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Abstract

International Journal of Exercise Science 18(4): 636-658, 2025. Individuals after anterior cruciate ligament reconstruction (ACLR) are less physically active than their uninjured peers, but little is known about their sedentary behavior (SB). This study aimed to identify patterns of SB in individuals six and 18 months after ACLR. Eighteen individuals after ACLR wore accelerometers for one week during six- and 18-month post-operative assessments (83.3% female, 19.7±5.6 years old, BMI 23.9±kg/m2). The percentage of awake time spent in SB was estimated. A multilevel (two time points – six and 18 months), multidimensional (13 hours) functional principal component analysis generated two sets of unique personalized principal component scores: between-participant (person level principal components, PPC) and within-participant (follow-up level principal components, FPC). An exploratory analysis compared SB patterns with structural and symptomatic signs of knee health outcomes. Participants averaged 65.4±7.5% and 65.7±9.0% time in SB at six and 18 months after ACLR, respectively. The first PPC identified an overall pattern of high levels of SB throughout the day. The first FPC identified a pattern of decreased SB in the morning and increased SB in the evening 18 months after ACLR compared to six months. Our exploratory analysis identified a potential association between this first FPC and knee health symptoms 18 months after ACLR. Different SB patterns existed six months after ACLR. Our findings suggest the time of day when individuals after ACLR are most sedentary and provide a foundation to develop and test interventions to reduce time in SB by substituting periods of physical activity.

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