Mechanical power during maximal treadmill walking and running in young and elderly men

This study determined mechanical power during movements specific to maximal walking and running using a non-motorized treadmill in 38 elderly [69.4 (5.0) years] and 50 young [24.3 (3.4) years] men. The mean mechanical power over a period of time covering six steps, during which the belt velocity peaked and then kept almost plateau, was determined as a performance score in each of maximal walking (WP) and running (RP). In terms of the value relative to body mass, the relative difference between the two age groups was greater for RP (61.7%) than for WP (21.4%) or isometric knee extension (34.1%) and flexion torque (43.8%). In the two groups, WP was significantly (P<0.05) correlated to knee extension (r=0.582 for the elderly and r=0.392 for the young) and flexion torque (r=0.524 for the elderly and r=0.574 for the young). Similarly, RP was also significantly (P<0.05) correlated to knee extension (r=0.627 for the elderly and r=0.478 for the young) and flexion torque (r=0.500 for the elderly and r=0.281 for the young). In these relationships, the WP adjusted statistically by thigh muscle torque was similar in the two age groups. However, the corresponding value for RP was significantly higher in the young than in the elderly. The findings here indicate that: (1) the difference between the young and elderly men in mechanical power is greater during maximal running than maximal walking, and (2) although the thigh muscle torque contributes to the power production during the two maximal exercise modes in the two age groups, the RP is greater in the young than in the elderly regardless of the difference in the thigh muscle torque.     

A new method for the evaluation of anaerobic running power in athletes

Summary A new maximal anaerobic running power (MARP) test was developed. It consisted ofn · 20-s runs on a treadmill with a 100-s recovery between the runs. During the first run the treadmill speed was 3.97 m · s^–1 and the gradient 5°. The speed of the treadmill was increased by 0.35 m · s^–1 for each consecutive run until exhaustion. The height of counter-movement jumps and blood lactate concentration ([1a^–]_b) were measured after each run. Submaximal ([la^– ] b = 3 mmol · l^–1 and 10 mmol · l^–1) and maximal speed and power ( , and , respectively) were calculated andW was expressed in oxygen equivalents according to the American College of Sports Medicine equation. Thirteen male athletes whose times over 400 m ranged from 47.98 s to 54.70 s served as subjects. In the MARP-test the speed at exhaustion was 6.89 (SD 0.28) m · s^–1 corresponding to a of 118 (SD 5) ml · kg^–1 · min^–1. The peak [1a^–]_b after exhaustion was 17.0 (SD 1.6) mmol · l^–1 . A significant correlation (r=0.89,P<0.001) was observed between the and the average speed in the 400-m sprint. The maximal 20-m sprinting speed on a track and correlated with both the and the 400-m speed. It was concluded that the new method allows the evaluation of several determinants of maximal anaerobic performance including changes in the force-generating capacity of leg muscles and [la^–]_b relative to the speed of the sprint running. The [1a^–]_b at submaximal sprinting speed was suggested as describing the anaerobic sprinting economy.     

Maximal mechanical power output and capacity of cyclists and young adults

Summary The maximal average power output ( ) has been examined in 10 male students, 22 pursuit and 12 sprint cyclists. In 24 of these subjects (8 students, 10 pursuit and 6 sprint cyclists), estimates of the maximal capacity ( ) of the short-term anaerobic energy yielding processes were made. The results show that the sprinters had a higher absolute (1241±266 W) and (16.7±4.9 kJ) than either the students (1019± 183 W, 14.7±2.8 kJ) or the pursuit cyclists (962±206 W, 14.0±2.9 kJ). However, the differences were removed when the values were standardised for muscle size. In the sprinters theW _max was attained at an optimal pedal frequency of 132±3 min⁻¹ and the estimated maximal velocity of pedalling ( ) was 262±8 min⁻¹. The comparable figures in the students and pursuit cyclists were 118±8 min⁻¹, 235±17 min⁻¹ and 122±6 min⁻¹, 242±12 min⁻¹ respectively. The coefficient of variation of duplicate measurements of was found to be ±9%. Using data of Wilkie (1968) for muscle phosphagen and glycolytic stores (27 mmol · kg⁻¹), it was estimated that the probable efficiency of the anaerobic processes during maximal cycling was 0.22. It was concluded that and are largely determined by body size and muscularity. The efficiency of anaerobiosis appears to be of the same order of magnitude as found for oxidative work.     

