Effects of Various Numbers of Runs on the Success of Hamstring Injury Prevention Program in Sprinters.

Studies have not adequately addressed the influence of fatigue, which is considered a major risk factor for hamstring injuries. Therefore, this study aimed to clarify how a muscle fatigue condition affects the success of hamstring injury prevention programs in sprinters. The study subjects were 613 collegiate male sprinters. They employed submaximal/maximal running for a large number of runs and supramaximal running for a small number of runs in daily training. The hamstring injury prevention program had become the most effective strategy in the past 24 seasons of track and field for preventing hamstring injuries. The number of sprinters who experienced hamstring injuries in three periods over the 24 seasons was recorded. The incidents of hamstring injuries during supramaximal running per athlete-seasons were 137.9, 60.6, and 6.7 for Periods I, II, and III, respectively, showing a significant decline (p < 0.01). Furthermore, the incidents of hamstring injuries during submaximal and maximal running per season showed no significant change. The results of this study indicate that by inducing muscle fatigue, a small number of runs makes hamstring injury prevention programs effective.

A 100-m Sprint Time Is Associated With Deep Trunk Muscle Thickness in Collegiate Male Sprinters.

Introduction: One reason athletes train their trunk muscles is that the body's trunk stability has been shown to prevent injury. However, the relationship between body trunk muscle thickness, particularly that of deep muscles, and athletic performance remains to be clarified. Purpose: We aimed to explore the relationship between 100-m sprint performance and the sizes of the trunk stabilizing muscles, the psoas major muscle (PM), transversus abdominis (TA), and multifidus muscle (MM), in collegiate sprinters. Methods: Fourteen male sprinters belonging to a university athletics club participated in this study. The thicknesses of the TA and MM were measured using an ultrasonic diagnostic apparatus (ProSound C3; Aloka, Tokyo, Japan). The cross-sectional area of the PM was assessed by a magnetic resonance imaging apparatus (Vantage Elan; Toshiba Medical Systems, Tokyo, Japan). The relationship between these anthropometric parameters and the 100-m sprint time was analyzed by Spearman's correlation coefficient, multi- regression analysis, and the change-point regression model. Results: The sizes (mean ± SD) of the muscles were: PM, 43.074 ± 7.35 cm2; TA, 4.36 ± 0.72 mm; and MM, 3.99 ± 0.48 cm. The mean 100-m sprint time was 11.00 ± 0.48 s. Spearman's correlation analysis revealed that the 100-m sprint time had a significant moderate negative correlation with TA (ρ = -0.691, p < 0.01) and a low negative but not significant correlation with MM (ρ = -0.327, p = 0.28), whereas PM did not show a significant or in-negligible correlation. The change-point regression model found the change-points in the 100-m sprint time and the thickness of the TA and MM at 4.70 mm (95% CI: 4.00-5.43 mm) and 3.84 cm (95% CI: 3.28-4.31 cm), respectively. The sprint time decreased with an increase in the thickness of the muscles up to the change-points, whereas it did not change even if the muscles became thicker than the change-points. The change-points were consistently observed when the thickness of the muscles was normalized by body mass. Conclusion: Sprint performance for 100-m was found to be associated with TA and MM thickness in a biphasic manner. As muscle thickness increased, the sprint time decreased, followed by a plateau phase.

The effectiveness of bench press training with or without throws on strength and shot put distance of competitive university athletes.

PURPOSE: Maximum force exertion against various resistance levels (heavy-light) is commonly implemented to improve both strength- and speed-oriented components of power. Medium-light resistances allow rapid accelerations, yet incur significant decelerations in the later concentric phase to bring the bar to a halt, which may limit the concentric effort and, therefore, the effectiveness of training. Accordingly, ballistic actions have been recommended. This study evaluated the effectiveness of power bench press training, with the bar thrown on a Smith machine (BPthrow) or without throwing (BPnon-throw), for developing strength and shot put distance. METHODS: Nine university shot-putters performed BPthrow and BPnon-throw at 50, 40 and 30% 1RM, as well as seated and standing shot put trials. Peak angular velocities at the elbow were measured in these tasks using a wireless electro-goniometer. Participants underwent 24 sessions of training (12 weeks) with either BPthrow (n = 5) or BPnon-throw (n = 4) at the three intensities (20 s × 2 sets at 50, 40 and 30% 1RM). RESULTS: The peak elbow velocity during BPthrow was 1.7 times greater than BPnon-throw for all intensities. The velocity of BPthrow at 30% 1RM (854.7°/s), however, was still slower than seated (1121.3°/s) and standing (1539.1°/s) shot puts. BPthrow training significantly improved 1RM (+ 10.0%) and the distances of seated (+ 11.7%) and standing (+ 3.8%) shot puts, while no performance changes occurred after BPnon-throw training. CONCLUSION: When undergoing power bench press against medium-light resistances, maximum ballistic actions are important strategies for improving 1RM and shot put performance of university shot-putters.

