The aim of the present study was to clarify relationships among the distribution of birth month, maturation and body size in young soccer players. We therefore examined physical and maturational ...differences between selected players, who were considered to have higher potential to play soccer at a professional level as decided subjectively by coaches, and unselected players. Participants were 332 elite soccer players (mean age = 12.2 ± 1.5 years; range = 9.1-15.0 years). Participants were divided into six categories (under = U10 to U15), depending on chronological age. Height, body mass skeletal age and maturation difference (skeletal age - chronological age) were compared among four groups (quarter = Q1 to Q4) depending on month of birth. Overall, the distribution of players across the four quarters was skewed such that numbers were greatest in Q1 and smallest in Q4. No significant differences in maturation difference were observed between birth quarters in any age category. On the other hand, except for the U14 age category, there were no significant differences in height between Q4 and Q1 players. However, the height of Q4 players was significantly smaller than those of Q1 in three (U11, U13 and U14, P < 0.01) of six categories when maturation difference was statistically controlled. Our results suggest a clear bias toward quarter of birth and this bias may depend to some extent on differences in individual skeletal age and body size. Individual biological maturation should thus be considered when selecting adolescent soccer players.
ABSTRACTHirose, N and Tsuruike, M. Differences in the electromyographic activity of the hamstring, gluteus maximus, and erector spinae muscles in a variety of kinetic changes. J Strength Cond Res ...32(12)3366–3372, 2018—This study aimed to clarify the differences in the electromyographic (EMG) activity of the semitendinosus (ST), semimembranosus (SM), biceps femoris long head (BFl), gluteus maximus (GM), and erector spinae (ES) muscles during leg curl and bridge exercises across different knee angles and isometric contraction outputs. Sixteen male volunteers participated in this study. The EMG of all targeted muscles was measured at 20 and 40% of the maximal voluntary isometric contraction (MVIC) in the leg curl and during bilateral and unilateral bridge exercises. The knee flexion angle was randomly set at 30, 60, 90, and 120° during each of the exercises. The obtained data were normalized by the MVIC of the corresponding muscle, and each of the normalized values was compared with that of the ST. The EMG activity of the ST was significantly greater at 120° of knee flexion than that of 30 and 60° of knee flexion during leg curl regardless of intensity (p < 0.05), in contrast with that of the SM and BFl. However, bridge exercises diminished this inverse relationship. The ES activity changed similarly to that of the hamstrings, and no difference was observed in the activity of the GM regardless of different knee angles during bridge exercise(s). The strength and conditioning professionals should alter the knee joint angle and load during bridge and leg curl exercises according to which hamstring muscle they want to strengthen because ST, SM, and BFl EMG activity varies depending on the intensity and knee angles during these exercises.
Background:
Throwing injuries of the shoulder and elbow are common among youth baseball players.
Hypothesis:
A prevention program will reduce the incidence of throwing injuries of the shoulder and ...elbow by 50% among youth baseball players.
Study Design:
Randomized controlled trial; Level of evidence, 1.
Methods:
The authors block randomized 16 youth baseball teams consisting of 237 players aged 9 to 11 years into an intervention group (8 teams, 117 players) and a control group (8 teams, 120 players). The intervention program consisted of 5 stretching, 2 dynamic mobility, and 2 balance training exercises performed during warm-up. Both groups were followed up for 12 months, during which the incidence of shoulder and elbow injuries was recorded. In addition, ball speed during pitching as a performance-related factor and variables of physical function (passive range of motion of the elbow, shoulder and hip, dynamic balance, and thoracic kyphosis angle) were assessed during the pre- and postintervention periods.
Results:
The incidence of shoulder and elbow injuries in the intervention group (1.7 per 1000 athlete-exposures) was significantly lower than that in the control group (3.1 per 1000 athlete-exposures) (hazard ratio, 1.940; 95% CI, 1.175-3.205; P = .010). The factors related to pitching performance, as assessed by ball speed, tended to increase in the intervention group as compared with the control group (P = .010). The program also improved shoulder horizontal adduction deficits on the dominant side, hip internal rotation on the nondominant side, and the thoracic kyphosis angle.