Effect of muscle temperature on leg extension force and short-term power output in humans

Summary The effect of changing muscle temperature on performance of short term dynamic exercise in man was studied. Four subjects performed 20 s maximal sprint efforts at a constant pedalling rate of 95 crank rev · min⁻¹ on an isokinetic cycle ergometer under four temperature conditions: from rest at room temperature; and following 45 min of leg immersion in water baths at 44; 18; and 12‡ C. Muscle temperature (Tm) at 3 cm depth was respectively 36.6, 39.3, 31.9 and 29.0‡ C. After warming the legs in a 44‡ C water bath there was an increase of ∼11% in maximal peak force and power (PP_max) compared with normal rest while cooling the legs in 18 and 12‡ C water baths resulted in reductions of ∼12% and 21% respectively. Associated with an increased maximal peak power at higher Tm was an increased rate of fatigue. Two subjects performed isokinetic cycling at three different pedalling rates (54, 95 and 140 rev · min⁻¹) demonstrating that the magnitude of the temperature effect was velocity dependent: At the slowest pedalling rate the effect of warming the muscle was to increase PP_max by ∼2% per ‡ C but at the highest speed this increased to ∼10% per ‡ C.     

Validation of a simple mechanical accelerometer (pedometer) for the estimation of walking activity

Summary A small (28 g) mechanical accelerometer has been tested by subjecting it to controlled bench tests consisting of repetitive vertical oscillations on two designs of test rig. The accelerometer's 3-digit display provided a cumulated score with a maximum of 99.9 units. This score was compared with an independent count of the imposed oscillations and found to be linear with time (r=0.996) and reproducible on retest (coefficient of variation=± 1.5%). The sensitivity ranged from 6.2 to 7.4 units/10,000 oscillations. The response was related to the maximal applied acceleration (calculated from the amplitude and frequency of the oscillations on the assumption that they were sinusoidal) and independent of the amplitude and frequency used. The threshold maximal acceleration was less than 2 m s^–2 and the response had reached a plateau at 4 ms^–2. During field studies the accelerometer was firmly attached over the hip in a waistband where it responded to the vertical accelerations produced by walking. When compared with an independent count of footsteps from a heel-mounted resistance pad the accelerometer score (after calibration) was not significantly different. The mean difference was (0.29±0.67, S.D.) 10³ steps in a younger group (n=8, mean age 39 years) and (0.46±1.08, S.D.) 10³ steps in an older group of women (n=6, mean age 65 years). Scores of around 10×10³ steps can be expected in a day in moderately active young subjects and 40 × 10³ steps in a week in the elderly. Simultaneously recorded scores from both right and left hips were not significantly different. In young subjects the mean difference was typically (1.08±0.8) 10³ steps in a daily score of 10 × 10³ steps and for old subjects (3.5±10.4) 10³ steps in a cumulated 6 day score of 40×10³ steps. The accelerometer can therefore be used as a pedometer to give an estimate of the number of footsteps taken over long periods.     

Standardization of measuring power output during wheelchair propulsion on a treadmill Pitfalls in a multi-center study

OBJECTIVE: In a multi-center study the power output of wheelchair propulsion, attained by a wheelchair drag test, differed among rehabilitation centers. The purpose of this study was to investigate what causes the differences in drag force among centers. METHODS: A set of standardized drag tests was performed while systematically varying the calibration set of the force transducer, the tester and the wheelchair. In addition, the actual calibrated velocity and slope of the treadmill were measured. RESULTS: Difference in drag force among centers was due to variation in wheelchair set-up and differences in the slopes between treadmills. The drag force was not significantly different when different testers performed the test. The belt velocity in almost all centers was lower than the manufacturer specified (assumed) velocity. CONCLUSION: The drag test appeared a robust test as far as the tester is considered. Variation in wheelchairs and differences in the actual slopes of the treadmills affected the imposed drag force. The assumed velocity of the treadmill led to an overestimation of the power output. The power output in the multi-center study should be recalculated using the measured velocities and the wheelchair set-up should be more standardized.     

