Steady-state Running Research Articles

Time course of recovery of vertical jump height and heart rate versus running speed after a 90-km foot race

The aim of this study was to characterize the time course of recovery of muscle function and the heart rate response to steady-state exercise following an ultramarathon. Eight male runners (46 ± 7 years; mean ± s) competing in the 90-km Comrades marathon and seven control runners (45 ± 6 years) with the same running experience (11 ± 3 years), but who did not run in the race, were recruited for the study. The heart rate response to various running speeds on the track was measured twice before the race. Squat jump, counter-movement jump and drop jump height were measured on three occasions before the race. The track tests were repeated on days 4, 11, 18, 25 and 32 after the race. The vertical jump tests were repeated on the day of the race and on days 1, 2, 3, 4, 5, 11, 18, 25 and 32 after the race. Although the heart rate response to steady-state exercise was elevated at all speeds (3.75-4.55 m . s ⊃1 ) for the duration of the study, this difference was only statistically significant on day 25 after the race (P < 0.05). Vertical jump height was significantly reduced in the experimental group immediately after the race (P < 0.00001), as was the squat jump for up to 18 days (P < 0.001) after the race. Actual height jumped in the squat jump was reduced by as much as 20 cm immediately after the race. Leg extensor muscle power, as measured by vertical jump height, is impaired in runners for up to 18 days after a 90-km ultramarathon. Furthermore, runners have a delayed exaggerated heart rate response to steady-state running at moderate to high intensities up to 25 days after an ultra-endurance event.

THE EFFECT OF EXERCISE INTENSITY ON ERYTHROPOIETIN LEVELS FOLLOWING ACUTE EXERCISE IN TRAINED RUNNERS 496

To expand our knowledge of the potential effects of endurance exercise on erythropoiesis, we examined the effects of high- and low-intensity running on plasma erythropoietin (EPO) levels in 10 well-trained runners. Using a repeated measures design, we compared high-intensity (90-92% VO2max) intermittent running (HI-bout), low-intensity (60% VO2max) steady state running (LO-bout), and a resting control (REST). The exercise bouts were 60 minutes in duration and were estimated to have equal energy expenditure. At six time points (pre, post, 4 hr, 12 hr, 24 hr, and 48 hr post exercise) we measured hemoglobin (Hb), hematocrit (Hct), red blood cell count (RBC), and EPO. Means for [Hb] and [EPO] are listed in the table. Although there was an apparent hemodilutional effect following the exercise treatments resulting in decreased [Hb] and Hct values post-exercise, no significant differences were found between treatments for [EPO]. These findings suggest that neither moderate or vigorous acute exercise alters erythropoietin in trained athletes. # Significantly different than the 24 Hr REST and LO-bout values. *Significantly different than the 48 Hr REST value.

Running performance and cardiovascular capacity are not impaired in creatine-depleted rats

Several published reports have indicated that derangement of the phosphocreatine/creatine (Cr) energy-buffering system via Cr analogue feeding results in cardiomyopathy when cardiac performance is assessed in vitro. The present study was designed to examine indexes of cardiac performance in rats that have been chronically Cr depleted. Adult (180 +/- 4 g) rats were assigned to a normal diet (ND) (n = 8) or a Cr-depletion diet (CD) group (n = 10). After 61 +/- 1 days of ad libitum feeding, measurements of steady-state exercise O2 consumption were made. Hemodynamic indexes were then assessed during incremental running to peak sustained levels. Rats were then killed and the left ventricle was excised. In the CD group Cr was depleted 82% and V1 isomyosin decreased while V2 increased. O2 consumption during steady-state running was not different in CD rats. The respiratory exchange ratios of CD rats reflected a bias toward fat utilization during the latter stages of prolonged exercise. The exercise heart rates and peak systolic blood pressures of CD rats were slightly lower than those of ND rats. Both negative and positive rates of left ventricular pressure development were significantly reduced at all running speeds in the CD rats. CD rats were capable of exercise performance equal to that of ND animals. The hemodynamic and metabolic data suggest that the adaptations seen in the CD animals may be similar to those reported after endurance training. These results indicate that chronic Cr depletion does not impair either the circulatory or exercise capacity of rodents.

