Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players

A Review of Countermovement and Squat Jump Testing Methods in the Context of Public Health Examination in Adolescence: Reliability and Feasibility of Current Testing Procedures

BACKGROUND

In the context of a public health physical fitness (PF) examination in adolescence, a countermovement jump (CMJ) and a squat jump (SJ) are two vertical jump (VJ) tests widely used to evaluate lower limb muscle strength and power, respectively. The main criticism of both the CMJ and SJ test is the lack of test standardization. Therefore, the objectives of this review are: (a) to gather information about both jumps; (b) to investigate whether it is possible to identify common procedures referred to in the CMJ and SJ technical execution, and (c) to design standard operating procedures (SOPs) to promote CMJ and SJ standardization in an adolescent population aged 12-18 years.

METHODS

The review partially adopted the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement (PRISMA). Due to growing attention in monitoring physical health through field tests in recent years, articles were collected using the PubMed, Web of Science, and Scopus databases from January 2009 to July 2019. Original articles in which CMJ or SJ were used to assess the muscular strength in adolescents were eligible for further analysis. Articles written in English was imposed as a limit.

RESULTS

A total of 117 studies met the inclusion criteria. The description of the CMJ and SJ test procedures was different within the literature, with discrepancies in the jump technique, number of jumps, and measurement devices used.

CONCLUSIONS

A lack of method standardization for both the CMJ and the SJ test was identified. Based on the literature, SOPs for both VJs were proposed. These are useful in the context of public health PF examination in adolescents, as they facilitate an unbiased comparison of jump performance data between published studies.

Effects of Slackline Training on Acceleration, Agility, Jump Performance and Postural Control in Youth Soccer Players

The goal of this study was to assess the effects of a supervised slackline training program in a group of soccer players. Thirty-four male division I under-19 players (16.64 ± 0.81 years) agreed to participate in the study. They were randomly divided into an experimental group (EG) and a control group (CG). The first group (EG) followed a 6-week supervised slackline training program (3 sessions/week; 5-9 min/session), while the CG performed only regular soccer training. Several variables were assessed in all participants: acceleration (20-m sprint test), agility (90º turns test), jump performance (squat jump, countermovement jump), and postural control (Center of Pressure ( CoP) testing: length, area, speed, Xmean, Ymean, Xspeed, Yspeed, Xdeviation, Ydeviation). Ratings of perceived exertion and local muscle ratings of perceived exertions were also recorded after each slackline training session. At post-tests, there was a significant increase only in the EG in acceleration, agility, squat jump and countermovement jump performance, as well as several CoP variables: area in the bipedal support on a firm surface, and length, area and speed in the left leg on a firm surface. The program was rated as “somewhat hard” by the players, while quadriceps, gastrocnemius and tibialis anterior were the most exerted muscles while slacklining. In conclusion, slackline training can be an effective training tool for young, high-level soccer players.

Improved maximal strength is not associated with improvements in sprint time or jump height in high-level female football players: a clusterrendomized controlled trial

Background

Maximal strength increments are reported to result in improvements in sprint speed and jump height in elite male football players. Although similar effects are expected in females, this is yet to be elucidated. The aim of this study was to examine the effect of maximal strength training on sprint speed and jump height in high-level female football players.

Methods

Two female football teams were team-cluster-randomized to a training group (TG) performing maximal strength training (MST) twice a week for 5 weeks, or control group (CG) doing their regular pre-season preparations. The MST consisted of 3–4 sets of 4–6 repetitions at ≥85% of 1 repetitions maximum (1RM) in a squat exercise. Sprint speed and jump height were assessed in 5-, 10- and 15 m sprints and a counter-movement jump (CMJ) test, respectively. Nineteen participants in TG (18.3 ± 2.7 years) and 14 in CG (18.3 ± 2.4 years) completed pre- and posttests and were carried forward for final analyses.

Results

There was no improvement in neither of the sprint times (p > 0.36), nor jump height (p = 0.87). The players increased their 1RM in squats (main of effect of time: p < 0.00, _pη² = 0.704), and an interaction effect of time x group was observed (p < 0.00, _pη² = 0.516) where the TG increased their 1RM more than the CT (between subjects effects: p < 0.001, _pη² = 0.965).

Conclusions

MST improved maximal strength in female football players to a large extent; however, the improvement in maximal strength did not result in any transference to sprint speed or jump height.

Trial registration

This study was registered at clinicaltrials.gov PRS (Protocol registration and results System) with the code NCT04048928, 07.08.2019, retrospectively registered.

Influence of Strength and Power Capacity on Change of Direction Speed and Deficit in Elite Team-Sport Athletes

The aim of the present study was to investigate the influence of maximum strength and power levels on change of direction (COD) ability and deficit in elite soccer and rugby players. Seventy-eight elite athletes (soccer, n = 46; rugby, n = 32) performed the following assessments: squat and countermovement jumps (SJ and CMJ), 1 repetition-maximum in the half-squat exercise (HS 1RM), peak power (PP) in the jump-squat exercise, and 20-m linear sprint and Zigzag COD tests. Utilizing the median split analysis, athletes were divided into two groups according to their HS 1RM and PP JS (e.g., higher and lower HS 1RM and higher and lower PP JS). The magnitude-based inference method was used to analyze the differences between groups in the physical performance tests. Athletes in the high strength and power groups outperformed their weaker and less powerful counterparts in all speed and power measurements (i.e., 5-, 10-, and 20-m sprint velocity, Zigzag COD speed, and CMJ and SJ height). In contrast, stronger and more powerful athletes displayed greater COD deficits. The present data indicate that players with superior strength-power capacity tend to be less efficient at changing direction, relative to maximum sprinting speed, despite being faster in linear trajectories. From these results, it appears that current strength and power training practices in team-sports are potentially not the “most appropriate” to increase the aptitude of a given athlete to efficiently utilize his/her neuromuscular abilities during COD maneuvers. Nevertheless, it remains unknown whether more multifaceted training programs are effective in decreasing COD deficits.

Lower-Body Power Relationships to Linear Speed, Change-of-Direction Speed, and High-Intensity Running Performance in DI Collegiate Women's Basketball Players

Basketball players need to sprint and change direction, and lower-body power (often measured by jump tests) should contribute. How different jumps relate to linear and change-of-direction (COD) speed, and high-intensity running has not been analyzed in Division I (DI) collegiate women’s basketballers. Twelve players completed the vertical jump (VJ), two-step approach jump (AppJ), and standing broad jump (SBJ). Average (AvgP) and peak power (PeakP), and PeakP: body mass (P:BM) were derived from VJ height; relative SBJ was derived from SBJ distance. Players also completed: 10 m and ¾ court sprints (linear speed), the pro-agility shuttle (COD speed), and the Yo-Yo Intermittent Recovery Test Level 1 (YYIRT1; high-intensity running). Pearson’s correlations (p < 0.05) calculated relationships between the jump and running tests. The AppJ correlated to the ¾ court sprint and pro-agility shuttle (r = -.663 to -.805). AvgP and PeakP correlated to the 10 m sprint, ¾ court sprint, and pro-agility shuttle (r = .589-.766). P:BM and relative SBJ correlated with all running tests (linear and COD speed r = -.620 to -.805; YYIRT1 r = .622.803). The AppJ stresses the stretch-shortening capacities of the legs, and this quality is important for faster linear and COD speed. AvgP and PeakP are influenced by body mass; while larger athletes produce greater power, they also may display slower 10 m sprint and pro-agility shuttle times, and lesser YYIRT1 performance. Strength coaches should ensure players can generate high relative power (i.e. P:BM, relative SBJ) for faster linear and COD speed, and high-intensity running.

