Teruo Nomura

Lower muscle co-contraction in flutter kicking for competitive swimmers

The purpose of this study was to examine the difference in muscle activation pattern and co-contraction of the rectus and biceps femoris in flutter-kick swimming between competitive and recreational swimmers, to better understand the mechanism of repetitive kicking movements during swimming. Ten competitive and 10 recreational swimmers swam using flutter kicks at three different velocities (100%, 90%, and 80% of their maximal velocity) in a swimming flume. Surface electromyographic signals (EMG) were obtained from the rectus (RF) and biceps femoris (BF), and lower limb kinematic data were obtained at the same time. The beginning and ending of one kick cycle was defined as when the right lateral malleolus reached its highest position in the vertical axis. The offset timing of muscle activation of RF in the recreational swimmers was significantly later at all velocities than in the competitive swimmers (47-48% and 26-33% of kick time of one cycle for recreational and competitive swimmers, respectively), although the kinematic data and other activation timing of RF and BF did not differ between groups. A higher integrated EMG of RF during hip extension and knee extension induced a higher level of muscle co-contraction between RF and BF in the recreational swimmers. These results suggest that long-term competitive swimming training can induce an effective muscle activation pattern in the upper legs.

Effect of standing postural deviations on trunk and hip muscle activity

[Purpose] It is very important to consider effects that postural deviations has on muscle activity when treating low back pain. Therefore, activities of trunk and hip joint muscles in healthy adults while they attempted three postural conditions of neutral, sway-back, and lordosis was compared and evaluated in this study. [Subjects and Methods] The subjects comprised 17 healthy adult male volunteers. The muscle activity and spinal curve were measured while the subjects attempted different postural conditions (neutral, sway-back, and lordosis) as defined in the text. [Results] Activity of trunk and hip inner muscles was decreased in sway-back posture, and only activity of the trunk back muscles was increased in lordosis. [Conclusion] This results were suggested that postural deviations affected muscle control in the lumbo-pelvic area.

Intracyclic Velocity Variation and Arm Coordination for Different Skilled Swimmers in the Front Crawl

Abstract The aim of this study was to examine whether the intracyclic velocity variation (IVV) was lower in elite swimmers than in beginner swimmers at various velocities, and whether differences may be related to arm coordination. Seven elite and nine beginner male swimmers swam front crawl at four different swimming velocities (maximal velocity, 75%, 85%, and 95% of maximal swimming velocity). The index of arm coordination (IDC) was calculated as the lag time between the propulsive phases of each arm. IVV was determined from the coefficient of variation of horizontal velocity within one stroke cycle. IVV for elite swimmers was significantly lower (26%) than that for beginner swimmers at all swimming velocities . In contrast, the IDC was similar between elite and beginner swimmers. These data suggest that IVV is a strong predictor of the skill level for front crawl, and that elite swimmers have techniques to decrease IVV. However, the IDC does not contribute to IVV differences between elite and beginner swimmers.