and LIPA minutes was 3.5±0.2 and 1.9±0.1 METs (metabolic equivalents), respectively. IMPA was positively associated with CRF after control for age, biological sex, bouted moderate-intensity physical activity and LIPA (partial r=0.09, p=0.05). IMPA intensity did not remain a predictor of CRF independent of covariates (p=0.08). LIPA was associated with CRF after control for age, biological sex and IMPA (r=0.15, p<0.05). The combination of IMPA and LIPA was associated with CRF independent of age and biological sex (partial r=0.20, p<0.001).Conclusions IMPA and LIPA were positively, but weakly, associated with CRF independent of age, biological sex and other physical activity variables. Among adults with overweight and obesity, the combination of IMPA and LIPA explained a greater variance (~4%) in CRF than either behaviour alone.