INFLUENCE OF MUSCLE FIBER COMPOSITION AND MUSCLE CROSS-SECTIONAL AREA ON MAXIMAL ISOMETRIC STRENGTH TOMOO RYUSHI and TETSUO FUKUNAGA Abstract The purpose of the present study is to investigate the influence of muscle cross-sectional area on maximal isometric strength (M. I. S.), and the influence of muscle fiber composition on the ratio of maximal isometric strength to muscle cross-sectional area in the leg extensor muscles. Muscle biopsies were taken from the right vastus lateralis of 16 healthy untrained males. Cross-sectional area of the leg extensor muscles were measured by ultrasonic measurements. Maximal isometric strength were determined as peak torques using an isokinetic dynamometer. Significant positive correlation was observed between muscle cross-sectional area and maximal isometric strength (r=0.61, p<0.05). The ratio of maximal isometric strength to muscle cross-sectional area was 2.6 }0.4 Nm/cm2 (mean }S. D.) with a wide range of values from 2.0 to 3.3 Nm/cm2. No relationship was observed to exist between the ratio of maximal isometric strength to muscle cross-sectional area and muscle fiber composition. From these results it can be concluded that muscle cross-sectional area plays a more important role in producing a high maximal isometric strength than muscle fiber composition, and that the large variations observed in the ratio of maximal isometric strength to muscle cross-sectional area may be caused by factors other than muscle fiber composition. (J. Physical Fitness Japan 1986, 35 : 168 `174 Department of Tokyo of Sports Sciences, College of Arts and Sciences, University
等尺 性 最大筋力に及ぼ す 筋断面積お よび筋 線 維組成の影響 筋 断 面 積 の 影 響,さ らに,筋 断 面 積 あ た りの 等 尺 状 態 で,膝 した.な 討 す る こ と を 目 的 と した. 連 続3回,常 を 伸 展 す る際 のpeak 性最 大筋 力 に 対 す る筋線 維 組 成 の 影響 につ い て 検 II.方 させ,そ 法 169 お,被 torqueを 測 定 験 者に は 充 分 な時 間 閭隔 をお い て に 最 大 努 力 でpeak torqueを 発 揮 の な かの最大 値 を 等 尺 性最 大 筋 力 と し た. A.被 験 者 C.筋 被 検 者 は 規 則 的 な ト レー ニ ン グ経 験 の な い 健 康 成 人 男 子16名 で あ っ た.彼 身 長 は169.8±5.2cm,体 ら の 年 齢 は21.1±2.0歳, 重 は62.4±6.1kgで あ っ た. B.等 生 検 と染色法 筋 サ ン プ ル は,Evansた 正 を 加 え た 方 法(図1)を の 外 側 部(外 側 広 筋)か ち の 方 法5)に 若 干 の 修 用 い て,右 大 腿 四 頭 筋 ら 採 取 した,採 取 部 位 は 腸骨 棘 と膝 蓋 骨 上緑 中央 部 と を結 んだ 線 の 遠 位 尺 性 最 大 筋力 の測 定 1/3の 部 位 か ら,さ ら に 外 側 へ1/2の 座 位 姿 勢 の 被 験 者 を シ ー トベ ル トを 用 い て 測 定 用 の 椅 子 に 胸 部 お よび 腹 部 を 固 定 した.さ ら に, 被 験 者 の 右 脚 の 足 頸 部 をCybex III(0 /sec)の レ バー に 固 定 し た の ち,右 膝 関 節 を90 に 保 持 し た Fig 1. A biopsy 部 位 で あ り, そ の 深 さ は 大 腿 の 太 さ と は 無 関 係 に筋 膜 か ら 垂 直 に3cmと し た.な お,被 験 者 す べ てに 対 し,ほ とん ど 同 じ 部 位 か ら採 取 す る よ う留 意 した(図1). 筋の 採 取 量 は 筋線 維数 に region(a) and the modified suctorial し て 平 均1,016(410 needle biopsy device(b).
琉 子,福 永 170 Fig 2. Cross-section ATPase 4. 3, stain dark FTb, FTc, exist in of (ph ; ST, light these 9.4), FTc, ; FTa. photographs muscle dark light ( fibers ; FTa, ; FTa, ; ST stained FTb, FTb, fibers, ; for FTc, (C) FTa light after myosin ; ST, ATPase. (B) preincubation fibers, : (A) after in FTb routine myosin preincubation fibers, ph 4. FTc in 6, fibers dark ph ; ST, do not
Table 1. Maximal isometric strength (M. I. S.), muscle cross-sectional area in leg extensor muscle and muscle fiber composition in m. vastuslateralis (n=16).
Fig 3. The relationship between the ratio of maximal isometric strength (M. I. S.) to muscle cross-sectional area and the percent of ST fibers (A), the relationship between the ratio of M. I. S. to muscle cross-sectional area and the percent area of ST fibers(b).
Fig 4. The relationship between maximal isometric strength (M. I. S.) and muscle crosssectional area in leg extensor muscle.
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