Expired air temperature during steady-state running

While some metabolic measurement systems measure expiratory temperature to standardize gas volumes, other systems use only an estimate. This study investigated the effect of prolonged exercise on expiratory temperature near the pneumotachometer to provide a basis for its estimation when actual measurement is unavailable. Seven active females each performed two 45-min treadmill runs at identical speeds (64.5% +/- 11.8% of VO2max) in which the pneumotachometer heater control was either set to 37 degrees C or turned off. Expired air temperatures were monitored with thermocouples at the nonrebreathing valve (VAL) and 1 cm upstream (UPS) and downstream (DNS) from the pneumotachometer screens. There were no temperature differences over time for any of the conditions, and there were no differences in the VAL or UPS temperatures between the heated and unheated conditions. DNS temperature was higher during the heated condition at all time periods (P < 0.01). Mean DNS temperatures for the heated and unheated condition were 30.2 +/- 1.0 degree C and 27.9 +/- 1.1 degrees C, respectively. We conclude that expired air temperatures near the pneumotachometer remain stable during extended steady-state exercise regardless of whether the pneumotachometer is heated or not.

Kron's reduction method applied to the time stepping finite element analysis of induction machines

The behavior of large induction motors during transient as well as steady state running conditions is of significant interest to the power industry. A variety of analytical predictive tools are employed to aid the design and predict their operation under transient and steady state conditions. This paper presents a strategy to reduce the required running time in order to make a parametric study of induction machines such as the assessment of different design options feasible. This is accomplished by reducing the number of finite element equations that must be solved while maintaining the same level of accuracy of solutions. This method is based on Kron's network reduction work for linear systems and has successfully been applied to large lumped parameter model of transformers. This paper illustrates the reduction method by comparing the flux density in the air gap for a complete FEM model of an induction machine to that of the reduced model. The results are essentially identical with a reduction in computational time of approximately 71%.

Implementation of an adaptive controller for the startup and steady‐state running of a biomethanation process operated in the CSTR mode

An adaptive control algorithm has been implemented on a biomethanation process to maintain propionate concentration, a stable variable, at a given low value, by steering the dilution rate. It was thereby expected to ensure the stability of the process during the startup and during steady-state running with an acceptable performance. The methane pilot reactor was operated in the completely mixed, once-through mode and computer-controlled during 161 days. The results yielded the real-life validation of the adaptive control algorithm, and documented the stability and acceptable performance expected.

Scheduling of automated guidence vehicle in a flowshop

In this paper, a simple flowshop manufacturing system with an automated guided vehicle (AGV) is considered under the frame of discrete event dynamic system (DEDS). The pseudo-linear DEDS model is established by using max-algebra approach and by determining the scheduling strategy of AGV. The model allows for evaluating dynamic behavior of system under a deterministic and circlic production process. Given any fixed time-consuming of processing activities and routing of AGV, the steady-state running rhythm of system can be determined from eigenvalue of the system, i.e., the average weights of the critical circuit of closed-loop network. Therefore, the assessment of static scheduling strategies of AGV can be made by means of evaluating the performance of manufacturing system.

Effects of voluntary exercise on bone mineral content in rats

We used a voluntary running model to explore the relationship between average daily running distance and bone mineral status of rats. A total of 60 male Sprague-Dawley rats were randomly assigned at 6 weeks of age to a sedentary control group (n = 22) or to a group with unlimited access to a running wheel (n = 38). The running distance of exercising rats was monitored daily, and steady-state running levels ranged from 3.2 to 18.1 km/day. At the end of the experimental period, femora and tibiae were dissected and bone mineral content (BMC, g/cm) and bone mineral density (BMD, g/cm2) were measured by single-photon absorptiometry. Cross-sectional morphometry was examined by taking a transverse section of the femoral middiaphysis. Hindlimb percentage fat was significantly higher in controls than in runners (20.0 +/- 1.2 versus 11.1 +/- 0.6, p less than 0.001), and soleus mass was greater in runners than in controls (371 +/- 8.1 versus 320 +/- 0.8 mg, p less than 0.001). Femoral and tibial lengths, weights, and volumes were significantly higher in runners than in controls (p less than 0.005). BMC and BMD were higher in runners than in controls at all sites apart from the distal femur. Cross-sectional areas at the femoral midshaft were greater in running rats than in sedentary controls (6.26 +/- 0.1 versus 5.45 +/- 0.3 mm2, p less than 0.02), as was the polar moment of inertia (15.6 +/- 0.6 versus 12.7 +/- 0.2 mm4, p less than 0.05). No positive correlation was found between distance run and BMC, BMD, cross-sectional area, or polar moment of inertia.(ABSTRACT TRUNCATED AT 250 WORDS)

