Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 72
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Sports Biomech ; 19(1): 1-25, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-29781788

RESUMO

The use of isometric strength testing, particularly the isometric mid-thigh pull (IMTP) has increased dramatically over the last decade. The IMTP and isometric squat (ISqT) provide one aspect of performance monitoring with variables such as peak force and rate of force development being derived from the force-time curve. The reliability of some of these variables is conflicting in the literature, and the reporting of the reliability is not standardised across the research. The majority of research only reports intraclass correlation coefficients with very few studies reporting coefficient of variation and 90% confidence intervals. Additionally, methods used to calculate variables from the force-time curve differ across studies. An aim of muscle strength testing is to provide normative values for specific sports, allowing coaches to distinguish between performance levels or evaluate the effects of training on performance. This narrative review aims to evaluate studies that have researched the reliability and/or reported normative data for both tests. Additionally, the testing protocols and the force-time curve analysis techniques utilised are discussed, concluding with practical applications for coaches on the uses and limitations of these tests. Results demonstrate that peak force is the most reliable measure and can be used to determine maximum strength capabilities.


Assuntos
Teste de Esforço/métodos , Força Muscular/fisiologia , Coxa da Perna/fisiologia , Levantamento de Peso , Fenômenos Biomecânicos , Humanos , Contração Isométrica/fisiologia , Valores de Referência , Reprodutibilidade dos Testes , Esportes/fisiologia
2.
PLoS One ; 14(12): e0225664, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31805080

RESUMO

Research examining the reliability of stiffness measures during hopping has shown strong consistency in leg-spring stiffness (kleg), but high variability in joint stiffness (kjoint) measures. Sled-based systems (SBS) reduce movement degrees-of-freedom and are used to examine stretch-shortening cycle (SSC) function under controlled conditions. The aim of this study was to examine the reliability of kleg and kjoint during single-leg hopping within an SBSKinematic and kinetic data were collected on four occasions (Day_1, Day_2, Day_3 and Day_3Offset). Participants completed two trials of single-leg hopping at different frequencies (1.5, 2.2 and 3.0 Hz) while attached to an inclined-SBS. Stiffness was determined using models of leg-spring (kleg) and torsional (kjoint) stiffness. Statistical analysis identified absolute and relative measures of reliability. Results showed moderate reliability for kleg at 1.5 Hz between inter-day testing bouts, and weak consistency at 2.2 and 3.0 Hz. Examination of intra-day comparisons showed weak agreement for repeated measures of kleg at 1.5 and 2.2 Hz, but moderate agreement at 3.0 Hz. Limits in kleg reliability were accompanied by weak-to-moderate agreement in kjoint measures across inter- and intra-day testing bouts. Results showed limits in the reliability of stiffness measures relative to previous reports on overground hopping. Lack of consistency in kleg and kjoint may be due to the novelty of hopping within the current inclined-SBS. Constraints imposed on the hopping task resulting from SBS design (e.g. additional chair mass, restricting upper body movement) may have also influenced limits in kleg and kjoint reliability. Researchers should consider these findings when employing inclined-SBS of a similar design to examine SSC function.

3.
Sports Biomech ; : 1-18, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31573420

RESUMO

In the sprint start, a defined sequence of distinct response delays occurs before the athlete produces a movement response. Excitation of lower limb muscles occurs prior to force production against the blocks, culminating in a movement response. The time delay between muscle excitation and movement, electromechanical delay (EMD), is considered to influence sprint start response time (SSRT). This study examined the delay in sprint start performance from EMD of the triceps surae muscle and examined whether certain sprinters gain an advantage in SSRT. Nineteen experienced sprinters performed sprint starts from blocks, with SSRT measured by an International Association of Athletics Federations (IAAF)-approved starting block system. EMD times were detected during a heel-lift experiment. Using revised SSRT limits, based on concerns over the validity of the IAAF 100 ms false start limit, EMD produced a significant moderate correlation with SSRT (r = 0.572, p = 0.011). Regression analysis determined that together, EMD and signal processing time (the delay between the auditory signal and muscle excitation) accounted for 37% of the variance in SSRT. Initial results suggest EMD is part of the response time process and that certain athletes may gain a performance advantage due to reduced EMD.

