Effects of shortening velocity and of oxygen consumption on efficiency of contraction in dog gastrocnemius

Previous observations have shown that, in isolated perfused dog gastrocnemii in situ, stimulated to aerobic rhythmic isotonic tetanic contractions (at about 40% of maximal isometric force), only about 20% of the overall metabolic power (proportional to the rate of O₂ consumption, O₂) was converted into mechanical power (Ẇ). Here we report that, in the same preparation, the maximal velocity during the shortening phase of each tetanus (v, mm s^–1) increased with the rate of energy dissipation, as given by the difference between O₂ and Ẇ (W kg^–1). The relationship between these variables was described by: v=2.85(O₂–Ẇ)^1.24 (R ²=0.85; n=17). A mathematical analysis of this equation shows that the overall mechanical efficiency (=ẆO₂ ^–1) decreased with increasing v (at constant O₂), whereas it increased with increasing O₂ (at constant v). The net effect of this state of affairs was that the decrease of over the entire range of work intensities was relatively minor (from 0.22 to 0.15), in spite of a large increase of v, (from 40 to 120 mm s^–1), thanks to the concomitant increase of O₂ (from 10 to 25 W kg^–1). So, under these experimental conditions, the energetics of work performance seems to be governed by two conflicting needs. The need for a sufficiently high shortening speed (and hence power output), itself requiring a sufficiently large energy dissipation rate, which, however, brings about a fall in . This is counteracted by the increased O₂, which in turn leads to an increased efficiency at the expense of a fall in shortening speed.This article was published in Human Muscular Function during Dynamic Exercise, Marconnet P, Saltin B, Komi P, Poortmans J (eds) Med Sport Sci 41 (series editors: M. Hebbelink, R.J. Shephard) pp. 1–9, Karger, Basel, 1996. It is reproduced with minor editorial modifications. Permission from Karger is gratefully acknowledged.     

Oxygen consumption and metabolic strain in rowing ergometer exercise

Summary Oxygen consumption ( ) when rowing was determined on a mechanically braked rowing ergometer (RE) with an electronic measuring device. was measured by an open spirometric system. The pneumotachograph valve was fixed to the sliding seat, thus reducing movement artefacts. A multi-stage test was performed, beginning with a work load of 150 W and increasing by 50 W every 2 minutes up to exhaustion. Serum lactate concentrations were determined in a 30 s break between the work stages. 61 examinations of oarsmen performing at maximum power of 5 W · kg⁻¹ or more were analysed. and heart rate (HR) for each working stage were measured and the regression line of on the work load (P) and an estimation error (s_xy) were calculated: (ml · min⁻¹) (S_xy = ± 337 ml,r = 0.98) Good reproducibility was found in repeated examinations. Similar spiroergometry was carried out on a bicycle ergometer (BE) with 10 well trained rowers and 6 trained cyclists. of rowing was about 600 ml · min⁻¹ higher than for bicycling in the submaximal stages for both groups. The of RE exercise was 2.6% higher than for oarsmen on BE, and the cyclists reached a greater on BE than the oarsmen. No differences were found between RE and BE exercise heart rate. The net work efficiency when rowing was 19% for both groups, experienced and inexperienced: when cycling it was 25% for cyclists and 23% for oarsmen.     

Changes in mechanical work during severe exhausting running

The possible contribution of muscular work to the increase in oxygen uptake (O₂) over time during running was investigated on 11 adult males who were asked to run until exhaustion at 90 (3)% [mean (SD)] of their maximal aerobic velocity on a treadmill ergometer. Ground reaction forces, expired gases and EMG from leg muscles were collected for 30 s at min 3 and during the last minute of the run. Subjects ran for 829 (165) s and showed an increase in O₂ of 179 (93) ml.min^–1 between min 3 and exhaustion. Increased ventilation explained 41 (27)% of the increase in O₂. Stride frequency slightly decreased but no significant differences were found in the mechanical work or in integrated EMG. It was concluded that, in running, the increase in O₂ could not be related to a drift in muscle work.     

