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Gal Ziv and Ronnie Lidor

The soccer goalkeeper (GK) is required to perform strenuous actions during practice sessions and actual games. One of the objectives of those professionals who work with GKs is to obtain relevant information on physical characteristics and physiological attributes of GKs, and to use it effectively when planning training programs for them. This article has three purposes: (a) to review a series of studies (n = 23) on physical characteristics, physiological attributes, and on-field performances of soccer GKs; (b) to outline a number of methodological limitations and research concerns associated with these studies; and (c) to suggest several practical recommendations for soccer coaches who work with GKs. Four main fndings emerged from our review: (a) professional adult GKs usually are over 180 cm tall and have a body mass of over 77 kg; (b) studies on agility and speed produced mixed results, with some showing similar values between GKs and field players and others showing reduced performance in GKs; (c) GKs usually have higher vertical jump values when compared with players playing the various field positions; (d) GKs cover approximately 5.5 km during a game, mostly by walking and jogging. Four methodological limitations and research concerns associated with the reviewed studies were discussed, among them the lack of a longitudinal approach and the lack of on-field performance studies. Three practical recommendations are made for coaches, one of which is that coaches should adopt a careful approach when selecting testing protocols and devices for the assessment of GKs’ physiological attributes.

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Mark D. Tillman, Rachel M. Criss, Denis Brunt and Chris J. Hass

The purposes of this study were to analyze double-limb, dominant-limb, and nondominant-limb landings, each with a two-footed takeoff, in order to detect potential differences in muscle activity and ground reaction forces and to examine the possible influence of leg dominance on these parameters. Each of the three jump landing combinations was analyzed in 11 healthy female volleyball players (age 21 ± 3 yrs; height 171 ± 5 cm, mass 61.6 ± 5.5 kg, max. vertical jump height 28 ± 4 cm). Ground reaction forces under each limb and bilateral muscle activity of the vastus medialis, hamstrings, and lateral gastrocnemius muscles were synchronized and collected at 1,000 Hz. Normalized EMG amplitude and force platform data were averaged over five trials for each participant and analyzed using repeated-measures ANOVA. During the takeoff phase in jumps with one-footed landings, the non-landing limb loaded more than the landing limb (p = 0.003). During the 100 ms prior to initial contact, single-footed landings generated higher EMG values than two-footed landings (p = 0.004). One-footed landings resulted in higher peak vertical loading, lateral loading, and rate of lateral loading than two-footed landings (p < 0.05). Trends were observed indicating that muscle activation during one-footed landings is greater than for two-footed landings (p = 0.053 vs. p = 0.077). The greater forces and rate of loading produced during single-limb landings implies a higher predisposition to injury. It appears that strategic planning and training of jumps in volleyball and other jumping sports is critical.

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Gerald T. Mangine, Jay R. Hoffman, Jose Vazquez, Napoleon Pichardo, Maren S. Fragala and Jeffrey R. Stout

The ultimate zone-rating extrapolation (UZR/150) rates fielding performance by runs saved or cost within a zone of responsibility in comparison with the league average (150 games) for a position. Spring-training anthropometric and performance measures have been previously related to hitting performance; however, their relationships with fielding performance measures are unknown.

Purpose:

To examine the relationship between anthropometric and performance measurements on fielding performance in professional baseball players.

Methods:

Body mass, lean body mass (LBM), grip strength, 10-yd sprint, proagility, and vertical-jump mean (VJMP) and peak power (VJPP) were collected during spring training over the course of 5 seasons (2007–2011) for professional corner infielders (CI; n = 17, fielding opportunities = 420.7 ± 307.1), middle infielders (MI; n = 14, fielding opportunities = 497.3 ± 259.1), and outfielders (OF; n = 16, fielding opportunities = 227.9 ± 70.9). The relationships between these data and regular-season (100-opportunity minimum) fielding statistics were examined using Pearson correlation coefficients, while stepwise regression identified the single best predictor of UZR/150.

