How Recovery Affects Your Immune System

You know how a relaxing holiday can help you recharge and tackle your goals—at work, at the gym and in life—with even more gusto than before? Well, it turns out your immune system can benefit from a little R&R too.

Quick biology refresher: Your immune system is a complex network of cells and proteins that serves as your body's first and best line of defence against harmful viruses and bacteria. To strengthen it, you want to focus on other areas of wellness—in this case, recovery—that directly affect the network.

"One hard, exhaustive bout of exercise, like going all out for an hour, will decrease the number and function of your white blood cells for a few hours", says Jimmy Bagley, PhD, an associate professor of kinesiology at San Francisco State University. Assuming you don't eat indoors at a restaurant or sip on your friend's smoothie afterwards, that's not a huge deal. But frequent, intense exercise may have a cumulative effect.

"People who exercise too much at a high intensity, without taking proper rest days, tend to have chronically high levels of inflammation", says Gregory Grosicki, PhD, an assistant professor of kinesiology at Georgia Southern University. "The inflammation compounds the more sessions you pile on back to back".

What can then happen is your immune cells try to fix the inflammation (they can't), leaving you more vulnerable to outside pathogens. "Your body becomes distracted by chronic inflammation, when it should be fighting the invader that's sitting in your nose", says Bagley.

Here's how to optimise your recovery routine to help keep your body's defensive team intact.

1. Space out truly tough workouts.
   You might think intense means a tough WOD. But Peake says endurance activities, like a long run or bike ride, especially if performed at a challenging pace, are a bigger concern. That's because the actual definition of intense exercise is "when you maintain a heart rate at or above 85 percent of the age-predicted maximum for 30 minutes or more", says Peake. (You probably don't need to do the maths to know when you're working at that level.)
   
   "Resistance exercise, on the other hand, is more intermittent, so it doesn't involve the same sustained levels of stress on the body as endurance exercise does", says Peake. And HIIT workouts tend to last less than an hour and have baked-in rest intervals, which offer a degree of mid-workout recovery, research shows. That said, for immunity and muscle-health purposes, you probably don't want to do them every single day either.
   
   Of course, that doesn't mean intense exercise is off the table. It just means you should take it easy afterwards, even if you're not that sore the next day. Try light activities, like stretching, walking, yoga and foam rolling, says Rebecca Breslow, MD, a sports medicine physician at the Department of Orthopaedic Surgery at Harvard Medical School. Movement gets immunity cells circulating and can help reduce stress that can compromise your system, adds Bagley. And if you are sore, wait for that achy feeling to subside before you push yourself again, says Breslow.
   
2. Prioritise those Zs.
   Growth hormone, which repairs your muscles and produces virus-fighting T cells, is released primarily during sleep. Peake says you should get a minimum of seven and a half hours a night, but allow for more if you're training extra hard.
   
3. Watch for signs of overtraining.
   No matter your sport, Dr Breslow says to take your volume down if you notice any telltale signs of overdoing it: unexplainable irritability, fatigue, excessive soreness or a change in appetite. "With mild symptoms of overtraining, we generally recommend a reduction in training volume and intensity by 50 to 75 percent for one or two weeks", Dr Breslow says. If you feel like those symptoms are affecting your day-to-day or not letting up after several easy days, limit yourself to 30 minutes of light, low-impact exercise (aka active recovery) for a few weeks, or until you start to feel normal again.
   
4. Factor in other stressors.
   Of course, exercise isn't the only thing that affects your immune system, for better or worse. Work problems and personal issues can also take their toll. Your body doesn't care why you're stressed. It only cares that you're stressed in the first place.
   
   "If you're experiencing social or work issues, then reduce the intensity of your training until you manage them", says Peake, in order to prevent throwing your immune system into overdrive. And add some mindfulness exercises to your routine: just 25 minutes of meditation reduced stress in a study published in "Psychoneuroendocrinology".
   
5. Just chill.
   While all of these tips can help keep your immune system healthy, stressing too much about whether you're doing recovery right is like taking one step forwards and two lunges back. So don't overthink it. Do what feels good for your mind and body when you need it, and your immune system will reap the rewards.