Higher levels of physical activity are unquestionably important for maintaining good physical and cognitive health. Surprisingly, however, we know relatively little about the amount of energy United States (U.S.) adults expend in physically active behaviors each day. 

One way to estimate the amount of energy expended in physical activity is to calculate one’s physical activity level (PAL) as the ratio of total energy expenditure to resting metabolic rate. Higher PALs have been associated with lower mortality risk in older adults, and they are often used to classify activity levels when calculating daily energy requirements. 

A PAL of < 1.4 is consistent with engaging only in basic activities of daily living and is classified as “inactive.” A PAL of > 1.6 is classified as “physically active.” Extreme PALs have been measured for elite riders during multiday cycling races (PAL > 2.5) and for hunter-gatherers in Tanzania (PAL ~2.0). 

Surprisingly, we were unaware of PAL estimates from representative samples of U.S. adults, or how much energy they expend in physically active behaviors on a given day. 

Our study, published in the May 2023 issue of Medicine & Science in Sports & Exercise®, addressed this gap by conducting a nationwide survey of 2,640 U.S. adults (20-75 years of age). The study used a self-administered previous-day recall instrument, Activities Completed over Time in 24 Hours (ACT24), to estimate PALs, and the results are a snapshot of PALs in U.S. adults on a given day. (The ACT24 is accurate for estimating PAL values in comparison to the doubly labeled water technique at the population level and is a freely available tool for researchers and educators to use in their work.) 

In our study, U.S. adults reported an average PAL of 1.63, and nearly 40% reported being “physically active” (PAL ≥ 1.6) on a given day. Men reported higher PALs (1.67) than women (1.59), and adults who were 65-74 years old reported lower PALs (1.58) than adults 20-34 years of age (1.66). Household and occupational activities were the behavioral drivers of higher PALs in the population, while exercise and recreational activities were instead minor contributors. 

The balance of time spent sedentary and physically active was a clear driver of higher PALs. Adults who were “physically active” spent 50% of their waking day sitting (8.0 hours/day) and the remaining time engaged in light-, moderate- or vigorous-intensity physical activity, for a total of 8.3 hours/day in daily activity. In contrast, “inactive” adults spent 81% of their waking day sedentary (12.1 hours/day). 

Our results provide the first estimates of physical activity energy expenditure in a representative sample of U.S. adults and describe the amount of sedentary time and types of physical activity that are associated with higher PALs. 

So, get up and go find a good PAL to be active with whenever you can. Nearly 40% of U.S. adult appear to be physically active on a given day — find your PAL and join them!  

We hope our findings spur further research in these areas. 

Charles E. Matthews, Ph.D., is a physical activity epidemiologist and senior investigator in the Division of Cancer Epidemiology and Genetics within the Metabolic Epidemiology Branch at the National Cancer Institute. His research focuses on understanding the health benefits of physical activity, the adverse health effects of sedentary time, and works to develop new, “better” methods to measure these behaviors in large epidemiologic studies. Connect with Dr. Matthews: charles.matthews2@nih.gov. 

Pedro Saint-Maurice, Ph.D., is a physical activity and sleep epidemiologist and research fellow in the Division of Cancer Epidemiology and Genetics within the Metabolic Epidemiology Branch at the National Cancer Institute. His research examines how profiles of sleep and ambulatory movement throughout the day are associated with cancer risk and mortality. Connect with Dr. Saint-Maurice: pedro.saintmaurice@nih.gov. 

Viewpoints presented in ACSM Bulletin commentaries reflect opinions of the authors and do not necessarily represent positions or policies of ACSM. Active Voice authors who have received financial or other considerations from a commercial entity associated with their topic must disclose such relationships at the time they accept an invitation to write for the ACSM Bulletin. 

It is a pleasure to serve as the ACSM topical representative for Skeletal Muscle, Bone, and Connective Tissue. I look forward to seeing everyone this year in beautiful Denver, CO. The 2023 ACSM Annual Meeting will feature a number of outstanding sessions on the interactions between exercise, skeletal muscle, bone, and connective tissue health. There are three sessions that I think will be of particular interest to conference attendees. The first is a highlighted symposium entitled, “Beyond the Weight room: The Importance of Skeletal Muscle in Health and Disease”. This session is scheduled for Thursday June 1, 2023 from 1:30 p.m. - 3:30 p.m.  The symposium will be chaired by Blake Rasmussen, Ph.D. from the University of Texas Medical Branch, and features two other outstanding speakers; Marni Boppart, Sc.D. FACSM from the University of Illinois at Urbana-Champaign, and Nicholas Greene, Ph.D., FACSM from the University of Arkansas. This session will discuss current research on the transcriptomic and metabolic response to early-phase recovery from skeletal muscle disuse in men and women, highlight the contribution of extracellular vesicles on skeletal muscle recovery following immobilization, and discuss the roles of biologic sex and altered muscle metabolism in cancer-induced cachexia. 

