Engaging in an adequate amount of physical activity (PA) during the toddler years (12-36 months) has not only been associated with physical health, but with positive cognitive and mental health outcomes as well. The first aim of this dissertation was to systematically review the literature on toddler PA assessment methods. We found 16 articles on this topic that met inclusion criteria, which highlights the notion that there are limited assessment methods available for use in toddlers. Most identified methods were developed using accelerometry, while a few survey-based methods have been created. Few studies have cross-validated methods developed for use in preschoolers in toddlers. No direct observation (DO) methods have been developed for use in toddlers. These DO tools can provide more information on the activity and social contexts of toddler PA behavior. The review also shed light on the lack of standardization across measurement protocols to facilitate comparability across studies. The second aim of this dissertation was to develop an observational tool (Observational System for Recording Physical Activity in Children – Toddler (OSRAC-T)) to assess PA in toddlers and determine if the tool was reliable. We created this tool by adapting the Observational System for Recording Physical Activity in Children – Preschool (OSRAC-P). This tool allows for the assessment of PA level, type, and context, in addition to activity initiation and prompts, and group context. In collaboration with experts, a new category to assess support (i.e., weight-bearing v. non-weightbearing) and new codes (e.g., tantrum) were added to the original code to better apply to toddlers. Using the OSRAC-T, toddlers spent the majority of the observed time sedentary (70%) and only a small amount of time was spent in moderate-to-vigorous PA (10%). Sit/squat and stand accounted for most activity types (68.6%). We concluded that the tool was a reliable observation system (k = 0.46 – 0.69). Additionally, comparable observations were made during live and video coded sessions (k = 0.47 – 0.83). This instrument can be used to inform toddler childcare providers or intervention design. The use of observation can be challenging for researchers due to the extensive time commitment needed and the potential for high levels of subjectivity in assessment, which leads many researchers to opt for accelerometer-based assessment methods. The final aim of this dissertation was to cross-validate various cut-points for assessing sedentary time (ST) and PA in toddlers using hip- and wrist-placed accelerometers and vertical axis and vector magnitude data. The same sample and methods were used for studies 2 and 3. Mean absolute difference (MAD), Pearson’s r correlation coefficient, and equivalence testing were calculated for all classification methods, for each activity intensity. Percentage of time classified as sedentary, light, or MVPA varied greatly between cut-points. Accelerometer placement or data axes used did not influence accuracy. No set of cut-points, applied to any intensity, were determined to be equivalent to direct observation. The variability in these estimation methods may be due to the varying epochs at which cut-points were calibrated or the way activity intensities were classified using direct observation. This dissertation addressed recent calls to advance physical activity assessment methods in young children, including toddlers. Further development in toddler activity assessment will lead to better intervention design to promote activity engagement.
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