can stretching really relieve muscle fatigue
After long-distance running, the body becomes fatigued, and muscles become stiff and weak. This is an indisputable fact. It is well known that stretching should be done after running to relax tense muscles and alleviate fatigue. So, what exactly happens to the muscles during stretching? Does stretching really relieve muscle fatigue?
1. What is fatigue?
To determine whether stretching is truly effective, we first need to understand what causes physical fatigue from exercise. Fatigue is defined as 'the inability of the body to maintain a predetermined intensity of exercise or to sustain its function at a specific level.' In other words, after exercising to a certain extent, the body becomes fatigued, and the working capacity of the muscles temporarily decreases.
The process of exercise-induced physical fatigue generally goes through the following four stages:
The above are the four stages of the fatigue process. From the perspective of fatigue location, it can be divided into central fatigue (brain and spinal cord) and peripheral fatigue (peripheral nerves).
Central fatigue involves neuroprotective inhibition, reduced motor neuron impulse discharge, increased inhibitory neurotransmitters, etc.; while peripheral fatigue includes muscle cell membrane disorder, sarcoplasmic reticulum function changes, and cross-bridge cycling issues, among others. In simpler terms: exercise-induced physical fatigue is caused by multiple factors, and the process is quite complex.
After fatigue, through natural rest or some recovery methods such as stretching and massage, to what extent can the functional state be restored? Or how long does it take to return to a vigorous state? The author will present an experiment to explain all this.
2. Let the data speak
First, the author used a device called a Muscle Status Tester (TMG) to measure the muscle status of dozens of subjects before and after high-intensity exercise. There are two key indicators:
One is called muscle contraction time (Tc), which refers to the speed of muscle contraction. The smaller the value, the more excited the muscle is, and the faster the contraction speed; the larger the value, the more fatigued the muscle is, and the slower the contraction speed.
The other is called muscle radial displacement (Dm). When the muscle contracts, its diameter increases, meaning the muscle becomes thicker. This indicator represents the degree of muscle thickening. When the muscle is stiff, this value is smaller, indicating muscle fatigue; when the muscle is relaxed and elastic, this value is larger, indicating a good muscle state.
Please see the experimental results in the figure below. The author tested the muscle status of the subjects at five time points: before training, immediately after training, immediately after stretching and relaxing, 24 hours after exercise, and 48 hours after exercise.
From the figure, we can see that after high-intensity training, due to fatigue, the muscle contraction time increases (Tc increases), and muscle stiffness increases (Dm decreases).
3. Stretching can only eliminate muscle stiffness
After static stretching, muscle stiffness is alleviated to a certain extent, but muscle contraction time hardly decreases. This fully demonstrates that stretching can effectively relieve muscle stiffness caused by fatigue, and this immediate effect is very obvious. However, restoring muscle excitability is not so easy. This study shows that it takes 48 hours for muscles to fully recover their original excitability after a single high-intensity training session. This is why we recommend resting for 2 days after a high-intensity training session.
4. Rest is the main method to eliminate fatigue
In other words, stretching can promote muscle relaxation after exercise but cannot restore muscle contraction ability. To restore muscle contraction ability, sufficient rest is necessary. If you start the next training session before the muscles are fully recovered, the muscles will be working with fatigue, which can easily lead to cumulative fatigue and exercise injuries. However, this does not mean that you must rest for 2 days after a high-intensity run before you can run again. You can do some core training or upper body training the day after the run because running mainly causes lower body fatigue. Doing some training that does not involve the lower body the day after running is completely fine.
5. Summary
Finally, to summarize, various recovery methods may not be as magical as imagined. Fatigue is a normal response of the body after exercise, and as long as the body is given enough rest time, it can fully recover on its own. However, this does not mean that recovery methods are useless. At the very least, they can reduce the feeling of muscle stiffness and tension, providing a good and comfortable feeling. This is the actual value of muscle stretching after exercise.