1,721,042 research outputs found
Hopping locomotion at different gravity : metabolism and mechanics in humans
No full textPrevious literature on the effects of low gravity on the mechanics and energetics of human locomotion already dealt with walking, running and skipping. The aim of the present study is to obtain a comprehensive view on that subject by including measurements of human hopping in simulated low gravity, a gait often adopted in many Apollo Missions and documented in NASA footage. Six subjects hopped at different speeds at terrestrial, Martian and Lunar gravity on a treadmill while oxygen consumption and 3D body kinematic were sampled. Results clearly indicate that hopping is too metabolically expensive to be a sustainable locomotion on Earth but, similarly to skipping (and running), its economy greatly (more than x10) increases at lower gravity. On the Moon, the metabolic cost of hopping becomes even lower than that of walking, skipping and running, but the general finding is that gaits with very different economy on Earth share almost the same economy on the Moon. The mechanical reasons for such a decrease in cost are discussed in the paper. The present data, together with previous findings, will allow also to predict the aerobic traverse range/duration of astronauts when getting far from their base station on low gravity planets
The effects of speed and performance level on race walking kinematics
No full textPurpose Race walking is a very technical discipline of athletics, which is regulated by two peculiar constraints: straighten knee from heel strike to midstance and flight phase absence while race-walking. For this reason, several studies addressed technical factors as determinant of ath- letes’ performance. The aim of this study was to analyse differences in technique across athletes’ levels (regional— national—international), and describe race walking kine- matics at increasing speeds.
Methods Fifteen athletes race-walked for 1 min on a treadmill at increasing speeds (from 2.78 m s-1 to exhaustion). Three-dimensional kinematics data were recorded through a motion capture system sampling at 300 Hz.
Results Step length, step frequency and flight time increased linearly with speed, but step length was the major determinant to raise speed. At increasing speeds, joints angles curves reported a backward time shift (e.g., antici- pation of the movement), without altering joints range of motion, a further evidence of the rules influence on ath- letes’ technique. Among athletes’ levels the only difference found regarded the maximal race walking speed: interna- tional 4.97 ± 0.25 m s-1, national 4.61 ± 0.14 m s-1 and regional 4.22 ± 0.14 m s-1. Conclusion Athletes’ angular kinematics did not change increasing race-walking speed and did not show differences among athletes’ performance level. Further studies with combined metabolic and electromyography analyses are needed to better elucidate performance determinants and discriminate athletes’ level
THE EFFECTS OF GRAVITY ON HUMAN LOCOMOTION REPERTOIRE: COST OF TRANSPORT & BODY CENTRE OF MASS ANALYSIS
Full text linkHuman legged locomotion has been widely studied from both mechanical and bioenergetics points of view, however some aspects are still unaddressed and this thesis aimed to analysed some of them. One of the two methods for calculating muscular work during locomotion, which is an interesting parameters that can describe locomotion and subjective featuring, concerns the body centre of mass (BCoM) movements. The BCoM is the ideal point of the body where all forces act, and especially in a multi segment body as the human body, it is much easier and useful to calculate and follow its trajectory as the movement of the whole body. In order to compute BCoM two methods can be used: a double integration of the ground reaction forces, the forces exerted by feet when in contact to the ground, based on Newton’s second law, which is considered the gold standard, and called Direct Dynamics; and the weighted mean of segments centre of mass (COM) obtained by motion analysis, called Inverse Dynamics. Segments mass and COM location are based on anthropometric tables, which are scaled on subjects’ lengths; this is an approximation and assumes that segments are rigid, introducing potential errors. Even if there is not a complete 3D validation of Inverse Dynamics as a function of speed in the human gaits, Inverse and Direct Dynamics are often used interchangeably. In the first part of the thesis Inverse and Direct Dynamics in the human locomotion repertoire were compared in order to analyse different models, based on different anthropometric tables, and validate Inverse Dynamics. BCoM trajectory in walking, running and skipping is well described by Inverse Dynamics models employing a