Have you recently noticed that you've gained weight around your stomach and become more easily fatigued? A decrease in muscle mass due to aging is a major cause of rapidly worsening blood sugar control. For those in their prime working years, aged 40-60, understanding the relationship between muscle and glucose metabolism is crucial for maintaining good health
This article provides a detailed explanation of the effects of lack of exercise on blood sugar levels and measures to efficiently improve glucose metabolism
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Muscles are the body's largest sugar-consuming tissue
In the human body, skeletal muscle is the largest tissue and plays a crucial role in energy metabolism and glucose uptake. When glucose consumed from food exceeds the body's capacity, it is stored as glycogen in the liver and muscles. In other words, the more muscle mass you have, the more glucose you can store
Furthermore, when you move your muscles through strength training or other exercises, blood flow increases, making it easier for glucose to be taken up by cells, and blood sugar levels decrease. However, when you reach a state of sarcopenia, where muscle mass decreases due to aging or lack of exercise, your body becomes unable to consume sugar sufficiently
Sources:Monthly Diabetes 2015/1 vol.7 No.1 | Pathophysiology and Treatment of Diabetes from the Perspective of Skeletal Muscle
Source:National Institute of Health Crisis Management Diabetes Information Center | The Story of Exercise for Diabetes
Source:Ministry of Health, Labour and Welfare | Health Japan 21 Action Support System ~Health Promotion Support Network~ "Blood Glucose Levels"
Source:Journal of the Japanese Society of Internal Medicine 109 vol.10 | Clinical Guidelines at a glance Sarcopenia Clinical Guidelines
The vicious cycle of insulin resistance caused by lack of exercise
When muscles weaken, a condition called insulin resistance develops in the body. This article will explain the mechanism of insulin resistance in detail
What is insulin?
Insulin is a type of hormone secreted by the beta cells of the islets of Langerhans in the pancreas. It plays an important role in regulating glucose metabolism and maintaining stable blood sugar levels
When you eat and your blood sugar levels rise, insulin is secreted, and cells take in glucose from the blood and use it as an energy source. Furthermore, excess glucose is synthesized into glycogen and triglycerides and stored through the action of insulin, which ultimately lowers blood sugar levels
Why lack of exercise can lead to insulin resistance
Insulin resistance refers to a condition in which the insulin sensitivity of tissues decreases, and insulin does not work properly. When muscle mass decreases due to lack of exercise, the capacity to absorb glucose also decreases, and the excess energy that has nowhere to go is stored as visceral fat
Excessive adipose tissue secretes inflammatory bioactive substances that are thought to interfere with the insulin signaling pathway. When these inflammatory bioactive substances impair the effectiveness of insulin, the brain sends a signal to the pancreas to "produce more insulin to lower blood sugar." As a result, the pancreas becomes exhausted from continuously secreting excessive amounts of insulin, eventually leading to full-blown diabetes
Source:Journal of the Japanese Society of Internal Medicine, Vol. 102, No. 10, October 10, 2013 | Adipose tissue dysfunction and insulin resistance.
Source:Ministry of Health, Labour and Welfare | Health Japan 21 Action Support System ~Health Promotion Support Network~ "Insulin"
A must-read for busy working adults! Habits to efficiently boost glucose metabolism
The key to breaking the vicious cycle of lack of exercise and insulin resistance is to consistently engage in regular exercise to "increase" and "prevent" muscle loss. Here are some specific habits you can incorporate into your daily life
motion
For effective aerobic exercise, aim for at least 150 minutes per week (three or more times a week) at an intensity that makes you sweat. Be careful not to go more than two consecutive days without exercise, because the increased insulin sensitivity from exercise lasts for about 24 to 48 hours afterward
Furthermore, it is recommended to perform strength training that puts stress on the muscles two to three times a week on non-consecutive days. However, it is important to perform the training at an appropriate intensity, taking into account your individual fitness level and risk of injury
Precautions for daily life
In addition to setting aside time for exercise, it's also essential to be mindful of increasing your activity level in daily life. The key is to incorporate walking and light physical activity, and to avoid sitting for more than 30 minutes at a time
Studies have reported that when people with type 2 diabetes interrupted their sedentary posture with "3 minutes of light activity every 30 minutes" for 8 hours after a meal, their post-meal blood glucose and insulin levels decreased. This could also be expected to improve hyperglycemia until the following morning
Medical approaches to male menopause
In men over 40, a decrease in male hormones (testosterone) is often a major cause of decreased muscle mass and increased visceral fat. In such cases, hormone replacement therapy, which supplements the deficient hormone to maintain muscle quality and improve insulin sensitivity, may be suitable for some. Under health insurance, testosterone is typically administered via intramuscular injection every 2 to 4 weeks until symptoms improve
Furthermore, in the field of regenerative medicine, cutting-edge treatments utilizing skeletal muscle stem cells are attracting attention. In 2025, a research group at Tokyo Metropolitan University Graduate School reported that even if skeletal muscle tissue is not damaged, transplanting stem cells into areas where muscle fibers have thinned due to aging can increase muscle mass. Currently, this is still in the animal experiment stage, but research aimed at creating a "body that is less prone to weight gain and fatigue" by efficiently consuming sugar is steadily progressing
Source:Diabetes Treatment Guidelines 2024 | Chapter 4 Exercise Therapy
Source:Japan Endocrine Society | Male Menopause (Age-Related Hypogonadism, LOH Syndrome)
Source:Achieving myoblast engraftment into intact skeletal muscle via extracellular matrix
summary
When muscle mass decreases, insulin resistance increases, making blood sugar control more difficult. The easiest way to address this is to maintain and increase muscle mass through regular exercise and frequent physical activity. If you are in your 40s or older and experience symptoms that suggest a decline in male hormones, it would be beneficial to consult a medical institution and consider hormone replacement therapy