Exploring the relationship of static and dynamic balance with muscle mechanical properties of the lower limbs in healthy young adults.

There is emerging evidence that mechanical properties of in vivo muscle tissues are associated with postural sway during quiet standing. However, it is unknown if the observed relationship between mechanical properties with static balance parameters generalise to dynamic balance. Thus, we determined the relationship between static and dynamic balance parameters with muscle mechanical properties of the ankle plantar flexors [lateral gastrocnemius (GL)] and knee extensors [vastus lateralis (VL)] in vivo. Twenty-six participants (men = 16, women = 10; age = 23.3 ± 4.4 years) were assessed for static balance [centre of pressure (COP) movements during quiet standing], dynamic balance (reach distances for the Y-balance test) and mechanical properties (stiffness and tone) of the GL and VL measured in the standing and lying position. Significant (p < .05) small to moderate inverse correlations were observed between the mean COP velocity during quiet standing with stiffness (r = -.40 to -.58, p = .002 to .042) and tone (r = -0.42 to -0.56, p = 0.003 to 0.036) of the GL and VL (lying and standing). Tone and stiffness explained 16%-33% of the variance in the mean COP velocity. Stiffness and tone of the VL measured in the lying (supine) condition were also inversely significantly correlated with Y balance test performance (r = -0.39 to -0.46, p = 0.018 to 0.049). These findings highlight that individuals with low muscle stiffness and tone exhibit faster COP movements during quiet standing, indicative of reduced postural control but also reveal that low VL stiffness and tone are associated with greater reach distances in a lower extremity reaching task, indicative of greater neuromuscular performance.

Influence of lower-limb muscular and tendon mechanical properties and strength on countermovement jump performance.

BACKGROUND: The aim of the study is to examine the relationship between measures of muscle and tendon mechanical properties and strength on countermovement jump (CMJ) performance. METHODS: Twenty-six physically active participants (males; N.=16: females; N.=10) were tested. Testing comprised of measuring the mechanical properties of lower limb muscles and tendons using myotonometry, isometric and isokinetic knee extensor strength through dynamometry, and CMJ's with a force platform. RESULTS: Large positive correlations were observed between CMJ jump height and Achilles tendon stiffness (N/m) (r=0.56) and Achilles tendon tone (Hz) (r=0.553). Large negative correlations were found between CMJ height and Achilles tendon elasticity (r=-0.658), and Achilles tendon relaxation (r=-0.572), and Achilles tendon creep (r=-0.589). Large correlations (r=0.592 to 0.659) were observed between CMJ height and all measures of isometric and isokinetic dynamometry measures. Achilles tendon stiffness, elasticity level and relaxation, and isokinetic peak concentric torque (N.m) explained 63% of this variance. CONCLUSIONS: Greater stiffness of the Achilles tendon may improve CMJ performance due to the improved transfer of concentric and eccentric force of the knee extensor muscles. Practitioners need to implement specific interventions to target increasing Achilles tendon stiffness to improve countermovement jump performance.

The effect of fatigue on first stance phase kinetics during acceleration sprint running in professional football players.

Nineteen professional football players (Age: 26±5 years; Height: 1.84±0.08 m; Mass: 83.4±8.9 kg) completed three x 30 m maximal acceleration sprints from a standing start before completing the Yo-Yo intermittent recovery test level 1. Three x 30 m maximal acceleration sprints were then repeated post-fatigue. Light gates recorded sprint times from 0-5 m, 0-10 m, 0-15 m and 0-30 m. Force platforms collected ground reaction force of the first stance phase of the sprint run. Differences between pre- and post-fatigue were observed in the sprint times over 0-15 m (P = 0.015; CI [0.007, 0.110]) and 0-30 m (P = 0.004; CI [0.056, 0.234]). Peak medial-lateral ground reaction force was lower (P = 0.045; CI [-0.146, -0.005]) post- than pre-fatigue. The ratio of force were significantly different between pre- and post-fatigue for the medial-lateral and anterior-posterior comparison (P = 0.017; CI [-0.063, -0.010]), and the medial-lateral and vertical comparison (P = 0.012; CI [-0.036, -0.007]). Football players altered their sprint mechanics to reduce medial-lateral loading and orient the force in an increased anteroposterior and vertical direction in order to maintain 0-10 m sprint performance. Practitioners should observe medial-lateral force contributions and improve sprint technical efficacy.

