Knee effusion affects knee mechanics and muscle activity during gait in individuals with knee osteoarthritis

SummaryObjectiveTo test the hypothesis that knee effusion presence in those with knee osteoarthritis (OA) alters knee joint muscle activation patterns and sagittal plane mechanics during gait.MethodsThirty-five patients with medial compartment knee OA were assessed for the presence of effusion using a brush test. Based on the results, they were assigned to the knee effusion (n = 17) and no knee effusion (n = 18) groups. Electromyograms from seven lower extremity muscles (lateral and medial gastrocnemius, vastus lateralis and medialis, rectus femoris and the lateral and medial hamstrings), leg motion and ground reaction forces were recorded during self-selected walking. Isometric knee extensor, plantar flexor and knee flexor strength were measured. Discrete measures from angular knee motion and net external moment of force waveforms were identified. Principal component analysis extracted electromyographic waveform features. Analysis of variance models tested for main effects (group, muscle) and interactions (α = 0.05). Bonferroni post-hoc testing was employed.ResultsNo differences in age, body mass index, knee pain, Western Ontario McMaster Osteoarthritis Index scores, gait velocity and muscle strength were found between groups (P > 0.05). Individuals with effusion had a greater overall quadriceps activation and prolonged hamstring activation into mid-stance (P < 0.05). Knee joint flexion angles were higher (P < 0.05) and net external knee extension (KE) moments in mid to late stance lower in the effusion group.ConclusionQuadriceps and hamstrings activation during walking were altered when effusions were present. Increased knee flexion (KF) angles and decreased KE moment in mid-late stance provide a mechanical explanation for the effect of joint effusion on muscle activation in those with knee OA

The Feasibility of Reducing and Measuring Sedentary Time among Overweight, Non-Exercising Office Workers

This study examined the feasibility of reducing free-living sedentary time (ST) and the convergent validity of various tools to measure ST. Twenty overweight/obese participants wore the activPAL (AP) (criterion measure) and ActiGraph (AG; 100 and 150 count/minute cut-points) for a 7-day baseline period. Next, they received a simple intervention targeting free-living ST reductions (7-day intervention period). ST was measured using two questionnaires following each period. ST significantly decreased from 67% of wear time (baseline period) to 62.7% of wear time (intervention period) according to AP (n = 14, P < 0.01). No other measurement tool detected a reduction in ST. The AG measures were more accurate (lower bias) and more precise (smaller confidence intervals) than the questionnaires. Participants reduced ST by ~5%, which is equivalent to a 48_min reduction over a 16-hour waking day. These data describe ST measurement properties from wearable monitors and self-report tools to inform sample-size estimates for future ST interventions

COLLECTIVE EFFICACY, THREAT, AND URBAN CHANGE: EXAMINING SOCIAL CONTROL FORCES IN AREAS OF GENTRIFICATION

Since the term gentrification was first coined in the 1960s, scholars have had an interest in understanding how this process of change can impact neighborhoods. Empirical research focusing on the relationship between gentrification and crime has yielded varying results, with little examination of the contextual mechanisms which may influence the relationship. In addition, little empirical attention has been devoted to the possibility of the spatial displacement of crime due to gentrification. The purpose of this dissertation is to contribute to our understanding of how gentrification impacts levels of crime in three ways. First, using data from the U.S. Census, the Project on Human Development in Chicago Neighborhoods, and the Chicago Transit Authority, I examine whether gentrification is significantly associated with lower levels of crime. Second, I examine levels of crime in gentrifying and adjacent areas to assess the presence of spatial displacement. Third, I incorporate two contextual factors - collective efficacy and perceived neighborhood change - to examine whether or not they modify the relationship between gentrification and crime. Analyses utilize multilevel modeling techniques and difference-in-differences estimation. Results offer preliminary support for the moderating roles of collective efficacy and perceived neighborhood change mechanisms on the relationship between gentrification and crime. While there is an overall negative association between gentrification and crime, this effect is strengthened with collective efficacy, but reversed with rising levels of perceived neighborhood change. Additionally, there is preliminary evidence that the spatial displacement of crime is not occurring as a result of gentrification. I conclude this dissertation with a discussion of the limitations, policy implications, and future directions for this area of research

Impact of accelerometer data processing decisions on the sample size, wear time and physical activity level of a large cohort study

Background: Accelerometers objectively assess physical activity (PA) and are currently used in several large-scale epidemiological studies, but there is no consensus for processing the data. This study compared the impact of wear-time assessment methods and using either vertical (V)-axis or vector magnitude (VM) cut-points on accelerometer output. Methods: Participants (7,650 women, mean age 71.4 y) were mailed an accelerometer (ActiGraph GT3X+), instructed to wear it for 7 days, record dates and times the monitor was worn on a log, and return the monitor and log via mail. Data were processed using three wear-time methods (logs, Troiano or Choi algorithms) and V-axis or VM cut-points. Results: Using algorithms alone resulted in "mail-days" incorrectly identified as "wear-days" (27-79% of subjects had >7-days of valid data). Using only dates from the log and the Choi algorithm yielded: 1) larger samples with valid data than using log dates and times, 2) similar wear-times as using log dates and times, 3) more wear-time (V, 48.1 min more; VM, 29.5 min more) than only log dates and Troiano algorithm. Wear-time algorithm impacted sedentary time (~30-60 min lower for Troiano vs. Choi) but not moderate-to-vigorous (MV) PA time. Using V-axis cut-points yielded ~60 min more sedentary time and ~10 min less MVPA time than using VM cut-points. Conclusions: Combining log-dates and the Choi algorithm was optimal, minimizing missing data and researcher burden. Estimates of time in physical activity and sedentary behavior are not directly comparable between V-axis and VM cut-points. These findings will inform consensus development for accelerometer data processing in ongoing epidemiologic studies. Electronic supplementary material The online version of this article (doi:10.1186/1471-2458-14-1210) contains supplementary material, which is available to authorized users

FUNCTIONAL DATA ANALYSIS: A NEW METHOD TO INVESTIGATE PACING STRATEGIES IN ELITE CANOE KAYAK SPRINT

The purpose of this study was to investigate pacing strategies used by elite flatwater canoe kayak sprint athletes in 12 Olympic events. Boat velocity data for canoe and kayak A-final races were extracted from the International Canoe Federation’s website for five major international competitions during the 2016 and 2017 seasons (n=374 boats; n=87 races). Principal component analysis was used to determine pacing strategies in 200, 500, and 1000 m races. Differences in pacing strategies between medalists and non-medalists were found only in 1000 m races. These findings reflected overall differences in boat velocity but also the timing of changes in boat velocity throughout the 1000 m race. This research shows that certain pacing strategies are associated with more success in canoe kayak sprint during long duration races