Results:

Significant correlations (P < .05) were observed between UZR/150 and body mass (r = .364), LBM (r = .396), VJPP (r = .397), and VJMP (r = .405). Of these variables, stepwise regression indicated VJMP (R = .405, SEE = 14.441, P = .005) as the single best predictor for all players, although the addition of proagility performance strengthened (R = .496, SEE = 13.865, P = .002) predictive ability by 8.3%. The best predictor for UZR/150 was body mass for CI (R = .519, SEE = 15.364, P = .033) and MI (R = .672, SEE = 12.331, P = .009), while proagility time was the best predictor for OF (R = .514, SEE = 8.850, P = .042).

Conclusions:

Spring-training measurements of VJMP and proagility time may predict the defensive run value of a player over the course of a professional baseball season.

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Geoff Minett, Rob Duffield and Stephen P. Bird

Purpose:

To investigate the effects of an acute multinutrient supplement on game-based running performance, peak power output, anaerobic by-products, hormonal profiles, markers of muscle damage, and perceived muscular soreness before, immediately after, and 24 h following competitive rugby union games.

Methods:

Twelve male rugby union players ingested either a comprehensive multinutrient supplement (SUPP), [RE-ACTIVATE:01], or a placebo (PL) for 5 d. Participants then performed a competitive rugby union game (with global positioning system tracking), with associated blood draws and vertical jump assessments pre, immediately post and 24 h following competition.

Results:

SUPP ingestion resulted in moderate to large effects for augmented 1st half very high intensity running (VHIR) mean speed (5.9 ± 0.4 vs 4.8 ± 2.3 m·min−1; d = 0.93). Further, moderate increases in 2nd half VHIR distance (137 ± 119 vs 83 ± 89 m; d = 0.73) and VHIR mean speed (5.9 ± 0.6 v 5.3 ± 1.7 m·min−1; d = 0.56) in SUPP condition were also apparent. Postgame aspartate aminotransferase (AST; 44.1 ± 11.8 vs 37.0 ± 3.2 UL; d = 1.16) and creatine kinase (CK; 882 ± 472 vs. 645 ± 123 UL; d = 0.97) measures demonstrated increased values in the SUPP condition, while AST and CK values correlated with 2nd half VHIR distance (r = −0.71 and r = −0.76 respectively). Elevated C-reactive protein (CRP) was observed postgame in both conditions; however, it was significantly blunted with SUPP (P = .05).

Conclusions:

These findings suggest SUPP may assist in the maintenance of VHIR during rugby union games, possibly via the buffering qualities of SUPP ingredients. However, correlations between increased work completed at very high intensities and muscular degradation in SUPP conditions, may mask any anticatabolic properties of the supplement.

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Gerrit Jan van Ingen Schenau, Maarten F. Bobbert and Arnold de Haan

This target article addresses the role of storage and reutilization of elastic energy in stretch-shortening cycles. It is argued that for discrete movements such as the vertical jump, elastic energy does not explain the work enhancement due to the prestretch. This enhancement seems to occur because the prestretch allows muscles to develop a high level of active state and force before starting to shorten. For cyclic movements in which stretch-shortening cycles occur repetitively, some authors have claimed that elastic energy enhances mechanical efficiency. In the current article it is demonstrated that this claim is often based on disputable concepts such as the efficiency of positive work or absolute work, and it is argued that elastic energy cannot affect mechanical efficiency simply because this energy is not related to the conversion of metabolic energy into mechanical energy. A comparison of work and efficiency measures obtained at different levels of organization reveals that there is in fact no decisive evidence to either support or reject the claim that the stretch-shortening cycle enhances muscle efficiency. These explorations lead to the conclusion that the body of knowledge about the mechanics and energetics of the stretch-shortening cycle is in fact quite lean. A major challenge is to bridge the gap between knowledge obtained at different levels of organization, with the ultimate purpose of understanding how the intrinsic properties of muscles manifest themselves under in-vivo-like conditions and how they are exploited in whole-body activities such as running. To achieve this purpose, a close cooperation is required between muscle physiologists and human movement scientists performing inverse and forward dynamic simulation studies of whole-body exercises.

