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Aaron Chin, David Lloyd, Jacqueline Alderson, Bruce Elliott and Peter Mills

The predominance of upper-limb elbow models have been based on earlier lower-limb motion analysis models. We developed and validated a functionally based 2 degree-of-freedom upper-limb model to measure rotations of the forearm using a marker-based approach. Data were collected from humans and a mechanical arm with known axes and ranges of angular motion in 3 planes. This upper-limb model was compared with an anatomically based model following the proposed ISB standardization. Location of the axes of rotation relative to each other was determined in vivo. Data indicated that the functional model was not influenced by cross-talk from adduction-abduction, accurately measuring flexion-extension and pronation-supination. The functional flexion-extension axis in vivo is angled at 6.6° to the anatomical line defined from the humeral medial to lateral epicondyles. The pronation-supination axis intersected the anatomically defined flexion-extension axis at 88.1°. Influence of cross-talk on flexion-extension kinematics in the anatomical model was indicated by strong correlation between flexion-extension and adduction-abduction angles for tasks performed by the subjects. The proposed functional model eliminated cross-talk by sharing a common flexion axis between the humerus and forearm. In doing so, errors due to misalignment of axes are minimized providing greater accuracy in kinematic data.

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Francisco Javier Alonso, Publio Pintado and José María Del Castillo

The use of the Hodrick-Prescott (HP) filter is presented as an alternative to the traditional digital filtering and spline smoothing methods currently used in biomechanics. In econometrics, HP filtering is a standard tool used to decompose a macroeconomic time series into a nonstationary trend component and a stationary residual component. The use of the HP filter in the present work is based on reasonable assumptions about the jerk and noise components of the raw displacement signal. Its applicability was tested on 4 kinematic signals with different characteristics. Two are well known signals taken from the literature on biomechanical signal filtering, and the other two were acquired with our own motion capture system. The criterion for the selection of cutoff frequency was based on the power spectral density of the raw displacement signals. The results showed the technique to be well suited to filtering biomechanical displacement signals in order to obtain accurate higher derivatives in a simple and systematic way. Namely, the HP filter and the generalized cross-validated quintic spline (GCVSPL) produce similar RMS errors on the first (0.1063 vs. 0.1024 m/s2) and second (23.76 vs. 23.24 rad/s2) signals. The HP filter performs slightly better than GCVSPL on the third (0.209 vs. 0.236 m/s2) and fourth (1.596 vs. 2.315 m/s2) signals.

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Jaclyn B. Caccese, Thomas A. Buckley and Thomas W. Kaminski

The Balance Error Scoring System (BESS) is often used for sport-related concussion balance assessment. However, moderate intratester and intertester reliability may cause low initial sensitivity, suggesting that a more objective balance assessment method is needed. The MobileMat BESS was designed for objective BESS scoring, but the outcome measures must be validated with reliable balance measures. Thus, the purpose of this investigation was to compare MobileMat BESS scores to linear and nonlinear measures of balance. Eighty-eight healthy collegiate student-athletes (age: 20.0 ± 1.4 y, height: 177.7 ± 10.7 cm, mass: 74.8 ± 13.7 kg) completed the MobileMat BESS. MobileMat BESS scores were compared with 95% area, sway velocity, approximate entropy, and sample entropy. MobileMat BESS scores were significantly correlated with 95% area for single-leg (r = .332) and tandem firm (r = .474), and double-leg foam (r = .660); and with sway velocity for single-leg (r = .406) and tandem firm (r = .601), and double-leg (r = .575) and single-leg foam (r = .434). MobileMat BESS scores were not correlated with approximate or sample entropy. MobileMat BESS scores were low to moderately correlated with linear measures, suggesting the ability to identify changes in the center of mass–center of pressure relationship, but not higher-order processing associated with nonlinear measures. These results suggest that the MobileMat BESS may be a clinically-useful tool that provides objective linear balance measures.

