Eccentric muscle contraction potentiates titin stiffness-related contractile properties in rat fast-twitch muscles

[Effectiveness of physical rehabilitation methods based on the impact of eccentric load in upper limb injuries]

The rehabilitation of patients after upper limb injuries is becoming increasingly relevant in current medical practice considering that this pathology is often occurred in professional athletes, elderly people, people with active lifestyle.

OBJECTIVE

To study the effectiveness of isolated therapeutic exercises (TE) with eccentric muscle loads when using rubber cable compared to traditional TE to restore functional capabilities of patients after upper limb injuries.

MATERIAL AND METHODS

The study included 38 patients with upper limb injuries diagnosed by orthopedic surgeon. Patients were randomly enrolled into group of isolated TE with eccentric muscle loads (group A, 20 patients, mean age 40.2±10.8 years) and group of traditional exercises (group B, 18 patients, mean age 38.6±12.3 years). The study consisted of anamnesis taking, clinical examination, functional tests applying (isometric dynamometry, joint mobility tests, functional scales and questionnaires). The rehabilitation effectiveness was assessed by comparing the indicators before and after treatment course.

RESULTS

There has been a significant improvement in muscle strength, movement amplitude and decrease of pain syndrome in patients rehabilitated by eccentric muscle loads. A comparison with a control group using traditional TE methods confirmed the superiority of eccentric exercises in reducing recovery time and improving functional performance.

CONCLUSION

The study confirmed the high effectiveness of eccentric muscular loads in the rehabilitation of patients after upper limb injuries. The method has shown significant improvement in clinical and functional indices, which allows to recommend it for inclusion in standard rehabilitation protocols. Further researches may extend application of this approach and reveal the TE effectiveness in other types of traumas and orthopedic injuries.

Re‑examining the mechanism of eccentric exercise‑induced skeletal muscle damage from the role of the third filament, titin (Review)

Intense and unaccustomed eccentric exercise has been extensively studied for its ability to induce muscle damage. However, the underlying mechanism of this phenomenon still requires further clarification. This knowledge gap arises from the need for explanation of the eccentric contraction through the sliding filament theory. The two-filament sarcomere model, which is consisted of thin and thick filaments, forms the basis of the sliding filament theory. The mechanisms of concentric and isometric contractions at the cellular and molecular levels are effectively described by this model. However, when relying solely on the cross-bridge swing, the sliding filament theory fails to account for specific observations, such as the stability of the descending limb of the force-length relationship curve. Recent evidence indicated that titin and the extracellular matrix (ECM) may play a protective role by interacting with the thick and thin filaments. During an eccentric contraction, titin serves as a third filament in the sarcomere, which helps regulate changes in passive force. The two-filament sarcomere model has limitations in explaining eccentric contraction, thus this compensates for those shortcomings. The present review explored the potential of replacing the two-filament sarcomere model with a three-filament sarcomere model, incorporating thin filaments, thick filaments and titin. This revised model offers a more comprehensive explanation of eccentric contraction phenomena. Furthermore, the sliding filament theory was investigated in the context of the three-filament sarcomere model. The double-layer protection mechanism, which involves increased titin stiffness and the ECM during eccentric contraction was explored. This mechanism may enhance lateral force transmission between muscle fibers and the ECM, resulting in sarcolemma and ECM shear deformation. These findings provided insight into the mechanism of eccentric exercise-induced skeletal muscle damage. Considering the three-filament sarcomere model and the double-layer protection mechanism, the present review offered a more logical and comprehensive understanding of the mechanism behind eccentric exercise-induced muscle damage.

Effects of eccentric contraction on force enhancement in rat fast-twitch muscle

The aim of this study was to elucidate the effects of eccentric contraction (ECC) on force enhancement in rat fast-twitch skeletal muscle. Gastrocnemius (GAS) muscles were subjected to 200 ECCs in situ by electrical stimulation. Immediately before and after the stimulation, isometric torque produced by ankle flexion was measured at an ankle angle of 90°. After the second torque measurement, the superficial regions of the muscles were dissected and subjected to biochemical and skinned fiber analysis. ECC did not induce changes in the amount of degraded titin. After ECC, isometric torques in the GAS muscles were markedly reduced, especially at low stimulation frequency. ECC increased passive torque in whole muscle and passive force in skinned fibers. Passive force enhancement and the ratio of passive force to the maximal Ca2+ -activated force, but not residual force enhancement, were augmented in the skinned fibers subjected to ECC. An ECC-induced increase in titin-based stiffness may contribute to the increased PFE. These results suggest that skeletal muscle is endowed with a force potentiation system that can attenuate ECC-induced force reductions.