Biomedical subjects

L P Ardigò

Publications and source records attributed to L P Ardigò.

10 recordsLinked to original sources

PubMed2006

Metabolic cost, mechanical work, and efficiency during walking in young and older men.

AIM: To investigate mechanical work, efficiency, and antagonist muscle co-activation with a view to better understand the cause of the elevated metabolic cost of walking (C(W)) in older adults. METHODS: Metabolic, mechanical and electromyographic measurements were made as healthy young (YOU; n = 12, age = 27 +/- 3 years) and older (OLD; n = 20, age = 74 +/- 3 years) men of equivalent body mass and leg length walked on a treadmill at four speeds (ranging from 0.83 to 1.67 m s(-1)). RESULTS: Net (above resting) C(W), determined by indirect calorimetry was 31% higher (average across speeds) in OLD (P < 0.05). The integrity of the passive pendulum like interchange of mechanical energies of the centre of mass (COM(B)), an energy-saving mechanism, was maintained in OLD. Furthermore, total mechanical work, determined from fluctuations in mechanical energy of COM(B) and of body segments relative to COM(B), was not significantly elevated in OLD. This resulted in a lower efficiency in OLD (-17%, P < 0.05). Co-activation, temporally quantified from electromyography recordings, was 31% higher in OLD for antagonist muscles of the thigh (P < 0.05). Thigh co-activation was moderately correlated with C(W) at three speeds (r = 0.38-0.52, P < 0.05). CONCLUSION: Healthy septuagenarians with no gait impairment have an elevated C(W) which is not explained by an elevation in whole body mechanical work. Increased antagonist muscle co-activation (possibly an adaptation to ensure adequate joint stability) may offer partial explanation of the elevated C(W).

Adult↗

PubMed2003

The optimal locomotion on gradients: walking, running or cycling?

On 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.

Adult↗

PubMed2001

The transmission efficiency of backward walking at different gradients.

The specialized design of the bipedal system towards forward locomotion has been assessed by measuring the metabolic cost and the mechanical work of both forward and backward walking on a treadmill at seven gradients from 0 to +32%. With respect to forward locomotion, backward walking implies: (1) a higher metabolic cost particularly at level gradient, while at steeper inclines the difference decreases, (2) the same mechanical internal work despite an increased stride frequency, (3) higher mechanical external work within a gradient range from 0 to +15%, (4) lower "energy recovery", i.e. the ability to save mechanical energy by moving as an inverted pendulum, mainly in level walking, and (5) as a consequence of the above results, a decrease of the efficiency of locomotion particularly at the 0% gradient. The transmission efficiency of backward walking, relative to the forward progression, was found to be about 65% in level locomotion, while at higher gradients it increased to and was maintained at a value of about 93%. The poorer economy of level backward walking could also be explained by an impaired elastic contribution in the last part of the double contact phase, while the similarity of the two gaits on higher gradients is caused by disruption of the pendulum-like paradigm due to the trajectory geometry of the body's centre of mass progressively losing its downward portion.

Adult↗

PubMed2000

Mechanical and metabolic profile of locomotion in adults with childhood-onset GH deficiency.

OBJECTIVE: 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 (GHD). SUBJECTS: Eight males with childhood-onset GHD (mean age+/-s.d.: 31.7+/-3.6 years; mean height: 145.1+/-6.7cm) 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 2-11km 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 8km 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.

Adult↗

PubMed1998

Using leg muscles as shock absorbers: theoretical predictions and experimental results of drop landing performance.