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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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Kyoung-Seok Yoo, Hyun-Kyung Kim and Jin-Hoon Park

The present study examined the technical characteristics of sliding performance from push-off until stone release in curling delivery. Five elite performance level curlers (> 7 years experience) and five subelite level curlers (< 3 years experience) were analyzed during the action of delivery of a curling stone. The joint angles, angular velocities, and moments of the body center of mass (COM) were determined based on three-dimensional kinematic data. The plantar pressure data were measured using a validated in-shoe system. The results indicated that the gliding time and horizontal velocity of the mass center of the body during the sliding phase were not significantly different between the elite and subelite groups. However, there were significant differences in the gliding distance and the rate of changes in velocity profiles of body COM between the two groups. The moment of the body COM from its relative position to the ankle of the support limb in the anterior/posterior direction was positive in elite curlers and negative in subelite curlers. In addition, larger ankle dorsiflexion and greater contact area of the sliding foot were observed in elite curlers. These data suggest a superior ability of elite curlers to maintain a regulated movement speed and balance control during the performance of a curling stone delivery.

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John H. Challis

This article presents and evaluates a new procedure that automatically determines the cutoff frequency for the low-pass filtering of biomechanical data. The cutoff frequency was estimated by exploiting the properties of the autocorrelation function of white noise. The new procedure systematically varies the cutoff frequency of a Butterworth filter until the signal representing the difference between the filtered and unfiltered data is the best approximation to white noise as assessed using the autocorrelation function. The procedure was evaluated using signals generated from mathematical functions. Noise was added to these signals so mat they approximated signals arising from me analysis of human movement. The optimal cutoff frequency was computed by finding the cutoff frequency that gave me smallest difference between the estimated and true signal values. The new procedure produced similar cutoff frequencies and root mean square differences to me optimal values, for me zeroth, first and second derivatives of the signals. On the data sets investigated, this new procedure performed very similarly to the generalized cross-validated quintic spline.

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Louis A. DiBerardino III, Chantal A. Ragetly, Sungjin Hong, Dominique J. Griffon and Elizabeth T. Hsiao-Wecksler

The regions of deviation method has been proposed as a technique for identifying regions of the gait cycle where joint motion deviates from normal (Shorter et al., 2008). The original statistical analysis distinguished only peak values during stance and swing. In the current article, we extend the approach by examining deviations from normal throughout the entire gait cycle using pointwise t tests. These methods were demonstrated on hind-limb joint angles of 21 Labrador Retrievers without and with cranial cruciate ligament disease. Results were compared with peak difference analysis previously performed on these subjects. All points in the gait cycle where symmetry deviations were significantly affected by cranial cruciate ligament disease (via pointwise t tests) were defined as regions of deviation from symmetry. Discriminant function analysis was used to consider single subjects and validate that these regions were truly areas of difference between groups. Regions of deviation encompassed previously determined significant peak differences, while extending analysis to additional areas of asymmetry. Discriminant function analysis suggested that the region of deviation method is a viable approach for distinguishing motion pattern differences. This enhanced method may help researchers better understand the mechanisms behind lameness and compensation.

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Robert H. Wellmon, Dawn T. Gulick, Mark L. Paterson and Colleen N. Gulick

Context:

Smartphones are being used in a variety of practice settings to measure joint range of motion (ROM). A number of factors can affect the validity of the measurements generated. However, there are no studies examining smartphone-based goniometer applications focusing on measurement variability and error arising from the electromechanical properties of the device being used.

Objective:

To examine the concurrent validity and interrater reliability of 2 goniometric mobile applications (Goniometer Records, Goniometer Pro), an inclinometer, and a universal goniometer (UG).

Design:

Nonexperimental, descriptive validation study.

Setting:

University laboratory.

Participants:

3 physical therapists having an average of 25 y of experience.

Main Outcome Measures:

Three standardized angles (acute, right, obtuse) were constructed to replicate the movement of a hinge joint in the human body. Angular changes were measured and compared across 3 raters who used 3 different devices (UG, inclinometer, and 2 goniometric apps installed on 3 different smartphones: Apple iPhone 5, LG Android, and Samsung SIII Android). Intraclass correlation coefficients (ICCs) and Bland-Altman plots were used to examine interrater reliability and concurrent validity.

