Exoskeletons Improve Locomotion Economy by Reducing Active Muscle Volume Exoskeletons that improve locomotion economy are typically engineered to reduce users’ limb-joint mechanical work or moments. Yet, limb-joint dynamics do not reflect muscle dynamics, which dictate whole-body metabolic energy expenditure. Here, we hypothesize that exoskeletons primarily reduce user metabolic energy expenditure across locomotion conditions by reducing active muscle volume. Corresponding Author: Owen N. Beck, Georgia Institute of Technology, School of Mechanical Engineering, 455 Callaway Manufacturing Research Center Building, 813 Ferst Dr NW, Atlanta, GA 30332, E-mail: obeck@gatech.edu Funding: Funding for this research was provided by grants to G.S. Sawicki from the U.S. Army Natick Soldier Research, Development and Engineering Center (W911QY18C0140) and the National Robotics Initiative via the National Institute of Nursing Research of the National Institutes of Health (R01NR014756). The content is solely the responsibility of the authors and does not necessarily represent the official views of the listed funding agencies. Conflicts of Interest: None © 2019 American College of Sports Medicine

Perspectives for Progress - A Framework to Evaluate Devices that Assess Physical Behavior Body-worn devices that estimate physical behavior have tremendous potential to address key research gaps. However, there is no consensus on how devices and processing methods should be developed and evaluated, resulting in large differences in summary estimates and confusion for end-users. We propose a phase-based framework for developing and evaluating devices that emphasizes robust validation studies in naturalistic conditions. Corresponding author: Patty S. Freedson, Professor Emerita, Department of Kinesiology, University of Massachusetts, Amherst, 10570 Carena Circle, Fort Myers, FL 33913, psf@kin.umass.edu; 413-695-1415 Funding Disclosure: Strath supported by R01CA215318; Staudenmayer supported by R01DK110148, R01CA215318 Conflicts of interest: Kate Lyden is a consultant for PAL Technologies, Inc. © 2019 American College of Sports Medicine

Overuse Injury: The Result of Pathologically Altered Myofascial Force Transmission? Overuse injuries are suggested to result from repetitive micro-damage eliciting pain in the affected tissue. Therapy commonly focuses on the area of symptom localization; however, such approach may oversimplify the true etiopathology. This review hypothesizes that the development of some sports-related soft tissue disorders, such as plantar fasciitis or lumbago, is promoted by pathologically altered force transmission from anatomically connected structures. Corresponding author: Jan Wilke, Department of Sports Medicine, Goethe University Frankfurt/Main, Germany, Ginnheimer Landstraße 39, D-60487 Frankfurt am Main, Fax: +49(0)69 798 24582, Phone: +49(0)69 798 24588. Email: wilke@sport.uni-frankfurt.de None of the authors received funding for this work and there was no conflict of interest. © 2019 American College of Sports Medicine

Amplified Neural Plasticity and Strength After Stroke Following stroke, sensorimotor brain networks and descending regulation are compromised but spinal interlimb neural connections remain morphologically intact. After cross-education strength and locomotion training, amplified neural plasticity and functional responses are observed in chronic stroke compared to neurologically intact participants. We hypothesize that post-stroke neuroplasticity is amplified because of the involvement of interlimb neural connections that persist from our quadrupedal ancestry. Corresponding Author: E. Paul Zehr, Rehabilitation Neuroscience Laboratory, PO Box 3010 STN CSC, University of Victoria, Victoria, BC Canada, V8W 3P1, pzehr@uvic.ca; 1-250-721-8379 Acknowledgments: This research was supported by funding to Dr. E. Paul Zehr from the Heart and Stroke Foundation (British Columbia and Yukon) and the Natural Sciences and Engineering Research Council (NSERC) of Canada. Declaration of Interest: The authors declare that they have no conflict of interest regarding the publication of this paper. This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. © 2019 American College of Sports Medicine

