Hamstring muscles’ function deficit during overground sprinting in track and field athletes with a history of strain injury

ABSTRACT

In this study, we aimed to clarify the characteristics of neuromuscular function, kinetics, and kinematics of the lower extremity during sprinting in track and field athletes with a history of strain injury. Ten male college sprinters with a history of unilateral hamstring injury performed maximum effort sprint on an athletic track. The electromyographic (EMG) activity of the long head of the biceps femoris (BFlh) and gluteus maximus (Gmax) muscles and three-dimensional kinematic data were recorded. Bilateral comparisons were performed for the EMG activities, pelvic anterior tilt angle, hip and knee joint angles and torques, and the musculotendon length of BFlh. The activity of BFlh in the previously injured limb was significantly lower than that in the uninjured limb during the late-swing phase of sprinting (p < 0.05). However, the EMG activity of Gmax was not significantly different between the previously injured and uninjured limbs. Furthermore, during the late-swing phase, a significantly more flexed knee angle (p < 0.05) and a decrease in BFlh muscle length (p < 0.05) were noted in the injured limb. It was concluded that previously injured hamstring muscles demonstrate functional deficits during the late swing phase of sprinting in comparison with the uninjured contralateral muscles.     

Reconfiguring public Internet access in Austin, TX: Wi-Fi's promise and broadband divides

This paper assesses the ways in which local actors are reconfiguring public access to broadband through the unlicensed spectrum. The process of adoption and configuration of public Wi-Fi networks in Austin, Texas, is the focus of our case study. Austin is one of the most “unwired” cities in the United States and increasingly known as a world-class industrial center in wireless. The development of strategic visions about public Wi-Fi services among user groups and local startups provided a fertile ground for diverse partnerships among nonprofit groups, broadband providers, wireless ISPs, and the city government. We also found that the popularity of the venue-sponsored or free-to-end-user model of access is supported by different providers that see their interests represented in the growth of public wireless broadband. However, the prevailing model of public Wi-Fi has a strong commercial bias. This, combined with the historical socioeconomic divides in the city, has resulted in an uneven geography of public Wi-Fi networks.     

Construction of mathematical knowledge through whole-class discussion

A word problem that requires addition of fractions with different denominators was presented to 11 classes of 4th- or 5th-graders, 10 years of age. It had three answer alternatives: adding the denominators and numerators separately, transforming fractions into decimals before adding them, and the standard, most appropriate solution. Students in each class were required to choose an alternative themselves, state their reason for the choice, and discuss which alternative would be right. After whole-class discussion, they were asked to choose an alternative again and nominate the student who had offered the most plausible idea. Then students in six classes were informed which alternative was the most appropriate, whereas those in five classes were not. Finally, the students, irrespective of the presence/absence of feedback, were required to solve the initial problem without the alternatives as the post-test, and two new problems as the transfer test.The results showed that (a) the students could offer more or less plausible arguments for or against each alternative, which in most classes included the correct explanation; (b) both vocal and silent students could write a mathematical expression for the post-test problem and manipulated it correctly, incorporating other students' ideas presented during the discussion, with or without the teacher's feedback, though their generalization was rather limited; and (c) the students could recognize and memorize reasonable explanations offered by other students in the discussion.     

Cell-enclosing gelatin-based microcapsule production for tissue engineering using a microfluidic flow-focusing system

Gelatin-based microcapsule production using a microfluidic system and the feasibility of the resultant microcapsules for constructing spherical tissues surrounded by heterogeneous cells were studied. The first cell-encapsulation and subsequent cell-enclosing microparticle encapsulation were achieved using a microfluidic flow-focusing droplet production system. A hollow-core structure of about 150 μm in diameter was developed by incubating the resultant microparticles at 37 °C, which induced thermal melting of the enclosed unmodified gelatin microparticles. Mammalian cells filled the hollow-cores after 4 days of incubation. A cell layer on the cell-enclosing microcapsules was developed by simply suspending the microcapsules in medium containing adherent fibroblast cells. This method may prove useful for the generation of gelatin microcapsules using a microfluidic system for formation of artificial tissue constructs.     

Simulation to clarify the effect of paddling motion on the hull behavior of a single kayak in a sprint race

The cause and effect relationship between the paddling motion and the hull behavior of a kayak in a sprint race has not been sufficiently investigated. The objective of this study was to investigate the effect of the paddling motion on the hull behavior by numerical simulation. A dynamic simulation model of a paddler, paddle and hull in a single kayak, which was previously developed, was used for the simulation. One standard paddling motion and three modified motions were prepared for the simulation. Three modified motions were created based on suggestions by coaches of the Japan Olympic team. These motions were thought to be often seen in paddlers of lower skill level and, therefore, empirically considered to be typically bad motions. From the simulation results, the following findings were obtained: in the simulation of the standard paddling motion, the averaged hull velocity was 5.4 m/s. This was consistent with the actual hull velocity of 5.5 m/s. Typically bad motions which induced undesirable hull fluctuations reduced the propulsive efficiency.     

Young Children's Understanding of the Mind-Body Distinction

4 experiments investigated children's understanding of the mind-body distinction. Children of ages 4 and 5 recognized not only the differential modifiability of changeable versus unchangeable human properties and bodily versus mental properties, but also the independence of activities of bodily organs from a person's intention (Experiment 1). When presented 3 types of causal explanations (i.e., intentional, vitalistic, mechanical), 6-year-olds chose most often as most plausible for bodily functions vitalistic explanations (i.e., those ascribing the phenomena to a relevant bodily organ's initiative and effortful engagement in activity); 8-year-olds chose the vitalistic explanations second most often, following mechanical ones (Experiment 2). However, 6-year-olds, as well as 8-year-olds and adults, did not always choose vitalistic explanations over intentional explanations (Experiment 3); whereas they tended to prefer vitalistic explanations for biological phenomena, they predominantly accepted intentional ones for psychological phenomena (Experiment 3A). These results suggest that children as young as 6 years of age have acquired a form of biology as an autonomous domain which is separate from that of psychology.     

Reading processes of English sentences in Japanese and Canadian students

Native skilled, non-native skilled, and non-native non-skilled English readers read English texts and their reading times of words were measured. The results showed that reading times of native skilled readers were independent from the word length, word location, and grammatical word classification compared to non-native readers. Reading times of nouns strongly correlated with reading skill of readers. Although non-native skilled readers comprehended text meanings well, however the pattern of reading time of words was still different from those of native reader.     

Functional differences in the activity of the hamstring muscles with increasing running speed

Abstract

In this study, we examined hamstring muscle activation at different running speeds to help better understand the functional characteristics of each hamstring muscle. Eight healthy male track and field athletes (20.1 ± 1.1 years) performed treadmill running at 50%, 75%, 85%, and 95% of their maximum velocity. Lower extremity kinematics of the hip and knee joint were calculated. The surface electromyographic activities of the biceps femoris and semitendinosus muscles were also recorded. Increasing the running speed from 85% to 95% significantly increased the activation of the hamstring muscles during the late swing phase, while lower extremity kinematics did not change significantly. During the middle swing phase, the activity of the semitendinosus muscle was significantly greater than that of the biceps femoris muscle at 75%, 85%, and 95% of running speed. Statistically significant differences in peak activation time were observed between the biceps femoris and semitendinosus during 95%max running (P < 0.05 for stance phase, P < 0.01 for late swing phase). Significant differences in the activation patterns between the biceps femoris and semitendinosus muscles were observed as running speed was increased, indicating that complex neuromuscular coordination patterns occurred during the running cycle at near maximum sprinting speeds.