The Effect of Plyometric Training in Volleyball Players: A Systematic Review

Volleyball is considered a very explosive and fast-paced sport in which plyometric training is widely used. Our purpose was to review the effects of plyometric training on volleyball players' performance. A systematic search was conducted according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines using PubMed, SciELO, SPORTDiscus, Medline, Scopus, Academic Search Complete, CINAHL and Web Science for articles published no later than December 2018. Any criteria were imposed for the included sample. The search focus was on interventional studies in which athletes underwent a plyometric program. To the 1831 articles found, another five were added, identified through other sources. Duplicated files were removed, titles and abstracts were screened, which left 21 remaining studies for extensive analysis. Results showed that the vertical jump (15 studies) was the major ability studied in plyometric training interventions, followed by strength (four studies), horizontal jump (four studies), flexibility (four studies) and agility/speed (three studies). In addition, it was observed that young (under 18 years old) female athletes were the most studied. The included studies indicated that plyometric training seems to increase vertical jump performance, strength, horizontal jump performance, flexibility and agility/speed in volleyball players. However, more studies are needed to better understand the benefits of plyometric training in volleyball players' performance.

The effects of a 4-week mesocycle of barbell back squat or barbell hip thrust strength training upon isolated lumbar extension strength

Objectives

Common exercises such as the barbell back squat (BBS) and barbell hip thrust (BHT) are perceived to provide a training stimulus to the lumbar extensors. However, to date there have been no empirical studies considering changes in lumbar extension strength as a result of BBS or BHT resistance training (RT) interventions.

Purpose

To consider the effects of BBS and BHT RT programmes upon isolated lumbar extension (ILEX) strength.

Methods

Trained male subjects (n = 14; 22.07 ± 0.62 years; 179.31 ± 6.96 cm; 79.77 ± 13.81 kg) were randomised in to either BBS (n = 7) or BHT (n = 7) groups and performed two training sessions per week during a 4-week mesocycle using 80% of their 1RM. All subjects were tested pre- and post-intervention for BBS and BHT 1RM as well as isometric ILEX strength.

Results

Analyses revealed that both BBS and BHT groups significantly improved both their BBS and BHT 1RM, suggesting a degree of transferability. However, the BBS group improved their BBS 1RM to a greater degree than the BHT group (p = 0.050; ∼11.8 kg/10.2% vs. ∼8.6 kg/7.7%, respectively). And the BHT group improved their BHT 1RM to a greater degree than the BBS group (p = 0.034; ∼27.5 kg/24.8% vs. ∼20.3 kg/13.3%, respectively). Neither BBS nor BHT groups significantly improved their isometric ILEX strength.

Conclusions

The present study supports the concept of specificity, particularly in relation to the movement mechanics between trunk extension (including pelvic rotation) and ILEX. Our data suggest that strength coaches, personal trainers, and trainees can self-select multi-joint lower-body trunk extension exercises based on preference or variety. However, evidence suggests that neither the BBS nor BHT exercises can meaningfully increase ILEX strength. Since strengthening these muscles might enhance physical and sporting performance we encourage strength coaches and personal trainers to prescribe ILEX exercise.

Effects of Plyometric Training on Physical Performance of Young Male Soccer Players: Potential Effects of Different Drop Jump Heights

PURPOSE

To compare the effects of plyometric drop jump (DJ) training against those induced by regular soccer training and assess the transference effect coefficient (TEC) of DJs ("trained exercises") performed from 20- (DJ20) and 40-cm (DJ40) height boxes with respect to different physical qualities (jumping, linear and change of direction speed, kicking, endurance, and maximal strength) in youth male soccer players.

METHODS

Participants were randomly divided into a control group (n = 20; age: 13.5 [1.9] y) and a DJ training group (n = 19; age: 13.2 [1.8] y), and trained for 7 weeks. A 2-way analysis of variance for repeated measures with the within-subject factor time (preintervention and postintervention) and between-subject factor group (intervention vs control) was performed. To calculate the TECs between the trained exercises (DJ20 and DJ40) and the physical tests, the ratio between the "result gains" (effect size [ES]) in the analyzed physical qualities and the result gains in the trained exercises were calculated. The TECs were only calculated for variables presenting an ES ≥ 0.2.

RESULTS

Significant improvements (ES = 0.21-0.46; P < .05) were observed in the DJ training group, except in linear sprint performance. The control group improved only the maximal strength (ES = 0.28; P < .05). Significant differences were observed in all variables (ES = 0.20-0.55; P < .05) in favor of the DJ training group, except for maximal strength (group × time interaction).

CONCLUSIONS

A plyometric training scheme based on DJs was able to significantly improve the physical performance of youth male soccer players. Overall, greater TECs were observed for DJ40 (0.58-1.28) than DJ20 (0.55-1.21).

Reliability of Squat Kinetics in Well-Trained Rugby Players: Implications for Monitoring Training

Appleby, BB, Cormack, SJ, and Newton, RU. Reliability of squat kinetics in well-trained rugby players: implications for monitoring training. J Strength Cond Res 33(10): 2635-2640, 2019-The aim of this study was to determine the within-session reliability in kinetic variables of the squat in well-trained athletes during a typical resistance training protocol. Fifteen subjects completed 2 testing sessions. Session 1 was establishment of 1 repetition maximum (1RM) squat, and session 2 involved 2 sets of 2 maximal effort repetitions of the squat at 70, 80, and 90% of 1RM with 3D motion analysis and ground reaction force (GRF) measurement using 2 in-ground triaxial force plates. Reliability was calculated using typical error ± 90% confidence limits, expressed as the coefficient of variation and intraclass correlation coefficient. The smallest worthwhile change (SWC%), calculated as 0.2 × between-subject SD, was used to determine the smallest important change in performance. Peak GRF and average GRF were found to have acceptable measures of reliability with the combined left and right leg average GRF capable of detecting the SWC. Independent limb contributions were reliable (left and right, or dominant and nondominant). Reliable kinetics can be obtained in back squat performance typical of a resistance training session in well-trained athletes. This suggests that coaches integrating force plate technology within training sessions may effectively capture between 1 and 6 training sets among several athletes, facilitating analysis and intervention on larger data sets.

Effects of in-season enhanced negative work-based vs traditional weight training on change of direction and hamstrings-to-quadriceps ratio in soccer players

The present study investigated the effects of in-season enhanced negative work-based training (ENT) vs weight training in the change of direction (COD), sprinting and jumping ability, muscle mass and strength in semi-professional soccer players. Forty male soccer players participated in the eight-week, 1 d/w intervention consisting of 48 squat repetitions for ENT using a flywheel device (inertia=0.11 kg·m^-2) or weight training (80%1 RM) as a control group (CON). Agility T-test, 20+20 m shuttle, 10 m and 30 m sprint, squat jump (SJ) and countermovement jump (CMJ), lean mass, quadriceps and hamstrings strength and the hamstrings-to-quadriceps ratio were measured. Time on agility T-test and 20+20 m shuttle decreased in ENT (effect-size =-1.44, 95% CI -2.24/-0.68 and -0.75, -1.09/-0.42 respectively) but not in CON (-0.33, -0.87/0.19 and -0.13, -0.58/0.32). SJ and CMJ height increased in both ENT (0.71, 0.45/0.97 and 0.65, 0.38/0.93) and CON (0.41, 0.23/0.60 and 0.36, 0.12/0.70). Overall, quadriceps and hamstrings strength increased in both ENT and CON (0.38/0.79), but the hamstrings-to-quadriceps ratio increased in ENT (0.31, 0.22/0.40) but not in CON (0.03, -0.18/0.24). Lean mass increased in both ENT (0.41, 0.26/0.57) and CON (0.29, 0.14/0.44). The repeated negative actions performed in ENT may have led to improvements in braking ability, a key point in COD performance. Semi-professional soccer players may benefit from in-season ENT to enhance COD and the negative-specific adaptations in muscle strength and hamstrings-to-quadriceps ratio.

