Why skeletal muscle matters for glucose handling, body composition, energy use and long-term metabolic resilience
When women think about metabolic health after 35, the conversation often begins with body weight, calories or whether the metabolism has somehow “slowed down.” Those questions are understandable, but they leave out a tissue that changes the meaning of all three: skeletal muscle.
Muscle produces movement, but it also takes up glucose, stores carbohydrate as glycogen, responds to insulin and uses fuel whenever it contracts. It contributes to fat-free mass and helps determine whether weight loss produces a smaller version of the same body or a stronger body with a more favourable ratio of muscle to fat.
This does not make muscle an anti-ageing cure or a guarantee against insulin resistance. Metabolic health is also influenced by genetics, sleep, cardiovascular fitness, food intake, body-fat distribution, medication, illness and the hormonal changes of midlife. Muscle is important because it is one of the largest modifiable parts of that system: it can be used, trained, preserved and, in many cases, built.
Metabolic health is not the same as being thin
Metabolic health describes how effectively the body regulates and uses energy. It includes the ability to keep blood glucose within an appropriate range, respond to insulin, manage blood lipids and blood pressure, and maintain a body composition that supports long-term function. No single measurement captures the whole picture.
A low body weight does not automatically indicate good metabolic health, just as a higher body weight does not reveal how much of that weight is muscle, fat, bone or water. Two women can have the same scale weight and very different waist measurements, strength levels, fat distribution and amounts of lean tissue.
This is why muscle matters before we discuss dieting. It changes what the body is made of, how much physical work it can perform and how much active tissue is available to receive and use fuel. Metabolic health is not created by muscle alone, but it cannot be fully discussed without it.
There is no metabolic cliff at 35
Nothing happens suddenly on a thirty-fifth birthday. The title “after 35” describes a useful time to become deliberate, not a biological deadline. Changes in muscle and body composition accumulate through activity levels, training history, repeated dieting, illness, sleep, total food intake and, later, the menopausal transition.
Longitudinal research in women aged approximately 47–55 found that the menopausal transition was associated with reductions in lean mass and muscle size at several anatomical levels. Women who remained more physically active tended to retain more muscle, although an observational association cannot prove that general activity completely prevents hormonally related change. [1, 2]
The useful conclusion is not that decline becomes inevitable. It is that muscle should no longer be treated as something the body will preserve regardless of how it is used or fed. Midlife is an opportunity to make preservation intentional while the starting point is still strong.
Muscle gives glucose somewhere useful to go
After a meal containing carbohydrate, digestion releases glucose into the bloodstream. Insulin helps direct that glucose into tissues where it can be used immediately or stored. Under insulin-stimulated experimental conditions, skeletal muscle is a principal site of whole-body glucose disposal, and much of the glucose entering muscle can be stored as glycogen for later activity. [3]
This is not an argument against carbohydrates or insulin. Carbohydrate is a normal fuel, and insulin is an essential hormone. The important question is whether the tissues receiving the signal are responsive and whether stored fuel is regularly used.
A trained muscle is not an empty container waiting for sugar. It is living tissue that continually turns fuel over. During movement and training it uses ATP, draws on glycogen and fat, and later replenishes what has been used. The repeated cycle of use and restoration is one reason active muscle is so relevant to metabolic resilience.
Muscle glycogen is a local fuel reserve. Unlike liver glycogen, which helps maintain blood glucose between meals, glycogen stored in a muscle fibre is kept mainly for that muscle's own work. Training also changes more than size: repeated contractions can alter glucose transporters, insulin-signalling proteins and the enzymes that determine how fuel is used. The metabolic value of muscle is therefore not described by kilograms alone; it also depends on what the tissue has been trained to do. [3-5]
Muscle contraction changes glucose handling
Insulin is one route by which glucose transport into muscle increases. Contraction provides another stimulus. When muscle fibres work, cellular signals move the glucose transporter GLUT4 towards the cell surface through pathways that are not identical to insulin signalling. After exercise, the trained muscle may also respond more effectively to insulin while it restores its fuel reserves.
Human training studies help translate this mechanism into something practical. In one study, six weeks of strength training increased insulin-mediated glucose uptake, GLUT4 content and elements of insulin signalling in trained skeletal muscle in people with type 2 diabetes as well as healthy control participants. [4]
A controlled six-month trial in young, non-obese women found that both endurance and resistance training improved glucose disposal, although the adaptations appeared to arise through somewhat different mechanisms. The resistance-training group increased fat-free mass, giving the body more tissue through which glucose could be handled. [5]
These studies should not be turned into a promise that lifting weights prevents diabetes. Some involved younger women or participants with an existing diagnosis, and a training study does not replace medical care. They do, however, demonstrate an important principle: glucose handling is influenced by what muscle is repeatedly trained to do.
More muscle can help—but active, responsive muscle matters more
It is tempting to reduce the subject to a simple slogan: more muscle creates a larger “sink” for glucose. There is truth in the idea, but the real physiology is more nuanced. Muscle mass alone does not guarantee insulin sensitivity. A person can have substantial muscle and still develop metabolic disease, while improvements in glucose handling can occur before a large visible increase in muscle size.
