Paper

• ポストアスリートのステータスデータベースを利用したコーチングアプリケーションの設計
  Oct. 2025, [Reviewed]

  DOI URL
• The association of lower trunk muscle strength with low back pain in elite lightweight judokas is dependent on lumber spine abnormalities
  Takashi Okada; Kazunori Iwai; Takayoshi Hakkaku; Koichi Nakazato
  Isokinetics and Exercise Science, 01 May 2022, [Reviewed]
  BACKGROUND:
  
  Lumbar radiological abnormalities (LRA) and trunk muscle weakness are major causes of the low back pain (LBP). We reported that the prevalence of LRA was approximately 90% in middle- and heavyweight-judokas, independent to the occurrence of LBP. However, the trunk muscle weakness, especially the rotators, plays a key role in occurrence of LBP in heavyweight judokas.
  
  OBJECTIVE:
  
  To examine the trunk muscle strength (TMS) and LRA impact on LBP occurrence in lightweight judokas.
  
  METHOD:
  
  The strength of the trunk extensors, flexors, and rotators was measured in 32 lightweight male judokas. LBP and LRA were identified using a questionnaire, X-ray, and MRI.
  
  RESULTS:
  
  The occurrence rate of LBP and LRA were 40.6% and 62.5%, respectively, without any significant correlation. Among judokas without LRA, TMS of those with LBP were significantly lower than those without LBP ([Formula: see text] 0.05, the extensor; 60[Formula: see text]/s: ES [d] [Formula: see text] 1.38, 90[Formula: see text]/s: ES [d] [Formula: see text] 0.78, and 120[Formula: see text]/s: ES [d] [Formula: see text] 0.37, flexor; 60[Formula: see text]/s: ES [d] [Formula: see text] 1.48, dominant rotator; 60[Formula: see text]/s: ES [d] [Formula: see text] 1.66, and 90[Formula: see text]/s: ES [d] [Formula: see text] 1.87, non-dominant rotator; 90[Formula: see text]/s: ES [d] [Formula: see text] 0.17, and dominant/non-dominant rotator ratio; 90[Formula: see text]/s: ES [d] [Formula: see text] 1.55). Moreover, there were significant negative correlations between LBP severity and TMS ([Formula: see text] 0.05, the extensor; 90[Formula: see text]/s: [Formula: see text] [Formula: see text]0.63, dominant rotator; 90[Formula: see text]/s: [Formula: see text] [Formula: see text]0.648, and dominant/non-dominant rotator ratio; 90[Formula: see text]/s: [Formula: see text] [Formula: see text]0.621) in judokas without LRA.
  
  CONCLUSION:
  
  Weak trunk musculature may be a co-factor in the occurrence of LBP in lightweight judokas without LRA.

  URLDOI URL
• Weight Category-dependent Trunk Muscle Strength and its Relation with LBP in Elite Judokas.
  Takashi Okada; Takayoshi Hakkaku; Kazunori Iwai; Koichi Nakazato
  Sports medicine international open, Jan. 2021, [Reviewed]
  Trunk muscle strength (TMS), especially rotator, is an important factor for both athletic performance and injury risks in judokas. However, the characteristics of TMS that depend on weight categories are still unclear. Although inadequate TMS might cause low back pain (LBP), the relationship between these two variables is not fully understood. In this study, weight category-dependent TMS and its relationship with LBP was investigated in Japanese judokas. The subjects were 66 male collegiate judokas, who were classified into the lightweight (N=14), middleweight (N=29) or heavyweight (N=23) category. The peak torques of extensor, flexor and rotator muscles were measured. The LBP group and non-LBP group were defined by questionnaire. TMS (normalized by body weight) in the heavier weight category showed a lower tendency in comparison with other categories, except for rotator strength. Significant differences were observed in the extensors (90 and 120 °/s; P<0.05) and flexors (60, 90 and 120 °/s; P<0.05). The LBP group (N=9) only showed significantly lower extensor (60 °/s; P<0.05) and right-rotator (60 °/s; P<0.01) strength in the heavyweight category compared with the non-LBP group (N=14). The relative TMS of judokas decreased in the heavyweight category, except for trunk rotator strength. Notably, low trunk extensor and rotator strengths are risk factors for LBP in heavyweight judokas.

  DOI URL
• METHODOLOGICAL DEVELOPMENT OF WRESTLING SHUTTLE TEST　　　　　　　　　　　　　　　
  Kazunori Iwai; Ray Takahashi; Kenichi Yumoto; Koichi Nakazato
  International Journal of Wrestling Science, Aug. 2018, [Reviewed]
• Asymmetrical and smaller size of trunk muscles in combat sports athletes with lumbar intervertebral disc degeneration.
  Iwai K; Koyama K; Okada T; Nakazato K; Takahashi R; Matsumoto S; Yamamoto Y; Hiranuma K
  SpringerPlus, Sep. 2016, [Reviewed]

