Hormonal changes throughout the menstrual cycle and increased anterior cruciate ligament laxity in females

Journal ArticleOBJECTIVE: To determine whether women experience significantly greater anterior cruciate ligament (ACL) laxity in conjunction with estrogen and progesterone surges during a normal 28- to 30-day menstrual cycle. DESIGN AND SETTING: Serial estrogen and progesterone levels were measured via radioimmunoassay procedures to identify the follicular and luteal phases of a subject's menstrual cycle and to determine periods of peak hormonal surges. Concomitant ACL laxity measures were taken using a knee arthrometer. Hormone levels and ACL laxity were assessed on days 1, 10, 11, 12, 13, 20, 21, 22, and 23 of the menstrual cycle. Day 1 corresponds to the menstrual phase, when estrogen and progesterone levels are at their lowest. Days 10 through 13 correspond to peak estrogen surge (follicular phase), and days 20 through 23 correspond to peak progesterone surge (luteal phase). SUBJECTS: Seven active females between the ages of 21 and 32 years with at least one apparently healthy knee (no known knee anomalies) volunteered for participation in this study. Each subject stated that she experienced a normal (28- to 30-day) menstrual cycle and was not currently taking any type of hormone therapy (eg, birth control medication). MEASUREMENTS: Blood was drawn on days 1, 10, 11, 12, 13, 20, 21, 22, and 23 of each subject's menstrual cycle, and ACL laxity measurements were assessed immediately after the blood draws. Estrogen and progesterone levels were determined via radioimmunoassay procedures, and ACL laxity was determined using a knee arthrometer. RESULTS: A within-subjects, repeated-measures analysis of variance was applied to determine the presence or absence of significant differences in ACL laxity values over the course of a subject's menstrual cycle. We found a significant difference in ACL laxity when comparing baseline levels of estrogen with peak levels of estrogen. A significant increase in ACL laxity was also noted when comparing baseline levels of progesterone with peak levels of progesterone. CONCLUSIONS: ACL laxity increased significantly throughout the menstrual cycle when comparing baseline with peak levels of estrogen and progesterone

Eccentric strain at long muscle length evokes the repeated bout effect.

Journal ArticleThe repeated bout effect (RBE) is a phenomenon characterized by less delayed onset muscle soreness (DOMS) and torque deficit after the second of 2 separate eccentric exercise bouts. Previous investigators have reported that shifting of optimum angle after an initial bout of eccentric exercise mediates the RBE. We hypothesized that an RBE for elbow extensor exercise occurs after an initial bout performed at long (starting position of 50 degrees to an end position of 130 degrees) but not short (starting position of 0 degrees to an end position of 80 degrees) muscle length because strain at long length evokes a shifting of the optimum angle to a longer length. Untrained women performed an initial bout at either long or short length (n = 9 per group) followed 1 week later by a repeated bout (RB) through the full ROM (0-130 degrees). Extensor torque and optimum angle was evaluated before, immediately after, and 2 days after each bout. A mechanical transducer depressed on the triceps brachii quantified DOMS. Torque deficits were 3% and 7% after exercise at short vs. long length, respectively. Two days after the RB, torque deficit was 8% and 1% for those previously exercising at short vs. long length (group x bout, p < 0.05). Greater DOMS (N) was observed after exercise at long (16 +/- 3) vs. short (23 +/- 2) length; whereas greater DOMS occurred for the short-length (17 +/- 2) vs. long (26 +/- 3) group after the RB (group x bout, p < 0.05). Optimum angle shifted to a longer length after exercise at long (+10 +/- 4 degrees) vs. short (+1 +/- 3 degrees) length (group x bout, p < 0.05). After the RB, those exercising previously at short length experienced a shift of +15 +/- 4 degrees (main effect, p < 0.05). The findings of this study indicate that the repetitive strain at long but not short muscle length evokes both immediate and sustained shifts in optimum angle to longer lengths, and that this shifting mediates (r(2) = 0.71) the RBE

Linking Urban Tree Cover Change and Local History in a Post-Industrial City

Municipal leaders are pursuing ambitious goals to increase urban tree canopy (UTC), but there is little understanding of the pace and socioecological drivers of UTC change. We analyzed land cover change in Philadelphia, Pennsylvania (United States) from 1970–2010 to examine the impacts of post-industrial processes on UTC. We interpreted land cover classes using aerial imagery and assessed historical context using archival newspapers, agency reports, and local historical scholarship. There was a citywide UTC increase of +4.3 percentage points. Substantial UTC gains occurred in protected open spaces related to both purposeful planting and unintentional forest emergence due to lack of maintenance, with the latter phenomenon well-documented in other cities located in forested biomes. Compared to developed lands, UTC was more persistent in protected open spaces. Some neighborhoods experienced substantial UTC gains, including quasi-suburban areas and depopulated low-income communities; the latter also experienced decreasing building cover. We identified key processes that drove UTC increases, and which imposed legacies on current UTC patterns: urban renewal, urban greening initiatives, quasi-suburban developments, and (dis)investments in parks. Our study demonstrates the socioecological dynamism of intra-city land cover changes at multi-decadal time scales and the crucial role of local historical context in the interpretation of UTC change

Using Systematic Observations to Understand Conditions that Promote Interracial Experiences in Neighbourhood Parks

We analysed observations from 31 neighbourhood parks, with each park mapped into smaller target areas for study, across five US cities generated using the System for Observing Play and Recreation in the Community (SOPARC). In areas where at least two people were observed, less than one-third (31.6%) were populated with at least one white and one non-white person. Park areas that were supervised, had one or more people engaged in vigorous activity, had at least one male and one female present, and had one or more teens present were significantly more likely to involve interracial groups (p \u3c 0.01 for each association). Observations in parks located in interracial neighbourhoods were also more likely to involve interracial groups (p \u3c 0.05). Neighbourhood poverty rate had a significant and negative relationship with the presence of interracial groups, particularly in neighbourhoods that are predominantly non-white. Additional research is needed to confirm the impact of these interactions. Urban planning and public health practitioners should consider the health benefits of interracial contact in the design and programming of neighbourhood parks

‘Stick that knife in me’: Shane Meadows’ children

This article brings Shane Meadows’ Dead Man's Shoes (2004) into dialogue with the history of the depiction of the child on film. Exploring Meadows’ work for its complex investment in the figure of the child on screen, it traces the limits of the liberal ideology of the child in his cinema and the structures of feeling mobilised by its uses – at once aesthetic and sociological – of technologies of vision

An interacting spin flip model for one-dimensional proton conduction

A discrete asymmetric exclusion process (ASEP) is developed to model proton conduction along one-dimensional water wires. Each lattice site represents a water molecule that can be in only one of three states; protonated, left-pointing, and right-pointing. Only a right(left)-pointing water can accept a proton from its left(right). Results of asymptotic mean field analysis and Monte-Carlo simulations for the three-species, open boundary exclusion model are presented and compared. The mean field results for the steady-state proton current suggest a number of regimes analogous to the low and maximal current phases found in the single species ASEP [B. Derrida, Physics Reports, {\bf 301}, 65-83, (1998)]. We find that the mean field results are accurate (compared with lattice Monte-Carlo simulations) only in the certain regimes. Refinements and extensions including more elaborate forces and pore defects are also discussed.Comment: 13pp, 6 fig