Physiological responses that account for the increased power output in speed skating using klapskates

The present study investigates which physiological sources support the increase in mechanical power output (W˙ _out) that can be obtained using klapskates in speed skating. It was hypothesized that the increase in W˙ _out could be achieved through an increase in gross efficiency or an increase in aerobic power (W˙ _aer). Six speed skaters performed a submaximal and maximal 1600-m skating test with both klapskates and conventional skates, to measure gross efficiency and maximal W˙ _aer during speed skating. The rate of oxygen uptake (V˙O₂) and post-exercise blood lactate concentrations ([La]) were measured and video recordings were made. W˙ _aer was calculated from V˙O₂. W˙ _out was derived from the power needed to overcome air and ice friction. Gross efficiency was calculated as the ratio of W˙ _out and W˙ _aer. In the maximal tests, the subjects skated faster with klapskates compared to conventional skates (10.0 vs 9.6 m · s⁻¹). They sustained the resulting higher W˙ _out with klapskates with an equal V˙O₂. [La] was, however, 1.7 mmol · l⁻¹ higher when klapskates were used, which might reflect an increase in anaerobic power. During the submaximal tests the skaters generated equal W˙ _out with both types of skate. Although not statistically significant, V˙O₂ and W˙ _aer were, on average, lower when klapskates were used compared to conventional skates [mean (SD) 0.3 (0.43) l · min⁻¹, 105 (143) W]. Despite the lack of a statistically significant difference in W˙ _aer, gross efficiency was shown to be significantly higher with klapskates compared to conventional skates (16.3% vs 14.8%, P=0.02). We conclude that the increase in W˙ _out when the subjects were using klapskates could be explained by an increase in gross efficiency rather than an increase in W˙ _aer. Accepted: 20 July 2000     

The effects in humans of rapid loss of body mass on a boxing-related task

The physiological effects of strategies for a rapid loss of body mass immediately before weighing-in for competition in weight-governed sports are unclear. This study examined the effects of a 3%–4% loss in body mass on a boxing-related task. Seven novice amateur boxers completed three 3 min rounds of simulated boxing on a prototype boxing ergometer in an euhydrated state (E-trial) and after exercise-induced thermal dehydration (D-trial). All subjects lost body mass following dehydration–mean body mass fell 3.8 (SD ± 0.3)% [77.3 (SD ± 11.3) to 74.4 (SD ± 10.7) kg, P < 0.001] – but changes in plasma volume (PV) were inconsistent. Four subjects suffered reductions in PV between 15% and 30%, one subject maintained his E-trial value and two recorded an increase. The D-trial mean PV value was 8.0 (SD ± 17.2)% lower but this fall was not statistically significant (P > 0.05). Analysis of D-trial boxing performance showed one subject maintained his performance over the two trials and a second improved 17.8%. A two-way ANOVA (condition × time) with repeated measures on both factors showed no significant main effect differences for condition (F _1,6=3.93 P > 0.05), time (F _1.83,48=1.12, P > 0.05) or interaction between them (F _1.93,48, P > 0.05). Furthermore, neither heart rate nor blood lactate responses in the boxing task differed between trials. These data were affected by the small sample. Power and effect size analysis using η² procedure and removing the outlier data produced a mean fall in boxing performance of 26.8%. However, some subjects appeared able to resist the deleterious effects of a rapid loss of body mass prior to competition and further research is needed to explain the mechanisms under-pinning this ability. Accepted: 12 May 2000     

On the mechanical power of joint extensions as affected by the change in muscle force (or cross-sectional area), ceteris paribus

This paper offers a reference prediction for the changes of mechanical power generated during a maximal (vertical, horizontal or inclined) joint extension, as a consequence of just the changes of muscle force or cross-sectional area (CSA). Ceteris paribus (all other things being equal), for a given joint, the exponents at which the force changes have to be raised to predict the duration, final speed and power of the maximal extension are –0.5, 0.5, and 1.5, respectively, for horizontal movements. For example, a force decrease of 30% leads to an increase of 19.5% of the duration of the extension and to a decrease of 16.3% and of 41.4% of its final speed and power. The equations for vertical or inclined extension performances are subject to the same exponents. However, the actual prediction is dependent upon the ratio between muscle strength and body weight, reflecting the fraction of the muscle strength (or CSA) acting against gravity during the manoeuvre. For instance, during a vertical extension, a force decrease of 30% leads to an increase of 30.9% of the duration of the extension and to a decrease of 29.3% and of 50.5% of its final speed and power. Based on the proposed model, a methodology is also described to detect the effects on the extension power of other determinants, in addition to CSA, of the useful force change (e.g. neuromuscular factors, motor control). Electronic Publication     

