Biomedical subjects

R C Woledge

Publications and source records attributed to R C Woledge.

At least 19 recordsLinked to original sources

PubMed2000

Energy storage by passive elastic structures in the mantle of sepia officinalis.

The passive elastic properties of the mantle of the cuttlefish Sepia officinalis have been characterized in experiments on intact mantle and on pieces cut from the mantle. The mantle was found to be very compliant over a wide range of circumferential strains, corresponding to a change in mantle circumferential strain of 0.45. Beyond this range of strain, the mantle was much stiffer, in both the circumferential direction, 0.542+/-0.025 MPa (mean +/- s.e.m., N=51) and through the thickness of the mantle wall, 0.152+/-0.041 MPa (N=11). Almost 80 % of the work done on the tissue during compression in the circumferential direction was recovered during elastic recoil of the tissue; this elastic work could contribute to refilling the mantle after a jet. Our estimates of the work done during a cycle of jetting and refilling show that such elastic work is small (approximately 1 %) compared with the contractile work done by the circular muscle fibres. However, although the elastic work is almost negligible in the overall energy budget, it is probably sufficient to power refilling of the mantle.

Animals↗

PubMed2000

Heat production and oxygen consumption during metabolic recovery of white muscle fibres from the dogfish Scyliorhinus canicula.

Oxygen consumption and heat production were measured during contraction and recovery of isolated, white muscle fibres from dogfish (Scyliorhinus canicula) at 19 degrees C. The contraction period consisted of 20 isometric twitches at 3 Hz; this was followed by a recovery period of 2 h without stimulation. We tested the hypothesis that recovery is wholly oxidative (not glycolytic) in these fibres. The following features support this hypothesis. (i) The ratio of total heat produced to oxygen consumed, 451+/-34 kJ mol(-)(1) (mean +/- s.e.m., N=29), was close to that expected for either the oxidation of carbohydrate, 473 kJ mol(-)(1), or the oxidation of fat, 439 kJ mol(-)(1). Even assuming the maximum value (95 % confidence limit) of the observed heat production, glycolysis could account for resynthesis of at most 18 % of the ATP used during the contractions. (ii) When the difference in rates of diffusion of oxygen and heat within the muscle are taken into account, the time courses of oxygen consumption and heat production match each other well during the entire recovery period. The efficiency of recovery (=energy used for ATP synthesis/energy available for ATP synthesis) was estimated from the results. This value, 84.0+/-20.1 % (mean +/- s.e.m., N=29), is relatively high and represents the first such measurement in functioning muscle.

Animals↗

PubMed2000

Heart rate and its variability change after the menopause.

Resting heart rate and heart rate variability of 33 postmenopausal women were compared with those of 50 premenopausal women of comparable activity level, none of whom had used hormone replacement therapy. Heart rate was measured as the mean of at least 600 consecutive R-R intervals obtained from electrocardiograph (ECG) records, and its variability as the standard deviation of these intervals. Activity levels were assessed by a scale modified from the Allied Dunbar National Fitness Survey (1992). There was a significant reduction in both mean R-R interval and the standard deviation in the postmenopausal women who had experienced their last menstrual period (LMP) 1 year or more prior to the observations being made, but no observable changes during the first year post menopause.

Adult↗

PubMed1999

Hormone replacement therapy increases isometric muscle strength of adductor pollicis in post-menopausal women.

A randomized open trial of hormone replacement therapy was used to assess changes in adductor pollicis muscle strength during 6-12 months of treatment with Prempak C 0.625(R) in comparison with an untreated control group. Muscle strength (maximal voluntary force; MVF), muscle cross-sectional area and bone mineral density were measured. Women entering the trial had oestrogen levels below 150 pmol.l-1, confirming their post-menopausal hormonal status. In the treated group, MVF increased by 12.4+/-1.0% (mean+/-S.E.M.) of initial MVF over the duration of treatment, while it declined slightly (2.9+/-0.9%) in the control group. This increase in strength could not be explained by an increase in muscle bulk, there being no significant increase in cross-sectional area during the study. Those subjects who were weakest at enrolment showed the greatest increases in muscle strength after treatment. Bone mineral density in total hip, Ward's triangle and total spine increased in the treated group, in agreement with previous studies. There was no correlation between the individual increases in bone mineral density and those in MVF.

