Biomedical subjects

G A Cavagna

Publications and source records attributed to G A Cavagna.

At least 19 recordsLinked to original sources

PubMed2000

The role of gravity in human walking: pendular energy exchange, external work and optimal speed.

During walking on Earth, at 1.0 g of gravity, the work done by the muscles to maintain the motion of the centre of mass of the body (W(ext)) is reduced by a pendulum-like exchange between gravitational potential energy and kinetic energy. The weight-specific W(ext) per unit distance attains a minimum of 0.3 J x kg(-1) x m(-1) at about 4.5 km x h(-1) in adults. The effect of a gravity change has been studied during walking on a force platform fixed to the floor of an aircraft undergoing flight profiles which resulted in a simulated gravity of 0.4 and 1.5 times that on Earth. At 0.4 g, such as on Mars, the minimum W(ext) was 0.15 J x kg(-1) x m(-1), half that on Earth and occurred at a slower speed, about 2.5 km x h(-1). The range of walking speeds is about half that on Earth. At 1.5 g, the lowest value of W(ext) was 0.60 J x kg(-1) x m(-1), twice that on Earth; it was nearly constant up to about 4.3 km x h(-1) and then increased with speed. The range of walking speeds is probably greater than that on Earth. A model is presented in which the speed for an optimum exchange between potential and kinetic energy, the 'optimal speed', is predicted by the balance between the forward deceleration due to the lift of the body against gravity and the forward deceleration due to the impact against the ground. In conclusion, over the range studied, gravity increases the work required to walk, but it also increases the range of walking speeds.

Energy Metabolism↗

PubMed1999

Effect of stretching on undamped elasticity in muscle fibres from Rana temporaria.

Muscle stiffness was measured from the undamped elastic recoil taking place when the force attained during ramp stretches of muscle fibres, tetanized on the plateau of the tension-length relation, was suddenly reduced to the isometric value developed before the stretch, T0. Sarcomere elastic recoil was measured on a tendon-free segment of the fibre by means of a striation follower. After small ramp stretches, stiffness increases to a value 1.33x greater than that measured during release from a state of isometric contraction to 0.9 T0. While the relative increase in stiffness is equal to that reported for fibres of Rana esculenta (Piazzesi et al., 1992), the absolute value of stiffness measured during release from isometric contraction is just over half. As stretch amplitude is increased, on the plateau of the force-length relation, stiffness decreases toward the isometric value. This finding shows that the decrease in stiffness with large stretches cannot be due to a decrease in myofilament overlap (as may be the case when stretching occurs on the descending limb of the tension-length relation, Sugi & Tsuchiya, 1988), but must be due to an effect of the ramp stretch per se. For a given stretch amplitude, the after-stretch transient shortening against T0 taking place after the elastic recoil (which is expression of the work enhancement induced by stretching, Cavagna et al., 1986, 1994) is similar in fibres with very different stiffness of their undamped elastic elements. This suggests that this work enhancement is not due to the recoil of damped elastic structures recruited during stretching because of sarcomere length inhomogenity, a condition which would result in a decrease in stiffness (Morgan et al., 1996).

Animals↗

PubMed1998

Walking on Mars.

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Biomechanical Phenomena↗

PubMed1998

The mechanics of running in children.

1. The effect of age and body size on the bouncing mechanism of running was studied in children aged 2-16 years. 2. The natural frequency of the bouncing system (fs) and the external work required to move the centre of mass of the body were measured using a force platform. 3. At all ages, during running below approximately 11 km h-1, the freely chosen step frequency (f) is about equal to fs (symmetric rebound), independent of speed, although it decreases with age from 4 Hz at 2 years to 2.5 Hz above 12 years. 4. The decrease of step frequency with age is associated with a decrease in the mass-specific vertical stiffness of the bouncing system (k/m) due to an increase of the body mass (m) with a constant stiffness (k). Above 12 years, k/m and f remain approximately constant due to a parallel increase in both k and m with age. 5. Above the critical speed of approximately 11 km h-1, independent of age, the rebound becomes asymmetric, i.e. f < fs. 6. The maximum running speed (Vf, max) increases with age while the step frequency at remains constant (approximately 4 Hz), independent of age. 7. At a given speed, the higher step frequency in preteens results in a mass-specific power against gravity less than that in adults. The external power required to move the centre of mass of the body is correspondingly reduced.

