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Biomedical subjects

R C Woledge

Publications and source records attributed to R C Woledge.

At least 19 recordsLinked to original sources
PubMed2006

Oestrogen status in relation to the early training responses in human thumb adductor muscles.

AIMS: The aims of this study were to identify the mechanisms for the early response to training in women of different oestrogen status and to determine whether any oestrogen and exercise effects on these would be additive. METHODS: We monitored training (ten 5-s contractions per day for 12 weeks)-induced changes in the size, strength, voluntary activation capacity and index of crossbridge force state (i.e. rapid stretch to isometric torque ratio), in the thumb adductor muscles of postmenopausal [eight who had never used, and 14 who were using, hormone replacement therapy (HRT)] and seven premenopausal eumenorrhoeic women. The contralateral untrained muscle was used as a control. RESULTS: There was a significant effect of oestrogen status on the magnitude of training-induced strength increment, with the non-HRT postmenopausal group exhibiting the greatest benefits (28 +/- 6%, P = 0.024) from training. There were no significant or commensurate changes in either cross-sectional area or voluntary activation capacity. The index of crossbridge force state improved most in the no-HRT group (19 +/- 7%, P < 0.05). CONCLUSIONS: Presence, rather than absence of oestrogen, is associated with relatively higher muscle function which limits the potential for any further training-induced increments in muscle performance, as would be expected if the muscle strengthening actions of training and oestrogen share a common, partially saturable physiological pathway. The mechanism that is involved in the early training-induced strength increment in the three differing oestrogen groups cannot be due to increased size or recruitment. It would appear instead that increased motor unit firing frequency is involved.

Adult↗
PubMed2003

Energy storage during stretch of active single fibres from frog skeletal muscle.

Heat production and force were measured during tetani of single muscle fibres from anterior tibialis of frog. During stimulation fibres were either kept under isometric conditions, or were stretched or allowed to shorten (at constant velocity) after isometric force had reached its plateau value. The energy change was evaluated as the sum of heat and work (work = integral of force with respect to length change). Net energy absorption occurred during stretch at velocities greater than about 0.35 L0 s-1 (L0 is fibre length at resting sarcomere length 2.10 microm). Heat produced by 1 mm segments of the fibre was measured simultaneously and separately; energy absorption is not an artefact due to patchy heat production. The maximum energy absorption, 0.092 +/- 0.002 P0L0 (mean +/- S.E.M., n = 8; where P0 is isometric force at L0), occurred during the fastest stretches (1.64 L0 s-1) and amounted to more than half of the work done on the fibre. Energy absorption occurred in two phases. The amount in the first phase, 0.027 +/- 0.003 P0L0 (n = 32), was independent of velocity beyond 0.18 L0 s-1. The quantity absorbed in the second phase increased with velocity and did not reach a limiting value in the range of velocities used. After stretch, energy was produced in excess of the isometric rate, probably from dissipation of the stored energy. About 34 % (0.031 P0L0/0.092 P0L0) of the maximum absorbed energy could be stored elastically (in crossbridges, tendons, thick, thin and titin filaments) and by redistribution of crossbridge states. The remaining energy could have been stored in stretching transverse, elastic connections between myofibrils.

Adenosine Triphosphate↗
PubMed2002

Isometric and isovelocity contractile performance of red muscle fibres from the dogfish Scyliorhinus canicula.

Maximum isometric tetanic force produced by bundles of red muscle fibres from dogfish, Scyliorhinus canicula (L.), was 142.4+/-10.3 kN m(-2) (N=35 fibre bundles); this was significantly less than that produced by white fibres 289.2+/-8.4 kN m(-2) (N=25 fibre bundles) (means +/- S.E.M.). Part, but not all, of the difference is due to mitochondrial content. The maximum unloaded shortening velocity, 1.693+/-0.108 L(0) s(-1) (N=6 fibre bundles), was measured by the slack-test method. L(0) is the length giving maximum isometric force. The force/velocity relationship was investigated using a step-and-ramp protocol in seven red fibre bundles. The following equation was fitted to the data: [(P/P(0))+(a/P(0))](V+b)=[(P(0)(*)/P(0))+(a/P(0))]b, where P is force during shortening at velocity V, P(0) is the isometric force before shortening, and a, b and P(0)(*) are fitted constants. The fitted values were P(0)(*)/P(0)=1.228+/-0.053, V(max)=1.814+/-0.071 L(0) s(-1), a/P(0)=0.269+/-0.024 and b=0.404+/-0.041 L(0) s(-1) (N=7 for all values). The maximum power was 0.107+/-0.005P(0)V(max) and was produced during shortening at 0.297+/-0.012V(max). Compared with white fibres from dogfish, the red fibres have a lower P(0) (49%) and V(max) (48%), but the shapes of the force/velocity curves are similar. Thus, the white and red fibres have equal capacities to produce power within the limits set by the isometric force and maximum velocity of shortening of each fibre type. A step shortening of 0.050+/-0.003L(0) (N=7) reduced the maximum isometric force in the red fibres' series elasticity to zero. The series elasticity includes all elastic structures acting in series with the attached cross-bridges. Three red fibre bundles were stretched at a constant velocity, and force (measured when length reached L(0)) was 1.519+/-0.032P(0). In the range of velocities used here, -0.28 to -0.63V(max), force varied little with the velocity.

Animals↗
PubMed2001

A variable inertial system for measuring the contractile properties of human muscle.

PURPOSE: A flywheel system of variable inertia is described for inferring the mechanical properties of human muscle during a single explosive movement. METHODS: The system consists of a lightweight aluminum disk mounted on a shaft onto which a driving cog is mounted. The inertia of the system can be varied from 0.024 to 0.69 kg.m(2) by attaching semicircular steel plates to the disk. A rotary encoder detects displacement of the wheel with a resolution of 1 degrees. Digital signals from the encoder are collected using an A/D converter interfaced to a PC. The data are then processed for the calculation of torque, velocity, power, work done, and acceleration. The mechanical properties of the muscles employed are inferred from calculations of flywheel displacement, time, and force. In addition, a pretension release mechanism can be incorporated into the system to allow isometric force to be developed before movement. This can increase power generation at the low inertias where the time of contraction is typically less than 200 ms. Seven subjects were test-retested using the device. Measures of both average and peak power were made. RESULTS: When mounted in the apparatus described by Bassey and Short, the maximum values for peak and average power were on average 965 +/- 103 and 448 +/- 47 W, respectively. Upon retesting, these results were found to be reliable (cv = 3.3% and 3.0%, respectively). CONCLUSIONS: The inertial system described has been shown to have validity in reproducibility and provided a suitable method of determining a number of muscle output properties during short-term single exertions. This tool could prove useful in a research or clinical setting and may also prove useful as a training device as it negates the need for a strain gauge or goniometer attachment.

Acceleration↗
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↗