Activity of mono- and biarticular leg muscles during sprint running

Summary A cinematographic recording of the movements of the lower limbs together with simultaneous emg tracings from nine lower limb muscles were obtained from two male track sprinters during three phases of a 100 m sprint run. The extensor muscles of the hip joint were found to be the primary movers by acceleration of the body's center of gravity (C.G.) during the ground phase of the running cycle. The extensors of the knee joint were also important in this, but to a minor extent, while the plantar flexors of the ankle joint showed the least contribution. The biarticular muscles functioned in a way different from the monoarticular muscles in the sense that they perform eccentric work during the flight and recovery phases and concentric work during the whole ground phase (support), whereas the monoarticular muscles are restricted first to eccentric work and then to concentric work during the ground phase. Furthermore, the biarticular muscles show variation (and rate of variation) in muscle length to a larger extent than the monoarticular muscles. Paradoxical muscle actions appear to take place around the knee joint, where the hamstring muscles, m. gastrocnemius, m. vastus laterialis and m. vastus medialis act as synergists by extending the knee joint during the last part of the ground phase.     

The amplitude of the slow component of oxygen uptake is related to muscle contractile properties

During constant-load exercise above the lactate threshold, oxygen-uptake kinetics deviate from the pattern seen below the threshold, with an additional, delayed component superimposed on the monoexponential pattern. It was hypothesised that this slow component is due to the progressive recruitment of type II muscle fibres. Oxygen uptake was measured for six male power athletes (group P) and six male endurance athletes (group E) during constant-load knee extension exercise tests in order to determine slow component amplitude. In addition, an electrical stimulation protocol was employed in order to assess the functional contractile profile and fatiguability of the knee extensors. The amplitude of the slow component during exercise was significantly (P<0.05) greater in group P than in group E when expressed as an absolute value [mean (SEM)=77 (17) ml min^–1 and 24 (16) ml min^–1] and when normalised to end-exercise oxygen uptake,O₂ [8.2 (0.5)% and 2.6 (1.8)%]. Group differences were observed for percentage force loss during the electrical stimulation protocol [50.0 (3.4)% and 31.5 (3.7)% for groups P and E, respectively], increase in relaxation time from start to end of the fatigue test [87.9 (15.5)% and 31.1 (11.9)%], and relaxation time for fresh muscle [32.4 (1.0) ms and 40.6 (2.1) ms]. These contractile parameters may indicate a higher proportion of type II fibres in group P compared with group E. These experiments have shown evidence of a relationship between the amplitude of the slow component and muscle contractile properties, indicating that the origin of the slow component may lie in the pattern of different muscle fibre types.     

Effects of muscular biopsy on the mechanics of running

Muscle biopsy is a widely used technique in protocols aiming at studying physical capacities and fiber profiles of athletes, and muscular adaptations to exercise. Side effects of biopsy alone on physiological parameters have recently been pointed out, and we sought to determine whether a single biopsy had effects on the main stride mechanical parameters. Ten male runners performed 4-min runs before and after undergoing a biopsy of their left vastus lateralis muscle. Step frequency and duty factor were significantly higher after biopsy (2.86 ± 0.14 vs. 2.82 ± 0.15 Hz, and 0.77 ± 0.04 vs. 0.75 ± 0.05, respectively), whereas other factors were significantly lower: maximal vertical ground reaction force (1,601 ± 240 vs. 1,643 ± 230 N), loading rate (53.9 ± 12.8 vs. 58.4 ± 13.5 bw s⁻¹), center of mass vertical displacement (0.056 ± 0.008 vs. 0.058 ± 0.008 m) and external mechanical work at each step (1.14 ± 0.10 vs. 1.24 ± 0.10 J kg⁻¹ step⁻¹). These effects were observed on the left (biopsed) leg, but also on the right one for the external mechanical work, the duty factor and the maximal vertical ground reaction force, showing that a single biopsy had both ipsi- and contralateral effects on running mechanics.     

