The Rate of Strength Muscle Imbalance Among Opposing Muscle Groups of Elite Athletes: A ‎Narrative Review ‎

Muscle imbalance and its amount and extent among opposing muscle groups is one of the important risk factors in causing musculoskeletal injuries. The aim of the present study was to evaluate the extent and rate of strength imbalances among opposing muscle groups of elite athletes.

To conduct the present review, the search history was searched through electronic search engines over the past two decades (2000 to 2020) at PubMed and Google Scholar. The keywords "Muscle", "Imbalance", "Athletics", "Muscle Imbalance", "Muscle Strength", "Rate", " Elite" are used for the search, along with related synonyms. Also, to search for Persian articles, the Iranian Magazines Database (MAGIRAN), the University Jihad Scientific Database (SID), the Islamic World Science Citation Database (ISC), the Iranian Medical Sciences Information Database (IRANMEDEX) and the Iranian Medical Library (MEDLIB) were used. Selected articles were obtained by considering the inclusion and exclusion criteria of the research.

Considering the inclusion and exclusion criteria of the present study, 28 articles (including 26 English articles and 2 Persian articles) were selected. The findings showed that in the knee joint, the ratio of opposite muscle imbalance (agonist / antagonist), for hamstring muscles to quadriceps (H: Q) were 63.2% and 61.8% respectively. These values ​​in the hip joint for abductor to adductor muscles (ABD: ADD) were 89.2% and 75.4% respectively. Mean of these values ​​in the ankle joint for dorsiflexor to plantarflexor muscles (DR: PL) were 35.3% and 35.6% respectively. The mean these values for inverter to aviator (I: E) muscles were 83.5% and 77.8% respectively. These values ​​in the shoulder joint for flexor to extensor muscles (FL: EX) respectively; were 76.8% and 72.8%. For external to internal retinal muscles (ER: IR) respectively; were 63.8% and 70.5%. The mean of these values ​​in the elbow joint for extensor to flexor muscles (EX: FL) respectively; were 92.3% and 91.6%. The mean of these values ​​in the scapular joint for the scapular to proximal scapular muscles (RT: PR) respectively; were 88.1% and 77%.

The results showed that in the evaluation of muscle imbalance in different groups in the upper and lower limb of elite athletes, certain relative values can be considered as quantitative and reference values. This reference is used to find out if the differences in muscle strength are such that they are considered muscle imbalance. Also, in assessing muscle strength imbalance, application of the isokinetic assessment method with the technique of 60 degrees per second is more beneficial. To conduct future studies in the field of muscle imbalance assessment, researchers recommend that in addition to strength imbalance, other aspects of muscle imbalance such as muscle length, flexibility, joint range of motion, muscular endurance, and structural profile of elite athletes should be considered.