Acceleration↗

PubMed1998

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".

Animals↗

PubMed1997

The resonant step frequency in human running.

At running speeds less than about 13 km h-1 the freely chosen step frequency (ffree) is lower than the frequency at which the mechanical power is minimized (fmin). This dissociation between ffree and fmin was investigated by measuring mechanical power, metabolic energy expenditure and apparent natural frequency of the body's bouncing system (fsist) during running at three given speeds with different step frequencies. The ffree requires a mechanical power greater than that at fmin mainly due to a larger vertical oscillation of the body at each step. Energy expenditure is minimal and the mechanical efficiency is maximal at ffree. At a given speed, an increase in step frequency above ffree results in an increase in energy expenditure despite a decrease in mechanical power. On the other hand, a decrease in step frequency below ffree results in a larger increase in energy expenditure associated with an increase in mechanical power. When the step frequency is forced to values above or below ffree, fsist is forced to change similarly by adjusting the stiffness of the bouncing system. However the best match between fsist and step frequency takes place only in proximity of ffree (2. 6-2.8 Hz). It is concluded that during running at speeds less than 13 km h-1 energy is saved by tuning step frequency to fsist, even if this requires a mechanical power larger than necessary.

Adult↗

PubMed1995

Energy-saving gait mechanics with head-supported loads.

In many areas of the world that lack a transportation infrastructure, people routinely carry extraordinary loads supported by their heads, for example the Sherpa of the Himalayas and the women of East Africa. It has previously been shown that African women from the Kikuyu and Luo tribes can carry loads substantially more cheaply than army recruits; however, the mechanism for their economy has remained unknown. Here we investigate, using a force platform, the mechanics of carrying head-supported loads by Kikuyu and Luo women. The weight-specific mechanical work, required to maintain the motion of the common centre of mass of the body and load, decreases with load in the African women, whereas it increases in control subjects. The decrease in work by the African women is a result of a greater conservation of mechanical energy resulting from an improved pendulum-like transfer of energy during each step, back and forth between gravitational potential energy and kinetic energy of the centre of mass.

Energy Metabolism↗

PubMed1995

External, internal and total work in human locomotion.

The muscle-tendon work performed during locomotion can, in principle, be measured from the mechanical energy of the centre of mass of the whole body and the kinetic energy due to the movements of the body segments relative to the centre of mass of the body. Problems arise when calculating the muscle-tendon work from increases in mechanical energy, largely in correctly attributing these increases either to energy transfer or to muscle-tendon work. In this study, the kinetic and gravitational potential energy of the centre of mass of the whole human body was measured (using a force platform) simultaneously with calculation of the kinetic and potential energy of the body segments due to their movements relative to the body centre of mass (using cinematography) at different speeds of walking and running. Upper and lower boundaries to the total work were determined by including or excluding possible energy transfers between the segments of each limb, between the limbs and between the centre of mass of the body and the limbs. It appears that the muscle-tendon work of locomotion is most accurately measured when energy transfers are only included between segments of the same limb, but not among the limbs or between the limbs and the centre of mass of the whole body.

Adult↗

PubMed1994

Storage and release of mechanical energy by contracting frog muscle fibres.