In-season in-field variable resistance training: effects on strength, power, and anthropometry of junior soccer players

BACKGROUND

Soccer players' leg muscular strength and power have been shown to be significant due to their association with soccer-specific performance including jumps, sprints, tackles and kicks. The aim of this study, therefore, was to examine the effects of an in-season in-field variable resistance training (VRT) program on strength, power, and anthropometry of junior soccer players.

METHODS

A team of male soccer players were randomly assigned into Experimental (N.=10) and Control groups (N.=10). The Control group performed 8 weeks of soccer training alone. The Experimental group performed squat VRT using chains in addition to soccer training. Measures before and after training included squat strength, countermovement jump, and anthropometric estimation of thigh muscle cross sectional area (CSA).

RESULTS

The VRT induced large improvements in absolute (34.45%; P=0.001; Cohen's d=1.78) and relative strength to thigh muscle CSA (21.53%; P=0.002; Cohen's d=1.04). Similarly, there were large (18.07%, P=0.007; Cohen's d=1.5) increases in jump height and medium gains in absolute peak power output (16.13%; P=0.009; Cohen's d=0.34) and relative peak power output to thigh muscle CSA (9.6%; P=0.002; Cohen's d=0.31). Further, there was a medium increase (5.9%, P=0.03; Cohen's d=0.36) in thigh muscle CSA. No significant changes were observed in the Control group.

CONCLUSIONS

In-season in-field biweekly squat VRT enhanced strength and power measures in junior soccer players.

Classification of Soccer and Basketball Players' Jumping Performance Characteristics: A Logistic Regression Approach

This study aimed to examine countermovement jump (CMJ) kinetic data using logistic regression, in order to distinguish sports-related mechanical profiles. Eighty-one professional basketball and soccer athletes participated, each performing three CMJs on a force platform. Inferential parametric and nonparametric statistics were performed to explore group differences. Binary logistic regression was used to model the response variable (soccer or not soccer). Statistical significance (p < 0.05) was reached for differences between groups in maximum braking rate of force development (RFD_Dmax, U₇₉ = 1035), mean braking rate of force development (RFD_Davg, U₇₉ = 1038), propulsive impulse (IMP_U, t₇₉ = 2.375), minimum value of vertical displacement for center of mass (S_BCMmin, t₇₉ = 3.135), and time difference (% of impulse time; Δ_Τ) between the peak value of maximum force value (F_Umax) and S_BCMmin (U₇₉ = 1188). Logistic regression showed that RFD_Davg, impulse during the downward phase (IMP_D), IMP_U, and Δ_Τ were all significant predictors. The model showed that soccer group membership could be strongly related to IMP_U, with the odds ratio being 6.48 times higher from the basketball group, whereas RFD_Davg, IMP_D, and Δ_Τ were related to basketball group. The results imply that soccer players execute CMJ differently compared to basketball players, exhibiting increased countermovement depth and impulse generation during the propulsive phase.

EFFECTS OF TRADITIONAL STRENGTH TRAINING AND OLYMPIC WEIGHTLIFTING IN HANDBALL PLAYERS

ABSTRACT Introduction Olympic weightlifting has been adopted as an alternative to plyometric exercise. However, the effects of these exercises in young handball athletes is not known. Objective To compare the effect of Olympic weightlifting training with traditional strength training on jumping, squatting and acceleration performance in young handball athletes. Ten female handball athletes were evaluated. After six weeks of regular training, the athletes underwent eight weeks of training specifically designed for the survey, with equivalence of the total volume of training and differences in the means used. The evaluations were performed after six weeks of regular training (Baseline), after four weeks of traditional strength training and after four weeks of Olympic weightlifting. Vertical Jumps with and without movement of the arms, acceleration of 10 m, 20 m and 30 m, and 1RM in squatting were quantified. Results Increases (p<0.05) were observed in accelerations and squatting in the Olympic weightlifting and in squatting in the traditional strength training. Differences in coordination, time to activation of the gastrocnemius, vastus lateralis, rectus femoris, biceps femoris and gluteus maximus, peak force and power and rate of force development between the jumps and exercises used in the training are hypotheses to be considered for the different responses adaptations found in the jumps. Conclusion The Olympic weightlifting training resulted in an increase in accelerations and strength, but not in vertical jump performance in young handball athletes. Level of Evidence I; Prognostic Studies - Investigation of the Effect of a Patient Characteristic on Disease Outcome.

Associations between Fitness Measures and Change of Direction Speeds with and without Occupational Loads in Female Police Officers

Female police officers may be required to pursue offenders on foot while wearing occupational loads. The aim of this study was to determine relationships between fitness measures and change of direction speed (CODS) in female police officers and the influence of their occupational loads. Retrospective data were provided for 27 female police officers (age = 32.19 ± 5.09 y, height = 162.78 ± 5.01 cm, and mass = 71.31 ± 13.42 kg) and included fitness measures of: lower-body power (standing long jump (SLJ)), upper-body and trunk muscle endurance (push-up (PU) and sit-up (SU)), aerobic power (estimated VO2max), and CODS (Illinois agility test). The CODS test was performed without and with occupational load (10 kg). Paired sample t-tests (between-load conditions) and Pearson's correlations (relationships between measures) were performed with linear regression analysis used to account for the contribution of measures to unloaded and loaded CODS performance. CODS was significantly slower when loaded (unloaded = ~23.17 s, loaded = ~24.14 s, p < 0.001) with a strong, significant relationship between load conditions (r = 0.956, p < 0.001). Moderate to strong, significant relationships were found between all fitness measures ranging from estimated VO2max (r = -0.448) to SU (r = -0.673) in the unloaded condition, with the strength of these relationships increasing in the loaded condition accounting for 61% to 67% of the variance, respectively. While unloaded agility test performance was strongly associated with loaded performance, female police officer CODS was significantly reduced when carrying occupational loads. A variety of fitness measures that influence officer CODS performances become increasingly important when occupational loads are carried.

Vertical Jump Performance in Hungarian Male Elite Junior Soccer Players

PURPOSE

Vertical jump is a common test to measure impulsive ability in soccer; however, limited normative data have been published on young soccer players from vertical jump measurements on a force platform. The purpose of this study was to provide normative values for three chronological age groups of male junior soccer players (U16, U17 and, U18 years).

METHOD

Vertical jump performance of 365 soccer players (16.4 ± 0.8 years) was assessed using a force platform measurement system. Net impulse, force, power, jump height (impulse-momentum), jump height (flight time) were reported for each age group for squat jump (SJ) and countermovement jump (CMJ).

RESULTS

Mean values ± SD of jump height were 32.9 ± 4.1, 33.5 ± 4.0, and 33.9 ± 4.2 cm for the three age groups respectively in SJ and 36.3 ± 3.8, 37.5 ± 3.9, and 38.6 ± 4.4 cm in the CMJ. Mean values of all age groups for maximum force and maximum power were 1559 ± 211 N and 3261 ± 492 watt respectively for SJ and 1598 ± 241 N and 3287 ± 502 watt for CMJ. Based on descriptive data, percentiles were reported for all examined variables.

CONCLUSIONS

Jump height and relative values were less sensitive discriminator variables between age groups in the studied age range, while maximum impulse, maximum force, and maximum power were more sensitive to changes in maturational status. Normative values can be used by the coaches in the interpretation and evaluation of their athletes' performance and for training and talent identification purposes.

