WHAT IS SO IMPORTANT ABOUT MUSCLE?

Quick takes

• Muscles not only move our joints, but also regulate and communicate with the organs in the body;

• Each time a muscle is used, it sends into the bloodstream an array of substances called myokines. There are thousands of myokines, thus muscles can send detailed information to impact bodily functions;

• We lose muscle as we age, each year after age 40 about 1% of muscle mass, 2% of muscle strength, and 5% of muscle power, but this is not inevitable;

• Sarcopenia is the name of the condition where muscle mass is reduced to the point of causing inflammation, which reduces muscle mass further;

• Muscle loss over time occurs in a stair-step manner caused by periods of immobility due to illness. Thus we should work on muscle mass and strength when we can to build up reserve, and also when bed bound if at all possible;

• We can also optimize strength gains by consuming enough protein, creatine, and omega 3s.

Favorite finds

• The BodySpec  or other body composition DEXA scan allows you to determine the amount of muscle present in arms and legs, which has been correlated with health outcomes.

• I’ve created a workbook to help you understand body composition, calculate how you compare to people your age in terms of muscle mass and fat distribution, and also how to evaluate your muscle quality.

• Grip strength is a health biomarker that can be estimated using an affordable meter, such as the Handexer Digital Strength Dynamometer;

• Fascinating podcast with Andrew Huberman and Pavel Tsatsouline reveals that lifting moderate weights and spacing out sets by 10 minutes leads to better gains in muscle strength (than lifting very heavy and spacing out only 2 minutes). The general idea is:
  - choose a weight that you can lift about 7-8 times

  - lift it only less than half that: 3 or 4 times

  - perform only 3 exercises (different muscle groups) over the course of 10 minutes

WHAT IS SO IMPORTANT ABOUT MUSCLE?

Deep Dive

As a physician, a common problem I’ve noticed is the tendency to compare the human body to a machine. This may explain how we have managed to underappreciate the importance of muscle.

WHAT ARE MUSCLES FOR?

The human body contains over 600 muscles according to Wikipedia, maybe up to 840, if you count muscles under voluntary control as well as smooth muscle and cardiac muscle. The obvious functions of muscle include (Mukund et al, 2020):

• Movement and locomotion

• Posture and stability

• Generating heat

• Energy storage

• Force generation

• Blood circulation

• Maintenance of the cardiac rhythm

• Regulation of organ systems like blood vessel diameter

• Control of the movement of food through the GI tract

• Control of bladder and gallbladder activity

• Helping to maintain cellular health by sensing oxygen levels

HOW MUSCLES TALK TO YOUR ORGANS

Far from being isolated tissue designed merely for movement, muscles function as sophisticated endocrine organs integrated with every system in your body. When muscles contract, they release thousands of hormone-like proteins called myokines into the bloodstream, which then travel to various organs exerting remarkable effects. About 650 myokines have been more rigorously studied and their effects include:

• Brain support: brain-derived neurotrophic factor (BDNF) and interleukin-6 (IL-6) enhance cognitive function;

• Adipose tissue modification: irisin promotes the browning of white adipose tissue, which improves metabolic efficiency. IL-6 reduces abdominal fat accumulation;

• Bone remodeling: IGF-1 and FGF-2 stimulate bone formation and suppress resorption, counteracting age-related bone loss. Irisin also enhances osteoblast bone building activity (Gomarasca et al 2020);

• Improving liver glucose metabolism and insulin sensitivity, reducing hepatic glucose production and regulating lipid oxidation (Laurens et al, 2020);

• Enhancing pancreatic β-cell function and thus insulin secretion (Laurens et al, 2020)';

• Improving the function of blood vessels (Laurens et al, 2020);

• Influencing gut bacterial ecology, and improving intestinal permeability (Bay and Pedersen, 2020). This, in turn, impacts the immune system;

• Directly impacting immunity, helping us fight cancer and harmful microbes.

A LANGUAGE BASED ON HORMONES

The complexity of these interactions is only now beginning to be understood, as each myokine can play different roles depending on its companions in the biochemical conversation. Each myokine may impact several organs, or target a specific organ. Each muscle function releases a different array of myokines. Thus these hormones provide the rest of the body with information on:

• Exercise type (resistance vs. endurance)

• Exercise intensity

• Exercise duration

• Muscle fiber type involvement

• Training status (conditioned vs. unconditioned muscles produce different myokine patterns)

• Whether exercise is occurring in the fed vs. fasted state

The temporal dimension adds another layer of complexity. Some myokine effects are immediate, while others involve cascading signaling pathways that unfold over hours or days. This allows for both acute responses to exercise and long-term adaptations.

