Metabolism slows with age, often due to impaired insulin sensitivity, and prevents skeletal muscles from taking up glucose from the blood and properly managing protein. However, the link between insulin resistance and muscle weakness goes beyond age. Lifestyle factors can increase the risk of losing muscle strength due to metabolic syndrome, type 2 diabetes, metabolic dysfunction-associated steatotic liver disease and other similar conditions.
Exercise and wellness professionals, such as bodyworkers, physical therapists, fitness trainers and students who study human anatomy, should deepen their understanding of how metabolism affects muscle strength to better help people living with poor metabolic health after 40.
Increasing Ectopic Fat Buildup
Insulin resistance and ectopic fat buildup drive each other in a continuous cycle. The former limits the amount of fuel entering insulin-sensitive tissues. When people consume more energy than they expend regularly, the excess calories overwhelm the capacity of subcutaneous fat tissues. The lipids spill over and get stored as ectopic fat in the pancreas, skeletal muscles and liver.
The buildup of lipid metabolic intermediates in organs that normally store little fat may disrupt metabolic processes, impairing the body’s function. Ectopic fat interferes with insulin signaling, starving the skeletal muscle cells of the glucose they need for fuel and strength.
Causing Mitochondrial Dysfunction
Metabolic stress causes mitochondria to break apart. Cells overloaded with fats and sugars compel these powerhouses to work harder, producing free radicals that injure them and the cells. Elevated stress disrupts oxidative phosphorylation, preventing mitochondria from generating enough cellular energy required for muscle contraction, maintenance and force production.
High volumes of ectopic fat deposits in skeletal muscles can result in lipotoxicity. This harmful metabolic process blocks insulin signaling and diminishes mitochondrial function, which sets off a vicious cycle that reduces glucose utilization in skeletal muscles, weakening muscle strength and decreasing muscle mass.
Triggering Inflammatory Cytokines
Metabolic dysfunction triggers the immune cells to release cytokines. Adipose tissue expansion creates a low-oxygen environment since stretched fat cells lack an ample blood supply, signaling distress. Mitochondrial stress can activate internal danger sensors, such as the NLRP3 inflammasome, in response to cellular stress and damage signals.
The presence of inflammatory cytokines disrupts normal insulin signaling pathways, thereby inducing insulin resistance. Healthy insulin action can suppress the inflammation. However, decreased insulin sensitivity allows these signaling proteins to flood the system further.
Reducing Testosterone Levels
The connection between metabolic syndrome and muscle loss in men lies in low testosterone. Patients are diagnosed with this group of conditions when they have at least three of these risk factors — a waist size of over 40 inches, high blood sugar, high triglycerides, high blood pressure and low good cholesterol.
Declining testosterone levels are common among men with metabolic syndrome. Since this sex hormone gradually decreases by 1% each year after men turn 40, the risk of muscle atrophy due to metabolic syndrome goes up upon reaching middle age. Low testosterone contributes to insulin resistance, increased body fat and reduced muscle mass. Excess abdominal fat converts testosterone into estrogen, so people with metabolic syndrome may have low testosterone and elevated estrogen levels at the same time.
How to Maintain Muscle Strength After 40
Age-related muscle weakness is common but can be slowed or mitigated. These practices help improve metabolism after 40 and minimize its negative effects on muscle strength.
Engaging in Resistance Training
Resistance training is key to building strength and increasing muscle mass. Stronger muscle tissues help raise the resting metabolic rate, as muscle burns more calories at rest than fat tissues do. Physical stress causes skeletal muscles to take up glucose from the bloodstream more efficiently, which increases insulin sensitivity.
Body weight and equipment-based exercises help trim visceral and overall fat mass. Less abdominal fat may slow the decline of testosterone levels and lower the risk of metabolic syndrome.
Prioritizing Adequate Recovery
Workouts promote extended calorie burn. The body expends energy to return to a resting state, causing it to continue using more oxygen and calories for 15 minutes to 48 hours after the workout.
The metabolic rate remains elevated during the recovery period because the body uses energy to repair microscopic muscle tears after resistance training. Sufficient recovery can also regulate insulin. Increasing insulin sensitivity enables cells to process nutrients properly rather than storing them as fat.
Consuming More Protein
Higher protein intake accelerates post-workout metabolic processes. This macronutrient has a high thermic effect of food, requiring more of its calories to break it down. Eating protein causes the metabolic rate to spike after physical activity and stabilizes daily calorie burn, which prevents the body from breaking down muscle for energy.
The International Society of Sports Nutrition recommends 20 to 40 grams of protein every three to four hours, paired with ample carbohydrates, to support muscle recovery. Salmon, eggs, Greek yogurt and sweet potatoes are digestible whole foods, making them good sources of nutrition post-workout.
Overcoming Workout Plateau
Resistance training plateaus slow metabolism. A lighter body and trained muscles require fewer calories to function. The resting metabolic rate drops significantly after losing body mass, a natural phenomenon designed to conserve energy and protect against potential starvation.
New workout routines help overcome fitness plateaus by causing the body to adapt to change once again. Diversifying exercises, increasing resistance, performing more repetitions than the previous session and cutting rest time between sets are good tactics.
Stay Active Between Workouts
Regular movement between formal workout sessions helps prevent metabolic slowdown. It sustains high energy expenditure throughout the day.
Walking supports active recovery from scheduled resistance training. Brief walks around the house and the neighborhood signal the muscles to continue processing fats and sugars efficiently. The CDC recommends brisk walking for 30 minutes for five days and doing two days of weight training per week to strengthen the muscles and get enough aerobic exercise.
Metabolism Can Positively Affect Muscle Strength
Age-related insulin resistance is a concern for metabolic health. When left unaddressed, its cascading effects on the body can make it challenging to maintain muscle strength after 40. The path to regain muscle strength is different for everybody, but many stand to benefit from regular exercise, adequate recovery and proper nutrition. Medical interventions also exist to treat underlying metabolic health conditions and negate their effects on the muscles.
Written by Dan Parks (dan@moddedmag.com)