Ecdysteroids as non-conventional anabolic agent: performance enhancement by ecdysterone supplementation in humans

Recent studies suggest that the anabolic effect of ecdysterone, a naturally occurring steroid hormone claimed to enhance physical performance, is mediated by estrogen receptor (ER) binding. In comparison with the prohibited anabolic agents (e.g., metandienone and others), ecdysterone revealed to be even more effective in a recent study performed in rats. However, scientific studies in humans are very rarely accessible. Thus, our project aimed at investigating the effects of ecdysterone-containing products on human sport exercise. A 10-week intervention study of strength training of young men (n = 46) was carried out. Different doses of ecdysterone-containing supplements have been administered during the study to evaluate the performance-enhancing effect. Analysis of blood and urine samples for ecdysterone and potential biomarkers of performance enhancement has been conducted. To ensure the specificity of the effects measured, a comprehensive screening for prohibited performance-enhancing substances was also carried out. Furthermore, the administered supplement has been tested for the absence of anabolic steroid contaminations prior to administration. Significantly higher increases in muscle mass were observed in those participants that were dosed with ecdysterone. The same hypertrophic effects were also detected in vitro in C2C12 myotubes. Even more relevant with respect to sports performance, significantly more pronounced increases in one-repetition bench press performance were observed. No increase in biomarkers for liver or kidney toxicity was noticed. These data underline the effectivity of an ecdysterone supplementation with respect to sports performance. Our results strongly suggest the inclusion of ecdysterone in the list of prohibited substances and methods in sports in class S1.2 "other anabolic agents".

Maximum acceleration performance of professional soccer players in linear sprints: Is there a direct connection with change-of-direction ability?

The purpose of this study was to examine the selective influences of the maximum acceleration capability on change of direction (COD) speed, COD deficit, linear sprint speed, sprint momentum, and loaded and unloaded vertical jump performances in forty-nine male professional soccer players (24.3 ± 4.2 years; 75.4 ± 5.4 kg; 177.9 ± 6.4 cm). Soccer players performed the assessments in the following order: 1) squat and countermovement jumps; 2) 20-m sprinting speed test; 3) Zigzag COD ability test; and 4) bar-power outputs in the jump squat exercise. Athletes were divided, using a median split analysis, into two different groups according to their maximum acceleration rates from zero to 5-m (e.g., higher and lower ACC 0-5-m). Magnitude-based inference was used to compare the differences in the physical test results between "higher" and "lower" acceleration groups. A selective influence of the maximum acceleration ability on speed-power tests was observed, as the higher acceleration group demonstrated likely to almost certain higher performances than the lower acceleration group in all measurements (effect sizes varying from 0.66 [for sprint momentum in 20-m] to 2.39 [for sprint velocity in 5-m]). Conversely, the higher acceleration group demonstrated a higher COD deficit when compared to the lower acceleration group (ES = 0.55). This indicates compromised efficiency to perform COD maneuvers in this group of players. In summary, it was observed that soccer players with higher maximum acceleration rates are equally able to jump higher, sprint faster (over short distances), and achieve higher COD velocities than their slower counterparts. However, they appear to be less efficient at changing direction, which may be related to their reduced ability to deal with greater entry and exit velocities, or counterbalance the associated mechanical consequences (i.e., greater inertia) of being faster and more powerful.

Predictive Factors of Elite Sprint Performance: Influences of Muscle Mechanical Properties and Functional Parameters

Loturco, I, Kobal, R, Kitamura, K, Fernandes, V, Moura, N, Siqueira, F, Cal Abad, CC, and Pereira, LA. Predictive factors of elite sprint performance: influences of muscle mechanical properties and functional parameters. J Strength Cond Res 33(4): 974-986, 2019-Sprint performance relies on many different mechanical and physiological factors. The purpose of this study was to identify, among a variety of strength-power exercises and tensiomyography (TMG) parameters, the best predictors of maximum running speed in elite sprinters and jumpers. To test these relationships, 19 power track and field athletes, 4 long jumpers, and 15 sprinters (men: 12; 22.3 ± 2.4 years; 75.5 ± 8.3 kg; 176.5 ± 5.6 cm; women: 7; 23.8 ± 4.2 years; 56.9 ± 5.4 kg; 167.4 ± 5.8 cm) were assessed using different intensities of TMG-derived velocity of contraction (Vc), squat and countermovement jumps, drop jump at 45 and 75 cm; and a 60-meter sprint time. In addition, the mean propulsive power (MPP) and peak power (PP) outputs were collected in the jump squat (JS) and half-squat (HS) exercises. Based on the calculations of the Vc at 40 mA, the athletes were divided (by median split analysis) into 2 groups: higher and lower Vc 40 mA groups. The magnitude-based inference method was used to compare the differences between groups. The correlations between mechanical and functional measures were determined using the Pearson's test. A multiple regression analysis was performed to predict sprint performance, using the Vc at 40 mA, jump heights, and JS and HS power outputs as independent variables. The higher Vc 40 mA group demonstrated likely better performances than the lower Vc 40 mA group in all tested variables. Large to nearly perfect significant correlations were found between sprint time, jump heights, and power outputs in both JS and HS exercises. Notably, the Vc 40 mA associated with the vertical jump height and MPP in JS explained >70% of the shared variance in sprint times. In conclusion, it was found that faster athletes performed better in strength-power tests, in both loaded and unloaded conditions, as confirmed by the strong correlations observed between speed and power measures. Lastly, the Vc also showed a marked selective influence on sprint and power capacities. These findings reinforce the notion that maximum running speed is a very complex physical capacity, which should be assessed and trained using several methods and training strategies.

Resetting the late timing of 'night owls' has a positive impact on mental health and performance

BACKGROUND

There is conflict between living according to our endogenous biological rhythms and our external environment, with disruptions resulting in negative consequences to health and performance. This is often documented in shift work and jet lag, but 'societal norms' (eg, typical working hours) can create profound issues for 'night owls', people whose internal biological timing predisposes them to follow an unusually late sleep-wake cycle. Night owls have also been associated with health issues, mood disturbances, poorer performance and increased mortality rates.

METHODS

This study used a randomized control trial design aimed to shift the late timing of night owls to an earlier time (phase advance), using non-pharmacological, practical interventions in a real-world setting. These interventions targeted light exposure (through earlier wake up/sleep times), fixed meals times, caffeine intake and exercise.

RESULTS

Overall, participants demonstrated a significant advance of ∼2 h in sleep/wake timings as measured by actigraphy and circadian phase markers (dim light melatonin onset and peak time of the cortisol awakening response), whilst having no adverse effect on sleep duration. Notably, the phase advance was accompanied by significant improvements to self-reported depression and stress, as well as improved cognitive (reaction time) and physical (grip strength) performance measures during the typical 'suboptimal' morning hours.

CONCLUSIONS

Our findings propose a novel strategy for shifting clock timing towards a pattern that is more aligned to societal demands that could significantly improve elements of performance, mental health and sleep timing in the real world.

Effects of Drop Height on Jump Performance in Male and Female Elite Adolescent Handball Players

Purpose: To examine the effects of drop height on drop-jump (DJ) performance and on associations between DJ and horizontal-jump/sprint performances in adolescent athletes. Methods: Male (n = 119, 2.5 [0.6] y post-peak-height velocity) and female (n = 120, 2.5 [0.5] y post-peak-height velocity) adolescent handball players (national level) performed DJs in randomized order using 3 drop heights (20, 35, and 50 cm). DJ performance (jump height, reactive strength index [RSI]) was analyzed using the Optojump Next system. In addition, correlations were computed between DJ height and RSI with standing-long-jump and 20-m linear-sprint performances. Results: Statistical analyses revealed medium-size main effects of drop height for DJ height and RSI (P < .001, 0.63 ≤ d ≤ 0.71). Post hoc tests indicated larger DJ heights from 20 to 35 and 35 to 50 cm (P ≤ .031, 0.33 ≤ d ≤ 0.71) and better RSI from 20- to 35-cm drop height (P < .001, d = 0.77). No significant difference was found for RSI between 35- and 50-cm drop height. Irrespective of drop height, associations of DJ height and RSI were small with 5-m-split time (-.27 ≤ r ≤ .05), medium with 10-m-split time (-.44 ≤ r ≤ .14), and medium to large with 20-m sprint time and standing-long-jump distance (-.57 ≤ r ≤ .22). Conclusions: The present findings indicate that, irrespective of sex, 35-cm drop heights are best suited to induce rapid and powerful DJ performance (ie, RSI) during reactive strength training in elite adolescent handball players. Moreover, training-related gains in DJ performance may at least partly translate to gains in horizontal jump and longer sprint distances (ie, ≥20-m) and/or vice versa in male and female elite adolescent athletes, irrespective of drop height.