Effects on efficiency in repetitive lifting of load and frequency combinations at a constant total power output

Sumary Boxes were lifted and lowered repetitively at three different combinations of load and frequency. These combinations were chosen such that the total mechanical power generated was constant. Effects of the varying load or frequency conditions (but constant total mechanical power) on the rate of energy expenditure (M) and on the mechanical efficiency (ME) were measured. Mechanical power was determined from film analysis and separated into external power (generated to lift the load) and internal power (to raise the lifter's body mass). The M was determined from oxygen consumption measurements. The ME was calculated in two ways, depending on the definition of mechanical power, including either the external power only (ME_ext) or the total power output (ME_tot). Despite a constant total mechanical power, M increased at higher loads and lower frequencies. This might be explained by the increasing isometric force required in postural and load control. The M increase resulted in a decrease of ME_tot. However, at higher loads and lower frequencies ME_ext increased, indicating that more external work can be done at the same energy costs at higher loads or lower frequencies, which could be of interest from the point of view of occupational physiology. It would seem that at higher loads or lower frequencies the increased costs for isometric muscle action do not outweigh the benefit of raising the body less frequently. Furthermore, it was found that the ME,, in lifting was much lower than the values reported for other kinds of activity. This was due to the large proportion of total power output that was internal power in repetitive lifting [e.g. 83.1% (at a load of 6 kg) in the present study].     

Coordination of fore and hind leg stepping in cats on a transversely-split treadmill

To gain insight into the mechanism of coordination of stepping in the fore and hind legs of quadrupeds, we examined the kinematics of leg movements and the motor patterns in fore and hind leg flexor muscles in decerebrate walking cats when the two pairs of legs stepped on separate treadmills running at different speeds. When the front treadmill was slowed progressively from 0.6 to 0.3 m/s with the rear treadmill running at 0.6 m/s, the rate of stepping in both the fore and hind legs decreased and a 1:1 stepping ratio was maintained. The decrease in the rate of stepping in the hind legs was due primarily to an increase in the duration of the swing phase. Slowing the speed of the rear treadmill while keeping the front treadmill speed at 0.6 m/s decreased the rate of stepping of the hind legs, but had relatively little influence on the average rate of stepping in the forelegs. In this situation stepping in the fore and hind legs was uncoupled and the time of stepping in one hind leg relative to the ipsilateral foreleg progressively shifted during a walking sequence. Analysis of the timing of electromyographic (EMG) recordings from flexor muscles of the hip and elbow joints yielded insight into the neuronal mechanisms underlying the asymmetry in slowing either the front or rear treadmill. We propose that ipsilateral pattern generating networks are asymmetrically coupled via descending inhibitory pathways and an ascending excitatory pathway. We discuss how the characteristics of these linkages are functionally appropriate for establishing the normal timing of stepping in the hind and forelegs during slow walking.     

Computational fluid dynamic analysis of the flow field in the newly developed inflow cannula for a bridge-to-decision mechanical circulatory support

The flow field of the newly developed inflow cannula designed for a bridge-to-decision circulatory support was numerically analyzed by computational fluid dynamics. This new cannula has elastic struts at the tip that enable minimal invasive insertion into the left ventricle while maintaining a wide inflow area by its lantern-like tip. The cannula’s hydrodynamic loss, including change in pressure loss due to deformation, and its thrombus potential were numerically examined. Hydraulic resistance of the cannula with blood analog fluid was 31 mmHg at the flow rate of 5.0 L/min. There were regions on the inner surface of the struts where the shear rate was <100 s⁻¹, and these regions can be a potential for thrombus formation, especially at low flow rates or under limited anticoagulant therapy.     

