4. Discussion
DOMS, Reduced muscle function, muscle soreness, EIMD, muscle damage, muscle [Muscle damage
INFILTRATION, CONTRACTIONS, INFLAMMATORY RESPONSE
The current study investigated the effectiveness of daily supplementation with GSM powder for four weeks to accelerate muscle recovery after EIMD in untrained males. Our findings show that GSM powder supplementation expedited muscle recovery following exercise-induced damage as determined by faster recovery of muscle function, reduction in plasma CK concentrations and decreased soreness of target muscle groups. The potential mechanism of action for GSM powder in supporting muscle recovery may be partially through modulating the post-exercise immune responses to facilitate muscle repair. Together, these results support our hypothesis that consuming GSM powder supports muscle recovery in untrained males following EIMD to the quadriceps. To our knowledge, this is the first study demonstrating the benefits of GSM powder as a functional food for supporting muscle recovery after exercise.Reduced muscle function following prolonged unaccustomed eccentric exercise is a classic indicator of muscle damage. Previous studies using a bench-stepping paradigm have reported up to a 20% reduction in peak isometric torque that persisted for 48 h post exercise in untrained cohorts [Previous nutrition intervention studies have investigated the benefits of supplementing with GSM and other marine-derived lipids in attenuating eccentric EIMD. Using a downhill running protocol to induce muscle damage to the quadriceps, supplementation with a GSM-derived lipid blend did not attenuate exercised-induced reductions in peak concentric and isometric torque of the quadriceps in trained and untrained runners [Delayed onset muscle soreness (DOMS) is a common outcome of unaccustomed physical activity, typically occurring between 24 to 72 h after exercise and gradually subsiding thereafter. The discomfort caused by DOMS adversely affects the execution of daily activities and athletic performance [Eccentric exercise can disrupt the highly arranged structure of skeletal muscle, releasing CK into circulation, which is a recognised biomarker of EIMD. Bench-stepping exercise has been reported to induce a delayed increase in plasma CK, peaking at 48 to 72 h post exercise and returning to baseline concentrations after 7 days of recovery [The functional benefits of GSM supplementation for supporting muscle recovery are largely attributed to the anti-inflammatory bioactivity of GSM constituents. Exercise-induced muscle damage signals the increased release of cytokines by skeletal muscle and resident immune cells, resulting in an acute dynamic inflammatory response. Of the cytokines measured in this study, only MCP-1 was significantly upregulated after exercise, and the significant increase in MCP-1 observed immediately post exercise was mitigated in the GSM powder group. MCP-1 is a potent chemokine that regulates the migration and infiltration of monocytes into damaged muscle tissue, where they differentiate to macrophages and clear damaged myofibers, facilitating the remodelling and repair of damaged muscle [Muscle damage protocols, such as repeated eccentric quadriceps maximal voluntary contractions and bench stepping, induce an increase in IL-6 that peaks 6 h post exercise then returns to pre-exercise concentrations following 24 h recovery [An interesting finding in this study was the intervention effect on post-exercise circulating NK cell populations. Acute exercise has been shown to lead to an immediate increase in circulating NK cell numbers post exercise that returns to pre-exercise levels within 24 h of recovery [Previous intervention studies have postulated that the anti-inflammatory and analgesic effects of GSM may only be partially explained by the bioactive properties of EPA and DHA [It is important to acknowledge that the present study had limitations. Participants were solely untrained men; therefore, the findings in this study may not be extrapolated to women or trained individuals. Training status has a significant influence on the physiological and biological parameters of muscle damage due to the highly adaptable nature of skeletal muscle to repeated exercise [