TY - JOUR

T1 - Chronic Sequelae After Muscle Strain Injuries

T2 - Influence of Heavy Resistance Training on Functional and Structural Characteristics in a Randomized Controlled Trial

AU - Bayer, Monika L.

AU - Hoegberget-Kalisz, Maren

AU - Svensson, Rene B.

AU - Hjortshoej, Mikkel H.

AU - Olesen, Jens L.

AU - Nybing, Janus D.

AU - Boesen, Mikael

AU - Magnusson, S. Peter

AU - Kjaer, Michael

N1 - Publisher Copyright: © 2021 The Author(s).

PY - 2021

Y1 - 2021

N2 - 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).

AB - 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).

KW - chronic muscle injury

KW - fatty infiltration

KW - heavy resistance training

KW - scar tissue

U2 - 10.1177/03635465211026623

DO - 10.1177/03635465211026623

M3 - Journal article

C2 - 34264782

AN - SCOPUS:85110102514

VL - 49

SP - 2783

EP - 2794

JO - American Journal of Sports Medicine

JF - American Journal of Sports Medicine

SN - 0363-5465

IS - 10

ER -