4.
J Sport Rehabil ; : 1-7, 2019 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-31586431

RESUMO

CONTEXT: Dynamic movement-based screens, such as the Landing Error Scoring System (LESS), are becoming more widely used in research and practical settings. Currently, 3 studies have examined the reliability of the LESS. These studies have reported good interrater and intrarater reliability. However, all 3 studies involved raters, who were founders of the LESS. Therefore, it is unclear whether the reliability reported reflects that which would be observed with practitioners without such specialized and intimate knowledge of the screen and only using the standardized set of instructions. OBJECTIVE: To investigate the interrater and intrarater reliability of the final score and the individual scoring criteria of the LESS. DESIGN: Reliability protocol. SETTING: Controlled laboratory. PARTICIPANTS: Two raters scored 30 male participants (age = 21.8 [3.9] y; height = 1.75 [0.46] m; mass = 75.5 [6.6] kg) involved in a variety of college sports. MAIN OUTCOME MEASURE: Two raters using only the standardized scoring sheet assessed the interrater reliability of the total score and individual scoring criteria independently of each other. The principal author scored the videos again 6 weeks later for the intrarater reliability component of the study. INTERVENTION: Participants performed a drop box landing from a 30-cm box was recorded with a video camera from the front and side views. RESULTS: The intraclass coefficients interrater and intrarater reliability for the total scores were excellent (intraclass coefficients range = .95 and .96; SEM = 1.01 and 1.02). The individual scoring criteria of the LESS had between moderate and perfect agreement using kappa statistics (κ = .41-1.0). CONCLUSION: The final score and individual scoring criteria of the LESS have acceptable reliability with raters using the standardized scoring sheet. Practitioners using only the standardized scoring sheet should feel confident that the LESS is a reliable tool.

5.
J Strength Cond Res ; 2019 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-31498222

RESUMO

Everard, E, Lyons, M, and Harrison, AJ. An examination of the relationship between the functional movement screen, landing error scoring system and 3D kinematic data during a drop jump task. J Strength Cond Res XX(X): 000-000, 2019-Tests such as the Functional Movement Screen (FMS) and Landing Error Scoring System (LESS) have become an established component of preparticipation screening. Despite their practical use, there is a lack of empirical evidence examining their relationship to established assessments of movement, such as 3D kinematics of a drop jump. Fifty-two male collegiate athletes undertook the LESS, FMS, and a drop jump where 3D lower-limb kinematic variables were assessed. Spearman correlations were conducted to examine the relationship between LESS, FMS, and drop-jump 3D kinematic variables. A series of independent t-tests examined differences in hip and knee kinematic variables in acceptable and poor FMS and LESS groups as determined by established cut-off scores. Landing Error Scoring System scores had significant moderate correlations with most kinematic variables (r = 0.35-0.64; p < 0.01). Subjects with poor LESS scores displayed significantly worse lower-limb kinematics compared with their high-scoring counterparts (effect size = 1.99-2.76, large effect). There were significant moderate correlations with maximal hip and knee flexion (r = 0.46 and 0.39 respectively; p < 0.01) and small or nonsignificant correlations between all other kinematic variables and FMS scores. Hip flexion and knee valgus at maximal displacement were the only kinematic variables significantly different between FMS groups (ES = 0.70-0.72, small-to-moderate effect). The results confirm limitations in the ability of the FMS to distinguish between groups for landing biomechanics.

6.
Phys Ther Sport ; 40: 59-65, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31479981

RESUMO

OBJECTIVES: To investigate factors associated with injury in amateur male and female rugby union players. DESIGN: A prospective cohort study. SETTING: Amateur rugby clubs in Ireland. PARTICIPANTS: Male (n = 113) and female (n = 24) amateur rugby union players from 5 of the top 58 amateur clubs in Ireland. MAIN OUTCOME MEASURES: Pre-season testing included physical tests assessing hamstring flexibility, dorsiflexion range of movement, adductor muscle strength and foot position. Wellness questionnaires assessed sleep quality (PSQI), coping skills (ACSI-28) and support levels (PASS-Q). Players were monitored throughout the season for injury. RESULTS: The time-loss match injury incidence rate was 48.2/1000 player hours for males and 45.2/1000 player hours for females. Two risk profiles emerged involving; 'age + navicular drop + training pitch surface' (53%) and 'age + navicular drop + groin strength' (16%). An inverse relationship between groin strength and groin injury was found for the 'backs' players (-0.307, p < 0.05). Using the PSQI, 61% of players had poor sleep quality, however no relationship between the wellness questionnaires and injury was found. CONCLUSION: Two injury risk profiles emerged, associated with subsequent injury occurrence. Using these risk profiles, individualized prevention strategies may be designed regarding deficits in groin muscle strength and identifying foot alignment.