  DOI URL
• ASSOCIATION BETWEEN TRUNK MUSCLE STRENGTH AND LOW BACK PAIN IN COLLEGIATE WRESTLERS WITHOUT LUMBAR DISC DEGENERATION　　　　　　　　　　　　　　　
  Shingo Matsumoto; Kazunori Iwai; Yoshimaro Yanagawa; Koichi Nakazato
  Jul. 2012, [Reviewed]
• 国民体育大会剣道競技における審判員の位置取りに関する実態調査　　　　　　　　　　　　　　　
  Mar. 2010, [Reviewed]
• PHYSICAL CHARACTERISTICS OF COLLEGIATE TRACK AND FIELD ATHLETES WITH LOW BACK PAIN
  SAITO YOSHINOBU; IWAI KAZUNORI; NAKAZATO KOICHI; IRIE KAZUNORI; MIZUNO MASUHIKO; NAKAJIMA HIROYUKI
  Japanese Journal of Physical Fitness and Sports Medicine, 01 Feb. 2009, [Reviewed]
  The purpose of this study was to clarify physical characteristics related to low back pain (LBP) in collegiate track and field athletes. We particularly focused on the nature of the track and field. The subjects were 21 male collegiate track and field athletes including only sprinters, hurdlers, long jumpers and triple jumpers. The examined parameters were physical characteristics, isokinetic flexor and extensor strength in the knee and trunk regions. The evaluation of LBP was estimated by a questionnaire test and orthopedic surgeons' diagnosis. According to these evaluations, we divided al...

  DOI URL 2
• SPORT-SPECIFIC CHARACTERISTICS OF TRUNK MUSCLES IN COLLEGIATE WRESTLERS AND JUDOKAS
  Kazunori Iwai; Takashi Okada; Koichi Nakazato; Hideo Fujimoto; Yosuke Yamamoto; Hiroyuki Nakajima
  JOURNAL OF STRENGTH AND CONDITIONING RESEARCH, Mar. 2008, [Reviewed]

  DOI URL
• ASSOCIATION BETWEEN PROGRESSION OF UNDERWEIGHT AND OVERWEIGHT STATUS AND PHYSICAL FITNESS IMPROVEMENTS IN THE YOUTH : A ONE-YEAR FOLLOW-UP STUDY
  IWAI KAZUNORI; MATSUKI MASAFUMI; KOSHIDA SENTARO; TANAKA KOSUKE; MIYASHITA KOJI; URABE YUKIO
  Japanese Journal of Physical Fitness and Sports Medicine, 2008, [Reviewed]
  The purpose of this study was to clarify whether changes in BMI were associated with physical fitness improvements in youth after a one-year period. The subjects were 287 youth male students aged between 15 and 18. A physical fitness test was conducted using the new physical fitness test with 8 items for youth aged between 12 and 19 years, developed by the Ministry of Education, Culture, Sports, Science and Technology of Japan to assess their physical fitness level at baseline and after a one-year period. The subjects were divided into 6 groups (LD, LI, ND, NI, HD, HI) by a combination of the baseline BMI value (low, normal, high) and the BMI change after the one year period (decreased, increased). These results of the present study demonstrated that physical fitness improvements were different in each subject group. There was no significant physical fitness improvement in the LD and HI groups, whereas the other groups showed significant improvements in their physical fitness level (P<0.01). The results suggest that adequate improvements in physical fitness occurred during youth period. However, their improvements in physical fitness may be hampered by progression of underweight and overweight status, respectively.

  DOI URL
• Body mass, nonspecific low back pain, and anatomical changes in the lumbar spine in judo athletes.
  Okada T; Nakazato K; Iwai K; Tanabe M; Irie K; Nakajima H
  The Journal of orthopaedic and sports physical therapy, Nov. 2007, [Reviewed]

  DOI URL
• Trunk muscle strength and disability level of low back pain in collegiate wrestlers
  K Iwai; K Nakazato; K Irie; H Fujimoto; H Nakajima
  MEDICINE AND SCIENCE IN SPORTS AND EXERCISE, Aug. 2004, [Reviewed]

  DOI URL
• PSYCHOLOGICAL CHARACTERISTICS OF UNIVERSITY WRESTLERS WITH LOW BACK PAIN : ASSESSMENT BY THE PSYCHOLOGICAL CONDITION INVENTORY TEST
  IWAI KAZUNORI; NAKAZATO KOICHI; IRIE KAZUNORI; ADACHI TAKUMI; NAKAJIMA HIROYUKI
  Japanese Journal of Physical Fitness and Sports Medicine, 2003, [Reviewed]
  The purpose of this study was to investigate relationships between low back pain (LBP) and psychological conditions in university wrestlers. We examined psychological conditions of seventy male university wrestlers using the Psychological Condition Inventory (PCI) test and evaluated whether psychological conditions have some relationships with LBP. Evaluations of LBP were based on a questionnaire test and the diagnosis of orthopedic surgeons. Based on the LBP evaluation, we assigned all wrestlers into two groups as the LBP group and the non-LBP group. We obtained the following results. There were twenty-eight university wrestlers (40%) in the LBP group and forty-two wrestlers (60%) in the non-LBP group. Wrestlers in the LBP group showed significantly high values in all factors relating to fatigue in comparison to the non-LBP group. We conclud that the university wrestlers with LBP feel fatigue in their minds and bodies.

  DOI URL
• 腰痛を有する大学レスリング選手の心理的コンディション
  Mar. 2002
• Physical characteristics of university wrestlers with low back pain
  Kazunori Iwai; Koichi Nakazato; Kazunori Irie; Hideo Fujimoto; Hiroyuki Nakajima
  Japanese Journal of Physical Fitness and Sports Medicine, 2002, [Reviewed]

  DOI URL