Showing papers in "Journal of Strength and Conditioning Research in 2011"

Validity and reliability of Optojump photoelectric cells for estimating vertical jump height.

Abstract: Vertical jump is one of the most prevalent acts performed in several sport activities. It is therefore important to ensure that the measurements of vertical jump height made as a part of research or athlete support work have adequate validity and reliability. The aim of this study was to evaluate concurrent validity and reliability of the Optojump photocell system (Microgate, Bolzano, Italy) with force plate measurements for estimating vertical jump height. Twenty subjects were asked to perform maximal squat jumps and countermovement jumps, and flight time-derived jump heights obtained by the force plate were compared with those provided by Optojump, to examine its concurrent (criterion-related) validity (study 1). Twenty other subjects completed the same jump series on 2 different occasions (separated by 1 week), and jump heights of session 1 were compared with session 2, to investigate test-retest reliability of the Optojump system (study 2). Intraclass correlation coefficients (ICCs) for validity were very high (0.997-0.998), even if a systematic difference was consistently observed between force plate and Optojump (-1.06 cm; p < 0.001). Test-retest reliability of the Optojump system was excellent, with ICCs ranging from 0.982 to 0.989, low coefficients of variation (2.7%), and low random errors (±2.81 cm). The Optojump photocell system demonstrated strong concurrent validity and excellent test-retest reliability for the estimation of vertical jump height. We propose the following equation that allows force plate and Optojump results to be used interchangeably: force plate jump height (cm) = 1.02 × Optojump jump height + 0.29. In conclusion, the use of Optojump photoelectric cells is legitimate for field-based assessments of vertical jump height.

Relationship between core stability, functional movement, and performance.

Abstract: The purpose of this study was to determine the relationship between core stability, functional movement, and performance. Twenty-eight healthy individuals (age = 24.4 ± 3.9 yr, height = 168.8 ± 12.5 cm, mass = 70.2 ± 14.9 kg) performed several tests in 3 categories: core stability (flexion [FLEX], extension [EXT], right and left lateral [LATr/LATl]), functional movement screen (FMS) (deep squat [DS], trunk-stability push-up [PU], right and left hurdle step [HSr/HSl], in-line lunge [ILLr/ILLl], shoulder mobility [SMr/SMl], active straight leg raise [ASLRr/ASLRl], and rotary stability [RSr/RSl]), and performance tests (backward medicine ball throw [BOMB], T-run [TR], and single leg squat [SLS]). Statistical significance was set at p ≤ 0.05. There were significant correlations between SLS and FLEX (r = 0.500), LATr (r = 0.495), and LATl (r = 0.498). The TR correlated significantly with both LATr (r = 0.383) and LATl (r = 0.448). Of the FMS, BOMB was significantly correlated with HSr (r = 0.415), SMr (r = 0.388), PU (r = 0.407), and RSr (r = 0.391). The TR was significantly related with HSr (r = 0.518), ILLl (r = 0.462) and SMr (r = 0.392). The SLS only correlated significantly with SMr (r = 0.446). There were no significant correlations between core stability and FMS. Moderate to weak correlations identified suggest core stability and FMS are not strong predictors of performance. In addition, existent assessments do not satisfactorily confirm the importance of core stability on functional movement. Despite the emphasis fitness professionals have placed on functional movement and core training for increased performance, our results suggest otherwise. Although training for core and functional movement are important to include in a fitness program, especially for injury prevention, they should not be the primary emphasis of any training program.

The role of rate of force development on vertical jump performance.

Abstract: The purpose of this study was to examine a) the relationship between rate of force development (RFD) and vertical jump (VJ) performance during a counter movement jump (CMJ), and b) the reliability of RFD recorded during the CMJ and squat jump (SJ) forms of the VJ. Twenty-three physically active men aged 23 ± 3.9 years participated in the study. Subjects completed 3 unloaded CMJ and 3 unloaded SJ in random order on a force plate. The RFD was measured during CMJ and SJ movements with vertical jump displacement (VJD) measured simultaneously during the CMJ only. Subjects incorporated arm swing to their CMJ technique to reach up as high as possible, and VJD was measured. All SJ were executed with both hands on the hips throughout the full range of movement. Peak rate of force development (PRFD), peak force (PF), and time to peak force (TPF) were significantly correlated to VJD during the CMJ (r = 0.68, r = 0.51, and r = -0.48, respectively). The RFD and TPF during the CMJ and SJ were associated with low test-retest reliability (coefficient of variation [CV]: 11.8-7.9%). Peak and average power, PF, and VJD produced high test-retest reliability (CV: 2.8-5.1%) during both the CMJ and SJ movements. Our results indicate that PRFD, a measure of explosive strength, and PF, a measure of maximal strength, are the primary contributors to VJD during the CMJ in physically active men. However, caution must be used when interpreting data using PRFD because of its low retest reliability.

A practical approach to monitoring recovery: development of a perceived recovery status scale.