1. Stretching a contracting muscle leads to greater mechanical work being done during subsequent shortening by its contractile component; the mechanism of this enhancement is not known. 2. This mechanism has been investigated here by subjecting tetanized frog muscle fibres to ramp stretches followed by an isotonic release against a load equal to the maximum isometric tension, T(o). Shortening against T(o) was taken as direct evidence of an absolute increase in the ability to do work as a consequence of the previous stretch. 3. Ramp stretches (0.5-8.6% sarcomere strain, confined to the plateau of the isometric tension-length relationship) were given at different velocities of lengthening (0.03-1.8 sarcomere lengths s-1). Isotonic release to T(o) took place immediately after the end of the ramp, or 5-800 ms after the end of the largest ramp stretches. The length changes taking place after release were measured both at the fibre end and on a tendon-free segment of the fibre. The experiments were carried out at 4 and 14 degrees C. 4. After the elastic recoil of the undamped elastic elements, taking place during the fall in tension at the instant of the isotonic release, a well-defined shortening took place against T(o) (transient shortening against T(o)). 5. The amplitude and time course of transient shortening against T(o) were similar at the fibre end and in the segment, indicating that it is due to a properly of the sarcomeres and not due to stress relaxation of the tendons. 6. Transient shortening against T(o) increased with sarcomere stretch amplitude up to about 8 nm per half-sarcomere independent of stretch velocity. 7. When a short delay (5-20 ms) was introduced between the end of the stretch and the isotonic release, the transient shortening against T(o) did not change; after longer time delays, the transient shortening against T(o) decreased in amplitude. 8. The velocity of transient shortening against T(o) increased with temperature with a temperature coefficient, Q10, of approximately 2.5. 9. It is suggested that transient shortening against T(o) results from the release of mechanical energy stored within the damped element of the cross-bridges. The cross-bridges are brought into a state of greater potential energy not only during the ramp stretch, but also immediately afterwards, during the first phase of stress relaxation.

Animals↗

PubMed1993

Effect of temperature and velocity of stretching on stress relaxation of contracting frog muscle fibres.

1. Active muscle resists stretch with a tension greater than it can develop at constant length, but at the end of lengthening the extra tension disappears, at first rapidly and then more slowly. 2. This unexplained trend of muscle stress relaxation was studied at two different temperatures (4 and 14 degrees C) and after ramp stretches of different velocity (0.2-2.2 fibre lengths s-1) on frog muscle fibres near slack length. 3. The velocity of the fast fall in tension increases with temperature much more than that of the slow fall. In addition, the amplitude of the fast fall in tension increases with the velocity of stretching whereas that of the slow fall decreases. 4. It is hypothesized that some of the energy absorbed by the muscle during stretching is used to raise the chemical energy level of the cross-bridges, and this energy transfer occurs during and after stretching.

Animals↗

PubMed1991

The two power limits conditioning step frequency in human running.

1. At high running speeds, the step frequency becomes lower than the apparent natural frequency of the body's bouncing system. This is due to a relative increase of the vertical component of the muscular push and requires a greater power to maintain the motion of the centre of gravity, Wext. However, the reduction of the step frequency leads to a decrease of the power to accelerate the limbs relatively to the centre of gravity, Wint, and, possibly, of the total power Wtot = Wext + Wint. 2. In this study we measured Wext using a force platform, Wint by motion picture analysis, and calculated Wtot during human running at six given speeds (from 5 to 21 km h-1) maintained with different step frequencies dictated by a metronome. The power was calculated by dividing the positive work done at each step by the duration of the step (step-average power) and by the duration of the positive work phase (push-average power). 3. Also in running, as in walking, a change of the step frequency at a given speed has opposite effects on Wext, which decreases with increasing step frequency, and Wint, which increases with frequency; in addition, a step frequency exists at which Wtot reaches a minimum. However, the frequency for a minimum of Wtot decreases with speed in running, whereas it increases with speed in walking. This is true for both the step-average and the push-average powers. 4. The frequency minimizing the step-average power equals the freely chosen step frequency at about 13 km h-1: it is higher at lower speeds and lower at higher speeds. The frequency minimizing the push-average power approaches the freely chosen step frequency at high speeds (around 22 km h-1 for our subjects). 5. It is concluded that the increase of the vertical push does reduce the step-average power, but that a limit is set by the increase of the push-average power. Between 13 and 22 km h-1 the freely chosen step frequency is intermediate between a frequency minimizing the step-average power, eventually limited by the maximum oxygen intake (aerobic power), and a frequency minimizing the push-average power, set free by the muscle immediately during contraction (anaerobic power). The first need prevails at the lower speed, the second at the higher speed.

Biomechanical Phenomena↗

PubMed1988

The determinants of the step frequency in running, trotting and hopping in man and other vertebrates.

