Skeletal muscle is more than a contractile tissue. It can release proteins, metabolites, and extracellular vesicles that participate in local and whole-body signalling. Those molecules are often described as myokines when they are produced by muscle, and exerkines when they are associated with exercise more broadly.
That is a productive area of research. It is also an area where a measured molecule can quickly become an exaggerated promise. A signal in blood is not automatically proof of where it came from, what it does in a person, or whether increasing it improves health.
What the terms mean
The categories overlap. A myokine may be a muscle-derived protein with local or distant effects; an exerkine is a broader exercise-responsive signal that may include proteins, metabolites, lipids, and extracellular-vesicle cargo. Modern reviews describe skeletal muscle as an endocrine and paracrine organ, while also emphasizing the need for better assays, tissue attribution, and causal experiments.
Exercise mode, intensity, duration, training status, nutrition, sleep, and sampling time can all change the signal measured. A post-exercise blood sample therefore describes a response to one context, not a universal “muscle message.”
What researchers are studying
Interleukin-6
Exercise can transiently increase interleukin-6 from working muscle. Its role depends on timing, concentration, tissue, and the surrounding physiological state. It is not accurate to label every exercise-related IL-6 response either “inflammation” or a guaranteed anti-inflammatory benefit.
Irisin and FNDC5
Irisin is often presented as a switch that turns white fat into calorie-burning brown fat. Human measurement and biological interpretation remain difficult, and the existence of a signal does not establish a predictable fat-loss effect from a particular lifting session. It should not be used to justify an “irisin-maximizing” workout.
Myostatin
Myostatin is part of a growth-regulatory family that can restrain muscle development. Rare genetic conditions and drug-development research show that the pathway matters biologically. They do not provide a safe supplement or training lever for bypassing normal limits.
Lactate, FGF21, and extracellular vesicles
These are examples of signals studied in exercise physiology, but their source, kinetics, and downstream effects vary. A change in lactate or a circulating protein is not the same as a change in muscle size, insulin sensitivity, cognition, or cancer risk.
What this means for training
The most defensible practical conclusion is ordinary: resistance and aerobic exercise can improve established outcomes such as strength, fitness, and function when programmed and performed consistently. Those outcomes do not require tracking a myokine panel or chasing a particular acute biomarker spike.
Use signalling research to understand mechanisms, not to replace outcome evidence. If a claim says that one exercise, supplement, sauna protocol, or timing strategy “maximizes” a molecule and therefore prevents disease or builds more muscle, ask whether the study measured a meaningful human outcome. Often it measured only a short-term concentration or cell-culture response.
Bottom line
Muscle-to-organ communication is real and scientifically important. The current evidence supports a complex, context-dependent signalling network—not a secret language with a simple translation into fat loss, anti-aging, cancer protection, or guaranteed hypertrophy. Train for measurable outcomes and treat circulating myokine claims as an active research area.
Evidence
Sources
- Hah et al., “Decoding the Endocrine Code of Skeletal Muscle” — 2026 review of myokines, exerkines, extracellular vesicles, and the limits of causal interpretation.
- Chow et al., “Exerkines in health, resilience and disease” — review of exercise-responsive signals and translational uncertainty.
- Exercise-mediated muscle-organ crosstalk review — context for interpreting proposed endocrine effects.
- Exercise-induced myokine research — an example of why timing, tissue source, and outcome selection matter.
Related reading
Limits of the evidence
Much of the field is mechanistic, acute, observational, or based on cell and animal models. Human circulating biomarkers can be difficult to attribute to one tissue and do not by themselves establish a clinically meaningful benefit.
APPLY IT IN THE GYM
Build the body people notice.
Surpass keeps working sets, recent performance, targets, and rest timing together on iPhone.
Start free on iPhone