When planning workout for myself or for my clients one of the critical aspect for me to think about is what type of stress am I planning to apply to the body. Choice of stress may differ based on your workout goal, however, just by having an idea can organize your routine for better results.
2 Types of Stress
There are 2 types of stress that you can apply to your body, mechanical and chemical stress. Mechanical stress is defined as internal resistance performed by the body against the external force applied to it. Simply put lifting weights. However, it does need to be resistance that is challenging for the body. Chemical stress defined as stress that cause damage or inflammation to the tissues (muscles, tendon, ligament) due to overuse or performing movement that the body is not familiar with. In exercise this can be applied by the increasing the volume (rep, sets, time under tension) of the exercises. In any form of exercise that we perform, these two stress will be applied but in a different ratio.
While training the body will produce acids such as lactic acids and pyruvate. Because our blood pH is about 7.4 which is neutral, while performing exercise blood pH will become more acidic because of acid production. Another thing that will happens to our body during the exercise is oxygen concentration decreases. This is happening because when contracting muscles, we are putting pressure on blood vessels which is restricting the blood flow.
So when you are focusing on mechanical stress, because of the load is high and volume is low blood pH and oxygen concentration change is minimal. However, when focusing on chemical stress, because of more repetitions, sets, and time under tension, those changes will be greater. This may sounds horrifying, however, the body has mechanism called homeostasis where the body will bring the pH level to neutral and oxygen concentration to normal. Because of this process, our body can recover and adapt to have stronger muscles, tendons, ligaments, lungs, blood vessels, heart and so on.
Example of Mechanical and Chemical Stress in Training
When the exercise is to lift 95% of your 1 repetition max for 2-5 repetitions, then the mechanical stress is more dominant over chemical stress. In this case what fatigues out first is your central nervous system. Therefore, for strength training, you do want to focus on mechanical stress where you will be performing methods that focuses on load (weight) like 5 by 5, cluster sets, Bulgarian methods and so on.
When the exercise is performed at higher repetitions such as 15-20 repetitions, then you will feel more of chemical stress where you know you can lift weight but the muscle is fatigued and may need to force the muscle contraction to complete the movement. This is happening because of changes in blood pH, oxygen concentration and so forth. Therefore, for hypertrophy or muscle growth training, you want to focus on applying chemical stress by using methods that focuses on exercise volume (rep, sets, time under tension) such as 3/7, giant sets, German Volume and so force.
It is useful to think of what stress you want to apply to get the results you are looking for, which will help organize your workout better and results will be more predictable.
Kota Shimada
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