Differences in lower-body stiffness between levels of netball competition

© 2015 National Strength and Conditioning Association. There are many notable differences in physical and skill attributes between competition levels, especially in team sports. Stiffness is an important mechanical factor to measure when considering athletic performance and injury incidence. Active vertical stiffness (K vert) during hopping and passive stiffness during lying and standing were measured during the preseason period for 46 female netballers (24.0 ± 3.7 years, 72.2 ± 7.6 kg, 175.2 ± 6.7 cm). Participants were classified as elite, sub-elite, representative or recreational based on their current level of competition. A 1-way analysis of variance revealed that elite players possessed significantly higher K vert than recreational players (p 0.018). Large effect sizes (ES) suggested that elite players also possessed higher K vert than sub-elite (d 1.11) and representative (d 1.11) players. A number of large and moderate ES were also present when comparing the passive stiffness of elite players to their lower-ranked counterparts. The results of this study suggest that elite players possess higher levels of active stiffness when compared with their lower-ranked counterparts. The differences in stiffness levels may contribute to a player's ability to physically perform at an elite level and also provide one explanation into elevated rates of injury at higher levels of competition

Effects of two neuromuscular training programs on running biomechanics with load carriage: a study protocol for a randomised controlled trial

Background In recent years, athletes have ventured into ultra-endurance and adventure racing events, which tests their ability to race, navigate, and survive. These events often require race participants to carry some form of load, to bear equipment for navigation and survival purposes. Previous studies have reported specific alterations in biomechanics when running with load which potentially influence running performance and injury risk. We hypothesize that a biomechanically informed neuromuscular training program would optimize running mechanics during load carriage to a greater extent than a generic strength training program. Methods This will be a two group, parallel randomized controlled trial design, with single assessor blinding. Thirty healthy runners will be recruited to participate in a six weeks neuromuscular training program. Participants will be randomized into either a generic training group, or a biomechanically informed training group. Primary outcomes include self-determined running velocity with a 20 % body weight load, jump power, hopping leg stiffness, knee extensor and triceps-surae strength. Secondary outcomes include running kinetics and kinematics. Assessments will occur at baseline and post-training. Discussion To our knowledge, no training programs are available that specifically targets a runner’s ability to carry load while running. This will provide sport scientists and coaches with a foundation to base their exercise prescription on

Muscle stiffness in females : measurement considerations and relationship with physical performance and injury risk in netball

University of Technology Sydney. Faculty of Health.NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. The hardcopy may be available for consultation at the UTS Library.NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- Stiffness is a mechanical property of human muscle that has been widely researched however, few studies have conducted research using female participants. Previously, stiffness has been related to performance variables and injury incidence in male and mixed-gender cohorts. Since stiffness levels differ significantly between the genders, it is important to explore the stiffness-performance and stiffness-injury relationships with all-female cohorts. Results from such studies will be particularly relevant to female dominant sports such as netball. Despite a high rate of participation in Australia and other Commonwealth countries, there is a distinct lack of research pertaining to factors relating to performance and injury in netball. To address these issues, four separate studies were undertaken. Study one determined the validity and reliability of three methods of stiffness assessment in females. The results indicated that myometry and the vertical hop test provided valid and reliable measures of stiffness in females. Study two compared the active and passive stiffness of females competing at four distinct levels of netball competition. The outcomes suggested that elite players possess higher levels of active stiffness when compared to lower-ranked counterparts. Study three compared the stiffness of female netballers to a number of performance variables associated with netball and other court/team sports. The results from study three revealed a number of relationships suggesting that higher levels of lower-body stiffness are advantageous for female athletes when performing rapid and/or repeated stretch-shorten cycle movements. Particularly strong relationships between the stiffness of the medial gastrocnemius and rapid stretch-shorten cycle movements were revealed, suggesting that the medial gastrocnemius is of particular importance when considering performance. Finally, study four examined the relationship between lower-body stiffness and injury incidence in netballers. The results suggested that elite and sub-elite netballers have a higher rate of injury incidence than recreational athletes. Specifically, relatively high stiffness of the soleus and Achilles tendon appears to be related to lower-body injury incidence in females, particularly at the elite level. The results from the four studies discussed in this thesis are relevant for female athletes, their coaches, conditioning staff, medical personnel and talent identification and development programs. Whilst these studies involved netballers, the results are also applicable to other team sport athletes, especially those playing court sports such as volleyball, basketball and European handball, which involve similar performance characteristics to netball