Abstract: The aim of this study was to develop and test the practical utility of a perceived recovery status (PRS) scale. Sixteen volunteers (8 men, 8 women) performed 4 bouts of high-intensity intermittent sprint exercise. After completion of the baseline trial, in a repeated-measures design, subjects were given variable counterbalanced recovery periods of 24, 48, and 72 hours whereupon they repeated an identical intermittent exercise protocol. After a warm-up period, but before beginning each subsequent bout of intermittent sprinting, each individual provided their perceived level of recovery with a newly developed PRS scale. Similar to perceived exertion during exercise, PRS was based on subjective feelings. The utility of the PRS scale was assessed by measuring the level of agreement of an individual's perceived recovery relative to their performance during the exercise bout. Perceived recovery status and change (both positive and negative) in sprint performance during multiple bouts of repeated sprint exercise were moderately negative correlated (r = -0.63). Additionally, subjects were able to accurately assess level of recovery using the PRS scale indicated by correspondence with negative and positive changes in total sprint time relative to their previous session. The ability to detect changes in performance using a noninvasive psychobiological tool to identify differences in performance was independent of other psychological and physiological markers measured during testing, because there were no differences (p > 0.05) among ratings of perceived exertion (RPE), heart rate, blood lactate concentration, or session RPE values among any of the performance trials. Although further study is needed, current results indicate a subjective approach may be an effective means for assessing recovery from day to day, at least under similar conditions.

Between-session reliability of four hop tests and the Agility T-Test

Abstract: The purposes of this study were firstly to investigate whether learning affects were present in the administration of 4 hop tests and the Agility T-test and secondly to assess the between-session reliability of these tests. Twenty-two recreational athletes (11 women: age 22.3 ± 3.7 years, height 167.7 ± 6.2 cm, weight 59.2 ± 6.9 kg and 11 men: age 22.8 ± 3.1 years, height 179.8 ± 4 cm, weight 79.6 ± 10 kg) took part in the study. The subjects performed 6 repetitions of each hop test and 4 repetitions of the Agility T-test once a week over a period of 3 weeks. Distances were normalized to leg length and presented as a percentage value for the single, triple and crossover hop. Results showed that there were significant differences in scores between genders and that learning affects were present in all tests. Intraclass correlation coefficients ranged from 0.76 to 0.92 for the hop tests and 0.82 to 0.96 for the Agility T-test. The results indicated that the hop and Agility T-tests are reliable tests for use with subjects in a clinical or team sport environment. The error measurement statistics presented could be of help to practitioners to determine whether changes in individuals' scores in the hop and Agility T-tests are because of a true change in performance or measurement error. Of most importance was the fact that all subjects achieved at least 90% limb symmetry index on all 4 hop tests. Therefore, we recommend that a minimum limb symmetry value of 90%, rather than previously recommended 85%, should be adopted during rehabilitation and conditioning.

A Systematic Review: Plyometric Training Programs for Young Children

Abstract: The purpose of this systematic review was to evaluate the efficacy and safety of plyometric training for improving motor performance in young children; to determine if this type of training could be used to improve the strength, running speed, agility, and jumping ability of children with low motor competence; and to examine the extent and quality of the current research literature. Primary research articles were selected if they (a) described the outcomes of a plyometric exercise intervention; (b) included measures of strength, balance, running speed, jumping ability, or agility; (c) included prepubertal children 5-14 years of age; and (d) used a randomized control trial or quasiexperimental design. Seven articles met the inclusion criteria for the final review. The 7 studies were judged to be of low quality (values of 4-6). Plyometric training had a large effect on improving the ability to run and jump. Preliminary evidence suggests plyometric training also had a large effect on increasing kicking distance, balance, and agility. The current evidence suggests that a twice a week program for 8-10 weeks beginning at 50-60 jumps a session and increasing exercise load weekly results in the largest changes in running and jumping performance. An alternative program for children who do not have the capability or tolerance for a twice a week program would be a low-intensity program for a longer duration. The research suggests that plyometric training is safe for children when parents provide consent, children agree to participate, and safety guidelines are built into the intervention.

Small-sided games in soccer: amateur vs. professional players' physiological responses, physical, and technical activities.

Abstract: The aim of this study was to examine the relationship between the playing level in soccer (i.e., amateur vs. professional players) and the physiological impact, perceptual responses, time-motion characteristics, and technical activities during various small-sided games (SSGs). Twenty international players (27.4 ± 1.5 years and 17.4 ± 0.8 km·h(-1) of vVO(2)max) and 20 amateur players of the fourth French division (26.3 ± 2.2 years and 17.0 ± 1.2 km·h(-1) of vVO(2)max) played 9 SSGs (i.e., 2 vs. 2, 3 vs. 3, and 4 vs. 4) in which the number of ball touches authorized by possession varied (1 ball touch authorized = 1T, 2 ball touches authorized = 2T, and Free Play = FP). Heart rate (HR), blood lactate ([La]), subjective perception of effort (rating of perceived exertion [RPE]), physical performance, and technical performance of all players were analyzed during all SSGs. Across the various SSGs, amateurs completed a lower percent of successful passes (p < 0.01), recorded higher RPE and [La] values, lost a greater amount of ball possessions (p < 0.001), and covered less total distance with respect to sprinting and high-intensity running (HIR). The HR responses, however, were similar when expressed as %HRmax and %HRreserve. The comparison of the professional and amateur soccer players' activities during SSGs showed that the playing level influenced the physiological responses, physical and technical activities. Consequently, this study has shown that the main differences between elite and amateur players within SSGs concerned their capacity to perform high-intensity actions (HIR and sprints) and execute various technical abilities (in particular number of ball lost per possession and percentage of successful passes).

The reliability of three devices used for measuring vertical jump height.