whole body marker set, where the main body segments are considered for BCoM calculation. On the contrary, simplified estimation models employing few markers, such as just one marker on the trunk or the mean of the pelvis, poorly match Direct Dynamics trajectory. Same results come from the further analysis of muscular work, where whole body models better describe and match Direct Dynamics data. Some interesting observations emerged from these analyses: i) two anthropometric tables with quite different segments definition reach the same results; ii) whole body models of Inverse Dynamics well matched Direct Dynamics values, validating this methods, whereas poor models should not be employed anymore; iii) the difference between Inverse and Direct Dynamics in the same gait is almost speed independent highlighting a systematic error, and among gaits it shows the same trend; iv) race walking BCoM trajectory cannot be described with any Inverse Dynamics models, therefore only ground reaction forces should be used for computation. Skipping is the third paradigm of human locomotion. Differently from walking and running, it was only investigated on level ground, addressing the much expensive cost of transport as the reason for its under use in day life activity; conversely it was displayed by astronauts of Apollo missions on the Moon. In the second part of this thesis the mechanics and bioenergetics of skipping on gradient was investigated since Ed Mitchell during Apollo 14 mission explicitly said “That nice skipping gait that I liked was very easy to do going downhill”. Gradient range was ±15%, the range of gradient presents on the Moon. On Earth skipping cost is higher than walking and running at all gradients and it decreases with speed, differently from the other gaits no minimum was found during downhill skipping, and it is impossible to skip at positive gradient steeper than 5% due to muscular demand and consequent fraction of metabolic power. When analysing mechanical parameters, the work done by muscles to move BCoM (WEXT) and the work done to accelerate limbs with respect to BCoM (WINT), skipping changes are similar to running with WEXT decreasing with downhill gradient and increasing speed, whereas WINT increases with speed. These results show that skipping on gradient can be performed on Earth only downhill due to the great metabolic demand. However, skipping cost of transport is always higher than walking and running at the same slopes. Based on these findings and astronauts’ choices, we could expect that gravity plays an important role on skipping and locomotion cost of transport, which are analysed and discussed in the third part of this thesis. Low gravity locomotion can be studied on Earth with different methods, the gold standard is the parabolic flight, since with the adequate angle of the airplane parabola it is possible to obtain gravity levels ranging from hypo-gravity (including 0 g) to hyper-gravity. However the time available at low gravity simulation is only about 30 seconds, which is too short for metabolic measurements. The second most used method is based on the body weight suspension, where subjects are unloaded of the desired body weight by the suspension of the body via bungee cords or springs. We re-vamped the Margaria’s low- gravity ‘cavedium’ with a treadmill and two bungee cords free to stretch until 16 m and let subjects walk, run and skip on a range of speed with Moon and Mars gravity, in order to study cost of transport and biomechanical parameters. Walking range of speed decreases with gravity and cost of transport decreases by 18% in hypo-gravity; higher decrements are shown in bouncing gaits, running and skipping. On the Moon their cost is the same and comparable with terrestrial walking values. Being on Earth was almost 40% higher than running, skipping shows the best decrease and a threefold gain in operative speed. This means that on the Moon human can skip three times faster than on Earth with the same metabolic power, whereas running gain is only twofold. Mechanically these cost changes can be explained by a reduction in pendulum-like recovery of energy in walking that needs a higher muscular work, whereas in skipping it is not shown. Moreover WEXT is lower in low gravity and a greater reduction of WINT in skipping compared with running can partially explain the major reduction in skipping cost. Another interesting aspect related to gait mechanics regards stability, and when the surface is slippery, as on the Moon due to regoliths, balance during support phase becomes an important issue. Skipping, compared to running, involves a shorter stance phase and also a double support, in which the trajectory of the flight can be adjusted. Moreover higher vertical forces on the ground and a greater angle at take off let the foot to be less slippery when pushing the body forward. Based on this biomechanical and bioenergetics analyses it can be concluded that human locomotion on hypo-gravity planets will be a bouncing gait and probably skipping could be preferred to running. Secondly the decrease of skipping cost up to walking values on Earth can explain the astronauts’ choice of skipping during Apollo missions