The more useful goal is therefore not simply to possess muscle, but to maintain muscle that is regularly contracting, supplied by blood, capable of storing glycogen and responsive to training. Strength, movement, cardiovascular activity, sleep and food quality remain part of the same metabolic picture.
This also explains why strength gains matter even when visible hypertrophy is slow. Strength depends not only on muscle size, but also on how effectively the nervous system recruits motor units, coordinates a movement and transmits force through the muscle-tendon system. A woman may therefore perform more work before the mirror shows a dramatic change. The neuromuscular system is becoming more capable; metabolic benefit does not need to wait for dramatic hypertrophy. [11]
Body composition tells us what scale weight cannot
Scale weight combines every tissue and fluid compartment into one number. It cannot show whether change came from fat, muscle, glycogen, water or a mixture of all four. This becomes especially important when a woman wants to reduce body fat.
Calorie restriction can lower weight, but the body does not lose only adipose tissue. Without an adequate training signal and sufficient protein, some of the loss may come from fat-free mass. The result can be a lighter body that is not proportionately firmer, stronger or more capable.
In a controlled study of older women during weight loss, resistance training helped preserve fat-free mass. In another randomised trial involving premenopausal women, combining a dietary intervention with progressive resistance training produced the largest decline in fat mass, while resistance training alone was the only condition that significantly increased lean mass. [6, 7]
These were relatively small studies and should not be treated as universal predictions. Their value lies in the direction of the evidence: when weight loss is the goal, nutrition creates the energy deficit, while resistance training helps tell the body that lean tissue remains necessary.
That is the difference between weight loss and body recomposition. Weight loss asks only for a smaller number. Body recomposition asks what is being reduced, what is being preserved and what kind of body will remain at the end of the process.
Muscle supports energy expenditure—but the effect is often exaggerated
Muscle is metabolically active at rest, but it is not a furnace that burns hundreds of extra calories simply because a small amount has been added. A commonly used organ-and-tissue model estimates resting skeletal-muscle expenditure at approximately 13 kilocalories per kilogram per day. The liver, brain, heart and kidneys use far more energy per kilogram, even though they are much smaller. [8]
Training can still influence resting energy expenditure, but responses vary. In one nine-month resistance-training study, resting metabolic rate increased by about five per cent on average, with wide differences between individuals; the change was not explained by added fat-free mass alone. [9]
The strongest case for muscle is therefore not that it allows unlimited food or permanently “boosts” metabolism. Its value is broader: muscle permits more physical work, preserves lean tissue during a fat-loss phase, stores and uses fuel, and gives the body greater functional capacity. The calories used at rest are only one small part of that story.
Resistance training supplies the signal
Daily activity is valuable, but muscle adapts specifically to the demands placed upon it. Resistance training asks the muscles to produce force against a load that can be increased over time. That load may come from machines, free weights, cables, elastic resistance or body-weight movements selected at an appropriate level.
In a 20-week controlled trial involving women aged 40–60, twice-weekly free-weight training improved squat and bench-press strength in both premenopausal and postmenopausal participants. Increases in measured muscle mass were clearer in the premenopausal women, which is a useful reminder that strength can improve even when visible hypertrophy is slower after menopause. [10]
The 2026 American College of Sports Medicine position stand concluded that progressive resistance training improves strength, muscle size, power and several measures of physical function. A simple foundation is to train all major muscle groups at least twice each week and to increase the challenge gradually as technique and capacity improve. [11]
One session creates a short-term metabolic effect; lasting change is cumulative. It develops as repeated training sessions and recovery periods add up to changes in muscle function and, when the stimulus supports it, muscle size. This is why consistency and gradual progression matter more than occasional exhaustive workouts. [11]
A practical programme does not need to be extreme. It needs to be progressive:
- train the major movement patterns and muscle groups rather than repeating only small isolated exercises;
- choose resistance that makes the working muscles contribute meaningfully while technique remains controlled;
- add repetitions, resistance, range of motion or training volume gradually rather than changing everything at once;
- allow enough recovery for performance to improve instead of treating exhaustion as proof of effectiveness;
- continue walking and cardiovascular activity for the benefits they provide, while recognising that they do not replace progressive resistance.
Protein and adequate food support the response
Training creates the reason for the body to retain and build muscle. Protein provides the amino acids required to repair and remodel that tissue. Adequate total energy, carbohydrates, fats, vitamins, minerals, sleep and recovery support the process around it.
Protein alone cannot create the adaptations of resistance training, and training cannot make an under-supplied body recover indefinitely. Research on healthy adults generally supports a higher protein intake when the goal is to gain or preserve muscle, particularly alongside resistance exercise or during an energy deficit. [12]
For the complete explanation of daily targets, meal distribution and protein quality, read Why Women 35+ Need More Protein Than They Think.