The Influence of Hamstring Muscle Peak Torque and Rate of Torque Development for Sprinting Performance in Football Players: A Cross-Sectional Study

Purpose: To investigate the association between hamstring muscle peak torque and rapid force capacity (rate of torque development, RTD) vs sprint performance in elite youth football players. Methods: Thirty elite academy youth football players (16.75 [1.1] y, 176.9 [6.7] cm, 67.1 [6.9] kg) were included. Isometric peak torque (in Newton meters per kilogram) and early- (0-100 ms) and late- (0-200 ms) phase RTD (RTD₁₀₀, RTD₂₀₀) (in Newton meters per second per kilogram) of the hamstring muscles were obtained as independent predictor variables. Sprint performance was assessed during a 30-m-sprint trial. Mechanical sprint variables (maximal horizontal force production [F_H0, in Newtons per kilogram], maximal theoretical velocity [V₀, in meters per second], maximal horizontal power output [P_max, in watts per kilogram]) and sprint split times (0-5, 0-15, 0-30, and 15-30 m, in seconds) were derived as dependent variables. Subsequently, linear-regression analysis was conducted for each pair of dependent and independent variables. Results: Positive associations were observed between hamstring RTD₁₀₀ and F_H0 (r² = .241, P = .006) and P_max (r² = .227, P = .008). Furthermore, negative associations were observed between hamstring RTD₁₀₀ and 0- to 5-m (r² = .206, P = .012), 0- to 15-m (r² = .217, P = .009), and 0- to 30-m sprint time (r² = .169, P = .024). No other associations were observed. Conclusions: The present data indicate that early-phase (0-100 ms) rapid force capacity of the hamstring muscles plays an important role for acceleration capacity in elite youth football players. In contrast, no associations were observed between hamstring muscle function and maximal sprint velocity. This indicates that strength training focusing on improving early-phase hamstring rate of force development may contribute to enhance sprint acceleration performance in this athlete population.

Effects of Creatine Supplementation on Athletic Performance in Soccer Players: A Systematic Review and Meta-Analysis

Studies have shown that creatine supplementation increases intramuscular creatine concentrations, favoring the energy system of phosphagens, which may help explain the observed improvements in high-intensity exercise performance. However, research on physical performance in soccer has shown controversial results, in part because the energy system used is not taken into account. The main aim of this investigation was to perform a systematic review and meta-analysis to determine the efficacy of creatine supplementation for increasing performance in skills related to soccer depending upon the type of metabolism used (aerobic, phosphagen, and anaerobic metabolism). A structured search was carried out following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines in the Medline/PubMed and Web of Science, Cochrane Library, and Scopus databases until January 2019. The search included studies with a double-blind and randomized experimental design in which creatine supplementation was compared to an identical placebo situation (dose, duration, timing, and drug appearance). There were no filters applied to the soccer players' level, gender, or age. A final meta-analysis was performed using the random effects model and pooled standardized mean differences (SMD) (Hedges's g). Nine studies published were included in the meta-analysis. This revealed that creatine supplementation did not present beneficial effects on aerobic performance tests (SMD, -0.05; 95% confidence interval (CI), -0.37 to 0.28; p = 0.78) and phosphagen metabolism performance tests (strength, single jump, single sprint, and agility tests: SMD, 0.21; 95% CI, -0.03 to 0.45; p = 0.08). However, creatine supplementation showed beneficial effects on anaerobic performance tests (SMD, 1.23; 95% CI, 0.55⁻1.91; p <0.001). Concretely, creatine demonstrated a large and significant effect on Wingate test performance (SMD, 2.26; 95% CI, 1.40⁻3.11; p <0.001). In conclusion, creatine supplementation with a loading dose of 20⁻30 g/day, divided 3⁻4 times per day, ingested for 6 to 7 days, and followed by 5 g/day for 9 weeks or with a low dose of 3 mg/kg/day for 14 days presents positive effects on improving physical performance tests related to anaerobic metabolism, especially anaerobic power, in soccer players.

Body Composition, Physical Fitness, Physical Activity and Nutrition in Polish and Spanish Male Students of Sports Sciences: Differences and Correlations

It is important to study differences in body composition, physical fitness and lifestyle behaviours between university students from different countries to develop country-specific recommendations on health promotion to provide to students when transitioning to university. The present study aimed to analyse differences in body composition, physical fitness and lifestyle behaviours between Polish and Spanish students of Sports Sciences. One-hundred-and-eighty-six male students participated (81 from Poland and 105 from Spain). Polish males were on average 21.5 ± 1.9 yrs old and Spanish males 21.5 ± 2.5. The body composition variables measured were body weight (kg), fat-free mass (FFM, kg and %), fat mass (FM, kg and %), total body water (TBW, kg and %), basal metabolic rate (BMR, kcal), body mass index (BMI, kg/m²), fat-free mass index (FFMI, kg/m²) and fat mass index (FMI, kg/m²). The physical fitness variables measured were squat jump (SJ, height in cm, power in watts and w/kg), countermovement jump (CMJ, height in cm, power in watts and w/kg), running speed (10, 20 and 30 m (time in s)), and progressive aerobic cardiovascular endurance run (PACER, stage, final speed in km/h, distance in m, VO₂max in mL/kg/min). Lifestyle variables measured were vigorous physical activity (VPA, days/week, min/week), moderate physical activity (MPA, days/week, min/week), walking (days/week, min/week), sitting (min/week), meals/day, vegetables/day, fruits/day, seafood/week, dairy products/week, sweets, chips, fast food/week, litres of liquid/day, litres of sugary drinks/day, alcohol/week and cigarettes/day. In comparison to Spanish students, Polish students had greater FFM (kg), greater TBW (kg), higher BMR, greater power in SJ, greater height and power in CMJ, lower times in running speed tests (10 and 20 m) and greater consumption of vegetables and liquids. In comparison to Polish students, Spanish students participated in more physical activity, and consumed more seafood, more dairy products, less sugary drinks, less alcohol and less tobacco. VPA and consumption of vegetables and liquids had positive influences on body composition and physical fitness. According to these results, universities should promote a healthy lifestyle in order to improve body composition and physical fitness in male students studying sport science. In the cases of Spain and Poland, special attention should be paid to the weak points detected in this study. This would be useful for avoiding future risk of diseases such as obesity or diabetes.