The use of muscles as power dissipators is investigated in this study, both from the modellistic and the experimental points of view. Theoretical predictions of the drop landing manoeuvre for a range of initial conditions have been obtained by accounting for the mechanical characteristics of knee extensor muscles, the limb geometry and assuming maximum neural activation. Resulting dynamics have been represented in the phase plane (vertical displacement versus speed) to better classify the damping performance. Predictions of safe landing in sedentary subjects were associated to dropping from a maximum (feet) height of 1.6-2.0 m (about 11 m on the moon). Athletes can extend up to 2.6-3.0 m, while for obese males (m = 100 kg, standard stature) the limit should reduce to 0.9-1.3 m. These results have been calculated by including in the model the estimated stiffness of the 'global elastic elements' acting below the squat position. Experimental landings from a height of 0.4, 0.7, 1.1 m (sedentary males (SM) and male (AM) and female (AF) athletes from the alpine ski national team) showed dynamics similar to the model predictions. While the peak power (for a drop height of about 0.7 m) was similar in SM and AF (AM shows a +40% increase, about 33 W/kg), AF stopped the downward movement after a time interval (0.219 +/- 0.030 s) from touch-down 20% significantly shorter than SM. Landing strategy and the effect of anatomical constraints are discussed in the paper.

Adult↗

PubMed1995

Metabolic and mechanical aspects of foot landing type, forefoot and rearfoot strike, in human running.

The study was undertaken to assess the metabolic and the mechanical aspects of two different foot strike patterns in running, i.e. forefoot and rearfoot striking (FFS and RFS), and to understand whether there is some advantage for a runner to use one or the other of the two landing styles. Eight subjects performed two series of runs (FFS and RFS) on a treadmill at an average speed of 2.50, 2.78, 3.06, 3.33, 3.61, 3.89, 4.17 m s-1. Step frequency, oxygen uptake, mechanical work, and its two components, external and internal, were measured. No differences were found for step frequency, mechanical internal work per unit time and oxygen uptake, while external and total mechanical work per unit time were significantly higher, 7-12%, for FFS. The higher external work was the result of an increase of the work performed against both gravitational and inertial forces. As the energy expenditure was the same it has been speculated that a higher storage and release of energy takes place in the elastic structures of the lower leg with FFS. In a different series of experiments on six subjects contact time, time of deceleration and time of acceleration were measured by means of a video camera while running on the treadmill at 2.50, 3.33 and 4.17 m s-1, both FFS and RFS. Time of deceleration is similar for FFS and RFS, but contact time and time of acceleration are shorter, respectively 12 and 25%, for FFS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Pygmy locomotion.

The hypothesis that Pygmies may differ from Caucasians in some aspects of the mechanics of locomotion was tested. A total of 13 Pygmies and 7 Caucasians were asked to walk and run on a treadmill at 4-12 km.h-1. Simultaneous metabolic measurements and three-dimensional motion analysis were performed allowing the energy expenditure and the mechanical external and internal work to be calculated. In Pygmies the metabolic energy cost was higher during walking at all speeds (P < 0.05), but tended to be lower during running (NS). The stride frequency and the internal mechanical work were higher for Pygmies at all walking (P < 0.05) and running (NS) speeds although the external mechanical work was similar. The total mechanical work for Pygmies was higher during walking (P < 0.05), but not during running and the efficiency of locomotion was similar in all subjects and speeds. The higher cost of walking in Pygmies is consistent with the allometric prediction for smaller subjects. The major determinants of the higher cost of walking was the difference in stride frequency (+9.45, SD 0.44% for Pygmies), which affected the mechanical internal work. This explains the observed higher total mechanical work of walking in Pygmies, even when the external component was the same. Most of the differences between Pygmies and Caucasians, observed during walking, tended to disappear when the speed was normalized as the Froude number. However, this was not the case for running. Thus, whereas the tested hypothesis must be rejected for walking, the data from running, do indeed suggest that Pygmies may differ in some aspects of the mechanics of locomotion.

Adult↗

PubMed1994

The transition between walking and running in humans: metabolic and mechanical aspects at different gradients.

