The field holds fascinating insights for researchers like Christopher Sundberg, PhD, an assistant professor of medicine in the UW School of Medicine and Public Health. Taking an integrative approach that includes cellular and molecular research as well as analysis of whole-body movement, Sundberg studies muscles for clues to why people lose strength faster than they lose muscle, why everyday tasks like climbing stairs become more fatiguing with age, and what interventions could protect those abilities.

Sundberg, who arrived at UW–Madison during the fall semester of 2025, makes his academic home in the UW School of Medicine and Public Health and devotes a portion of his time to the UW School of Education’s Department of Kinesiology, which helps support his work for example, by providing access to specialized kinesiology research facilities.

The collaborative recruitment was part of UW–Madison’s RISE-THRIVE initiative, an effort to attract top scholars at all stages of their careers to focus on two key areas: the science of immunology and the study of the healthspan.

How do you describe your field and your research into how muscles age?

Integrative muscle physiology explores how our skeletal muscle function arises from coordinated processes across biological systems. Rather than studying muscles only under a microscope, or only in terms of whole-body movement, researchers in my lab make connections across all levels of biological scale. We measure how strong and powerful a muscle is, how quickly it fatigues and how it moves the body, and then we trace those outcomes back to the muscle fibers themselves, including the proteins that make them function, how they produce energy, and how they adapt to different stimuli, such as exercise. It’s an approach that asks not only, “What changes with aging?”  but also “Why do those changes matter, and how do they affect everyday function?”

This field has evolved rapidly as advances in technologies, including artificial intelligence, allow us to connect detailed biological measurements directly to how muscles perform in people. In the context of aging, integrative muscle physiology provides a foundation for understanding mobility loss, fatigue and functional decline, which are issues that affect healthy aging. By linking biological changes to real-world outcomes, this work may help explain why people of the same age can have very different physical abilities and aging trajectories. It may ultimately improve strategies to support healthier aging for more people.

How did you become interested in studying muscle performance?

As a Division I-A student-athlete playing football at the University of Wyoming, I saw firsthand that athletic performance could vary dramatically among individuals, despite seemingly similar training programs, motivations and opportunities. Although we could measure and track outcomes such as speed, strength and endurance, we often lacked insight into the underlying physiological mechanisms driving these differences. Much of the variability in strength, fatigue and training adaptations remained unexplained. I came to appreciate that many performance-limiting factors were rooted in neuromuscular physiology, yet the mechanisms were poorly characterized, particularly in humans. This realization motivated my interest in studying muscle function across biological scales and ultimately led me toward a research career focused on the physiological factors that limit human performance across the lifespan.

What is exciting about your lab’s approach to studying aging muscle function, and how is it different from approaches used in the past?

Our lab is built on the idea that no single level of analysis is sufficient to truly understand muscle function. We study humans performing real tasks, like walking, generating force, and producing power, and then link those biomechanical measures to neuromuscular activation, single-fiber mechanics, and molecular alterations. What sets our work apart is that these measurements are not isolated; they come from the same individuals, allowing us to directly connect cellular and molecular biology to whole-muscle performance. By integrating all these approaches within the same study design, we hope to identify the mechanisms that cause fatigue and limit mobility and functional independence. This integrative framework is essential to designing effective targeted interventions.

Historically, many studies have examined molecular aging of muscle without direct linkage to functional outcomes, or they have characterized functional decline without identifying underlying mechanisms. As a result, we’ve often lacked a clear understanding of causality. By studying the entire system, we hope to identify which changes drive declines in power and fatigue, and which are simply bystanders. This approach should help us avoid targeting pathways that look interesting biologically but don’t meaningfully affect function.

Source: https://www.med.wisc.edu/news/muscles-role-the-aging-process/