Validation of α-actin as a marker of muscle damage in different sports

Résumé

Sport physiologists require serum markers of sarcomeric damage that provide information to discriminate between overtraining syndrome and adaptative microtraumas, and to identify whether the origin of the damage is metabolic or mechanical. The markers most frequently used to evaluate muscular damage nowadays are creatine kinase and lactate dehydrogenase, but they both are cytosolic, not of sarcomeric origin. In the present work we investigated the usefulness of α-actin, sarcomeric protein of the skeletal muscle, for this purpose given its role in muscle contraction. Our results translated into 6 articles published in international journals. In the first paper we compared three groups of subjects that adhered to different weekly training schedules. We found that α-actin concentration in serum, and therefore sarcomeric injury, is directly proportional to the hours of training. In the second paper we proved that the practice of physical activity in a hypoxic environment does not alter the release of α-actin post-exercise. Twelve swimmers performed three types of training with incremental intensities in both normoxia and hypoxia, showing similar values of α-actin in serum regardless of the situation. This finding suggests that sarcomeric damage is not affected by the catecholamine-induced metabolic stimulation that takes place during training in a hypoxic environment. In the third paper we compared the basal muscular damage of a group of athletes that received a supplement of α-tocopherol with a control group that did not receive the supplement. Supplementation did not affect the release of α-actin into blood. In the fourth paper we designed a test of incremental strength based on explosive and short-duration movements (half-squat), with the goal of identifying the fatigue threshold of single muscles. Classic physiological variables such as heart rate and lactate concentration were investigated, but they were found to be not suitable for this purpose. In contrast, regression/correlation between increasing weightloads and their respective electromyographic values fitted an exponential curve that allowed us to pinpoint the aforementioned threshold as an inflection point. In the fifth paper we used the test mentioned above and demonstrated that two exercises as different as bench press and half-squat induced the release of similar values of α-actin, which suggests that the structure of the sarcomere was not affected in either exercise. In contrast to this finding, the cytosolic markers creatine kinase isoenzyme MB (CK-MB) and lactate dehydrogenase increased after the bench press exercise, probably because the load is distributed throughout a larger muscular mass and, therefore, the damage was less severe. Lastly, in the sixth paper both male and female athletes were enrolled to perform an incremental strength half-squat exercise. Males and females exhibited similar serum values of α-actin, LDH and CK-MB. However, significantly greater α-actin values were obtained in males when concentration of this protein was normalized by the volemia, probably due to the larger muscle mass of males.