EXERCISE HELPS strengthen your immune system, but too much exercise weakens it. So what determines the sweet spot? That’s the question asked by a neat new study from Neil Walsh and his colleagues at Bangor University, just published in Medicine & Science in Sports & Exercise.
The key difference about the new study is that, unlike hundreds of previous studies, they measure immune function “in vivo” rather than in test tubes or animals:
While hundreds of studies have explored the links between exercise and immune function, nearly all use rodents or approximate immune function by measuring the abundance of certain markers in the blood or saliva. But the immune system is a co-ordinated network throughout the body that includes neural and hormonal responses, so testing the response of a few cells in a test tube doesn’t give a reliable prediction of immune behaviour, Walsh says.
In a study published this month in Medicine & Science in Sports & Exercise, Walsh and his team administered a chemical called diphenylcyclopropenone (DPCP) through a patch on the lower back, 20 minutes after exercise bouts of various lengths and intensities. DPCP is an antigen that triggers the development of a brand new immune response; the strength of the response can be assessed by applying more DPCP to the skin four weeks later and measuring the resulting redness and skin thickening.
Using this technique, the researchers compared 30 minutes of “moderate” treadmill running, 30 minutes of “intense” running (where you’d struggle to maintain a conversation), 120 minutes of “moderate” running, and a control group with no running.
The conclusion was clear: a long duration of exercise (120 minutes) causes a temporary weakening of immune function, while short (30 minutes) intense exercise doesn’t. How generalisable is this finding? That’s very hard to say. For example, would long bike rides, which are generally less “stressful” on the body compared to long runs, produce the same effect? What role does overall fitness play – i.e. if you’re used to running two hours every weekend, does it cease to be a stress? Do all aspects of immune function follow a similar pattern as this particular one measured in the study? Is 120 moderate minutes simply a harder workout than 30 intense minutes? All these are open questions, and I certainly don’t think we should oversimplify the takeaway message. But it’s an interesting new approach to studying exercise immunology, and it offers some food for thought about how duration and intensity affect immune function.