Analysis of Variance↗

PubMed1998

Changes in isometric force of mouse soleus muscle during the oestrous cycle.

Muscles excised from young female mice at known phases of the oestrous cycle were studied in vitro to determine if there are variations in force analogous to those that occur in vivo during the menstrual cycle in women. Oestrous phase was determined from vaginal smears. The maximum isometric and eccentric forces of pairs of isolated soleus muscles were measured. The first muscle was studied immediately after dissection, the second after incubation in Ringer solution for up to 2 h. Normalised isometric muscle force in the first muscle of each pair depended on the oestrous phase, the force being greatest during dioestrus. There was a negative correlation between normalised force and the eccentric/isometric force ratio. Neither of these phenomena was found with the second muscle of each pair. These results show that in mouse soleus muscle cross-bridge function does vary according to the phase of the oestrous cycle. However, the rise in force does not follow the pattern of the rise in blood oestrogen levels as it does in humans, and in the mouse the effect on cross-bridge function washes out after a few hours in vitro.

Animals↗

PubMed1998

Contraction with shortening during stimulation or during relaxation: how do the energetic costs compare?

White muscle fibres from dogfish were used to compare the energetic costs of shortening by fully active muscle and by relaxing muscle. The muscle preparation was tetanized for 0.6 s and shortened either during stimulation or during relaxation. The distance shortened was 1 mm (about 15% L0, the muscle length optimum for force) and the velocity was 3.5 or 7.0 mm s-1 (about 15 or 30% V0, the maximum velocity of shortening). Isometric tetani at L0 were also investigated. Mechanical work and heat production were measured, and work + heat was taken as a measure of energetic cost. Both work and the energetic cost were higher with shortening during stimulation than with shortening during relaxation. The results suggest that shortening during relaxation, which is known to occur during locomotion in vivo, may be an energy-saving strategy.

Adenosine Triphosphatases↗

PubMed1998

Possible effects of fatigue on muscle efficiency.

The efficiency of energy transduction is defined as the ratio of the work done by a muscle to the free energy change of the chemical processes driving contraction. Two examples of the experimental measurement of muscle efficiency are: (1) the classical method of Hill which measures the value during a steady state of shortening, (2) measuring the overall efficiency during a complete cycle of a sinusoidal process, which comes closer to the situation during natural locomotion. The reasons why fatigue might lower efficiency are the following. (1) The reduction in PCr concentration and increase in Pi and Cr concentration which are characteristic of fatigued muscle, reduce the free energy of PCr splitting. This will reduce the efficiency of the recovery process. It is not known whether the efficiency of the initial process is increased to compensate. (2) There is a general conflict between efficiency and power output when motor units are chosen for a task or when the timing of activation is decided. During fatigue more powerful units have to be used to achieve a task which is no longer within the scope of less powerful units. (3) The slowing of relaxation that is sometimes found with fatigue may make it impossible to achieve the short periods of activity required for optimum efficiency during rapid cyclical movements. A reason why fatigue might increase efficiency is that muscles are thought to be more efficient energy converters when not fully activated than when fully active. Full activation is often not achieved in muscle which is considerably fatigued. Available observations do not allow us to find where the balance between these factors lies. The conclusion is thus that experiments of both the types discussed here should be performed.

Animals↗

PubMed1998

A study of force and cross-sectional area of adductor pollicis muscle in female hip fracture patients.

