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Influence of Maturation Status on Eccentric Hamstring Strength Improvements in Youth Male Soccer Players After the Nordic Hamstring Exercise

Benjamin Drury, Thomas Green, Rodrigo Ramirez-Campillo, and Jason Moran

Purpose: This study examined the effects of a 6-week Nordic hamstring exercise (NHE) program in youth male soccer players of less mature (pre–peak height velocity [PHV]) or more mature (mid/post-PHV) status. Methods: Forty-eight participants were separated into pre-PHV (11.0 [0.9] y) or mid/post-PHV (13.9 [1.1]) groups and further divided into experimental (EXP) and control groups with eccentric hamstring strength assessed (NordBord) both before and after the training program. Participants in the EXP groups completed a periodized NHE program performed once or twice weekly over a 6-week period. Results: The NHE program resulted in moderate and small increases in relative eccentric hamstring strength (in newtons per kilogram) in the pre-PHV EXP (d = 0.83 [0.03–1.68]) and mid-PHV EXP (d = 0.53 [−0.06 to 1.12]) groups, respectively. Moderate increases in the same measure were also seen in the between-groups analyses in the pre-PHV (d = 1.03 [0.23–1.84]) and mid-PHV (d = 0.87 [0.22–1.51]) groups, with a greater effect observed in the former. Conclusion: The results from this study demonstrate that a 6-week NHE program can improve eccentric hamstring strength in male youth soccer players, with less-mature players achieving mostly greater benefits. The findings from this study can aid in the training prescription of NHE in youth male soccer players.

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Potential Role of Plyometric Training in the Development of Motor Performance Skills: A Narrative Review

Andrew Sortwell, Michael Newton, Daniel A. Marinho, Jorge Knijnik, and Rodrigo Ramirez-Campillo

Offering children chances to optimize their engagement in physical activities during their life span is one of the major aims of school physical education (PE). To this end, the maximum development of motor performance skills can help primary school children participate in various physical activities throughout their lives. The purpose of this review was to examine the effects of plyometric training activities on motor performance skills of children and the application of plyometrics within the PE setting. Relevant studies on the topics of motor performance skills, plyometrics, athlete development, and motor development in children and adolescents were examined. The paper reveals that plyometric training activities can improve motor performance skills such as running, jumping, and kicking. The literature also suggests that children’s exposure to plyometric exercises may result in an accelerated improvement in primary school PE class. This review concludes with a proposal to enhance children’s motor performance skills using plyometric exercises in primary PE classes.

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Effects of a Combined Upper- and Lower-Limb Plyometric Training Program on High-Intensity Actions in Female U14 Handball Players

Mehrez Hammami, Rodrigo Ramirez-Campillo, Nawel Gaamouri, Gaith Aloui, Roy J. Shephard, and Mohamed Souhaiel Chelly

Purpose: To analyze the effects of a 9-week plyometric training program on the sprint times (5, 10, 20, and 30 m), change-of-direction speed (modified T test and modified Illinois test), jumping (squat jump, countermovement jump, countermovement jump with arms, and horizontal 5-jump test), upper-body strength (right and left handgrip, back extensor strength, and medicine ball throw), and balance (Y and stork balance tests) of female handball players. Methods: Athletes were randomly divided into experimental (n = 21; age = 13.5 [0.3] y) and control (n = 20; age = 13.3 [0.3] y) groups. Training exercises and matches were performed together, but the experimental group replaced a part of their normal regimen by biweekly upper- and lower-limb plyometric training. Results: Both groups improved performance, but to a greater extent in the experimental group compared with controls for 20- and 30-m sprint times (Δ% = 9.6, P < .05, d = 0.557 and Δ% = 20.9, P < .001, d = 1.07, respectively), change of direction (T test: P < .01, Δ% = 14.5, d = 0.993 and Illinois test: P < .01, Δ% = 7.9, d = 0.769), vertical and horizontal jumping (P < .05), all measures of upper-limb strength (P < .001), and left-leg stork balance (P < .001, Δ% = 49.9, d = 1.07). Conclusions: A plyometric training program allows female junior handball players to improve important components of their physical performance.

