The influence of barefoot and shod running on Triceps-surae muscle strain characteristics

The aim of the current investigation was to determine the effects of barefoot and shod running on the kinematics of the Triceps-Surae muscle group. Twelve male participants ran at 4.0 m.s-1 (± 5%) in both barefoot and shod conditions. Kinematics were measured using an eight-camera motion analysis system. Muscle kinematics from the lateral Gastrocnemius, medial Gastrocnemius and Soleus were obtained using musculoskeletal modelling software (Opensim v3.2). The results showed that muscle strain for the lateral Gastrocnemius (barefoot = 1.10 & shod = 0.33 %), medial Gastrocnemius (barefoot = 1.07 & shod = 0.32 %) and Soleus (barefoot = 3.43 & shod = 2.18 %) were significantly larger for the barefoot condition. Given the proposed association between the extent of muscle strain and the etiology of chronic muscle strain pathologies, the current investigation shows that running barefoot may place runners at greater risk from Triceps-Surae strain injuries

The Australian Business Cycle: A Coincident Indicator Approach

This paper constructs coincident indices of Australian economic activity using techniques for estimating approximate factor models with many series, using data that begin in the early 1960s. The resulting monthly and quarterly indices both provide plausible measures of the Australian business cycle. The indices are quite robust to the selection of variables used in their construction, the sample period used in estimation, and the number of factors included. Notably, only a small number of factors is needed to adequately capture the business cycle. The coincident indices provide a much smoother representation of the cycle in economic activity than do standard national accounts measures, especially in the period prior to the early 1980s. Accordingly, they suggest that the marked decline in volatility evident in quarterly Australian GDP growth that occurred up to the 1980s may overstate the reduction in the volatility of economic activity and may at least partially reflect improvements in the measurement of GDP. Because the coincident indices present a smoother perspective of the business cycle in the 1960s and 1970s, they identify fewer recessions in this period than does GDP. Over the past 45 years, the coincident indices locate three recessions – periods when there was a widespread downturn in economic activity; in 1974–1975, 1982–1983 and 1990–1991.business cycle; factor models; coincident indicator; Australia

Effects of minimalist and maximalist footwear on Achilles tendon load in recreational runners

The current investigation aimed to comparatively examine the effects of minimalist, maximalist and conventional footwear on Achilles tendon forces (ATF) during running. Twelve male runners (age 23.11±5.01 years, height 1.78±0.10 cm and body mass 77.13±7.89 kg) ran at 4.0 m/s in the three footwear conditions. ATF’s were calculated using Opensim software allowing the magnitudal and temporal aspects of the ATF to be quantified. Differences between footwear were examined using one-way repeated measures ANOVA. The results showed the peak ATF was significantly larger in minimalist footwear (5.97±1.38 body weight (BW)) compared to maximalist (5.07±1.42 BW). In addition it was revealed that ATF per mile was significantly larger in minimalist (492.31±157.72 BW) in comparison to both maximalist (377.31±148.06 BW) and conventional (402.71±125.51 BW) footwear. Given the relationship between high ATF and Achilles tendon degradation, the current investigation indicated that minimalist footwear may increase runners risk for Achilles tendon injury

A preconditioned Newton-Krylov method for computing steady-state pulse solutions of mode-locked lasers

Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2008.Includes bibliographical references (p. 47-48).We solve the periodic boundary value problem for a mode-locked laser cavity using a specially preconditioned matrix-implicit Newton-Krylov solver. Solutions are obtained at least an order of magnitude faster than with dynamic simulation, the standard method. Our method is demonstrated experimentally on a one-dimensional temporal model of an eight femtosecond mode-locked laser operating in the dispersion-managed soliton regime. Our solver is applicable to finding the steady-state solution of any nonlinear optical cavity with moderate self phase modulation, such as those of solid state lasers, and requires only a model for the round-trip action of the cavity. We conclude by proposing avenues of future work to improve the method's convergence and expand its applicability to lasers with higher degrees of cavity nonlinearity. Our approach can be extended to spatio-temporal cavity models, potentially allowing for the first feasible simulation of the full dynamics of Kerr-lens mode locking.by Jonathan R. Birge.S.M

Influence of a knee brace intervention on perceived pain and patellofemoral loading in recreational athletes

Background: The current investigation aimed to investigate the effects of an intervention using knee bracing on pain symptoms and patellofemoral loading in male and female recreational athletes. Methods: Twenty participants (11 males & 9 females) with patellofemoral pain were provided with a knee brace which they wore for a period of 2 weeks. Lower extremity kinematics and patellofemoral loading were obtained during three sport specific tasks, jog, cut and single leg hop. In addition their self-reported knee pain scoreswere examined using the Knee injury and Osteoarthritis Outcome Score. Datawere collected before and after wearing the knee brace for 2 weeks. Findings: Significant reductions were found in the run and cut movements for peak patellofemoral force/pressure and in all movements for the peak knee abduction moment when wearing the brace. Significant improvements were also shown for Knee injury and Osteoarthritis Outcome Score subscale symptoms (pre: male= 70.27, female = 73.22 & post: male = 85.64, female = 82.44), pain (pre: male = 72.36, female = 78.89 & post: male = 85.73, female = 84.20), sport (pre: male = 60.18, female = 59.33 & post: male = 80.91, female =79.11), function and daily living (pre: male = 82.18, female = 86.00 & post: male = 88.91, female = 90.00) and quality of life (pre: male= 51.27, female= 54.89 & post: male= 69.36, female= 66.89). Interpretation:Male and female recreational athleteswho suffer frompatellofemoral pain can be advised to utilise knee bracing as a conservative method to reduce pain symptoms

On the Tail Behaviour of Aggregated Random Variables

In many areas of interest, modern risk assessment requires estimation of the extremal behaviour of sums of random variables. We derive the first order upper-tail behaviour of the weighted sum of bivariate random variables under weak assumptions on their marginal distributions and their copula. The extremal behaviour of the marginal variables is characterised by the generalised Pareto distribution and their extremal dependence through subclasses of the limiting representations of Ledford and Tawn (1997) and Heffernan and Tawn (2004). We find that the upper tail behaviour of the aggregate is driven by different factors dependent on the signs of the marginal shape parameters; if they are both negative, the extremal behaviour of the aggregate is determined by both marginal shape parameters and the coefficient of asymptotic independence (Ledford and Tawn, 1996); if they are both positive or have different signs, the upper-tail behaviour of the aggregate is given solely by the largest marginal shape. We also derive the aggregate upper-tail behaviour for some well known copulae which reveals further insight into the tail structure when the copula falls outside the conditions for the subclasses of the limiting dependence representations

Effects of foot orthoses on patellofemoral load in recreational runners

The most common chronic injury in recreational runners is patellofemoral pain. Whilst there is evidence to suggest that orthotic intervention may reduce symptoms in runners who experience patellofemoral pain the mechanism by which their clinical effects are mediated is currently poorly understood. The aim of the current investigation was to determine whether foot orthoses reduce the loads experienced by the patellofemoral joint during running. Patellofemoral loads were obtained from fifteen male runners who ran at 4.0 m·s-1. Patellofemoral loads with and without orthotics were contrasted using paired t-tests. The results showed that patellofemoral joint loads were significantly reduced as a function of running with the orthotic device. The current investigation indicates that through reductions in patellofemoral loads, foot orthoses may serve to reduce the incidence of chronic running injuries at this joint