Anthropometric and Motor Characteristics of South African National Level Female Soccer Players

Data regarding anthropometric and motor characteristics of elite national level female soccer players are scarce. Determining these characteristics may likely assist in evaluating the specificity of current training programmes, identify players who might lack specific qualities deemed critical for the successful execution of their tactical roles, and benchmark norms for developing future playing talent. Therefore, the aims of this study were to describe anthropometric and motor characteristics of South African national level female soccer players (n = 37) and determine possible differences with regard to their playing position. The following measurements and tests were performed: anthropometry (body mass index and sum-of-skinfolds), the countermovement jump, sprints (10 m, 20 m and 40 m), upper body muscle endurance (push-ups) and the Yo-Yo Intermittent Recovery Test - level 1. One-way analysis of variance revealed few differences in the main outcome variables. Fischer Least Significant Difference (LSD) showed that strikers had a greater body mass index than midfielders and defenders (both p = 0.04) and goalkeepers were heavier than defenders (p = 0.02). Goalkeepers were slower than strikers and defenders over 10 m (p = 0.01; p = 0.03) and 20 m (p = 0.001; p = 0.01). Midfielders were slower than strikers over 20 m (p = 0.02), and with strikers and defenders over 40 m (both p = 0.04). Defenders performed better than goalkeepers in the upper body muscle endurance test (p = 0.02). In conclusion, both strikers and defenders require speed to win ball possession, which may explain their fast sprint times. However, the similarity of certain motor characteristics across playing positions may suggest that conditioning coaches train players similarly, irrespective of their tactical position. The authors suggest that South African fitness professionals, particularly at a club level, develop physical conditioning programs specific to each field position. Furthermore, fitness assessments should occur on a continuous basis and comparisons should be made with existing normative data in order to guide the development of players over the course of their careers.

Effects of Low-Moderate Load High-Velocity Resistance Training on Physical Performance of Under-20 Futsal Players

Resistance training (RT) is an effective methodology to improve physical performance of athletes. However, up to now, no studies have addressed the RT benefits in under-20 futsal players. The purpose of this study was to evaluate the effects of six weeks of RT with high-velocity movements, low-to-moderate loads, and low volume on physical performance of under-20 futsal players. A total of 21 players were divided into two groups: A control group (CG, n = 10) and a RT group (RTG, n = 11). The RTG performed two weekly training sessions constituted by leg-press, jumps, and sprints, along with three futsal training sessions, while the CG only performed the futsal training. Before and after the intervention, the sprint time in 0–10 m (T₁₀), 10–20 m (T_10–20), and 0–20 m (T₂₀), the countermovement jump (CMJ) height, the T-Test time, the kicking ball speed (KBS), and the maximum dynamic strength in the leg-press, were assessed. In post-test, significant improvements in CMJ, T-Test, KBS, and leg-press were found for the RTG, whilst a significant decrease in T_10–20 was evidenced in the CG. The present results suggested that RT based on high velocity movements, low-to-moderate loads, and low volume produce positive effects on physical performance of under-20 futsal players.

Power-to-Strength Ratio Influences Performance Enhancement with Contrast Training

PURPOSE

The effectiveness of contrast training (CST) for improving explosive exercise performance is modulated by various individual characteristics; however, further work is required to define these factors.

METHODS

Subelite male Australian Football players (n = 22; age, 19 ± 2 yr; body mass, 80.4 ± 9.4 kg; one-repetition maximum [1-RM] half squat, 172 ± 18 kg; mean ± SD) completed two experimental trials involving two sets of squat jumps (six repetitions at 30% 1-RM) performed either alone (CTL condition) or after half squats (six repetitions at 85% 1-RM; CST condition).

RESULTS

Squat jump peak power was similar between CTL and CST during set 1 (mean change: ±90% confidence interval, 2.8% ± 2.0%; effect size [ES]: ±90% confidence interval, 0.13 ± 0.09; P = 0.079) and set 2 (0.3% ± 1.7%; ES, 0.01 ± 0.08; P = 0.781). Peak power enhancement with CST was not related to maximal (1-RM half squat) strength (r = 0.001, P = 0.884), but was negatively correlated with both baseline peak power (r = 0.44, P < 0.001) and power-to-strength ratio (PSR); that is, the ratio between baseline peak power and 1-RM half squat strength (r = 0.65, P < 0.001). Using a median split, analyses were performed in participants with a low PSR (LPSR group; PSR = 15.4-19.1 W·kg; n = 11) or high PSR (HPSR group, PSR = 19.4-24.7 W·kg; n = 11). Peak power was enhanced with CST for the LPSR (8.1% ± 3.9%; ES, 0.44 ± 0.21; P = 0.004) but not HPSR (-2.1% ± 1.3%; ES, -0.14 ± 0.09; P = 0.010) groups.

CONCLUSION

The PSR appears to influence the effectiveness of CST, with performance enhancement more likely in those with a lower PSR.

The Effect of In-Season Traditional and Explosive Resistance Training Programs on Strength, Jump Height, and Speed in Recreational Soccer Players

PURPOSE

Resistance training is often performed in a traditional training style using deliberate relatively longer repetition durations or in an explosive training style using maximal intended velocities and relatively shorter repetition durations. Both improve strength, "power" (impulsivity), and speed. This study compared explosive and traditional training over a 6-week intervention in 30 healthy young adult male recreational soccer players.

METHOD

Full body supervised resistance training was performed 2 times a week using 3 sets of each exercise at 80% of one repetition maximum to momentary failure. Outcomes were Smith machine squat 1 repetition maximum, 10 meter sprint time, and countermovement jump.

RESULTS

Both groups significantly improved all outcomes based on 95% confidence intervals not crossing zero. There were no between-group differences for squat 1 RM (TRAD = 6.3[5.1 to 7.6] kg, EXP = 5.2[3.9 to 6.4] kg) or 10 meter sprint (TRAD = -0.05[-0.07 to -0.04] s, EXP = -0.05[-0.06 to -0.03] s). Explosive group had a significantly greater increase in countermovement jump compared to the traditional group (TRAD = 0.7[0.3 to 1.1] cm, EXP = 1.3[0.9 to 1.7] cm).

CONCLUSION

Both the traditional training and explosive training performed to momentary failure produced significant improvements in strength, speed, and jump performance. Strength gains are similar independent of intended movement speed. However, speed and jump performance changes are marginal with resistance training.

Differences in Sprint Mechanical Force-Velocity Profile Between Trained Soccer and Futsal Players

PURPOSE

To compare the sprint mechanical force-velocity (F-V) profile between soccer and futsal players. A secondary aim was, within each sport, to study the differences in sprint mechanical F-V profile between sexes and players of different levels.

METHODS

A total of 102 soccer players (63 men) and 77 futsal players (49 men) who were competing from the elite to amateur levels in the Spanish league participated in this investigation. The testing procedure consisted of 3 unloaded maximal 40-m sprints. The velocity-time data recorded by a radar device were used to calculate the variables of the sprint acceleration F-V profile (maximal theoretical force [F₀], maximal theoretical velocity [V₀], maximal power [P_max], decrease in the ratio of horizontal to resultant force [DRF], and maximal ratio of horizontal to resultant force [RFpeak]).

RESULTS

Futsal players showed a higher F₀ than soccer players (effect size [ES] range: 0.11-0.74), while V₀ (ES range: -0.48 to -1.15) and DRF (ES range: -0.75 to -1.45) was higher for soccer players. No significant differences were observed between soccer and futsal players for P_max (ES range: -0.43 to 0.19) and RFpeak (ES range: -0.49 to 0.30). Men and high-level players presented an overall enhanced F-V profile compared with women and their lower-level counterparts, respectively.

CONCLUSIONS

The higher F₀ and lower V₀ of futsal players could be caused by the game's specific demands (larger number of accelerations but over shorter distances than in soccer). These results show that the sprint mechanical F-V profile is able to distinguish between soccer and futsal players.

