Muscle Protein Breakdown & Synthesis

ReMuscle protein breakdown (MPB) and muscle protein synthesis (MPS) are the two sides of muscle protein turnover, the ongoing cycle of tearing down old or damaged muscle proteins and building new ones. In simple terms, MPB is the process of breaking muscle proteins into amino acids for recycling, while MPS is the creation of new muscle proteins from those amino acids. This cycle never stops: human tracer studies indicate that approximately 1–2% of muscle proteins are degraded and resynthesized daily, even at rest, to maintain muscle health and responsiveness to training. Understanding how MPB and MPS respond to exercise and nutrition explains why protein is essential for performance, endurance, and recovery, and how to maintain or build muscle over time.

Understanding Muscle Protein Breakdown

Muscle protein breakdown is the controlled degradation of muscle proteins into amino acids. These amino acids can be reused within muscle, shuttled to other tissues, or oxidized for energy in specific conditions.

Muscle protein turnover is the balance between breakdown and synthesis over time; it maintains muscle quality, clears damaged proteins, and enables adaptation to training. While breakdown rises after exercise in a fasted state, adequate protein intake typically offsets this increase and shifts the balance toward repair and growth.

Common triggers that increase MPB:

• Fasting or sustained calorie deficit.
• Intense physical activity (especially in a fasted or under-fueled state).
• Illness, high stress, or inadequate recovery.

Exploring Muscle Protein Synthesis

Muscle protein synthesis is the process of building new muscle proteins from available amino acids, which is a response stimulated by resistance exercise and dietary protein, particularly high-quality sources.

In healthy adults, MPS is the main driver that changes in response to training and nutrition to determine net muscle gain or loss. The effectiveness of MPS depends on protein type, digestion rate, and amino acid composition. Ingestion of proteins with higher essential amino acid content, particularly leucine, like rubisco in Leaft Blade, can result in a greater increase in muscle protein synthesis rates.

The Balance Between Breakdown and Synthesis

Net protein balance (NPB) is the difference between MPS and MPB. When synthesis exceeds breakdown, muscle is gained; when breakdown exceeds synthesis, muscle is lost.

Under normal conditions, about 1–2% of muscle proteins turn over daily to maintain tissue quality and readiness. This baseline can be steered toward growth or loss by training and nutrition.

Resistance exercise increases both MPS and MPB, priming the muscle for remodelling. The direction of the net effect depends on whether amino acids and energy supply is adequate, with sufficient protein intake helping tipping the balance positive.

Nutrition is key, without protein, net balance often remains negative despite elevated synthesis from exercise. Timely protein intake is key. Taking protein before, during and after exercise allows a ready supply of amino acids for MPS to occur.  

How Exercise Influences Muscle Protein Turnover

Resistance training elevates both MPS and MPB, when paired with adequate protein intake MPS predominates, supporting muscle growth. Without adequate protein, net muscle protein balance remains negative even though synthesis is elevated, underscoring the importance of protein timing for recovery and gains. Endurance training also raises turnover, typically to a lesser degree, with meaningful effects on repair, mitochondrial remodeling, and fatigue resistance.

What happens to muscle proteins around a workout:

• Before: In the fasted state, baseline turnover is modest; muscles are primed by prior training and nutrition.
• During: Mechanical tension and metabolic stress trigger signaling that raises both MPB and the sensitivity of MPS to amino acids.
• Immediately after: MPS responsiveness peaks, but net balance stays negative until amino acids arrive.
• 0–2 hours post: Protein ingestion rapidly elevates MPS above MPB, initiating repair and adaptation.
• 2-24 hours post: MPS can remain elevated, especially after novel or higher-volume resistance training. 

Intense exercise can reduce blood flow to the gut resulting in injury to the intestines, reducing the ability of the body to absorb protein when it’s needed most. If protein had been consumed pre or during exercise, there is likely to be circulating amino acids ready for immediate MPS representing an effective feeding strategy to improve amino acid availability to optimize post-exercise recovery.

The Role of Protein Nutrition in Muscle Maintenance

Dietary protein is digested into amino acids, absorbed into the bloodstream, and used to build new muscle proteins. For most active adults, 1.2–2 g of high-quality protein per kg body weight is recommended per day.

Even distribution across meals and a pre-sleep protein serving can further enhance overnight recovery and remodeling, especially after late training sessions.

Protein’s Impact on Performance and Endurance

When MPS is consistently supported, muscles repair faster, soreness diminishes, and athletes return to training with more strength and stamina. Multiple trials show that protein paired with exercise improves net muscle gain and accelerates performance recovery.

A complete protein contains all nine essential amino acids required for muscle repair and metabolic functions linked to energy and performance. Digestion speed also matters, fast digesting proteins can quickly elevate blood amino acids for rapid utilization in MPS, while slower digestion proteins offer sustained supply throughout the day. 

Ultimately, supporting muscle protein synthesis comes down to both protein quality and speed of delivery. Leaft Blade stands out as a rapidly digestible, complete protein, providing all essential amino acids in a form that moves quickly from ingestion to circulation. This shortens the time between eating and amino acid availability, helping fuel muscle protein synthesis precisely when it is needed most.

Frequently asked questions

What is muscle protein synthesis, and why is it important?

Muscle protein synthesis is the building of new muscle proteins from amino acids; it underpins repair, growth, and recovery after exercise.

How does resistance training affect muscle protein breakdown and synthesis?

It elevates both, but when combined with adequate protein intake, protein synthesis increases more than protein breakdown, leading to net muscle gain.

What role do amino acids play in muscle protein synthesis?

Amino acids are the raw materials for new muscle proteins, directly fueling repair and adaptation after training or injury.