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Pirjo Kejonen, Kari Kauranen, Ahti Niinimaa and Heikki Vanharanta

Context:

Balance evaluation and training are typically included in rehabilitation after sport injuries.

Objective:

To evaluate and compare the maximal velocities and accelerations of balancing movements during 2-leg stance with eyes open and closed. The effect of age on the measured values was also evaluated.

Design:

Cross-sectional study.

Participants:

100 healthy, randomly selected subjects (50 men, 50 women; age 31–80 years).

Setting:

Body-movement values were measured with the Mac Reflex motion-analysis system.

Intervention:

Subjects stood barefoot.

Main Outcome Measures:

ANOVAs were used to explain the body movements. The location of measurement, presence or absence of vision, and subjects’ age and gender were used as explanatory variables.

Results:

With eyes closed, all measured body parts had significantly higher maximal velocity and acceleration values than with eyes open. Age seemed to affect the acceleration values.

Conclusion:

Visual information was found to significantly influence movement values. Exercises should be done under various conditions to improve standing balance abilities.

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Steven Rowson, Jonathan G. Beckwith, Jeffrey J. Chu, Daniel S. Leonard, Richard M. Greenwald and Stefan M. Duma

The high incidence rate of concussions in football provides a unique opportunity to collect biomechanical data to characterize mild traumatic brain injury. The goal of this study was to validate a six degree of freedom (6DOF) measurement device with 12 single-axis accelerometers that uses a novel algorithm to compute linear and angular head accelerations for each axis of the head. The 6DOF device can be integrated into existing football helmets and is capable of wireless data transmission. A football helmet equipped with the 6DOF device was fitted to a Hybrid III head instrumented with a 9 accelerometer array. The helmet was impacted using a pneumatic linear impactor. Hybrid III head accelerations were compared with that of the 6DOF device. For all impacts, peak Hybrid III head accelerations ranged from 24 g to 176 g and 1,506 rad/s2 to 14,431 rad/s2. Average errors for peak linear and angular head acceleration were 1% ± 18% and 3% ± 24%, respectively. The average RMS error of the temporal response for each impact was 12.5 g and 907 rad/s2.

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Jonathan G. Beckwith, Jeffrey J. Chu and Richard M. Greenwald

Although the epidemiology and mechanics of concussion in sports have been investigated for many years, the biomechanical factors that contribute to mild traumatic brain injury remain unclear because of the difficulties in measuring impact events in the field. The purpose of this study was to validate an instrumented boxing headgear (IBH) that can be used to measure impact severity and location during play. The instrumented boxing headgear data were processed to determine linear and rotational acceleration at the head center of gravity, impact location, and impact severity metrics, such as the Head Injury Criterion (HIC) and Gadd Severity Index (GSI). The instrumented boxing headgear was fitted to a Hybrid III (HIII) head form and impacted with a weighted pendulum to characterize accuracy and repeatability. Fifty-six impacts over 3 speeds and 5 locations were used to simulate blows most commonly observed in boxing. A high correlation between the HIII and instrumented boxing headgear was established for peak linear and rotational acceleration (r 2 = 0.91), HIC (r 2 = 0.88), and GSI (r 2 = 0.89). Mean location error was 9.7 ± 5.2°. Based on this study, the IBH is a valid system for measuring head acceleration and impact location that can be integrated into training and competition.

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Ryu Nagahara, Alberto Botter, Enrico Rejc, Masaaki Koido, Takeshi Shimizu, Pierre Samozino and Jean-Benoit Morin

Purpose:

To test the concurrent validity of data from 2 different global positioning system (GPS) units for obtaining mechanical properties during sprint acceleration using a field method recently validated by Samozino et al.

Methods:

Thirty-two athletes performed maximal straight-line sprints, and their running speed was simultaneously measured by GPS units (sampling rate: 20 or 5 Hz) and either a radar or laser device (devices taken as references). Lower-limb mechanical properties of sprint acceleration (theoretical maximal force, theoretical maximal speed, maximal power) were derived from a modeling of the speed–time curves using an exponential function in both measurements. Comparisons of mechanical properties from 20- and 5-Hz GPS units with those from reference devices were performed for 80 and 62 trials, respectively.

