1,721,055 research outputs found
Il costo energetico: fattori che lo determinano
No full textIl costo energetico del nuoto (C) è definito
come l’energia spesa per coprire una
determinata distanza; per produrre un’elevata
velocità, C dovrebbe essere il minore
possibile. C dipende dalla resistenza
idrodinamica (Wd: è vantaggioso avere un
valore basso), dall’efficienza propulsiva
(ηp) e dall’efficienza totale (ηo) (è vantaggioso
avere questi due valori alti). Sfortunatamente,
questi parametri sono piuttosto
difficili da misurare e i metodi finora proposti
in letteratura per misurare/calcolare
questi fattori danno risultati molto diversi
tra loro
The energy cost of level walking before and after hydro-kinesi therapy in patients with spastic paresis
No full textIn this study the energy cost of level walking was measured in 23 patients with stationary spastic paresis before and after a two-week treatment (45 min daily) of hydro-kinesi therapy, the latter consisting of passive and active movements in warm (32°C) sea water, free swimming and water immersion walking. Among the subjects (80.2±13.2 kg body mass; 56.0±14.6 years of age; 10.7±6.6 years of duration of spasticity), 12 were affected by hemiparesis, 4 by multiple sclerosis and 7 by spinal cord injury. The energy cost of level walking (Cw) was measured before and after therapy from the ratio of the overall steady-state oxygen consumption to the effective speed of progression. The differences in Cw due to the treatment, at matched speeds, were found to be negligible at speeds higher than 0.75 m · s-1 (less than 5%) but to increase, with decreasing speed, up to about 17% at 0.1 m · s-1. The treatment was therefore effective in improving the gait characteristics of the subjects, through a decrease of their Cw, mainly at low speeds of progression. © Munksgaard, 1998
La ricerca aerospaziale studia il nuoto
No full textDal 17 al 21 di settembre si è svolto a Tsukuba
in Giappone il XIII Congresso di Biomeccanica
e Medicina del Nuoto.
Questo Congresso è il più importante al
mondo per quanto riguarda le attività natatorie,
si svolge ogni quattro anni ed è nato
dall’interesse di diversi ricercatori che hanno
sentito la necessità di confrontarsi nello
studio di sport resi particolarmente complessi
per l’ambiente in cui si svolgono.
Il Congresso ha visto la prima edizione nel
1970 a Bruxelles e raramente (solo 4 volte)
è stato organizzato fuori dall’Europa.
Tsukuba è la più grande città universitari
La valutazione del velocista
No full textIn questo articolo viene proposto un nuovo modello di valutazione per i velocisti nel nuoto. Si basa sulla misurazione dei fattori che determinano la prestazione della massima velocità di nuoto attraverso il rapporto tra propulsione e resistenza idrodinamica: Vmax= ∛((W'TOT*ep)/k). I velocisti della Nazionale Italiana di Nuoto sono stati testati presso i laboratori della Scuola di Scienze Motorie dell’Università di Bologna
Effect of swim cap model on passive drag
No full textHydrodynamics plays an important role in swimming because even small decreases in a swimmer’s drag can lead to performance improvements. During the gliding phases of a race, the head of a swimmer is an important point of impact with the fluid, and the swim cap, even if it covers only a small portion of the swimmer’s body, can have an influence on drag. The purpose of this study was to investigate the effects on passive drag (Dp) of wearing 3 different types of swim caps (LSC: a lycra cap; CSC: a silicone cap; HSC: a silicone helmet cap without seams). Sixteen swimmers were tested at 3 velocities (1.5, 1.7, 1.9 m/s), and the Dp measurements were repeated at each condition 5 times. A statistical analysis revealed significant differences in drag (p , 0.01) among caps: Dp is 5–6.5% lower for HSC than for CSC at all speeds and 6% lower in HSC than CSC at 1.9 m/s. No differences in Dp were observed between LSC and CSC at all speeds. Thus, the differences in Dp are based on the type of material (lycra vs. silicone) and on the presence/ lack of seams: the HSC swim cap is the most rigid, the most adherent to the swimmer’s head, and does not allow the
formation of wrinkles compared with the other 2 investigated swim caps. Therefore, the following conclusions can be made: (a) swimmers should take care when selecting their swim cap if they want to improve the fluid dynamics at the “leading edge” of their body and (b) because Dp is affected by the swim cap model, care should be taken when comparing data from different studies, especially at faster investigated
speeds
Potenza propulsiva e potenza frenante. La ricerca di un equilibrio nello stile libero
No full textQuando un atleta nuota a velocità costante le forze propulsive (thrust force = Ft) sono uguali alle forze resistenti (drag force = Fd) ed è possibile scrivere che: Ft – Fd = 0 (Toussaint 1992)
