Active Voice: Resistance Training May Reduce Cardiovascular Risk
By Paul R. Nagelkirk, Ph.D., FACSM, and Kayla M. Soave, M.S.

Resistance training (i.e., weightlifting) is increasing in popularity and is now recognized as an important component of a general exercise program. The current Physical Activity Guidelines for Americans recommend regular muscle-strengthening exercise for healthy men and women, older adults and adults with chronic conditions. The proposed benefits of regular resistance training typically focus on improved neuromuscular function, strength, endurance and bone density. However, a growing body of evidence suggests resistance exercise may also induce adaptations to the cardiovascular system.

Most cardiovascular events such as heart attack and stroke are caused by a blood clot (i.e., thrombosis) that partially or completely blocks blood flow, thus restricting delivery of oxygen to important organs and tissues. This is a considerable problem in the U.S. as approximately 2.7 million Americans experience a clot-induced event each year. Acute bouts of exertion are known to transiently increase blood clotting activity, potentially leading to exercise-induced complications, as discussed in the ACSM & AHA Joint Position Statement on Exercise and Acute Cardiovascular Events. However, regular exercise training causes adaptations that reduce the potential to create a blood clot and increase the capacity to dissolve a clot once it forms. This is one of the ways that regular exercise is theorized to improve heart health. A substantial body of evidence indicates that aerobic exercise, in particular, causes these beneficial adaptations. Much less is known, however, about the effects of resistance exercise training on blood-clotting potential.

In our recent study, published in the November issue of Medicine & Science in Sports & Exercise®, 16 healthy women and men completed a resistance training program that was based on ACSM guidelines for improving muscular strength. Participants trained three times per week for eight weeks. Each training session included two to three sets of eight exercises, targeting all major muscle groups, performed at an intensity that corresponded with 60%-80% 1RM. The key finding of this study was a significant training-induced reduction in plasminogen activator inhibitor-1 (PAI-1), a protein that inhibits activity of the plasminogen system, which dissolves blood clots. This adaptation suggests the capacity to dissolve blood clots is enhanced after training. PAI-1 concentration is independently associated with adverse events such as stroke and myocardial infarction. Thus, our findings suggest that eight weeks of resistance training reduces the risk of thrombotic events in healthy adults. The mechanisms underlying this adaptation are unclear and may involve changes in body composition or activity of the renin-angiotensin system. The plasminogen system also plays a role in skeletal muscle remodeling, so the reduction in PAI-1 observed in our study may suggest a mechanism for training-induced muscle hypertrophy.

Not only is resistance training an important component of an exercise program because of its effects on muscular fitness and bone density; it may also induce adaptations that reduce risk of cardiovascular complications. Our observations may have important implications for exercise scientists and practitioners, and we hope they will lead to many new research questions about strength training and cardiovascular health.

About the authors:
Paul R. Nagelkirk, Ph.D., FACSM, is the director of the Integrative Exercise Physiology Laboratory and an associate professor of exercise science at Ball State University. His research focuses on vascular responses and adaptations to exercise, with particular emphasis on blood coagulation and fibrinolysis. Dr. Nagelkirk is an active member of ACSM and the Midwest Regional Chapter. He is a past president of Midwest ACSM, and presently serves on ACSM’s Science Integration & Leadership Committee, as well as the Credentials Committee.

Kayla M. Soave, M.S., is a Ph.D. student in the Exercise & Cardiovascular Health Outcomes Laboratory and currently serves as the coordinator for the Human Energy Research Laboratory at Michigan State University. Her research interests include the effects of acute and chronic resistance exercise on cardiovascular health. She is an active member of ACSM and the Midwest Regional Chapter.

Viewpoints presented in SMB 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 SMB.