Mathematical models of the spatial distribution of retinal oxygen tension and consumption,including changes upon illumination

To better understand oxygen utilization by the retina, a mathematical model of oxygen diffusion and consumption in the cat outer, avascular retina was developed by analyzing previously recorded profiles of oxygen tension (PO₂) as a function of retinal depth. Simple diffusion modelling of the oxygen distribution through the outer retina is possible because the PO₂ depends only on diffusion from the choroidal and retinal circulations and on consumption within the tissue. Several different models were evaluated in order to determine the best one from the standpoints of their ability to represent the data and to agree with physiological reality. For the steady state one-dimensional diffusion model adopted (the special three-layer diffusion model), oxygen consumption was constant through the middle layer and zero in the layers near the choroid and near the inner retina. On the average, the oxygen consuming layer, as found by nonlinear regression for each profile, extended from about 75% to 85% of the retinal depth from the vitreous. This is a narrow band through the mid-region of the photoreceptors. Oxygen consumption of the entire avascular retina, determined from fitting eight PO₂ profiles measured in light-adapted retinas, averaged 2.7 ml O₂(STP)/(100 g tissue · min), while the value determined from fitting thirty-two PO₂ profiles measured in dark-adapted retinas averaged 4.4 ml O₂(STP)/(100 g tissue · min). Consumption in the light was thus only 60% of that in the dark. This suggests that the outer retina is at greater risk of hypoxic injury in the dark than in the light, a fuinding of considerable clinical significance.     

Influence of the oxygen uptake slow component on the aerobic energy cost of high-intensity submaximal treadmill running in humans

During high-intensity running, the oxygen uptake (V˙O₂) kinetics is characterised by a slow component which delays the attainment of the steady-state beyond the 3rd min of exercise. To assess if the aerobic energy cost of running measured at the 3rd min (C ₃) adequately reflects the variability of the true aerobic energy cost measured during the steady-state (C _ss), 13 highly-trained runners completed sessions of square-wave running at intensities above 80% maximal oxygen uptake (V˙O_2max) on a level treadmill. To evaluate the time at which the steady-state V˙O₂ was attained (t _ss), the V˙O₂ responses were described using a general double-exponential equation and t _ss was defined as the time at which V˙O₂ was less than 1% below the asymptotic value given by the model. All the subjects achieved a steady state for intensities equal to or greater than 92% V˙O_2max, and 8 out of 13 achieved it at 99% V˙O_2max. In all cases, t _ss was less than 13 min. For intensities greater than 85% V˙O_2max, C _ss was significantly higher than C ₃ and was positively related to %V˙O_2max (r= 0.44; P < 0.001) while C ₃ remained constant. The C ₃ only explained moderately the variability of C _ss (0.39 < r ² < 0.72, depending on the velocity or the (relative intensity at which the relationship was calculated). Moreover, the excess aerobic energy cost of running the (difference between C _ss and C ₃) was well predicted by age (0.90 < r ² < 0.93). Therefore, when the aerobic profile of runners is evaluated, it is recommended that their running efficiencies at velocities which reflect their race intensities should be determined, with V˙O₂ data being measured at the true steady-state.     

Force kinetics and oxygen consumption during bicycle ergometer work in racing cyclists and reference-group

Summary The forces acting on the right crank of a bicycle ergometer were measured in 18 male subjects (6 racing cyclists, 8 students of physical education, 4 long distance runners) during an incremental exercise test. Oxygen consumption ( ) was simultaneously determined by means of a breath-by-breath method.Differences in peak values of the typical force record might indicate a different force distribution during each cranking cycle. When compared to the reference group, the racing cyclists showed peak values that were significantly lower at all levels of work load. Oxygen consumption during the initial 20 min of the test was found to be significantly lower in the cyclist group (cyclists: 37.2±3.2 l, reference group: 41.1±3.9 l). These results suggest that a different force distribution during a crank revolution might lead to an improved gross efficiency in the cyclist group. The findings might be due to different fractions of ST-fibres in the exercising muscle.     

Effect of short-term energy intake level and exercise on oxygen consumption in men

Summary The influence of short-term energy intake and cycle exercise on oxygen consumption in response to a 1.5 MJ test meal was investigated in ten young, adult men. On the morning after a previous day's low-energy intake (LE regimen) of 4.5 MJ, the mean resting oxygen consumption increased by 0.7 ml · kg^–1 · min^–1 after the test meal (P<0.025). After a high-energy intake (HE regimen) of 18.1 MJ, the resting measurement was unchanged (+0.4 ml · kg^–1 · min^–1) after the meal (n.s.). These trends are the reverse of what would be expected if oxygen consumption in response to feeding is a factor in the acute control of body weight. The mean fasting oxygen consumption during cycle exercise at 56% of (constant work) for both LE and HE prior intakes was not different at 31.1 ml · kg^–1 · min^–1. Oxygen consumption during exercise increased after feeding by 0.5 ml · kg^–1 · min^–1 on the LE regimen (n.s.) and decreased by 1.2 ml · kg^–1 · min^–1 on the HE regimen (n.s.). These results are also the reverse of what would be expected if oxygen consumption in response to exercise is related to short-term energy intake.     