Conclusion:
A prevention program decreases throwing injuries of the shoulder and elbow and enhances the parameter of pitching performance in youth baseball players.
Background:
Youth baseball players are at high risk for elbow injuries, which can lead to future functional disability.
Purpose:
To evaluate the effectiveness of a prevention program to lower the ...risk of medial elbow injury in these athletes.
Study Design:
Cohort study; Level of evidence, 2.
Methods:
Youth baseball players, 8 to 11 years old, without a history of elbow and shoulder pain, were allocated to either the intervention (n = 136) or control (n = 169) group. The intervention consisted of 9 strengthening and 9 stretching exercises, performed during warm-up or at home, with high compliance defined as completion of the program 1 or more times per week. The following outcome variables were measured: clinical assessment of the elbow and shoulder joint, ultrasonography assessment of the elbow, and assessment of physical function (passive range of motion of the elbow, shoulder, and hip; strength of the shoulder and scapular muscles; and measurement of the thoracic kyphosis angle). The clinical and ultrasonography assessments were measured at baseline and at 3-month intervals over the 1-year follow-up. Physical function outcomes were measured at baseline and at the endpoint of the follow-up. The primary endpoint of effectiveness was the incidence of medial elbow injury. Secondary endpoints were absolute measures of physical function and change in these measures over the 1-year follow-up.
Results:
The incidence rate of medial elbow injury was significantly lower in the intervention group (0.8/1000 athlete-exposures) than the control group (1.7/1000 athlete-exposures) (hazard ratio, 50.8%; 95% CI, 0.292-0.882; P = .016). The program improved total range of shoulder rotation (dominant side), hip internal rotation (nondominant side), shoulder internal rotation deficit (bilaterally), lower trapezius muscle strength (dominant side), and the thoracic kyphosis angle. Improvements in the following variables of physical function were predictive of a lower rate of medial elbow injury: increased total shoulder total rotation (odds ratio OR, 0.973; 95% CI, 0.950-0.997), increased hip internal rotation of the nondominant side (OR, 0.962; 95% CI, 0.936-0.989), and decreased thoracic kyphosis angle (OR, 1.058; 95% CI, 1.015-1.103).
Conclusion:
A prevention program aiming to improve physical function can prevent medial elbow injury in youth baseball players.
To examine differences in resistance exercise-induced hormonal responses among young athletes according to their maturity levels.
A total of 12 collegiate and 32 junior high school male athletes were ...enrolled. The junior high school participants were divided into pre-peak height velocity (PHV) and post-PHV groups, according to their PHV ages. The salivary testosterone, cortisol, and human growth hormone levels were analyzed before (pre), immediately after (post), and at 15 minutes after performing body weight resistance exercise.
The testosterone levels were higher in the collegiate than in the junior high school group (P < .01) and increased after 15 minutes of exercise (P < .01). A significant decrease in the cortisol levels postexercise in the junior high school groups (P < .01) and an increase in the human growth hormone levels at 15 minutes after exercise in the post-PHV group were observed (P < .01). In the collegiate and post-PHV groups, the testosterone-to-cortisol ratio increased post and at 15 minutes after exercise (P < .01). The testosterone-to-cortisol ratio values were higher in the collegiate than in the post-PHV (at preexercise and at 15 min after P < .01) and pre-PHV groups (at all times P < .01).
Exercise-induced acute hormonal responses to resistance exercise may depend on individuals' maturity levels, even in those having the same age.
