Background: There is some evidence that simply measuring physical activity alone can increase self-reported physical activity behaviour. Objective measures of physical activity in intervention studies have increased substantially over the last decade. Yet, there is no synthesised evidence of observed changes in the control group physical activity in trials that have used objective physical activity measurement approaches. Understanding factors associated with control group increases (or decreases) in physical activity may have implications for planning physical activity research and in clinical settings where objective measures of physical activity may be used. The aim of this systematic review is to describe changes in objectively measured physical activity that have occurred within control groups in primary care physical activity intervention studies and, if possible, identify factors that are potentially associated with these changes. Methods: The PRISMA-P reporting guidelines for systematic review protocols will be followed. Five electronic databases (PubMed, MEDLINE, SPORTDiscuss, PsychINFO, CINAHL) will be searched to identify physical activity controlled (randomised, cluster, quasi-experimental) studies conducted with adults in primary care. Search terms will be based on previous systematic reviews, and only peer-reviewed articles published in English will be considered. The main outcome measure is the change in objectively measured physical activity within the control group. Risk of bias will be assessed using the Cochrane Collaboration tool and the Risk Of Bias in Non-randomised Studies - of Interventions tool. Meta-analyses will be conducted where possible among studies with sufficient homogeneity. Discussion: This systematic review and meta-analysis will determine the extent to which physical activity measurement alone is associated with changes in objectively measured physical activity levels in control groups in primary care. Findings from this study will inform future physical activity intervention research and practice. If measuring physical activity alone is associated with increases in physical activity levels that may be considered beneficial for health, this could indicate that measurement alone may be a low cost, efficient and effective method to increase a proprotion of the population's physical activity levels.