Relationship of Strength and Conditioning Metrics to Success on the Army Ranger Physical Assessment Test

Barringer, ND, McKinnon, CJ, O'Brien, NC, and Kardouni, JR. Relationship of strength and conditioning metrics to success on the army ranger physical assessment test. J Strength Cond Res 33(4): 958-964, 2019-The purpose of our study was to compare standard strength and conditioning assessments in the Ranger Athlete Warrior (RAW) assessments to a tactical assessment of the Ranger Physical Assessment Test (RPAT) to determine what influence, if any, that they may have on the RPAT outcome. We analyzed RAW and RPAT data on 1,141 soldiers attempting the Ranger Assessment and Selection Program I (RASP I) for entrance into the 75th Ranger Regiment as part of their routine program data collection from July 2014 to July 2017. We found better performance in the broad jump, pull-ups, and average 300-yard shuttle time was associated with improved odds of passing the RPAT. For every increasing 2.54 centimeters in broad jump, the odds of passing the RPAT increased by 4% (OR = 1.04, 95% CI [1.01-1.07]). Each additional pull-up was associated with 6% better odds (OR = 1.06, 95% CI [1.01-1.12]) of passing the RPAT, and every second faster in the 300-yard shuttle was associated with 9% better odds of passing the RPAT (OR = 1.09, 95% CI [1.03-1.14]). The results of this study indicate that lower-body power, pulling strength, and anaerobic conditioning seemed to have the greatest influence on RPAT success. Our current results provide guidance to Strength Coaches or TSAC-Fs preparing tactical athletes for this specific or similar tactical assessment as better performance was found for tactical athletes with greater lower-body power, pulling strength, and anaerobic endurance.

RESTORING KNEE EXTENSOR STRENGTH AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION: A CLINICAL COMMENTARY

One of the main priorities of rehabilitation after anterior cruciate ligament reconstruction (ACLR) surgery is the restoration of knee extensor muscle strength. Residual deficits in knee extensor muscle size and strength after injury are linked to poor biomechanics, reduced knee function, increased knee osteoarthritis risk, as well as heightened risk of re-injury upon return to sport. Most studies indicate that knee extensor muscle strength is typically not resolved prior to return to sport. This clinical commentary discusses strategies to optimize and accelerate the recovery of knee extensor strength post-surgery, with the purpose to support the clinician with evidence-based strategies to implement into clinical practice. Principally, two strategies exist to normalize quadriceps strength after surgery, 1) limiting strength loss after injury and surgery and 2) maximizing and accelerating the recovery of strength after surgery. Optimal preparation for surgery and a focused attempt to resolve arthrogenic muscle inhibition are essential in the pre and post-operative period prior to the inclusion of a periodized strength training program. Often voluntary strengthening alone is insufficient to fully restore knee extensor muscle strength and the use of electrical stimulation and where necessary the use of blood flow restriction training with low loads can support strength recovery, particularly in patients who are significantly load compromised and experience pain during exercise. Resistance training should employ all contraction modes, utilize open and closed kinetic chain exercise of both limbs, and progress from isolated to functional strength training, as part of a periodized approach to restoring neuromuscular function. Furthermore, thinking beyond the knee musculature and correcting core and hip dysfunction is also important to ensure an optimal knee extension strengthening program. The purpose of this clinical commentary is to provide a series of evidenced based strategies which can be implemented by clinicians responsible for the rehabilitation of patients after ACLR.

LEVEL OF EVIDENCE

5.

Drop Jump Asymmetry is Associated with Reduced Sprint and Change-of-Direction Speed Performance in Adult Female Soccer Players

Studies that examine the effects of inter-limb asymmetry on measures of physical performance are scarce, especially in adult female populations. The aim of the present study was to establish the relationship between inter-limb asymmetry and speed and change-of-direction speed (CODS) in adult female soccer players. Sixteen adult players performed a preseason test battery consisting of unilateral countermovement jump (CMJ), unilateral drop jump (DJ), 10 m, 30 m, and 505 CODS tests. Inter-limb asymmetry was calculated using a standard percentage difference equation for jump and CODS tests, and Pearson's r correlations were used to establish a relationship between asymmetry and physical performance as well as asymmetry scores themselves across tests. Jump-height asymmetry from the CMJ (8.65%) and DJ (9.16%) tests were significantly greater (p < 0.05) than asymmetry during the 505 test (2.39%). CMJ-height asymmetry showed no association with speed or CODS. However, DJ asymmetries were significantly associated with slower 10 m (r = 0.52; p < 0.05), 30 m (r = 0.58; p < 0.05), and 505 (r = 0.52⁻0.66; p < 0.05) performance. No significant relationships were present between asymmetry scores across tests. These findings suggest that the DJ is a useful test for detecting existent between-limb asymmetry that might in turn be detrimental to speed and CODS performance. Furthermore, the lack of relationships present between different asymmetry scores indicates the individual nature of asymmetry and precludes the use of a single test for the assessment of inter-limb differences.

Can Positioning Systems Replace Timing Gates for Measuring Sprint Time in Ice Hockey?

This study explores whether positioning systems are a viable alternative to timing gates when it comes to measuring sprint times in ice hockey. We compared the results of a single-beam timing gate (Brower Timing) with the results of the Iceberg optical positioning system (Optical) and two radio-based positioning systems provided by InMotio (Radio 1) and Kinexon (Radio 2). The testing protocol consisted of two 40 m linear sprints, where we measured sprint times for a 11 m subsection (Linear Sprint 11), and a shuttle run (Shuttle Total), including five 14 m sprints. The exercises were performed by six top-level U19 field players in regular ice hockey equipment on ice. We quantified the difference between measured sprint times e.g., by Mean Absolute Error (MAE) (s) and Intra Class Correlation (ICC). The usefulness of positioning systems was evaluated by using a Coefficient of Usefulness (CU), which was defined as the quotient of the Smallest Worthwhile Change (SWC) divided by the Typical Error (both in s). Results showed that radio-based systems had a higher accuracy compared to the optical system. This concerned Linear Sprint 11 (MAEOptical = 0.16, MAERadio1 = 0.01, MAERadio2 = 0.01, ICCOptical = 0.38, ICCRadio1 = 0.98, ICCRadio2 = 0.99) as well as Shuttle Total (MAEOptical = 0.07, MAERadio1 = 0.02, MAERadio2 = 0.02, ICCOptical = 0.99; ICCRadio1 = 1.0, ICCRadio2 = 1.0). In Shuttle Total, all systems were able to measure a SWC of 0.10 s with a probability of >99% in a single trial (CUOptical = 4.6, CURadio1 = 6.5, CURadio2 = 5.1). In Linear Sprint 11 an SWC of 0.01 s might have been masked or erroneously detected where there were none due to measurement noise (CUOptical = 0.6, CURadio1 = 1.0, CURadio2 = 1.0). Similar results were found for the turning subsection of the shuttle run (CUOptical = 0.6, CURadio1 = 0.5, CURadio2 = 0.5). All systems were able to detect an SWC higher than 0.04 s with a probability of at least 75%. We conclude that the tested positioning systems may in fact offer a workable alternative to timing gates for measuring sprints times in ice hockey over long distances like shuttle runs. Limitations occur when testing changes/differences in performance over very short distances like an 11 m sprint, or when intermediate times are taken immediately after considerable changes of direction or speed.

Association Between the Force-Velocity Profile and Performance Variables Obtained in Jumping and Sprinting in Elite Female Soccer Players

PURPOSE

To quantify the magnitude of the association between the same variables of the force-velocity (FV) profile and the performance variables (unloaded-squat-jump height and 20-m sprint time) obtained during jumping and sprinting testing and to determine which mechanical capacity (ie, maximum force [F₀], maximum velocity [V₀], or maximum power [P_max]) presents the highest association with the performance variables.

METHODS

The FV profile of 19 elite female soccer players (age 23.4 [3.8] y, height 166.4 [5.6] cm, body mass 59.7 [4.7] kg) was determined during the jumping and sprinting tasks. The F₀, V₀, FV slope, P_max, and FV imbalance (difference respect to the optimal FV profile in jumping and the decrease in the ratio of horizontal force production in sprinting) were determined for each task.

