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Relationships between maximum effort isometric and concentric-eccentric isokinetic trunk extension forces
610
Abstracts
FORCE-VELOCITY RELATION OF THE WAIST FLEXORS AT VARIOUS John W. Chow and Warren 0. Darling Department of Exercise Science, The University of Iowa, Iowa City, IA 52242-1111, USA.
ACTIVATION
LEVELS
The purpose of this study was to quantify the force-velocity (FV) relation of the wrist flexors at various activation levels , measured aa a fraction of the maximum Using the quick-release method, FV data were collected at isometric strength (F_). The FV data at different five different activation levels from four subjects. activation levels of each subject were fitted remarkably well with Hill's characteristic equation -- F = (F_b - av)/(v + b), where F is muscle force, v is In general, the shortening velocity shortening velocity, a and b are Hill constants. decreased with activation. Most of the a/F_ values at 100% and 80% activation levels lay between 0.5 and 0.6, which are greater than those obtained from isolated muscles and muscle fibers. Using normalized data, first order polynomials relating the Hill constants and activation levels were obtained. Both a and b were found to increase with increasing activation. When the FV curves were forced to converge at the maximum shortening velocity (V,), there were drastic changes in the shape of the curves, especially when the shortening velocity was greater than 20% of v_.
RELATIONSIiIPSBETWEENMAKIMUM EFFORT ISOMETRICAND CONCENTRIC-ECCENTRICISOKINBTICTRUNKEXTENSIONFORCES M.D. Grabiner Department of Biomedical Engineering The Cleveland Clinic Foundation, Cleveland, OH, 44195. The relationships between static and dynamic measurements of trunk muscle function have not been clearly defined. The purpose of this study was to characterize functional relationships between trunk extensor function as measured by peak force during isometric, isokinetic concentric and &kinetic eccentric conditions. Ten male and female subjects performed maximum effort (MVE) isometric trunk extension at five trunk angles and MVE isokinetic trunk extension through a 70 deg range of motion at speeds from -250 to 250 deg/s. Isometric MVE at 30 degrees trunk extension was significantly less than that at other trunk angles which were not signiiicantly different from one another. Peak isokinetic concentric and eccentric trunk extension forces were found to be statisticslly unrelated to isometric MVE with correlations that were generally nonsign&ant and of weak to moderate amplitude. Regression analysis revealed that peak isokinetic concentric and eccentric forces could be characterized entirely by speed terms. Regression further revealed that isokinetic MVE for concentric speeds between 60 and 150 deg/s could be predicted using 30 deg/s MVE. Isokinetic MVE for eccentric contractions could not be predicted using concentric force. Predicting isokinetic eccentric MVE for speeds from 60 to 150 deg/s using the 30 deg/s eccentric MVE, although statistically significant, was not as effective. The results of the present study demonstrate an independence between maximum effort isometric and isokinetic trunk extension performance, and within &kinetic performance, an independence between concentric and eccentric performance.
STRETCH-SHORTENINGCYCLE KINEMATICS AND MUSCLE FORCE POTENTIATIONOF TJ3E RAT TIBJALJS ANTERIOR MUSCLE David Hawkins Department of Physical Education University of California, Davis, California 95616 A study of the rat tibialis anterior (TA) muscle-tendon (MT) complex was conducted to investigate the relationship between muscle force and stretch-shortening cycle variables of stretch rate, stretch amplitude, and initial muscle length. Stretch amplituaes of 1 mm, 2 mm, 3 mm, and 4 mm were imposed on active muscle at rates of 1 mm/s, 10 mmis, and LOOmmk. Stretch- were initiatedfrom MT lengthsrangingfrom 4 mm less than the optimum length (lo), to 2 mm greater than the optimumlength. Optimum length was deftaed as the MT lengthat which the maximumactive muscle force was geuemted. Muscle force recorded at the end of each stretchwas compared to the isometricforce gene-ratedby the muscleat ZUIinitial length equal to the previouslystretchedMT length. The ratio of these two forces was used to describe the amouot of force potent&d during the active muscle stretch. Resultsindicate that the amount of force potentiated was most sensitive to the initial MT length and the stretch we.. There was no force potentiakd during slow stretch rates of 1 mm/s. The fast stretch rates of 100 mm/s produced no force potentiation for initial MT IengtJ~ below lo-3 mm, but did potentiate the force 10 96 to 20 % at longer initial MT lqths. Stretch rates of 10 mm/s c&sistently produced the greatest force potentiation, values being approximately 0 46, 10 46, 15 %, 25 96, and 25 46 for initial MT lengths of lo-4 mm, 10-3 mm, lo-2 mm, lo-l mm, and lo respectively.
