The effect of exercise on cytokines: implications for musculoskeletal health: a narrative review, 2022, Sophie Docherty et al

Abstract
The physiological effects of physical exercise are ubiquitously reported as beneficial to the cardiovascular and musculoskeletal systems. Exercise is widely promoted by medical professionals to aid both physical and emotional wellbeing; however, mechanisms through which this is achieved are less well understood.

Despite numerous beneficial attributes, certain types of exercise can inflict significant significant physiological stress. Several studies document a key relationship between exercise and immune activation. Activation of the innate immune system occurs in response to exercise and it is proposed this is largely mediated by cytokine signaling. Cytokines are typically classified according to their inflammatory properties and evidence has shown that cytokines expressed in response to exercise are diverse and may act to propagate, modulate or mitigate inflammation in musculoskeletal health.

The review summarizes the existing literature on the relationship between exercise and the immune system with emphasis on how exercise-induced cytokine expression modulates inflammation and the immune response.

Summary box
What’s already known

• It is widely recognised that regular exercise promotes healthy living in terms of a person’s physical and psychological wellbeing.
  
  
• The relationship between exercise and the immune system provides an opportunity to explore the complex interaction between basic physiological and immunological mechanisms in musculoskeletal health and disease.

What this review shows

• Activation of the innate immune system occurs in response to exercise and it is proposed this is largely mediated by cytokine signalling.
  
  
• Emphasises how exercise-induced cytokine expression modulates inflammation and the immune response.
  
  
• Discusses how exercise induced cytokine production is crucial in maintaining musculoskeletal health and how it is altered in disease.

Conclusions
Exercise induces significant physiological changes in the immune system, including characteristic cytokine responses. Most notable is a marked elevation in muscle-derived IL-6 which, despite being traditionally regarded as a potent pro-inflammatory cytokine, helps orchestrate an anti-inflammatory immune response in exercise.

Despite IL-6 and pro-inflammatory cytokines being implicated in various chronic musculoskeletal conditions, this exercise-induced increase in IL-6 does not appear to lead to inflammatory exacerbations in these conditions, with exercise generally conferring beneficial effects. This interaction raises intriguing questions about how to best utilize this effect for the treatment of these conditions and offers exciting research opportunities within the fields of sports medicine and immunobiology, both clinically and experimentally.

With continued research, exercise and its associated cytokine profile may provide an effective therapeutic avenue that will lessen the burden of musculoskeletal disease.
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I think that study might be the equivalent of trying to understand traffic flows in megacities by taking a few snapshots of vehicles in a few locations. There's a whole lot more complexity involved. Just as an example, a crash might have some obvious effects on local traffic, but also some less obvious effects further away due to the crash being reported on the radio, or phone messaging, or some other communication link.

This study might be of some use, but there's a lot more complexity to be studied further.