Five subjects walked and ran at overlapping speeds and different gradients on a motorized treadmill. At each gradient the speed was obtained at which walking and running have the same metabolic cost (Sm) and the speed of spontaneous (Ss) transition between the two gaits was measured. Ss was found to be statistically lower than Sm at all gradients, the difference being in the range of 0.5-0.9 km h-1. The motion analysis of walking reveals that at all gradients and at increasing speed: (1) the percentage of recovery, an index of mechanical energy saving related to the pendulum-like characteristic of walking, decreases; (2) the lower limb spread reaches a limit in walking; and consequently (3) both the stride frequency and the internal mechanical work, due to limb acceleration in relation to the body centre of mass, increase much more in walking than in running. Switching to a run, although implying a higher frequency, makes the internal work decrease as a result of the lower limb spread. In this paper several influences, such as the 'ratings of perceived exertion' (RPE), on the choice of beginning to run when it is more economical to walk, are discussed. A tentative hypothesis on the determinants of Ss, which is emphasized to be a speed which has to be studied in detail but is generally avoided in locomotion, is based on a comfort criterion from peripheric afferences and is reflected by the fact that at Ss a running stride costs as much as a walking stride.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Mechanical determinants of the minimum energy cost of gradient running in humans.

The metabolic cost and the mechanical work of running at different speeds and gradients were measured on five human subjects. The mechanical work was partitioned into the internal work (Wint) due to the speed changes of body segments with respect to the body centre of mass and the external work (Wext) due to the position and speed changes of the body centre of mass in the environment. Wext was further divided into a positive part (W+ext) and a negative part (W-ext), associated with the energy increases and decreases, respectively, over the stride period. For all constant speeds, the most economical gradient was -10.6 +/-0.5% (S.D., N = 5) with a metabolic cost of 146.8 +/- 3.8 ml O2 kg-1 km-1. At each gradient, there was a unique W+ext/W-ext ratio (which was 1 in level running), irrespective of speed, with a tendency for W-ext and W+ext to disappear above a gradient of +30% and below a gradient of -30%, respectively. Wint was constant within each speed from a gradient of -15% to level running. This was the result of a nearly constant stride frequency at all negative gradients. The constancy of Wint within this gradient range implies that Wint has no role in determining the optimum gradient. The metabolic cost C was predicted from the mechanical experimental data according to the following equation: [formula: see text] where eff- (0.80), eff+ (0.18) and effi (0.30) are the efficiencies of W-ext, W+ext and Wint, respectively, and el- and el+ represent the amounts of stored and released elastic energy, which are assumed to be 55J step-1. The predicted C versus gradient curve coincides with the curve obtained from metabolic measurements. We conclude that W+ext/W-ext partitioning and the eff+/eff- ratio, i.e. the different efficiency of the muscles during acceleration and braking, explain the metabolic optimum gradient for running of about -10%.

Adult↗

PubMed1993

Mechanical determinants of gradient walking energetics in man.

1. The metabolic cost and the mechanical work at different speeds during uphill, level and downhill walking have been measured in four subjects. 2. The mechanical work has been partitioned into the internal work (W(int)), due to the speed changes of body segment with respect to the body centre of mass (BCM), and the external work (W(ext)), related to the position and speed changes of the BCM in the environment. 3. W(ext) has been further divided into a positive part W+ext) and a negative one (W-(ext)), associated with the energy increases and decreases, respectively, over the stride period. 4. For all constant speeds the most economical gradient has been found to be -10.2% (+/- 0.8 S.D.). 5. At each gradient there is a unique W+ext/W-ext ratio (= 1 in level walking), regardless of speed, with a tendency for W-ext and W+ext to vanish above +15% and below -15% gradient, respectively. 6. W(int) is constant at each speed regardless of gradient. This is partly explained by an only slight decrease in stride frequency at increasing gradient. W(int) constancy implies that it has no role in determining the optimum gradient. 7. A linear multiple regression relating W+ext and W-ext to the metabolic cost at different gradients showed that negative (eff-) and positive (eff+) efficiencies decrease with increasing speed (from 0.912 to 0.726, and from 0.182 to 0.146, respectively). The eff-/eff+ ratio, however, remains rather constant (4.995 +/- 0.125 S.D.). 8. We conclude that the measured W(ext), the W+ext/W-ext partitioning and eff-/eff+ ratio, i.e. the different efficiency of the muscles used as force and brake generators, can explain the metabolic optimum gradient at about -10%.

Adult↗