R. D. Woittiez

Influence of muscle architecture on the length-force diagram of mammalian muscle

The functions and geometrical characteristics of a pennate and a parallel-fibered muscle in rats are quantified and compared to each other. The pennate medial gastrocnemius and the more parallel fibered semimembranosus are investigated in fourteen male Wistar rats. The length force diagram, twitch time characteristics and muscle architecture are quantified.In the parallel fibered semimembranosus the length of the muscle fibres is about 70% of the muscle optimum length (the length at which the muscle performs maximal active force), while in the pennate fibered gastrocnemius the length of the muscle fibres is 36% of the muscle optimum length. The active length force diagrams normalized with respect to the muscle optimum length show considerable differences between semimembranosus and gastrocnemius: The normalized active length force diagram runs from about 71%–129% of the muscle optimum length for the semimembranosus and from about 82–118% for the gastrocnemius. The latter muscle also has a steeper normalized passive length force curve and produces more active tetanic force per gram muscle (877 g/g for gastrocnemius versus 379 g/g for semimembranosus).No differences between the semimembranosus and gastrocnemius are found with respect to the passive tension at twitch optimum length (38 g/cm2 versus 32 g/cm2), the maximal active tension (1.27 kg/cm2 versus 1.18 kg/cm2) and the twitch contraction time at twitch optimum length (43.8 ms versus 48.4 ms).It is concluded that several functional characteristics show a linear relationship with the index of architecture, a measure for the muscle architecture, while others (especially time and tension characteristics) are independent of muscle architecture.

Muscle economy of isometric contractions as a function of stimulation time and relative muscle length

For rat medial gastrocnemius muscle economy (i.e. the ratio of time integral of force and total energy-rich phosphate consumption) was calculated. Muscles in situ at 35°C were stimulated to perform either one continuous or several repetitive isometric contractions at one muscle length in the range from 70% to 130% of optimum muscle length for force generation. Whereas during one continuous contraction economy increased, no differences in economy were found between 6, 12 or 18 successive contractions. Economy during intermittent exercise was always lower than during continuous exercise. The difference in economy is a result of different rates of metabolism, whereas no difference was found for force generation. Economy was highest at optimum muscle length for force generation and decreased at muscle lengths smaller as well as greather than optimum muscle length. Force-dependent energy consumption was calculated by substracting the force-independent part (obtained by extrapolation) from total energy consumption. The calculated force produced per μmol force-dependent energy-rich phosphate consumption was similar in muscles stretched beyond optimum length. In contrast, a decreasing amount of force per μmol force-dependent energy-rich phosphate consumption was observed at lengths smaller than optimum length.

The instantaneous torque-angular velocity relation in plantar flexion during jumping

Torques, angular velocities, and power of the ankle joint during plantar flexion were measured in jumping experiments in order to achieve insight into shape and magnitude of the instantaneous torque-angular velocity relation in a complex movement. Twelve trained subjects performed maximal vertical jumps from a semi-squatting position with 100 degrees of flexion in the knee joint. Ground reaction force measurements and film analyses were used to calculate instantaneous torques, angular velocities, and power outputs during plantar flexion. The shape of the instantaneous torque-angular velocity was different from the well-known hyperbolic force-velocity relation for isolated muscles. Maximal power output (2499 +/- 751 [SD] W) occurred at 60% of the mean maximal torque (301 +/- 62 N X m) and 80% of the mean maximal angular velocity (970 degrees/s). The maximal power output was six times larger than the power output reported in the literature for maximal isokinetic (monoarticular) plantar flexions. Influences like storage of energy in the series elastic component of Hills muscle model and the role of polyarticular muscles in transporting energy from knee to ankle are discussed. It is concluded that many more selective studies will be necessary before it is possible to relate intrinsic muscle properties to the performance of muscles in poly-articular complex movements.

Influence of muscle architecture on the length-force diagram

The normalized active length-force diagram of the m. gastrocnemius medialis of the rat is extremely narrow as can be predicted on the basis of its architecture with the aid of a threedimensional muscle model.

