scholarly journals Effect of muscle temperature on rate of oxygen uptake during exercise in humans at different contraction frequencies

2002 ◽  
Vol 205 (7) ◽  
pp. 981-987
Author(s):  
Richard A. Ferguson ◽  
Derek Ball ◽  
Anthony J. Sargeant
Keyword(s):  
Mechanical Efficiency ◽  
Human Muscle ◽  
Hot Water ◽  
Muscle Temperature ◽  
Energy Turnover ◽  
Cycling Exercise ◽  
Contraction Frequency ◽  
Cross Bridge ◽  
Pedalling Rate ◽  
The Right

SUMMARY The effect of elevated human muscle temperature on energy turnover was investigated during cycling exercise (at 85 % of V̇O2max) at a contraction frequency of 60 revs min-1. Muscle temperature was passively elevated prior to exercise by immersion of the legs in a hot water bath (42 °C). During exercise at this low pedalling rate, total energy turnover was higher (P<0.05) when muscle temperature was elevated compared with normal temperature (70.4±3.7 versus 66.9±2.4 kJ min-1, respectively). Estimated net mechanical efficiency was found to be lower when muscle temperature was elevated. A second experiment was conducted in which the effect of elevated human muscle temperature on energy turnover was investigated during cycling exercise (at 85 % of V̇O2max) at a contraction frequency of 120 revs min-1. Under the conditions of a high pedalling frequency, an elevated muscle temperature resulted in a lower energy turnover (P<0.05) compared with the normal muscle temperature (64.9±3.7 versus 69.0±4.7 kJ min-1, respectively). The estimated net mechanical efficiency was therefore higher when muscle temperature was elevated. We propose that, in these experiments, prior heating results in an inappropriately fast rate of cross-bridge cycling when exercising at 60 revs min-1, leading to an increased energy turnover and decreased efficiency. However, at the faster pedalling rate, the effect of heating the muscle shifts the efficiency/velocity relationship to the right so that cross-bridge detachment is more appropriately matched to the contraction velocity and, hence, energy turnover is reduced.

Similar effects of cooling and fatigue on eccentric and concentric force-velocity relationships in human muscle

2001 ◽  
Vol 90 (6) ◽  
pp. 2109-2116 ◽  
Author(s):  
C. J. De Ruiter ◽  
A. De Haan
Keyword(s):  
Isometric Force ◽  
Human Muscle ◽  
Muscle Temperature ◽  
Adductor Pollicis Muscle ◽  
Concentric Contractions ◽  
Cycling Rate ◽  
Concentric Force ◽  
Cross Bridge ◽  
Different Temperatures ◽  
Force Velocity

The purpose of this study was to investigate the effects of muscle temperature and fatigue during stretch (eccentric) and shortening (concentric) contractions of the maximally electrically activated human adductor pollicis muscle. After immersion of the lower arm in water baths of four different temperatures, the calculated muscle temperatures were 36.8, 31.6, 26.6, and 22.3°C. Normalized (isometric force = 100%) eccentric force increased with stretch velocity to maximal values of 136.4 ± 1.6 and 162.1 ± 2.0% at 36.8 and 22.3°C, respectively. After repetitive ischemic concentric contractions, fatigue was less at the lower temperatures, and at all temperatures the loss of eccentric force was smaller than the loss of isometric and concentric force. Consequently, normalized eccentric forces increased during fatigue to 159.7 ± 4.6 and 185.7 ± 7.3% at 36.8 and 22.3°C, respectively. Maximal normalized eccentric force increased exponentially ( r 2 = 0.95) when V max was reduced by cooling and/or fatiguing contractions. This may indicate that a reduction in cross-bridge cycling rate could underlie the significant increases in normalized eccentric force found with cooling and fatigue.

scholarly journals Interaction between muscle temperature and contraction velocity affects mechanical efficiency during moderate-intensity cycling exercise in young and older women

2009 ◽  
Vol 107 (3) ◽  
pp. 763-769 ◽  
Author(s):  
Martin P. Bell ◽  
Richard A. Ferguson
Keyword(s):  
Older Women ◽  
Ventilatory Threshold ◽  
Fiber Type ◽  
Mechanical Efficiency ◽  
Moderate Intensity ◽  
Muscle Temperature ◽  
Energy Turnover ◽  
Mechanical Power Output ◽  
Velocity Relationship ◽  
Relationship Of

The effect of elevated muscle temperature on mechanical efficiency was investigated during exercise at different pedal frequencies in young and older women. Eight young (24 ± 3 yr) and eight older (70 ± 4 yr) women performed 6-min periods of cycling at 75% ventilatory threshold at pedal frequencies of 45, 60, 75, and 90 rpm under control and passively elevated local muscle temperature conditions. Mechanical efficiency was calculated from the ratio of energy turnover (pulmonary O2 uptake) and mechanical power output. Overall, elevating muscle temperature increased ( P < 0.05) mechanical efficiency in young (32.0 ± 3.1 to 34.0 ± 5.5%) and decreased ( P < 0.05) efficiency in older women (30.2 ± 5.6 to 27.9 ± 4.1%). The different effect of elevated muscle temperature in young and older women reflects a shift in the efficiency-velocity relationship of skeletal muscle. These effects may be due to differences in recruitment patterns, as well as sarcopenic and fiber-type changes with age.