Results:

The percentage bias showed a wide range of overestimation or underestimation for both systems (-7.9% to 9.7% and -5.1% to 2.9% for 20- and 5-Hz GPS), while the ranges of its 90% confidence limits for 20-Hz GPS were markedly smaller than those for 5-Hz GPS. These results were supported by the correlation analyses.

Conclusions:

Overall, the concurrent validity for all variables derived from 20-Hz GPS measurements was better than that obtained from the 5-Hz GPS units. However, in the current state of GPS devices’ accuracy for speed–time measurements over a maximal sprint acceleration, it is recommended that radar, laser devices, and timing gates remain the reference methods for implementing the computations of Samozino et al.

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Timothy A. Burkhart and David M. Andrews

The effectiveness of wrist guards and modifying elbow posture for reducing impact-induced accelerations at the wrist and elbow, for the purpose of decreasing upper extremity injury risk during forward fall arrest, has not yet been documented in living people. A seated human pendulum was used to simulate the impact conditions consistent with landing on outstretched arms during a forward fall. Accelerometers measured the wrist and elbow response characteristics of 28 subjects following impacts with and without a wrist guard, and with elbows straight or slightly bent. Overall, the wrist guard was very effective, with significant reductions in peak accelerations at the elbow in the axial and off-axis directions, and in the off-axis direction at the wrist by almost 50%. The effect of elbow posture as an intervention strategy was mixed; a change in magnitude and direction of the acceleration response was documented at the elbow, while there was little effect at the wrist. Unique evidence was presented in support of wrist guard use in activities like in-line skating where impacts to the hands are common. The elbow response clearly shows that more proximal anatomical structures also need to be monitored when assessing the effectiveness of injury prevention strategies.

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Timothy C. Sell, Jonathan S. Akins, Alexis R. Opp and Scott M. Lephart

Proximal anterior tibia shear force is a direct loading mechanism of the anterior cruciate ligament (ACL) and is a contributor to ACL strain during injury. Measurement of this force during competition may provide insight into risk factors for ACL injury. Accelerometers may be capable of measuring tibial acceleration during competition. The purpose of this study was to examine the relationship between acceleration measured by a tibia-mounted accelerometer and proximal anterior tibia shear force as measured through inverse dynamics and peak posterior ground reaction forces during two leg stop-jump tasks. Nineteen healthy male subjects performed stop-jump tasks across increasing jump distances. Correlation coefficients were calculated to determine if a relationship exists between accelerometer data and proximal anterior tibia shear force and peak posterior ground reaction force. An analysis of variance was performed to compare these variables across jump distance. Significant correlations were observed between accelerometer data and peak posterior ground reaction force, but none between accelerometer data and proximal anterior tibia shear force. All variables except peak proximal anterior tibia shear force increased significantly as jump distance increased. Overall, results of this study provide initial, positive support for the use of accelerometers as a useful tool for future injury prevention research.

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Antonio M. López, Diego Álvarez, Rafael C. González and Juan C. Álvarez

Pedometers are basically step counters usually used to estimate the distance walked by a pedestrian. Although their precision to compute the number of steps is quite accurate (about 1%), their feasibility to estimate the walked distance is very poor, as they do not consider the intrinsic variability of human gait. Reported results show values of 10% of precision in optimal conditions, increasing to 50% when conditions differ. Electronic accelerometer-based pedometers base their functioning on a basic processing of the vertical acceleration of the waist. Recently, different approaches have been proposed to relate such signals to the step length. This can lead to an improvement of the performance of this kind of device for estimating the walked distance. In this article, we analyze four gait models applied to the vertical accelerations of the body’s center of gravity, three biomechanical and one empirical. We compare their precision and accuracy. Results support the superior performance of three of them over an ideal pedometer. We also analyze their feasibility to be implemented in pedometer-like devices.

