Biochemical and neuromuscular biomarkers to monitor hamstrings muscle damage and recovery

[eng] Hamstring muscles are significantly affected by high volume or intensity, unaccustomed or eccentric-based exercises, as a result of muscle strain-induced damage during common movements in team sports (e.g., repeated late swing phases of the running gait cycle) or training methods (e.g., flywheel training). This process of eccentric exercise-induced muscle damage leads to a loss of performance, and most importantly, an increased risk of hamstrings myotendinous injuries. Consequently, it is necessary to identify the recovery status of the hamstring muscles during the post-exercise recovery period, using rapid and cost-effective testing procedures. Therefore, the purpose of the thesis was to assess the different phases of the hamstrings muscle damage-recovery continuum after different exercise models through hamstring-specific neuromuscular tests and associated structural and oxidative damage biomarkers. In Study I, 29 healthy, physically active, young adults (15 males, 14 females) were evaluated during 72 hours after a repeated-sprint training (10x40m, recovery: 3'). The results revealed a high inter-individual variability, identifiable through the assessment of maximal voluntary isometric contraction (MVIC) torque by means of the 90ºhip:20ºknee test. In addition, participants who lost MVIC torque during the 72-hour recovery period also showed an increase in perceived hamstrings soreness, posterior chain range of motion (ROM) loss by the Jurdan test (only male participants), as well as an upregulation of structural (creatine kinase [CK], sarcomeric mitochondrial CK [sMtCK]) and oxidative damage (malondialdehyde [MDA], oxidative stress index [OSI]) biomarkers. In contrast, participants who did not lose hamstrings MVIC torque also showed no changes in the other neuromuscular and biochemical biomarkers. Subsequently, in Study II, 19 male, regional first-division soccer players were monitored during the 72-hour recovery period after a soccer match. The results demonstrated that early rate of force development (RFD) metrics required more than 72 hours to be recovered after a soccer match. Likewise, rapid force-generating capacity decrements were accompanied by a decrease in posterior chain ROM by the Jurdan test, and an increase in perceived hamstrings soreness and structural (CK, sMtCK) and oxidative damage (MDA, OSI) biomarkers during the recovery period. Finally, a new exercise was designed to specifically target the hamstring muscles (Study III). The results indicated that the novel exercise designed triggers a significant activation of all 4 hamstring muscles, being the lateral positioning muscles (i.e., long and short head of the biceps femoris) the most activated hamstring muscles. Then, in Study IV, 30 healthy, physically active, young adults (15 males, 15 females) were monitored during the recovery period after a training session (5 sets x 10 repetitions). The results indicated that MVIC torque and RFD through the 90ºhip:20ºknee test were not recovered within 72 hours, as well as posterior chain ROM by the Jurdan test (only male participants) and perceived hamstrings soreness. Finally, the decrease in hamstrings neuromuscular capacities was also accompanied by an increase in biomarkers of structural (CK, sMtCK) and oxidative damage (MDA, OSI) to the myocyte during the 72-hour recovery period. Based on the findings of the studies comprising this thesis, a standard 72-hour recovery period is not adequate to recover the hamstring muscles after sprint-based exercises or flywheel training. The recovery status of the hamstring muscles can be monitored using the 90ºhip:20ºknee test, especially through early rate of force development (RFD) metrics in both men and women. The screening can be accompanied by the Jurdan test for posterior chain ROM in men, and by serum biomarkers of structural (CK, sMtCK) and oxidative (MDA, OSI) damage. Using this screening, training workloads could be adapted in each microcycle to balance optimizing training with muscle recovery, thus decreasing the risk of myotendinous injuries.