NO SHORTCUTS!

This is why I remain skeptical of the possibility of an "exercise pill" – a pharmaceutical that might deliver exercise's benefits without the effort. The intricate interplay between individual physiology, gut microbiome, and the complex "language" spoken by muscles during different types of activity creates a symphony that seems impossible to reduce to a single compound.

HOW TO OPTIMIZE MUSCLE

Recent research highlighted in Dr. Rhonda Patrick's podcast reveals a critical insight: muscle development has optimal windows. For women, the teenage years represent a crucial period, while men experience their prime muscle-building years from early 20s through their 40s. 

Beginning adulthood with higher-quality muscle mass – with optimized fiber orientation tailored to individual activities – provides significant advantages for long-term health.

As adults, we can still optimize muscle mass and quality with regular strength training, consuming sufficient protein, and optimizing other hormones (such as testosterone) and nutrients (such as omega 3 fatty acids).

WHAT OLDER ADULTS SHOULD FOCUS ON

Luc van Loon, a prominent researcher in muscle metabolism and aging from Maastricht University, has made significant contributions to our understanding of age-related muscle loss (sarcopenia) and potential interventions (LIm et al, 2025). His key teachings include:

1. Anabolic Resistance: Van Loon has demonstrated that aging muscles become less responsive to protein intake and exercise stimuli—a phenomenon called "anabolic resistance." This means older adults require more protein and stronger exercise stimuli to achieve the same muscle protein synthesis response as younger individuals.

2. Protein Timing and Distribution: His research emphasizes the importance of protein distribution throughout the day. Rather than consuming protein primarily at dinner (as many older adults do), van Loon recommends spreading intake across meals, with approximately 25-30g of high-quality protein per meal to overcome the anabolic threshold.

3. Overnight Muscle Loss: Van Loon has conducted pioneering work showing that overnight fasting periods result in accelerated muscle protein breakdown in the elderly. This led to his research on pre-sleep protein consumption (particularly casein) to support overnight muscle maintenance.

4. Exercise + Nutrition Synergy: His work consistently demonstrates that the combination of resistance exercise and protein intake produces synergistic effects that are greater than either intervention alone, particularly in older populations.

5. Muscle Disuse Acceleration: His studies show that even short periods of disuse (like hospitalization or bed rest) can dramatically accelerate muscle loss in older adults, with some patients losing 1kg of muscle mass during just 5 days of hospitalization. Maintaining a minimum of strength training while on bedrest (if that is safe) could be critical.

KEY ROLE OF THE NERVOUS SYSTEM

Another fascinating aspect of muscle development involves neurological adaptation. Strength gains arise partly from changes at the neuronal level, as motor neurons literally learn to produce more force with the same muscle fibers. This explains why spacing exercise repetitions with 10-minute intervals often proves more effective for strength development than the conventional 30-90 second rest periods between sets. Similar to spaced repetition in learning (waiting 10 minutes rather than 1 minute between self-quizzing), optimal muscle training follows neurological principles. Memory formation involves modifications in synaptic communication, and "learning" to generate greater force likewise requires time for neuronal adaptation.

COOKBOOKS

Bay ML, Pedersen BK. Muscle-Organ Crosstalk: Focus on Immunometabolism. Front Physiol. 2020

Gomarasca M, Banfi G, Lombardi G. Myokines: The endocrine coupling of skeletal muscle and bone. Adv Clin Chem. 2020

Laurens C, Bergouignan A, Moro C. Exercise-Released Myokines in the Control of Energy Metabolism. Front Physiol. 2020

Lim C, McKendry J, Lees M, Atherton PJ, Burd NA, Holwerda AM, van Loon LJC, McGlory C, Mitchell CJ, Smith K, Wilkinson DJ, Stokes T, Phillips SM. Turning over new ideas in human skeletal muscle proteostasis: What do we know and where to from here? Exp Physiol. 2025

Mukund K, Subramaniam S. Skeletal muscle: A review of molecular structure and function, in health and disease. Wiley Interdiscip Rev Syst Biol Med. 2020