Objectives: To evaluate the effects of brief bouts of exercise spread throughout the day, termed 'exercise snacks', on cardiorespiratory and muscular fitness, and cardiometabolic health outcomes in physically inactive adults and older adults (aged ≥65 years).

Design: Systematic review and meta-analysis.

Data sources: Seven databases were searched from inception to April 2025.

Eligibility criteria: Randomised controlled trials (RCTs) of adults and older adults, comparing exercise snacks with non-exercising controls.

Results: 11 RCTs (n=414; 69.1% women, mean age 18.7±0.8 to 74.2±5.6 years) were included. Exercise snacks were defined as structured bouts lasting ≤5 min, performed at least twice daily, ≥3 times/week, for ≥2 weeks. The interventions varied in duration (4-12 weeks), frequency (3-7 days/week) and intensity (moderate-to-vigorous to near-maximal). Exercise snacks significantly improved cardiorespiratory fitness in adults (g=1.37, 95% CI 0.58 to 2.17; p<0.005; I²=71.4 %, k=6) and muscular endurance in older adults (g=0.40, 95% CI 0.06 to 0.75; p=0.02; I²=0 %, k=4), with moderate and very low certainty of evidence, respectively. No significant effects were observed for lower limb muscular strength or cardiometabolic outcomes, including body composition, blood pressure and blood lipid profiles. High compliance (91.1%) and adherence (82.8%) rates were observed.

Conclusions: Moderate certainty of evidence indicated that exercise snacks improved cardiorespiratory fitness in physically inactive adults. However, evidence for benefits on muscular endurance in older adults was limited, and the current data do not support their effectiveness for improving other cardiometabolic health markers.

Prospero registration number: CRD42024616514.