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Barbara C. Belyea, Ethan Lewis, Zachary Gabor, Jill Jackson and Deborah L. King

Context: Lower-extremity landing mechanics have been implicated as a contributing factor in knee pain and injury, yet cost-effective and clinically accessible methods for evaluating movement mechanics are limited. The identification of valid, reliable, and readily accessible technology to assess lower-extremity alignment could be an important tool for clinicians, coaches, and strength and conditioning specialists. Objective: To examine the validity and reliability of using a handheld tablet and movement-analysis application (app) for assessing lower-extremity alignment during a drop vertical-jump task. Design: Concurrent validation. Setting: Laboratory. Participants: 22 healthy college-age subjects (11 women and 11 men, mean age 21 ± 1.4 y, mean height 1.73 ± 0.12 m, mean mass 71 ± 13 kg) with no lower-extremity pathology that prevented safe landing from a drop jump. Intervention: Subjects performed 6 drop vertical jumps that were recorded simultaneously using a 3-dimensional (3D) motion-capture system and a handheld tablet. Main Outcomes Measures: Angles on the tablet were calculated using a motion-analysis app and from the 3D motion-capture system using Visual 3D. Hip and knee angles were measured and compared between both systems. Results: Significant correlations between the tablet and 3D measures for select frontal- and sagittal-plane ranges of motion and angles at maximum knee flexion (MKF) ranged from r = .48 (P = .036) for frontal-plane knee angle at MKF to r = .77 (P < .001) for knee flexion at MKF. Conclusion: Results of this study suggest that a handheld tablet and app may be a reliable method for assessing select lower-extremity joint alignments during drop vertical jumps, but this technology should not be used to measure absolute joint angles. However, sports medicine specialists could use a handheld tablet to reliably record and evaluate lower-extremity movement patterns on the field or in the clinic.

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Paul B. Gastin, Denny Meyer, Emy Huntsman and Jill Cook

Purpose:

To assess the relationships between player characteristics (including age, playing experience, ethnicity, and physical fitness) and in-season injury in elite Australian football.

Design:

Single-cohort, prospective, longitudinal study.

Methods:

Player characteristics (height, body mass, age, experience, ethnicity, playing position), preseason fitness (6-min run, 40-m sprint, 6 × 40-m sprint, vertical jump), and in-season injury data were collected over 4 seasons from 1 professional Australian football club. Data were analyzed for 69 players, for a total of 3879 player rounds and 174 seasons. Injury risk (odds ratio [OR]) and injury severity (matches missed; rate ratio [RR]) were assessed using a series of multilevel univariate and multivariate hierarchical linear models.

Results:

A total of 177 injuries were recorded with 494 matches missed (2.8 ± 3.3 matches/injury). The majority (87%) of injuries affected the lower body, with hamstring (20%) and groin/hip (14%) most prevalent. Nineteen players (28%) suffered recurrent injuries. Injury incidence was increased in players with low body mass (OR = 0.887, P = .005), with poor 6-min-run performance (OR = 0.994, P = .051), and playing as forwards (OR = 2.216, P = .036). Injury severity was increased in players with low body mass (RR = 0.892, P = .008), tall stature (RR = 1.131, P = .002), poor 6-min-run (RR = 0.990, P = .006), and slow 40-m-sprint (RR = 3.963, P = .082) performance.

Conclusions:

The potential to modify intrinsic risk factors is greatest in the preseason period, and improvements in aerobic-running fitness and increased body mass may protect against in-season injury in elite Australian football.

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Adam S. Lepley, Allison M. Strouse, Hayley M. Ericksen, Kate R. Pfile, Phillip A. Gribble and Brian G. Pietrosimone

Context:

Components of gluteal neuromuscular function, such as strength and corticospinal excitability, could potentially influence alterations in lower extremity biomechanics during jump landing.

Objective:

To determine the relationship between gluteal muscle strength, gluteal corticospinal excitability, and jump-landing biomechanics in healthy women.

Setting:

University laboratory.

Design:

Descriptive laboratory study.

Participants:

37 healthy women (21.08 ± 2.15 y, 164.8 ± 5.9 cm, 65.4 ± 12.0 kg).

Interventions:

Bilateral gluteal strength was assessed through maximal voluntary isometric contractions (MVIC) using an isokinetic dynamometer. Strength was tested in the open chain in prone and side-lying positions for the gluteus maximus and gluteus medius muscles, respectively. Transcranial magnetic stimulation was used to elicit measures of corticospinal excitability. Participants then performed 3 trials of jump landing from a 30-cm box to a distance of 50% of their height, with an immediate rebound to a maximal vertical jump. Each jump-landing trial was video recorded (2-D) and later scored for errors.

