Why Muscle Contraction Is More Than Exercise

Exercise is good for the brain; it lifts mood, sharpens focus, and improves sleep, but what most people do not know is why. And understanding the why turns out to matter considerably for how you think about physical training as part of a wider stress and resilience strategy.

The answer starts with a discovery made in the early 2000s by a Danish researcher at the University of Copenhagen, Dr Bente Klarlund Pedersen. Her work demonstrated something that changed how scientists understood the role of muscle in the body: when skeletal muscle contracts, it releases biochemical signalling molecules into the bloodstream that communicate with distant organs, including the brain.

She named these molecules myokines.

Skeletal muscle, it turned out, functions as a genuine endocrine organ, capable of producing and secreting hundreds of peptides that exert endocrine effects on tissues throughout the body, including the brain, liver, adipose tissue, bone, gut, and pancreas [1, 2]. This was not a minor refinement of existing knowledge. It was a paradigm shift in how exercise-induced benefits are understood.

What myokines actually do

The myokine field has expanded significantly since Pedersen’s original work, and several key myokines have now been identified that cross the blood-brain barrier and directly influence brain function [3].

BDNF is the most extensively studied in relation to brain health. BDNF is a neurotrophin vital to the survival, growth, and maintenance of neurons in key brain circuits involved in emotional and cognitive function [4], and its release is significantly amplified by muscular contraction. It promotes neuroplasticity, the brain’s capacity to adapt, form new connections, and regulate itself. Reduced BDNF is consistently associated with depression, cognitive decline, and impaired stress resilience.

Exercise-induced BDNF in skeletal muscle can cross the blood-brain barrier, supporting the potential benefits of BDNF on mind and mood, and preliminary results suggest that BDNF may be a promising predictor of intervention responses among individuals with depression [5].

Irisin is another myokine of particular relevance. Released from muscle during both aerobic and resistance exercise, irisin crosses the blood-brain barrier and initiates a neuroprotective genetic programme in the hippocampus [6]. The hippocampus is involved in memory, emotional regulation, and the body’s stress response. Irisin’s capacity to upregulate BDNF in this region makes it a significant link between physical training and psychological function.

IGF-1 is another exercise-released molecule that works in partnership with BDNF. Produced in both the liver and muscle, it travels to the brain where it supports the growth, repair, and protection of brain cells and amplifies the neuroplastic effects of BDNF itself [5].

Why this matters for stress and mood

The implications of this research for stress resilience are significant and largely absent from mainstream conversations about mental health and performance.

When muscles contract regularly, they keep sending those biochemical signals to the brain, supporting mood, sleep, and the brain’s ability to regulate stress [3]. When it doesn’t, those signals go quiet. This is not a theoretical claim. The pathway from muscle contraction to brain function is well established in the research.

For people under sustained pressure, chronic work demands, poor sleep, and accumulated stress load, this matters directly. The brain’s capacity to stay regulated and resilient is not just a psychological question. It depends partly on the biochemical environment that regular physical activity creates [7].

Put simply: a brain that is regularly supported by myokine signalling is more adaptable, more able to regulate its own stress response, and more resilient under pressure. A brain that isn’t is working harder with less support — regardless of how much mindset work or psychological intervention is applied on top.

The body is not separate from the mental load. It is part of the infrastructure that carries it.

Why physical training sits within a stress resilience strategy

The traditional framing of exercise is mechanical: it burns energy, builds strength, and improves cardiovascular function. That framing is accurate, but it is incomplete. Muscle is not just producing force. It is actively communicating with the rest of the body and the brain.

This is why physical training belongs inside an integrated approach to stress and resilience as a direct input into brain regulation. The psychological and neurofeedback layers of a resilience programme address how the brain processes and regulates experience. The muscular layer influences the biochemical conditions under which that regulation occurs.

These are not parallel tracks. They are interactive. A brain supported by adequate myokine signalling has more neuroplastic capacity to work with. The work that happens in the other layers, the psychological reflection, the neurofeedback training, the breathing retraining, operates on better-prepared ground.

The efficiency of contraction: where EMS becomes relevant

One of the most interesting findings in myokine research is that the signal is triggered by the muscle contraction itself, not by how hard you are working, how fast your heart is beating, or how much effort you feel you are making.

This is where EMS (electric muscle stimulation) strength training becomes directly relevant.