Abstract: The purpose of this investigation was to assess the intrasession and intersession reliability of the Vertec, Just Jump System, and Myotest for measuring countermovement vertical jump (CMJ) height. Forty male and 39 female university students completed 3 maximal-effort CMJs during 2 testing sessions, which were separated by 24-48 hours. The height of the CMJ was measured from all 3 devices simultaneously. Systematic error, relative reliability, absolute reliability, and heteroscedasticity were assessed for each device. Systematic error across the 3 CMJ trials was observed within both sessions for males and females, and this was most frequently observed when the CMJ height was measured by the Vertec. No systematic error was discovered across the 2 testing sessions when the maximum CMJ heights from the 2 sessions were compared. In males, the Myotest demonstrated the best intrasession reliability (intraclass correlation coefficient [ICC] = 0.95; SEM = 1.5 cm; coefficient of variation [CV] = 3.3%) and intersession reliability (ICC = 0.88; SEM = 2.4 cm; CV = 5.3%; limits of agreement = -0.08 ± 4.06 cm). Similarly, in females, the Myotest demonstrated the best intrasession reliability (ICC = 0.91; SEM = 1.4 cm; CV = 4.5%) and intersession reliability (ICC = 0.92; SEM = 1.3 cm; CV = 4.1%; limits of agreement = 0.33 ± 3.53 cm). Additional analysis revealed that heteroscedasticity was present in the CMJ when measured from all 3 devices, indicating that better jumpers demonstrate greater fluctuations in CMJ scores across testing sessions. To attain reliable CMJ height measurements, practitioners are encouraged to familiarize athletes with the CMJ technique and then allow the athletes to complete numerous repetitions until performance plateaus, particularly if the Vertec is being used.

Effect of core stability training on throwing velocity in female handball players.

Abstract: The purpose was to study the effect of a sling exercise training (SET)-based core stability program on maximal throwing velocity among female handball players. Twenty-four female high-school handball players (16.6 ± 0.3 years, 63 ± 6 kg, and 169 ± 7 cm) participated and were initially divided into a SET training group (n = 14) and a control group (CON, n = 10). Both groups performed their regular handball training for 6 weeks. In addition, twice a week, the SET group performed a progressive core stability-training program consisting of 6 unstable closed kinetic chain exercises. Maximal throwing velocity was measured before and after the training period using photocells. Maximal throwing velocity significantly increased 4.9% from 17.9 ± 0.5 to 18.8 ± 0.4 m·s in the SET group after the training period (p < 0.01), but was unchanged in the control group (17.1 ± 0.4 vs. 16.9 ± 0.4 m·s). These results suggest that core stability training using unstable, closed kinetic chain movements can significantly improve maximal throwing velocity. A stronger and more stable lumbopelvic-hip complex may contribute to higher rotational velocity in multisegmental movements. Strength coaches can incorporate exercises exposing the joints for destabilization force during training in closed kinetic chain exercises. This may encourage an effective neuromuscular pattern and increase force production and can improve a highly specific performance task such as throwing.

Factors that differentiate acceleration ability in field sport athletes.

Abstract: Speed and acceleration are essential for field sport athletes. However, the mechanical factors important for field sport acceleration have not been established in the scientific literature. The purpose of this study was to determine the biomechanical and performance factors that differentiate sprint acceleration ability in field sport athletes. Twenty men completed sprint tests for biomechanical analysis and tests of power, strength, and leg stiffness. The sprint intervals analyzed were 0-5, 5-10, and 0-10 m. The subjects were split into a faster and slower group based on 0- to 10-m velocity. A 1-way analysis of variance determined variables that significantly (p ≤ 0.05) distinguished between faster and slower acceleration. All subject data were then pooled for a correlation analysis to determine factors contributing most to acceleration. The results showed that 0- to 5-m (∼16% difference) and 0- to 10-m (∼11% difference) contact times for the faster group were significantly lower. Times to peak vertical and horizontal force during ground contact were lower for the faster group. This was associated with the reduced support times achieved by faster accelerators and their ability to generate force quickly. Ground contact force profiles during initial acceleration are useful discriminators of sprint performance in field sport athletes. For the strength and power measures, the faster group demonstrated a 14% greater countermovement jump and 48% greater reactive strength index. Significant correlations were found between velocity (0-5, 5-10, and 0-10 m) and most strength and power measures. The novel finding of this study is that training programs directed toward improving field sport sprint acceleration should aim to reduce contact time and improve ground force efficiency. It is important that even during the short sprints required for field sports, practitioners focus on good technique with short contact times.

Using the load-velocity relationship for 1RM prediction.

Abstract: The purpose of this study was to investigate the ability of the load-velocity relationship to accurately predict a bench press 1 repetition maximum (1RM). Data from 3 different bench press studies (n = 112) that incorporated both 1RM assessment and submaximal load-velocity profiling were analyzed. Individual regression analysis was performed to determine the theoretical load at zero velocity (LD0). Data from each of the 3 studies were analyzed separately and also presented as overall group mean. Thereafter, correlation analysis provided quantification of the relationships between 1RM and LD0. Practically perfect correlations (r = ∼0.95) were observed in our samples, confirming the ability of the load-velocity profile to accurately predict bench press 1RM.

Biochemical and endocrine responses to impact and collision during elite Rugby League match play.