Main Outcome Measures:

MVICs normalized to body mass were used to assess strength in the gluteal muscles of the dominant and nondominant limbs. Corticospinal excitability was assessed by means of active motor threshold (AMT) and motor-evoked potentials (MEP) elicited at 120% of AMT. The Landing Error Scoring System (LESS) was used to evaluate jump-landing biomechanics.

Results:

A moderate, positive correlation was found between dominant gluteus maximus MEP and LESS scores (r = .562, P = .029). No other significant correlations were observed for MVIC, AMT, or MEP for the gluteus maximus and gluteus medius, regardless of limb.

Conclusions:

The findings suggest a moderate relationship between dominant gluteus maximus corticospinal excitability and a clinical measure of jump-landing biomechanics. Further research is required to substantiate the findings and expand our understanding of the central nervous system’s role in athletic movement.

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Oliver Faude, Anke Steffen, Michael Kellmann and Tim Meyer

Purpose:

To analyze performance and fatigue effects of small-sided games (SSG) vs high-intensity interval training (HIIT) performed during a 4-wk in-season period in high-level youth football.

Methods:

Nineteen players from 4 youth teams (16.5 [SD 0.8] y, 1.79 [0.06] m, 70.7 [5.6] kg) of the 2 highest German divisions completed the study. Teams were randomly assigned to 1 of 2 training sequences (2 endurance sessions per wk): One training group started with SSG, whereas the other group conducted HIIT during the first half of the competitive season. After the winter break, training programs were changed between groups. Before and after the training periods the following tests were completed: the Recovery-Stress Questionnaire for Athletes, creatine kinase and urea concentrations, vertical-jump height (countermovement jump [CMJ], drop jump), straight sprint, agility, and an incremental field test to determine individual anaerobic threshold (IAT).

Results:

Significant time effects were observed for IAT (+1.3%, ηp 2 = .31), peak heart rate (–1.8%, ηp 2 = .45), and CMJ (–2.3%, ηp 2 = .27), with no significant interaction between groups (P > .30). Players with low baseline IAT values (+4.3%) showed greater improvements than those with high initial values (±0.0%). A significant decrease was found for total recovery (–5.0%, ηp 2 = .29), and an increase was found for urea concentration (+9.2%, ηp 2 = .44).

Conclusion:

Four weeks of in-season endurance training can lead to relevant improvements in endurance capacity. The decreases in CMJ height and total-recovery score together with the increase in urea concentration might be interpreted as early signs of fatigue. Thus, the danger of overtaxing players should be considered.

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Deborah L. King and Barbara C. Belyea

Context: Landing kinematics have been identified as a risk factor for knee injury. Detecting atypical kinematics in clinical settings is important for identifying individuals at risk for these injuries. Objective: To determine the reliability of a handheld tablet and application (app) for measuring lower-extremity kinematics during drop vertical-jump landings. Design: Measurement reliability. Setting: Laboratory. Participants: 23 healthy young adults with no lower-extremity injuries and no contraindications for jumping and landing. Intervention: Subjects performed 6 drop vertical jumps that were captured with an iPad2 and analyzed with a KinesioCapture app by 2 novice and 2 experienced raters. Three trials each were captured in the frontal and sagittal planes. Main Outcome Measures: Frontal-plane projection angles, knee flexion, and hip flexion at initial contact and maximum knee flexion were measured. ICC and SEM were calculated to determine intertrial and interrater reliability. One-way ANOVAs were used to examine differences between the measured angles of the raters. Results: Average intertrial reliability ranged from .71 to .98 for novice raters and .77 to .99 for experienced raters. SEMs were 2.3-4.3° for novice raters and 1.6-3.9° for experienced raters. Interrater ICC2,1 was .39-.98 for the novice raters and .69-.93 for the experienced raters. SEMs were smallest with the experienced raters, all less than 1.5°. Conclusion: A handheld tablet and app is promising for evaluating landing kinematics and identifying individuals at risk for knee injury in a clinical setting. Intertrial reliability is good to excellent when using average trial measures. Interrater reliability is fair to excellent depending on experience level. Multiple trials should be assessed by a single rater when assessing lower-extremity mechanics with a handheld tablet and app, and results may vary with experience level or training.