RESULTS

Very large correlations between both tasks were observed for P_max (r = .75) and the performance variables (r = -.73), as well as moderate correlations for V₀ (r = .49), while the F₀ (r = -.14), the FV slope (r = -.09), and the FV imbalance (r = .07) were not significantly correlated between both tasks. The P_max obtained during each specific task was the mechanical capacity most correlated with its performance variable (r = .84 in jumping and r = .99 in sprinting).

CONCLUSIONS

The absence of significant correlations between some of the FV relationship parameters suggests that, for an individualized training prescription based on the FV profile, both jumping and sprinting testing procedures should be performed with elite female soccer players.

One-Repetition-Maximum Measures or Maximum Bar-Power Output: Which Is More Related to Sport Performance?

PURPOSE

To compare the associations between optimum power loads and 1-repetition-maximum (1RM) values (assessed in half-squat and jump-squat exercises) and multiple performance measures in elite athletes.

METHODS

Sixty-one elite athletes (15 Olympians) from 4 different sports (track and field [sprinters and jumpers], rugby sevens, bobsled, and soccer) performed squat and countermovement jumps, half-squat exercise (to assess 1RM), half-squat and jump-squat exercises (to assess bar-power output), and sprint tests (60 m for sprinters and jumpers and 40 m for the other athletes). Pearson product-moment correlation test was used to determine relationships between 1RM and bar-power outputs with vertical jumps and sprint times in both exercises.

RESULTS

Overall, both measurements were moderately to near perfectly related to speed performance (r values varying from -.35 to -.69 for correlations between 1RM and sprint times, and from -.36 to -.91 for correlations between bar-power outputs and sprint times; P < .05). However, on average, the magnitude of these correlations was stronger for power-related variables, and only the bar-power outputs were significantly related to vertical jump height.

CONCLUSIONS

The bar-power outputs were more strongly associated with sprint-speed and power performance than the 1RM measures. Therefore, coaches and researchers can use the bar-power approach for athlete testing and monitoring. Due to the strong correlations presented, it is possible to infer that meaningful variations in bar-power production may also represent substantial changes in actual sport performance.

Examination of Physical Characteristics and Positional Differences in Professional Soccer Players in Qatar

Physical characteristics in professional soccer differ between competition levels and playing positions, and normative data aid practitioners in profiling their players to optimize performance and reduce injury risk. Given the paucity of research in Arabic soccer populations, the purpose of this study was to provide position-specific normative values for professional players competing in the Qatar Stars League. One hundred and ninety-five players completed a musculoskeletal assessment as part of an annual periodic health examination. Tests included measures of range of motion (hip, ankle, and hamstring), bilateral and unilateral jump performance, and quadriceps/hamstring (isokinetic/NordBord), hip adduction/abduction (eccentric), and groin (isometric) strength. Descriptive data were examined, and positional differences were analyzed using a one-way analysis of variance (ANOVA). Goalkeepers were significantly heavier (p < 0.01), had a higher body mass index (p < 0.05) than outfield positions and demonstrated greater absolute strength. Defenders were the strongest relative to body mass, and these differences were significant (p < 0.05) versus goalkeepers and strikers. No meaningful between-group comparisons were apparent for jumping or range of motion tests. Compared to mean values from other professional leagues, soccer players in Qatar appear to be shorter, lighter and display inferior strength and jump capacities. These data can be used to tailor training and rehabilitation programs to the specifics of the league and position in which the athletes compete.

Selective Influences of Maximum Dynamic Strength and Bar-Power Output on Team Sports Performance: A Comprehensive Study of Four Different Disciplines

This study examined the selective influences of one-repetition maximum (1RM) values [assessed in the half-squat (HS)] and bar-power production [assessed in both HS and jump squat (JS) exercises] on the physical performance of male and female team sport athletes from four different sports. Three-hundred and three elite players (31 Olympians) from four different disciplines (47 male soccer players, 58 female soccer players, 28 male handball players, 58 female handball players, 49 male rugby players, and 63 male futsal players) participated in this study. The physical tests were performed over 2 consecutive days for soccer and rugby players, and in 1 day for the remaining athletes. On the first day, rugby and soccer athletes performed squat jumps (SJ), countermovement jumps (CMJ), and HS 1RM. On the second day, they executed HS and JS tests (to assess the maximum bar-power output) and the linear and change-of-direction (COD) speed tests. For the other players, the sequence of the measurements was the same; however, they did not perform the HS exercise. Athletes were separated, using a median split analysis, into two distinct groups, according to their bar-power output in both JS and HS exercises and their performance in HS 1RM. The magnitude-based inferences method was used to examine the differences between "higher" and "lower" performance groups. Overall, the bar-power outputs were better connected to improved acceleration, speed, and jump performance than the 1RM measures. From these findings, it is possible to infer that players able to produce higher bar-power outputs are likely to sprint faster and jump higher. Therefore, coaches involved in team sports are strongly encouraged to use the bar-power method to evaluate the athletic performance of their players.

THERABAND® CLX gold reduces knee-width index and range of motion during overhead, barbell squatting

This study examined the influence of the Theraband^TM CLX gold band on lower-limb muscle activity and kinematics during an overhead barbell squat. Participants performed two sets (band and no-band) of 12 repetitions of overhead barbell squats at 25% bodyweight. Three-dimensional kinematics were measured using motion capture with rigid bodies placed bilaterally on the foot, shank, thigh and thorax. Electromyography was collected from seven, bilateral muscles of the lower-limb and was unchanged for all muscles between conditions. Medial knee collapse was calculated using a knee-width index (KWI) ratio of the distance between the lateral epicondyles of the femur and the lateral malleoli. Average KWI was smaller during the band condition for the concentric (No band: 0.99 ± 0.05, Band: 0.97 ± 0.06, p < 0.05) and eccentric phases (No band: 1.00 ± 0.06, Band: 0.97 ± 0.05, p < 0.05). KWI was significantly smaller with the use of the Theraband^TM CLX. As the gold band is the strongest of the CLX offerings, any benefit of increased proprioception may have been lost due to the high resistance of the band. Further research examining the dose-response of elastic band resistance to knee alignment may be needed to inform proper exercise prescription.

The Importance of Muscular Strength: Training Considerations

This review covers underlying physiological characteristics and training considerations that may affect muscular strength including improving maximal force expression and time-limited force expression. Strength is underpinned by a combination of morphological and neural factors including muscle cross-sectional area and architecture, musculotendinous stiffness, motor unit recruitment, rate coding, motor unit synchronization, and neuromuscular inhibition. Although single- and multi-targeted block periodization models may produce the greatest strength-power benefits, concepts within each model must be considered within the limitations of the sport, athletes, and schedules. Bilateral training, eccentric training and accentuated eccentric loading, and variable resistance training may produce the greatest comprehensive strength adaptations. Bodyweight exercise, isolation exercises, plyometric exercise, unilateral exercise, and kettlebell training may be limited in their potential to improve maximal strength but are still relevant to strength development by challenging time-limited force expression and differentially challenging motor demands. Training to failure may not be necessary to improve maximum muscular strength and is likely not necessary for maximum gains in strength. Indeed, programming that combines heavy and light loads may improve strength and underpin other strength-power characteristics. Multiple sets appear to produce superior training benefits compared to single sets; however, an athlete's training status and the dose-response relationship must be considered. While 2- to 5-min interset rest intervals may produce the greatest strength-power benefits, rest interval length may vary based an athlete's training age, fiber type, and genetics. Weaker athletes should focus on developing strength before emphasizing power-type training. Stronger athletes may begin to emphasize power-type training while maintaining/improving their strength. Future research should investigate how best to implement accentuated eccentric loading and variable resistance training and examine how initial strength affects an athlete's ability to improve their performance following various training methods.