1,720,981 research outputs found
The relationship between the mechanical work and the metabolic cost of locomotion in horses
No full textThree-dimensional motion capture and metabolic assessment were performed on four standardbred horses while walking, trotting and galloping on a motorized treadmill at different speeds, The mechanical work was partitioned into the internal work (W-INT), due to the speed changes of body segments with respect to the body centre of mass, and the external work (W-EXT), due to the position and speed changes of the body centre of mass with respect to the environment. The estimated total mechanical work (W-TOT=W-INT+W-EXT) increased with speed, while metabolic work (C) remained rather constant. As a consequence, the 'apparent efficiency' (eff(APP)=W-TOT/C) increased from 10% (walking) to over 100% (galloping), setting the highest value to date for terrestrial locomotion. The contribution of elastic structures in the horse's limbs was evaluated by calculating the elastic energy stored and released during a single bounce (W-EL,(BOUNCE)), which was approximately 1.23 J kg(-1) for trotting and up to 6 J kg(-1) for galloping. When taking into account the elastic energy stored by the spine bending and released as W-INT, as suggested in the literature for galloping, W-EL,(BOUNCE) was reduced by 0.88 J kg(-1). Indirect evidence indicates that force, in addition to mechanical work, is also a determinant of the metabolic energy expenditure in horse locomotion.Three-dimensional motion capture and metabolic assessment were performed on four standardbred horses while walking, trotting and galloping on a motorized treadmill at different speeds. The mechanical work was partitioned into the internal work (W(INT)), due to the speed changes of body segments with respect to the body centre of mass, and the external work (W(EXT)), due to the position and speed changes of the body centre of mass with respect to the environment. The estimated total mechanical work (W(TOT)=W(INT)+W(EXT)) increased with speed, while metabolic work (C) remained rather constant. As a consequence, the 'apparent efficiency' (effAPP=W(TOT)/C) increased from 10% (walking) to over 100% (galloping), setting the highest value to date for terrestrial locomotion. The contribution of elastic structures in the horse's limbs was evaluated by calculating the elastic energy stored and released during a single bounce (W(EL,BOUNCE)), which was approximately 1.23 J kg-1 for trotting and up..
The optimal locomotion on gradients: walking, running or cycling?
No full textOn level ground, cycling is more economical than running, which in turn is more economical than walking in the high speed range. This paper investigates whether this ranking still holds when moving on a gradient, where the three modes are expected to be mainly facing the same burden, i.e. to counter gravity. By using data from the literature we have built a theoretical framework to predict the optimal mode as a function of the gradient. Cycling was found to be the mode of choice only below 10-15% gradient, while above it walking was the least expensive locomotion type. Seven amateur bikers were then asked to walk, run and ride on a treadmill at different gradients. The speed was set so as to maintain almost constant the metabolic demand across the different gradients. The results indicate that the "critical slope", i.e. the one above which walking is less expensive than cycling (and running), is about 13-15%. One subject was loaded during bipedal gaits with a bicycle-equivalent mass, to simulate to cross-country cycling situation. The critical slope was close to 20%, due to the higher metabolic cost of loaded walking and running. Part of the findings can be explained by the mechanically different paradigms of the three locomotion types
Mechanical and metabolic profile of locomotion in adults with childhood-onset GH deficiency
No full textObjective: The aim of the present study was to evaluate the energy cost and the mechanical work of locomotion in a group of adults with childhood- onset GH deficiency (GILD). Subjects: Eight males with childhood-onset GHD (mean age ± S.D.: 31.7 ± 3.6 years; mean height: 145.1 ± 6.7 cm) and six age-, sex- and exercise-matched normal subjects were studied. Design: GHD patients and healthy controls were requested to walk and run in the speed range of 2-11 km h-1. For each condition, simultaneous mechanical and metabolic measurements were taken. Methods: Oxygen consumption, and mechanical internal and external work of locomotion were evaluated with standard open-circuit respirometry and three-dimensional motion analysis respectively. Results: External work was not significantly different between GHD patients and healthy controls, while internal work was higher for patients at all speeds. In walking, the relationships between both the mechanical energy recovery and the metabolic cost with speed were shifted towards lower speeds in patients. As a consequence, the optimal speed of walking, i.e. the speed at which the cost of locomotion is minimum, was lower for GHD patients. Stride frequency was significantly higher (11.2-11.3%) for GHD patients at all speeds of walking and running. GHD patients were unable to run at speeds higher than 8 km h-1 for the time needed to reach a metabolic steady state. Conclusion: It appears that both the mechanics and energetics of locomotion in short-statured adults with childhood-onset GHD are not strikingly different from those of healthy controls, thus demonstrating a substantial 'normality' in this group of GHD patients at metabolically attainable speeds. The 'harmonic' body structure and the adherence to allometric transformations in these patients do not exclude the possibility of a different metabolic role of GH in normally statured adults with childhood-onset GHD and in those with acquired GHD, taking into account the well recognized heterogeneity of the adult GHD syndrome