EMS works by delivering electrical impulses to the muscles, causing them to contract, without requiring the cardiovascular exertion of conventional training. And research confirms that this electrically induced contraction is enough to trigger myokine release. Studies have shown that EMS produces measurable increases in both BDNF and cathepsin B, two key muscle-derived molecules that cross the blood-brain barrier and support neuroplasticity [8, 9]. Cathepsin-B promotes BDNF production in the hippocampus, the brain region involved in memory, mood, and stress regulation.

In plain terms: the brain-supportive benefits of muscle contraction require the muscle to contract. EMS delivers that stimulus efficiently and safely, recruiting a large amount of muscle throughout the body in a single session.

For adults who are time-constrained, managing fatigue or injury, or who simply need an effective alternative to conventional training, this matters. The contraction is the signal. EMS delivers it.

How this connects to IHHT and the metabolic layer

Myokines do not work in isolation. Their release depends partly on the health of the cellular machinery that powers muscle contraction. This is where IHHT — Intermittent Hypoxic-Hyperoxic Training enters the picture.

IHHT works at the mitochondrial level, improving how efficiently your cells produce and use energy. This matters for myokine signalling because many of the key myokines, including irisin, are produced through the same cellular pathway that mitochondrial training supports [7]. In other words, a body that produces energy efficiently is also a body that communicates more effectively between its muscle and its brain.

Think of it this way. EMS stimulates the contraction that triggers myokine release. IHHT supports the cellular energy infrastructure that underpins the whole process. Strength training provides the ongoing, sustained stimulus that keeps those signals active over time.

Each addresses a different layer of the same system. Together they do something that no single intervention achieves alone, they support the physical layer of resilience not just mechanically, but biochemically. Which is, it turns out, what exercise has always been doing. The research just now explains why.

The bottom line

Muscle is not passive tissue that benefits the body only through force production. It is an endocrine organ in continuous biochemical communication with the brain.

When muscles contract, they release signalling molecules that cross the blood-brain barrier, stimulate neuroplastic growth factors, reduce neuroinflammation, support mood regulation, and improve the brain’s capacity to adapt under stress. When muscle is inactive or undertrained, those signals go quiet and one consequence is a less adaptable, less resilient brain operating in a less supportive biochemical environment.

Physical training is not an optional addition to a stress resilience strategy. It is one of the primary inputs that directly support the brain.

The body has always known this. The research is catching up.

What to read next: Muscle Is a Health Asset: Why Adults Need to Protect It

Back to main guide: Strength, Muscle and Physical Capacity

References

1. Pedersen, B.K. & Febbraio, M.A. (2008). Muscle as an endocrine organ: focus on muscle-derived interleukin-6. Physiological Reviews, 88(4), 1379–1406.
2. Severinsen, M.C.K. & Pedersen, B.K. (2020). Muscle–organ crosstalk: the emerging roles of myokines. Endocrine Reviews, 41(4), 594–609.
3. Rai, M. & Demontis, F. (2022). Muscle-to-brain signalling via myokines and myometabolites. Brain and Behaviour, 12(1), e2476.
4. Phillips, C. (2017). Brain-derived neurotrophic factor, depression, and physical activity: making the neuroplastic connection. Neural Plasticity, 7260130.
5. Chacón-García, M. et al. (2024). Myokines and the brain: a novel neuromuscular endocrine loop. Journal of Neuropsychiatry and Clinical Neurosciences.
6. Jiménez-Maldonado, A. et al. (2021). Multiple roles in neuroprotection for the exercise-derived myokine irisin. Frontiers in Aging Neuroscience, 13, 649929.
7. Yuan, Y. et al. (2025). Exercise orchestrates systemic metabolic and neuroimmune homeostasis via the brain–muscle–liver axis. European Journal of Medical Research, 30, 412.
8. Sánchez-Martínez, J. et al. (2019). Neuromuscular electrical stimulation: a new therapeutic option for chronic diseases based on contraction-induced myokine secretion. Frontiers in Physiology, 10, 1463.
9. Vints, W.A.J. et al. (2024). Influence of stimulation frequency on brain-derived neurotrophic factor and cathepsin-B production in healthy young adults. Journal of Comparative Physiology B, 194, 543–553.
10. Frontiers in Physiology (2024). Muscle–brain crosstalk mediated by exercise-induced myokines. Frontiers in Physiology, 15, 1488375.