Synergistic Dominance Induced by Hip Extension Exercise Alters Biomechanics and Muscular Activity During Sprinting and Suggests a Potential Link to Hamstring Strain.

ABSTRACT: Iguchi, J, Hojo, T, Fujisawa, Y, Kuzuhara, K, Yanase, K, Hirono, T, Koyama, Y, Tateuchi, H, and Ichihashi, N. Synergistic dominance induced by hip extension exercise alters biomechanics and muscular activity during sprinting and suggests a potential link to hamstring strain. J Strength Cond Res 37(9): 1770-1776, 2023-Hamstring strain is likely to occur during the late swing phase or the first half of the stance phase in sprinting. During the late swing phase, the hamstrings and gluteus maximus (Gmax) contract eccentrically to decelerate the lower limb. We hypothesized that, when the Gmax becomes dysfunctional because of delayed onset muscle soreness (DOMS), the hamstring workload is increased (i.e., there is synergetic dominance), which could lead to an increased risk of strain. A total of healthy 15 male undergraduate or graduate students (age 23.1 ± 1.28 years) were recruited to perform exercises and maximal sprints. On day 1, before subjects performing DOMS-causing exercises, and on day 3, while subjects were experiencing DOMS in the Gmax, lower-limb biomechanical and muscle activity data were recorded using a motion analysis system and electromyography (EMG), respectively. Data were analyzed and compared between day 1 and day 3. Hip flexion angle on day 3 was significantly lower than that on day 1, but the opposite was true for the knee flexion angle (P < 0.05). Vastus medialis (VM), biceps femoris (BF), and Gmax muscle activities on day 3 were significantly higher than those on day 1 (P < 0.05). Peak propulsive forces on day 3 were significantly higher than those on day 1 (P < 0.05). Kinematic changes such as decreased hip flexion angle and EMG changes such as increased BF EMG activity on day 3 to compensate for the loss of function of the Gmax may potentially increase the risk of hamstring strain.

Seasonal Changes in Anthropometric, Physiological, Nutritional, and Performance Factors in Collegiate Rowers.

Iguchi J, Kuzuhara, K, Katai, K, Hojo, T, Fujisawa, Y, Kimura, M, Yanagida, Y, and Yamada, Y. Seasonal changes in anthropometric, physiological, nutritional, and performance factors in collegiate rowers. J Strength Cond Res 34(11): 3225-3231, 2020-Well-controlled seasonal distribution of training intensity seems to be an important variable for endurance athletes' success as competitors and for avoidance of overtraining. The aim of this study was to examine the interrelationships of training distribution, body composition, energy intake/expenditure, and rowing ergometer performance throughout the 2012-2013 season. In this study of 15 collegiate male rowers, most of whom started rowing during their time at the university, we divided the 2012-2013 season (total 37 weeks) into 3 phases (off-season, December to mid-March, 16 weeks; pre-season, late March-April, 5 weeks; and in-season, May-August, 16 weeks) and analyzed the transition of 2,000-m rowing ergometer time, training intensity/volume, body composition (body mass and body fat), and energy intake/expenditure in each phase. There were significant main effects of the training time by the intensities; 2,000-m rowing ergometer time; energy expenditure; and protein, fat, and carbohydrate intake across the seasons (p < 0.05). Two findings were particularly important. First, on-water high-intensity training, especially for inexperienced rowers, may contribute to improvement of 2,000-m rowing ergometer performance. Second, higher intake of carbohydrate, and to a lesser degree, protein, is necessary for optimal training adaptation (e.g., increase of muscle glycogen content), and results in better 2,000-m performance on the rowing ergometer. Also, those findings may be beneficial to the coaches who are interested in designing the well-controlled seasonal training program, which is especially intended to improve the 2,000-m rowing ergometer performance as well as avoidance of overtraining.

Risk Factors for Injury Among Japanese Collegiate Players of American Football Based on Performance Test Results.