The relationship between lower-body stiffness and dynamic performance

© 2014, Published by NRC Research Press. Greater levels of lower-body stiffness have been associated with improved outcomes for a number of physical performance variables involving rapid stretch-shorten cycles. The aim of this study was to investigate the relationship between several measures of lower-body stiffness and physical performance variables typically evident during team sports in female athletes. Eighteen female athletes were assessed for quasi-static stiffness (myometry) for several isolated muscles in lying and standing positions. The muscles included the medial gastrocnemius (MedGast), lateral gastrocnemius, soleus, and Achilles tendon. Dynamic stiffness during unilateral hopping was also assessed. Participants were separated into relatively stiff and compliant groups for each variable. A number of significant differences in performance were evident between stiff and compliant subjects. When considering the quasi-static stiffness of the MedGast in lying and standing positions, relatively stiff participants recorded significantly superior results during agility, bounding, sprinting, and jumping activities. Stiffness as assessed by hopping did not discriminate between performance ability in any test. Relationships highlighted by MedGast results were supported by further significant differences in eccentric utilisation ratio and drop jump results between stiff and compliant groups for the lateral gastrocnemius and soleus in lying and standing positions. Higher levels of lower-body stiffness appear to be advantageous for females when performing rapid and (or) repeated stretch-shorten cycle movements, including sprinting, bounding, and jumping. Further, the stiffness of the MedGast is of particular importance during the performance of these activities. It is important for practitioners working with athletes in sports that rely upon these activities for success to consider stiffness assessment and modification

Validity and reliability of three methods of stiffness assessment

© 2016 Background Stiffness is commonly assessed in relation to injury and athletic performance. The purpose of this research was to compare the validity and reliability of 3 in vivo methods of stiffness assessment using 1 cohort of participants. Methods To determine inter-day reliability, 15 female netballers were assessed for stiffness twice within 1 week using unilateral hopping (vertical stiffness), free oscillations of the calf, and myometry of various muscles of the triceps surae. To establish convergent construct validity, stiffness was compared to static and dynamic strength measurements. Results Test–retest stiffness results revealed that vertical stiffness produced moderate to high reliability results and myometry presented moderate to very high reliability. In contrast, the free oscillation technique displayed low to moderate reliability. Vertical stiffness demonstrated a significant correlation with rate of force development during a squat jump, whilst myometer stiffness measurements from 3 sites in the lower limb revealed significant correlations with isometric rate of force development. Further, significant negative correlations were evident between the eccentric utilisation ratio and various myometer stiffness results. No relationships were established between the free oscillation technique and any of the performance measurements. Conclusion These results suggest that vertical stiffness and myometry are valid and reliable methods for assessing stiffness

Factors affecting jump performance in professional Australian rules footballers

Aim. This study examined factors contributing to jump performance in professional Australian Rules Football (ARF) players. Methods. Thirty-two ARF players performed a countermovement jump (CMJ) and were divided into groups based on jump performance: high calibre (HC) or low calibre (LC). During CMJ assessment, force, rate of force development, movement velocity and power were measured. Physical measures included mass, height, age, lower body strength, eccentric utilization ratio and leg stiffness (Kleg). HC and LC groups were compared to determine the variables contributing to jump performance and correlation and regression analyses also aided in identifying such variables. CMJ height was higher in the HC group (P<0.001). Results. The HC group demonstrated a higher CMJ velocity (9.8%, P=0.004) and CMJ power (14.4%, P=0.042) when compared to the LC group. Further, the HC group demonstrated 7.5% higher Kleg than the LC group (P=0.019). Spearman's rho correlations demonstrated moderate-large relationships between jump height and strength, velocity and power, while the regression analysis revealed velocity was the sole predictive variable of jump performance. Jumping performance clearly differs within a group of professional ARF athletes. Conclusion. Movement velocity appears to be an important factor contributing to jump performance; however, lower body power and Kleg are also important for jump performance

The validity and reliability of 5-Hz global positioning system units to measure team sport movement demands