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High-Speed Bodyweight Resistance Training Improves Functional Performance Through Maximal Velocity in Older Females

Cristian Jaque, Phillip Véliz, Rodrigo Ramirez-Campillo, Jason Moran, Paulo Gentil, and Jorge Cancino

The authors compared the effects of bodyweight resistance training at moderate- or high-speed conditions on muscle power, velocity of movement, and functional performance in older females. In a randomized, single-blinded noncontrolled trial, participants completed 12 weeks (three sessions/week) of bodyweight resistance training at high (n = 14; age = 70.6 ± 4.3 years) or moderate (n = 12; age = 72.8 ± 4.2 years) speeds. Data were analyzed with an analysis of variance (Group × Time) with α level set at <.05. After the intervention, timed up and go test performance (p < .05) and the rising from a chair test mean (22.4%) and maximal velocity (28.5%), mean (24.4%) and maximal power (27.7%), normalized mean (25.1%), and normalized maximal power (28.5%) increased in the high-speed group (p < .05). However, the moderate-speed group achieved no improvements (Δ6.7–14.4%; p > .2). The authors conclude that high-speed bodyweight resistance training is an effective and economically practical strategy to improve the functional capacity of older women relevant to daily life activities.

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Association Between Lower Trapezius Isometric Strength and Y-Balance Test Upper Quarter Performance in College Volleyball Players

Guillermo Mendez-Rebolledo, Ann M. Cools, Rodrigo Ramirez-Campillo, Elias Quiroz-Aldea, and Fernanda A.P. Habechian

Context: Knowing the possible association between the isometric strength of the shoulder rotators, scapular muscles, and the Y-balance test upper quarter (YBT-UQ) performance could help identify which indicators of shoulder stability should be considered in this field test. This study aimed to determine whether the isometric strength of the shoulder rotators and scapular muscles is associated with the YBT-UQ performance of the dominant upper limb in amateur volleyball players. Design: Cross-sectional study. Methods: A convenience sample of 22 male and 18 female volleyball players (≥12 h of training/week) between 18 and 26 years of age. The isometric strength of the middle trapezius, lower trapezius, serratus anterior, internal, and external rotator muscles was assessed with a handheld dynamometer. Participants performed the YBT-UQ in the superolateral, medial, and inferolateral directions. The absolute isometric peak force (in Newtons) was normalized to body weight (in Newtons per kilogram) for each muscle test. For each YBT-UQ direction, the distance (in centimeters) was normalized for upper limb length (in percentage). A backward multiple linear regression analysis was used to determine the associations between variables. Results: The analysis revealed that the isometric strength of the lower trapezius (β = 26.82; 95% confidence interval, 21.24–32.40) is associated with inferolateral YBT-UQ performance (adjusted R 2 = .706; P < .001). This factor explains 70% of the variability of the YBT-UQ in the inferolateral direction. Conclusions: Lower trapezius isometric strength is associated with inferolateral YBT-UQ performance of the dominant upper limb in amateur volleyball players. These findings could help in the development of more specific training programs and rehabilitation goals according to the performance of the athletes in the test.

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The Effects of Combined Balance and Complex Training Versus Complex Training Only on Measures of Physical Fitness in Young Female Handball Players

Helmi Chaabene, Yassine Negra, Senda Sammoud, Jason Moran, Rodrigo Ramirez-Campillo, Urs Granacher, and Olaf Prieske

Purpose: To examine the effects of balance exercises conducted prior to complex training (bCT) versus complex training (CT) only on measures of physical fitness in young female elite handball players. Methods: Participants aged 17 years were randomly assigned to bCT (n = 11) or CT (n = 12). The 2 training interventions lasted 8 weeks with 2 sessions per week in replacement of some technical/tactical handball exercises and were matched for total training volume. Before and after training, tests were performed for the evaluation of proxies of muscle power (countermovement jump height, standing long-jump distance, and reactive strength index), muscle strength (back half-squat 1-repetition maximum), dynamic balance (Y-balance test), linear sprint speed (20-m sprint test), and change-of-direction speed (T test). Results: Two-factor repeated-measures analysis of variance revealed significant group × time interactions for the reactive strength index (d = 0.99, P = .03) and Y-balance test score (d = 1.32, P < .01). Post hoc analysis indicated significant pre–post reactive strength index improvements in CT (d = 0.69, P = .04) only. For the Y-balance test, significant pre–post increases were found in bCT (d = 0.71, P = .04) with no significant changes in CT (d = 0.61, P = .07). In addition, significant main effects of time were observed for half-squat 1-repetition maximum, countermovement jump, standing long jump, and T test performance (d = 1.50 to 3.10, P < .05). Conclusions: Both bCT and CT interventions were effective in improving specific measures of physical fitness in young elite female handball players. If the training goal is to improve balance in addition, balance exercises can be conducted within a CT training session and prior to CT exercises.