scholarly journals The Frank-Starling mechanism involves deceleration of cross-bridge kinetics and is preserved in failing human right ventricular myocardium

2015 ◽  
Vol 309 (12) ◽  
pp. H2077-H2086 ◽  
Author(s):  
Nima Milani-Nejad ◽  
Benjamin D. Canan ◽  
Mohammad T. Elnakish ◽  
Jonathan P. Davis ◽  
Jae-Hoon Chung ◽  
...  
Keyword(s):  
Heart Failure ◽  
Right Ventricular ◽  
Muscle Length ◽  
Human Myocardium ◽  
Force Frequency ◽  
Heart Failure Patients ◽  
Cycling Rate ◽  
Physiological Conditions ◽  
Cross Bridge ◽  
The Right

Cross-bridge cycling rate is an important determinant of cardiac output, and its alteration can potentially contribute to reduced output in heart failure patients. Additionally, animal studies suggest that this rate can be regulated by muscle length. The purpose of this study was to investigate cross-bridge cycling rate and its regulation by muscle length under near-physiological conditions in intact right ventricular muscles of nonfailing and failing human hearts. We acquired freshly explanted nonfailing ( n = 9) and failing ( n = 10) human hearts. All experiments were performed on intact right ventricular cardiac trabeculae ( n = 40) at physiological temperature and near the normal heart rate range. The failing myocardium showed the typical heart failure phenotype: a negative force-frequency relationship and β-adrenergic desensitization ( P < 0.05), indicating the expected pathological myocardium in the right ventricles. We found that there exists a length-dependent regulation of cross-bridge cycling kinetics in human myocardium. Decreasing muscle length accelerated the rate of cross-bridge reattachment ( ktr) in both nonfailing and failing myocardium ( P < 0.05) equally; there were no major differences between nonfailing and failing myocardium at each respective length ( P > 0.05), indicating that this regulatory mechanism is preserved in heart failure. Length-dependent assessment of twitch kinetics mirrored these findings; normalized dF/d t slowed down with increasing length of the muscle and was virtually identical in diseased tissue. This study shows for the first time that muscle length regulates cross-bridge kinetics in human myocardium under near-physiological conditions and that those kinetics are preserved in the right ventricular tissues of heart failure patients.

THE THERAPEUTIC USE OF LEECHES IN CHILDREN AS DESCRIBED IN 1825

PEDIATRICS ◽  
1969 ◽  
Vol 44 (1) ◽  
pp. 83-83
Author(s):  
T. E. C.
Keyword(s):  
Therapeutic Use ◽  
The Body ◽  
Hot Water ◽  
Brown Colour ◽  
Excellent Description ◽  
Yellow Line ◽  
The Right

Leeches were used in the treatment of many pediatric conditions until relatively recently. Many physicians prescribed leeches, especially in the treatment of the purported symptoms caused by teething. William Moss,1 for example, advised applying two or three leeches at one time on the foot or heel of teething infants where "bleeding is a remedy much to be depended on when the symptoms of heat, fever, drowsiness, and startings are urgent." The following is an excellent description of the indications for leeching in children, as given by Dr. James Kennedy in 1825: Leeching, so as to abstract blood from a particular part sustaining inflammation, fulness, or pain, is very useful in many diseases especially those of children. . . . When the leech is of the right or medicinal kind, its body has a blackish brown colour, marked on the back with six yellow spots, and edged with a yellow line on each side:—these spots, however, as well as the lines, grow faint and almost disappear at certain seasons. . . . The mouth forms, as it were, the body of a pump and its tongue the sucker; and, by the working of this . . . mechanism, the blood is made to rise up into the conduit which conveys it to the animal's stomach. . . . Leeches may be employed in every case where topical bleedings are required, or where venesection cannot be performed. Before applying them, all the parts should be carefully washed;—first, with hot water and soap, for the purpose of removing, as much as possible, the particles of the cutaneous excretion which the leech instinctively dislikes, especially if impregnated in any degree with the odour of medicine;—and secondly, with milk and water as warm as can be endured, with the object of stimulating the superficial vessels and filling them with red blood.

scholarly journals Waterways, Ice Permeability at Depth, and Water Pressures at Glacier D’Argentière, French Alps

1983 ◽  
Vol 29 (102) ◽  
pp. 227-239 ◽  
Author(s):  
Didier Hantz ◽  
Louis Lliboutry
Keyword(s):  
Free Surface ◽  
Water Level ◽  
Pore Pressure ◽  
Time Lag ◽  
Extensive Study ◽  
Hot Water ◽  
Clear Cut ◽  
Melt Water ◽  
Glacier Ice ◽  
The Right

AbstractTo clear up the changes which had happened at the subglacial catchment of glacier d’Argentière, an extensive study, with 31 borings and a coring down to the bottom (240 m) was performed in 1979/80, just upstream from the catchment, in an overdeepened area. The behaviour of the water level during boring with a hot water jet, and just after, was different from one bore hole to another, mainly because transient leaks appeared in the walls of bore holes. Next, the water level fluctuated slowly, in the same way in most of the deep bore holes, showing that glacier ice below about 100 m deep is slightly pervious. What is so measured is the pore pressure of water in deep ice. The piezometric gradient between bore holes, and the time lag between fluctuations of water level, which increases with distance from the right bank, shows that there is no waterway at the bottom of the overdeepened area, save at its up-stream end. Most of the melt water must flow between ice and rock along the right bank, its free surface rising by about 150 m during the increased discharge in June. No clear-cut correlation between the bottom pore pressure and the air temperature or the discharge at the subglacial catchment down-stream was found.