Peak running speed can be used to monitor neuromuscular fatigue from a standardized running test in team sport athletes
No full textThis study compared the sensitivity of peak running speed (PRS) measured during a submaximal run test (SRT) with a countermovement jump (CMJ) test to provide an alternate method of measuring neuromuscular fatigue (NMF). The study involved 20 semi-professional academy soccer players who performed a SRT and CMJ test, 24-hours pre-match, 24-, 48-, 72- and 96-hours post-match. Moderate decreases (effect-size (ES) ± 90% confidence intervals) were observed 24-hours post-match for CMJH; ES -0.70 ± 0.19, CMJPV; ES -0.92 ± 0.27 and PRS; ES -0.58 ± 0.11 with small decreases in CMJH; ES -0.36 ± 0.13 and PRS; ES -0.27 ± 0.23 still evident 48-hours post-match before returning to baseline 72-hours post-match. The results confirm PRS as an inexpensive alternate method of measuring NMF which, allows instantaneous real-time feedback on NMF. This can allow changes to be made immediately on-field within the post-match recovery phase without the need for further analysis or equipment
Running Stride Length And Rate Are Changed And Mechanical Efficiency Is Preserved After Cycling In Middle-Level Triathletes
No full textAlthough cycling impairs the subsequent metabolic cost and performance of running in some triathletes, the consequences on mechanical efficiency (Eff) and kinetic and potential energy fluctuations of the body center of mass are still unknown. The aim of this study was to investigate the effects of previous cycling on the cost-of-transport, Eff, mechanical energy fluctuations (Wtot), spring stiffness (Kleg and Kvert) and spatiotemporal parameters. Fourteen middle-level triathletes (mean ± SD: maximal oxygen uptake, V ̇ O2max = 65.3 ± 2.7 ml.kg−1.min−1, age = 30 ± 5 years, practice time = 6.8 ± 3.0 years) performed four tests. Two maximal oxygen uptake tests on a cycle ergometer and treadmill, and two submaximal 20-minute running tests (14 km.h−1) with (prior-cycling) and without (control) a previous submaximal 30-minute cycling test. No differences were observed between the control and post-cycling groups in Eff or Wtot. The Eff remains unchanged between conditions. On the other hand, the Kvert (20.2 vs 24.4 kN.m−1) and Kleg (7.1 vs 8.2 kN.m−1, p < 0.05) were lower and the cost-of-transport was higher (p = 0.018, 3.71 vs 3.31 J.kg−1.m−1) when running was preceded by cycling. Significantly higher stride frequency (p < 0.05, 1.46 vs 1.43 Hz) and lower stride length (p < 0.05, 2.60 vs 2.65 m) were observed in the running after cycling condition in comparison with control condition. Mechanical adjustments were needed to maintain the Eff, even resulting in an impaired metabolic cost after cycling performed at moderate intensity. These findings are compatible with the concept that specific adjustments in spatiotemporal parameters preserve the Eff when running is preceded by cycling in middle-level triathletes, though the cost-of-transport increased
Effects of Gradient and Speed on Uphill Running Gait Variability
Full text linkBackground: The aim of this study was to investigate the effects of gradient and speed on running variability (RV) and local dynamic stability (LDS) during uphill running. Hypotheses: (1) Both gradient and speed increase metabolic effort, in terms of heart rate (HR) and perceived exertion (CR10), in line with the contemporary literature, and (2) gradient increases RV and impairs LDS. Study design: “Crossover” observational design. Level of Evidence: Level 3. Methods: A total of 25 runners completed 10-minute running trials in 3 different conditions and in a randomized order: gradient at 0% (0CON), 2% (2CON), and 2% at isoefficiency speed (2IES). 0CON and 2CON speeds were calculated as the “best 10-km race performance” minus 1 km·h−1, whereas 2IES speed was adjusted to induce the same metabolic expenditure as 0CON. HR and perceived exertion as well as running kinematic variables were collected across all trials and conditions. Running variability was calculated as the standard deviation of the mean stride-to-stride intervals over 100 strides, while LDS was expressed by the Lyapunov exponent (LyE) determined on running cycle time over different running conditions. Results: Increases in HR and CR10 were observed between 0CON and 2CON (P < 0.001) and between 2IES and 2CON (P < 0.01). Higher RV was found in 2CON compared with 0CON and 2IES (both P < 0.001). Finally, the largest LyE was observed in 2IES compared with 0CON and 2CON (P = 0.02 and P = 0.01, respectively). Conclusion: Whereas RV seems to be dependent more on metabolic effort, LDS is affected by gradient to a greater extent. Clinical Relevance: Running variability could be used to monitor external training load in marathon runners
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
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
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