Abstract: The purpose of this study was to investigate the relationship between the prematch and short-term postmatch biochemical and endocrine responses to the intensity, number, and distribution of impacts associated with collisions during elite Rugby League match play. Seventeen elite male Rugby League players each provided blood and saliva samples 24 hours prematch, 30 minutes prematch, 30 minutes postmatch, and then at 24-hour intervals for a period of 5 days postmatch to determine plasma creatine kinase concentration ([CK]) and salivary cortisol concentration ([sCort]). The intensity, number, and distribution of impact forces experienced by players during match play were recorded using portable global positioning systems (GPSs). The change in the dependent variables at each sample collection time was compared to 24 hours prematch and 30-minute prematch measures. The [CK] and [sCort] increased significantly (p 10.1G) during match play was significantly correlated (p 8.1G. [CK] remained elevated 120 hours postmatch identifying that at least 5 days modified activity is required to achieve full recovery after elite Rugby League match play.

Performance analysis of elite Rugby League match play using global positioning systems.

Abstract: The aim of this study was (a) to examine the physiological demands of competitive Rugby League match play using portable Global Positioning Systems (GPSs) to monitor players' movement patterns and heart rate (HR) and (b) examine positional comparisons to determine if players' physiological requirements are influenced by their playing position during Rugby League match play. Twenty-two elite male Rugby League players were monitored during 5 regular season competition matches using portable GPS software. There was no difference in the total distance traveled between backs (5,573 ± 1,128 m) and forwards (4,982 ± 1,185 m) during match play. Backs and forwards had an average HR of approximately 80% of their maximum (162 ± 11 and 165 ± 12 b · min(-1), respectively) throughout each match. Backs achieved greater maximum running speed (8.6 ± 0.7 m · s(-1)), completed a greater number of sprints (18 ± 6), had less time between sprints (3.2 ± 1.1 minutes), achieved a greater total duration of sprinting (44.7 ± 9.1 seconds), and covered more distance sprinting (321 ± 74 m) than forwards did (6.8 ± 0.7 m · s(-1), 11 ± 5, 5.2 ± 2.2 minutes, 25.8 ± 9.2 seconds, and 153 ± 38 m, respectively). The GPS successfully provided real-time feedback to identify significant positional differences in distances covered, running speed characteristics, and the physiological demands of competitive Rugby League match play.

Effects of running velocity on running kinetics and kinematics.

Abstract: Sixteen semiprofessional Australian football players performed running bouts at incremental velocities of 40, 60, 80, and 100% of their maximum velocity on a Woodway nonmotorized force treadmill. As running velocity increased from 40 to 60%, peak vertical and peak horizontal forces increased by 14.3% (effect size [ES] = 1.0) and 34.4% (ES = 4.2), respectively. The changes in peak vertical and peak horizontal forces from 60 to 80% were 1.0% (ES = 0.05) and 21.0% (ES = 2.9), respectively. Finally, the changes in peak vertical and peak horizontal forces from 80% to maximum were 2.0% (ES = 0.1) and 24.3% (ES = 3.4). In addition, both stride frequency and stride length significantly increased with each incremental velocity (p < 0.05). Conversely, contact times and the vertical displacement of the center of mass significantly decreased with increased running velocity (p < 0.05). A significant positive correlation was found between horizontal force and maximum running velocity (r = 0.47). For the kinematic variables, only stride length was found to have a significant positive correlation with maximum running velocity (r = 0.66). It would seem that increasing maximal sprint velocity may be more dependent on horizontal force production as opposed to vertical force production.

Test-retest reliability of the five-repetition sit-to-stand test: a systematic review of the literature involving adults.

Abstract: The 5-repetition sit-to-stand test (FRSTST) is a widely used measure of functional strength, particularly among older adults. The purpose of this review was to summarize the findings of research using the intraclass correlation coefficient (ICC) to describe the test-retest reliability of the FRSTST. A search of 3 electronic databases and hand searches were used to identify relevant articles. Information on the subjects, test sessions and the ICCs reported was abstracted from the articles. The searches identified 10 relevant articles. The ICCs reported in the articles ranged from 0.64 to 0.96. The adjusted mean ICC calculated from the reported ICCs was 0.81. The test-retest reliability of the FRSTST can be interpreted as good to high in most populations and settings.

Heart Rate Responses and Technical Comparison Between Small- vs. Large-Sided Games in Elite Professional Soccer

Abstract: This study aims to examine the difference in heart rate (HR) responses and technical activities placed upon European elite players when exposed to 2-sided games differing in the number of players and playing area. Fifteen male soccer players from a Scottish Premier League team (26.3 ± 4.85 years, 182.4 ± 6.99 cm, 79.5 ± 8.05 kg, VO2max of 54.36 ± 5.45 ml·kg(-1)·min(-1)) performed both small (3 vs. 3 plus goalkeepers) and large (9 vs. 9 plus goalkeepers) sided games each lasting for 3 × 5 minutes interspersed with 4-minute passive recovery during the 2009-2010 season. The HR responses and players' technical actions were recorded throughout all sided games. Results show that small-sided games (SSG) induced significantly (p 85% maximal HR zone (p < 0.05, large effect) as compared to large-sided games. Technical analysis revealed a large practical difference (effect size ranged from 1.5 to 21.2) between small- and large-sided games: less number of blocks, headers, interceptions, passes, and receives but more dribbles, shots, and tackles in SSG. Furthermore, SSG induced significantly lesser total ball contacts per game (p < 0.05, large effect) but significantly greater ball contacts per individual (p < 0.05, large effect) when compared to larger-sided games. The different technical requirements also enable coaches to carry out training games more suitable to specific playing positions such as SSG for midfielders (more dribbles, tackles, and ball contacts per player) strikers (more shots), and large-sided games for defender (more blocks, headers, and interceptions).