Association between Yogurt Consumption and Intestinal Microbiota in Healthy Young Adults Differs by Host Gender.

Human intestinal microbiota are influenced by various factors viz. diet, environment, age, gender, geographical, and socioeconomic situation, etc. among which diet has the most profound impact. However, studies investigating this impact have mostly included subjects from diverse geographic/socioeconomic backgrounds and hence the precise effects of dietary factors on gut microbiota composition remain largely confounded. Herein, with an aim to evaluate the association between dietary habits, specifically yogurt consumption, and the gut microbiota in healthy young adults sharing similar age, lifestyle routine, geographical setting, etc., we conducted a cross-sectional study wherein 293 collegiate freshmen answered a questionnaire about their frequency of yogurt consumption over the last 2 months and provided stool specimens for microbiota analysis. Fecal microbiota were analyzed by highly sensitive reverse-transcription-quantitative-PCR assays targeting bacterial 16S rRNA molecules. Fecal organic acids were measured by HPLC. Overall, the gut microbiota were predominated (97.1 ± 8.6%) by Clostridium coccoides group, Clostridium leptum subgroup, Bacteroides fragilis group, Bifidobacterium and Atopobium cluster. Interestingly, after adjusting the data for yogurt consumption, females were found to have higher total bacterial (P = 0.013) and Bifidobacterium (P = 0.046) count and fecal pH (P = 0.007) and lower fecal concentration of total organic acids (P = 0.030), succinic acid (P = 0.007) and formic acid (P = 0.046) as compared to males. Altogether, yogurt consumption showed positive linear association with Lactobacillus and Lactobacillus gasseri subgroup in both male and female subjects; however, several gender-specific disparities were also detected in this yogurt-microbiota association. Yogurt consumption demonstrated a negative association with L. sakei subgroup, Enterobacteriaceae and Staphylococcus in males but shared a positive association with L. casei subgroup and succinic acid in female subjects. The study manifests the association between yogurt consumption and gut microbiota in a healthy homogeneous cohort and show how this association can differ by host gender. The findings should be helpful for prospective studies investigating the diet-microbiome interaction in human health and disease.

Prevention of Hamstring Injuries in Collegiate Sprinters.

BACKGROUND: No studies have been reported on how strength, agility, and flexibility training reduce the occurrence of hamstring injuries in sprinters. Therefore, a program for preventing hamstring injury in these athletes has not been established. PURPOSE: To document the incidence of hamstring injuries during times when different prevention strategies were employed to see whether a particular prevention program reduced their occurrence. STUDY DESIGN: Descriptive epidemiology study. METHODS: The study subjects were a total of 613 collegiate male sprinters trained by the same coach over 24 seasons. Tow training was used throughout the research period as a normal sprint training method. The hamstring injury prevention program evolved over time. From 1988 to 1991 (period 1), prevention focused on strength training alone; from 1992 to 1999 (period 2), a combination of strength and agility training was used; and from 2000 to 2011 (period 3), the program incorporated strength, agility, and flexibility training. The incidence of hamstring injuries was compared for each of the 3 prevention strategies. RESULTS: The incidence of hamstring injuries per athlete-seasons was 137.9 for period 1, 60.6 for period 2, and 6.7 for period 3. A significant difference was observed in the incidence of hamstring injury according to the different prevention programs (χ2(2) = 31.78, P < .001, effect size: Cramer V = 0.23, 1 - ß = 0.999). Residual analysis showed that the number of hamstring injuries for period 1 was significantly greater than the expected value (P < .01), whereas that for period 3 was significantly lower than the expected value (P < .01). CONCLUSION: The incidence of hamstring injuries in sprinters decreased as agility and flexibility were added to strength training.

