Does Skeletal Muscle Store Triglycerides? The Truth About Intramuscular Fat

December 20, 2025 •

4 min read

Research has long confirmed that skeletal muscle can contain modest yet significant stores of triglyceride, acting as an important depot of fuel. These intramuscular triglycerides (IMTGs) serve as a readily available energy source for muscle contraction, particularly during prolonged endurance exercise.

Quick Summary

Skeletal muscle stores triglycerides (IMTGs) in lipid droplets for use as an energy source, especially during moderate-intensity endurance exercise. While a vital fuel for active individuals, excessive IMTG accumulation is linked to insulin resistance in sedentary people.

Key Points

Yes, skeletal muscle stores fat: Specifically, intramyocellular triglycerides (IMTGs) are stored in lipid droplets within muscle cells, a distinct depot from typical body fat.
IMTGs fuel exercise: These fat stores are a critical energy source, especially during prolonged, moderate-intensity endurance exercise, contributing significantly to overall energy production.
Metabolic flexibility is key: High IMTG levels can be healthy or unhealthy. In athletes, high levels are associated with high insulin sensitivity due to efficient fat oxidation, whereas in sedentary individuals, high levels are linked to insulin resistance.
Exercise improves utilization: Regular exercise training increases the muscle's oxidative capacity and metabolic flexibility, allowing for more efficient use of IMTGs for energy.
Fiber type matters: Type I, or slow-twitch, muscle fibers, which are more oxidative, typically store more IMTGs than their Type II counterparts, reflecting their different metabolic functions.
Excess can be detrimental: In inactive states, a poor balance between fatty acid uptake and oxidation can lead to the accumulation of lipid metabolites that interfere with insulin signaling.

What are Intramuscular Triglycerides (IMTGs)?

Unlike the subcutaneous or visceral fat that is typically associated with body fat, intramyocellular triglycerides (IMTGs) are lipid droplets stored directly within the muscle fibers themselves. This internal fat depot, also known as intramuscular fat, is a crucial source of energy for muscle contraction. Researchers distinguish IMTGs from extramyocellular triglycerides (EMCL), which are stored in adipocytes and the connective tissue between muscle fibers. The amount of IMTG stored can vary significantly depending on an individual's diet, exercise habits, and overall metabolic health. The storage of IMTGs is part of a healthy metabolic process, but its accumulation can signal potential metabolic issues in sedentary populations.

The Role of IMTGs as a Fuel Source

When muscle fibers contract, they need a constant supply of energy in the form of ATP. This energy is generated from the oxidation of various fuels, including blood glucose, muscle glycogen, and fatty acids from both the bloodstream and intramyocellular triglyceride stores. During rest, and especially during prolonged, moderate-intensity aerobic exercise, IMTGs become a primary fuel source. The body hydrolyzes IMTGs into free fatty acids, which are then transported to the mitochondria within the muscle cell and broken down through β-oxidation to produce ATP. The rate of IMTG utilization is influenced by exercise intensity and duration. For example, studies have shown that IMTG contribution to total energy production is significant during moderate-intensity exercise, peaking around 65% of VO2max.

The "Athlete's Paradox" and Insulin Resistance

One of the most intriguing aspects of intramuscular fat is the so-called "athlete's paradox." It refers to the observation that highly trained endurance athletes often have high IMTG levels but possess high insulin sensitivity, while sedentary or obese individuals with similarly high IMTG levels are often insulin resistant. This paradox highlights the critical importance of a muscle's metabolic flexibility and capacity to utilize IMTGs.

Key differences include:

Metabolic Flexibility: Trained athletes have a high capacity to switch between oxidizing carbohydrates and fats for fuel. Their muscles are highly efficient at tapping into IMTG stores during exercise.
Oxidative Capacity: The muscles of trained athletes possess more mitochondria and a greater oxidative capacity, allowing for the efficient use of fatty acids from IMTGs.
Incomplete Oxidation: In sedentary, insulin-resistant individuals, fat oxidation pathways may be impaired. This leads to the buildup of metabolic byproducts, such as diacylglycerols and ceramides, which interfere with insulin signaling.

This evidence suggests that the health implication of IMTG storage is not the volume of fat itself, but rather the muscle's ability to metabolize it effectively.

