Active Voice: If the Heart Is a Muscle, Can Lifting Weights Strengthen It?
By Kevin Boldt, Ph.D., and Walter Herzog, Ph.D.

When asked about exercising their hearts, most people think about doing aerobic exercise like running, biking or swimming. There is a good reason why these activities are colloquially referred to as “cardio.” The benefits of aerobic exercise training on cardiovascular health are many, varied and well documented in the scientific literature. However, there is emerging evidence regarding the cardio-protective effects of resistance exercise training. Links between muscular strength (assessed by measures ranging from handgrip dynamometry to 1-RM testing of bench press or leg press) and cardiovascular disease risk have been reported in a growing number of studies. It has been suggested that resistance training, independent of aerobic fitness, exerts a protective effect on the heart. However, the mechanisms underlying this protective effect are not fully understood.

In our study, published in the August 2021 issue of Medicine & Science in Sports & Exercise®, we subjected rats to either aerobic-only exercise (treadmill running; 60 minutes for five days/week), resistance-only exercise (weighted ladder climbing; three days/week) or a combination of the two modalities (three days of running and two days of climbing). Following 12 weeks of training, we performed an echocardiography to determine the structural adaptations of the heart, as well as performed mechanical testing on isolated strips of cardiac tissue to identify possible mechanical adaptations. All exercise interventions led to structural and mechanical adaptations of the heart. However, hearts adapted differently depending on the exercise type. Interestingly, the animals who performed both aerobic and resistance exercise adapted with characteristics of both the aerobic-only and resistance-only training responses.

ACSM’s physical activity guidelines for adults include both 150 minutes or more of moderate-to-vigorous aerobic physical activity and two days of muscle strengthening activities per week. Often when these guidelines are presented, especially in the context of cardiac health, the focus is on the 150 minutes of aerobic activity. However, based on our results, the addition of two days per week of resistance exercise may provide important additional benefits and should not be ignored. In fact, there are many benefits for participating in cross-training programs (including both resistance and aerobic exercise). These include greater muscular endurance and strength, elevated lactate threshold, improved movement economy, increased insulin sensitivity, and improved blood cholesterol levels. Our findings extend this list to include positive structural and mechanical adaptations of the heart.

Whether an individual’s goal is to prevent or recover from cardiovascular disease or to improve their 10k race time, the benefits of resistance exercise training should not be overlooked. There has been a lot of effort convincing people to think about getting in their daily steps, but what about their daily reps?

About the authors:
Kevin Boldt, Ph.D., CSEP-CEP, NSCA-CSCS, recently completed his Ph.D. at the University of Calgary and is currently an assistant professor in kinesiology at Trent University. His research centers around understanding how cardiac and skeletal muscles adapt and ways to enhance their function through modulating exercise training and diet. Connect with Kevin at or

Walter Herzog, Ph.D., is a full professor in kinesiology, engineering, medicine and veterinary medicine at the University of Calgary. He is the Canada Research Chair for Cellular and molecular biomechanics and the Killam Memorial Chair for interdisciplinary research. His primary research focuses on skeletal muscle mechanics and muscle properties, with an emphasis on the molecular mechanisms of muscle contraction and the changing role of the structural protein titin in active and passive muscle. He is an associate editor of
Exercise and Sport Sciences Reviews.

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.