Effect of bout duration on exercise intensity and technical performance of small-sided games in soccer.

Abstract: To examine whether the increase in bout duration would affect the exercise intensity and technical actions, we manipulated bout duration during a typical small-sided game drill (SSG) in male soccer players Nineteen players (mean ± SD: age 24 ± 4 years, body mass 74 ± 4 kg, and height 180 ± 5 cm) completed three bouts of a 3-a-side drill at three different bout durations: 2, 4, and 6 minutes Exercise intensity was quantified using heart rate (HR) and rating of perceived exertion (RPE) A nonsignificant duration × bout interaction was found for HR (p = 0757) Heart rates of bout 1 were significantly lower than bout 2 (p = 0004) and bout 3 (p = 0049) The effect of duration was close to significance for HR (p = 0057) with 6-minute SSG significantly lower than 4-minute SSG (p = 0004) Duration × bout interaction did not reach the significance for RPE (p = 0096) The RPE significantly increased along the bouts (p 0111) A significant effect of bout was only found for successful passes (p = 0018) Partially confirming our hypothesis, the increase in bout duration from 2 to 6 minutes resulted in a decrease in intensity only between the 4- and 6-min SSG However, duration did not influence the technical actions and proficiency The magnitude of changes in HR (895 vs 878 of maximum) is probably not enough to induce different training adaptations Therefore, coaches can use different bout durations with minimal impact on exercise intensity and without compromising technical proficiency

Effects of Speed, Agility, Quickness Training Method on Power Performance in Elite Soccer Players

Abstract: The purpose of this study was to evaluate the effects of the speed, agility, quickness (SAQ) training method on power performance in soccer players. Soccer players were assigned randomly to 2 groups: experimental group (EG; n = 50) and control group (n = 50). Power performance was assessed by a test of quickness--the 5-m sprint, a test of acceleration--the 10-m sprint, tests of maximal speed--the 20- and the 30-m sprint along with Bosco jump tests--squat jump, countermovement jump (CMJ), maximal CMJ, and continuous jumps performed with legs extended. The initial testing procedure took place at the beginning of the in-season period. The 8-week specific SAQ training program was implemented after which final testing took place. The results of the 2-way analysis of variance indicated that the EG improved significantly (p < 0.05) in 5-m (1.43 vs. 1.39 seconds) and in 10-m (2.15 vs. 2.07 seconds) sprints, and they also improved their jumping performance in countermovement (44.04 vs. 4.48 cm) and continuous jumps (41.08 vs. 41.39 cm) performed with legs extended (p < 0.05). The SAQ training program appears to be an effective way of improving some segments of power performance in young soccer players during the in-season period. Soccer coaches could use this information in the process of planning in-season training. Without proper planning of the SAQ training, soccer players will most likely be confronted with decrease in power performance during in-season period.

Assessment of Physical Fitness Aspects and Their Relationship to Firefighters' Job Abilities

Abstract: The purpose of this study was to identify the relationships between various fitness parameters and firefighting performance on an "Ability Test" (AT) that included a set of 6 simulated firefighting tasks. The relationships between each fitness parameter and each task of the AT were determined. Ninety firefighters participated in this study (age 33 ± 7 years). The AT completion time was associated with abdominal strength (r = -0.53, p < 0.01), relative power (r = -0.44, p < 0.01), upper-body muscular endurance (push-ups, r = -0.27, p < 0.05) (sit-ups, r = -0.41, p < 0.01), and upper-body strength (1 repetition maximum bench press, r = -0.41, p < 0.01). In addition, poor performance on the AT was associated with high resting heart rate (r = 0.36, p < 0.01), high body mass index (r = 0.34, p < 0.01), high body fat (BF)% (r = 0.57, p < 0.01), increasing age (r = 0.42, p < 0.01), and large waist size (r = 0.67, p < 0.01). Multiple regression analyses indicated that a significant (F[5, 53] = 14.02, p < 0.01) proportion (60%) of the variation observed in the AT was explained by the variation of the fitness parameters used in the model. This study demonstrated that fitness variables, such as abdominal strength, power (step test), push-ups, resting Hr, and BF%, contributed significantly to the predictive power of firefighters' AT performance. The findings of this study may be useful to fire department instructors and trainers in the design and implementation of training programs that are more specifically tailored to improving both individual firefighting skills and general fire suppression performance.

Relationships Between Force–Time Characteristics of the Isometric Midthigh Pull and Dynamic Performance in Professional Rugby League Players

Abstract: There is considerable conflict within the literature regarding the relevance of isometric testing for the assessment of neuromuscular function within dynamic sports. The aim of this study was to determine the relationship between isometric measures of force development and dynamic performance. Thirty-nine professional rugby league players participated in this study. Forty-eight hours after trial familiarization, participants performed a maximal isometric midthigh pull, with ∼120-130° bend at the knee, countermovement jump (CMJ), and a 10-m sprint. Force-time data were processed for peak force (PF), force at 100 milliseconds (F100ms), and peak rate of force development (PRFD). Analysis was carried out using Pearson's product moment correlation with significance set at p < 0.05. The PF was not related to dynamic performance; however, when expressed relative to body weight, it was significantly correlated with both 10-m time and CMJ height (r = -0.37 and 0.45, respectively, p < 0.05). The F100ms was inversely related to 10-m time (r = -0.54, p < 0.01); moreover, when expressed relative to body weight, it was significantly related to both 10-m time and CMJ height (r = -0.68 and 0.43, p < 0.01). In addition, significant correlations were found between PRFD and 10-m time (r = -0.66, p < 0.01) and CMJ height (r = 0.387, p < 0.01). In conclusion, this study provides evidence that measures of maximal strength and explosiveness from isometric force-time curves are related to jump and sprint acceleration performance in professional rugby league players.

