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Christopher Joyce, Angus Burnett and Miccal Matthews

No method currently exists to determine the location of the kick point during the golf swing. This study consisted of two phases. In the first phase, the static kick point of 10 drivers (having identical grip and head but fitted with shafts of differing mass and stiffness) was determined by two methods: (1) a visual method used by professional club fitters and (2) an algorithm using 3D locations of markers positioned on the golf club. Using level of agreement statistics, we showed the latter technique was a valid method to determine the location of the static kick point. In phase two, the validated method was used to determine the dynamic kick point during the golf swing. Twelve elite male golfers had three shots analyzed for two drivers fitted with stiff shafts of differing mass (56 g and 78 g). Excellent between-trial reliability was found for dynamic kick point location. Differences were found for dynamic kick point location when compared with static kick point location, as well as between-shaft and within-shaft. These findings have implications for future investigations examining the bending behavior of golf clubs, as well as being useful to examine relationships between properties of the shaft and launch parameters.

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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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Stefan C. Garcia, Jeffrey J. Dueweke and Christopher L. Mendias

Context: Manual isometric muscle testing is a common clinical technique used to assess muscle strength. To provide the most accurate data for the test, the muscle being assessed should be at a length in which it produces maximum force. However, there is tremendous variability in the recommended positions and joint angles used to conduct these tests, with few apparent objective data used to position the joint such that muscle-force production is greatest. Objective: To use validated anatomically and biomechanically based musculoskeletal models to identify the optimal joint positions in which to perform manual isometric testing. Design: In silico analysis. Main outcome measure: The joint position which produces maximum muscle force for 49 major limb and trunk muscles. Results: The optimal joint position for performing a manual isometric test was determined. Conclusion: Using objective anatomical models that take into account the force-length properties of muscles, the authors identified joint positions in which net muscle-force production was predicted to be maximal. This data can help health care providers to better assess muscle function when manual isometric strength tests are performed.

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Andre Filipe Santos-Magalhaes and Karen Hambly


The assessment of physical activity and return to sport and exercise activities is an important component in the overall evaluation of outcome after autologous cartilage implantation (ACI).


To identify the patient-report instruments that are commonly used in the evaluation of physical activity and return to sport after ACI and provide a critical analysis of these instruments from a rehabilitative perspective.

Evidence Acquisition:

A computerized search was performed in January 2013 and repeated in March 2013. Criteria for inclusion required that studies (1) be written in English and published between 1994 and 2013; (2) be clinical studies where knee ACI cartilage repair was the primary treatment, or comparison studies between ACI and other techniques or between different ACI generations; (3) report postoperative physical activity and sport participation outcomes results, and (4) have evidence level of I–III.

Evidence Synthesis:

Twenty-six studies fulfilled the inclusion criteria. Three physical activity scales were identified: the Tegner Activity Scale, Modified Baecke Questionnaire, and Activity Rating Scale. Five knee-specific instruments were identified: the Lysholm Knee Function Scale, International Knee Documentation Committee Score Subjective Form, Knee Injury and Osteoarthritis Outcome Score, Modified Cincinnati Knee Score, and Stanmore-Bentley Functional Score.


Considerable heterogeneity exists in the reporting of physical activity and sports participation after ACI. Current instruments do not fulfill the rehabilitative needs in the evaluation of physical activity and sports participation. The validated instruments fail in the assessment of frequency, intensity, and duration of sports participation.

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Boris I. Prilutsky

In this response, the major criticisms of the target article are addressed. Terminology from the target article that may have caused some confusion is clarified. In particular, the tasks that have the basic features of muscle coordination, as identified in the target article, have been limited in scope. Anew metabolic optimization criterion suggested by Alexander (2000) is examined for its ability to predict muscle coordination in walking. Issues concerning the validation of muscle force predictions, the rules of muscle coordination, and the role of directional constraints in coordination of two-joint muscles are discussed. It is shown in particular that even in one-joint systems, the forces predicted by the criterion of Crowninshield and Brand (1981) depend upon the muscle moment arms and the physiological cross-sectional areas in much more complex ways than either previously assumed in the target article, or incorrectly derived by Herzog and Ait-Haddou (2000). It is concluded that the criterion of Crowninshield and Brand qualitatively predicts the basic coordination features of the major one- and two-joint muscles in a number of highly skilled, repetitive motor tasks performed by humans under predictable conditions and little demands on stability and accuracy. A possible functional significance of such muscle coordination may be the minimization of perceived effort, muscle fatigue, and/or energy expenditure.