The purpose of this research was to investigate the validity and the reliability of 5-Hz MinimaxX global positioning system (GPS) units measuring athlete movement demands. A team sport simulation circuit (files collected from each unit = 12) and flying 50-m sprints (files collected from each unit = 34) were undertaken, during which the total distance covered; peak speed; player load; the distance covered; time spent and number of efforts performed walking, jogging, running, highspeed running, and sprinting were examined. Movement demands were also separately categorized into low-intensity activity, high-intensity running, and very high-intensity running. The results revealed that GPS was a valid and reliable measure of total distance covered (p > 0.05, percentage typical error of measurement [%TEM] 0.05, %TEM 5-10%). Further, GPS was found to be a reliable measure of player load (%TEM 4.9%) and the distance covered, time spent, and number of efforts performed at certain velocity zones (%TEM 10%). The level of GPS error was found to increase along with the velocity of exercise. The findings demonstrated that GPS is capable of measuring movement demands performed at velocities 20 km·h -1. © 2012 National Strength and Conditioning Association

Movement demands and match performance in professional Australian football

This study examined the relationship between coaches perception of match performance and movement demands in Australian Football. Movement demands were collected from 21 professional players over 12 matches during one Australian Football League season, with 69 player files collected. Additionally, match events relative to playing time and distance covered, along with player physical characteristics were collected. Based on coaches subjective rating of match performance (out of 20), relatively high calibre (HC) players (15/20) were compared with relatively low calibre (LC) players (9/20) for all variables. The HC players were older (+17%, p=0.011), spent a greater percentage of time performing low-speed running (+2%, p=0.039), had more kicks (38%, p=0.001) and disposals (35%, p=0.001) per min and covered less distance per kick (50%, p=0.001) and disposal (44%, p=0.001) than the LC group, with the effect sizes also supporting this trend. Further, HC players covered less distance (14%, p=0.037), spent less percentage of time (17%, p=0.037) and performed fewer (9%, p=0.026) efforts per min high-speed running than LC players, which was further confirmed by the effect sizes. Movement demands and match events are related to coaches perception of match performance in professional Australian Football. Further, high levels of involvement with the football appeared to be more important to performance than high exercise speed. © Georg Thieme Verlag KG • Stuttgart New York

Relationship between stiffness and lower body soft-tissue injury in professional Australian Rules footballers

Leg stiffness is a modifiable mechanical property that may be related to soft tissue injury risk. The purpose of this study was to examine mean leg stiffness and bilateral differences in leg stiffness across an entire professional Australian Football League (AFL) season, and determine whether this parameter was related to the incidence of lower body soft tissue injury. The stiffness of the left and right legs of 39 professional AFL players (age 24.4 +/- 4.4 years, body mass 87.4 +/- 8.1 kg, stature 1.87 +/- 0.07 m) was measured using a unilateral hopping test at least once per month throughout the season. Injury data were obtained directly from the head medical officer at the football club. Mean leg stiffness and bilateral differences in leg stiffness were compared between the injured and non-injured players. There was no difference between the season mean leg stiffness values for the injured (219.3 +/- 16.1 N . m(-1) . kg(-1)) and non-injured (217.4 +/- 14.9 N . m(-1) . kg(-1); P = 0.721) groups. The injured group (7.5 +/- 3.0%) recorded a significantly higher season mean bilateral difference in leg stiffness than the non-injured group (5.5 +/- 1.3%; P = 0.05). A relatively high bilateral difference in leg stiffness appears to be related to the incidence of soft tissue injury in Australian football players. This information is of particular importance to medical and conditioning staff across a variety of sports

Seasonal variation of leg stiffness in professional Australian rules footballers

Leg stiffness (Kleg) is an important component to consider in both performance and injury in the Australian Football League (AFL). Kleg has not yet been examined longitudinally throughout an entire AFL season. A unilateral hop test was used to measure Kleg in the left and right legs of 25 professional AFL players (24.9 ± 4.3 years, 86.8 ± 8.1 kg, 187.0 ± 7.3 cm). Kleg was assessed at least once permonth for each participant. Furthermore, the session rate of perceived exertion method was used to quantify the average weekly training loads experienced by the participants. One-way analysis of variance revealed no significant difference between the average monthly bilateral Kleg scores; however, average weekly training loads varied between 1,400 and 2,000 AU, depending on the training period. Thirteen participants were randomly selected to perform hop tests on 2 consecutive weeks. Reliability tests revealed these measurements to have a typical error of the measurement of 4.15% and an intraclass correlation of 0.8, proving the methods to be reliable. Although training intensity appears to vary, Kleg does not fluctuate significantly across an entire AFL season, suggesting that weekly training loads between 1,400 and 2,000 AU may be prescribed without the risk of fluctuating stiffness levels. © 2013 National Strength and Conditioning Association