The second symposium I would like to highlight is entitled, “Mechanisms and Considerations for Musculoskeletal Anabolic Resistance in Healthy Adults under Physiological Stress”. This session is scheduled for Wednesday May 31, 2023 from 3:45 p.m. - 5:45 p.m. and features four outstanding scientists. Speakers include Stefan Pasiakos, Ph.D., FACSCM, Jess Gwin, Ph.D., and Julie Hughes, PhD., FACSM from the U.S. Army Research Institute of Environmental Medicine, and Kristin Popp, Ph.D. from Massachusetts General Hospital. This session will highlight the mechanisms contributing to musculoskeletal anabolic resistance in healthy adults exposed to physiological stress in sport and during military training, and will provide considerations for targeted exercise, nutrition, and pharmacologic interventions to overcome musculoskeletal anabolic resistance and promote tissue growth under stress. 

The final symposium that I would like to highlight is entitled, “Oxygen and Striated Muscle Function” and features four of the leading experts on skeletal muscle metabolism and health. The session is scheduled for Friday June 2, 2023 from 1:30 p.m. - 3:30 p.m. Speakers include, Mike Hogan, Ph.D., FACSM from the University of California, San Diego, L. Bruce Gladden, Ph.D., FACSM from Auburn University, David Poole, Ph.D., FACSM from Kansas State University, Sarah Kuzmiak-Glancy, Ph.D., from the University of Maryland, and Anni Vanhatalo, Ph.D., FACSM from the University of Exeter. This session will recount and discuss: a) oxygen and skeletal muscle function, b) oxygen and lactate accumulation and oxygen uptake on-kinetics, c) oxygen and cardiac muscle function, and d) oxygen and athletic performance. Given the importance of oxygen availability in aging and many chronic diseased states, this session will appeal to a broad audience from basic scientists and those with applied interests. 

In addition to these sessions there are five excellent Tutorial Lectures throughout the week, an oral free communication session on “Skeletal Muscle and Resistance Training” (Friday 9:30 a.m.), a thematic poster session on “Skeletal Muscle in Health and Disease” (Wednesday 9:30 a.m.), and several poster sessions spread throughout the week. 

Learn more about the other featured sessions in Skeletal Muscle, Bone, and Connective Tissue and the many other sessions that will be presented at the 2023 ACSM Annual Meeting here.

Join Us at the ACSM Annual Meeting

Gordon Fisher, Ph.D., FACSM is a Professor at the University of Alabama at Birmingham (UAB) Department of Human Studies, and holds Senior Scientist positions in the Center for Exercise Medicine, Nutrition and Obesity Research Center, and the Diabetes Research Center at UAB. 

The liver plays a crucial role in numerous metabolic processes necessary to leading a healthy life, including those essential to metabolism, such as storing energy and regulating blood sugar. Exercise has been shown to improve liver health by reducing fat in the liver, improving insulin sensitivity, reducing inflammation, boosting the immune system and improving mental health. The great news here is that it doesn’t matter what type of exercise you choose to perform — any exercise is beneficial for the liver, and exercise prescription can be tailored to meet individual needs and preferences. That means that as an exercise professional, you can incorporate aerobic training, resistance training, high-intensity interval training (HIIT), low-impact HIIT and more. Several studies have even looked at the impact of yoga and Pilates on liver health, and although the results are mixed, in the right setting these may also provide benefit. 

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of liver disease and, in parallel with the obesity pandemic, now affects one out of three adults worldwide. NAFLD occurs when there is abnormal accumulation of fat in the liver not caused by alcohol consumption. NAFLD has been linked to obesity, insulin resistance and physical inactivity, and it can progress to a more severe form of liver disease called nonalcoholic steatohepatitis (NASH). Over time, NASH can lead to cirrhosis or liver cancer, which in some cases may require a lifesaving liver transplantation. 

While many factors lead to the development of NAFLD, physical inactivity plays a major role. In light of this, the American College of Sports Medicine® (ACSM) held a roundtable discussion on NAFLD and physical activity in summer 2022. The roundtable brought together experts in the fields of hepatology, exercise physiology and behavioral health. The roundtable discussion highlighted the importance of physical activity in the prevention and treatment of NAFLD, finding that patients with NAFLD who exercise regularly can expect a number of benefits to liver health, including a reduction in liver fat accumulation, improved histologic disease activity, favorably changing body composition, improved glycemic control and lowered cardiovascular risk. Importantly, many of these findings can be expected without significant weight loss. 

The roundtable group reached a consensus, recommending that individuals with NAFLD should engage in regular physical activity, ideally for at least 150 minutes per week of moderate-intensity aerobic exercise, such as brisk walking, or 75 minutes of vigorous-intensity aerobic exercise, such as jogging or cycling. Resistance training can be considered two days a week in order to improve muscle mass and strength. The experts also discussed the potential benefits of HIIT in individuals with NAFLD, and preliminary data suggests HIIT is as effective as either moderate- or vigorous-intensity aerobic exercise training. The roundtable faculty also acknowledged that individuals with NAFLD face many barriers to completing regular physical activity, including fatigue, joint pain and a lack of time. Exercise prescriptions that include a gradual progression of exercise, starting with low-impact activities and incorporating rest periods, may be beneficial to help remove these barriers and improve adherence. 

