Naoki Mukai

Effect of Resistance Exercise Training on Bone Formation and Resorption in Young Male Subjects Assessed by Biomarkers of Bone Metabolism

We studied the effects of high intensity resistance exercise training on bone metabolism in 17 young adult Oriental males (23–31 years) by measuring sensitive biomarkers of bone formation and resorption. The subjects were assigned to a training group and a sedentary group. The training group followed a weight training program three times per week for 4 months. In the training group, serum osteocalcin concentration and serum bone‐specific alkaline phosphatase activity were significantly increased within the first month after the beginning of resistance exercise training, and the elevated levels remained throughout the training period, while there was no significant change in plasma procollagen type‐I C‐terminal concentration. Urinary deoxypyridinoline excretion was transiently suppressed and returned to the initial value but was never stimulated during the 4 months. These results suggest that the resistance exercise training enhanced bone formation without prior bone resorption. In the sedentary group, there was no significant difference in bone metabolic markers except plasma procollagen type‐I C‐terminal, which continuously decreased during the experimental period. There were no significant changes in total and regional bone mineral density in either group. In conclusion, (1) resistance exercise training increased markers of bone formation, while it transiently suppressed a marker of bone resorption, and (2) such adaptive changes of bone metabolism to resistance exercise training occurred during the early period of the training, before changes in bone density were observable through densitometry.

Lumbar Intervertebral Disk Degeneration in Athletes

Background Several studies have reported that physical loading related to competitive sports activities is associated with lumbar intervertebral disk degeneration. However, the association between types of sports activities and disk degeneration has not been clarified. Hypothesis The frequencies of disk degeneration may vary with the competitive sport because of the different postures and actions specific to each sport. Study Design Cross-sectional study (prevalence); Level of evidence, 3. Methods Study participants were 308 well-trained university athletes (baseball players, basketball players, kendo competitors, runners, soccer players, swimmers) and 71 nonathlete university students (reference group). Disk degeneration was evaluated using T2-weighted magnetic resonance imaging. A self-reported questionnaire concerning low back pain was also conducted. Results The proportions of the participants who had disk degeneration among the baseball players (odds ratio, 3.23) and the swimmers (odds ratio, 2.95) were significantly higher than among the nonathletes using logistic regression analysis. When all patients were grouped together, the association between lifetime experience of low back pain and participants with disk degeneration was significant, and a linear association between the degree of severest low back pain experienced and participants with disk degeneration, analyzed by a Cochran-Mantel-Haenszel test, was also significant. Conclusion Continuous competitive baseball and swimming activities during youth may be associated with disk degeneration. Furthermore, the study indicates that the experience of severe low back pain might be a predictor of disk degeneration in youth. The authors hope that preventive measures and management to protect against disk degeneration and low back pain in athletes will be established by further studies based on these results.

Relationship Between Low Back Pain and Competitive Sports Activities During Youth

Background Low back pain is a significant problem not only for the adult, but also during youth. However, the relationship between low back pain during youth and the duration or types of competitive sports has not been clarified. Hypothesis Low back pain during youth is associated with the duration and types of competitive sports. Study Design Cross-sectional study; Level of evidence, 4. Methods Study participants were 4667 new university students who, from 2004 to 2006, answered a questionnaire concerning low back pain and their participation in competitive sports. The participants were divided into a “no” group (NO), a middle group (MID), and a high group (HI) based on the duration of participation in competitive sports. The answers to the questionnaire were analyzed using the Cochran-Mantel-Haenszel test. Furthermore, we selected students who had participated in the same sport for 5 or more years and categorized the students according to the type of sport. Differences in low back pain among the groups were analyzed using logistic regression with the NO group as the reference group. Results There were statistically significant linear associations in the NO, MID, and HI groups, with 50.0%, 61.8%, and 71.7%, respectively, of the students experiencing low back pain. Among the NO, MID, and HI groups, 4.4%, 5.7%, 9.6%, respectively, had experienced school absence due to low back pain; and 4.0%, 8.5%, and 14.6%, respectively had low back pain with associated lower extremity pain and numbness. All 8 sports groups that were analyzed had experienced low back pain significantly higher than the NO group, and the odds ratios differed by sport with the highest (3.8) for the volleyball group. Conclusion Excessive exposure to competitive sports activities during youth was associated with low back pain and symptoms in the lower extremities, with the severity varying with the sport. To reduce low back pain in youth, factors that may be causing low back pain, such as sport-specific postures and motions, need to be investigated.

Differences in EMG Activity in Scapular Plane Abduction under Variable Arm Positions and Loading Conditions

PURPOSE The present study was performed to investigate the activities of four shoulder muscles-the supraspinatus, the middle deltoid, the infraspinatus, and the upper trapezius-in scapular plane abduction in various exercise conditions. METHODS Eight male subjects (mean +/- SD: 23.4 +/- 1.3 yr) with an asymptomatic nondominant left shoulder participated in this study. Each subject performed scapular plane abduction with humeral external rotation (full can position) and with humeral internal rotation (empty can position), producing constant target torques of 4 and 12 N.m, respectively. In addition, the subjects performed each exercise in the supine position with the limb supported by straps. Electromyogram (EMG) was recorded with intramuscular electrodes at the supraspinatus and infraspinatus, and with surface electrodes placed at the middle deltoid and upper trapezius. The EMG activity (RMS) of each muscle was normalized according to the highest EMG activity (100% MVC) during a maximum manual muscle test for the corresponding muscle (% MVC). RESULTS EMG activity of the supraspinatus was significantly greater than those of the other shoulder muscles in the full can position from 10-20 degrees to 50-60 degrees arcs with a target torque of 4 N.m (P < 0.05). In contrast, the supraspinatus and middle deltoid showed similar EMG activities under other exercise conditions. CONCLUSIONS These results suggest that there is an exercise condition that induces greater activity of the supraspinatus in scapular plane abduction.

Influence of knee alignment on quadriceps cross-sectional area

Previous studies of methods for stimulating the individual muscles composing the quadriceps femoris have not considered the structural features of a subjects knee joint. In this study, we compared the ratios of the individual muscles composing the quadriceps between subjects with different knee alignments using magnetic resonance (MR) imaging. A total of 18 healthy males were examined: 6 normal knees (age, 23.0+/-0.6 yr; femorotibial angle (FTA), 176.8+/-0.4 degrees), 6 genu varum (age, 21.8+/-2.9 yr; FTA, 181.7+/-2.6 degrees) and 6 genu valgum (age, 21.0+/-1.6 yr; FTA, 172.3+/-1.5 degrees). The cross-sectional areas (CSAs) of quadriceps muscles were obtained by MR imaging of the entire left thigh. The CSAs of the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM) and vastus intermedius (VI) muscles were obtained by MR imaging of the entire left thigh in a supine position. The VM/VL ratio was also obtained by dividing the CSA of the VM by that of the VL and compared among the three groups of subjects with different knee alignments. The genu varum group showed a significantly higher %CSA of VM in the CSA of the quadriceps (VM/Quad) (49.0+/-2.6%) than values for the other two groups. The genu valgum group showed significantly higher values of RF/Quad (15.2+/-2.1%) and VL/Quad (40.6+/-4.0%) than the other groups. The VM/VL ratio was significantly higher in the genu varum than in values for the other two groups. This difference in CSA, in respect to knee alignment, may be considered when devising muscle training programs.

Evaluation of the cartilaginous acetabulum by magnetic resonance imaging in developmental dysplasia of the hip.

MRI findings for 51 hips in 45 pediatric patients (mean age 2.3 years; range, 1.1–4.1 years) with suspected acetabular dysplasia or residual subluxations were analyzed retrospectively. We attempted to predict the growth of osseous acetabulum and future acetabular coverage on MRI performed at 2 years of age. The cut-off value of the cartilaginous angle was 18° for the cartilage acetabular index and 13° for the cartilage center edge angle. However, follow-up assessments to monitor the progress of changes in the congruity between femoral head and acetabular development are important.