Effect of prior metabolic rate on the kinetics of oxygen uptake during moderate-intensity exercise

Pulmonary oxygen uptake ( ) dynamics during moderate-intensity exercise are often assumed to be dynamically linear (i.e. neither the gain nor the time constant (τ) of the response varies as a function of work rate). However, faster, slower and unchanged kinetics have been reported during work-to-work transitions compared to rest-to-work transitions, all within the moderate-intensity domain. In an attempt to resolve these discrepancies and to improve the confidence of the parameter estimation, we determined the response dynamics using the averaged response to repeated exercise bouts in seven healthy male volunteers. Each subject initially performed a ramp-incremental exercise test for the estimation of the lactate threshold ( ). They then performed an average of four repetitions of each of three constant-work-rate (WR) tests: (1) between 20 W and a work rate of 50% (WR50) between 20 W and 90% (step 1→2), (2) between WR50 and 90% (step 2→3), and (3) between 20 W and 90% (step 1→3); 6 min was spent at each work rate increment and decrement. Parameters of the kinetic response of phase II were established by non-linear least-squares fitting techniques. The kinetics of were significantly slower at the upper reaches of the moderate-intensity domain (step 2→3) compared to steps 1→2 and 1→3 [group mean (SD) phase II τ: step 1→2 25.3 (4.9) s, step 2→3 40.0 (7.4) s and step 1→3 32.2 (6.9) s]. The off-transient values of τ were not significantly different from each other: 36.8 (16.3) s, 38.9 (11.6) s and 30.8 (5.7) s for steps 1→2, 2→3 and 1→3, respectively. Surprisingly, the on-transient gain (G, ) was also found to vary among the three steps [G=10.56 (0.42) ml·min^–1·W^–1, 11.85 (0.64) ml·min^–1·W^–1 and 11.23 (0.52) ml·min^–1·W^–1 for steps 1→2, 2→3 and 1→3, respectively]; the off-transient G did not vary significantly and was close to that for the on-transient step 1→3 in all cases. Our results do not support a dynamically linear system model of during cycle ergometer exercise even in the moderate-intensity domain. The greater oxygen deficit per unit power increment in the higher reaches of the moderate-intensity domain necessitates a greater transient lactate contribution to the energy transfer, or a greater phosphocreatine breakdown, or possibly both. Electronic Publication     

Influence of running pace upon performance: Effects upon treadmill endurance time and oxygen cost

Summary Three possible patterns of pacing (type 1, fast/slow; type 2, slow/fast; and type 3, steady rate) were compared over a 1400 m, 4 min run. The subsequent running time to exhaustion at 370 m·min^–1 was significantly longer with a type 1 than with a type 2 protocol (P<0.05). The steady rate pattern gave results intermediate between type 1 and type 2 pacing. Data for oxygen debt and recovery heart rate confirmed the superiority of type 1 pacing. Possible explanations included (1) a reduction of inefficient anaerobic work, and (2) a greater mechanical efficiency associated with the better matching of required effort to a tapering physiological power. Runners should aim at a steady physiological rather than a steady physical load.     