Exercise is a great way to address NAFLD and its associated metabolic conditions, including obesity, diabetes, hypertension and more. By reducing liver fat and improving overall health, exercise may help prevent complications of liver disease and can improve quality of life. All patients with NAFLD should be encouraged to be as physically active as they can be! 

Dr. Jonathan Stine is an Associate Professor of Medicine and Public Health Science at Penn State. As an internationally recognized liver expert with a research and clinical focus on nonalcoholic fatty liver disease (NAFLD) and exercise, he has authored more than 90 peer-reviewed papers, including multinational consensus guidelines. Stine is the recipient of multiple research grants and awards from the American Association for the Study of Liver Diseases, American Cancer Society and National Institutes of Health. Dr. Stine is the NAFLD consultant to the American College of Sports Medicine’s Exercise is Medicine initiative and recently co-chaired the International Roundtable on NAFLD and Physical Activity for ACSM. Dr. Stine serves as the Fatty Liver Program Director as well as the Liver Center Research Director for Penn State.  

The 2023 ACSM Annual Meeting is packed with more Biomechanics and Neural Control of Movement content than ever before. This year, the Biomechanics and Neural Control of Movement topical area has seven special sessions (i.e., symposia and tutorial lectures), additional content being offered exclusively online, and an exciting group of interdisciplinary topics being presented through the free communication sessions.  

The free communication portion of the Biomechanics and Neural Control of Movement content will begin with a podium session on “Parkinson's Disease” (Wednesday May 31, 9:30 – 11:30 a.m.) and poster sessions on “Baseball & Softball Biomechanics” and “Methods & Alternative Measurement Techniques” Wednesday May 31, 9:30 a.m. – 12:30 p.m.). Other free communication sessions include: a thematic poster session titled, “Arthritis” (Friday, June 2, 3:45 – 5:45 p.m.) which will include research on arthritis and osteoarthritis;  a thematic poster session titled, “Biomechanical Considerations for ACL Injury & Rehabilitation” (Thursday June 1, 9:30 – 11:30 a.m.); a rapid-fire podium session titled, “Special Topics in Gait Biomechanics” (Thursday June 1, 3:45 – 5:45 p.m.); a thematic poster session on “Running Injury” (Friday June 2, 1:30 – 3:30 p.m.); and poster sessions dedicated to running mechanics, concussions, military health biomechanics, aging, ankle instability, jumping & landing biomechanics, among other great topics. 

Our showcase highlighted symposium this year is “Moving & Shaking: Biomechanical and Motor Considerations for Cancer Treatment and Rehab” (Thursday June 1, 1:30 – 3:30 p.m). Presenters include David Lipps, Ph.D. (University of Michigan), Srikant Vallabhajosula, Ph.D. (Elon University), Shane Murphy, Ph.D. (University of Wisconsin, Lacrosse), and Lise Worthen-Chaudhari, PhD, MFA, CMES (Ohio State University) and chaired by Ajit Chaudhari, PhD, FACSM (Ohio State University). This symposium will present the biomechanical and motor effects of cancer and cancer treatment including the effects on neuromuscular tissues and human functional performance. Preliminary data from exercise interventions to improve biomechanical function in cancer patients will be presented and considerations for designing therapeutic interventions that consider movement capabilities of cancer patients and reduce the risk of falls will be discussed. An additional goal of this symposium is to highlight the importance of small, pragmatic trials as critical steppingstones to increase our understanding of the biomechanical challenges facing cancer survivors and our ability to improve exercise and mobility-focused interventions for them. 

The two symposia for the Biomechanics and Neural Control of Movement topical area include:

Wednesday May 31, 1:30 – 3:30 p.m. “Can a Causal Framework Improve the Science and Rehabilitation of the Injured Runner?” presented by Chris Napier, PT, Ph.D. (Simon Fraser University), Rich Willy, PT, Ph.D. (University of Montana, Missoula), Emily Kraus, MD (Stanford University), Shalaya Kipp, MS (University of British Columbia), as well as distance runner and author, Lauren Fleshman. The historical focus on a single factor (e.g., biomechanics, strengthening) has not been effective in the prevention of running-related injuries. This symposium will discuss a causal framework that considers the complexity of injury within the context of the runner and the complex interaction between runner’s biomechanics, applied training loads, energy availability, nutrition, physiology, and psychology. Examining running injuries from this framework may be more insightful in the prevention and treatment of running related injuries than historical approaches. Overall, this proposal aims to present a multi-disciplinary approach, including discussion from the athlete’s perspective, to challenge and improve upon current approaches to the research and care of the injured runner. 

Allison H. Gruber, Ph.D., FACSM, is an Associate Professor of Kinesiology in the Indiana University School of Public Health – Bloomington. She is the Topical Representative for Biomechanics and Neural Control of Movement and a previous chairperson of the ACSM Biomechanics Interest Group. Her research interests include the mechanisms of running-related musculoskeletal injuries, wearable technology, and using advanced analysis techniques to better understand biomechanical signals for gait analysis. Symposia summaries were compiled based on information provided by the submitter.