Chronic Sequelae After Muscle Strain Injuries: Influence of Heavy Resistance Training on Functional and Structural Characteristics in a Randomized Controlled Trial

Abstract

Background: Muscle strain injury leads to a high risk of recurrent injury in sports and can cause long-term symptoms such as weakness and pain. Scar tissue formation after strain injuries has been described, yet what ultrastructural changes might occur in the chronic phase of this injury have not. It is also unknown if persistent symptoms and morphological abnormalities of the tissue can be mitigated by strength training. Purpose: To investigate if heavy resistance training improves symptoms and structural abnormalities after strain injuries. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A total of 30 participants with long-term weakness and/or pain after a strain injury of the thigh or calf muscles were randomized to eccentric heavy resistance training of the injured region or control exercises of the back and abdominal muscle. Isokinetic (hamstring) or isometric (calf) muscle strength was determined, muscle cross-sectional area measured, and pain and function evaluated. Scar tissue ultrastructure was determined from biopsy specimens taken from the injured area before and after the training intervention. Results: Heavy resistance training over 3 months improved pain and function, normalized muscle strength deficits, and increased muscle cross-sectional area in the previously injured region. No systematic effect of training was found upon pathologic infiltration of fat and blood vessels into the previously injured area. Control exercises had no effect on strength, cross-sectional area, or scar tissue but a positive effect on patient-related outcome measures, such as pain and functional scores. Conclusion: Short-term strength training can improve sequelae symptoms and optimize muscle function even many years after a strain injury, but it does not seem to influence the overall structural abnormalities of the area with scar tissue. Registration: NCT02152098 (ClinicalTrials.gov identifier).

Chronic changes in muscle architecture and aponeurosis structure following calf muscle strain injuries

“…One potential explanation could be the extensive fat infiltration, which we reported in a previous study on chronic muscle strain injuries. 10 Despite our inability to quantify the microscopic ultrastructure of the distal muscle fascicles and the aponeurosis in the injured GM in this study, which would have required biopsies from the site, it is quite clear that muscle fascicles behave differently. Although we lack displacement measurements of the aponeurosis during movement, the significant enlargement of the aponeurosis at any site measured, which becomes even more pronounced at contraction does suggest that the material of the aponeurosis, its organization and thereby likely also the material properties are different compared to the uninjured calf.…”

“…The present study measured significantly shortened fascicles at rest and at peak contraction at the most distal part and while we have not obtained sarcomere data in this study, our previous report based on biopsy material from chronic strain injured muscle showed disordered, hypercontracted sarcomeres, and loss of sarcomere structure. 10 Together, these data suggest that the architecture and function of the injured GM is permanently changed. So far, it is unknown whether targeted eccentric training This study is not without limitations.…”

“…Previous results from our group support this assertion. 10 Whether this is due to a weakening of the aponeurosis material properties, or the inability of the distal GM to contract due to lesser motor unit recruitment, cannot be answered based on these data. Significant loss of muscle mass is reported post muscle strain injuries, in both hamstrings and calf muscles.…”

“…This means that the interface is resistant to high muscular forces and able to efficient transmit muscular force to the aponeurosis, tendon, and then bone. However, previous studies have documented that strain injuries often cause long-standing muscle atrophy, [8][9][10] fibrosis, and fatty infiltration in both the hamstring and calf muscles, 10 which suggest that the repair process is incomplete.…”

Exploring the Potential Mechanisms of Melilotus officinalis (L.) Pall. in Chronic Muscle Repair Patterns Using Single Cell Receptor-Ligand Marker Analysis and Molecular Dynamics Simulations

“…Muscles can be damaged by external forces, biological factors, and chemical factors [ 6 , 7 ]. Excessive chronic injuries will lead to scar formation and fat infiltration [ 8 , 9 ]. Therefore, understanding the factors influencing muscle repair can help promote skeletal muscle repair [ 10 , 11 ].…”