Mechanical properties of passive rat muscle during sinusoidal stretching

The dynamic passive response of the left gastrocnemius medialis muscle of thirty male Wistar rats was studied as a function of muscle dimensions and absolute and relative amount of connective tissue. Values of the absolute active and passive length-force curves (active force, passive force, active working range) correlated well (coefficients of correlation in a range of 0.62–0.92) with morphological variables (such as muscle optimum length, mean muscle fibre optimum length, physiological cross section, muscle weight and amount of intramuscular connective tissue). To eliminate dimensional effects the active and passive length-force curves were normalized taking maximal active twitch force and muscle optimum length as reference values (100%). The width of the normalized active length-force curve (relative active working range) was correlated negatively with muscle weight, muscle optimum length and physiological cross section. Relative amount of connective tissue and passive tension at optimum length (both independent of muscle dimensions) were positively correlated, indicating that passive muscles are stiffer when relative amount of intramuscular connective tissue is higher. Sinusoidal movements with several amplitudes and frequencies of movement were imposed on the passive gastrocnemius medialis muscle over a range of muscle lengths. In accordance with the approximately exponential increase of static passive muscle force with length, muscle length has a large influence on the shape and magnitude of the hysteresis diagrams resulting from sinusoidal movements: the value of all variables selected increases approximately exponentially with muscle length with the exception of the value of loss tangent, a factor indicating the amount of energy dissipated during each cycle relative to the amount of energy stored and released elastically. Velocity of movement has only minor influence on variables of the hysteresis diagrams as is shown by changing the frequency of movement. As loss tangent and relative amount of connective tissue did not vary with muscle dimensions in the muscles studied, it is likely that material properties of the components causing passive resistance were similar in these muscles.

Twitch characteristics in relation to muscle architecture and actual muscle length.

The length dependence of twitch time characteristics is quantified for several skeletal muscles of the rat: lateral gastrocnemius, medial gastrocnemius, plantaris, soleus and semimembranosus. It is shown that muscle architecture influences the length dependent behaviour of twitch time characteristics of muscles. Twitch contraction time is less susceptible to length changes of the muscles than the twitch relaxation time. With the exception of the relaxation time in the second part of the relaxation, the twitch time characteristics behave different with respect to their dependence on fibre length, in fact muscles that differ in architecture.It is concluded that twitch time characteristics are dependent on the actual muscle length and therefore should be determined at a well defined length.

A multipurpose muscle ergometer

A fast (0.1 mm steps within 2 ms), strong (40 N continuously) and accurate (resolution 0.002 N and 1.0 micron) muscle ergometer was developed to test dynamic and static properties of mammalian muscle. Both for twitches and for tetani isometric, isokinetic and isotonic contractions can be measured accurately. Force-velocity data and time to peak-force data of four EDL muscles, as well as force-extension data of their serial tendinous structures are shown to demonstrate the machine.

Influence of muscle dimensions on economy of isometric exercise in rat medial gastrocnemius muscles in situ

SummaryThe effect of muscle dimensions on economy (force-time integral divided by the amount of energy utilized) was investigated in male rats (body mass range 95–490 g), anaesthetized with pentobarbital. The medial gastrocnemius muscle in situ performed 6 maximal isometric contractions of 350 ms duration (1 · s−1) at twitch optimum length at 35°C. The areas under the 6 time-force curves were added to obtain force-time integral of the experiment. Differences of concentrations of ATP, phosphocreatine and lactate between experimental and contralateral (resting) muscles were used to calculate high-energy phosphate consumption due to stimulation. Muscle mass and cross-sectional area increased (approximately +400% and +300%, respectively) over the rat body mass range studied. Muscle length and length of the most distal fibre bundle increased by approximately 17 mm and 4 mm, respectively. Force-time integral (N · s) increased proportional to cross-sectional area whereas high-energy phosphate consumption (μmoles) increased proportional to muscle mass. The relative fraction of the total energy consumption utilized for force-independent processes was independent of rat body mass. The economy of the actomyosin system was unaffected during growth, whereas economy of the whole muscle decreased during growth by approximately 30% (p<0.001). The effect of muscle dimensions on economy is discussed with respect to human endurance capacity measured by voluntary isometric contractions.

Inter-individual differences in the passive resistance of the human knee

Abstract The passive resistance of the knee to angular motion in the flexion-extension plane was investigated in groups of healthy males (n = 29) and females (n = 20). ‘Least square’ fitting procedures proved to be reliable for approximating the equilibrium angle of the knee and variables of the moment/angle diagrams. To assess the influence of the dimensions of the lower limb on the resistance of the knee, a multiple regression analysis was performed, using seven dimensional parameters of the lower limb. The results indicate that for males 35–77% (mean 58%) of the total variance is accounted for by the dimensional parameters. For females this range is 9–74% (mean 44%). Differences between males and females exist in all selected resistance variables. To decrease the influence of dimensional parameters, the slopes of the exponential curves relating moment and knee angle are expressed as percentages of the absolute moment values. When the values of these ‘relative slopes’ are used, differences between males and females become less in flexion and are absent when the knee is extended. These results indicate that male-female differences can partly be ascribed to differences in dimensions.

Passive Resistance of the Knee after Anterior Cruciate Ligament Reconstruction

In this study the data of dynamic mechanical tests were used as objective criteria to evaluate the results of a combined extra- and intra-articular reconstruction of the anterior cruciate ligament (ACL). With these tests the passive response of the knee and its surrounding tissues to sinusoidal strain in the flexion-extension plane was quantified.