7.
Med Devices (Auckl) ; 12: 227-234, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31354368

RESUMO

Background: Osteoarthritis of the shoulder or glenohumeral joint is a painful condition that can be debilitating. Intra-articular injection with hyaluronic acid should be considered for patients not responding adequately to physical therapy or anti-inflammatory medication. Methods: This was a single-arm, open-label, prospective study of a single intra-articular injection of NASHA (non-animal hyaluronic acid) in patients with symptomatic glenohumeral osteoarthritis. Patients were followed up for 26 weeks post-treatment, during which time rescue medication with acetaminophen was permissible. The study objective was to demonstrate that a single injection of NASHA is well tolerated with an over-6-month 25% reduction in shoulder pain on movement, assessed using a 100-mm visual analog scale. Results: Forty-one patients were enrolled, all of whom received study treatment. The mean decrease in shoulder pain on movement score over the 6-month study period was -20.1 mm (95% CI: -25.2, -15.0 mm), corresponding to a mean reduction of 29.5% (22.0, 37.0%). Statistically significant improvements were also observed in shoulder pain at night and patient global assessment. There was no clear change over time in the percentage of patients using rescue medication and mean weekly doses were below 3500 mg. Seventeen patients (41.5%) experienced adverse events, all of which were mild or moderate. Two adverse events (both shoulder pain) were deemed related to study treatment. Conclusion: This study provides preliminary evidence that a single injection of NASHA may be efficacious over 6 months and well tolerated in patients with symptomatic glenohumeral osteoarthritis. Larger studies are needed for confirmation.

8.
Hum Mov Sci ; 66: 449-458, 2019 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-31176256

RESUMO

The purpose of this study was to examine the effect of speed on coordination and its variability in running gait using vector coding analysis. Lower extremity kinematic data were collected for thirteen recreational runners while running at three different speeds in random order: preferred speed, 15% faster and 15% lower than preferred speed. A dynamical systems approach, using vector coding and circular statistics, were used to quantify coordination and its variability for selected hip-knee and knee-ankle joint couplings. The influence of running speed was calculated from the continuous data sets of the running cycle, allowing for the identification of time percentages where differences existed. Results indicate that increases in running speed produced moderate alterations in the frequency of movement patterns which were not enough to alter classification of coordination. No effects of speed on coordination variability were observed. This study has demonstrated that coordination and coordination variability is generally stable in the range of ±15% around of preferred speed in recreational runners.

11.
J Strength Cond Res ; 2019 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-31009436

RESUMO

Furlong, L-AM, Harrison, AJ, and Jensen, RL. Measures of strength and jump performance can predict 30-m sprint time in Rugby Union players. J Strength Cond Res XX(X): 000-000, 2019-Performance and fitness monitoring in Rugby Union often include jumping, sprinting, and strength tests, but repeatability of and relationships between these measures are unclear. The level of interindividual variability in these relationships and their sprint time predictive capabilities are also unknown. This study examined the reliability of, and relationship between, countermovement (CMJJH), squat (SJJH), and rebound (RBJJH) jump heights, rebound jump contact time (RBJCT), estimated 1 repetition maximum back squat relative to body mass (SQBM), and reactive strength index (RSI) to 30-m sprint time of subelite, semiprofessional Rugby Union players. Measurement reliability was very good, with high average intraclass correlation coefficients (≥0.9) and low coefficient of variation (<10.1%). All variables were significantly (p < 0.01) correlated to each other (r > 0.575), except for SQBM (only related to CMJJH, r = 0.621) and RBJCT (only related to RSI, r = -0.727). SJJH and SQBM were the strongest and most consistent predictors of time to 30 m (R = 0.754 ± 0.081; SEE = 0.166 ± 0.025), but variability in SEE magnitude was observed across the group during bootstrapping. Cross-validation showed a mean difference between actual and predicted 30 m times equivalent to 0.22% of the group average time to 30 m. These results support the importance of multiple aspects of fitness training in Rugby Union players for improving performance in short-duration sprinting activities, but highlight the individual nature of their relative importance. Measures of strength and power can be used to predict short sprint performance by the strength and conditioning professional.