ABSTRACTYoshimura, A, Inami, T, Schleip, R, Mineta, S, Shudo, K, and Hirose, N. Effects of self-myofascial release using a foam roller on range of motion and morphological changes in musclea ...crossover study. J Strength Cond Res XX(X)000–000, 2019—Self-myofascial release using a foam roller (FR) is effective in improving range of motion (ROM) in at least some conditions. However, its mechanism is still unclear. Therefore, this study investigated potential acute muscle morphological changes after the FR intervention and aimed to clarify the mechanism of increases in ROM by the FR intervention. We hypothesized that the FR intervention may increase ROM because of changes in fascicle length (FL) and aponeurosis displacement. This crossover study, involving 22 male university students (21.5 ± 1.3 years, 170.6 ± 4.0 cm, and 64.1 ± 8.9 kg; mean ± SD), compared the FR intervention targeting the gastrocnemius muscle with the control trial. The outcome measures were maximum passive ankle ROM, morphology of the gastrocnemius muscle (FL and aponeurosis displacement) during passive ankle plantar flexor movement, degree of pain during the FR intervention, and sensation of the triceps surae muscle. Although ROM of both dorsiflexion and plantar flexion increased significantly after the FR intervention (p < 0.01), no significant differences were found in FL and aponeurosis displacement before and after the FR intervention. The mean perception of pain during the FR intervention was rated as “slightly uncomfortable,” corresponding to a 2.3 ± 2.4-cm on a 9.5-cm visual analog scale. We found that the FR intervention did not influence the morphology of muscle. It is necessary to investigate other factors related to ROM as the next step of this study.
Background:
Programs to prevent anterior cruciate ligament (ACL) injuries in female basketball players are scarce. Also, ACL injury prevention training that focuses on hip joint function has not been ...reported.
Purpose:
To determine the effectiveness of a hip-focused ACL injury prevention program in female basketball players.
Study Design:
Cohort study; Level of evidence, 2.
Methods:
A prospective intervention study was conducted for 12 years. Incidence rates of ACL injuries were collected in the first 4 years (observation period) from college female basketball players. After the observation period, a hip-focused ACL injury prevention program was implemented for 8 years (intervention period). A total of 309 players (mean ± SD age, 19.6 ± 1.2 years; height, 163.7 ± 5.6 cm; weight, 59.1 ± 5.1 kg; body mass index, 22.0 ± 1.4) were tracked in the observation period and compared with 448 players (age, 19.6 ± 1.1 years; height, 162.6 ± 5.8 cm; weight, 58.0 ± 5.7 kg; body mass index, 21.9 ± 1.5) who participated in the intervention period. Athlete-exposures (AEs), ACL numbers and mechanisms of injury (MOIs), relative risk (RR), absolute risk reduction (ARR), numbers needed to treat (NNT), and compliance were analyzed.
Results:
There were 16 ACL injuries (13 noncontact MOIs) in the 4-year observation period, whereas 9 ACL injuries (8 noncontact MOIs) were recorded in the 8-year intervention period. The overall ACL injury incidence was 0.25/1000 AEs in the 4-year observation period compared with 0.10/1000 AEs in the 8-year intervention period, respectively. Compared with the 4-year observation period, significant RR reduction was observed (0.38; 95% CI, 0.17-0.87; P = .017) with ARR and NNT of 0.032 (95% CI, 0.027-0.037) and 31.6 (95% CI, 27.1-37.7), respectively, in the 8-year intervention period. The noncontact ACL injury incidence was 0.21 per 1000 AEs during the 4-year observation period compared with 0.08/1000 AEs in the 8-year intervention period, which also showed significant RR reduction (0.37; 95% CI, 0.15-0.92; P = .026), with ARR and NNT of 0.024 (95% CI, 0.020-0.029) and 41.3 (95% CI, 34.6-51.3), respectively. The mean compliance rate during the intervention periods (8 years) was 89%.
Conclusion:
A hip-focused injury prevention program demonstrated significant reduction in the incidence of ACL injury in female collegiate basketball players.
