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  • 1
    ISSN: 1439-6327
    Keywords: Key words  Force velocity relationship  ;  Muscle power  ;  Electromyography  ;  Bench press
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Although explosive power in lower-body movements has been extensively studied, there is a paucity of research examining such movements in the upper body. This study aimed to investigate the influence of load and the stretch shortening cycle (SSC) on the kinematics, kinetics, and muscle activation that occurs during maximal effort throws. A total of 17 male subjects performed SSC and concentric only (CO) bench throws using loads of 15%, 30%, 45%, 60%, 75%, 90% and 100% of their previously determined one repetition maximum bench press. The displacement, velocity, acceleration, force and power output as well as the electromyogram (EMG) from pectoralis major, anterior deltoid, and triceps brachii were recorded for each throw. The results were compared using multivariate analysis of variance with repeated measures. A criterion alpha level of P ≤ 0.05 was used. Similar force velocity power relationships were determined for this multijoint upper-body movement as has been found for isolated muscles, single joint movements, and vertical jumping. The highest power output was produced at the 30% [563 (104) W] and 45% [560 (86) W] loads during the SSC throws. Force output increased as a function of load; however, even the lighter loads resulted in considerable force due to the high accelerations produced. Average velocity, average and peak force, and average and peak power output were significantly higher for the SSC throws compared to the CO throws. However, peak velocity and height thrown were not potentiated by performing the pre-stretch because the duration and range of movement allowed the ability of the muscle to generate force at high shortening velocities to dominate the resulting throw. As such, explosive movements involving longer concentric actions than experienced during brief SSC movements may be limited by the ability of the muscle to produce force during fast contraction velocities.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1439-6327
    Keywords: Key words Electrophoresis  ;  Myosin heavy chain  ;   Densitometry  ;  Image processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The relative content of myosin heavy chain (MHC) isoforms IIb, IIa and I in human skeletal muscle taken from the m. vastus lateralis of 30 healthy male subjects was analysed using mini-gel electrophoresis. Repeated electrophoretic gels utilizing the same methods were produced for all subjects and the determination of MHC protein bands was performed using a digital scanner and National Institutes of Health (NIH) Image software and laser densitometry. A comparison between the NIH Image processing technique and laser densitometry revealed differences of 6.47%, 6.35% and 6.84% between these measurement techniques for MHC-IIb, -IIa and -I isoforms, respectively. The percentage technical error of measurement (TEM%) between electrophoretic gels was shown to be 19.1%, 17.8% and 14.2%, with regard to percentage of occurrence of MHC-IIb, -IIa and -I isoforms respectively. The variation in electrophoretic gel analyses was shown to be 5.7%, 7.3% and 5.5%, with regard to the percentage of MHC-IIb, -IIa and -I isoforms respectively. Intra-class correlations comparing NIH Image and laser densitometry produced r values in the range 0.38–0.63. Comparisons between and within gel analyses produced r values in the range 0.59–0.94 and 0.93–0.98, respectively. Analyses of variance revealed no significant differences (P 〈 0.05) between analysis techniques, between␣gels or within gels for the measurement of MHC-IIb, -IIa and -I isoforms. The inter-gel error between fibre subgroups was moderate for the two type-II MHC populations and less for type-I MHC; the intra-individual error in the measuring technique used for classifying the MHC-IIb, -IIa and -I protein bands was small. The results obtained in this investigation showed consistent trends which may reflect a false classification of the type-II MHC populations for the inter-gel and intra-individual analyses. The NIH Image software and digitizing process was shown to be a valid and reliable method for distinguishing between MHC protein bands of human skeletal tissue as separated by mini-gel electrophoretic techniques.
    Type of Medium: Electronic Resource
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