筋力トレーニングによる中高年女性の筋力増加とその要因としての筋の動員と筋肥大の経時的変化

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It has been documented that the adaptive response in muscle force production capabilities is determined by neural activation (recruitment and discharge frequency of motor units) and morphological alternation (hypertrophy). To date, however, accumulation of this information with respect to middle-aged and elderly women has been limited. Thus, the purpose of this study was to investigated the physiological mechanisms underlying the time course change in muscle strength gain with respect to the relative contributions of both neural, especially muscle recruitment, and muscle hypertrophic factors in middle-aged and elderly women using magnetic resonance imaging (MRI) and its transverse relaxation time (T2) variable. Eight middle-aged and elderly women (range : 59-70years old) and six young women (range : 22-29 years old) performed isokinetic knee and hip extension/flexion training twice a week for 8 weeks at an angular velocity of 60°/sec (5 repetitions/set : 2 sets/day), 240°/sec (10 repetitions/set : 2 sets/day) and 120°/sec (5 repetitions/set : 2 sets/day) using isokinetic dynamometer. The maximum voluntary strength was determined as the one repetition maximum for isotonic knee extension exercise. MRI was used to determine the muscle volume of quadriceps femoris (QF) muscles. As an index of muscle recruitment, relative activated cross-sectional area (%-actCSA) of the QF muscles, which represented an area greater than the resting T2 + 1 SD in MRI pixels, was calculated at rest and immediately after knee extension exercise based on T2-weighted MR images. The isotonic strength, muscle volume, and %-actCSA of QF muscles were measured before and after 2, 4, 6, and 8 weeks of resistance training. Multiple regression analysis was performed to determine which factors (recruitment or hypertrophy) contributed to strength gain atthe measured each period. As a result, the muscle recruitment factorplayed a major role in strength gain in the early phase of resistance training in both groups and then the muscle hypertrophic factor gradually dominated over the muscle recruitment factor in the contribution to the strength gain in both groups. In middle-aged and elderly women, however, the time course of muscle hypertrophic factor domination over the muscle recruitment factor was more delayed than that in young women. These results suggest that a longer period of resistance training allowed the muscle to hypertrophy in middle-aged and elderly women, thus physiological determinants (muscle recruitment / hypertrophic factor) that have been altered by aging affect the course of resistance training.
日本体力医学会の論文
2003-08-01

筋力トレーニングによる中高年女性の筋力増加とその要因としての筋の動員と筋肥大の経時的変化

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