This study aimed to investigate the influence of the task type on the relative electromyography (EMG) activity of biceps femoris long head (BFlh) to semitendinosus (ST) muscles, and of proximal to ...distal regions during isometric leg-curl (LC) and hip-extension (HE). Twenty male volunteers performed isometric LC with the knee flexed to 30° (LC30) and 90° (LC90), as well as isometric HE with the knee extended (HE0) and flexed to 90° (HE90), at 40% and 100% maximal voluntary contraction (MVIC). Hip position was neutral in all conditions. EMG activity was recorded from the proximal and distal region of the BFlh and ST muscles. BFlh/ST was calculated from the raw root-mean-square (RMS) amplitudes. The RMS of 40% MVIC was normalized using MVIC data and the proximal/distal (P/D) ratio of normalized EMG (NEMG) was calculated. The BFlh/ST ratio was higher in HE0 than in LC90 during MVIC and 40% MVIC (p<0.05), and was higher in HE90 than in LC90 (p<0.05) during 40% MVIC at the proximal region, whereas no difference was observed between HE0 and LC30. There was no inter-task difference in BFlh/ST ratio in the distal region. Furthermore, the P/D ratio was higher in LC90 than in LC30 and HE0 (p<0.05) in BFlh and ST muscles, and was higher in HE90 than in LC30 and HE0 (p<0.05) in BFlh during 40% MVIC. However, there was no difference in P/D ratio between LC30 and LC90, and HE0 and HE90. This showed that there was no task-dependent difference in the EMG activity of the BFlh muscle relative to the ST muscle between prone hip extension and prone knee flexion when the knee joint was set at an equivalent angle. Similarly, there was no task-dependent difference in the NEMG of the proximal region relative to the distal region in BFlh and ST muscles during 40% MVIC.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Nishiumi, D, Yamaguchi, S, Kurokawa, T, Wakamiya, K, and Hirose, N. Force-velocity profiling during the braking phase of countermovement jump: Relationship to eccentric strength and validity ...of the 2-point method.
J Strength Cond Res
37(11): 2141–2148, 2023—The aims of this study were threefold: to investigate the force-velocity profile during the braking phase (bFVP) of the countermovement jump (CMJ) and its relationship with other performance indicators, and whether it could be measured using the two-point method. Sixteen trained men performed 6 different loaded CMJs (0%, 32 kg, 60, 80, 100, and 120% body mass), and eccentric strength measurements were determined. Scatter plots were created using the mean force and velocity during the braking phase of each loaded CMJ. The corrected Akaike’s information criterion (AICc) was calculated by fitting linear, quadratic, and cubic regression equations to the bFVP and compared using the 1-way analysis of variance and Bonferroni’s post hoc tests. A correlation analysis was performed between the bFVP and other performance indicators. A bias assessment was performed to validate the 2-point method of the bFVP. The significance level was set at
p
< 0.05. The AICc in the linear regression equation was significantly lower (
p
< 0.05) than those in the other regression equations. Significant correlations were found between the slope and theoretical maximum force of the bFVP obtained from the linear regression equation and eccentric 1 repetition maximum. The acceptable condition for bias was met by 0–120%. The bFVP is likely to have a linear relationship and can be associated with eccentric strength. Furthermore, the 2-point method in bFVP has validity.
ABSTRACTKoyama, T, Rikukawa, A, Nagano, Y, Sasaki, S, Ichikawa, H, and Hirose, N. Acceleration profile of high-intensity movements in basketball games. J Strength Cond Res XX(X)000–000, 2020—This ...study aimed to elucidate movements that require greater acceleration during basketball games, their occurrence frequency, and compare acceleration components. Eighteen male collegiate basketball players (age19.5 ± 0.8 years) were enrolled. Triaxial accelerometer was used to measure acceleration and a synchronized video was recorded. Moments that generated resultant accelerations >4, 6, and 8 G, and their coincided movements were identified. Ratios and frequencies of the extracted movements were calculated and Jonckheere-Terpstra trend test was used to examine which movement rate increased when acceleration threshold increased. In addition, the top 7 movements that generated a resultant acceleration >6 G among the combination of basketball-specific movements were extracted. Their resultant, mediolateral, vertical, and anteroposterior accelerations were identified and compared using one-way analysis of variance. Cohenʼs d was used to calculate effect sizes. All p < 0.05 were considered statistically significant. The extracted frequencies were 33.6, 9.1, and 2.3 cases per minute for >4 G, >6 G, and >8 G, respectively. As the threshold increased, the rate of deceleration, landing, and physical contact increased. The mediolateral acceleration of physical contact was significantly greater than other movements, whereas the vertical acceleration of landing and deceleration was significantly greater than other movements. Thus, acceleration component analysis was performed to classify movement types. Greater acceleration appeared frequently in movement during defense. It is suggested that many defense movements involve a reaction to the ball and opponent. There are many passive movements during defense and speed changes rapidly. If many passive movements occur when defending, larger physical load is applied, and may lead to fatigue.
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