Development and cross-validation of a circumference-based predictive equation to estimate body fat in an active population.

Objective: The U.S. Army uses sex-specific circumference-based prediction equations to estimate percent body fat (%BF) to evaluate adherence to body composition standards. The equations are periodically evaluated to ensure that they continue to accurately assess %BF in a diverse population. The objective of this study was to develop and validate alternative field expedient equations that may improve upon the current Army Regulation (AR) body fat (%BF) equations. Methods: Body size and composition were evaluated in a representatively sampled cohort of 1904 active-duty Soldiers (1261 Males, 643 Females), using dual-energy X-ray absorptiometry (%BFDXA), and circumferences obtained with 3D imaging and manual measurements. Sex stratified linear prediction equations for %BF were constructed using internal cross validation with %BFDXA as the criterion measure. Prediction equations were evaluated for accuracy and precision using root mean squared error, bias, and intraclass correlations. Equations were externally validated in a convenient sample of 1073 Soldiers. Results: Three new equations were developed using one to three circumference sites. The predictive values of waist, abdomen, hip circumference, weight and height were evaluated. Changing from a 3-site model to a 1-site model had minimal impact on measurements of model accuracy and performance. Male-specific equations demonstrated larger gains in accuracy, whereas female-specific equations resulted in minor improvements in accuracy compared to existing AR equations. Equations performed similarly in the second external validation cohort. Conclusions: The equations developed improved upon the current AR equation while demonstrating robust and consistent results within an external population. The 1-site waist circumference-based equation utilized the abdominal measurement, which aligns with associated obesity related health outcomes. This could be used to identify individuals at risk for negative health outcomes for earlier intervention.

Rapid adjustments to autonomic control of cardiac rhythm at the onset of isometric exercise in healthy young adults.

Sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) influences on cardiac rhythm at the onset of exercise, a time of rapid autonomic adjustments, are clinically important areas of investigation. Continuous wavelet transform (CWT) involves time-frequency-based heart rate variability (HRV) analysis allowing investigation of autonomic influences on cardiac rhythm during short durations of exercise. Therefore, the purpose of this study was to characterize SNS and PNS influences on cardiac rhythm at the onset of isometric exercise in healthy young adults. CWT analysis was retrospectively applied to R-R interval data (electrocardiogram) previously collected from 14 healthy young adults (26 ± 2 years) who performed 30-s, one-legged, isometric, calf exercise at 70% maximal voluntary contraction (MVC; 70% MVC trial) or rested (0% MVC trial). Absolute and normalized low-frequency (aLF, nLF; 0.04-0.15 Hz) and high-frequency (aHF, nHF; 0.15-0.4 Hz) bands and LF/HF were used to analyze one 30-s baseline period and six 5-s time windows during the 30-s exercise (70% MVC) or rest (0% MVC). Statistical analysis involved two-way analysis of variance with post-hoc analysis. aHF, aLF, LF/HF, nHF, and nLF displayed a trial-time interaction (all p ≤ 0.027). In the 70% compared to the 0% MVC trial, aHF and nHF were lower after 5-30 s (all p ≤ 0.040), aLF was lower after 20-30 s (all p ≤ 0.011) and LF/HF and nLF were higher after 5-20 s (all p ≤ 0.045). These results indicate the reduction of the PNS influence on cardiac rhythm begins sooner than the augmentation of the SNS influence at the onset of isometric exercise in healthy young adults.

Biomechanical Changes Following Knee Arthroplasty During Sit-To-Stand Transfers: Systematic Review.

BACKGROUND: Knee arthroplasty (KA) is a common and effective surgical procedure that allows patients with knee osteoarthritis to restore functional ability and relieve pain. Sit-to-stand is a common demanding task during activities of daily living and is performed more than 50 times per day. The purpose of this systematic review is to obtain a comprehensive understanding of biomechanical changes during sit-to-stand transfers following KA. METHODS: Relevant articles were selected through MEDLINE (PubMed), Scopus, Embrace, and Web of Science. Articles were included if they met the following inclusion criteria: (1) underwent KA without restriction on the arthroplasty design, (2) involve kinematic, kinetic, or muscle activity variables as the primary outcome measure, (3) evaluated sit-to-stand, and (4) were written in English. RESULTS: A total of 13 articles were included in the current systematic review. The KA group exhibited altered movement patterns as compared to healthy controls. Considering the time course of recovery, improvement in knee joint kinematics was found up to 2 years but kinetic changes indicate intensified contralateral limb loading. For comparisons for limbs, limb differences were apparent, but those differences were resolved by 1 year. CONCLUSION: Despite the inevitable changes in kinematics, kinetics, and muscle activity in sit-to-stand since KA, it appears to be important to restore quadriceps strength for the operative limb in order to minimize risk for subsequent joint problems.