Effects of postnatal maturation on energetics and cross-bridge properties in rat diaphragm

2002 ◽  
Vol 92 (3) ◽  
pp. 1074-1082 ◽  
Author(s):  
Gilles Orliaguet ◽  
Olivier Langeron ◽  
Belaid Bouhemad ◽  
Pierre Coriat ◽  
Yves LeCarpentier ◽  
...  
Keyword(s):  
Mechanical Efficiency ◽  
Total Force ◽  
Rat Diaphragm ◽  
Shortening Velocity ◽  
Cross Sectional ◽  
Muscle Energetics ◽  
Postnatal Maturation ◽  
Cross Bridge ◽  
Velocity Relationship ◽  
Force Velocity

The effects of maturation on cross-bridge (CB) properties were studied in rat diaphragm strips obtained at postnatal days 3, 10, and 17 and in adults (10–12 wk old). Calculations of muscle energetics and characteristics of CBs were determined from standard Huxley equations. Maturation did not change the curvature of the force-velocity relationship or the peak of mechanical efficiency. There was a significant increase in the total number of CBs per cross-sectional area (m) with aging but not in single CB force. The turnover rate of myosin ATPase increased, the duration of the CB cycle decreased, and the velocity of CBs decreased significantly only after the first week postpartum. There was a linear relationship between maximum total force and m ( r = 0.969, P < 0.001), and between maximum unloaded shortening velocity and m ( r = 0.728, P < 0.001). When this study in the rat and previous study in the hamster are compared, it appears that there are few species differences in the postnatal maturation process of the diaphragm.

scholarly journals Resting myosin cross-bridge configuration in frog muscle thick filaments.

1986 ◽  
Vol 102 (2) ◽  
pp. 610-618 ◽  
Author(s):  
M Cantino ◽  
J Squire
Keyword(s):  
Myosin Head ◽  
Freeze Fracture ◽  
Optical Diffraction ◽  
Outer Diameter ◽  
X Ray ◽  
Cross Bridge ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
Cross Bridges ◽  
The Right

Clear images of myosin filaments have been seen in shadowed freeze-fracture replicas of single fibers of relaxed frog semitendinosus muscles rapidly frozen using a dual propane jet freezing device. These images have been analyzed by optical diffraction and computer averaging and have been modelled to reveal details of the myosin head configuration on the right-handed, three-stranded helix of cross-bridges. Both the characteristic 430-A and 140-150-A repeats of the myosin cross-bridge array could be seen. The measured filament backbone diameter was 140-160 A, and the outer diameter of the cross-bridge array was 300 A. Evidence is presented that suggests that the observed images are consistent with a model in which both of the heads of one myosin molecule tilt in the same direction at an angle of approximately 50-70 degrees to the normal to the filament long axis and are slewed so that they lie alongside each other and their radially projected density lies along the three right-handed helical tracks. Any perturbation of the myosin heads away from their ideal lattice sites needed to account for x-ray reflections not predicted for a perfect helix must be essentially along the three helical tracks of cross-bridges. Little trace of the presence of non-myosin proteins could be seen.

Design of Lead Screw Actuators for Wearable Robotic Applications

2005 ◽  
Author(s):  
Kevin W. Hollander ◽  
Thomas G. Sugar
Keyword(s):  
High Weight ◽  
Weight Ratio ◽  
Design Procedure ◽  
Mechanical Efficiency ◽  
Human Muscle ◽  
Wearable Robot ◽  
Screw Design ◽  
Lead Screw ◽  
Standard Lead ◽  
Robotic Applications

A wearable robot is a controlled and actuated device that is in direct contact with its user. As such, the implied requirements of this device are that it must be portable, lightweight and most importantly safe. To achieve these goals an actuator with a good ‘power to weight’ ratio, good mechanical efficiency, good ‘strength to weight’ ratio and that is safe is desired. The design of the standard lead screw does not normally perform well in any of these categories. The typical lead screw has low pitch angles and large radii, thereby yielding low mechanical efficiencies and high weight. However, using the design procedure outlined in this text both efficiency and weight are improved, thus yielding a lead screw system with performances that rival human muscle. The result of an example problem reveals a feasible lead screw design that has a ‘power to weight’ ratio of 277W/kg, approaching that of the DC motor driving it, at 312W/kg, as well as a mechanical efficiency of 0.74, and a maximum ‘strength to weight’ ratio of 11.3kN/kg(1154kgf/kg).

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