Abstracts
FORCE-VELOCITY RELATION OF THE WAIST FLEXORS AT VARIOUS John W. Chow and Warren 0. Darling Department of Exercise Science, The University of Iowa, Iowa City, IA 52242-1111, USA.
ACTIVATION
LEVELS
The purpose of this study was to quantify the force-velocity (FV) relation of the wrist flexors at various activation levels , measured aa a fraction of the maximum Using the quick-release method, FV data were collected at isometric strength (F_). The FV data at different five different activation levels from four subjects. activation levels of each subject were fitted remarkably well with Hill's characteristic equation -- F = (F_b - av)/(v + b), where F is muscle force, v is In general, the shortening velocity shortening velocity, a and b are Hill constants. decreased with activation. Most of the a/F_ values at 100% and 80% activation levels lay between 0.5 and 0.6, which are greater than those obtained from isolated muscles and muscle fibers. Using normalized data, first order polynomials relating the Hill constants and activation levels were obtained. Both a and b were found to increase with increasing activation. When the FV curves were forced to converge at the maximum shortening velocity (V,), there were drastic changes in the shape of the curves, especially when the shortening velocity was greater than 20% of v_.
RELATIONSIiIPSBETWEENMAKIMUM EFFORT ISOMETRICAND CONCENTRIC-ECCENTRICISOKINBTICTRUNKEXTENSIONFORCES M.D. Grabiner Department of Biomedical Engineering The Cleveland Clinic Foundation, Cleveland, OH, 44195. The relationships between static and dynamic measurements of trunk muscle function have not been clearly defined. The purpose of this study was to characterize functional relationships between trunk extensor function as measured by peak force during isometric, isokinetic concentric and &kinetic eccentric conditions. Ten male and female subjects performed maximum effort (MVE) isometric trunk extension at five trunk angles and MVE isokinetic trunk extension through a 70 deg range of motion at speeds from -250 to 250 deg/s. Isometric MVE at 30 degrees trunk extension was significantly less than that at other trunk angles which were not signiiicantly different from one another. Peak isokinetic concentric and eccentric trunk extension forces were found to be statisticslly unrelated to isometric MVE with correlations that were generally nonsign&ant and of weak to moderate amplitude. Regression analysis revealed that peak isokinetic concentric and eccentric forces could be characterized entirely by speed terms. Regression further revealed that isokinetic MVE for concentric speeds between 60 and 150 deg/s could be predicted using 30 deg/s MVE. Isokinetic MVE for eccentric contractions could not be predicted using concentric force. Predicting isokinetic eccentric MVE for speeds from 60 to 150 deg/s using the 30 deg/s eccentric MVE, although statistically significant, was not as effective. The results of the present study demonstrate an independence between maximum effort isometric and isokinetic trunk extension performance, and within &kinetic performance, an independence between concentric and eccentric performance.
STRETCH-SHORTENINGCYCLE KINEMATICS AND MUSCLE FORCE POTENTIATIONOF TJ3E RAT TIBJALJS ANTERIOR MUSCLE David Hawkins Department of Physical Education University of California, Davis, California 95616 A study of the rat tibialis anterior (TA) muscle-tendon (MT) complex was conducted to investigate the relationship between muscle force and stretch-shortening cycle variables of stretch rate, stretch amplitude, and initial muscle length. Stretch amplituaes of 1 mm, 2 mm, 3 mm, and 4 mm were imposed on active muscle at rates of 1 mm/s, 10 mmis, and LOOmmk. Stretch- were initiatedfrom MT lengthsrangingfrom 4 mm less than the optimum length (lo), to 2 mm greater than the optimumlength. Optimum length was deftaed as the MT lengthat which the maximumactive muscle force was geuemted. Muscle force recorded at the end of each stretchwas compared to the isometricforce gene-ratedby the muscleat ZUIinitial length equal to the previouslystretchedMT length. The ratio of these two forces was used to describe the amouot of force potent&d during the active muscle stretch. Resultsindicate that the amount of force potentiated was most sensitive to the initial MT length and the stretch we.. There was no force potentiakd during slow stretch rates of 1 mm/s. The fast stretch rates of 100 mm/s produced no force potentiation for initial MT IengtJ~ below lo-3 mm, but did potentiate the force 10 96 to 20 % at longer initial MT lqths. Stretch rates of 10 mm/s c&sistently produced the greatest force potentiation, values being approximately 0 46, 10 46, 15 %, 25 96, and 25 46 for initial MT lengths of lo-4 mm, 10-3 mm, lo-2 mm, lo-l mm, and lo respectively.