Factors Affecting IMTG Storage and Utilization

Several physiological factors influence the storage and use of intramyocellular triglycerides:

Muscle Fiber Type: The composition of muscle fibers plays a significant role. Type I (slow-twitch) muscle fibers, which are more oxidative, contain higher amounts of IMTG compared to Type II (fast-twitch) glycolytic fibers.
Exercise Intensity and Duration: IMTG utilization is most prominent during prolonged, submaximal endurance exercise. During high-intensity exercise, muscles rely more heavily on carbohydrates (glycogen).
Adrenergic Control: Hormones such as adrenaline and noradrenaline help regulate the mobilization of IMTGs during exercise.
Diet: Dietary fat availability influences IMTG levels. A high-fat diet can increase IMTG content, potentially leading to insulin resistance if not balanced with sufficient exercise. Conversely, low carbohydrate availability can accelerate IMTG mobilization.

IMTG in Health vs. Disease

Below is a comparison highlighting the differing roles of intramyocellular triglycerides in trained versus sedentary individuals.


Feature	Trained Endurance Athlete	Sedentary Individual
IMTG Level	Can be very high as an adaptation for efficient fuel use.	Elevated levels correlate with poor metabolic health.
Insulin Sensitivity	High. Muscle cells effectively respond to insulin.	Low (Insulin Resistance). Muscle cells respond poorly to insulin.
IMTG Role	Readily available fuel for oxidation, supporting prolonged exercise.	Accumulation can lead to a buildup of toxic lipid metabolites.
Metabolic Flexibility	High capacity to switch between fuel sources based on demand.	Impaired ability to transition efficiently between lipid and carbohydrate fuels.
Overall Effect	Enhanced performance and metabolic health.	Increased risk of type 2 diabetes and metabolic disorders.

Conclusion: The Nuanced Relationship

In conclusion, the question of whether skeletal muscle stores triglycerides is unequivocally answered with a "yes." Skeletal muscle serves as an active metabolic hub, storing lipids in the form of intramuscular triglycerides (IMTGs) within myocellular lipid droplets. The significance of this fat storage, however, is highly context-dependent. For the highly active individual, particularly the endurance athlete, IMTG represents a critical and readily accessible fuel source that supports performance and metabolic efficiency. In contrast, for the sedentary person, an accumulation of IMTG can become a marker of metabolic dysfunction and a contributing factor to insulin resistance. The key differentiator is not the presence of intramuscular fat, but the muscle's capacity for metabolic flexibility—the ability to efficiently mobilize and oxidize that stored fat for energy. Exercise training is a powerful modulator that enhances this capacity, shifting the role of IMTG from a potential metabolic liability to a performance-enhancing asset. Acute exercise increases triglyceride synthesis in skeletal muscle of sedentary individuals provides further reading on this topic.

Frequently Asked Questions

Intramyocellular lipid (IMCL), or IMTG, is fat stored inside the muscle fibers within lipid droplets. Extramyocellular lipid (EMCL) is fat stored outside the muscle cells, in the connective tissue.

During physical activity, the body releases fatty acids from triglycerides through a process called hydrolysis. These fatty acids are then transported into the muscle cells' mitochondria, where they are oxidized to produce ATP.

Endurance-trained athletes develop an increased capacity to both store and use IMTGs for energy. Their muscles have a greater oxidative capacity, allowing them to rely more on fat as a fuel source during prolonged exercise.

High IMTG levels are correlated with insulin resistance in sedentary individuals, but not necessarily in athletes. The ability to efficiently utilize the fat is the key factor. Impaired oxidation, not storage itself, is the issue.

Metabolic flexibility is the muscle's ability to efficiently switch between using different fuel sources, like fat and carbohydrates, depending on the body's energy needs. It prevents the negative effects of excess IMTG accumulation.

Engaging in regular endurance exercise is the most effective method. This type of training increases the number and efficiency of mitochondria in muscle cells, enhancing your body's ability to burn fat.

No. Type I, or slow-twitch, oxidative muscle fibers typically store more triglycerides than Type II, or fast-twitch, glycolytic fibers. This difference aligns with their primary energy sources and function.