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Skeletal muscle is the dominant organ in locomotion and energy metabolism so that maintaining skeletal muscle function is a prerequisite for our health and independent living throughout the life. A loss or decrease in skeletal muscle function leads to increased morbidity and mortality through the development of secondary diseases such as metabolic syndrome, type 2 diabetes, obesity, cardiovascular and respiratory disease. Identifying mechanisms which influence the processes regulating skeletal muscle function is a key priority. The recent discovery of microRNAs (miRNAs) provides a new knowledge controlling skeletal muscle function. miRNAs suppress gene expression through either in inhibition of protein translation or in degradation of the mRNA transcripts through a process similar to RNA interference (RNAi). This review provides the current understanding in skeletal muscle miRNA biology and focuses on their role and regulation under physiological conditions with exercise.

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Relationships between low back pains and psychological factors among college students

Shintaro Endo ; Hidetoshi Kanou ; Takayuki Ishiwata ; Haruyasu Katou ; Michio Yasukawa ; Takashi Nigorikawa ; Kazuo Oishi

Japanese Journal of Physical Fitness and Sports Medicine.2012;61(1):71-78.

The purpose of this study was to clarify the relationship between the low back pain of college students and psychological factors by using a questionnaire for low back pains and five psychological tests. The tests consisted of the Hopkins Symptom Checklist (HSCL), State-Trait Anxiety Inventory (STAI), Purpose in Life (PIL) test, Hassles Scale for students and Type A test. The subjects were 337 college students (126 male, 211 female) ranging in age from 19 to 22 (mean ± SD: 20.2 ± 1.3) years. Seventy-four subjects whose lower back pain was thought to be caused by organic factors were excluded. The 263 subjects (102 males, 161 females, mean ± SD: 20.1 ± 1.1 years) were divided into three groups (NP: subjects with no pain, PND: subjects with pain but no difficulties in daily life, PD: subjects with pain and difficulties in daily life) by degrees of low back pain. The PD subjects showed a more negative attitude than those in the PND and/or NP groups for four tests, i.e., Hassles Scale and the psychosomatic component of the HSCL and State-Trait Anxiety Inventory tests. It was suggested that low back pain was related to psychological factors such as stress and anxiety.

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Influence of the torque generating capacity of the lower extremity muscles on the running and jump performance in primary and junior high school boys

Takaya Yoshimoto ; Yohei Takai ; Eiji Fujita ; Yuko Fukunaga ; Hirofumi Kintaka ; Hidetsugu Nishizono ; Hiroaki Kanehisa ; Masayoshi Yamamoto

Japanese Journal of Physical Fitness and Sports Medicine.2012;61(1):79-88.

This study aimed to determine the relationships between the torque generating capacity of the lower extremity muscles and either running or jump performance in primary and junior high school boys. A total of 102 primary and junior high school boys participated in this study. Muscle thicknesses (MTs) of the knee extensors and plantar flexors were determined using ultrasonography. Muscle volumes (MVs) of the knee extensors and plantar flexors were estimated using MTs and limb lengths. The isometric joint torques (TQs) for knee extensors and ankle plantar flexors were measured using myometer. MV and TQ were divided by body mass (MV/BM and TQ/BM, respectively). Running velocity was measured using a non-motorized treadmill. The counter movement jump (CMJ) and squat jump (SJ) were performed on a matswitch system. The flight time was measured and used to calculate the heights of CMJ and SJ using the following equation; height (cm) = g × (flight time)² /8/10. As the result of multiple regression analysis, age, MV/BM and TQ/BM were selected as predictors of running velocity in the primary school boys, whereas TQ and lean body mass in junior high school boys. In the primary school boys, TQ/BM and body fat mass was selected as significant contributors for SJ and CMJ performances, whereas, in the junior high school boys, TQ and the percent of body fat for SJ performance and MV/BM and TQ for CMJ performance. Thus, the present results indicate that the relationships between torque generating capacity of the lower extremity muscles and either running or jump performance differ between primary and junior high school boys. It may be assumed that, for running and jump performances, muscle mass and strength become determinant factors in junior high school boys, whereas their values relative to body mass in primary school boys.

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Influence of bending the trunk forward during drop landing on muscles around the knee joint

Kazuaki Hamada ; Yukio Urabe ; Yuki Yamanaka

Japanese Journal of Physical Fitness and Sports Medicine.2012;61(1):89-93.

The aim of the present study was to investigate whether personal hamstring muscular activation increased by landing with the trunk bent forward. First, 14 healthy female university students were instructed to perform normal drop landing from a 40 cm-high box on both legs. Second, subjects were directed to perform drop landing with the trunk bent forward. Using images obtained from a high-speed video camera, the upper center of mass was calculated in the sagittal plane for determining the differences in these landings. For 0.1 second after toe contact, the muscular activation of quadriceps femoris and hamstring muscles was analyzed using an electromyogram (EMG), and these findings were compared between the 2 types of landings. There was no significant difference in the activation of quadriceps femoris, but the activation tended to decrease during landing with the trunk bent forward. However, the activation of hamstring muscles increased significantly during landing with the trunk bent forward compared with that during normal landing. During landing with the trunk bent forward, the activation of hamstring muscles increased, and the activation of quadriceps femoris tended to decrease. Because contraction of hamstring muscles decreases tension in the anterior cruciate ligament, the findings of this study may help in the prevention of anterior cruciate ligament (ACL) injury.

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