The Kinematic and Kinetic Development of Sprinting and Countermovement Jump Performance in Boys.

BACKGROUND: The aim of the study was to examine the kinematics and kinetics of sprint running and countermovement jump performance between the ages of 8-9, and 11-12 years old boys in order to understand the developmental plateau in performance. METHODS: 18 physically active boys (Age: 10.1 ± 1.6), in an under 9 years old (U9) and an under 12 years old (U12) group performed 15 m sprints and countermovement jumps. A 3D motion analysis system (200 Hz), synchronized with four force platforms (1,000 Hz), was used to collect kinematic and kinetic data during the first stance phase of the sprint run and the countermovement jump. RESULTS: The U12 group had a significantly greater height (U9: 1.364 ± 0.064 m; U12: 1.548 ± 0.046 mm), larger mass (U9: 30.9 ± 3.5 kg; U12: 43.9 ± 5.0 kg), superior sprint performance over 0-5 m (U9: 1.31 ± 0.007 s; U12: 1.23 ± 0.009 s) and 0-15 m (U9: 3.20 ± 0.17 s; U12: 3.01 ± 0.20 s), and increased jump height (U9: 0.17 ± 0.06 m; U12: 0.24 ± 0.10 m) than the under nine group. During the first stance phase of the sprint the U12 group had a significantly greater vertical (U9: 0.22 ± 0.02 BW/s; U12: 0.25 ± 0.03 BW.s) and horizontal impulse (U9: 0.07 ± 0.02 BW/s; U12: 0.09 ± 0.03 BW.s) than the U9 group. When performing a countermovement jump the U12 group had a significantly greater mean average eccentric force (U9: 407.3 ± 55.0 N; U12: 542.2 ± 65.1 N) and mean average concentric force (U9: 495.8 ± 41.3 N; U12: 684.0 ± 62.1 N). Joint kinematics for the countermovement jump were significantly different between age groups for the ankle range of motion (U9: 80.6 ± 17.4°; U12: 64.1 ± 9°) and knee minimum joint angle (U9: -5.7 ± 3.9°; U12: 0.0 ± 4.4°). Conclusion: The study demonstrates for the first time that the development of physically active boys between the ages of 8-9 to 11-12 years increased the ground reaction forces and impulses during sprint running and countermovement jumps, but that sprint running technique had not developed during this period. Furthermore, countermovement jump technique was still emerging at the age of 8-9 years old. Practitioners need to implement on-going fine-grained sprint running and CMJ technique sessions to ensure that the increased force producing capabilities that come with age are appropriately utilized.

First-stance phase force contributions to acceleration sprint performance in semi-professional soccer players.

BACKGROUND: Sprint running is a key determinant of player performance in soccer that is typically assessed and monitored using temporal methods. PURPOSE: The aim of this study was to examine the relationship between ground reaction force kinetics at the first step and sprint running performance in soccer players in order to enhance the development of training and assessment methods. METHODS: Nineteen semi-professional soccer players participated (mean ± s: age 21.1 ± 1.9 years, body mass 79.4 ± 7.3 kg and stature 1.79 ± 0.06 m). The participants completed 20 m acceleration sprint runs as timing gates recorded split times between 0-5, 5-10, 10-15, 15-20 and 0-20 m. A force plate captured vertical, anteroposterior and mediolateral ground reaction force data (1000 Hz) of the first right foot strike stance phase. RESULTS: Ground reaction force metrics, including peak anteroposterior propulsive force (r = 0.66 to 0.751; P = .000 to .002), peak vertical ground reaction force (r = 0.456 to 0.464; P = .045 to .05), average medial-lateral/anteroposterior orientation angle (r = -0.463; P = .023), and average anteroposterior/vertical orientation angle (r = -0.44; P = .03) were correlated with one or all split times between 0-5 m, 5-10 m, 10-15 m, 15-20 m and 0-20 m. CONCLUSIONS: Acceleration sprint running in soccer requires minimised mediolateral and increased anteroposterior loading in the stance phase. Multi-component ground reaction force measures of the first step in acceleration sprint runs are important for developing performance assessments, and understanding force application techniques employed by soccer players.