La marcia
No full textLa marcia fa la sua comparsa ai Giochi Olimpici di Londra nel 1908. La sua andatura è caratterizzata da particolari adattamenti biomeccanici del passo. Nel corso degli anni la velocità di gara è notevolmente aumentata. Viene analizzato dapprima il trend della velocità dei migliori atleti negli ultimi venti anni, in seguito, è discusso alla luce di due maggiori cambiamenti avvenuti nella metodologia dell’allenamento. Infine, sono presentati i dati relativi alla “pacing strategy” nelle due distanze di gara: la venti e la cinquanta chilometr
Skipping as the gait of choice in hypo-gravity : metabolic and biomechanical insights from level and gradient experiments on Earth
No full textStudies from Cavagna and Margaria, and more recently from our research group, demonstrated the dynamical limits of walking and running when moving in low gravity. We also studied ‘skipping’ (i.e. the placement of two successive feet on the ground followed by the flight), a gait displayed by kids, rarely by adults (but frequently by lemurs), which has the biomechanical potential to be used as the gait of choice in those conditions, as witnessed by astronauts of Apollo missions who spontaneously adopted it to move faster on the Lunar surface. In preparation to simulated and ‘real’ hypo-gravity experiments on this gait, we present here the extension of previous knowledge about skipping on Earth, focusing on the gradients most commonly found on the Moon. We used metabography to assess
metabolic cost of transport and 3D motion analysis to elucidate mechanical aspects of that locomotion type. The results confirm at all gradients the higher (average) ground reaction force during the contact phase, with respect to running at the same speed, which would allow to confidently face the Lunar and Martian surface where the dust and regoliths affect, in addition to a lower gravity, the locomotion dynamics. Skipping is confirmed to imply a higher metabolic cost than ‘normal’ locomotion for humans, a problem that would be mitigated by the lower body weight in hypo-gravity conditions
The 3D trajectory of the body centre of mass and other mechanical aspects of race walking
No full textRace Walking (RW) athletes are required to have always at least one foot in contact with the ground. While coded as a variety of ‘walking’ (W), potential and kinetic energy of the body centre of mass (BCoM) are in phase as in running (R). Aims of this work were to measure the 3D BCoM trajectory, in order to check the resemblance with W or R, and its speed dependence. 16 athletes were tested on treadmill and on 5 force platforms at different speeds by using both direct and inverse dynamics techniques. On treadmill BCoM was computed from the kinematics of 11 rigid segment model, sampled by 8 Vicon MX cameras at 300Hz. The RW trajectory was found to be different both from W, with the lowest position reached at single mid-support and the highest one during double support, and from R, since left and right semi-trajectories do not meet at their top. Also, RW trajectory has a smaller vertical excursion than in R, as a result of the discipline constraint. Symmetry indices (one for each spatial axis) of BCoM kinematics on the treadmill are greater and more consistent in RW than in W or R, witnessing the high athletic level of the participants. The trajectories from inverse dynamics were found to be differently shaped and wider than from the direct dynamics (the golden standard) due to the 3D position bias of BCoM induced by RW peculiar hip movement. A methodological study will be designed to minimize that bias by optimizing the marker set used to measure the trunk movement
Race walking angular displacement at increasing speed
No full textAim: The aim of this study was to describe the angular displacements during race walking (RW) in the three planes of motion and at incremental speeds. In fact, in the literature RW angles have been mostly described, focusing on few speeds and sagittal plane of motion.1
Method: 15 athletes race-walked on a treadmill at incremental speed (2.78 – 4.73 m/s). Kinematic data were recorded at 300 Hz (Vicon MX) by using an 18 markers biomechanical model defining 11 anatomical segments (trunk, arm, forearm, tight, shank, foot). Angular displacement was computed frame by frame and its values at heel strike (HS), midstance (MID) and toe off (TO) were highlighted.
