1,720,984 research outputs found
The effect of torsional shoe sole stiffness on knee moment and gross efficiency in cycling
No full textSupplementary data for the article:
Fletcher, J.R., Asmussen, M.J., Nigg, S., MacIntosh, B.R. and B.M Nigg. Effect of shoe torsional stiffness on the energetics and kinetics of cycling. Journal of Sports Sciences.
available at http://dx.doi.org/10.1080/02640414.2019.1565650
Running economy from a muscle energetics perspective
Full text linkThe economy of running has traditionally been quantified from the mass-specific oxygen uptake; however, because fuel substrate usage varies with exercise intensity, it is more accurate to express running economy in units of metabolic energy. Fundamentally, the understanding of the major factors that influence the energy cost of running (E-run) can be obtained with this approach. E-run is determined by the energy needed for skeletal muscle contraction. Here, we approach the study of E-run from that perspective. The amount of energy needed for skeletal muscle contraction is dependent on the force, duration, shortening, shortening velocity, and length of the muscle. These factors therefore dictate the energy cost of running. It is understood that some determinants of the energy cost of running are not trainable: environmental factors, surface characteristics, and certain anthropometric features. Other factors affecting E-run are altered by training: other anthropometric features, muscle and tendon properties, and running mechanics. Here, the key features that dictate the energy cost during distance running are reviewed in the context of skeletal muscle energetics.articl
Energy cost of running and Achilles tendon stiffness in man and woman trained runners
Full text linkThe energy cost of running (Erun), a key determinant of distance running performance, is influenced by several factors. Although it is important to express Erun as energy cost, no study has used this approach to compare similarly trained men and women. Furthermore, the relationship between Achilles tendon (AT) stiffness and Erun has not been compared between men and women. Therefore, our purpose was to determine if sex‐specific differences in Erun and/or AT stiffness existed. Erun (kcal kg−1 km−1) was determined by indirect calorimetry at 75%, 85%, and 95% of the speed at lactate threshold (sLT) on 11 man (mean ± SEM, 35 ± 1 years, 177 ± 1 cm, 78 ± 1 kg, V˙O2max = 56 ± 1 mL kg−1 min−1) and 18 woman (33 ± 1 years, 165 ± 1 cm, 58 ± 1 kg, V˙O2max = 50 ± 0.3 mL kg−1 min−1) runners. AT stiffness was measured using ultrasound with dynamometry. Man Erun was 1.01 ± 0.06, 1.04 ± 0.07, and 1.07 ± 0.07 kcal kg−1 km−1. Woman Erun was 1.05 ± 0.10, 1.07 ± 0.09, and 1.09 ± 0.10 kcal kg−1 km−1. There was no significant sex effect for Erun or RER, but both increased with speed (P < 0.01) expressed relative to sLT. High‐range AT stiffness was 191 ± 5.1 N mm−1 for men and 125 ± 5.5 N mm−1, for women (P < 0.001). The relationship between low‐range AT stiffness and Erun was significant at all measured speeds for women (r2 = 0.198, P < 0.05), but not for the men. These results indicate that when Erun is measured at the same relative intensity, there are no sex‐specific differences in Erun or substrate use. Furthermore, differences in Erun cannot be explained solely by differences in AT stiffness. e00178 Here, we show that when energy cost of running is normalized to body mass, at similar relative speeds of running, no sex‐specific differences in substrate use nor in the energy cost of running exist among similarly trained runners. Furthermore, the stiffness of the Achilles tendon (AT) of women is lower than in males, but the relationship between Erun and AT stiffness is not different between the sexes.articl
Changes in Achilles tendon stiffness and energy cost following a prolonged run in trained distance runners
Full text linkDuring prolonged running, the magnitude of Achilles tendon (AT) length change may increase, resulting in increased tendon strain energy return with each step. AT elongation might also affect the magnitude of triceps surae (TS) muscle shortening and shortening velocity, requiring greater activation and increased muscle energy cost. Therefore, we aimed to quantify the tendon strain energy return and muscle energy cost necessary to allow energy storage to occur prior to and following prolonged running. 