Relationship between stability and variability of the core in dynamic reaching tasks

Core stability is important to many functional and athletic tasks. Motion variability has been proposed as a measure to characterize core stability. Based on motor learning theories, the current study hypothesized  that variability and stability of core movements show a U-shaped relationship and further investigated whether functional range of motion (“mobility”) or speed of motion affect this relationship.  Twenty-four healthy subjects performed 20 cycles of two different unilateral hand reaching tasks for both the left and right hand under stable and unstable conditions. Reach targets were positioned to trigger large core movements. Specifically, the anterior target was positioned midsagittal at arm length´s distance and hip height. Two posterior targets (60 degrees posterior to neutral stance frontal plane) on both the left and right side were high (at arm length distance and height with accrued 10 cm) and low (arm length distance at hip height). Kinematic data were recorded and three-dimensional angles between pelvis and thorax (core) were calculated. Pearson correlation coefficients and paired T-tests were calculated to assess variability, mobility and speed of the core movements. A parabolic function was fitted to the variability data and the quality of the fit was assessed by calculating adjusted R-squared values.  In the sagittal plane, variability could be modeled with a U-shaped distribution; in the other planes of motion this was the case in 2 of 4 reaching tests. In two tests, movement speed changed between the stable and unstable conditions. Mobility did not appear to affect variability in the stable condition, but some correlations were observed in the unstable condition. The relationship between mobility and variability, and the change in variability were task-specific

Influence of Anthropometry, Age, Sex, and Activity Level on the Hand Reach Star Excursion Balance Test

The influence of anthropometric measurements, age, sex, and activity level have been found to influence tests of dynamic postural control such as the star excursion balance test (SEBT). The hand reach star excursion balance test (HSEBT) measures different aspects of dynamic postural control. The purpose of the present study was to explore the influence of these factors on the HSEBT. A convenience sample of 223 subjects performed four horizontal (L45, R45, L135, and R135) and two rotational (LROT and RROT) reaches. The influence of anthropometric measurements (height, arm length, leg length, and wingspan) on reach measurements were assessed using stepwise multiple linear regression. Influence of age (young: <20 years; adult: >20 years), sex (male; female) and activity level (athletes; recreational) on reach measurements were analyzed using independent samples t-test (p < 0.05) and interpreted using effect size (Cohens d) and established values of minimal detectable change (MDC). Wingspan explained a significant portion of the variance of only R45 (34.6%) and L45 (11.7%) reach measurements and normalized (percentage of wingspan). A medium effect of age, sex, and activity level was observed for normalized L45 and R45 reaches (d = 0.50–72). Group differences greater than MDC values and a medium effect for age (d = 0.55) and activity level (d = 0.75) were observed for the R135 reach. L45 and R45 reaches should be normalized to wingspan, but not the other reaches. Between individual or group comparisons should consider age, activity level and sex as potential covariates

Validity of Velocity Measurements of a Motorized Resistance Device During Change of Direction

The aim of this study was to determine validity of velocity measurements of a motorized resistance device (MRD) during change of direction (CoD). Eight male (age: 22.1 ± 4.2 yrs; weight: 83.3 ± 17.1 kg; height: 181.6 ± 12.6 cm) and three female participants (age: 21.7 ± 1.5 yrs; mass: 69.7 ± 2.4 kg; height: 167.0 ± 3.6 cm) completed the modified 505 CoD test (m505) with turning off the left and right foot while exposed to external loads (3, 6, and 9 kg) provided by the MRD. Three-dimensional kinematic data were measured (200 Hz) for all tests using a full-body marker set with an additional marker placed on the pulley used to attach the carabiner (CAR) at the end of the line from the MRD to the participant. Average velocity of overall center of mass (COMvel), pelvis (COMpelvis_vel), and pulley (CARvel) was then calculated and compared to the velocity measured by MRD (MRDvel) in 0.5 s intervals 1.5 s before and after CoD. Average velocities from these intervals were then compared using correlational, Bland–Altman analysis, coefficient of variation (CV), and statistical parametric mapping (SPM). Mostly, excellent correlations were observed and ranged from 0.93 to 1.00, 0.53 to 1.00 and 0.93 to 1.00 for the 3, 6, and 9 kg load conditions, respectively. CV values ranged from 0.3 to 3.2%, 0.8 to 4.3%, and 1.5 to 7.7% for the CARvel, COMpelvis_vel, and COMvel comparisons, respectively. The biases for CARvel comparisons ranged from −0.027 to 0.05 m/s, −0.246 to 0.128 m/s and −0.486 to 0.082 m/s across all load conditions and time intervals for the CARvel, COMpelvis_vel, and COMvel comparisons, respectively. SPM analysis indicated significant differences between MRDvel and COMvel and COMpelvis_vel over short time periods during the CoD, but no difference between MRDvel and CARvel. The velocity measurements obtained by a MRD during a m505 test are valid as low biases, low CV’s, and high correlations are observed for the MRDvel to CARvel comparison. As single points of measurement (i.e., laser) has been proven useful to assess other athletic tasks (i.e., sprint running), the single point CARvel comparison is an appropriate comparison for validating MRDvel measurements during the m505 test