Analyses of associations between reactive oxygen metabolites and antioxidant capacity and related factors among healthy adolescents.

Evidence based on epidemiologic investigations using biochemical parameter is meaningful for health promotion and administration among adolescents. We conducted Reactive Oxygen Metabolites (ROM) and Biological Antioxidant Potentials (BAP) tests, along with a questionnaire survey, for a sample of 74 high school students (16.51±0.11 years of aged mean±SE), to investigate the associations between ROM, BAP, and related factors, including BMI and blood biochemical data. Venous blood samples (approximately 7cc) were collected. At the same time, each individual's information was obtained from the questionnaire. The mental health status was investigated using the Center for Epidemiologic Study Depression scale (CES-D) included in the same questionnaire. The mean values and standard errors of all variables were calculated. In addition, the relationships between ROM and BAP with these factors were analyzed. The results revealed the preferred levels of ROM (261.95 ± 9.52 U.CARR) and, BAP (2429.89±53.39 µmol/L) and blood biochemical data. Few significant relationships between two markers and related factors were found. So, we detected a cluster with an imbalance between ROM and BAP, which means low antioxidant ability, whereas the other clusters had conditions with moderate balance or good balance between them. Moreover, we determined the Oxidative stress-Antioxidant capacity ratio (OAR), using the ROM and BAP values, in order to clarify the characteristic of the detected clusters.However, comparative analyses across the three clusters did not yield significant differences in all related factors. No correlations between ROM, BAP and related factors were indicated, although significant association between ROM and BAP was observed (R2=0.1156, R=0.340, P=0.013). The reason for these results can be explained by the influences of good health and young age. On the other hand, present study suggests that some latent problems among adolescents may be related to unhealthy conditions in the future. Also, this study indicated that ROM and BAP may be useful as markers of the oxidative stress status. After this, further investigations using biomarkers based on epidemiologic design should be conducted, to reveal the reliability of the present results.

Strength deficits identified with concentric action of the hip extensors and eccentric action of the hamstrings predispose to hamstring injury in elite sprinters.

STUDY DESIGN: Prospective cohort study. OBJECTIVES: In this prospective cohort study of elite sprinters, muscle strength of the hip extensors, as well as of the knee extensors and flexors, was measured to determine a possible relationship between strength deficits and subsequent hamstring injury within 12 months of testing. The method used for testing muscle strength simulated the specific muscle action during late swing and early contact phases when sprinting. BACKGROUND: There have been no prospective studies in elite sprinters that examine the concentric and eccentric isokinetic strength of the hip extensors and the quadriceps and hamstring muscles in a manner that reflects their actions in late swing or early contact phases of sprinting. Consequently, the causal relationship between hip and thigh muscle strength and hamstring injury in elite sprinters may not be fully understood. METHODS AND MEASURES: Isokinetic testing was performed on 30 male elite sprinters to assess hip extensors, quadriceps, and hamstring muscle strength. The occurrence of hamstring injury among the subjects was determined during the year following the muscle strength measurements. The strength of the hip extensors, quadriceps, and hamstring muscles, as well as the hamstrings-quadriceps and hip extensors- quadriceps ratios were compared. RESULTS: Hamstring injury occurred in 6 subjects during the 1-year period. Isokinetic testing at a speed of 60 degrees /s revealed weakness of the injured limb with eccentric action of the hamstring muscles and during concentric action of the hip extensors. When performing a side-to-side comparison for the injured sprinters, the hamstring injury always occurred on the weaker side. Differences in the hamstrings-quadriceps and hip extensors-quadriceps strength ratios were also evident between uninjured and injured limbs, and this was attributable to deficits in hamstring strength. CONCLUSION: Hamstring injury in elite sprinters was associated with weakness during eccentric action of the hamstrings and weakness during concentric action of the hip extensors, but only when tested at the slower speed of 60 degrees /s.