Kicking-ass into your 90s…optimising for future muscle function

Optimal muscle function is one of the most critical components of enabling individuals to be “kicking-ass into their 9th decade”, as my friend and colleague Dr Jack Kreindler would say. By midlife, we start to lose muscle mass (around 3–5% per decade after age 30 on average) [PMID: 19533617; PMID: 11477465], but the good news is that proper exercise and nutrition can significantly slow or even reverse this trend.

Figure 1: Age-related decline in skeletal muscle mass. Adapted from: PMID: 19533617

While muscle mass naturally declines with age, research shows that targeted exercise and nutrition can preserve both strength and function. Studies demonstrate that muscle function (how well muscles perform) is a stronger predictor of health than muscle size alone [PMID: 28549705; PMID: 36873826]. By understanding the science of training and recovery, individuals can maintain high physical performance well into older age.

Muscle power typically declines first with aging, followed by muscle strength, and then muscle mass. The rate of decline in muscle power is greater than that of strength or mass, beginning as early as the fourth decade of life and accelerating with advancing age. This early and rapid loss of power is primarily due to selective loss of size and impaired function of fast-twitch (Type II) muscle fibers, as well as nerve-muscle changes that disproportionately affect the ability to generate force quickly [PMID: 41016071].

Strength, endurance and hypertrophy: what’s the difference?

The way you train determines how your muscles adapt. Classic exercise science describes a “repetition continuum”: low-rep, heavy load training builds maximal strength, moderate-rep training is ideal for muscle hypertrophy (size gains), and high-rep, lighter load training builds muscular endurance [PMID: 33671664]. Muscular strength is defined as the ability to exert maximal force against resistance, typically characterized by lifting heavy weights at high intensities. Hypertrophy training is primarily aimed at increasing muscle size, whilst muscular endurance emphasises the ability to sustain prolonged effort. 

In practice, this framework has translated to recommendations for 1–5 reps per set with very heavy weight for strength goals, 8–12 reps with moderate weight for muscle growth, and 15+ reps with lighter weight for endurance. However, this prescriptive formula is misleading. Research now confirms these are not hard-and-fast rules.

Evidence supports the idea that heavy loads improve maximal strength, especially when strength is tested using the same type of exercises as used in training. This is the principle of specificity; that your body adapts best to what it practices most. However, when strength is tested using neutral tests not used in training, there is little difference across the loading strategies. For muscle growth, the evidence suggests that similar hypertrophy can occur across a broad range of loads, as long as the effort is close to failure [PMID: 40827709]. 

That means there’s no single “ideal” rep range for size gains. However, moderate loads (e.g. 8–12 reps) tend to be more efficient. This rep range is high enough to accumulate time-under-tension (ie the amount of time the muscle is actively lifting) and metabolic stress in the muscle, but heavy enough to also create mechanical tension and some muscle fiber damage, which are all stimuli for growth. Hypertrophy training causes the individual muscle fibers to grow thicker (by adding more myofibrillar proteins and/or fluid and glycogen storage in the muscle). Over time, this leads to visible increases in muscle size. Light loads require long, fatiguing sets which may impact adherence, while heavy loads often need more sets to achieve equal hypertrophy, and may increase joint stress or overtraining risk. There may be some benefit to mixing loading ranges, but more research is needed to confirm if this improves results meaningfully.

When it comes to muscular endurance, the evidence is mixed. Light loads may help, especially in lower body exercises, but overall, there’s no strong support for the benefit of a specific loading strategy. Also, most of this research has been done in men. Given that women tend to be more fatigue-resistant, it's possible that men and women may respond differently to training loads.

Why you can get stronger without getting bigger

Whilst some may pursue additional muscle mass for their specific goals, it’s easy to be distracted that muscle mass should be the primary target. A good example of this, given we know that for healthy longevity, function rather than mass is the holy grail, is the Instagram account of https://www.instagram.com/vladimirshmondenko/?hl=en who brings a touch of entertainment the debate of muscle size versus function. 

One common complaint (predominantly from the male population!), is the timeline of progress: how long does it take for muscles to get “functional” and strong, before they noticeably grow? You will have noticed this when you see the plates going up but notice a lack of visible progress or movement on the virtual needle of your smart scales. In the first weeks of a program, most strength gains come from neural adaptations, not from adding new muscle tissue. When training for strength, a number of adaptations in the neuromuscular system occur that mean that your nervous system gets better at recruiting muscle fibers and coordinating movement. Much of this early strength gain comes from neural improvements allowing better “motor unit activation”, and “muscle-firing rate, and synchronization”, scientific jargon for explaining that your body learns to use the muscle you already have more effectively. Over time, strength training can then also induce hypertrophy, but the initial focus is on making your existing muscle fibers fire faster and harder.