Reliability of phase-specific outcome measurements in change-of-direction tests using a motorized resistance device

This study aims to determine test-retest reliability of phase-specific information during initial acceleration, deceleration, and re-acceleration phases of different change-of-direction (CoD) tests using a motorized resistance device (MRD). A total of 21 participants (16 males and five females, with mean age of 22.3 ± 3.9 years, body mass of 75.2 ± 6.9 kg, height of 177.9 ± 6.8 cm) completed the modified 505 (m505), 10-0-5, and 15-0-5 CoD tests on four different test sessions while exposed to an external load (3 kg) provided by the MRD. Outcome variables included overall and phase-specific kinetic (force, power, and impulse) and kinematic (time, distance, velocity, and acceleration/deceleration) data during the initial acceleration, deceleration, and re-acceleration phases. The deceleration and re-acceleration phases were further divided into two subphases, namely, early and late subphases, using 50% of maximum velocity. Reliability was assessed using an intraclass correlation coefficient (ICC), coefficient of variation (CV), typical error (TE), and minimal detectable change (MDC). Good to excellent ICC values (>0.75) and acceptable (<10%) to good (<5%) CV values were observed for most outcome measurements. Specifically, 80.1% (822 out of 1,026) of all variables showed good or better relative reliability (i.e., ICC ≥ 0.75), while 97.0% (995 out of 1,026) of all variables showed acceptable or better absolute reliability (i.e., CV < 10%). In conclusion, the present study demonstrates that the MRD can obtain reliable phase-specific outcome measurements across different CoD tests, providing coaches and researchers with new opportunities to advance our understanding of CoD ability and inform more advanced CoD training prescriptions

KNEE KINEMATICS AND KINETICS OF SPORT-SPECIFIC FAKE-AND-CUT MANEUVERS OF VARYING COMPLEXITY IN FEMALE HANDBALL PLAYERS

The purpose of this study was to 1) compare knee joint kinematics and kinetics of fake-and-cut tasks of varying complexity in 51 female handball players and 2) present a case study of one athlete who ruptured her ACL three weeks post data collection. External knee joint moments and knee joint angles in all planes at the instance of the peak external knee abduction moment (KAM) as well as moment and angle time curves were analyzed. Peak KAMs and knee internal rotation moments were substantially higher than published values obtained during simple change-of-direction tasks and, along with flexion angles, differed significantly between the tasks. Introducing a ball reception and a static defender increased joint loads while they partially decreased again when anticipation was lacking. Our results suggest to use game-specific assessments of injury risk while complexity levels do not directly increase knee loading. Extreme values of several risk factors for a post-test injured athlete highlight the need and usefulness of appropriate screenings