OBJECTIVES: To determine the extent of muscle weakness in older female hip fracture patients compared with healthy older and young women; to determine the extent to which this weakness is caused by a decline of the force produced per unit area of muscle rather than by a decline in muscle bulk; and to investigate the mechanism of the decline in force per unit area. DESIGN: This was an open study of three groups of subjects, two age matched older groups and one young group. SETTING: University College London, Royal Free Hospital, and St. Thomas's Hospital, London. PARTICIPANTS: Twenty-nine older female hip fracture patients (mean age 85.6 +/- 0.9 SEM), 18 healthy older women (mean age 84.7 +/- 1.2 SEM), and 43 young women (mean age 28.9 +/- 1.2 SEM). MEASUREMENTS: Adductor pollicis muscle maximum voluntary force (MVF) during isometric and pliometric contractions and cross-sectional area (CSA), body weight, height, and demi-span. RESULTS: Isometric MVF was lowest in the hip fracture group. In both older groups, isometric MVF and CSA were lower than in the young women. Only part of this weakness in the older groups could be explained by the smaller CSAs. The isometric force per unit area (MVF/CSA) was also lower in both older groups, the hip fracture patients again having the lowest values. Analysis of variance showed a significant difference between groups. The age-related declines in pliometric force were much less than the declines in isometric force. This resulted in an increase in the pliometric/isometric force ratio both for the hip fracture patients and for the healthy older women compared with that for young women. CONCLUSION: In comparison with the results from young women, the adductor pollicis muscles of female hip fracture patients were even weaker than those of healthy older women when normalized for muscle size. This decline in isometric MVF/CSA accounted for at least half of the overall weakness in the hip fracture patients. Inasmuch as pliometric force is maintained in situations where weakness is caused by a decline in the force produced per muscle cross-bridge, this is the likely mechanism of the declines in isometric MVF/CSA observed in this study.

Adult↗

PubMed1998

Predictions of the time course of force and power output by dogfish white muscle fibres during brief tetani.

The aim of this study was to identify the principal factors that determine the time course of force and power output by muscle during patterns of stimulation and movement similar to those during fish swimming. Fully activated, white muscle fibres isolated from dogfish Scyliorhinus canicula were used to characterize the force-velocity relationship of the contractile component (CC) and the stress-strain relationship of the passive, elastic component (SEC) in series with the CC. A simple model of the time course of crossbridge activation during brief contractions was devised. Using the mechanical properties of the CC and SEC and the activation time course, force and power were predicted for brief contractions with constant-velocity movement and also for brief contractions starting at various times during sinusoidal movement. The predicted force and power were compared with observations for these patterns of stimulation and movement. The predictions matched the observations well for the period during stimulation. Matching of force was much less good for some specific conditions during relaxation, the period during which force persists after the end of stimulation. If either the slow rise of activation or the SEC was omitted from the calculation, the predictions were poor, even during stimulation. Additional factors which may influence force are discussed. These include the after-effects of shortening and stretch, the variation of force during constant-velocity stretch and non-uniform behaviour within the muscle.

Animals↗

PubMed1998

Distinguishing metabolic heat from condensation heat during muscle recovery.

When a thermopile is used to measure the heat production of isolated muscle, the muscle is surrounded by gas saturated with water vapour, initially in equilibrium with the muscle. After contraction, the osmolarity of the muscle is raised so that it is no longer in equilibrium with the gas around it, and condensation will occur. When artificial muscles of known osmolarity were placed on a thermopile surrounded by gas in equilibrium with a solution of lower osmolarity, their temperature was found to be raised (by 102.7 mK osmol-1 l). This temperature increase was greatly reduced by covering the artificial muscle with a Teflon film. Experiments on living muscle from the dogfish Scyliorhinus canicula showed that muscle temperature was higher 2 min after a series of 20 twitches at 3 Hz if the muscle was not covered by Teflon than if it was covered. The Teflon covering did not diminish the muscle's contractile performance. We conclude that the condensation of water does contribute to the heat measured during the recovery period, but that when the muscle is covered by Teflon film condensation heat can largely be prevented so that only genuine metabolic recovery heat is produced.

Animals↗

PubMed1998

Muscle energetics during unfused tetanic contractions. Modelling the effects of series elasticity.

