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Regular physical activity is strongly recommended to avoid overweight and obesity as well as related diseases such as diabetes and cardiovascular disease. But according to the World Health Organization, one in four adults does not get enough exercise. Scientists are now revealing that one of our muscles, the soleus muscle, located in the calf, has the ability to improve metabolic health even while sitting.
Inactive muscle fibers have been shown to require little energy; therefore, the body’s oxidative metabolism is low during many hours of the day spent sitting. ” During periods of inactivity, skeletal muscle accounts for only about 15% of postprandial glucose oxidation “, specify the researchers. What if we could find a way to maintain a high metabolism during these periods of inactivity, in other words burn calories without movement?
The soleus is a strong muscle located on the back of the leg that runs from just below the knee to the heel. Marc Hamilton, a professor of health and human performance at the University of Houston, found that properly activated this muscle can significantly improve metabolic health. His research, presented in the journal iSciencesuggest that this approach would be more effective in improving blood sugar regulation than all currently proposed solutions (diet, intermittent fasting, sports activity, etc.).
A muscle that can work for hours without straining
Oxidative metabolism is the process by which the body uses oxygen to burn metabolites such as blood glucose or fats to provide the energy necessary for its functioning; this process obviously depends on the immediate energy needs of the muscles. This is why oxidative metabolism is reduced to a minimum at rest.
During physical activity, glycogen, stored in the muscles, is one of the main carbohydrates used for energy production (it is then broken down into glucose). However, muscle biopsies revealed that glycogen contributes very little to the nutrition of the soleus muscle. ” When properly activated, the soleus muscle can elevate local oxidative metabolism to high levels for hours, not just minutes, using a different fuel mix. », Hamilton explains.
The scientist discovered that this calf muscle is able to use other fuels, including glucose circulating in the blood and fat. The advantage is that this type of metabolism is not limited – whereas muscles that are more dependent on glycogen can no longer function when the stores are depleted. The soleus muscle can thus function for hours without strain or fatigue.
Hamilton and colleagues tested the SPU on 25 participants (including 13 women), with a wide range of BMI, age, sitting time, and daily steps. These people spent an average of 10.7 (± 2.1) hours a day sitting. All were equipped with a “soleus pump,” an electrostimulation device specially developed by the Hamilton team that activates the soleus muscle differently than when standing or walking. The device aims to increase oxygen consumption in the muscle.
” This is the first joint effort to develop a specialized type of contractile activity aimed at optimizing human metabolic processes. “, emphasizes the researcher. The approach is called the Soleus Pushup (SPU).
Significant effects on sugar and fat metabolism
While the volunteers sit with their feet flat on the ground and their muscles perfectly relaxed, the soleus pump lifts the heel while the forefoot remains on the ground. After reaching the maximum amplitude, the foot passively relaxes. Contrary to appearances, movement is at odds with walking, the scientists explain: when walking, the amount of energy consumed is minimal; with the soleus pump, the muscle uses as much energy as possible for a long time. ” It is a powerful physiological movement that benefits from the unique properties of the soleus “, sums up the team. Contractions of the UPs approximately double whole-body oxygen consumption compared to that observed at rest while sitting.
The researchers monitored the participants’ metabolic rate and carbohydrate oxidation during the postprandial period (after a meal), after ingesting 75 g of glucose. The effects are significant: three hours after consuming the glucose drink, the team was able to observe a 52% improvement in blood sugar variability (about 50 mg/dL less) and a 60% reduction in insulin requirements.
This approach to maintaining a functioning flat muscle metabolism is also effective at doubling the normal rate of fat metabolism during fasting periods between meals, thus lowering blood fat levels. ” Amplification of otherwise negligible local energy expenditure by isolated contractions improved systemic VLDL triglyceride homeostasis [ndlr : des lipoprotéines de très basse densité] and largely glucose ”, reports the team.
Regardless of a person’s level of physical activity, excessive sitting has been shown to increase the risk of heart disease, diabetes, dementia and more. Increasing metabolism in this way would significantly reduce the incidence of these chronic diseases. We are preparing additional publications that focus on how to teach people how to properly perform this unique movement without the fancy lab equipment used in this study.