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Lauren C. Benson, Stephen C. Cobb, Allison S. Hyngstrom, Kevin G. Keenan, Jake Luo and Kristian M. O’Connor

clearance throughout swing for people with a variety of walking patterns, and especially those at risk for falling, is warranted. A principal components analysis (PCA) approach to quantifying foot clearance and foot clearance variability may resolve these issues. PCA can be used to identify modes of

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Dan Weaving, Clive Beggs, Nicholas Dalton-Barron, Ben Jones and Grant Abt

insights communicated to coaches. In this regard, the use of dimension reduction techniques, such as principal component analysis (PCA) 11 , 19 and single value decomposition (SVD), 20 are gaining popularity within sports performance research. For example, PCA and SVD have been used in studies examining

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Igor Ramathur Telles Jesus, Roger Gomes Tavares Mello and Jurandir Nadal

During muscle fatigue analysis some standard indexes are calculated from the surface electromyogram (EMG) as root mean square value (RMS), mean (Fmean), and median power frequency (Fmedian). However, these parameters present limitations and principal component analysis (PCA) appears to be an adequate alternative. In this context, we propose two indexes based on PCA to enhance the quantitative muscle fatigue analysis during cyclical contractions. Signals of vastus lateralis muscle were collected during a maximal exercise test. Twenty-four subjects performed the test starting at 12.5 W power output with increments of 12.5 W⋅min–1, maintaining cadence of 50 rpm until voluntary exhaustion. The epochs of myoelectric activation were identified and used to estimate the power spectra. PCA was then applied to the power spectra of each subject. The standard (ST) and Euclidean (ED) distances were employed to estimate the alteration occurred due to fatigue. For comparison, the standard indexes were calculated. ST, ED, and RMS value were adequate for muscle fatigue analysis. Among these parameters, ST was more sensitive with higher effect size. Moreover, the Fmean and Fmedian were not sensitive to fatigue. The proposed method based on PCA of EMG in frequency domain allowed producing fatigue indexes suitable for cyclical contractions.

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Grant E. Norte, Jay N. Hertel, Susan A. Saliba, David R. Diduch and Joseph M. Hart

assessment program, we aim to identify tests that provide the most meaningful information about a population of interest. Principal component analysis (PCA) is an analytical technique that can help in this regard by reducing the dimensionality of a larger set of measures to provide a clearer interpretation

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Dan Weaving, Nicholas E. Dalton, Christopher Black, Joshua Darrall-Jones, Padraic J. Phibbs, Michael Gray, Ben Jones and Gregory A.B. Roe

translate this information into actionable manipulation of the training process. 5 , 18 One such capable approach is principal component analysis (PCA), which attempts to explain the maximal amount of information (ie, variance) within a data set that consists of multiple variables, such as those often found

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Thomas G. Almonroeder, Lauren C. Benson and Kristian M. O’Connor

The mechanism of action of a foot orthotic is poorly understood. The purpose of this study was to use principal components analysis (PCA) to analyze the effects of a prefabricated foot orthotic on frontal plane knee and ankle mechanics during running. Thirty-one healthy subjects performed running trials with and without a foot orthotic and PCA was performed on the knee and ankle joint angles and moments to identify the dominant modes of variation. MANOVAs were conducted on the retained principal components of each waveform and dependent t tests (P < .05) were performed in the case of significance. Mechanics of the ankle were not affected by the foot orthotic. However, mechanics of the knee were significantly altered as subjects demonstrated an increase in the magnitude of the knee abduction moment waveform in an orthotic condition. Subjects also demonstrated a significant shift in the timing of the knee abduction moment waveform toward later in the stance phase in the orthotic condition. These orthotic effects were not related to subject’s foot mobility, measured using the navicular drop test. The mechanism of action of a foot orthotic may be related to their effect on the timing of frontal plane knee loading.

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Lauren C. Benson and Kristian M. O’Connor

About half of all runners sustain a running-related injury every year. Exertion may contribute to risk of injury by altering joint mechanics. The purpose of this study was to examine the effects of exertion on runners’ joint mechanics using principal component analysis (PCA). Three-dimensional motion analysis of the lower extremity was performed on 16 healthy female runners before and after their typical training run. PCA was used to determine exertion-related changes in joint mechanics at the ankle, knee, and hip. Statistical significance for repeated-measures MANOVA of the retained principal components at each joint and plane of motion was at P < .05. Exercise effects were identified at the ankle (greater rate of eversion [PC2: P = .027], and decreased plantar flexion moment [overall: P = .044] and external rotation moment [PC3: P = .003]), knee (increased adduction [overall: P = .044] and internal rotation [PC3: P = .034], and decreased abduction moment [overall: P = .045]), and hip (increased internal rotation [PC1: P = .013] and range of mid- to late-stance rotation [PC2: P = .009], and decreased internal rotation moment [PC1: P = .001]). The observed changes in running mechanics reflect a gait profile that is often linked to running injury. The effects of more strenuous activity may result in mechanics that present an even greater risk for injury.

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Kristian M. O’Connor, Carl Johnson and Lauren C. Benson

The function of the hamstrings in protecting the ACL is not fully understood. The purpose of this study was to determine how landing knee mechanics were affected by hamstrings fatigue, analyzed with principal components analysis (PCA). Knee joint mechanics were collected during single-leg stride landings that were followed by lateral and vertical jumps. An isokinetic fatigue protocol was employed to reduce hamstrings strength by 75% at the cessation of the exercise protocol. On the landing test day, participants performed the stride landing maneuvers before and after the fatigue protocol. PCA was performed on the landing knee joint angle, moment, and power waveforms, and MANOVAs were conducted on the retained PCs of each waveform (P < .05). On the strength test day, hamstrings strength recovery was assessed with an identical fatigue protocol followed by strength assessment ~75 s after the cessation of exercise. Pre- and postexercise hamstrings strength on this day was assessed with a dependent t test (P < .05). The hamstrings strength remained significantly reduced by ~8% postexercise (75 s). For stride landings followed by vertical jumps, there were significantly reduced knee flexion angles, extensor moments, and energy absorption. This was indicative of a stiffer landing strategy postfatigue, which has been associated with increased ACL loading.

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Nancy D. Groh and Greggory M. Hundt

, IL, USA). The data was transferred into the program and a confirmatory factor analysis was performed using principal component analysis (PCA) to evaluate the dimensionality of the scale. All items underwent PCA with varimax rotation. Factors with an eigenvalue above 1.00 were kept. Cronbach alpha was

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Sarahjane Belton, Gavin Breslin, Stephen Shannon, Wesley O’Brien, Ben Fitzpatrick, Tandy Haughey, Fiona Chambers, Danielle Powell, Darryl McCullagh and Deirdre Brennan

on the patterns of PA participation of younger children during specific time periods is needed. 7 A number of international studies are worthy of note in this regard and are discussed below. Using principal components analysis (PCA), Trost et al 8 found that adolescents (12–16 y) weekday and