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Assessing Shortened Field-Based Heart-Rate-Variability-Data Acquisition in Team-Sport Athletes

Lucas A. Pereira, Andrew A. Flatt, Rodrigo Ramirez-Campillo, Irineu Loturco, and Fabio Y. Nakamura


To compare the LnRMSSD and the LnRMSSD:RR values obtained during a 5-min stabilization period with the subsequent 5-min criterion period and to determine the time course for LnRMSSD and LnRMSSD:RR stabilization at 1-min analysis in elite team-sport athletes.


35 elite futsal players (23.9 ± 4.5 y, 174.2 ± 4.0 cm, 74.0 ± 7.5 kg, 1576.2 ± 396.3 m in the Yo-Yo test level 1).


The RR-interval recordings were obtained using a portable heart-rate monitor continuously for 10 min in the seated position. The 2 dependent variables analyzed were LnRMSSD and LnRMSSD:RR. To calculate the magnitude of the differences between time periods, effect-size (ES) analysis was conducted. To assess the levels of agreement, intraclass correlation coefficients (ICC) and Bland-Altman plots were used.


The LnRMSSD and LnRMSSD:RR values obtained during the stabilization period (0–5 min) presented very large to nearly perfect ICCs with the values obtained during the criterion period (5–10 min), with trivial ESs. In the ultra-short-term analysis (ie, 1-min segments) the data showed slightly less accurate results, but only trivial to small differences with very large to nearly perfect ICCs were found.


LnRMSSD and LnRMSSD:RR can be recorded in 5 min without traditional stabilization periods under resting conditions in team-sport athletes. The ultra-short-term analysis (1 min) also revealed acceptable levels of agreement with the criterion.

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Effects of an Eccentric Hamstrings Training on Components of Physical Performance in Young Female Handball Players

Helmi Chaabene, Yassine Negra, Jason Moran, Olaf Prieske, Senda Sammoud, Rodrigo Ramirez-Campillo, and Urs Granacher

Purpose: This study examined the effects of an 8-week Nordic hamstring exercise (NHE) training on components of physical performance in young female handball players. Methods: Participants were allocated to an experimental group (EG; n = 10; age: 15.9 [0.2] y) and a control group (CG; n = 9; age: 15.9 [0.3] y). The EG performed NHE (2–3 sessions/wk) in replacement of some handball-specific drills, whereas the CG followed regular handball training. Pretraining and posttraining tests were carried out for the assessment of sprint speed (5 m, 10 m, and 20 m), jump performance (countermovement jump [CMJ] height), change-of-direction (t test), and repeated-sprint ability (RSA total time [RSAtotal], RSA best time [RSAbest], and RSA fatigue index [RSAFI]). Data were analyzed using magnitude-based inferences. Results: Within-group analyses for the EG showed moderate performance improvements for 5, 10, and 20 m (effect size [ES] = 0.68–0.82), t test (ES = 0.74), and CMJ (ES = 0.85). Trivial to small improvements were observed for RSA (ES = −0.06 to 0.35). For the CG, within-group outcomes showed performance decrements with moderate (t test [ES = 0.71]), small (5 m [ES = 0.46] and RSAbest [ES = 0.20]), and trivial magnitude (10 m [ES = 0.10], 20 m [ES = 0.16], and RSAtotal [ES = 0.00]). Furthermore, trivial to small performance improvements were found for CMJ (ES = 0.10) and RSAFI (ES = 0.5). Between-group analyses revealed small to large effects in favor of EG for 5 m (ES = 1.07), 10 m (ES = 0.66), 20 m (ES = 0.53), t test (ES = 1.38), and RSA (ES = 0.68–0.78). A trivial between-group difference was demonstrated for CMJ (ES = −0.01). Conclusions: The NHE training intervention, in replacement of some handball-specific drills, was more effective than regular handball training in improving physical performance (ie, linear sprint time, jumping, change-of-direction, and RSA) in young female handball players.