14 trained male (n = 10) and female (n = 4) distance runners (24 +/- 4 years, 1.72 +/- 0.09 m, 61 +/- 10 kg, (V) over barO(2)max 64.6 +/- 5.8 ml.kg(-1).min(-1)) ran 90 minutes (RUN) at approximately 85% of lactate threshold speed (sLT). Prior to and following RUN, AT stiffness and running energy cost (E-run) at 85% sLT were determined. AT energy return was calculated from AT stiffness, measured with dynamometry and ultrasound and estimated TS force during stance. TS energy cost was estimated on the basis of AT force and assumed crossbridge mechanics and energetics. Following RUN, AT stiffness was reduced from 328 +/- 172 N.mm(-1) to 299 +/- 148 N.mm(-1) (p = 0.022). E-run increased from 4.56 +/- 0.32 J.kg(-1).m-1 to 4.62 +/- 0.32 J.kg(-1).m-1 (p = 0.049). Estimated AT energy return was not different following RUN (p = 0.99). Estimated TS muscle energy cost increased significantly by 11.8 +/- 12.3 J.stride(-1), (p = 0.0034), accounting for much of the post-RUN increase in E-run (8.6 +/- 14.5 J.stride(-1), r(2) = 0.31). These results demonstrate that a prolonged, submaximal run can reduce AT stiffness and increase E-run in trained runners, and that the elevated TS energy cost contributes substantially to the elevated E-run.articl
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Can changes in midsole bending stiffness of shoes affect the onset of joint work redistribution during a prolonged run?
Full text linkObjective: To investigate if changing the midsole bending stiffness of athletic footwear can affect the onset of lower limb joint work redistribu-tion during a prolonged run.Methods: Fifteen trained male runners (10-km time of<44 min) performed 10-km runs at 90% of their individual speed at lactate threshold (i.e.,when change in lactate exceeded 1 mmol during an incremental running test) in a control and stiff shoe condition on two occasions. Lower limbjoint kinematics and kinetics were measured using a motion capture system and a force-instrumented treadmill. Data were acquired every 500 m.Results: Prolonged running resulted in a redistribution of positive joint work from distal to proximal joints in both shoe conditions. Compared tothe beginning of the run, less positive work was performed at the ankle (approximately 9%;p0.001) and more positive work was performedat the knee joint (approximately 17%;p0.001) at the end of the run. When running in the stiff shoe condition, the onset of joint work redistri-bution at the ankle and knee joints occurred at a later point during the run.Conclusion: A delayed onset of joint work redistribution in the stiff condition may result in less activated muscle volume, because ankle plantarflexor muscles have shorter muscles fascicles and smaller cross-sectional areas compared to knee extensor muscles. Less active muscle volumecould be related to previously reported decreases in metabolic cost when running in stiff footwear. These results contribute to the notion thatfootwear with increased stiffness likely results in reductions in metabolic cost by delaying joint work redistribution from distal to proximal joints.articl
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
How Can Biomechanics Improve Physical Preparation and Performance in Paralympic Athletes?: A Narrative Review
Full text linkRecent research in Paralympic biomechanics has offered opportunities for coaches, athletes, and sports practitioners to optimize training and performance, and recent systematic reviews have served to summarize the state of the evidence connecting biomechanics to Paralympic performance. This narrative review serves to provide a comprehensive and critical evaluation of the evidence related to biomechanics and Paralympic performance published since 2016. The main themes within this review focus on sport-specific body posture: the standing, sitting, and horizontal positions of current summer Paralympic sports. For standing sports, sprint and jump mechanics were assessed in athletes with cerebral palsy and in lower-limb amputee athletes using running-specific prostheses. Our findings suggest that running and jumping-specific prostheses should be ‘tuned’ to each athlete depending on specific event demands to optimize performance. Standing sports were also inclusive to athletes with visual impairments. Sitting sports comprise of athletes performing on a bike, in a wheelchair (WC), or in a boat. WC configuration is deemed an important consideration for injury prevention, mobility, and performance. Other sitting sports like hand-cycling, rowing, and canoeing/kayaking should focus on specific sitting positions (e.g., arm-crank position, grip, or seat configuration) and ways to reduce aero/hydrodynamic drag. Para-swimming practitioners should consider athlete-specific impairments, including asymmetrical anthropometrics, on the swim-start and free-swim velocities, with special considerations for drag factors. Taken together, we provide practitioners working in Paralympic sport with specific considerations on disability and event-specific training modalities and equipment configurations to optimize performance from a biomechanical perspective.articl
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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