Bone adapts to its loading environment throughout the lifespan, with peak bone mass accrual occurring during childhood and adolescence. Therefore, understanding how physical activity (PA) impacts bone during childhood and adolescence is especially important. Accelerometers are commonly used to measure PA and examine its associations with bone outcomes. In this thesis, I investigated whether using new accelerometry metrics to synthesize count-based accelerometry PA data would help uncover associations between specific parameters of PA and bone strength. First, I compared PA measured by older (count-based) and newer accelerometers (raw accelerations), to determine whether they were comparable. I discovered that count-based data is not directly comparable between the two accelerometers;​ however, minutes per day in different intensities of activity (e.g., sedentary, light, moderate, and vigorous) are comparable (mean bias <5 min/d at all intensities). I then compared count-based (older format) and raw accelerations (newer format) and found that although a conversion from count- based to raw accelerations is not possible, a metric initially designed for use with raw accelerations (the intensity gradient (IG)) can be reproduced with count data (mean bias = -0.15;​ 95% LOA [-0.65, 0.34]). Second, using four years of longitudinal data from over 300 children and adolescents, I examined whether IG and a daily impact score (DIS) were more strongly associated with bone strength than a metric traditionally used to examine these associations, minutes per day spent in vigorous physical activity (VPA). These metrics differ in that both the IG and DIS use the full spectrum of accelerometry data, whereas VPA does not. Furthermore, the DIS weights the intensity of the accelerations more heavily than the number. Using linear mixed effects models, I determined that the DIS was positively associated with bone strength independent of VPA (β_DIS = 25.2 (7.0, 43.6), p <0.05;​ β_VPA = 3.2 (-6.1, 1.4), p = 0.67), indicating that short, high-intensity physical activity is best for bone strength accrual in children and adolescents. These findings should be used to inform physical activity guidelines with the aim of improving bone strength in children and adolescents.