CAN A SIMPLIFIED KNEE ABDUCTION MOMENT ESTIMATION BE USED FOR ATHLETE SCREENING? IMPLICATIONS FOR ACL INJURY PREVENTION

This study aimed to compare a simplified calculation of the knee abduction moment with the traditional inverse dynamics calculation when athletes perform fake-cut maneuvers with different complexities. In the simplified calculation, we multiply the force vector with its lever arm to the knee, projected onto the local coordinate system of the proximal thigh, hence neglecting the inertial contributions from distal segments. We found very strong ranking consistency using Spearman’s rank correlation coefficient when using the simplified method compared to the traditional calculation. Independent of the tasks, the simplified method resulted in higher moments than the inverse dynamics. This was caused by ignoring the moment caused by segment linear acceleration generating a counteracting moment by about 7%. An alternative to the complex calculations of inverse dynamics can be used to investigate the contributions of the GRF magnitude and its lever arm to the knee

Biomechanical and Neuromuscular Performance Requirements of Horizontal Deceleration: A Review with Implications for Random Intermittent Multi-Directional Sports

Rapid horizontal accelerations and decelerations are crucial events enabling the changes of velocity and direction integral to sports involving random intermittent multi-directional movements. However, relative to horizontal acceleration, there have been considerably fewer scientific investigations into the biomechanical and neuromuscular demands of horizontal deceleration and the qualities underpinning horizontal deceleration performance. Accordingly, the aims of this review article are to: (1) conduct an evidence-based review of the biomechanical demands of horizontal deceleration and (2) identify biomechanical and neuromuscular performance determinants of horizontal deceleration, with the aim of outlining relevant performance implications for random intermittent multi-directional sports. We highlight that horizontal decelerations have a unique ground reaction force profile, characterised by high-impact peak forces and loading rates. The highest magnitude of these forces occurs during the early stance phase (< 50 ms) and is shown to be up to 2.7 times greater than those seen during the first steps of a maximal horizontal acceleration. As such, inability for either limb to tolerate these forces may result in a diminished ability to brake, subsequently reducing deceleration capacity, and increasing vulnerability to excessive forces that could heighten injury risk and severity of muscle damage. Two factors are highlighted as especially important for enhancing horizontal deceleration ability: (1) braking force control and (2) braking force attenuation. Whilst various eccentric strength qualities have been reported to be important for achieving these purposes, the potential importance of concentric, isometric and reactive strength, in addition to an enhanced technical ability to apply braking force is also highlighted. Last, the review provides recommended research directions to enhance future understanding of horizontal deceleration ability