Specificity of jumping, sprinting, and quick change-of-direction motor abilities.

Abstract: Despite being addressed in a number of previous studies, the controversy regarding the generality vs. specificity of jumping, sprinting, and change-of-direction speed (CODS) abilities still remains unresolved. Here, we tested the hypotheses that jumping, sprinting, and CODS represent separate and specific motor abilities, and that the jumping ability based on concentric and slow stretch-shortening cycle (SSC) is relatively independent of the same ability based on fast SSC. Eighty-seven male college athletes performed 3 concentric/slow SSC and 3 fast SSC jump tests, 4 sprint tests, and 3 CODS tests. The hypotheses were tested by means of the principal component factor analysis (PCA). The applied procedure reduced the greater number of manifest variables to a smaller number of independent latent dimensions or factors and, thereafter, assessed the relationships among them. The PCA revealed a relatively simple and consistent structure consisting of 4 separate factors that explained nearly 80% of variance of the applied tests. The factors appeared to correspond to the sprinting ability, concentric/slow SSC jumping ability, fast SSC jumping ability, and CODS ability. Further analyses revealed that the extracted factors were mainly independent, because they shared only between 6 and 23% of the common variance. These results supported our hypotheses regarding the specificity of jumping, sprinting, and CODS abilities, and specificity of the concentric/slow SSC and fast SSC jumping abilities. Coaches and strength and conditioning professionals should, therefore, use separate performance tests for the assessment of the studied abilities.

Markers of postmatch fatigue in professional Rugby League players.

Abstract: The aim of the present study was to identify neuromuscular, biochemical, and endocrine markers of fatigue after Rugby League match play. Seventeen elite Rugby League players were monitored for a single match. Peak rate of force development (PRFD), peak power (PP), and peak force (PF) were measured during a countermovement jump (CMJ) on a force plate pre and postmatch play. Saliva and blood samples were collected 24 hours prematch, 30 minutes prematch, 30 minutes postmatch, and then at 24-hour intervals for a period of 120 hours to determine plasma creatine kinase concentration ([CK]) and salivary cortisol concentration ([sCort]). There were significant (p < 0.05) decreases in PRFD and PP up to 24 hours postmatch with PF significantly (p < 0.05) decreased immediately postmatch. The [sCort] significantly (p < 0.05) increased from 24 hours prematch to 30 minutes prematch and up to 24 hours postmatch compared with 24 hours prematch. Plasma [CK] significantly (p < 0.05) increased 30 minutes postmatch with a peak occurring 24 hours postmatch and remained elevated above 24 hours prematch for at least 120 hours postmatch. There were significant (p < 0.05) correlations between the increase in [CK] and reduction in PRFD 30 minutes postmatch and 24 hours postmatch. The [sCort] was significantly (p < 0.05) correlated with the reduction in PF 30 minutes postmatch. Results demonstrate that neuromuscular function is compromised for up to 48 hours after match play. Elevated [CK] despite 120-hour recovery indicate that damage to muscle tissue after Rugby League match play may persist for at least 5 days postmatch. Despite the prolonged presence of elevated [CK] postmatch, strength training 48 hours postmatch may have resulted in a compensatory increase in PRFD supporting the inclusion of strength training during the short-term postmatch recovery period.

Anthropometric and physiological characteristics of young soccer players according to their playing positions: relevance for competition success

Abstract: The aim of this study was to establish the anthropometric and physiological profiles of young soccer players according to their playing position and to determine their relevance for competition success. Three hundred and twenty-one young male soccer players participated in the study. Players, age 15.63 (±1.82) years, range 12�19 years, were classified into the following groups: Goalkeepers (n = 35), Central Defenders (n = 53), External Defenders (n = 54), Central Midfielders (n = 61), External Midfielders (n = 46), and Forwards (n = 72). The anthropometric variables of participants (height, weight, body mass index, 6 skinfolds, 4 diameters, and 3 perimeters) were measured. Also, their somatotype and body composition (weights and percentages of fat, bone, and muscle) were calculated. Participants performed the 20-m progressive run test to estimate their relative [latin capital V with dot above]O2max, a sprint test (30 m flat), and 3 jump tests (squat jump, countermovement jump, and Abalakov test). External Midfielders were the leanest and shortest. In contrast, Central Defenders and Goalkeepers were found to be the tallest and heaviest players. They also had the largest fat skinfolds. In general, the results show that heavier and taller young soccer players performed better in vertical jumps and 30-m sprint, whereas leaner players performed better in the 20-m progressive run test. Players were classified into 2 groups according to the final ranking of their teams at the end of the season. Players from successful teams performed slightly better than players from unsuccessful teams in the physiological test, but these differences were not statistically significant. Moreover, players from successful teams were found to be leaner and more muscular than their unsuccessful counterparts.