During an unfused tetanic contraction the contractile component stretches and then is stretched by the series elasticity in the muscle fibre during each tension oscillations. This causes the heat rate to increase, from increased metabolic rate, during the time when the contractile component is shortening. During the time when the contractile component is being stretched there is heat produced within the contractile component from dissipation of the work stored in the contractile component. A simulation is used to show that these effects are not negligible when the effects of shortening velocity on energy output rate is determined using unfused contraction. The overall effects resemble those that would be produced in a muscle if the effect of shortening velocity in accelerating the rate of cross-bridge cycling were reduced at low activation levels.

Animals↗

PubMed1998

Shortening during stimulation vs. during relaxation. How do the costs compare?

White muscle fibres from dogfish were used to investigate the energetic cost of shortening by fully active muscle and by relaxing muscle. The muscle preparation was tetanized for 0.6 s and shortened by 1 mm (about 15% L0) at 7 mm/s (about 30% V0) either during stimulation or during relaxation. Isometric tetani at L0 were also investigated. Mechanical work was calculated from force and length change. Work + heat was taken as a measure of energetic cost. Both work and energetic cost were higher for shortening during stimulation than during relaxation. We also evaluated separately the work and heat associated with the contractile component and with the series elastic component. Work stored in the series elasticity could be completely recovered as external work when the shortening occurred during relaxation.

Animals↗

PubMed1997

Mechanical and energy characteristics during shortening in isolated type-1 muscle fibres from Xenopus laevis studied at maximal and submaximal activation.

The mechanical and energy characteristics of isolated fast-twitch muscle fibres (type 1) of Xenopus laevis in isometric- and isovelocity contractions were measured at 20 degrees C. The fibres were stimulated at either 60 Hz or 20 Hz to produce contractions at different levels of activation. The high stimulation frequency gave fused contractions, while at the low stimulation frequency tension fluctuated. When maximum isometric force had been reached, the fibres were shortened by 10% of the fibre length at different velocities. At 60 Hz stimulation during shortening the rate of heat production increased above the isometric rate of heat production. At 20 Hz stimulation during shortening, however, the rate of heat production was not different from the isometric rate of heat production. Mechanical efficiency was the same at the high and low level of activation. The actomyosin efficiency (i.e. the mechanical efficiency corrected for "activation heat") was highest at the low level of activation. We conclude that in fast-twitch muscle fibres from X. laevis, actomyosin efficiency is highest for partially activated muscle. From a comparison of the present results with those obtained from a study of slow-twitch muscle fibres presented earlier, it is concluded that fast-twitch muscle fibres are less efficient than slow-twitch muscle fibres.

Actomyosin↗

PubMed1997

Interpreting the relation between force and cross-sectional area in human muscle.

The maximum force a muscle can produce depends on its cross-sectional area (CSA). However, the exact interpretation of this relationship has been a matter of controversy. Recently, the controversy has centered on whether the measurements are best correlated using regression analysis or ratio standards. Applying regression analysis to this problem implies that all the experimental error is in the measurement of force. Thus, confusion may arise by failure to take account of errors in the measurement of CSA. Using a statistical model, we show how regression analysis can be misleading as error is introduced into the measurement of CSA as well as that of force. Because neither the errors in force nor CSA can be quantified in the experimental situation, we conclude that ratio standards are less likely to mislead although the accuracy of the result depends on the degree of correlation between force and CSA in the muscle measured.

Biomechanical Phenomena↗

PubMed1997

Recovery after contraction of white muscle fibres from the dogfish Scyliorhinus canicula.