Iguchi, J, Watanabe, Y, Kimura, M, Fujisawa, Y, Hojo, T, Yuasa, Y, Higashi, S, and Kuzuhara, K. Risk factors for injury among Japanese collegiate players of American football based on performance test results. J Strength Cond Res 30(12): 3405-3411, 2016-The purpose of this study was to identify how risk factors for injury during American football are related to players' physical strength as determined using typical performance tests. One hundred 53 Japanese collegiate players of American football were recruited for this study. Eight potential risk factors were evaluated: position (skill vs. lineman), body mass index, back squat one-repetition maximum, vertical jump height, power, height, body weight, and previous injury. Using multivariate Cox regression, we examined how these factors were associated with knee sprain, ankle sprain, and hamstring strain. We recorded 63 injuries (17 knee sprains, 23 ankle sprains, and 23 hamstring strains). Players with higher power were at significantly greater risk for knee sprains (p = 0.04), those with low power had a significantly higher incidence of ankle sprain (p = 0.01), and vertical jump height was a significant predictor of hamstring strain (p = 0.02). We identified several independent predictors of injuries associated with American football. Our findings may contribute to the development of effective screening tests and prevention exercises.

Injuries in a Japanese Division I collegiate american football team: a 3-season prospective study.

CONTEXT: Previous research on American football injuries in Japan has focused on incidence proportion in terms of the number of injuries divided by the number of players. This is the first study to examine injury rates over several seasons. OBJECTIVE: To conduct a prospective study of injuries in a Japanese Division I collegiate American football team over the 2007 through 2009 seasons. DESIGN: Cohort study. SETTING: Collegiate football team at Doshisha University, Kyoto, Japan. PATIENTS OR OTHER PARTICIPANTS: All 289 athletes who played on the collegiate Division I football team during the 2007 through 2009 seasons. MAIN OUTCOME MEASURE(S): A certified athletic trainer kept a daily record of all practice and game injuries. Injury rates were calculated according to season, injury type, body part, severity, and mechanism. Injuries were also analyzed according to position of player, school year, and playing experience. RESULTS: The game injury rate (GIR; 32.7 injuries/1000 athlete-exposures) was higher than the practice injury rate (PIR; 10.9 injuries/1000 athlete-exposures) over the 3 seasons (P < .05). The PIR was higher among Japanese players than the comparable United States collegiate football injury rates (5.8-7.0 injuries/1000 athlete-exposures). Ankle and foot injuries occurred more frequently during games, whereas thigh and gluteal injuries occurred more frequently during practices. CONCLUSIONS: Our data show differences between games and practices in terms of injury rates, body parts injured, and positions of players injured. The high PIR in Japan may be due to the increased contact during practices and length of practices compared with the United States. Further research involving multiple teams is recommended to validate the trends noted in this study. The expanded data set could assist in the development of safety regulations and preventive interventions for Japanese football.

Physical and performance characteristics of Japanese division 1 collegiate football players.

Iguchi, J, Yamada, Y, Ando, S, Fujisawa, Y, Hojo, T, Nishimura, K, Kuzuhara, K, Yuasa, Y, and Ichihashi, N. Physical and performance characteristics of Japanese division 1 collegiate football players. J Strength Cond Res 25(12): 3368-3377, 2011-This study aimed to establish the physical and performance characteristics of football players in the Japanese Division 1 collegiate football program and perform a comparison of these characteristics between Japanese (n = 208) and US Division 1 football players (n = 797). The following comparisons were made: (a) between a higher-ranked university team vs. a lower-ranked university team in Japan, (b) between different playing positions in Japan, (c) between starters and nonstarters in Japan, and (d) between playing positions in Japan vs. those in the United States. The results of this study suggest that players in the higher-ranked university team were heavier, stronger in back squat, jumped higher, and had greater power than those on the lower-ranked team. Furthermore, linemen were generally characterized by larger size, greater strength, and more fat as compared with backs. On the other hand, backs tended to be faster, smaller in physical size, have higher vertical jump height, and show greater relative strength than linemen did. Starters were taller, heavier, stronger, had more powerful, and more fat-free mass than nonstarters. Finally, our results revealed that players in the United States were superior to players in Japan in all body status comparisons (p < 0.01). This study revealed that performance and superior body composition are essential for the success of a football player. Power and strength seem to be key factors in defining good football performance.