Nutrition

While resistance training provides the stimulus for muscle adaptation, the fuel we use to provide the building material is important. Many already understand that protein and a balanced diet are important but some nutritional considerations might alter depending on the focus of whether your goal is muscle growth, strength, or endurance. Rather than a blanket formula approach to nutrition for training, the concept of periodisation (adjusting the diet according to the work/training planned for that day) or to “fuel for the work required” is recommended [PMID: 29453741; PMID: 26891166]. 

For muscle hypertrophy, a caloric intake that supports growth is usually needed (often a slight surplus of calories) and sufficient protein/amino acids to repair and build muscle tissue. Before diving into the hot topic of protein, it’s important to avoid focusing on one component of the diet at the detriment of another. For example, fibre is overlooked for its link with muscle health. Data demonstrate that individuals with greater fiber consumption have higher relative lean mass and grip strength [PMID: 34585852] The mechanism is thought to involve modulation of the gut-muscle axis: dietary fiber promotes gut microbial diversity and the production of short-chain fatty acids, which may reduce systemic inflammation and improve amino acid availability, thereby mitigating anabolic resistance (see below) and supporting muscle protein building in older adults. 

Protein is anabolic (the growth signal). Think of protein as the bricks and mortar for your muscle, without enough of it, your body can’t build and remodel muscle fibers effectively. A protein-rich diet (with a focus on high-quality sources like lean meats, fish, dairy or plant proteins that contain all of the essential amino acids) is strongly linked to better muscle gains [PMID: 36873826; PMID: 29414855; PMID: 35187864; PMID: 38931241; PMID: 28642676]. High-quality protein sources, including both animal and plant-based proteins, can support muscle gains when consumed in sufficient quantities [PMID: 36822394].

The critical question around protein is often not just how much, but when. While the magnitude of benefit is nuanced, we know two factors matter: total daily intake and distribution. The American College of Sports Medicine recommends that protein intake be distributed evenly across meals (every 3–5 hours), with approximately 0.25–0.3 g/kg body weight per meal. They also suggest that immediate post-exercise protein ingestion may maximize muscle protein synthesis and potentially enhance gains in muscle mass and strength over time, whilst also improving recovery during delayed onset muscle soreness [PMID: 26891166]. However, the window to fuel for optimal muscle building is up to 24 hours after exercise [PMID: 28642676] and more recent reviews of the evidence suggest that total daily protein intake is the primary determinant of muscle mass gains, and that specific timing (e.g., post-exercise vs. other times) does not confer additional benefit for muscle hypertrophy in healthy adults, including those in their 30s to 60s [PMID: 32232404; PMID: 32429355]. One study found that casein protein before bed can increase protein building overnight [PMID: 22330017]. Very high protein intake hasn’t been shown to be more beneficial but might have specific use cases in trained athletes eg when in a hypocaloric (energy deficit phase) [PMID: 26891166]. 

Whilst a big calorie surplus might not be required for strength gains, an adequate intake of carbohydrate to replenish glycogen in muscles (so you can hit your next heavy workout with full intensity), and adequate protein to repair any muscle damage from heavy loading is required. Hydration and micronutrients (like electrolytes, vitamins, minerals) are also critical in supporting nerve and muscle function during maximal efforts.

For endurance training, the nutritional emphasis often shifts more towards carbohydrates and overall energy, since long-duration or high-rep exercise heavily depletes glycogen stores. Endurance athletes typically ensure they have good carbohydrate availability for their workouts and events. However, protein remains important for endurance athletes too as it helps repair muscle fibers and can even be used as a minor fuel source in long efforts. If you’re mostly doing endurance work but want to maintain muscle mass, pay attention that you’re not undereating protein. Another consideration is that endurance training burns a lot of calories, so if your goal is to also build some muscle, be mindful to eat enough. Many avid runners or cyclists struggle to add muscle because their high activity level creates a calorie deficit that their diet isn’t compensating for.

In summary, while optimal protein distribution and post-exercise timing may offer modest benefits, ensuring adequate total daily protein intake remains the most important factor for muscle hypertrophy and function.