12.
Int J Sports Physiol Perform ; : 1-8, 2019 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-30958061

RESUMO

PURPOSE: To examine the relationships between the isometric midthigh pull (IMTP), isometric squat (ISqT), and sprint acceleration performance in track-and-field sprinters and to determine whether there are differences between men and women. METHODS: Fifteen male and 10 female sprinters performed 3 maximal-effort IMTPs, ISqTs, and 3 × 30-m sprints from blocks. RESULTS: Among the men, the results showed significant negative correlations between IMTP and ISqT peak force; relative peak force; force at 100, 150, and 200 ms; rate of force development (0-150 and 0-200 ms); and impulse (0-200 ms) and 0- to 5-m time (r = -.517 to -.714; P < .05). IMTP impulse (B = -0.582, P = .023) and ISqT relative peak force (B = -0.606, P = .017) significantly predicted 0- to 5-m time. Among the women, no IMTP or ISqT variables significantly correlated with any sprint times. Men measured significantly higher than women for all IMTP measures except relative peak force. Men were significantly faster than women at all splits. When comparing measures of the ISqT, there were no significant differences between men and women. CONCLUSIONS: Variables measured during the IMTP and ISqT significantly correlated with 0- to 5-m sprint performance in male athletes. Isometric strength can have a sizable influence on 0- to 5-m time, but in some cases, the maximum effect could be very small.

13.
J Sports Sci ; 37(14): 1591-1599, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30724701

RESUMO

This study examined the kinetic and temporal differences between countermovement jumps (CMJs) and eccentrically loaded CMJs. A survey of 109 coaches and athlete showed that 87% of respondents regularly used jumps with added mass within training. Sixteen male and thirteen female track and field athletes from sprinting, hurdling and jumping events performed 5 bodyweight CMJs 5 jumps wearing a weighted jacket and 5 eccentrically loaded dumbbell (LDB) jumps trials in a randomised order. Peak force (PF), peak power (PP), flight time (FT), concentric time (CON-T), eccentric time (ECT), total time (TIME) and eccentric/concentric ratio (E/C-Ratio) were obtained from force plate data. Statistically significant differences (p < 0.05) with moderate to large magnitude effect sizes were found between men and women in FT, PP and PF but not in any of the temporal variables. The results indicated that the WJ decreased FT in men (↓9%) and women (↓10%) but LDB jumps had similar FT to CMJ. Overall, the results showed that LDB increased the E/C Ratio (↑50% and ↑42%) and decreased CON-T (↓37% and ↓25%) compared with WJ and CMJ respectively. LDB jumping is not recommended as a training modality as it tends to disrupt the relative timing of the jump action.


Assuntos
Desempenho Atlético/fisiologia , Exercício Pliométrico , Treinamento de Resistência/métodos , Atletismo/fisiologia , Adulto , Fenômenos Biomecânicos , Teste de Esforço/métodos , Feminino , Humanos , Cinética , Masculino , Força Muscular , Adulto Jovem
14.
J Strength Cond Res ; 2019 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-30747902

RESUMO

Healy, R, Kenny, IC, and Harrison, AJ. Resistance training practices of sprint coaches. J Strength Cond Res XX(X): 000-000, 2019-This study describes the results of a survey of resistance training practices of sprint coaches. This study investigated why sprint coaches prescribe resistance training to their athletes, what exercises they select, and what factors are involved with their selection. Forty-one of 73 (56%) sprint coaches with mean ± SD coaching experience of 8.4 ± 6.4 years were included in this study. Coaches completed an online questionnaire consisting of 5 sections: (a) informed consent, (b) coach background information, (c) coach education and qualifications, (d) coaches' views on resistance training, and (e) exercise selection and preference. The results showed that coaches prescribe resistance training to their sprint athletes to develop strength and power, which they believe will transfer to sprint performance. Coaches prescribed a wide variety of traditional, ballistic, and plyometric exercises, with the hurdle jump found to be the most widely prescribed exercise (93% of coaches surveyed). Coaches selected exercises for a variety of reasons; however, the 3 most prominent reasons were: (a) performance adaptations; (b) practicality; and (c) the targeting of muscles/muscle groups. Coaches prioritized exercises that specifically developed strength, power, and reactive strength for their sprint athletes. This research can be used to develop educational resources for sprint coaches who wish to use resistance training with their athletes. In addition, sprint coaches can use the data presented to expand their current exercise repertoire and resistance training practices.