Work load during floor cleaning. The effect of cleaning methods and work technique

Cardiovascular and muscle load levels were evaluated during floor cleaning. A group of 12 experienced female cleaners participated in the study. Of the subjects 6 used a mopping method and 6 a traditional scrub and cloth method. Heart rate, oxygen consumption, rating of perceived exertion, electromyography from the trapezius muscle and video recordings were obtained during floor cleaning. With respect to relative heart rate and oxygen consumption the two groups did not differ. The results revealed a high cardiovascular load corresponding on average to 53% of the individual maximal oxygen uptake. In addition 65% of the observed period was spent with the back in a position forward flexed more than 20°. The time spent in extreme forward back flexion was shorter for the mopping group. Both groups exhibited high static, median and peak shoulder muscle load levels of 10%, 25% and 54% maximal voluntary contraction, respectively. At the same time, however, the mopping group tended to have a higher shoulder load than the group using the scrub and cloth method. Furthermore, electromyographic signs of fatigue in the trapezius muscle indicated a more stereotype activation of the shoulder muscles during mopping than during scrubbing. Based on these results, it was concluded that mopping cannot be recommended as less strenuous than scrubbing.     

心宁胶囊对犬心脏血流动力学及心肌耗氧量的影响

目的：研究心宁胶囊对麻醉开胸犬心脏血流动力学及心肌耗氧量的影响,探索其对心脏功能的药理作用及作用机制。方法：将20只犬随即分成模型组、阳性药物组、心宁胶囊高、低剂量组,观察麻醉犬冠状动脉血流量、心肌耗氧量和心率等指标的变化。结果：与模型组比较,心宁胶囊具有增加冠脉血流量、降低心肌耗氧量等作用（P〈0.05）。结论：心宁胶囊对犬心脏血流动力学及心肌耗氧量有调整和改善作用。     

High oxygen extraction combined with extensive oxygen consumption in the rat liver perfused with fluosol-DAR,a new perfluoro compound emulsion

Different O₂ values of the perfused rat liver and the metabolic turnover of urea and glucose, with and without substrate loads, were measured in a hemodiluted control group and in a group perfused with the perfluoro compound emulsion (PFC) Fluosol-DA^{R 1}. The following results were obtained. The basal O₂ consumption with PFC was 6.42 and 6.51 ml O₂/(min·100 g liver), respectively, both being higher than in the control group, despite the fact that the latter revealed values of a good oxidative metabolism compatible with that found for larger species in situ. With substrate loads the values increased to a mean of 8.62 ml O₂/(min·100 g) for periods of 20 min and more. Also O₂ extractions of 95% could be found like otherwise mostly in cases with severely reduced O₂ supply and under diminished O₂ consumption. This seems to be due to the increased surface area of the O₂ transporting particles with a mean diameter of 0.1 m. Furthermore, the linear O₂ delivery of physically dissolved oxygen from PFC enables a higher O₂ pressure to remain in the outflowing perfusate after the same amount of oxygen is consumed, provided sufficiently high arterial O₂ pressures are used. Finally, an increase of intracellular O₂ concentration rather than O₂ tension by incorporated PFC particles might play a role.—The substrate turnover values were compared with those in the literature; they are within the normal range.Supported by a grant from the DFG     

高原出血性休克羊的氧运送,氧耗量及心功能变化

本文探讨高原邮血性休克氧运送，氧耗量及血流动力学变化特征。出生生长于３６５８米高原绵羊以Ｗｉｇｇｅｒ氏方法引起出血休克。其结果如下：（１）在低血压期及再输血后５ｈ氧运送量，氧耗量及心输出量减少，但动脉－混合静脉血氧含量差增加，ＰａＯ２及动脉血含氧无明显变化。这些结果表明氧耗量下降是心输出量减少的结果。（２）两侧心室的心泵血功能和等容收缩及弛张期功能降低，回输血后所有上述指标恢复正常，这表明心功能障     