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Sean P. Flanagan and George J. Salem

In the analysis of human movement, researchers often sum individual joint kinetics to obtain a single measure of lower extremity function. The extent to which these summed measures relate to the mechanical objectives of the task has not been formally validated. The criterion validity of these measures was established with comparisons to the mechanical objective of two multiple-joint tasks. For the Work task 18 participants performed a loaded barbell squat using 4 resistances while instrumented for biomechanical analysis. For the Power they performed 2 predetermined amounts of work at both self-selected and fast speeds. Using inverse dynamics techniques, the peak net joint moment (PM) was calculated bilaterally in the sagittal plane at the ankle, knee, and hip and was summed into a single measure. This measure was correlated with the task objectives using simple linear regression. Similar procedures were used for the average net joint moment (AM), peak (PP), and average (AP) net joint moment power, and the net joint moment impulse (IM) and work (IP). For the Work task all 6 measures were significantly correlated with the task objective, but only AM, PM, and IP had correlation coefficients above 0.90. For the Power task, IM was not significantly correlated with the task objective, and only AP had a correlation coefficient above 0.90. These findings indicate that the validity of summing individual kinetic measures depends on both the measure chosen and the mechanical objective of the task.

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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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Jonathon S. Schofield, Eric Parent, Justin Lewicke, Jason P. Carey, Marwan El-Rich and Samer Adeeb

Sit-to-stand transfer is a common prerequisite for many daily tasks. Literature often assumes symmetric behavior across the left and right side. Although this assumption of bilateral symmetry is prominent, few studies have validated this supposition. This pilot study uniquely quantifies peak joint moments and ground reaction forces (GRFs), using a Euclidian norm approach, to evaluate bilateral symmetry and its relation to lower limb motor-dominance during sit to stand in ten healthy males. Peak joint moments and GRFs were determined using a motion capture system and inverse dynamics. This analysis included joint moment contributions from all three body planes (sagittal, coronal, and axial) as well as vertical and shearing GRFs. A paired, one-tailed t test was used, suggesting asymmetrical joint moment development in all three lower extremity joints as well as GRFs (P < .05). Furthermore, using an unpaired two-tailed t test, asymmetry developed during these movements does not appear to be predictable by participants’ lower limb motor-dominance (P < .025). Consequently, when evaluating sit-to-stand it is suggested the effects of asymmetry be considered in the interpretation of data. The absence of a relationship between dominance and asymmetry prevents the suggestion that one side can be tested to infer behavior of the contralateral.

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Laura Seidl, Danijel Tosovic and J. Mark Brown

Whole muscle mechanomyography (MMG) has gained considerable interest in recent years for its ability to noninvasively determine muscle contractile properties (ie, contraction time [Tc], half-relaxation time [1/2Tr], and maximal displacement [Dmax)]). The aim of this study was to evaluate the test-retest reliability of two fairly novel MMG transducers: a laser-displacement sensor (LDS) and contact-displacement sensor (CDS). MMG was conducted on the rectus femoris muscle of 30 healthy individuals on 4 separate occasions. Test-retest reliability was quantified using intraclass correlation coefficients (ICCs). Both sensors were reliable for time-derived parameters Tc (ICCs, 0.85–0.88) and 1/2Tr (0.77–0.89), with Dmax identified as the most reproducible parameter (0.89–0.94). The 2 sensors produced similar Tc and Dmax measures, although significant (P < .05) systematic bias was identified with the CDS recording higher mean values, on average. However, these differences may not be considered clinically significant. The wide limits of agreement identified between 1/2Tr measures (–19.0 ms and 25.2 ms) are considered unreliable from a clinical perspective. Overall, MMG demonstrated good-to-excellent reliability for the assessment of muscle contractile properties with no significant differences identified between sessions, thus further validating its applicability as a noninvasive measure of muscle contractile properties.

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Mario A. DiMattia, Ann L. Livengood, Tim L. Uhl, Carl G. Mattacola and Terry R. Malone


The Trendelenburg and single-leg-squat (SLS) tests are purported measures of hip-abduction strength that have not been previously validated.


To correlate isometric hip-abduction strength to frontal-plane hip motion during an SLS and determine the criterion validity of a clinical-observation-analysis method to grade an SLS against 2-dimensional kinematic analysis.


Single-measure, concurrent validity.


Biodynamics research laboratory.


50 uninjured participants.

Main Outcome Measures:

Hip-abduction strength and hip and knee kinematic data during a Trendelenburg test and an SLS.


A weak, positive correlation between hip-abduction strength and hip-adduction angle was found during both the Trendelenburg (r = .22, P = .13) and the SLS (r = .21, P = .14) tests. The observation-analysis method revealed a low sensitivity, .23, and a higher specificity, .86, when compared with the kinematic data.


The usefulness of the Trendelenburg and SLS test in screening hip-abductor strength in a healthy physically active population is limited. The origin of observable deficits during SLS requires further objective assessment.