Ratings of Perceived Exertion Among Standard Treadmill Protocols and Steady State Running

The purpose of this study was to determine if differences exist in ratings of perceived exertion (RPE) at a predetermined relative heart rate between two standard treadmill protocols and steady state exercise in a field setting. Thirty healthy male (N = 15) and female (N = 15) volunteers were maximally tested using the standard Bruce and a modified Balke (3.0 mph with 2.5% grade each two minutes) protocols. Each subject was randomly assigned to one treadmill protocol first, and then completed the second test forty-eight hours later. Within forty-eight hours following the second treadmill test, all subjects completed a field exercise trial consisting of an 800-m run. During the field trial an investigator paced each subject to an individualized target heart rate (75% maximal heart rate reserve) calculated from the treadmill tests. The total exercise time for the field trial was 4:31 +/- 0:22 and 5:36 +/- 0:47 min for the males and females, respectively. During the last 50 m of the field trial, RPE values were recorded. Comparisons of the rating of perceived exertion at the target heart rate (RPE at THR) were made using a 2-way (Gender x Trials) ANOVA with repeated measures across trials. There was a significant gender x trials interaction for RPE at THR, with males reporting significantly higher values during the treadmill tests as compared to the females (BRUCE = 13.5 +/- 1.6 vs 12.2 +/- 1.8; BLAKE = 15.9 +/- 2.3 vs 13.7 +/- 2.4). There was no difference noted between genders for RPE at THR during the field trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Lactate and gas exchange responses to incremental and steady state running.

This study compared the oxygen uptake (VO2) and running velocity at which the lactate threshold (LT), the ventilatory threshold (VT), and the maximal lactate steady state (MSSLA), and the maximal VO2 steady state (MSSVO2) occurred in 11 trained male runners (mean age = 22.4 years, range 18-28 years). Each underwent an incremental treadmill test to exhaustion. The LT was defined by a systematic, continuous increase in arterialised venous blood lactate; the VT was determined by an abrupt rise in VE.VO2(-1) without an increase in VE.VCO2(-1). Each subject also completed a series of steady state treadmill runs of 20 minutes duration. The MSSLA was determined as the highest velocity and VO2 at which lactate concentration increased by less than 0.2 mmol.l-1 from minute 10 to minute 20. The MSSVO2 was determined as the highest velocity or VO2 at which a steady state in VO2 was not delayed for more than 3 minutes (with a steady state defined as VO2 within 0.2 l.min-1 of the average VO2 over the last 10 minutes of each test). Each subject also completed a 5 km time trial run to assess performance. No significant differences were found among the four variables expressed either as VO2 or velocity. Significant correlations were found between MSSLA and MSSVO2 (r = 0.74) expressed as VO2, and between MSSLA and MSSVO2 (r = 0.90), MSSVO2 and VT (r = 0.70) and MSSLA and VT (r = 0.67) expressed as velocity. A stepwise regression analysis found MSSLA (expressed as velocity) to be the best predictor of 5 km performance (r = 0.87). It was concluded that (a) MSSLA and MSSVO2 are closely related, and (b) MSSLA is a good predictor of performance and may be an important, objective measure of cardiorespiratory endurance capacity.

Mechanism of beneficial effect of beta-adrenergic blockade on exercise-induced myocardial ischemia in conscious dogs.

