Wearable accelerometer-based activity monitors (AMs) are used to estimate energy expenditure and ground reaction forces in free-living environments, but a lack of standardized calibration and data reporting methods limits their utility. The objectives of this study were to (1) design an inexpensive and easily reproducible AM testing system, (2) develop a standardized calibration method for accelerometer-based AMs, and (3) evaluate the utility of the system and accuracy of the calibration method. A centrifuge-type device was constructed to apply known accelerations (0-8g) to each sensitive axis of 30 custom and two commercial AMs. Accelerometer data were recorded and matrix algebra and a least squares solution were then used to determine a calibration matrix for the custom AMs to convert raw accelerometer output to units of g’s. Accuracy was tested by comparing applied and calculated accelerations for custom and commercial AMs. AMs were accurate to within 4% of applied accelerations. The relatively inexpensive AM testing system (< $100) and calibration method has the potential to improve the sharing of AM data, the ability to compare data from different studies, and the accuracy of AM-based models to estimate various physiological and biomechanical quantities of interest in field-based assessments of physical activity.
Crystal L. Coolbaugh and David A. Hawkins
Shonn P. Hendee, Richard M. Greenwald, and Joseph J. Crisco
In this study we investigated the compressive quasi-static mechanical properties and dynamic impact behavior of baseballs. Our purpose was to determine if static testing could be used to describe dynamic ball impact properties, and to compare static and dynamic properties between traditional and modified baseballs. Average stiffness and energy loss from 19 ball models were calculated from quasi-static compression data. Dynamic impact variables were determined from force–time profiles of balls impacted into a flat stationary target at velocities from 13.4 to 40.2 m/s. Peak force increased linearly with increasing ball model stiffness. Impulse of impact increased linearly with ball mass. Coefficient of restitution (COR) decreased with increasing velocity in all balls tested, although the rate of decrease varied among the different ball models. Neither quasi-static energy loss nor hysteresis was useful in predicting dynamic energy loss (COR2). The results between traditional and modified balls varied widely in both static and dynamic tests, which is related to the large differences in mass and stiffness between the two groups. These results indicate that static parameters can be useful in predicting some dynamic impact variables, potentially reducing the complexity of testing. However, some variables, such as ball COR, could not be predicted with the static tests performed in this study.
Toshiki Kobayashi, Fan Gao, Nicholas LeCursi, K. Bo Foreman, and Michael S. Orendurff
orthoses. The mechanical properties of AFOs, such as stiffness (moment per degree) and energy efficiency (ratio of released energy to stored energy), have been characterized using various mechanical testing devices, 1 – 3 and their effects on gait in individuals with neuromuscular diseases have been
Iain Hannah, Andy Harland, Dan Price, Heiko Schlarb, and Tim Lucas
A dynamic finite element model of a shod running footstrike was developed and driven with 6 degree of freedom foot segment kinematics determined from a motion capture running trial. Quadratic tetrahedral elements were used to mesh the footwear components with material models determined from appropriate mechanical tests. Model outputs were compared with experimental high-speed video (HSV) footage, vertical ground reaction force (GRF), and center of pressure (COP) excursion to determine whether such an approach is appropriate for the development of athletic footwear. Although unquantified, good visual agreement to the HSV footage was observed but significant discrepancies were found between the model and experimental GRF and COP readings (9% and 61% of model readings outside of the mean experimental reading ± 2 standard deviations, respectively). Model output was also found to be highly sensitive to input kinematics with a 120% increase in maximum GRF observed when translating the force platform 2 mm vertically. While representing an alternative approach to existing dynamic finite element footstrike models, loading highly representative of an experimental trial was not found to be achievable when employing exclusively kinematic boundary conditions. This significantly limits the usefulness of employing such an approach in the footwear development process.
Arnel Aguinaldo and Andrew Mahar
This study evaluated the effects of running shoes—with two types of cushioning column systems—on impact force patterns during running. Kinematic and ground reaction force data were collected from 10 normal participants wearing shoes with the following cushions: 4-column multicellular urethane elastomer (Shoe 1), 4-column thermoplastic polyester elastomer (Shoe 2), and 1-unit EVA foam (Shoe 3). Participants exhibited significantly lower impact force (p = .02) and loading rate (p = .005) with Shoe 2 (1.84 ± 0.24 BW; 45.6 ± 11.6 BW/s) compared to Shoe 1 (1.94 ± 0.18 BW; 57.9 ± 12.1 BW/s). Both cushioning column shoes showed impact force characteristics similar to those of a top-model running shoe (Shoe 3), and improved cushioning performance over shoes previously tested in similar conditions. Alterations in impact force patterns induced by lower limb alignment and running speed were negligible since participants did not differ in ankle position, knee position, or speed during all shod running trials. Ankle plantarflexion, however, was higher for barefoot running, indicating an apparent midfoot strike. Mechanical testing of each shoe during physiologic, cyclic loading demonstrated that Shoe 3 had the greatest stiffness, followed by Shoe 2 and Shoe 1. Shoe 1 was the least stiff of the two shoes with cushioning column systems, yet it displayed a significantly higher impact loading rate during running, possibly due to rearfoot motion alterations induced by the stiffer shoe. This study showed that even in similar shoe types, impact force and loading rate values could vary significantly with midsole cushion constructions. The findings of this study suggest that using these newer running shoes may be effective for runners who want optimal cushioning during running.
Scott W. Cheatham and Russell Baker
efferent descending pathways. 6 Future validation studies are needed that compare this testing technique with mechanical testing methods to directly compare the results between clinician and machine application. Limitations Although clinical applicability may have been increased with this novel testing
Liana M. Tennant, Erika Nelson-Wong, Joshua Kuest, Gabriel Lawrence, Kristen Levesque, David Owens, Jeremy Prisby, Sarah Spivey, Stephanie R. Albin, Kristen Jagger, Jeff M. Barrett, James D. Wong, and Jack P. Callaghan
stiffness. Discussion The primary objective of this study was to determine if in vivo mechanical testing of spinal stiffness and clinical segmental mobility assessments provide similar information in the lumbar spine. Contrary to our hypothesis, the only significant correlation was between the results of
Johan Cassirame, Hervé Sanchez, and Jean-Benoit Morin
effect. Before each competition, the track has to be checked by official judges, but no normative values or mechanical tests are described or warranted for this verification. Pole vault is a complex sport with many determinants of performance that occur during run-up or after takeoff. 9 , 10 Although it
Daniel J. Brinkmann, Harald Koerger, Albert Gollhofer, and Dominic Gehring
decreasing the midfoot stiffness. As a result, the mechanically tested forefoot–midfoot ratios ranged from 0.093 to 0.615. Participants were not allowed to manually inspect their footwear and were blind to the footwear conditions at all times. The respective footwear conditions were randomized. Data for both
Ben Langley, Mary Cramp, and Stewart C. Morrison
single model and manufacturer for each type of shoe may limit the ability to extrapolate the findings of this study beyond running shoes highly similar to those assessed, due to differences in shoe construction between models/manufacturers. The lack of any mechanical testing to quantify the properties of