15.
Phys Ther Sport ; 35: 79-88, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30472491

RESUMO

OBJECTIVES: To describe the development, implementation and evaluation of a comprehensive injury surveillance system. DESIGN: The four phases; i) A survey of 58 medical professionals working in amateur rugby. ii) The design of a web-based injury surveillance system (IRISweb). iii) Recruitment of 21 of the top 58 amateur clubs to use IRISweb. iv) An evaluation survey of the 21 participating clubs. SETTING: Irish amateur rugby clubs. PARTICIPANTS: Medical professionals working in amateur rugby. MAIN OUTCOME MEASURES: Phase one investigated the injury monitoring practices in operation prior to the IRIS project. Phase four investigated the effectiveness and usefulness of IRISweb. RESULTS: Twenty-one clubs were recruited, however 2 clubs failed to provide a full season of data (10% dropout rate). Eighty-two percent of the remaining 19 clubs rated IRISweb as 'good' or 'very good'. Facilitators of injury surveillance were; increased player adherence (65%) and notifications to update the system (59%), however, poor player adherence (71%) and medical staff availability (24%) were the main barriers. CONCLUSIONS: The IRIS project is the first prospective long-term injury surveillance system in Irish amateur rugby, effectively tracking injuries to guide future evidence-based injury prevention strategies. This study highlights facilitators and barriers to injury surveillance within amateur sport.


Assuntos
Traumatismos em Atletas/epidemiologia , Monitoramento Epidemiológico , Futebol Americano/lesões , Internet , Atletas , Feminino , Humanos , Irlanda , Masculino , Inquéritos e Questionários
16.
J Sports Sci ; 37(9): 1055-1063, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30422061

RESUMO

This study examined fundamental movement skill (FMS) proficiency among male (N = 216) and female (N = 198) Irish primary school pupils from Year 2 to Year 7 (9.0 ± 1.7 years). Following anthropometric measurements, participants were video-recorded performing 15 FMS and scored using the TGMD-3, Victorian Fundamental Movement skills Manual and the Get skilled: Get active guidelines. Percentage mastery ranged between 1.4% (gallop) and 35.7% (slide). A two-way ANOVA evaluated the effect of sex (male/female) and class group (Year 2/3/4/5/6/7) on individual skills, locomotor subtest, object-control subtest and total TGMD-3 (GMQ) scores. No significant sex ×class interaction effects were found. Large effect sizes were reported for male superiority in object-control subtest (ηp2 = 0.26) and GMQ (ηp2 = 0.16) scores (both p < 0.001). Older classes had higher object-control subtest scores than younger classes, but scores plateaued after Year 5. Furthermore, overweight participants had significantly lower locomotor subtest (p < 0.001, d = 0.7), object-control subtest (p = 0.03, d = 0.3) and GMQ scores (p < 0.001, d = 0.5) than non-overweight participants. This study highlights very poor levels of FMS mastery among Irish schoolchildren and stresses the need for developmentally appropriate, FMS intervention programmes that are inclusive regardless of age, sex or weight status.


Assuntos
Peso Corporal , Destreza Motora , Movimento , Fatores Etários , Análise de Variância , Criança , Teste de Esforço , Feminino , Humanos , Irlanda , Masculino , Fatores Sexuais
17.
J Strength Cond Res ; 33(11): 3039-3048, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-29939904

RESUMO

Healy, R, Smyth, C, Kenny, IC, and Harrison, AJ. Influence of reactive and maximum strength indicators on sprint performance. J Strength Cond Res 33(11): 3039-3048, 2019-The primary aim of this study was to assess the relationship between reactive and maximal strength measures with 40 m sprint performance and mechanical properties. Fourteen male and 14 female sprinters participated in this study. On the first day, subjects performed 40 m sprints with 10-m split times recorded in addition to maximal theoretical velocity, maximal theoretical force and peak horizontal power, which were calculated from force-velocity relationships. On the second day, subjects performed isometric midthigh pulls (IMTPs) with peak force (PF) and relative PF calculated, drop jumps (DJs) and vertical hopping where the reactive strength index (RSI) was calculated as jump height (JH) divided by contact time (CT). Pearson correlations were used to assess the relationships between measures and independent samples t-tests were used to assess the differences between men and women. No significant correlations were found between DJ and hopping RSI and sprint measures. A significant strong positive correlation was found between IMTP PF and peak horizontal power in men only (r = 0.61). The male sprinters performed significantly better in all recorded measures apart from hopping (CT, JH and RSI) and DJ CT where no significant differences were found. The lack of association between reactive and maximal strength measures with sprint performance is potentially because of the test's prolonged CTs relative to sprinting and the inability to assess the technical application of force. Several methods of assessing reactive strength are needed that can better represent the demands of the distinct phases of sprinting e.g., acceleration, maximum velocity.


