IWAI, K., K. NAKAZATO, K. IRIE, H. FUJIMOTO, and H. NAKAJIMA. Trunk Muscle Strength and Disability Level of Low Back Pain in Collegiate Wrestlers. Med. Sci. Sports Exerc., Vol. 36, No. 8, pp. 1296–1300, 2004. Introduction/Purpose: Low back pain (LBP) is a frequent injury in athletes. This study examined the relationship between isokinetic trunk muscle strength and the functional disability level of chronic LBP. We particularly focused on the existence of radiological abnormalities (RA) in the lumbar region. Methods: Subjects were 53 collegiate wrestlers. Trunk extensor and flexor muscle strength was measured at three angular velocities (60, 90, and 120°·s⁻¹). The examined parameters for trunk muscle strength were peak torque, work, average torque, and average power. The disability level of LBP was estimated by using two questionnaires. Based on the RA evaluation with x-ray and MRI, all 53 wrestlers were assigned to two groups as the RA group (N = 35, 66%) and the non-RA group (N = 18, 34%). Correlations between trunk muscle strength and the disability level of LBP in each group were analyzed with Spearman's rank test. Results: Without considering the disability level, there were 14 subjects with LBP (40%) in the RA group and 8 (44%) in the non-RA. Significantly correlated parameters with the disability level of LBP could be observed only when the subjects were restricted to the non-RA group. The correlated parameters with the two questionnaires were peak torque at 120°·s⁻¹, work at 60°·s⁻¹ and 90°·s⁻¹, and average torque at 90°·s⁻¹ and 120°·s⁻¹. There were no significantly correlated parameters in the RA group. None of the trunk flexor parameters were significantly correlated with the disability level of LBP. Conclusion: The relatively low strength of trunk extensors may be one of the factors related to nonspecific chronic low back pain in collegiate wrestlers.

In this study, we investigated the effects of resistance training protocols with different loads on muscle hypertrophy and strength. Twenty-one participants were randomly assigned to 1 of 3 (n = 7 for each) resistance training (RT) protocols to failure: High load 80 % 1RM (8–12 repetitions) (H group), low load 30 % 1RM (30–40 repetitions) (L group) and a mixed RT protocol (M group) in which the participants switch from H to L every 2 weeks. RT consisted of three sets of unilateral preacher curls performed with the left arm 3 times/week with 90 s rest intervals between sets. The right arm served as control. Maximum voluntary contraction (MVC) of the elbow flexors (elbow angle: 90°) and rate of force development (RFD, 0–50, 50–100, 100–200 and 200–300 ms) were measured. Cross-sectional area (CSA) of the elbow flexors was measured via magnetic resonance imaging (MRI). All measurements were conducted before and after the 8 weeks of RT (72–96 h after the last RT). Statistical evaluations were performed with two-way repeated measures (time × group). After 8 weeks of 3 weekly RT sessions, significant increases in the left elbow flexor CSA [H: 9.1 ± 6.4 % (p = 0.001), L: 9.4 ± 5.3 % (p = 0.001), M: 8.8 ± 7.9 % (p = 0.001)] have been observed in each group, without significant differences between groups. Significant changes in elbow flexor isometric MVC have been observed in the H group (26.5 ± 27.0 %, p = 0.028), while no significant changes have been observed in the M (11.8 ± 36.4 %, p = 0.26) and L (4.6 ± 23.9 %, p = 0.65) groups. RFD significantly increased during the 50–100 ms phase in the H group only (p = 0.049). We conclude that, as long as RT is conducted to failure, training load might not affect muscle hypertrophy in young men. Nevertheless, strength and RFD changes seem to be load-dependent. Furthermore, a non-linear RT protocol switching loads every 2 weeks might not lead to superior muscle hypertrophy nor strength gains in comparison with straight RT protocols.

High-intensity muscle contractions (HiMCs) are known to increase c-Myc expression that is known to stimulate ribosome biogenesis and protein synthesis in most cells. However, although c-Myc mRNA transcription and c-Myc mRNA translation have been shown to be upregulated following resistance exercise concomitantly with increased ribosome biogenesis, this connection has not been tested directly. We investigated the effect of adeno-associated virus (AAV)-mediated c-Myc overexpression, with or without fasting or percutaneous electrical stimulation-induced HiMC, on ribosome biogenesis and protein synthesis in adult mouse skeletal muscles. AAV-mediated overexpression of c-Myc in mouse skeletal muscles for 2 wk increased the DNA polymerase subunit POL1 mRNA, 45S-pre-rRNA, total RNA, and muscle protein synthesis without altering mechanistic target of rapamycin complex 1 (mTORC1) signaling under both ad libitum and fasted conditions. RNA-sequencing (RNA-seq) analyses revealed that c-Myc overexpression mainly regulated ribosome biogenesis-related biological processes. The protein synthesis response to c-Myc overexpression mirrored the response with HiMC. No additional effect of combining c-Myc overexpression and HiMC was observed. Our results suggest that c-Myc overexpression is sufficient to stimulate skeletal muscle ribosome biogenesis and protein synthesis without activation of mTORC1. Therefore, the HiMC-induced increase in c-Myc may contribute to ribosome biogenesis and increased protein synthesis following HiMC. NEW & NOTEWORTHY Resistance exercise is known to increase c-Myc expression, which is known to stimulate ribosome biogenesis and protein synthesis in a variety of cells. However, whether the increase in c-Myc stimulates ribosome biogenesis and protein synthesis in skeletal muscles remains unknown. We found that c-Myc overexpression is sufficient to stimulate skeletal muscle ribosome biogenesis and protein synthesis without activation of mTORC1.

Cross-sectional study of a specific population. To investigate the prevalence and coprevalence of nonspecific low back pain (nsLBP) and lumbar radiological abnormalities (LRA) in judo athletes. nsLBP and LRA occur frequently in judo athletes. High body mass has been reported to be associated with both nsLBP and LRA. The subjects comprised 82 male judo athletes (mean +/- SD age, 20.1 +/- 0.9 years) from 3 weight categories: lightweight (n = 29), middleweight (n= 31), and heavyweight (n = 22). The presence of nsLBP was evaluated using a questionnaire. LRA were examined using plain-film radiographs and magnetic resonance imaging. The prevalence of nsLBP and LRA were compared among weight categories. The prevalence of nsLBP in the lightweight, middleweight, and heavyweight categories was 34.5%, 32.3%, and 40.9%, respectively. For LRA, prevalence for the 3 weight categories was 65.5%, 90.3%, and 90.9%, respectively (middle-weight and heavyweight greater prevalence than lightweight [P<.05]). The prevalence of LRA in athletes with nsLBP in each category was 50.0%, 100%, and 88.9%, respectively (middleweight greater prevalence than lightweight [P<.05]). The prevalence of LRA in athletes without nsLBP in each category was 73.7%, 85.7%, and 92.3%, respectively. The prevalence of LRA was approximately 90% in the middleweight and heavyweight categories, which was greater than for the lightweight category. There was a large coprevalence of nsLBP and LRA. However, many judo athletes without nsLBP had LRA. The presence of LRA may not have a direct association with nsLBP.

Background: Although muscle strain injury models are frequently employed, highly invasive procedures, including surgical intervention, are typically used to produce these models. In this study, a minimally invasive model of acute strain injury was produced with a single eccentric contraction. Hypothesis: The authors tested whether the severity of strain injury in the in vivo gastrocnemius depends on the excursion of the ankle. Study Design: Controlled laboratory study. Methods: Animals were randomly assigned to 2 groups: a small range of motion group (90°-105°, n = 10) and a large range of motion group (90°-125°, n = 10). Tetanically activated gastrocnemius muscles with percutaneous electrical stimulation were simultaneously elongated by forced dorsiflexion of the ankle joint. Results: Isometric tetanic force of the large range of motion group was significantly lower than the pretreatment control 1, 2, and 3 days after treatment. Such reduction was not observed in the small range of motion group. Apparent pathologic damage was observed in the large range of motion group throughout the study period of 10 days. Conclusions: A larger range of motion causes more damage in eccentric contraction by using the in vivo model. Clinical Relevance: This in vivo model is useful to elucidate mechanisms of prevention and recovery of strain injury.