Specific supplements

Creatine is one of the most studied supplements in this domain. In my recent article, we discussed the specific benefits for women. Supplementing with creatine increases creatine phosphate stores in muscles. The practical effect is often a boost in strength, power, and the ability to squeeze out an extra rep or two, which over time leads to greater training adaptations. There is a mountain of evidence for creatine’s benefits in terms of muscular health, and novel research is looking into the cognitive benefits too [PMID: 40944139; PMID: 39519498; PMID: 37432300].

Beta-alanine is a non-essential amino acid that, once ingested, helps increase the levels of carnosine in your muscles which results in a buffering in the muscles to delay that burning fatigue feeling and allows you to sustain intense exercise for longer [PMID: 26175657; PMID: 27797728]. For muscle function, beta-alanine may indirectly support gains by allowing higher training volumes and intensities, particularly during high-volume resistance training with short rest intervals. However, beta-alanine does not directly increase maximal strength or muscle mass; its primary benefit is in buffering acidosis and delaying fatigue, which can facilitate more effective training sessions [PMID: 40995761].

Caffeine is also well-established as an ergogenic aid for power and strength performance. It acts as a central nervous system stimulant, reducing perceived exertion and increasing alertness, which can acutely enhance strength, power output, and training volume. Typical effective doses are 3–6 mg/kg body weight, taken about 60 minutes before exercise [PMID: 39170391; PMID: 39408214; PMID: 37650704].

More recent research has looked at nitrate supplementation via beetroot shots/juices and found some aspects of muscle function, such as power and strength, are enhanced when taken before exercise [PMID: 36417361; PMID: 41010367].

Barriers to building muscle

Many individuals face barriers to muscle hypertrophy despite doing “all the right things” in the gym and seeing strength increase. 

Training volume: You might be seeing strength gains on a few heavy sets, but stimulating muscle growth often requires more total volume (sets × reps) directed at a specific muscle. Evidence shows a clear dose-response relationship between training volume and muscle growth. If the same routine hasn’t resulted in changes, there may be a case to consider increasing volume gradually (add an extra set or two, or train each muscle group more frequently per week). On the flip side, too much volume without adequate recovery can also lead to plateaus. There’s a sweet spot: push enough to challenge the muscle, but not so much that you chronically exceed your ability to recover. Pay attention to signs of overtraining (extreme soreness, dropping performance, fatigue) and adjust accordingly.

Recovery: Muscle isn’t built in the gym, it’s built between sessions when you recover. An underestimated factor in hypertrophy is sleep. Poor sleep or too little of it can blunt muscle gains in multiple ways. Sleep is when your body releases growth hormone and increases the muscle repair processes. Chronic sleep deprivation creates a catabolic (muscle-breaking) state, reducing muscle protein synthesis and increasing cortisol (a stress hormone), while lowering testosterone and other growth factors. In fact, just one night of total sleep deprivation can drop muscle protein synthesis rate by ~18% [PMID: 33400856]. 

Nutrition: You can’t build a house without bricks. In muscle terms, protein/amino acids are your bricks and calories are your energy supply. A very common barrier to hypertrophy is simply that a person’s diet isn’t supporting their goal. They might be unintentionally undereating, very common when also trying to lose fat or due to a busy lifestyle, forgetting meals. To put on muscle mass, you generally need to be in at least a slight caloric surplus and consume ample protein but for those in a phase of trying to lose fat by being in a calorie deficit, an increased protein requirement might be holding back muscle gains [PMID: 26891166]. As highlighted earlier, whole-food, quality protein is crucial for optimal muscle growth. Don’t skimp on overall quality nutrition either: fruits, vegetables, healthy fats, and whole grains support recovery and hormonal balance too, the latter being an important barrier to consider too.

