Have you ever wondered why some people build muscle faster than others, despite similar workout routines and diets? Factors like genetics, training intensity, exercise selection, training frequency, and nutrition all affect the gains you get from strength training. By adjusting these variables, you can boost your muscle hypertrophy gains.

So, how do muscles grow? When you exercise, you subject your muscles to stress, which leads to muscle damage, and that damage causes adaptations that lead to muscle hypertrophy and strength gains. However, not all stress is equal in terms of muscle growth. Two main types of stress affect muscle growth: metabolic stress and mechanical stress. Knowing the difference between the two can help you maximize the results you get from your training.

What Is Metabolic Stress?

Metabolic stress occurs when your muscles work so hard that they produce more metabolites than they can adequately clear from your bloodstream.  These metabolites, such as lactate, hydrogen ions, and phosphates, accumulate in your muscles and contribute to fatigue and that burning sensation you get in your muscles when you’re working them to near failure.

When you engage in high-rep, high-intensity resistance training, you create metabolic stress in your muscles. This stress signals your body to produce more growth hormone and activates pathways that stimulate muscle protein synthesis. By consistently pushing your muscles to the point of metabolic stress, you can stimulate muscle growth and achieve the gains you’re looking for.

However, you can also induce metabolic stress through other training methods, including occlusion training, and endurance training. By maximizing metabolic stress, athletes and fitness enthusiasts can promote muscle growth and improve their overall fitness levels. Metabolic stress is an important mechanism for achieving muscle hypertrophy.

Here’s how to put it into practice. Pick 4-6 compound exercises that you feel comfortable doing at a high intensity. Examples include squats, lunges, push-ups, pull-ups, and kettlebell swings. Set a timer for 30 seconds and do as many reps as you can with good form during that time. Then, take a 30-second rest before moving on to the next exercise. Repeat the cycle until you’ve completed all the exercises.

What Is Mechanical Stress?

Mechanical stress, on the other hand, occurs when you place your muscles under significant tension or load. This type of stress is associated with heavy weightlifting exercises, such as squats, deadlifts, and bench presses.

Mechanical stress causes microscopic tears in your muscle fibers, which then repair and grow back stronger. To maximize mechanical stress, you would lift heavy weights and do enough repetitions to fatigue the muscle.

To generate more mechanical stress, focus on time under tension (TUT) or the time you hold the muscle under tension and perform the exercise through its full range of motion without using momentum. Increasing time under tension can stimulate muscle growth through mechanical means.

Each Type of Stress Stimulates Muscle Growth in Different Ways

Both types of stress contribute to muscle growth, but they affect your muscles in different ways. Metabolic stress leads to an increase in muscle cell swelling. The cellular swelling signals the release of hormones that contribute to muscle growth, including anabolic hormones like growth hormone and insulin-like growth factor 1 (IGF-1), which further promote muscle growth.

Additionally, metabolic stress can lead to the activation of nutrient-sensitive signaling pathways, such as the mammalian target of rapamycin (mTOR), which are critical for protein synthesis and muscle growth. Therefore, while metabolic stress can be uncomfortable and challenging, it can also be an essential component of a well-designed exercise program aimed at promoting muscle growth and development.

Mechanical stress, on the other hand, directly damages your muscle fibers, which then trigger the repair and growth process. This type of stress occurs when you subject your muscles to force, causing the muscle fibers to be stretched and overloaded. This overload causes small amounts of damage to the muscle fibers, which triggers the repair and growth process.

The muscle fibers that are damaged during mechanical stress are replaced by new muscle fibers, which are stronger and more resilient than the old ones. This process leads to an increase in muscle size, strength, and endurance.

Mechanical tension is a strong stimulus for muscle hypertrophy and an increase in muscle strength and you maximize it with high mechanical loading of the muscle (≥60{967bf23b37ec6a673a83041540b3f904a815b4119ddf673afb961c1e7592ebdd}–70{967bf23b37ec6a673a83041540b3f904a815b4119ddf673afb961c1e7592ebdd} of the one repetition maximum [1RM]).

Is Mechanical or Metabolic Stress Better?

So, which type of stress enhances muscle growth mot? The truth is both are important for muscle growth. However, the optimal balance between the two depends on your goals and training preferences.

If you’re looking to build muscle endurance, such as for running or cycling, then focusing on metabolic stress through high-rep exercises can be beneficial. This type of training increases blood flow and oxygen delivery to your muscles, which can improve your endurance and stamina.

On the other hand, if you’re looking to build muscle size and strength, then focusing on mechanical stress through heavy weightlifting exercises is key. This type of training directly damages your muscle fibers, which then grow back stronger and larger. Mechanical stress also increases muscle fiber activation, leading to greater muscle recruitment and growth.

However, you get both metabolic and mechanical stress with certain approaches. For example, using a weight that’s heavy enough to cause momentary fatigue after eight to 12 reps, combined with short rest intervals between sets, can create the ideal environment for both mechanical and metabolic stimuli.

Keep in mind that everyone’s body is different, and what works for one person may not work for another. It’s important to experiment with different types of training and find what works best for your body and your goals.

In addition to exercise, nutrition also plays a crucial role in muscle growth. To support muscle growth, you need to consume enough calories and protein to fuel the repair and growth process. Aim for a diet that is high in protein, complex carbohydrates, and healthy fats.

Conclusion

Both metabolic stress and mechanical stress are important for muscle growth, but they affect your muscles in different ways. To optimize your muscle growth, find the right balance between the two based on your goals and training preferences. And don’t forget to fuel your muscles with a balanced diet to support the repair and growth process. Keep experimenting and pushing yourself, and you’ll be on your way to building strong, healthy muscles in no time!

References:

• Current Opinion in Physiology . Volume 10, August 2019, Pages 90-95.
• “Time under tension: Here’s how it actually affects muscle growth.” 08 Sept. 2022, https://www.livescience.com/time-under-tension.
• Krzysztofik M, Wilk M, Wojdała G, Gołaś A. Maximizing Muscle Hypertrophy: A Systematic Review of Advanced Resistance Training Techniques and Methods. Int J Environ Res Public Health. 2019 Dec 4;16(24):4897. doi: 10.3390/ijerph16244897. PMID: 31817252; PMCID: PMC6950543.
• Strength Training: In Search of Optimal Strategies to Maximi… : Exercise and Sport Sciences Reviews (2023). Available at: https://journals.lww.com/acsm-essr/Fulltext/2021/01000/Strength_Training__In_Search_of_Optimal_Strategies.2.aspx (Accessed: 1 April 2023).

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