Cardiorespiratory and metabolic adaptations to hyperoxic training

This study examined the effects of hyperoxic training on specific cardiorespiratory and metabolic responses. A group of 19 male subjects trained for 5 weeks on a cycle ergometer at 70% of hyperoxic or normoxic maximal heart rate, the hyperoxic group (HG) breathing 70% O₂, the normoxic group (NG) breathing 21% O₂. The subjects were tested pre- and post-training under both hyperoxia and normoxia. Measurements included cardiac output , stroke volume (SV), heart rate (HR), pulmonary ventilation , oxygen consumption , partial pressure of oxygen (PO₂), partial pressure of inspired carbon dioxide (PCO₂), blood lactate concentration [L], and fiber type composition. The was significantly lower at submaximal work rates (P < 0.05) and maximal increased after training in both groups for both test conditions; hyperoxic was lower than normoxic (P < 0.05). The maximal increased significantly (P < 0.05) in both groups for both tests and was 11%–12% higher during hyperoxia. Post-training maximal heart rate (HR_max) was significantly decreased (P < 0.05) at the same absolute work rate regardless of the training group or test type. The SV was increased at each work rate and was unchanged. The maximal increased significantly (P < 0.05) for both groups and types of test: for normoxia: NG 27.3–30.4 l · min^–1 and HG 30.3–32.31 · min^–1 and for hyperoxia: NG 24.7–25.6 and HG 27.9–31.2 l · min^–1. Although working at the same intensity relative to HR_max, HG showed significantly lower [L] following a single training session, yet maximal values were unchanged after training. Both groups showed a significant increase in the percentage of type IIA fibers post-training but HG retained a larger percentage of HB fibers. Mitochondrial enzymes; citrate kinase, 3-hydroxyacyl CoA dehydrogenase, and cytochrome c-oxidase were increased in the normoxic trained subjects (P < 0.05). In summary, training induced adaptive responses in maximal aerobic power, HR, SV, , [L], and muscle fiber type composition, independent of inspired PO₂. Intramuscular data suggested there may be some differences between hyperoxic and normoxic training and these were substantiated by mitochondrial enzyme and lactate findings. Our data would suggest that transport mechanisms may limit the ability to increase aerobic power.     

Oxygen consumption and mechanical performance of dog gastrocnemius muscle with artificially increased blood flow

Summary In dogs anesthetized with morphine, chloralose and urethane O₂ consumption, lactic acid production and mechanical performance of the gastrocnemius muscle were measured during supramaximal stimulation to rhythmic isotonic tetanic contractions of varied force and duration. The muscle was artificially perfused with arterial blood at flow rates higher by a factor of 2 to 4 than those obtained with intact blood supply and normal arterial blood pressure.It was attempted to subdivide the total net O₂ consumption into two components attributable to shortening (dynamic work) and to maintenance of contraction (static work), respectively. The O₂ consumption attributable to maintenance of contraction turned out to be nearly independent of the load (2 to 8 kg), averaging 260 ml/kg muscle and minute of stimulation With 8 kg load the O₂ consumed for one shortening was equal to the O₂ consumed for maintenance of a contraction during 0.40 seconds; with 2 kg load the corresponding time was 0.24 seconds.Comparison with measurements performed with normal blood supply showed that for the same load and stimulation parameters the mechanical performance was about equal whereas the O₂ uptake was considerably higher in the overperfused muscle. Lactic acid formation rate was small in all cases and energetically rather insignificant. Possible mechanisms underlying the observed dependency of O₂ uptake upon blood flow are discussed.     

Effect of calcium on Na-K-ATPase activity in depolarized rat cortical synaptosomes as determined on the basis of oxygen consumption

Summary The oxygen consumption of rat cortical synaptosomes together with its ouabain-sensitive component were measured after veratrine-induced depolarization in the presence and in the absence of calcium, and with calcium added after depolarization by veratrine or potassium. Taking the ouabainsensitive component of oxygen consumption as an indicator of Na-K-ATPase activity it was concluded that calcium entry during depolarization decreased synaptosomal Na-K-ATPase activity only slightly and in a protracted manner. Consequently, Ca⁺⁺-induced inhibition of Na-K-ATPase does not seem to serve as a trigger mechanism of transmitter release.     

Influence of plyometric training on the mechanical impedance of the human ankle joint

The objective of this work was to study the effects of plyometric training on the mechanical properties of the ankle joint in humans. Changes in the mechanical parameters of this musculo-articular structure were quantified with the aid of a sinusoidal perturbation technique. This technique allowed the expression of the mechanical impedance of the musculo-articular system in terms of stiffness, viscosity and inertia. Measurements were performed under passive conditions and when the subject performed plantar flexion. A 7-week period of training induced a decrease in the slope of the relationship between stiffness and plantar flexion torque, whereas passive stiffness was increased. A slight decrease in viscosity and an invariability in inertia were also found. These results are interpreted in terms of the possible adaptations of the musculo-articular structure and ultrastructure involved in the performance of plantar flexion. Accepted: 11 April 1997