Anabolic resistance: Hormones play a huge role in muscle development. The elephant in the room for midlife individuals is the natural decline in anabolic hormones like testosterone (in men) and estrogen (in women) that occurs with age. Men’s testosterone levels typically drop about 1–2% per year after age 40, and women experience a big hormonal shift during menopause that can affect muscle mass [PMID: 1719016]. Lower sex hormones can make it harder to build muscle (and easier to lose it) compared to the 20s. For men, testosterone is a key driver of muscle protein synthesis.  Without jumping into a whole different topic of testosterone replacement, for most, the strategy is to fight the decline by staying consistent with resistance training (which in itself boosts or at least maintains hormone levels), eating a nutrient-dense diet, and considering lifestyle factors that optimise hormones (like reducing chronic stress, getting enough sleep, moderating alcohol). Resistance training is actually one of the best ways to naturally elevate or maintain testosterone and growth hormone levels as we age. Ensuring high quality protein becomes more important from 50s onwards due to this anabolic resistance too. Older adults may require higher intakes to overcome anabolic resistance, and leucine-rich sources are particularly effective.  Older adults require protein intakes about 67 % higher than their younger counterparts to maximally stimulate postprandial muscle protein synthesis rates [PMID: 36822394]. 

Summing it all up

Ultimately, the route to maintaining optimal muscle function and high performance into your ninth decade is an exercise in physiological resilience. This is not a one-size-fits-all training formula, but a personalised, nuanced and holistic approach. Success is found not just in the weight you lift, but in the intensity of effort applied, the consistency of protein signaling (especially given the challenge of anabolic resistance with age), and, critically, the quality of recovery. By viewing sleep as a non-negotiable performance tool, managing your workload to avoid the catabolic effects of chronic inflammation, and considering incorporating evidence-based supplements like creatine, you build the metabolic health, strength, and functional capacity necessary to ensure your best decades are ahead of you.

Q&As

Q: What is the typical rate of muscle mass decline (sarcopenia) in adults after age 30?

A: Muscle mass decreases approximately 3–8% per decade after the age of 30, with the rate of decline accelerating significantly after age 60.

Q: For long-term health, what is considered a more useful predictor of outcomes: muscle mass or muscle function?

A: Muscle function (strength) dominates the scientific literature as the most useful predictor of outcomes related to long-term health and performance, rather than muscle mass.

Q: How does low-load resistance training compare to high-load training (HL-RET) for muscle size gains (hypertrophy)?

A: Studies show that low-load resistance exercise training (20–25 repetitions) taken to volitional failure results in comparable increases in muscle size (hypertrophy) to high-load training (3–5 repetitions).

Q: If load is not the sole factor for hypertrophy, what is the critical determinant?

A: The intensity of effort, specifically training close to volitional muscular failure, is a critical driver for hypertrophy across a wide spectrum of loading zones.

Q: Why do most strength gains occur quickly during the first weeks of a new program?

A: Most initial strength gains come from neural adaptations, such as improved motor unit activation and coordination, as the nervous system learns to recruit existing muscle fibers more effectively.

Q: What is Net Protein Balance (NPB), and why must it be positive for muscle growth?

A: NPB is the algebraic difference between Muscle Protein Synthesis (MPS) and Muscle Protein Breakdown (MPB). Muscle growth (hypertrophy) occurs only when NPB is positive, meaning MPS exceeds MPB.

Q: What two primary factors synergistically promote a positive Net Protein Balance (NPB)?

A: Resistance exercise (external loading) and protein consumption (hyperaminoacidemia) are the two primary factors that independently and synergistically influence NPB.

Q: How does anabolic resistance affect protein requirements in older adults?

A: Older adults may require protein intakes approximately 67% higher than their younger counterparts to maximally stimulate postprandial muscle protein synthesis rates, due to age-related anabolic resistance.

Q: What is the mechanism and proven safety profile of Creatine Monohydrate?

A: Creatine Monohydrate (CM) is the most effective ergogenic supplement for increasing high-intensity exercise capacity and lean body mass. It is safe for both short- and long-term use in otherwise healthy individuals, with extensive research refuting myths of renal impairment. 

Q: What is the effective duration and mechanism of Beta-Alanine supplementation?

A: Beta-alanine works by increasing muscle carnosine concentrations, which buffers the hydrogen ions that cause metabolic fatigue. It provides a modest benefit for intense exercise lasting up to approximately 25 minutes. 

Q: How does chronic lack of sleep create a catabolic (muscle-breaking) state?

A: Sleep deprivation weakens muscle recovery by increasing protein breakdown and adversely affecting protein synthesis. It also disrupts the release of human growth hormone (hGH), which is vital for growth and repair processes during Slow-Wave Sleep (SWS).

Q: How does chronic systemic inflammation (from overtraining) impede hypertrophy?

A: Chronic inflammation activates cytokines (like TNF-α) that downregulate protein synthesis, severely limiting the body's ability to build new muscle tissue.

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