An analysis of the rebound of the body in backward human running.

Step frequency and energy expenditure are greater in backward running than in forward running. The differences in the motion of the centre of mass of the body associated with these findings are not known. These differences were measured here on nine trained subjects during backward and forward running steps on a force platform at 3-17 km h(-1). In contrast to previous reports, we found that the maximal upward acceleration of the centre of mass and the aerial phase, averaged over the whole speed range, are greater in backward running than in forward running (15.7 versus 13.2 m s(-2), P=1.9×10(-6) and 0.098 versus 0.072 s, P=2.4×10(-5), respectively). Opposite to forward running, the impulse on the ground is directed more vertically during the push at the end of stance than during the brake at the beginning of stance. The higher step frequency in backward running is explained by a greater mass-specific vertical stiffness of the bouncing system (499 versus 352 s(-2), P=2.3×10(-11)) resulting in a shorter duration of the lower part of the vertical oscillation of the centre of mass when the force is greater than body weight, with a similar duration of the upper part when the force is lower than body weight. As in a catapult, muscle-tendon units are stretched more slowly during the brake at the beginning of stance and shorten more rapidly during the push at the end of stance. We suggest that the catapult-like mechanism of backward running, although requiring greater energy expenditure and not providing a smoother ride, may allow a safer stretch-shorten cycle of muscle-tendon units.

Running backwards: soft landing-hard takeoff, a less efficient rebound.

Human running at low and intermediate speeds is characterized by a greater average force exerted after 'landing', when muscle-tendon units are stretched ('hard landing'), and a lower average force exerted before 'takeoff', when muscle-tendon units shorten ('soft takeoff'). This landing-takeoff asymmetry is consistent with the force-velocity relation of the 'motor' (i.e. with the basic property of muscle to resist stretching with a force greater than that developed during shortening), but it may also be due to the 'machine' (e.g. to the asymmetric lever system of the foot operating during stance). Hard landing and soft takeoff-never the reverse-were found in running, hopping and trotting animals using diverse lever systems, suggesting that the different machines evolved to comply with the basic force-velocity relation of the motor. Here we measure the mechanical energy of the centre of mass of the body in backward running, an exercise where the normal coupling between motor and machine is voluntarily disrupted, in order to see the relevance of the motor-machine interplay in human running. We find that the landing-takeoff asymmetry is reversed. The resulting 'soft landing' and 'hard takeoff' are associated with a reduced efficiency of positive work production. We conclude that the landing-takeoff asymmetry found in running, hopping and trotting is the expression of a convenient interplay between motor and machine. More metabolic energy must be spent in the opposite case when muscle is forced to work against its basic property (i.e. when it must exert a greater force during shortening and a lower force during stretching).

Biomechanics of locomotion in Asian elephants.

Elephants are the biggest living terrestrial animal, weighing up to five tons and measuring up to three metres at the withers. These exceptional dimensions provide certain advantages (e.g. the mass-specific energetic cost of locomotion is decreased) but also disadvantages (e.g. forces are proportional to body volume while supportive tissue strength depends on their cross-sectional area, which makes elephants relatively more fragile than smaller animals). In order to understand better how body size affects gait mechanics the movement of the centre of mass (COM) of 34 Asian elephants (Elephas maximus) was studied over their entire speed range of 0.4-5.0 m s(-1) with force platforms. The mass-specific mechanical work required to maintain the movements of the COM per unit distance is approximately 0.2 J kg(-1) m(-1) (about 1/3 of the average of other animals ranging in size from a 35 g kangaroo rat to a 70 kg human). At low speeds this work is reduced by a pendulum-like exchange between the kinetic and potential energies of the COM, with a maximum energy exchange of approximately 60% at 1.4 m s(-1). At high speeds, elephants use a bouncing mechanism with little exchange between kinetic and potential energies of the COM, although without an aerial phase. Elephants increase speed while reducing the vertical oscillation of the COM from about 3 cm to 1 cm.

The bounce of the body in hopping, running and trotting: different machines with the same motor.

The bouncing mechanism of human running is characterized by a shorter duration of the brake after 'landing' compared with a longer duration of the push before 'takeoff'. This landing-takeoff asymmetry has been thought to be a consequence of the force-velocity relation of the muscle, resulting in a greater force exerted during stretching after landing and a lower force developed during shortening before takeoff. However, the asymmetric lever system of the human foot during stance may also be the cause. Here, we measure the landing-takeoff asymmetry in bouncing steps of running, hopping and trotting animals using diverse lever systems. We find that the duration of the push exceeds that of the brake in all the animals, indicating that the different lever systems comply with the basic property of muscle to resist stretching with a force greater than that developed during shortening. In addition, results show both the landing-takeoff asymmetry and the mass-specific vertical stiffness to be greater in small animals than in large animals. We suggest that the landing-takeoff asymmetry is an index of a lack of elasticity, which increases with increasing the role of muscle relative to that of tendon within muscle-tendon units.

Old men running: mechanical work and elastic bounce.