The energy cost of swimming and its determinants
Full text linkThe energy expended to transport the body over a given distance (C, the energy cost) increases with speed both on land and in water. At any given speed, C is lower on land (e.g., running or cycling) than in water (e.g., swimming or kayaking) and this difference can be easily understood when one considers that energy should be expended (among the others) to overcome resistive forces since these, at any given speed, are far larger in water (hydrodynamic resistance, drag) than on land (aerodynamic resistance). Another reason for the differences in C between water and land locomotion is the lower capability to exert useful forces in water than on land (e.g., a lower propelling efficiency in the former case). These two parameters (drag and efficiency) not only can explain the differences in C between land and water locomotion but can also explain the differences in C within a given form of locomotion (swimming at the surface, which is the topic of this review): e.g., differences between strokes or between swimmers of different age, sex, and technical level. In this review, the determinants of C (drag and efficiency, as well as energy expenditure in its aerobic and anaerobic components) will, thus, be described and discussed. In aquatic locomotion it is difficult to obtain quantitative measures of drag and efficiency and only a comprehensive (biophysical) approach could allow to understand which estimates are “reasonable” and which are not. Examples of these calculations are also reported and discussed
Characterization of the in vivo transient responses of the femoral cartilage by means of quantitative ultrasound imaging techniques
No full textBackground: Quantitative ultrasound (QUS) techniques are new diagnostic tools able to identify changes in structural and material properties of the investigated tissue. For the first time, we evaluated the capability of QUS techniques in determining the in vivo transient changes in knee joint cartilage after a stressful task. Methods: An ultrasound scanner collecting B-mode and radiofrequency data simultaneously was used to collect data from the femoral cartilage of the right knee in 15 participants. Cartilage thickness (CTK), ultrasound roughness index (URI), average magnitude ratio (AMR), and Nakagami parameters (NA) were evaluated before, immediately after and every 5 min up to 45 min a stressful task (30 min of running on a treadmill with a negative slope of 5%). Results: CTK was affected by time (main effect: p < 0.001). Post hoc test showed significant differences with CTK at rest, which were observed up to 30 min after the run. AMR and NA were affected by time (p < 0.01 for both variables), while URI was unaffected by it. For AMR, post hoc test showed significant differences with rest values in the first 35 min of recovery, while NA was increased compared to rest values in all time points. Conclusion: Data suggest that a single running trial is not able to modify the integrity of the femoral cartilage, as reported by URI data. In vivo evaluation of QUS parameters of the femoral cartilage (NA, AMR, and URI) are able to characterize changes in cartilage properties over time
The energy cost of walking or running on sand
No full textOxygen uptake ( {Mathematical expression}O2) at steady state, heart rate and perceived exertion were determined on nine subjects (six men and three women) while walking (3-7 km · h-1) or running (7-14 km · h-1) on sand or on a firm surface. The women performed the walking tests only. The energy cost of locomotion per unit of distance (C) was then calculated from the ratio of {Mathematical expression}O2 to speed and expressed in J · kg-1 · m-1 assuming an energy equivalent of 20.9 J · ml O2-1. At the highest speeds C was adjusted for the measured lactate contribution (which ranged from approximately 2% to approximately 11% of the total). It was found that, when walking on sand, C increased linearly with speed from 3.1 J · kg-1 · m-1 at 3 km · h-1 to 5.5 J · kg-1 · m-1 at 7 km · h-1, whereas on a firm surface C attained a minimum of 2.3 J · kg-1 · m-1 at 4.5 km · h-1 being greater at lower or higher speeds. On average, when walking at speeds greater than 3 km · h-1, C was about 1.8 times greater on sand than on compact terrain. When running on sand C was approximately independent of the speed, amounting to 5.3 J · kg-1 · m-1, i.e. about 1.2 times greater than on compact terrain. These findings could be attributed to a reduced recovery of potential and kinetic energy at each stride when walking on sand (approximately 45% to be compared to approximately 65% on a firm surface) and to a reduced recovery of elastic energy when running on sand. © 1992 Springer-Verlag
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