Hand reach star excursion balance test

Background: Different tests for dynamic postural control; i.e., the ability to maintain a stable base while completing a movement, are frequently used to assess functional and athletic performance. Current tests primarily target either the lower extremities or the trunk and the upper extremities. In addition, these tests have variable demands on functional mobility, which is defined as the combination of the range of motion (ROM) of multiple joints used to accomplish ecological tasks. Currently there are no tests of dynamic postural control that simultaneously impose three-dimensional mobility demands on the trunk, lower and upper extremities. The purpose of this thesis was to develop a new test of dynamic postural control to target these shortcomings and to establish 1) validity; 2) reliability; 3) the influence of potential covariates such as anthropometry, age, sex and level of physical activity; and 4) the influence on overhead athletic performance. Methods: The thesis is based on four different research projects that used an observational design with a total of 222 participants; these projects represent the development of the hand reach star excursion balance tests (HSEBT). Standardized testing procedures were developed by a group of experts, based on: 1) starting position; 2) task; 3) measurement; and 4) ending position, which served as content validity. In study I, criterion-related and construct validity were explored. Specifically, the magnitudes of joint movements used to assume maximum HSEBT reach positions were quantified using motion capture (Qualisys Oqus 400 cameras, Qualisys AB, Gothenburg, Sweden) and compared to joint movements in the comparable star excursion balance test (SEBT) and normative ROM values. Criterion-related (concurrent) validity was established by comparing reach measurements calculated from motion capture data to those visually obtained using Bland Altman and correlational analysis. Construct validity was assessed by correlating outcome measurements (reach, composite scores and area calculations) from the HSEBT with the comparable SEBT. In study II, inter-rater and testretest reliability was assessed from the outcome measurements of three experienced testers using intraclass correlation coefficients (ICC), with the calculation of stability measurements (standard error or measurement and coefficient of variation) and minimal detectable change. The influence of anthropometry, age, sex and level of physical activity was explored in study III. Stepwise linear regression was used to determine the influence of these factors on reach measurements. Independent samples t-tests were used to determine betweengroup (age, sex and level of physical activity) differences with calculation of effect sizes and group difference comparisons to minimal detectable change values (study II). The influence of HSEBT reach measurements on athletic performance (overhead team handball throwing) in an elite female population was explored for both throwing velocity, calculated from motion capture data, and accuracy, via mean radial error calculated from video records, using Pearson correlational analysis. Main results: The HSEBT elicited significantly greater joint movements than the SEBT in 18 out of 22 joint movement comparisons. The magnitude of these joint movements was comparable to the ranges of normative ROM values for 8 out of 22 joint movements. Excellent correlations were observed between visually observed and calculated reach measurements from motion capture data for 18 out of 20 tests (r ≥ 0.90) with a shared variance that ranged from 81 to 97%. For the remaining two tests good correlations were observed (r = .79 and .89). The fixed biases observed (range = 2.2 to 12.8 cm, −6.0 to 11.2° and 23.7%) can be partially explained by the methods used to calculate reach measurements. Different composite and area scores for the HSEBT and SEBT had variable correlations (range r = .269 to .823), with a wider range of observed values for the individual reaches (range r = -.182 to .822). The strongest correlations were observed for the anterior composite, area and reach measurement comparisons (range r = .515 to .823). In Study II moderate to high test-retest reliability was observed for 19 out of 20 reaches (range ICC = 0.80 to 0.96). The inter-rater reliability was high for all reaches (range ICC = 0.90 to 0.98). Minimal detectable change values ranged from 0.9–7.9 cm and 4.7–7.2° for all reaches. Wingspan (study III) explained 34.6 and 11.7% of the variance of two HSEBT reaches. When normalized (% of wingspan) the same reaches were influenced by age, sex and level of physical activity with significant between-group differences, and moderate effect sizes (range d = .50 to .72). In addition, one non-normalized reach was influenced by age and level of physical activity (range d = .55 to .75). HSEBT reach measurements are not correlated with throwing velocity (range r = -.530 to .395), but with mean radial error for some reaches (range r = .149 to .666) (study IV). Conclusions: The HSEBT is a valid and reliable measure of dynamic postural control that measures different aspects of dynamic postural control compared to the SEBT, especially in the lateral and posterior directions. Greater joint movements of the lower extremity, trunk and shoulder joint are elicited by the HSEBT than the SEBT, making it a useful addition to tests of functional mobility. Reach specific normalization to wingspan is indicated, and age, sex and level of physical activity should be accounted for when performing between-individual and group comparisons for specific HSEBT reaches. No beneficial effect of increased HSEBT reach measurements on throwing performance could be established in elite female team handball players

The influence of anthropometry, age, gender and activity level on dynamic postural control

Test measurements for selected HSEBT reaches and age with identifiers for gender and type of activit

Isokinetic strength training of kinetic chain exercises of a professional tennis player with a minor partial internal abdominal oblique muscle tear ? A case report

Objective: To present a case of a right-handed professional tennis player with a left internal abdominal oblique muscle tear sustained while serving. We document the progress of a rehabilitation program consisting of primarily kinetic chain isokinetic strength training where symmetrical measurements (<10% side difference) of force and dynamic postural control were used as criteria for return to sport. Methods: Isokinetic exercises (bilateral rotational pull, unilateral vertical press and unilateral anterior push) to target trunk specific demands of the serve (flexion, rotation and lateral flexion) were done using robotic resistance. Dynamic postural control was assessed using the hand reach star excursion balance test (HSEBT). The rehabilitation program lasted 3.5 weeks (eight sessions). Results: At baseline isokinetic strength tests that imposed concentric muscle function demands of the injured muscle had lower force measurements (range: -32.1 to −71.9%). These force measurements improved (range: 166.1–296.5%) and were symmetrical (range: +1.6 to +7.3%) on return to sport. In addition, the HSEBT test with the greatest asymmetry (−20 cm) improved to symmetrical (+2 cm) on return to sport. Conclusion: Symmetrical isokinetic force and dynamic postural control measurements were successful return to sport criteria as the player since has remained pain free (2 years)