Why Exercise Capacity Can Be Different for People With Type 1 Diabetes

When you exercise hard, your body's ability to deliver and use oxygen determines how long and intensely you can perform. For people with type 1 diabetes, this oxygen delivery system doesn't always work as efficiently as it does for people without diabetes. Yet some athletes with type 1 diabetes compete at professional levels in endurance sports. This gap between individual experiences prompted researchers to investigate: What exactly changes in the body when type 1 diabetes affects exercise capacity?

The answer isn't simple. A new review of scientific literature identifies which parts of the oxygen delivery system—sometimes called the 'oxygen cascade'—are actually impaired by type 1 diabetes.

Research consistently shows that the heart's pumping power and the volume of blood circulating are affected in people with type 1 diabetes, even before complications develop. The heart's stroke volume—the amount of blood pumped with each beat—appears reduced. This matters because a smaller blood volume and less efficient pumping means less oxygen reaches working muscles.

Think of it like a delivery system: if fewer trucks (blood cells) are available and they carry less cargo (oxygen), the destination (your muscles) receives less fuel. This appears to be one of the most reliable factors limiting exercise capacity across people with type 1 diabetes, though it doesn't affect everyone equally.

Your muscle cells contain tiny structures called mitochondria—essentially the power plants that convert oxygen into usable energy. Growing evidence suggests mitochondrial dysfunction can occur in type 1 diabetes, which may reduce how efficiently muscles use oxygen once it arrives. This dysfunction also appears linked to oxidative stress, a harmful process in cells.

However, researchers acknowledge uncertainty about how much mitochondrial problems contribute to overall exercise limitations. The emerging evidence is important, but the science is still developing.

Perhaps the most important finding is this: exercise capacity limitations in type 1 diabetes don't stem from a single point of failure. Instead, problems are distributed across multiple steps—from how the heart pumps, to blood volume, to how muscles receive blood, to how cells use oxygen. This variation across multiple systems helps explain why the impact differs so much from person to person.

What emerges clearly from the research is that blood sugar control—measured by HbA1c—plays a stronger role than how long someone has had diabetes. Someone with well-controlled type 1 diabetes for many years may have better exercise capacity than someone with shorter disease duration but less stable blood sugar. This suggests that lifestyle factors and management choices directly influence athletic performance.

This research doesn't change how you manage diabetes, but it deepens our understanding of why exercise feels different for people with type 1 diabetes. The fact that multiple systems are involved explains why some people compete professionally while others experience more significant limitations—the balance of these factors differs individually.

The clear connection to blood sugar control reinforces what many people with type 1 diabetes already know: stability in glucose management supports athletic performance. If you're interested in understanding your own exercise capacity, these research insights show that the full picture involves your heart, blood volume, and muscle metabolism working together.

Source: Sports medicine (Auckland, N.Z.). Evidence type: PubMed indexed literature. Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.