Recovery after contraction of white muscle fibres of dogfish was investigated using 31P-NMR and measurements of heat production. The muscle fibres were stimulated to perform either a single isometric tetanus or a series of brief isometric tetani; the NMR measurements showed that approximately half of the phosphocreatine (PCr) was used. The period of activity was followed by a recovery period without stimulation. Both NMR and heat measurements agreed in showing that recovery was very slow, requiring at least 60 min for PCr resynthesis and for the production of recovery heat. The NMR results showed that changes in intracellular pH and in the concentrations of PCr and intracellular phosphate (Pi) had very similar time courses. Intracellular pH moved in the alkaline direction during the period of activity and then returned monotonically during recovery. The non-phosphate buffer power was 13.0 +/- 3.1 mmol l-1 intracellular water per pH unit (N = 4, mean +/- S.E.M.). The results are consistent with the view that oxidative processes resynthesize PCr during recovery, which is slow because of the low mitochondrial content of these muscle fibres.

Animals↗

PubMed1997

A comparison of the activation of muscles moving the patella in normal subjects and in patients with chronic patellofemoral problems.

The activation of the oblique fibres of vastus medialis, the postero-lateral fibres of vastus lateralis, and rectus femoris was studied by surface electromyography, during the force development of a maximal isometric contraction, performed near full extension (20 degrees of flexion), by 49 patients with chronic patellofemoral problems and 20 normal subjects. In the normal subjects activation of oblique portions of the vasti was in advance of force rise, during the time for 80% tension development. In the patient group, however, the activation of these lagged behind force rise. Force rise was slower in the patients even though the contraction was generally pain free. In all groups the activation of these two sections of the muscle remained approximately synchronous, suggesting that they have a reciprocal action in controlling patellar position, disruption of which might contribute to patellofemoral problems.

Adult↗

PubMed1996

Changes in maximal voluntary force of human adductor pollicis muscle during the menstrual cycle.

1. Muscle strength of the adductor pollicis (AP) was studied throughout the menstrual cycle to determine whether any variation in force is similar to the known cyclical changes in ovarian hormones. Three groups of young women were studied: trained regularly menstruating athletes (trained), untrained regularly menstruating (untrained) and trained oral contraceptive pill users (OCU). In addition a group of untrained young men was studied as controls. 2. Maximum voluntary force (MVF) of AP was measured over a maximum period of 6 months. Ovulation was detected by luteinizing hormone measurements or change in basal body temperature. There was a significant increase in MVF (about 10%) during the follicular phase of the menstrual cycle when oestrogen levels are rising, in both the trained and untrained groups. This was followed by a similar in MVF around the time of ovulation. Neither the OCU nor the male subjects showed cyclical changes in MVF.

Adolescent↗

PubMed1995

Comparison of energy output during ramp and staircase shortening in frog muscle fibres.

1. We compared the rates of work and heat production during ramp shortening with those during staircase shortening (sequence of step releases of the same amplitude, separated by regular time intervals). Ramp or staircase shortening was applied to isolated muscle fibres (sarcomere length, 2.2 microns; temperature, approximately 1 degree C) at the plateau of an isometric tetanus. The total amount of shortening was no greater than 6% of the fibre length. 2. During ramp shortening the power output showed a maximum at about 0.8 fibre lengths per second (Lo s-1), which corresponds to 1/3 the maximum shortening velocity (Vo). For the same average shortening velocity during staircase shortening (step size, approximately 0.5% Lo) the power output was 40-60% lower. The rate of heat production for the same average shortening velocity was approximately 45% higher during staircase shortening than during ramp shortening. 3. The relation between rate of total energy output and shortening velocity was well described by a second order regression line in the range of velocities used (0.1-2.3 Lo s-1). For any shortening velocity the rate of total energy output (power plus heat rate) was not statistically different for staircase (step size, approximately 0.5% Lo) and ramp shortening. 4. The mechanical efficiency (the ratio of the power over the total energy rate) during ramp shortening had a maximum value of 0.36 at 1/5 Vo; during staircase shortening, for any given shortening velocity, the mechanical efficiency was reduced compared with ramp shortening: with a staircase step of about 0.5% Lo at 1/5 Vo the efficiency was approximately 0.2. 5. The results indicate that a cross-bridge is able to convert different quantities of energy into work depending on the different shortening protocol used. The fraction of energy dissipated as heat is larger during staircase shortening than during ramp shortening.

Acoustic Stimulation↗