Strength and Power Predictors of Swimming Starts in International Sprint Swimmers

Abstract: Start performance (as defined by time to 15 m) has been shown to be a key performance indicator during 50-m freestyle swimming; however, there is limited information with regard to the key strength and power variables that influence start performance during sprint swimming. In light of the above, this study aimed to examine the key strength and power predicators of start performance in 50-m freestyle swimming. Eleven male British international sprint swimmers (age 21.3 ± 1.7 years; mass 78.1 ± 11.2 kg; and height 1.8 ± 0.1 m) participated in this study. Within 1 week, swimmers performed the following tests: 3 repetition maximum (3RM) squat strength, countermovement jump (CMJ) on a portable force platform, and a measure of start time performance (time to 15 m under 50-m freestyle conditions). The start time was measured using a standard racing platform to which a portable force platform was mounted, and all starts were recorded using 2 cameras. This setup allowed for the quantification of time to 15 m, peak vertical force (PVF), and peak horizontal force (PHF). Data were analyzed using Pearson's product moment correlation with significance set at p 0.05). Furthermore, lower body strength was a key determinant of jump height (r = 0.69), power (r = 0.78), PVF (r = 0.62), and PHF (r = 0.71) (p < 0.05). This study provides evidence of the importance of lower body strength and power to start time in international 50-m sprint swimmers.

Age, sex, and finish time as determinants of pacing in the marathon.

Abstract: Previous researchers have suggested that faster marathoners tend to run at a more consistent pace compared with slower runners. None has examined the influence of sex and age on pacing. Therefore, the purpose of this study was to determine the simultaneous influences of age, sex, and run time on marathon pacing. Pacing was defined as the mean velocity of the last 9.7 km divided by that of the first 32.5 km (closer to 1.0 indicates better pacing). Subjects were 186 men and 133 women marathoners from the 2005, 2006, and 2007 races of a midwestern U.S. marathon. The course was a 1.6 km (1 mile) loop with pace markers throughout, thus facilitating pacing strategy. Each 1.6-km split time was measured electronically by way of shoe chip. The ambient temperature (never above 5°C) ensured that hyperthermia, a condition known to substantially slow marathon times and affect pacing, was not likely a factor. Multiple regression analysis indicated that age, sex, and run time (p 0.05 for each) suggests that the effects of 1 independent variable is not dependent upon the levels of others. We conclude that older, women, and faster are better pacers than younger, men, and slower marathoners, respectively. Coaches can use these findings to overcome such tendencies and increase the odds of more optimal pacing.

Relationship between functional movement screen and athletic performance.

Abstract: Tests such as the functional movement screen (FMS) and maximal strength (repetition maximum strength [1RM]) have been theorized to assist in predicting athletic performance capabilities. Some data exist concerning 1RM and athletic performance, but very limited data exist concerning the potential ability of FMS to assess athletic performance. The purpose of this investigation was to determine if FMS scores or 1RM is related to athletic performance, specifically in Division I golfers in terms of sprint times, vertical jump (VJ) height, agility T-test times, and club head velocity. Twenty-five National Collegiate Athletic Association Division I golfers (15 men, age = 20.0 ± 1.2 years, height = 176.8 ± 5.6 cm, body mass = 76.5 ± 13.4 kg, squat 1RM = 97.1 ± 21.0 kg) (10 women, age = 20.5 ± 0.8 years, height = 167.0 ± 5.6 cm, body mass = 70.7 ± 21.5 kg, squat 1RM = 50.3 ± 16.6) performed an FMS, 1RM testing, and field tests common in assessing athletic performance. Athletic performance tests included 10- and 20-m sprint time, VJ height, agility T-test time, and club head velocity. Strength testing included a 1RM back squat. Data for 1RM testing were normalized to body mass for comparisons. Correlations were determined between FMS, 1RMs, and athletic performance tests using Pearson product correlation coefficients (p <= 0.05). No significant correlations existed between FMS and 10-m sprint time (r = -0.136), 20-m sprint time (r = -0.107), VJ height (r = 0.249), agility T-test time (r = -0.146), and club head velocity (r = -0.064). The 1RM in the squat was significantly correlated to 10-m sprint time (r = -0.812), 20-m sprint time (r = -0.872), VJ height (r = 0.869), agility T-test time (r = -0.758), and club head velocity (r = 0.805). The lack of relationship suggests that FMS is not an adequate field test and does not relate to any aspect of athletic performance. Based on the data from this investigation, 1RM squat strength appears to be a good indicator of athletic performance.

The acute effects of a warm-up including static or dynamic stretching on countermovement jump height, reaction time, and flexibility.

Abstract: The purpose of this research was to compare the effects of a warm-up with static vs. dynamic stretching on countermovement jump (CMJ) height, reaction time, and low-back and hamstring flexibility and to determine whether any observed performance deficits would persist throughout a series of CMJs. Twenty-one recreationally active men (24.4 ± 4.5 years) completed 3 data collection sessions. Each session included a 5-minute treadmill jog followed by 1 of the stretch treatments: no stretching (NS), static stretching (SS), or dynamic stretching (DS). After the jog and stretch treatment, the participant performed a sit-and-reach test. Next, the participant completed a series of 10 maximal-effort CMJs, during which he was asked to jump as quickly as possible after seeing a visual stimulus (light). The CMJ height and reaction time were determined from measured ground reaction forces. A treatment × jump repeated-measures analysis of variance for CMJ height revealed a significant main effect of treatment (p = 0.004). The CMJ height was greater for DS (43.0 cm) than for NS (41.4 cm) and SS (41.9 cm) and was not less for SS than for NS. Analysis also revealed a significant main effect of jump (p = 0.005) on CMJ height: Jump height decreased from the early to the late jumps. The analysis of reaction time showed no significant effect of treatment. Treatment had a main effect (p < 0.001) on flexibility, however. Flexibility was greater after both SS and DS compared to after NS, with no difference in flexibility between SS and DS. Athletes in sports requiring lower-extremity power should use DS techniques in warm-up to enhance flexibility while improving performance.