What this means in ordinary life
Supporting metabolic health does not require living like a competitive athlete. It means creating a body that receives regular reasons to remain muscular and capable, then feeding that body in a way that supports the work.
A realistic starting structure is:
- two or more well-planned resistance-training sessions each week;
- regular walking or other cardiovascular movement for heart health, endurance and total activity;
- protein-centred meals distributed across the day rather than one large serving at dinner;
- enough carbohydrate to support daily life and training, rather than treating it as a metabolic enemy;
- fat loss pursued at a moderate pace when needed, with strength and lean-tissue preservation treated as outcomes;
- progress assessed through strength, measurements, clothing fit, energy, recovery and consistency—not scale weight alone.
The next article in this series will move from tissue to the plate: why stable energy begins with meal structure, and how protein, purposeful carbohydrate, plants and dietary fat can be combined without turning food into a rigid set of rules.
The aim is metabolic capacity—not a permanently smaller body
Women are often encouraged to respond to midlife changes by continually removing food and trying to occupy less physical space. That approach can reduce weight, but it does not automatically build the tissue that helps the body handle fuel, maintain strength and remain active.
Muscle offers a different direction. It asks not only how little the body can eat or weigh, but what it can preserve, use and do. The goal is not to chase an artificially high metabolic rate. It is to build enough active tissue, training capacity and nutritional structure for the body to remain responsive through midlife and beyond.
That is the Strong & Calm approach: muscle as a metabolic resource, strength training as a long-term practice, and nutrition as the structure that supports both.
A practical next step
References
1. Juppi HK, Sipilä S, Cronin NJ, et al. Role of menopausal transition and physical activity in loss of lean and muscle mass: a follow-up study in middle-aged Finnish women. Journal of Clinical Medicine. 2020;9(5):1588. doi:10.3390/jcm9051588.
2. Sipilä S, Törmäkangas T, Sillanpää E, et al. Muscle and bone mass in middle-aged women: role of menopausal status and physical activity. Journal of Cachexia, Sarcopenia and Muscle. 2020;11(3):698–709. doi:10.1002/jcsm.12547.
3. DeFronzo RA, Jacot E, Jequier E, Maeder E, Wahren J, Felber JP. The effect of insulin on the disposal of intravenous glucose: results from indirect calorimetry and hepatic and femoral venous catheterization. Diabetes. 1981;30(12):1000–1007. doi:10.2337/diab.30.12.1000.
4. Holten MK, Zacho M, Gaster M, Juel C, Wojtaszewski JFP, Dela F. Strength training increases insulin-mediated glucose uptake, GLUT4 content, and insulin signaling in skeletal muscle in patients with type 2 diabetes. Diabetes. 2004;53(2):294–305. doi:10.2337/diabetes.53.2.294.
5. Poehlman ET, Dvorak RV, DeNino WF, Brochu M, Ades PA. Effects of resistance training and endurance training on insulin sensitivity in nonobese, young women: a controlled randomized trial. Journal of Clinical Endocrinology & Metabolism. 2000;85(7):2463–2468. doi:10.1210/jcem.85.7.6692.
6. Campbell WW, Haub MD, Wolfe RR, et al. Resistance training preserves fat-free mass without impacting changes in protein metabolism after weight loss in older women. Obesity. 2009;17(7):1332–1339. doi:10.1038/oby.2009.2.
7. Miller T, Mull S, Aragon AA, Krieger J, Schoenfeld BJ. Resistance training combined with diet decreases body fat while preserving lean mass independent of resting metabolic rate: a randomized trial. International Journal of Sport Nutrition and Exercise Metabolism. 2018;28(1):46–54. doi:10.1123/ijsnem.2017-0221.
8. Wang Z, Ying Z, Bosy-Westphal A, et al. Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure. American Journal of Clinical Nutrition. 2010;92(6):1369–1377. doi:10.3945/ajcn.2010.29885.
9. Aristizabal JC, Freidenreich DJ, Volk BM, et al. Effect of resistance training on resting metabolic rate and its estimation by a dual-energy X-ray absorptiometry metabolic map. European Journal of Clinical Nutrition. 2015;69:831–836. doi:10.1038/ejcn.2014.216.
10. Isenmann E, Kaluza D, Havers T, et al. Resistance training alters body composition in middle-aged women depending on menopause: a 20-week control trial. BMC Women’s Health. 2023;23:526. doi:10.1186/s12905-023-02671-y.
11. Currier BS, D’Souza AC, Fiatarone Singh MA, et al. American College of Sports Medicine position stand: resistance training prescription for muscle function, hypertrophy, and physical performance in healthy adults—an overview of reviews. Medicine & Science in Sports & Exercise. 2026;58(4):851–872. doi:10.1249/MSS.0000000000003897.
12. Nunes EA, Colenso-Semple L, McKellar SR, et al. Systematic review and meta-analysis of protein intake to support muscle mass and function in healthy adults. Journal of Cachexia, Sarcopenia and Muscle. 2022;13(2):795–810. doi:10.1002/jcsm.12922.