It is known that muscular force is reduced in old age. We investigate what are the effects of this phenomenon on the mechanics of running. We hypothesized that the deficit in force would result in a lower push, causing reduced amplitude of the vertical oscillation, with smaller elastic energy storage and increased step frequency. To test this hypothesis, we measured the mechanical energy of the centre of mass of the body during running in old and young subjects. The amplitude of the oscillation is indeed reduced in the old subjects, resulting in an approximately 20% smaller elastic recovery and a greater step frequency (3.7 versus 2.8 Hz, p=1.9x10(-5), at 15-17 km h(-1)). Interestingly, the greater step frequency is due to a lower aerial time, and not to a greater natural frequency of the system, which is similar in old and young subjects (3.6 versus 3.4 Hz, p=0.2). Moreover, we find that in the old subjects, the step frequency is always similar to the natural frequency, even at the highest speeds. This is at variance with young subjects who adopt a step frequency lower than the natural frequency at high speeds, to contain the aerobic energy expenditure. Finally, the external work to maintain the motion of the centre of mass is reduced in the old subjects (0.9 versus 1.2 J kg(-1) m(-1), p=5.1x10(-6)) due to the lower work done against gravity, but the higher step frequency involves a greater internal work to reset the limbs at each step. The net result is that the total work increases with speed more steeply in the old subjects than in young subjects.

Muscle work enhancement by stretch. Passive visco-elasticity or cross-bridges?

Tetanized frog muscle fibres subjected to ramp stretches on the plateau of the tension-length relation, followed by an isotonic release against a load equal to the maximum isometric tension (T0), exhibit a well defined transient shortening against T0 which was attributed to the release of mechanical energy stored during stretching within the damped element of the cross-bridges. However, this interpretation has recently been challenged, and 'transient shortening against T0' has instead been attributed to elastic elements strained because of non-uniform distribution of lengthening within the fibre volume. The 'excess length change', resulting from the recoil of these elastic elements, was found i) to increase continuously with stretch amplitude up to 50 nm per h.s. with a 100 nm per h.s. strain, ii) to decrease steadily with the decrease in force during stress relaxation after the ramp stretch, and iii) to increase on the descending limb of the tension-length relation where sarcomere inhomogeneity is greater. In contrast, the transient shortening against T0: i) reaches a plateau at 8 nm per half sarcomere after about 50 nm per half sarcomere strain, ii) remains constant during the temperature dependent, fast phase of stress relaxation, when the excess in force above isometric reduces to about one half, iii) also occurs on the ascending limb of the tension-length relation where sarcomere inhomogeneity is drastically reduced. As a consequence of these differences we conclude that transient shortening and 'excess length change' do not "reflect the same underlying process".

[2 cases of Potter's syndrome]. / Due casi di sindrome di Potter.

In this report, we describe two patients with Potter's syndrome classical signs and take the opportunity to discuss about the etiopathogenetic hypothesis concerning various phenotypical expressions of that syndrome.

[Treatment of diaphragmatic paralysis in the newborn infant]. / Il trattamento della paralisi diaframmatica del neonato.

The paralysis of the diaphragm in the newborn is a rare pathological event. The "paradoxical movement" of the affected emidiaphragm can sometimes determine a important respiratory insufficiency. Medical treatment involves supplying oxygen, CPAP by means of a nasal cannula or mechanical ventilation with PEEP. Surgical plication of the affected emidiaphragm is recommended when a regular diaphragmatic function is not restored at 5-6 weeks of age and in the presence of serious respiratory insufficiency. Three cases are reported in this article which needed different therapeutical approaches.

[Hospital experience in active immunoprophylaxis against HBV]. / Esperienza ospedaliera di immunoprofilassi attiva anti HBV.

According to the Ministry of Health, at the paediatric section of Central Hospital of Rovigo, a vaccination campaign against HBV was undertaken in the year 1985 with the main purpose to reduce the sickness-rate and the mortality by HBV. Two vaccination patterns have been applied and they show to be efficient. 46 risk-subjects divided into two groups were vaccinated: group A: newborn, sons of women HBc Ag positive; group B: children living together with carriers or subjects sick of hepatitis B. The group A subjects had undergone to passive immunoprophylaxis at birth and to a vaccination cycle. The group B subjects only vaccination. The research of antibody titres produced by the vaccination demonstrated in the majority of cases greater than 121 IU/L. Only about 25% of vaccinated subjects showed a feeble movement of transaminases. The children's parents have cooperated very well.

[Prevalence of group B beta-hemolytic Streptococcus colonization in a sample of 23,312 pregnant women and newborn infants]. / La prevalenza della colonizzazione da streptococco beta-emolitico di gruppo B in un campione di 23.312 donne gravide e neonati.

We report the prevalence of colonization of Group B Streptococci in a given population referred to a limited area in the north-west of Italy. 23.312 pregnant women were tested. Group B Streptococci have been isolated from genital cultures in 0.18-13.2% (mean 8.18). The prevalence of Group B streptococcal colonization from ear, throat and ocular cultures of newborn infants from colonized mothers was 11.55%. Incidence of infection in neonates has varied from 0 to 2.33% (1.5 per 1000 live births).