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Jon L. Oliver and Robert W. Meyers

Purpose:

The purpose of the current study was to assess the reliability of a new protocol that examines different components of agility using commercially available timing gates.

Methods:

Seventeen physically active males completed four trials of a new protocol, which consisted of a number of 10-m sprints. Sprints were completed in a straight line or with a change of direction after 5 m. The change of direction was either planned or reactive, with participants reacting to a visual light stimulus.

Results:

There was no systematic bias in any of the measures, although random variation was reduced in the straight acceleration and planned agility when considering only the fnal pair of trials, with mean coefficients of variation (CV) of 1.6% (95%CI, 1.2% to 2.4%) and 1.1% (0.8% to 1.7%), respectively. Reliability of reactive agility remained consistent throughout with mean CVs of approximately 3%. Analyses revealed a high degree of common variance between acceleration times and both planned (r 2 = .93) and reactive (r 2 = .83) agility, as well as between the two agility protocols (r 2 = .87).

Conclusion:

Both planned and reactive agility could be measured reliably. Protocol design and use of a light stimulus in the reactive test emphasize physical abilities comparable with other test measures. Therefore, inclusion of a reactive light stimulus does not appear to require any additional perceptual qualities.

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Alex V. Rowlands, John M. Schuna Jr., Victoria H. Stiles and Catrine Tudor-Locke

Background:

Previous research has reported peak vertical acceleration and peak loading rate thresholds beneficial to bone mineral density (BMD). Such thresholds are difficult to translate into meaningful recommendations for physical activity. Cadence (steps/min) is a more readily interpretable measure of ambulatory activity.

Objective:

To examine relationships between cadence, peak vertical acceleration and peak loading rate during ambulation and identify the cadence associated with previously reported bone-beneficial thresholds for peak vertical acceleration (4.9 g) and peak loading rate (43 BW/s).

Methods:

Ten participants completed 8 trials each of: slow walking, brisk walking, slow running, and fast running. Acceleration data were captured using a GT3×+ accelerometer worn at the hip. Peak loading rate was collected via a force plate.

Results:

Strong relationships were identified between cadence and peak vertical acceleration (r = .96, P < .05) and peak loading rate (r = .98, P < .05). Regression analyses indicated cadences of 157 ± 12 steps/min (2.6 ± 0.2 steps/s) and 122 ± 10 steps/min (2.0 ± 0.2 steps/s) corresponded with the 4.9 g peak vertical acceleration and 43 BW/s peak loading rate thresholds, respectively.

Conclusions:

Cadences ≥ 2.0 to 2.6 steps/s equate to acceleration and loading rate thresholds related to bone health. Further research is needed to investigate whether the frequency of daily occurrences of this cadence is associated with BMD.

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Joseph P. Hunter, Robert N. Marshall and Peter J. McNair

The literature contains some hypotheses regarding the most favorable ground reaction force (GRF) for sprint running and how it might be achieved. This study tested the relevance of these hypotheses to the acceleration phase of a sprint, using GRF impulse as the GRF variable of interest. Thirty-six athletes performed maximal-effort sprints from which video and GRF data were collected at the 16-m mark. Associations between GRF impulse (expressed relative to body mass) and various kinematic measures were explored with simple and multiple linear regressions and paired t-tests. The regression results showed that relative propulsive impulse accounted for 57% of variance in sprint velocity. Relative braking impulse accounted for only 7% of variance in sprint velocity. In addition, the faster athletes tended to produce only moderate magnitudes of relative vertical impulse. Paired t-tests revealed that lower magnitudes of relative braking impulse were associated with a smaller touchdown distance (p < 0.01) and a more active touchdown (p < 0.001). Also, greater magnitudes of relative propulsive impulse were associated with a high mean hip extension velocity of the stance limb (p < 0.05). In conclusion, it is likely that high magnitudes of propulsion are required to achieve high acceleration. Although there was a weak trend for faster athletes to produce lower magnitudes of braking, the possibility of braking having some advantages could not be ruled out. Further research is required to see if braking, propulsive, and vertical impulses can be modified with specific training. This will also provide insight into how a change in one GRF component might affect the others.