Researchers reveal soleus muscle helps to burn fat while sitting

Published in iScience on August 4, the study designates that soleus pushups are more efficient than popular remedies like exercise, weight loss, and intermittent fasting at maintaining an elevated oxidative metabolism to improve blood glucose homeostasis.

“We never dreamed that this muscle has this type of capacity. It's been inside our bodies all along, but no one ever investigated how to use it to optimize our health, until now,” said Professor Hamilton.

“When activated correctly, the soleus muscle can raise local oxidative metabolism to high levels for hours, not just minutes, and does so by using a different fuel mixture.”

Soleus uses fat and blood glucose

Professor Hamilton and his team carried out muscle biopsies to understand what really makes this possible. Biopsies showed there was minimal glycogen contribution to fueling the soleus. Instead of breaking down glycogen, the soleus can use other types of fuels such as blood glucose and fats.

"The soleus's lower-than-normal reliance on glycogen helps it work for hours effortlessly without fatiguing during this type of muscle activity because there is a definite limit to muscular endurance caused by glycogen depletion," Hamilton said.

"As far as we know, this is the first concerted effort to develop a specialized type of contractile activity centered around optimizing human metabolic processes."

When the SPU was put to the test, the overall effects on blood chemistry included a 52 percent improvement in blood glucose (sugar) excursion and a 60 percent reduction in the need for insulin three hours after consuming a glucose drink.

It doesn't mean you don't need to do exercise

Briefly, "While seated with feet flat on the floor and muscles relaxed, the heel rises while the front of the foot stays put. When the heel gets to the top of its range of motion, the foot is passively released to come back down. The aim is to simultaneously shorten the calf muscle while the soleus is naturally activated by its motor neurons," suggests the study. However, this doesn't mean that you don't need to move much or exercise.

The researchers are eager to clarify that this is not the latest diet or exercise advice. It is a strong physiological action that takes advantage of the soleus's distinctive qualities.

Abstract:

Slow oxidative muscle, most notably the soleus, is inherently well equipped with the molecular machinery for regulating blood-borne substrates. However, the entire human musculature accounts for only ∼15% of the body’s oxidative metabolism of glucose at the resting energy expenditure, despite being the body’s largest lean tissue mass. We found the human soleus muscle could raise local oxidative metabolism to high levels for hours without fatigue, during a type of soleus-dominant activity while sitting, even in unfit volunteers. Muscle biopsies revealed there was minimal glycogen use. Magnifying the otherwise negligible local energy expenditure with isolated contractions improved systemic VLDL-triglyceride and glucose homeostasis by a large magnitude, e.g., 52% less postprandial glucose excursion (∼50 mg/dL less between ∼1 and 2 h) with 60% less hyperinsulinemia. Targeting a small oxidative muscle mass (∼1% body mass) with local contractile activity is a potent method for improving systemic metabolic regulation while prolonging the benefits of oxidative metabolism.