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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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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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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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Christian A. Clermont, Lauren C. Benson, W. Brent Edwards, Blayne A. Hettinga and Reed Ferber

The purpose of this study was to use wearable technology data to quantify alterations in subject-specific running patterns throughout a marathon race and to determine if runners could be clustered into subgroups based on similar trends in running gait alterations throughout the marathon. Using a wearable sensor, data were collected for cadence, braking, bounce, pelvic rotation, pelvic drop, and ground contact time for 27 runners. A composite index was calculated based on the “typical” data (4–14 km) for each runner and evaluated for 14 individual 2-km sections thereafter to detect “atypical” data (ie, higher indices). A cluster analysis assigned all runners to a subgroup based on similar trends in running alterations. Results indicated that the indices became significantly higher starting at 20 to 22 km. Cluster 1 exhibited lower indices than cluster 2 throughout the marathon, and the only significant difference in characteristics between clusters was that cluster 1 had a lower age–grade performance score than cluster 2. In summary, this study presented a novel method to investigate the effects of fatigue on running biomechanics using wearable technology in a real-world setting. Recreational runners with higher age–grade performance scores had less atypical running patterns throughout the marathon compared with runners with lower age–grade performance scores.

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

Low foot clearance and high variability may be related to falls risk. Foot clearance is often defined as the local minimum in toe height during swing; however, not all strides have this local minimum. The primary purpose of this study was to identify a nondiscrete measure of foot clearance during all strides, and compare discrete and nondiscrete measures in ability to rank individuals on foot clearance and variability. Thirty-five participants (young adults [n = 10], older fallers [n = 10], older nonfallers [n = 10], and stroke survivors [n = 5]) walked overground while lower extremity 3D kinematics were recorded. Principal components analysis (PCA) of the toe height waveform yielded representation of toe height when it was closest to the ground. Spearman’s rank order correlation assessed the association of foot clearance and variability between PCA and discrete variables, including the local minimum. PCA had significant (P < .05) moderate or strong associations with discrete measures of foot clearance and variability. An approximation of the discrete local minimum had a weak association with PCA and other discrete measures of foot clearance. A PCA approach to quantifying foot clearance can be used to identify the behavioral components of toe height when it is closest to the ground, even for strides without a local minimum.

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Robyn F. Madden, Kelly A. Erdman, Jane Shearer, Lawrence L. Spriet, Reed Ferber, Ash T. Kolstad, Jessica L. Bigg, Alexander S.D. Gamble and Lauren C. Benson

Purpose: To determine the effects of low-dose caffeine supplementation (3 mg/kg body mass) consumed 1 h before the experiment on rating of perceived exertion (RPE), skills performance (SP), and physicality in male college ice hockey players. Methods: Using a double-blind, placebo-controlled, randomized crossover experimental design, 15 college ice hockey players participated in SP trials and 14 participated in scrimmage (SC) trials on a total of 4 d, with prescribed ice hockey tasks occurring after a 1-h high-intensity practice. In the SP trials, time to complete and error rate for each drill of the validated Western Hockey League Combines Testing Standard were recorded. Peak head accelerations, trunk contacts, and offensive performance were quantified during the SC trials using accelerometery and video analysis. RPE was assessed in both the SP and SC trials. Results: RPE was significantly greater in the caffeine (11.3 [2.0]) than placebo (9.9 [1.9]) condition postpractice (P = .002), with a trend toward greater RPE in caffeine (16.9 [1.8]) than placebo (15.7 [2.8]) post-SC (P = .05). There was a greater number of peak head accelerations in the caffeine (4.35 [0.24]) than placebo (4.14 [0.24]) condition (P = .028). Performance times, error rate, and RPE were not different between intervention conditions during the SP trials (P > .05). Conclusions: A low dose of caffeine has limited impact on sport-specific skill performance and RPE but may enhance physicality during ice hockey SCs.