1. During each step of running, trotting or hopping part of the gravitational and kinetic energy of the body is absorbed and successively restored by the muscles as in an elastic rebound. In this study we analysed the vertical motion of the centre of gravity of the body during this rebound and defined the relationship between the apparent natural frequency of the bouncing system and the step frequency at the different speeds. 2. The step period and the vertical oscillation of the centre of gravity during the step were divided into two parts: a part taking place when the vertical force exerted on the ground is greater than body weight (lower part of the oscillation) and a part taking place when this force is smaller than body weight (upper part of the oscillation). This analysis was made on running humans and birds; trotting dogs, monkeys and rams; and hopping kangaroos and springhares. 3. During trotting and low-speed running the rebound is symmetric, i.e. the duration and the amplitude of the lower part of the vertical oscillation of the centre of gravity are about equal to those of the upper part. In this case, the step frequency equals the frequency of the bouncing system. 4. At high speeds of running and in hopping the rebound is asymmetric, i.e. the duration and the amplitude of the upper part of the oscillation are greater than those of the lower part, and the step frequency is lower than the frequency of the system. 5. The asymmetry is due to a relative increase in the vertical push. At a given speed, the asymmetric bounce requires a greater power to maintain the motion of the centre of gravity of the body, Wext, than the symmetric bounce. A reduction of the push would decrease Wext but the resulting greater step frequency would increase the power required to accelerate the limbs relative to the centre of gravity, Wint. It is concluded that the asymmetric rebound is adopted in order to minimize the total power, Wext + Wint.

Animals↗

PubMed1987

Mechanical work, oxygen consumption, and efficiency in isolated frog and rat muscle.

The total work done during shortening, in repeated stretch-shortening cycles and the subsequent recovery oxygen consumption were measured in isolated frog (Rana esculenta) sartorius at 12 degrees C and rat (Wistar strain) extensor digitorum longus (EDL) and soleus at 20 degrees C. Two procedures were followed. In the first, the muscles were lengthened in the relaxed state and stimulated isometrically just before and during the first part of shortening. The peak efficiency (positive work done divided by the energetic equivalent of the oxygen consumed) was approximately 25% at 0.75-1.5 muscle lengths/s (Lo/s) in sartorius, 19% at 1.0 Lo/s in EDL, and 15% at 0.5 Lo/s in the soleus. In contrast to the measured efficiency values, the ratio between the tension-time integral and the oxygen consumption (the economy) is greater in soleus than in EDL. In the second procedure, stimulation began before stretching and continued during the first part of shortening. In this case, the efficiency attained values of approximately 35% in sartorius, 50% in EDL, and 40% in soleus. These values are in rough agreement with those measured in vivo during running.

Animals↗

PubMed1986

The determinants of the step frequency in walking in humans.

The mechanical power spent during walking in lifting and accelerating the centre of mass, Wext, has been measured at three given speeds maintained at different step frequencies: at any given speed, Wext is smaller the greater the step frequency used. The mechanical power spent in accelerating the limbs relative to the centre of mass during walking at a given speed, but with different step frequencies, Wint, was calculated from previous data obtained during free walking (Cavagna & Kaneko, 1977). At a given walking speed, Wint increases with the step frequency. The total power, Wtot = Wext + Wint, reaches a minimum at a step frequency which is 20-30% less than the step frequency freely chosen at the same period. The step frequency at which Wtot is minimum increases with speed in a similar way to the natural step frequency during free walking.

Adult↗

PubMed1986

Mechanical transients initiated by ramp stretch and release to Po in frog muscle fibers.

Single fibers from the tibialis muscle of Rana temporaria were subjected to ramp stretches during tetanic stimulation at a sarcomere length of approximately 2 microns. Immediately after the stretch, or after different time delays, the active fiber was released against a constant force equal to the isometric force (Po) exerted immediately before the stretch. Four phases were detected after release: an elastic recoil of the fiber's undamped elements, a transient rapid shortening, a marked reduction in the velocity of shortening (often to 0), and an apparently steady shortening (sometimes absent). Increasing the amplitude of the stretch from approximately 2 to 10% of the fiber rest length led to an increase in phase 2 shortening from approximately 5 to 10 nm per half-sarcomere. Phase 2 shortening increased further (up to 14 nm per half-sarcomere) if a time interval of 5-10 ms was left between the end of large ramp stretches and release to Po. After 50- to 100-ms time intervals, shortening occurred in two steps of approximately 5 nm per half-sarcomere each. These findings suggest that phase 2 is due to charging, during and after the stretch, of a damped element, which can then shorten against Po in at least two steps of approximately 5 nm/half sarcomere each.