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Jump-Rope Training: Improved 3-km Time-Trial Performance in Endurance Runners via Enhanced Lower-Limb Reactivity and Foot-Arch Stiffness

Felipe García-Pinillos, Carlos Lago-Fuentes, Pedro A. Latorre-Román, Antonio Pantoja-Vallejo, and Rodrigo Ramirez-Campillo

Context: Plyometric training promotes a highly effective neuromuscular stimulus to improve running performance. Jumping rope (JR) involves mainly foot muscles and joints, due to the quick rebounds, and it might be considered a type of plyometric training for improving power and stiffness, some of the key factors for endurance-running performance. Purpose: To determine the effectiveness of JR during the warm-up routine of amateur endurance runners on jumping performance, reactivity, arch stiffness, and 3-km time-trial performance. Methods: Athletes were randomly assigned to an experimental (n = 51) or control (n = 45) group. Those from the control group were asked to maintain their training routines, while athletes from the experimental group had to modify their warm-up routines, including JR (2–4 sessions/wk, with a total time of 10–20 min/wk) for 10 weeks. Physical tests were performed before (pretest) and after (posttest) the intervention period and included jumping performance (countermovement-jump, squat-jump, and drop-jump tests), foot-arch stiffness, and 3-km time-trial performance. Reactive strength index (RSI) was calculated from a 30-cm drop jump. Results : The 2 × 2 analysis of variance showed significant pre–post differences in all dependent variables (P < .001) for the experimental group. No significant changes were reported in the control group (all P ≥ .05). Pearson correlation analysis revealed a significant relationship between Δ3-km time trial and ΔRSI (r = −.481; P < .001) and ΔStiffness (r = −.336; P < .01). The linear-regression analysis showed that Δ3-km time trial was associated with ΔRSI and ΔStiffness (R 2 = .394; P < .001). Conclusions : Compared with a control warm-up routine prior to endurance-running training, 10 weeks (2–4 times/wk) of JR training, in place of 5 minutes of regular warm-up activities, was effective in improving 3-km time-trial performance, jumping ability, RSI, and arch stiffness in amateur endurance runners. Improvements in RSI and arch stiffness were associated with improvements in 3-km time-trial performance.

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Basal Serum Cortisol and Testosterone/Cortisol Ratio Are Related to Rate of Na+ Lost During Exercise in Elite Soccer Players

Mauricio Castro-Sepulveda, Jorge Cancino, Rodrigo Fernández-Verdejo, Cristian Pérez-Luco, Sebastian Jannas-Vela, Rodrigo Ramirez-Campillo, Juan Del Coso, and Hermann Zbinden-Foncea

During exercise, the human body maintains optimal body temperature through thermoregulatory sweating, which implies the loss of water, sodium (Na+), and other electrolytes. Sweat rate and sweat Na+ concentration show high interindividual variability, even in individuals exercising under similar conditions. Testosterone and cortisol may regulate sweat Na+ loss by modifying the expression/activity of the cystic fibrosis transmembrane conductance regulator. This has not been tested. As a first approximation, the authors aimed to determine whether basal serum concentrations of testosterone or cortisol, or the testosterone/cortisol ratio relate to sweat Na+ loss during exercise. A total of 22 male elite soccer players participated in the study. Testosterone and cortisol were measured in blood samples before exercise (basal). Sweat samples were collected during a training session, and sweat Na+ concentration was determined. The basal serum concentrations of testosterone and cortisol and their ratio were (mean [SD]) 13.6 (3.3) pg/ml, 228.9 (41.4) ng/ml, and 0.06 (0.02), respectively. During exercise, the rate of Na+ loss was related to cortisol (r = .43; p < .05) and to the testosterone/cortisol ratio (r = −.46; p < .01), independently of the sweating rate. The results suggest that cortisol and the testosterone/cortisol ratio may influence Na+ loss during exercise. It is unknown whether this regulation depends on the cystic fibrosis transmembrane conductance regulator.