Results:

Interrater reliability for each of the smartphone apps, inclinometer and UG were excellent (ICC = .995–1.000). Concurrent validity was also good (ICC = .998–.999). Based on the Bland-Altman plots, the means of the differences between the devices were low (range = –0.4° to 1.2°).

Conclusions:

This study identifies the error inherent in measurement that is independent of patient factors and due to the smartphone, the installed apps, and examiner skill. Less than 2° of measurement variability was attributable to those factors alone. The data suggest that 3 smartphones with the 2 installed apps are a viable substitute for using a UG or an inclinometer when measuring angular changes that typically occur when examining ROM and demonstrate the capacity of multiple examiners to accurately use smartphone-based goniometers.

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James R. Rosemeyer, Bradley T. Hayes, Craig L. Switzler and Charlie A. Hicks-Little

Context:

Core stability has been shown to affect lower-extremity motion, but activation of the core has also been observed just before movements of the upper extremity. However, there is limited evidence regarding the effects that core musculature has on upper-extremity strength.

Objective:

To determine the effects of core fatigue on maximal shoulder strength.

Design:

Crossover study.

Setting:

Sports-medicine research laboratory.

Participants:

23 participants (15 male and 8 female, age 21.3 ± 2.5 y, height 174.5 ± 10.3 cm, weight 71.3 ± 12.0 kg).

Intervention:

All participants performed maximal voluntary isometric contractions in 3 different planes (sagittal, frontal, transverse) of shoulder-joint motion. A core-fatiguing protocol was conducted, and the same 3 shoulder-strength tests were repeated and compared with the initial measurements.

Main Outcome Measures:

Strength measures were recorded in kilograms with a dynamometer.

Results:

Results showed a significant decrease in strength in the frontal (−0.56 ± 1.06 kg, P = .020) and transverse (−0.89 ± 1.49 kg, P = .012) planes but not in the sagittal plane (−0.20 ± 0.98 kg, P > .05). Furthermore, regardless of the specific strength test measured, results revealed that the 1st (−7.05% ± 11.65%, P = .012) and 2nd (−5.71% ± 12.03%, P = .042) strength-test measurements after the fatiguing protocol were significantly decreased, while the 3rd strength-test measurement (−4.19% ± 12.48%, P = .140) did not show statistical significance.

Conclusion:

These results indicate that decrease in core stability may have an influence on shoulder strength. The literature suggests that the core is designed for endurance, and this study helps validate its recovery properties. Further research is needed to determine the significance of this effect and how injury rates coincide.

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Paul F. Greene, Christopher J. Durall and Thomas W. Kernozek

Context:

A torso-elevated side support (TESS) has previously been described for measuring endurance of the lateral trunk muscles. In some individuals, however, TESS performance may be hindered by upper extremity pain or fatigue. For this reason a novel test, the feet-elevated side-support test (FESS), was examined.

Objective:

To determine intersession reliability of a FESS and a TESS on the left and right sides using a single examiner, to evaluate the relationship between tests, and to compare reasons for test termination.

Design:

Nonexperimental prospective repeated measures.

Setting:

University laboratory.

Participants:

A convenience sample of 60 healthy participants from a university community (17 men, 43 women; age 21.1 ± 2.2 y; height 169.9 ± 9.5 cm; weight 67.1 ± 11.9 kg).

Results:

Intraclass correlation coefficient between 3 testing sessions = .87 with right FESS, .86 with left FESS, .78 with right TESS, and .91 with left TESS. Pearson correlation coefficients ranged from .59 (between left FESS and left TESS in women) to .75 (between left FESS and left TESS in men). Upper extremity pain or fatigue was the reason given for test termination in 42.5% of participants during the TESS and 5.0% during the FESS (P = .000, Fisher exact test).

Conclusions:

FESS and TESS had comparable intersession reliability by the same evaluator. Moderate to high correlations were found between FESS and TESS scores, suggesting that the tests assess similar qualities. Far fewer participants terminated the FESS because of upper extremity pain or fatigue. Thus, the FESS may be a suitable alternative to the previously validated TESS, particularly for individuals with upper extremity pain or weakness.