The physiological rationale underlying the use of sericin in the context of muscle recovery is based on multiple documented properties: wound-healing activity, modulation of the inflammatory response, and the ability to promote cell proliferation and differentiation. However, translating these properties into an actual functional benefit for skeletal muscle—especially under conditions of exercise-induced metabolic stress or neuromuscular damage—requires a critical analysis of the available experimental evidence.
Preclinical evidence
The most significant contribution to understanding the role of this protein in muscle recovery comes from studies conducted on animal models of peripheral nerve injury. In particular, the sciatic nerve compression model in Wistar rats has provided a reproducible experimental paradigm to evaluate the effects of sericin on neuromuscular regeneration, both in association with and as an alternative to physical exercise.
A controlled study analyzed the effect of topical application of 100 μL of hydrolyzed sericin on the injured nerve, combined with a swimming protocol with a 10% body weight overload for three weeks. The results showed that, although nerve injury induced a significant reduction in muscle mass and phenotypic alterations of muscle fibers, the combination of sericin and physical exercise was not able to significantly modify functional grip strength parameters, nor the morphometry of neuromuscular junctions.
These findings are particularly relevant when considered in light of the observed histological changes. Histochemical analysis demonstrated that nerve injury led to a reduction in the percentage of type I (slow-twitch) fibers, while not significantly altering the distribution of type IIa and IIb fibers. However, neither sericin alone nor its combination with physical exercise affected the cross-sectional area of muscle fibers, suggesting that the biopolymer does not exert a direct effect on preventing denervation-induced atrophy in this experimental model.
Physical exercise and sericin
The choice of exercise protocol represents a critical variable in interpreting the results. In the aforementioned model, swimming with overload was implemented 72 hours after nerve injury, with progressively increasing duration (15, 20, and 25 minutes in the first, second, and third week, respectively). This protocol was selected to simulate functional rehabilitation conditions typically employed in clinical practice.
A methodologically relevant aspect is that physical exercise alone proved effective in maintaining intramuscular connective tissue, suggesting a protective role of physical activity on muscle structure. However, the addition of sericin did not enhance this effect, raising questions about the synergy between pharmacological and rehabilitative interventions in the acute post-injury phase.
Grip strength assessment, conducted through eight serial measurements over the course of the experimental protocol, revealed a significant reduction in strength in all groups subjected to nerve injury compared to controls, with no appreciable differences between groups treated with sericin, exercise, or their combination. This finding suggests that, at least in the context of an experimental axonotmesis, sericin does not modify the functional deficit induced by denervation.
Metabolic implications A key contribution to understanding the mechanisms through which sericin might influence muscle recovery comes from recent studies on amino acid metabolism in muscle stem cells. Sericin, being a serine-rich protein, may provide a critical metabolic substrate for regenerative processes. Research conducted on murine models and human muscle progenitor cells has shown that serine and glycine are essential for the proliferation of muscle stem cells and progenitor cells.
In particular, it has been observed that human muscle progenitor cells depend on extracellular availability of serine and glycine to expand their population, showing a limited capacity for de novo synthesis of these amino acids. Restriction of serine and glycine induces cell cycle arrest in the G0/G1 phase, impairing the regenerative capacity of skeletal muscle. Studies in aged mice have also shown that a serine- and glycine-free diet, administered after notexin-induced injury, results in reduced muscle fiber size and increased interstitial adipocyte infiltration, suggesting that the availability of these amino acids is crucial to prevent pathological muscle remodeling.
These findings open interesting perspectives for the use of sericin as a source of serine in contexts of muscle damage. However, it should be emphasized that evidence regarding the bioavailability of sericin and its actual metabolism into free serine at the tissue level remains limited, representing a significant knowledge gap.
Applications in sports science Applications of sericin in sports science are not limited to the reparative context but also include potential effects on performance and muscle fatigue. A study conducted on sports garments treated with sericin explored their effects on physiological responses during exercise. The results showed that sericin-treated clothing was associated with lower oral body temperature, heart rate, and sweat rate compared to controls.
Correlation analysis suggested that moisture at the garment–skin interface is a key determinant of these effects. By improving the absorption and breathability properties of the fabric, sericin may facilitate sweat evaporation, reducing skin moisture and consequently attenuating thermoregulatory and cardiovascular responses. This mechanism could translate into a reduction in physiological load during exercise, with potential implications for fatigue management.
It is important to note that the same authors reported lower subjective perception of fatigue in subjects wearing sericin-treated clothing, while objective performance tests (reaction time and Kraepelin test) did not show statistically significant differences. This discrepancy between subjective perception and objective measures suggests caution in interpreting the results and highlights the need for controlled studies with objective functional endpoints.
Critical considerations and research perspectives An integrated analysis of the available evidence reveals a complex and partially contradictory picture regarding the effectiveness of sericin in muscle recovery and fatigue management. On one hand, peripheral nerve injury models have not demonstrated significant functional benefits associated with sericin use, either alone or in combination with physical exercise. On the other hand, studies on amino acid metabolism suggest a critical role of serine, a constituent of sericin, in the proliferation processes of muscle progenitor cells.
Several hypotheses may explain this discrepancy. First, the route of administration represents a crucial variable: while in nerve injury studies sericin was applied locally to the injured nerve, beneficial effects on muscle regeneration would likely require systemic bioavailability or local availability at the level of damaged muscle tissue. Second, the timing of intervention may influence efficacy: acute administration of sericin immediately after injury may not be optimal to support later phases of regeneration, which require sustained amino acid supply in the days following damage.
Third, it is necessary to consider that the nerve injury models used represent a condition of denervation, which differs substantially from exercise-induced muscle fatigue or direct muscle damage. Applications in sports science may therefore require different experimental paradigms, focusing on metabolic stress and myofibrillar damage repair rather than neuronal regeneration.
