Author

Jean Ramsay

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Adapted Human Biodynamics

Supervisor

Cameron J. R. Blimkie

Language

English

Abstract

The present investigation was undertaken to examine the effects of resistance training on maximal voluntary strength, muscle cross-sectional area and contractile properties in prepubescent boys. A second purpose was to observe the time course and identify the possible mechanism(s) underlying strength development in this population. Thirteen boys (9-11y) volunteered for each of the training (T) and control (C) groups. Training consisted of between3-5 sets of six exercises. Subjects trained 3 times weekly for two phases of 10 weeks at intensities betweetn 75-85% of the 1 repetition maximum(RM). Performance measures (1RM) were recorded for bench press (BP) and leg press(LP) on a Global Gym station for both experimental and control groups. The 1 RM double arm curl and leg extension were measured for the experimental group only, on the training device. Maximal voluntary isometric strength (MVC), isokinetic strength (IS) and contractile properties were measured for the right elbow flexors (EF) and knee extensors (KE). The interpolated twitch technique was used to determine % motor unit activation (MUA) and computerized axial tomography (CAT) was used to determine EF and KE cross-sectional area (CSA). All data were analysed using ANOVA with a Tukey post hoc test, with the exception of % MUA (Friedman two-way analysis of variance). High day today and trial to trial reliability was obtained for voluntary strength measurements. Wide fluctuations were observed in day to day and trial to trial reliability of the evoked contractile properties. While CAT was judged a satisfactory method for measuring total limb and total lean cross-sectional area, questions were raised concerning the reliability and accuracy of the technique in discerning between individual muscle bellies. Significant training effects on voluntary strength were observed for BP (+35 %) , LP (+22%), EFIS (+26 %), KEIS (+20%), EFMVC(+37%) (P<.01),and at joint angles 90 and 120 for KEMVC (P<.05). Muscular endurance, defined as the number of repetitions performed at the end of the study with the pre-test 1 RM, was also significantly increased for the BP and LP with training (P<0.1). For the contractile properties, training significantly increased EF (+30 %, P<.01) and KE (+30%, P<.05) twitch torque. With the exception of EF maximum rate of torque relaxation (MRTR) (+20 %, P<.05) all other time-related contractile properties were not affected by training. However, maximurn rate of torque development (MRTD) for both muscle groups showed a trend toward increasing. There were no significant effects of training on CSA or % MUA, however, there was a trend towards increased MUA f-or elbow flexion and knee extension in the trained group. In conclusion, resistance training increased voluntary strength of EF during both phases of training. Voluntary strength of KE increased mostly during the first 10 weeks of training. Although the strength gains were independent of changres in muscle CSA, significant increases in twitch torque combined with trends in some of the timerelated contractile properties, during the second phase of training, suggest possible adaptations in muscle extensibility or excitation-contraction coupling. While these changes may explain part of the observed increases in strength, neurological adaptations such as increased MUA, improved motor skill, better co-contraction of the synergist muscle groups and increased inhibition of the antagonist muscle groups are likely the major determinants of the strength gains in this study.

McMaster University Library

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