Results: Angular displacement in the frontal plane: leg was adducted at HS increasing its angle until MID; adduction started during swing after the sagittal knee extension. The pelvis was in the neutral position at HS, and after a flexion until MID, it extended back to neutral position at TO; during swing phase a specular displacement was shown. The 'shoulder' tilt showed a pattern comparable with pelvic tilt, but flexing in the contralateral side. The arm range of motion was about 30°, starting with an abducted position at HS and reaching the maximal abduction value at TO. The elbow was adducted at HS, abducting during stance with a plateau before TO, before being adducted again.
Transverse plane: hip was forward rotated at HS and moved backward during stance reaching a minimum/maximum before TO, while the maximum/minimum was before HS. The shoulder was rotate forward at HS, and rotated backward until TO passing through a neutral position at MID. The angle between the upper and lower trunk reached similar maximal values at HS and TO, whereas it was null at MID. The arm angle showed an asymmetrical pattern, and a higher value at TO than at HS.
Sagittal plane: Ankle, knee and hip angles were similar to those reported in the literature. Trunk was in the neutral position at HS, then flexed forward until TO and extended back to HS. The arm was in the most posterior position at HS (of the contralateral leg) still extended at MID, and flexed at HS. The extension was almost three times the flexion. Elbow was flexed at HS, during first stance it extended with maximum at MID, then flexed again to neutral position at TO (neutral position = 90°).
Conclusion: Speed influenced angular displacements anticipating their pattern with relation to a reduced stance time phase. No significant changes of angular maximal values between speeds were measured with few exceptions between the slowest and fastest speeds. Finally the further calculation of the angular displacements in the frontal and transverse plane exhibit a comprehensive description of RW kinematics, which seems to be necessary for some angles such as arm and pelvi
L’effetto della velocità e del livello prestativo sulla tecnica di marcia
No full textLa marcia è una disciplina dell’atletica regolamentata da due vincoli locomotori piuttosto peculiari: il ginocchio deve essere bloccato dal primo contatto del piede a terra fino alla verticale e l’assenza di fase di volo tra i passi durante tutta la durata della competizione. Per questa ragione la tecnica è definita un parametro determinante la prestazione dell’atleta. Tuttavia, un’analisi quantitativa completa della cinematica della marcia in un ampio spettro di velocità è ancora mancante, limitando perciò la conoscenza e l’allenamento dei parametri chiave per migliorare la tecnica. Lo scopo di questo studio è di descrivere la cinematica della marcia a diverse velocità e di analizzarne le differenze in atleti di livello prestativo differente (regionale, nazionale e internazionale). Quindici atleti hanno marciato su di un nastro trasportatore a velocità incrementali (da 2,78 m/s fino a esaurimento). L’analisi cinematica sui tre piani di movimento è stata acquisita mediante un sistema optoelettronico a 300 Hz. I risultati hanno mostrato che l’ampiezza, la frequenza del passo e il tempo di volo aumentano linearmente con la velocità, ma l’ampiezza del passo è il maggior determinante per incrementare la velocità. L’analisi angolare ha mostrato che l’incremento della velocità porta a un’anticipazione del movimento senza alterare i valori di picco angolare, un’evidenza della standardizzazione imposta dalla regola. L’unica differenza riscontrata tra gli atleti di differente livello prestativo riguarda la massima velocità raggiunta: 4,97±0,25 m/s internazionali; 4,61±0,14 m/s nazionali e 4,22±0,14 m/s regionali. In conclusione, la tecnica non cambia al variare della velocità, è solo eseguita in un tempo inferiore, e non è la discriminante del livello prestativo degli atleti. Studi futuri che combinino fattori metabolici, elettromiografici e cinematici sembrano necessari per indagare più approfonditamente i fattori determinanti il livello prestativo
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