Myoelectric signal as a quantitative measure of muscle mechanical output

The estimation of muscle tension and velocity of shortening from the myoelectric signal have been considered in numerous papers. These papers consider the estimates of each variable separately, with the other appearing in the estimation as a constant parameter. The work described in this paper develops a model for the relationship between a muscle’s mechanical outputs and the myoelectric signal. The model suggests that the myoelectric signal is related directly to the muscle mechanical power via a nonlinear differential equation in velocity of shortening. The model is general in that it includes as special cases the isometric and anisometric constant-velocity work of other authors and agrees with their experimental results. In this work anisometric experiments are performed on the biceps brachii muscle to verify the model. Estimates of muscle velocity of shortening and mechanical power are obtained from the myoelectric signal during anisometric contractions and the results agree well with the actual velocity and power. The model points out that the myoelectric signal is a direct measure of muscle tension only under isometric conditions.     

The effect of external loading upon power output in stair climbing

Summary Previous studies have examined man's ability to produce external power output during maximal repetitive work cycles of short duration. It appears, however, that there were methodological limitations which would inherently mask man's true capacities. Consequently, we examined the effect of variable external loads upon external power output as measured by running upstairs. Fourteen male subjects (16–31 years of age) who regularly participated in competitive sports performed maximal stair step tests under five experimental loading conditions (no external load, 10.1, 19.2, 24.2, and 29.2kg). Significant increases (P<0.05) in external power output were found. External power output increased from a mean of 15.9 W·kg^–1±1.0 (unloaded condition) to 18.5 W·kg^–1±1.5 (external load of 29.2 kg). This is the first modern investigation demonstrating that external loads effect external power output as measured by this technique.     

In vitro cultivation of the microsporidian:Enterocytozoon salmonis using a newly developed medium for salmonid lymphocytes

Summary Techniques have been established for the continuous culture of a newly recognized salmonid microsporidian parasiteEnterocytozoon salmonis in salmonid mononuclear leukocytes. Utilization of human recombinant interleukin-2 (HrIL-2) and polyclonal mitogens in the culture medium supported viability of salmonid mononuclear leukocytes which allowed proliferation of the intracellular microsporidian parasite. The microsporidian maintained in primary culture for 45 days was infective both in cultures of mononuclear leukocytes and in juvenile salmonids. Additional passages of the agents from primary cultures to new cultures of uninfected mononuclear leukocytes have allowed continuous in vitro propagation ofE. salmonis. The parasites from these cultures retained developmental stages from early meronts to mature spores that were identical to those observed in naturally infected fish. Also, after cryopreservation in liquid nitrogen the parasites maintained their infectivity for juvenile chinook salmon and cell cultures of mononuclear leukocytes. The development of methods for the in vitro culture ofE. salmonis has made possible investigation of the effect of this microsporidian on immune functions of its key target cell, the mononuclear leukocyte.     

Online estimation of cardiac output from respiratory data using a gradient method

This paper presents a method for estimating cardiac output, using only respiratory measurements and a mathematical model fo the respiratory system. Direct measurement of cardiac output requires the surgical insertion of a flow-meter around the pulmonary artery, and hence is restricted to procedures with experimental animals. In man, cardiac output is generally estimated using indirect means, such as by measuring the concentration of a dye in the arterial circulation as a result of its injection into the venous circulation. The degree cf dilution of the dye (after adequate mixing) can be used to estimate the flow. The technique presented in this paper is also an indirect noninvasive procedure based on CO₂ measurements. It differs from other indirect methods primarily in that it uses an on-line dynamic model of the respiratory system and makes use of a parameter-estimation algorithm. The method is based on the fact that cardiac output is a parameter in the respiratory system. A mathematical model of this system is simulated on a computer and forced (on-line) with a signal proportional to the subject's total ventilation. the output of the model is a signal representing the end-tidal exhaled partial pressure of carbon dioxide, PCO₂. The computer generated end-tidal PC O₂ is compared with the measured PC O₂ obtained from CO₂ analyser. The comparison is based on the squared difference between these two signals at the end of each breath. This error measure is minimised automatically by the computer adjusting the model cardiac output. Experimental procedures and computer techniques are presented. The resulting values of cardiac output in the model were compared with experimental data obtained using dye-dilution techniques with five mongrel dogs weighing 10–15 kg. The computer-generated estimates are shown to agree with experimental data to within 15%, with over half of the estimates agreeing within 4%.     