Transcallosal Control of Bilateral Actions The corpus callosum is an important neural structure for controlling and coordinating bilateral movements of the upper limbs; however, there remains a substantial lack of knowledge regarding its association with lower limb control. We argue that transcallosal structure is an integral neural mechanism underlying control of the lower limbs and callosal degradation is a key contributor to mobility declines. Corresponding Author: Brett W. Fling, Ph.D., Assistant Professor – Health and Exercise Science Department, Assistant Professor – Molecular, Cellular & Integrative Neurosciences Program, Colorado State University, (970) 491-3451; Brett.Fling@colostate.edu Disclosure of funding: This work was supported in part by funding from a National Multiple Sclerosis Society Pilot Research Grant (PP-1708-29077) and a David Mahoney Neuroimaging Grant from the Dana Foundation. Conflict of interest: The authors have no conflicts to report. © 2019 American College of Sports Medicine

Macrophage Regulation of Muscle Regrowth from Disuse in Aging Skeletal muscle immune cells, such as macrophages, are necessary for proper regrowth following muscle disuse. We suggest that the important role of macrophages concerning muscle regrowth following disuse is divergent compared to young mice (i.e. dysregulated) during the recovery period. Modulation of macrophages may be a promising future therapeutic target to enhance the impaired muscle growth during recovery from disuse in older adults. Corresponding author: M. J. Drummond, University of Utah, Department of Physical Therapy and Athletic Training, 520 Wakara Way, Salt Lake City, UT 84108-1213, USA. Email: micah.drummond@hsc.utah.edu Funding: This work was supported by the National Institute of Aging (R01AG050781, R21AG042699), the National Center for Complementary and Integrative Health (R01AT009268) and the National Institute of Arthritis and Musculoskeletal and Skin Diseases (F32AR072481). Authors declare no conflict of interest © 2019 American College of Sports Medicine

Perspectives for Progress - Female Athlete Triad and Relative Energy Deficiency in Sport: A Focus on Scientific Rigor We examine the scientific evidence supporting The Female Athlete Triad and Relative Energy in Sport (RED-S) syndromes. More research is necessary to advance the understanding of both syndromes; however, it is premature to consider RED-S as an evidence-based syndrome. Future research should specifically define RED-S components, determine its clinical relevance, and establish the causality of relative energy deficiency on RED-S outcomes. Address for Correspondence: Nancy I. Williams, Sc.D., FACSM, FNAK, Professor and Head, Department of Kinesiology, Co-Director, Women's Health and Exercise Laboratory, The Pennsylvania State University, 276 Recreation Building, University Park, PA 16802. Email: niw1@psu.edu; Phone: 814-863-1163 Conflicts of interest; disclosure of funding: none © 2019 American College of Sports Medicine

Carbohydrate Availability as a Regulator of Energy Balance with Exercise We explore the novel hypothesis that carbohydrate availability is involved in the regulation of energy balance with exercise, via hormonal and neural signals. We propose that carbohydrate availability could play a direct mechanistic role and partially explain previously-documented relationships between a more active lifestyle and tighter control of energy balance. Corresponding author: Javier T. Gonzalez, Department for Health, University of Bath, BA2 7AY, United Kingdom. Tel: 0(+44) 1225 38 5518; E-mail: J.T.Gonzalez@bath.ac.uk, ORCID ID: 0000-0002-9939-0074. Funding: No funding was received for the preparation of this manuscript. Conflicts of interest: J.T.G. has received research funding and/or has acted as a consultant for Arla Foods Ingredients, Lucozade Ribena Suntory, Kenniscentrum Suiker and Voeding, and PepsiCo. J.A.B. has received research funding and/or has acted as a consultant for GlaxoSmithKline, Lucozade Ribena Suntory, Kellogg’s, Nestlé and PepsiCo and is a scientific advisor to the International Life Sciences Institute (ILSI). D.T. has received funding and acted as a consultant for Unilever. © 2019 American College of Sports Medicine