Mechanical power output is a key performance-determining variable in many cyclic sports. In rowing, instantaneous power output is commonly determined as the dot product of handle force moment and oar angular velocity. The aim of this study was to show that this commonly used proxy is theoretically flawed and to provide an indication of the magnitude of the error. To obtain a consistent dataset, simulations were performed using a previously proposed forward dynamical model. Inputs were previously recorded rower kinematics and horizontal oar angle, at 20 and 32 strokes∙min−1. From simulation outputs, true power output and power output according to the common proxy were calculated. The error when using the common proxy was quantified as the difference between the average power output according to the proxy and the true average power output (P̅residual), and as the ratio of this difference to the true average power output (ratiores./rower). At stroke rate 20, P̅residual was 27.4 W and ratiores./rower was 0.143; at stroke rate 32, P̅residual was 44.3 W and ratiores./rower was 0.142. Power output in rowing appears to be underestimated when calculated according to the common proxy. Simulations suggest this error to be at least 10% of the true power output.
In wheelchair sports, the use of Inertial Measurement Units (IMUs) has proven to be one of the most accessible ways for ambulatory measurement of wheelchair kinematics. A three-IMU configuration, with one IMU attached to the wheelchair frame and two IMUs on each wheel axle, has previously shown accurate results and is considered optimal for accuracy. Configurations with fewer sensors reduce costs and could enhance usability, but may be less accurate. The aim of this study was to quantify the decline in accuracy for measuring wheelchair kinematics with a stepwise sensor reduction. Ten differently skilled participants performed a series of wheelchair sport specific tests while their performance was simultaneously measured with IMUs and an optical motion capture system which served as reference. Subsequently, both a one-IMU and a two-IMU configuration were validated and the accuracy of the two approaches was compared for linear and angular wheelchair velocity. Results revealed that the one-IMU approach show a mean absolute error (MAE) of 0.10 m/s for absolute linear velocity and a MAE of 8.1◦/s for wheelchair angular velocity when compared with the reference system. The twoIMU approach showed similar differences for absolute linear wheelchair velocity (MAE 0.10 m/s), and smaller differences for angular velocity (MAE 3.0◦/s). Overall, a lower number of IMUs used in the configuration resulted in a lower accuracy of wheelchair kinematics. Based on the results of this study, choices regarding the number of IMUs can be made depending on the aim, required accuracy and resources available.
Background. Deviant shoulder girdle movement is suggested as an eminent factor in the etiology of shoulder pain. Reliable measurements of shoulder girdle kinematics are a prerequisite for optimizing clinical management strategies. Purpose. The purpose of this study was to evaluate the reliability, measurement error, and internal consistency of measurements with performance-based clinical tests for shoulder girdle kinematics and positioning in patients with shoulder pain. Data Sources. The MEDLINE, Embase, CINAHL, and SPORTDiscus databases were systematically searched from inception to August 2015. Study Selection. Articles published in Dutch, English, or German were included if they involved the evaluation of at least one of the measurement properties of interest. Data Extraction. Two reviewers independently evaluated the methodological quality per studied measurement property with the 4-point-rating scale of the COSMIN (COnsensus-based Standards for the selection of health Measurement INstruments) checklist, extracted data, and assessed the adequacy of the measurement properties. Data Synthesis. Forty studies comprising more than 30 clinical tests were included. Actual reported measurements of the tests were categorized into: (1) positional measurement methods, (2) measurement methods to determine dynamic characteristics, and (3) tests to diagnose impairments of shoulder girdle function. Best evidence synthesis of the tests was performed per measurement for each measurement property. Limitations. All studies had significant limitations, including incongruence between test description and actual reported measurements and a lack of reporting on minimal important change. In general, the methodological quality of the selected studies was fair to poor. Conclusions. High-quality evidence indicates that measurements obtained with the Modified Scapular Assistance Test are not reliable for clinical use. Sound recommendations for the use of other tests could not be made due to inadequate evidence. Across studies, diversity in description, performance, and interpretation of similar tests was present, and different criteria were used to establish similar diagnoses, mostly without taking into account a clinically meaningful context. Consequently, these tests lack face validity, which hampers their clinical use. Further research on validity and how to integrate a clinically meaningful context of movement into clinical tests is warranted.
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