Can arm movements improve postural stability during challenging standing balance tasks?

BACKGROUND: There is growing evidence that arm movements make a substantial and functionally relevant contribution to dynamic balance. Additional insight of the important role of arm movements may be gained by quantifying the effects of arm restriction on the performance of commonly recommended static balance tasks of increasing difficulty. RESEARCH QUESTION: The purpose of the present study was to determine whether restricting/permitting arm movements influences postural sway during tasks of various levels of difficulty. METHODS: A total of 20 healthy and physically active adults (females; n = 10; age, 20.7 ±â€¯1.3 years) randomly completed (a) quiet standing postural control tasks of increasing difficulty (bipedal, tandem, unipedal) on a fixed and foam surface, and (b) a dynamic postural control task (Y balance test), under two different verbally conveyed instructions of arm position; (1) restricted arm movement and (2) free arm movement. Centre of pressure outcomes measured during quiet standing served as a measure of static balance performance. RESULTS: The results showed that restricting movements of the arms elicited large magnitude (Cohen's d = 0.97 - 1.28) increases in mediolateral postural sway (P < 0.05) but not anteroposterior (P > 0.05) sway. These effects were only observed during challenging (tandem and unipedal) standing balance tasks. Restricting arm movements elicited a marked reduction in the Y Balance reach distance (all directions, P < 0.001, d = -0.53 to -1.15). SIGNIFICANCE: The findings from the present study suggest that the contribution of the arms only become relevant when frontal plane balance is challenged. Moreover, the data indicate that arm movements are vital for the control of mediolateral postural sway.

Dynamic Postural Control in Children: Do the Arms Lend the Legs a Helping Hand?

There is growing empirical evidence lending support to the existence of an "upper body strategy" to extend the ankle and hip strategies in maintaining upright postural stability among adults. Both postural stability and arm movement functions are still developing in children. Therefore, enquiry concerning arm contribution to postural stability among children is needed. This proof of concept study seeks to determine whether the arms play a functionally relevant role in dynamic postural control among children. Twenty-nine children (girls, n = 15; age, 10.6 ± 0.5 years; height, 1.48 ± 0.08 m; mass, 42.8 ± 11.4 kg; BMI, 19.2 ± 3.7 kg/m2) completed three dynamic balance tests; (1) Y Balance test®, (2) timed balance beam walking test, (3) transition from dynamic to static balance using the dynamic postural stability index (DPSI). Each test was performed with free and restricted arm movement. Restricting arm movements elicited a marked degradation in the Y Balance reach distance (all directions, P ≤ 0.001, d = -0.85 to -1.13) and timed balance beam walking test (P ≤ 0.001, d = 1.01), while the DPSI was the only metric that was not different between free and restricted arm movements (P = 0.335, d = -0.08). This study provides direct evidence that the arms play a functionally relevant role in dynamic balance performance among children. These findings may provide the impetus to develop training interventions to improve the use of the arms in activities of daily living.

Kinematic adaptations in sprint acceleration performances without and with the constraint of holding a field hockey stick.

The aim of this study was to investigate the technique adaptations made when performing sprint-based tasks without (free condition) and with (constrained condition) the constraints of carrying a field hockey stick. Three free and three constrained maximal sprint accelerations were performed by 18 experienced university male field hockey players (age = 20 +/- 1 years, body mass = 73.3 +/- 7.1 kg, and stature = 1.78 +/- 0.05 m). An automatic motion analysis system tracked sagittal plane active marker locations (200 Hz). M sprint velocity during the 18-22 m (free: 8.03 +/- 0.43 m/s; constrained: 7.93 +/- 0.36 m/s) interval was significantly (p = 0.03) different between free and constrained conditions. While the M stride length and stride frequency was similar between free and constrained conditions in the 2-13 m capture volume, the free condition elicited a 0.10 m/s faster (p = 0.03) stride velocity. Further significant differences were found between free and constrained kinematic profiles (p < or = 0.05) for the hip angular velocity at touchdown during the 2-12 m interval of the sprints and in the overall sprint technique coordination between free and constrained conditions. Performance and technique adaptations indicated that sprint-training protocols for field sports should integrate specific equipment constraints to ensure explicit replication of the mechanical demands of the skills underpinning superior performance.