We examined the importance of decreased heart rate in the beneficial effect of beta-adrenergic blockade on exercise-induced regional myocardial ischemia and contractile dysfunction in conscious dogs with single vessel coronary stenosis (ameroid constrictor). Studies were performed during control treadmill exercise, which produced regional myocardial ischemia (blood flow measured with microspheres) and wall dysfunction (measured using sonomicrometers). A second run was performed after the administration of atenolol (0.3-1.0 mg/kg i.v.), and the reduced heart rate caused by atenolol during early steady-state running was then prevented by atrial pacing during the latter portion of the run. Atenolol reduced the exercise heart rate from 217 +/- 25 beats per minute (SD, n = 9) to 166 +/- 15, and ischemic zone wall thickening during systole improved from 27 +/- 22% of the resting value in the control run to 50 +/- 25% of the resting value in the atenolol run (p less than 0.01). Atrial pacing then increased heart rate to 217 +/- 23 beats per minute, and regional wall thickening deteriorated to 15 +/- 25% of the resting value. Regional subendocardial blood flow in the ischemic zone during atrial pacing with atenolol was slightly less than that observed in the control run, in both ischemic and control zones, indicating no remaining beneficial effect of atenolol when heart rate reduction was eliminated. We conclude that the only significant mechanism for the improvement in exercise-induced ischemia and wall motion produced by atenolol is a reduction in the exercise heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of laboratory test results with long distance runners.

Appropriate tests can be used to accurately estimate: an individual's potential for success in long distance running; his current level of conditioning; his appropriate training and racing paces; and his ideal bodyweight. The proposed tests include the study of VO2max, running efficiency, maximal steady-state, and body composition. Based on a review of the literature it was determined that VO2max, running efficiency, and body composition provide the information about long distance running potential, including specific paces for various events. Maximal steady-state running pace (pace that elicits 2 mmol/L lactate) identifies appropriate running paces for various events. Relative maximal steady-state oxygen consumption (% VO2max) identifies the current level of conditioning. A comparison of maximal steady-state, running efficiency, and body composition by assessing current status with optimums, provide guidelines for appropriate changes.

Cockroaches on a treadmill: Aerobic running

Five species of cockroach were tested on a miniature treadmill at three velocities as O 2 consumption ( V ̇ O 2 ) was measured: Gromphadorhina chopardi, Blaberus discoidalis, Eublaberus posticus, Byrsotria fumagata and Periplaneta americana. All cockroaches showed a classical aerobic response to running: V ̇ O 2 increased rapidly from a resting rate to a steady-state ( V ̇ O 2ss ): t 1 2 on-response varied from under 30 s to 3 min. Recovery after exercise was rapid as well; t 1 2 off-response varied from under 30 s to 6 min. These times are faster or similar to mammalian values. V ̇ O 2 varied directly with velocity as in running mammals, birds and reptiles. V ̇ O 2 during steady-state running was only 4–12 times higher than at rest. Running is energetically much less costly per unit time than flying, but the cost of transport per unit distance is much more expensive for pedestrians. The minimal cost of transport ( M run), the lowest V ̇ O 2 necessary to transport a given mass a specific distance, is high in cockroaches due to their small size. The new data suggest that insects may be less economical than comparable sized vertebrates.

Energetics of Cockroach Locomotion

ABSTRACT Cockroaches, Gromphadorhina portentosa, were run at different speeds for 20 min on a miniature treadmill enclosed in a lucite respirometer while oxygen consumption was continuously monitored. The data collected on these 5 g insects are remarkably similar to those obtained on vertebrates. rises rapidly with the onset of exercise ; the on-response was about 1 min with steady-state reached within 4 min at the fastest speed, 0-12 km/h. Recovery was rapid ; the off-response was 4-6 min, with total recovery achieved in less than 1 h. The tracheal system appears to be a highly efficient mode of O2 conductance in contrast to the crustacean method of delivery involving gills and circulation. (ml O2/g.h) at steady-state running varies directly with velocity (V). The regression equation at 24 °C is . The F-intercept, at zero velocity, is 2·4 times the actual resting rate of 0-19 ml O2/g.h. Temperature does not change the slope of the regression line but shifts it up or down in accordance with a simple Q10 effect. Incline running produces no changes compared to level running. The minimum cost of transport, the lowest necessary to transport a given mass a specific distance, is high in cockroaches (4-92 ml O2/g.km) and comparable to that expected for a small quadrupedal or bipedal pedestrian vertebrate.