Anaerobic chemical changes and mechanical output during isometric tetani of rat skeletal muscle in situ

The time course was examined of the energy-rich phosphate usage and exerted isometric tetanic force in electrically stimulated rat quadriceps muscle. The maximal rate of energy-rich phosphate usage was calculated from the changes in the intramuscular concentrations of phosphocreatine, lactate, ATP and inosine monophosphate (IMP) and was somewhat higher than those calculated on the basis of exercise in vivo. The IMP concentration increased directly from the onset of the contraction until after about 11 s it remained constant. The increase in the IMP concentration coincided with a decrease in the ATP concentration. The relationship between mechanical output and energy usage was examined in two wasy (i) by calculating the ratio time integral of the force (FTI) and the total energy-rich usage (P _tot) and (ii) by calculating the ratio Force (F _t) to the energy flux (dP _tot/dt) at a certain timet.Whereas the ratio FTI/P _tot showed a hyperbolic relationship, the ratioF _t/(dP _tot/dt) showed a parabolic relationship From the latter finding and from the results described in the literature it is concluded that the ratio mechanical output/energy-rich phosphate usage depends on the conditions under which exercise is carried out. Recovery under aerobic conditions from a maximal tetanic isometric contraction sustained for 15 s was slow compared to results of experiments in vivo.     

Alternative strategies for exercise critical power estimation in patients with COPD

Exercise critical power (CP) has been shown to represent the highest sustainable work rate (WR) in patients with chronic obstructive pulmonary disease (COPD). Parameter estimation, however, depends on 4 high-intensity tests performed, on different days, to the limit of tolerance (T _lim). In order to establish a milder protocol that would be more suitable for disabled patients, we contrasted CP derived from 4, 3 and 2 tests (CP₄, CP₃ and CP₂) in 8 males with moderate COPD. In addition, CP was calculated from 2 single-day tests performed on an inverse sequence (CP_2AB and CP_2BA): CP values within 5 W from CP₄ were assumed as “clinically-acceptable” estimates. We found that [CP₄–CP₃] and [CP₄–CP₂] differences were within 5 W in 8 and 6 patients, respectively (95% confidence interval of the differences=−1.3 to 3.5 W and −11.5 to 6.5 W). There was a systematic decline on T _lim when an exercise bout was performed after a previous test on the same day (P<0.05). Consequently, substantial differences were found between CP₄ and any of the CP estimates obtained from single-day tests. In conclusion, clinically-acceptable estimates of CP can be obtained by using 3 or, in most circumstances, 2 constant WR tests in patients with moderate COPD—provided that they are not performed on the same day.     

A comparison of the effect of external loading upon power output in stair climbing and running up a ramp

Summary Previous studies have shown that external loading increases the power output measured during stair climbing. However, it was noted in an earlier study that stairtreads form mechanical contraints which limit the extent to which a subject can be externally loaded, and, thereby, make it impossible to observe maximal power output for this type of activity. The purpose of this study was to compare the effects of external loading upon power output when running up stairs or a ramp. Since a ramp is free of the mechanical constraints of stairtreads, it was felt that higher power output values would be achieved using the ramp, and that it would be possible to observe an asymptote in power output which could not be obtained for stair climbing. Seven male subjects performed maximal ramp and stair climbing tests under five experimental loading conditions (no external load, 10.1, 19.2, 24.2, and 29.2 kg). For the ramp, it was possible to employ a sixth loading condition of 34.2 kg. For stair climbing, the mean (±SD) power output values under the five experimental conditions were 16.6±0.7, 17.3±1.3, 18.5±1.0, 18.6±1.5, and 18.9±1.7 W·kg^–1, respectively. In contrast, the mean (± SD) power output values observed while running up the ramp were 18.8±1.4, 19.9±1.6, 20.5±1.6, 20.1±2.1, 20.3±2.1, and 19.8±1.9 W·kg^–1, respectively. At each experimental condition, the differences between the ramp and stairs was significant (P<0.05). For the ramp, the highest mean power output occurred at a load of 19.2 kg. Beyond this load, power output progressively declined. In contrast, for the stairs, the highest power output occurred at a load of 29.2 kg. The results of this study demonstrate that the effect of loading upon power output measurements can be extended to running up a ramp. Furthermore, unlike stair climbing, it was possible using the ramp to observe a maximal power output value for each subject.