1,720,976 research outputs found
A theory of energy cost and speed of climbing.
No full textClimbing is an interesting form of quadrupedal locomotion on vertical substrates, and also a popular recreational activity. However, a theory of locomotor energetics of climbing has not been devised yet. Here we discuss an analytical model, based on simple physical principles, that gives the energy cost as a function of the vertical speed. We found that the energy cost monotonically decreases with speed, so that to minimize the energy spent to climb one should ascend at the highest possible speed. We propose that the actual climbing speed derives from the requirement of minimizing simultaneously the work per unit time as well as the work per unit length. Our predictions are in excellent agreement with measurements carried out on elite climbers
Influence of ascent speed on rock climbing economy
No full textIn some types of human and animal locomotion, speed influences the amount of metabolic energy expended per unit mass and distance (energy cost, EC) and as speed decreases or increases away from a healthy person's self-selected speed (SS S), the EC increases. When asked to climb a vertical wall using their preferred speed, similar to walking, climbers with the same level of skill spontaneously select comparable speeds. The present research was designed to investigate how speed of ascent affects the EC of climbing; we were also interested in finding out whether climbers with the same level of skill exhibit a common SS S and if it is correlated with optimal economy (i. e. minimum EC). A representative experimental set-up was prepared to quantify the economy of rock climbing by measuring steady-state oxygen intake (VO 2) in very skilled climbers while climbing at their SS S and at higher (H S) and lower (L S) speed, and computing the relative EC. The main findings were: (a) climbers with the same level of skill exhibited the same preferred climbing speed (10.2 ± 1.5 m·min -1) at the same fraction of their maximum VO 2 (VO 2peak) measured on a cycle ergometer (71.7 ± 15.2%), and (b) climbing economy continuously increased as speed increased from L S to H S. Thus climbing at the SSS does not correspond to the optimal economy. A possible explanation for these findings may be that although it does not match the minimum EC, the SS S would be the best compromise between the need to reduce the time spent in isometric work (useless and costly) and the need to avoid early muscle fatigue due to increased speed and frequency of muscle contraction
Energy cost and efficiency of ski mountaineering. A laboratory study.
No full textThe purpose of this study is to estimate the energy cost of ski mountaineering at different speeds under laboratory conditions.By using roller skis on a motorized treadmill we have estimated the energy cost and biomechanics parameters of ski mountaineering as a function of climbing speed at the gradient of 21\%.The metabolic energy spent for unit mass and distance, C, shows a broad minimum of about 10.6±0.2 J kg-1m-1 at roughly 3.5 km h-1. In addition we find a size-dependent effect: tall subjects spend less metabolic energy for unit mass and distance than small subjects at the same speed.The value of C measured in laboratory agrees with that obtained in the field at the preferred speed. This shows that skiers self select a speed that minimizes their metabolic cost. The dependence of C on the subject's size is explained by a simple model of the skier's dynamics. In addition we have calculated the ratio between mechanical work and metabolic energy, which may give some hints on the efficiency as a function of the speed. It turns out that efficiency increases with the speed up to a maximum located at around 4.5 km/h
Myoelectric signs of fatigue during constant and rhythmic isometric contractions
No full textLinear and non linear analysis of surface EMG has been carried out in order to describe and/or differentiate isometric contractions either with constant muscular effort or during rhythmic exercises
Amplitude and spectral characteristics of biceps Brachii sEMG depend upon speed of isometric force generation
No full text
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
- …