Assuntos
Desempenho Atlético/fisiologia , Força Muscular , Corrida/fisiologia , Aceleração , Adolescente , Adulto , Atletas , Estudos Transversais , Teste de Esforço , Feminino , Humanos , Masculino , Adulto Jovem
18.
J Sports Sci ; 37(4): 370-377, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30058950

RESUMO

The purpose of this study was to determine the effects of training on the force-, velocity-, and displacement-time curves using principal component analysis (PCA) to examine the pre to post intervention changes. Thirty-four trained women basketball players were randomly divided into training and control groups. The training intervention consisted of full squats combined with repeated jumps. The effects of the intervention were analysed before and after the training period of 6 weeks by comparing the principal component scores. The magnitude of differences within-/between-group were calculated and expressed as standardised differences. After the intervention period, clear changes in principal components were observed in the training group compared to the control group. These were related to the execution of a vertical jump with a faster and deeper countermovement that was stopped with greater force. This resulted in greater force from the start of the upward movement phase which was maintained for a longer time. This increase in force throughout a greater range of motion increased the take-off velocity and consequently jumping height.


Assuntos
Desempenho Atlético , Exercício Pliométrico , Análise de Componente Principal , Adulto , Atletas , Basquetebol , Feminino , Humanos , Adulto Jovem
19.
Sports (Basel) ; 6(4)2018 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-30373113

RESUMO

Simulation studies show that jump performance can be improved by increasing the depth of countermovement. The purpose of this study was to determine how modifications to the depth of countermovement lead to changes in jump height and the biomechanical parameters related to center of mass displacement and force application. Twenty-nine competitive males participated in this investigation, performing nine countermovement jumps using a self-selected, a deep, and a shallow crouch position. Jump height and relative net vertical impulse were greater when using a deeper crouch position, compared to the self-selected position. Force application variables did not report differences, when the deeper countermovement was compared to the self-selected countermovement; although, the shallower countermovement showed higher values in force application parameters. The deeper countermovement jumps achieved higher velocities of the center of mass than the self-selected jumps, while shallower jumps produced lower velocities than the self-selected jumps. The results of this investigation were consistent with simulation studies, showing that deep countermovements increase net vertical impulse, leading to a higher jump height. In addition, the maximum downward velocity was higher, when the crouch position was deeper. Conversely, force-applied variables did not change when jump performance was increased.

20.
J Sport Health Sci ; 7(3): 372-377, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30356665

RESUMO

Background: Mathematical models propose leg length as a limiting factor in determining the maximum walking velocity. This study evaluated the effectiveness of a leg length-based model in predicting maximum walking velocity in an applied race walking situation, by comparing experienced and novice race walkers during conditions where strictly no flight time (FT) was permitted and in simulated competition conditions (i.e., FT ≤ 40 ms). Methods: Thirty-four participants (18 experienced and 16 novice race walkers) were recruited for this investigation. An Optojump Next system (8 m) was used to determine walking velocity, step frequency, step length, ground contact time, and FT during race walking over a range of velocities. Comparisons were made between novice and experienced participants in predicted maximum velocity and actual velocities achieved with no flight and velocities with FT ≤ 40 ms. The technical effectiveness of the participants was assessed using the ratio of maximum velocity to predicted velocity. Results: In novices, no significant difference was found between predicted and maximum walking speeds without FT but there was a small 5.8% gain in maximum speed when FT ≤ 40 ms. In experienced race walkers, there was a significant reduction in maximum walking speed compared with predicted maximum (p < 0.01) and a 11.7% gain in maximum walking speed with FT ≤ 40 ms. Conclusion: Leg length was a good predictor of maximal walking velocity in novice walkers but not a good predictor of maximum walking speed in well-trained walkers who appear to have optimised their walking technique to make use of non-visible flight periods of less than 40 ms. The gain in velocity above predicted maximum may be a useful index of race walking proficiency.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA