exercise increases or decreases immunity

Usually, we advise people who are frail and lack exercise to engage in physical activity to boost their immune system. Consequently, some people enthusiastically head to the sports field and run thirty laps in one go, only to end up bedridden the next day... thinking: Are you kidding me? They then swear never to exercise again. And that's the end of it...

So, isn't running and other exercises supposed to enhance our physical fitness and improve our immune function? Why do we fall ill when we start exercising without getting injured? (Running thirty laps right off the bat without getting injured but falling ill is quite unscientific! You should get injured first, right?)

We usually believe that once we develop a regular exercise habit, with a fixed frequency and duration of running/exercise each week, it benefits our disease resistance. However, research shows that in a resting state, there is no significant difference in immune function between those with regular exercise habits and those without.

So, should we still run? Those of you with relatively weak constitutions, please don't waver in your determination to gear up and go running. Read the following explanations before making a decision.

Here, we will discuss the relationship between exercise and immune function, focusing on the 'open window' theory and the 'J' curve model.

1. 'Open Window' Theory

From a physiological perspective, when the body engages in high-intensity acute exercise, it is in a state of high stress (stress refers to the chemical and bioelectrical changes in our body caused by environmental changes, similar to feeling nervous before an exam, with cold hands and feet, sweaty palms, or a racing heart before a competition).

The flow of blood speeds up, and the lymphocytes in our blood, which are primarily responsible for immune function, increase sharply during this period. However, after the high-intensity acute exercise ends, the level of lymphocytes drops rapidly, and their activity decreases.

These fluctuations can lead to a temporary decline in our body's immune function. A single acute exercise session can cause this lowered immune function to last for about 3-72 hours. During this time, various bacteria, microorganisms, and viruses can easily invade our body, making us more susceptible to diseases.

Therefore, we refer to this period of lowered immunity as the 'open window' period. This term vividly illustrates that during this stage, external pathogens can easily invade the body, as the body's 'window' does not close promptly to fend off intruders. Once they enter through the open window, they can easily cause diseases. Moreover, the greater the exercise intensity and duration, the more significant the impact on the body's immune function.

2. 'J' Curve Model

Numerous studies have found a close relationship between our body's immune function and exercise load, intensity, and duration. People who do not exercise regularly are in a natural immune state, while high-intensity, high-load, prolonged, and frequent exercise can strongly suppress our body's immune function.

Therefore, we hope to find a middle ground, a reasonable intensity, frequency, and duration that can improve the condition of being frail and sickly while effectively enhancing immune function.

Research has shown a subtle relationship between the intensity of exercise we choose and the rate of upper respiratory tract infections. Compared to the resting level of non-exercisers, moderate-intensity regular physical activity can reduce the rate of upper respiratory tract infections, while excessive intensity can increase it, forming a 'J' shaped curve.

Therefore, finding the appropriate exercise load and duration for ourselves is the correct choice to better cope with lowered immune function! It's not about giving up exercise entirely or pushing ourselves to the limit in one go, hoping to achieve results overnight...

3. Summary

OK, I believe everyone now understands the two theories! Here are some practical tips:

Moderate, scientifically guided running/exercise is more beneficial than prolonged inactivity;

Running/exercise should not be done on a whim, nor should one hope to achieve results overnight. Respect science, plan reasonably, tailor it to the individual, listen to your body, and progress gradually;

When starting to run or resuming after a long break, be sure to control the intensity and duration of the exercise;

Remember, don't leave the body's 'window' open too wide or for too long; and don't let the 'J' curve grow too high!