The acute potentiating effects of back squats on athlete performance

Abstract: Crewther, BT, Kilduff, LP, Cook, CJ, Middleton, MK, Bunce, PJ, and Yang, G-Z. The acute potentiating effects of back squats on athlete performance. J Strength Cond Res 25(12): 3319-3325, 2011-This study examined the acute potentiating effects of back squats on athlete performance with a specific focus on movement specificity and the individual timing of potentiation. Nine subelite male rugby players performed 3 protocols on separate occasions using a randomized, crossover, and counterbalanced design. Each protocol consisted of performance testing before a single set of 3 repetition maximum (3RM) back squats, followed by retesting at ∼15 seconds, 4, 8, 12, and 16 minutes. The 3 tests were countermovement jumps (CMJs), sprint performance (5 and 10 m), and 3-m horizontal sled pushes with a 100-kg load. Relationships between the individual changes in salivary testosterone and cortisol concentrations and performance were also examined. The 3RM squats significantly (p < 0.001) improved CMJ height at 4 (3.9 ± 1.9%), 8 (3.5 ± 1.5%), and 12 (3.0 ± 1.4%) minutes compared with baseline values, but no temporal changes in sprinting and sled times were identified. On an individual level, the peak relative changes in CMJ height (6.4 ± 2.1%, p < 0.001) were greater than the 3-m sled (1.4 ± 0.6%), 5-m (2.6 ± 1.0%), and 10-m sprint tests (1.8 ± 1.0%). In conclusion, a single set of 3RM squats was found effective in acutely enhancing CMJ height in the study population, especially when the recovery period was individualized for each athlete. The study results also suggest that the potentiating effects of squats may exhibit some degree of movement specificity, being greater for those exercises with similar movement patterns. The current findings have practical implications for prescribing warm-up exercises, individualizing training programs, and for interpreting postactivation potentiation research.

Prehabilitation Before Total Knee Arthroplasty Increases Strength and Function in Older Adults With Severe Osteoarthritis

Abstract: Preparing for the stress of total knee arthroplasty (TKA) surgery by exercise training (prehabilitation) may improve strength and function before surgery and, if effective, has the potential to contribute to postoperative recovery. Subjects with severe osteoarthritis (OA), pain intractable to medicine and scheduled for TKA were randomized into a usual care (UC) group (n = 36) or usual care and exercise (UC + EX) group (n = 35). The UC group maintained normal daily activities before their TKA. The UC + EX group performed a comprehensive prehabilitation program that included resistance training using bands, flexibility, and step training at least 3 times per week for 4-8 weeks before their TKA in addition to UC. Leg strength (isokinetic peak torque for knee extension and flexion) and ability to perform functional tasks (6-minute walk, 30 second sit-to-stand repetitions, and the time to ascend and descend 2 flights of stairs) were assessed before randomization at baseline (T1) and 1 week before the subject's TKA (T2). Repeated-measures analysis of variance indicated a significant group by time interaction (p < 0.05) for the 30-second sit-to-stand repetitions, time to ascend the first flight of stairs, and peak torque for knee extension in the surgical knee. Prehabilitation increased leg strength and the ability to perform functional tasks for UC + EX when compared to UC before TKA. Short term (4-8 weeks) of prehabilitation was effective for increasing strength and function for individuals with severe OA. The program studied is easily transferred to a home environment, and clinicians working with this population should consider prehabilitation before TKA.

Influence of previous experience on resistance training on reliability of one-repetition maximum test.

Abstract: The 1-repetition maximum test (1RM) has been widely used to assess maximal strength However, to improve accuracy in assessing maximal strength, several sessions of the 1RM test are recommended The aim of this study was to analyze the influence of previous resistance training experience on the reliability of 1RM test Thirty men were assigned to the following 2 groups according to their previous resistance training experience: no previous resistance training experience (NOEXP) and more than 24 months of resistance training experience (EXP) All subjects performed the 1RM tests in bench press and squat in 4 sessions on distinct days There was a significant session × group effect in bench press (F = 309; p < 003) and squat (F = 276; p < 005) showing that only the NOEXP increased maximal strength between the sessions Significant increases (p < 005) in maximal strength occurred in the NOEXP between session 1 and the other sessions in bench press (session 1 vs 2 = +38%; session 1 vs 3 = +74%; session 1 vs 4 = +101%), and squat (session 1 vs 2 = +76%; session 1 vs 3 = +101%; session 1 vs 4 = +112%) Moreover, in bench press, maximal strength in sessions 3 and 4 were significantly higher than in session 2 The results of the present study suggest that the reliability of the 1RM test is influenced by the subject's previous experience in resistance training Subjects without experience in resistance training require more practice and familiarization and show greater increases in maximal strength between sessions than subjects with previous experience in resistance training