Animals↗

PubMed1985

Efficiency of vertebrate locomotory muscles.

We have examined the efficiency of vertebrate striated muscle at two different organizational levels: whole animals and isolated muscles. Terrestrial locomotion is used as a model of 'normal' muscular contraction; animal size and running speed are used as independent variables in order to change either the metabolic requirements of the muscles or the mechanical power production by the muscles over a wide range of values. The weight-specific metabolic power input to an animal increases nearly linearly with speed and increases with decreasing body size, while the weight-specific mechanical power output increases curvilinearly with speed and is independent of size. Consequently, the efficiency of the muscles in producing positive work increases with speed and the peak efficiency increases with increasing body size, attaining values of over 70% in large animals, but only 7% in small ones. The isolated muscle experiments were performed on frog muscle, and rat 'fast' and 'slow' muscles. We measured the work done, the oxygen consumed during recovery from the stimulation, and calculated the efficiency and the 'economy' (the cost of maintaining tension). The muscles were made to: (i) emulate the contractions seen during locomotion, i.e. shorten after a pre-stretch; or (ii) shorten at the same velocity and from the same muscle length as in (i), but without the pre-stretch. It was found that in mammalian muscles the peak efficiency with a pre-stretch attained high values, approaching the peak efficiencies in large animals. The maximum efficiency (attained at 1 length s-1 in fast muscle and at 0.5 lengths s-1 in slow muscle) did not differ much in the two muscles, whereas economy was greater in the slow muscle than in the fast muscle.

Animals↗

PubMed1985

Storage and release of mechanical energy by active muscle: a non-elastic mechanism?

In frog muscle fibres, tetanically stimulated at a sarcomere length of about 2 micron, stretched at a velocity of 1 lengths-1 and released against a force equal to the maximum isometric, P0, a phase of rapid isotonic shortening takes place after release. As the amplitude of the stretch is increased from 1.5 to 9% of the initial length: (1) the amount of rapid isotonic shortening increases up to 9-10 nm per half sarcomere and (2) the stiffness of the fibre (an indication of the number of bridges attached) decreases to a value about equal to that measured during an isometric contraction. If a 5-10 ms delay is left between the end of stretch and release, the amount of rapid isotonic shortening increases to about 12 nm hs-1. A 300-500 ms delay, however, results in a decrease in rapid isotonic shortening to about 5 nm hs-1 and also results in a velocity transients against P0 that are similar to those described during release from a state of isometric contraction. It is concluded that the force attained after large, fast stretches is due to a greater force developed by each bridge and not to a greater number of bridges. After the elastic recoil (when the force is suddenly reduced to P0), these strained bridges are able to shorten by about 12 nm hs-1, suggesting that, during and immediately after stretching, they are charged to levels of potential energy greater than those attained in an isometric contraction.

Animals↗

PubMed1983

The mechanics of walking in children.

The work done at each step, during level walking at a constant average speed, to lift the centre of mass of the body, to accelerate it forward, and to increase the sum of both gravitational potential and kinetic energies, has been measured at various speeds on children of 2-12 years of age, with the same technique used previously for adults (Cavagna, 1975; Cavagna, Thys & Zamboni, 1976). The pendulum-like transfer between potential and kinetic energies (Cavagna et al. 1976) reaches a maximum at the speed at which the weight-specific work to move the centre of mass a given distance is at a minimum ('optimal' speed). This speed is about 2 X 8 km/hr at 2 years of age and increases progressively with age up to 5 km/hr at 12 years of age and in adults. The speed freely chosen during steady walking at the different ages is similar to this 'optimal' speed. At the 'optimal' speed, the time of single contact (time of swing) is in good agreement with that predicted, for the same stature, by a ballistic walking model assuming a minimum of muscular work (Mochon & McMahon, 1980). Above the 'optimal' speed, the recovery of mechanical energy through the potential-kinetic energy transfer decreases. This decrease is greater the younger the subject. A reduction of this recovery implies a greater amount of work to be supplied by muscles: at 4 X 5 km/hr the weight-specific muscular power necessary to move the centre of mass is 2 X 3 times greater in a 2-year-old child than in an adult.

Adult↗