The biological basis of aptitude: the endurance runner

SummaryAptitude for a particular sport is governed by many factors, not least of which are obvious environmental influences. There are, however, individuals who, through genetic endowment, have the necessary biological characteristics which identify them as potentially elite athletes. These characteristics have been described more fully for endurance athletes because prolonged, almost steady-state running, lends itself more readily to investigation by biologists, than do the more complex sports.These studies show that the potentially elite endurance athlete is an individual endowed with an above average cardio-respiratory system, capable of a high rate of oxygen transport and carbon dioxide elimination. Not only does the elite endurance athlete have a greater rate of oxygen transport than the average sportsman or sportswoman, but the muscles receiving the oxygen are composed mainly of type I, i.e. low-twitch oxidative fibres, which are designed for endurance exercise. Furthermore, the elite endurance athlete also appears to be pre-programmed genetically to lay down less fat, in the form of sub-cutaneous adipose tissue, than the average sportsman or sportswoman of the same age and sex.Although genetic endowment dictates the potential ability of an individual for sustained high speed running, only appropriate training will allow the realization of this potential and so enable the individual to join the fraternity of the world's elite endurance athletes.

Cost of locomotion and heat balance during rest and running from 0 to 55 degrees C in a patas monkey.

A young patas monkey was run on a treadmill for 15-20 min at speeds in excess of 15 km times h-1 over a range of laboratory air temperatures from 0 to 55 degrees C. Cost of locomotion for the monkey was 83% that predicted for a running mammal of similar weight, 4 kg. At the highest steady-state running of speeds, the patas monkey's energy expenditure was 11 times the resting rate. Heat storage and respiratory evaporation during running each accounted for less than 16% of the heat production. Cutaneous evaporation, mainly sweating, was the major means of heat loss at high ambient temperatures and during heavy exercise. Maximum sweat rates of 0.5 mg times cm-2 times min-1 found in these experiments approach the sweat rates of humans. Whole-body dry thermal conductance increased 2-3 times the rest value at a given temperature. Environmentally gained heat contributed about two-thirds of the total heat load on the patas monkey at rest at 53 degrees C. At these same temperatures, environmental and metabolic heat loads were about equal when the animal ran at moderately high speeds (11-13.4 km times h-1).

Study of the magnetic field in superconducting alternators

In this paper, the radial and tangential components of the magnetic field inside a three-phase turbogenerator with superconducting field winding and with a rotating screen of any number of elements are calculated with reference to a twodimensional study and to steady state and transient running.

Time course adaptations in cardiac and skeletal muscle to different running programs.

The effects of chronic "steady-state" and high-speed interval running were investigated on time-course changes in certain biochemical properties of cardiac and skeletal muscle fiber types of rats. Nine weeks of the interval program resulted in significant increased (15%) in both cardiac enlargement and ATPase activity of myofibrils; whereas increases in these parameters were only transient and not significant at the termination of the program involving steady-state running. Neither program induced appreciable alterations in citrate synthase and phosphofructokinase activity in cardiac muscle. In fast-twitch white fibers, "steady-state" training induced only a transient 45% increase in citrate synthase activity in contrast to a progressive twofold change with interval training. Both programs resulted in similar increases (45-50%) in citrate synthase activity in fast-twitch and slow-twitch red fibers. However, the patterns of increase for both fiber types differed between the two programs. These findings suggest that training programs incorporating elements of both "steady-state" incline and high-speed interval running can potentially induce respiratory enzyme adaptations in the greatest spectrum of rodent skeletal muscle fibers in addition to inducing adaptations to enhance contractile potential in cardiac muscle.

TRANSIENTS IN SUPERCONDUCTING ALTERNATORS WITH TORQUE COMPENSATING SHELLS

ABSTRACT In this machine the torque is not transmitted mechanically to the field winding but by an asynchronous link. The field winding is free to rotate inside the driving shaft, which acts as the squirrel cage of an induction motor. In the steady state the field winding turns at synchronous speed and the driving shaft slightly faster. During a transient the shaft acts as an electromagnetic shell protecting the low temperature parts of the cryostat from high torques and the superconducting coil from varying magnetic fields. In this paper the steady-state running, the fault torques, the critical clearing time, the steady state stability, and the losses in cold metallic parts, are compared with those of a classical superconducting alternator.

On poor separation in a magnetically driven shock tube

Observations made at steady-state running conditions in a magnetically driven shock tube, with parallel-plate electrodes, showed that for a given discharge voltage, sufficient separation between the shock and the current-sheet occurred only at relatively high discharge pressures. As a comparison, poor separations were also noted in conventional diaphragm-type shock tubes running at low initial pressures. It is demonstrated that the observed poor separation can be explained by a mass leakage, instead of through the wall boundary layer, but through the current-sheet itself.