QUANTIFICATION OF FUNCTIONAL SHOULDER EXTERNAL TO INTERNAL MOMENT RATIO USING ISOKINETICS BETWEEN SWIMMERS AND A CONTROL GROUP

S. Tavernari^1,2, K. Vassis², P. Gkrilias³, E. Lagouvardou^1,2, G. Vasilopoulos², I. Poulis^1,2

¹School of Health Sciences, University of Thessaly, Faculty of Physiotherapy, Lamia, Greece, ²Human Performance and Rehabilitation Laboratory, Faculty of Physiotherapy, Lamia, Greece, ³School of Health Sciences, University of Peloponnese, Department of Physiotherapy, Sparta, Greece

Background: Muscular strength balance between agonist and antagonist muscles is of fundamental importance for shoulder joint stability. Isokinetic evaluation of IR and ER strength can help determine a profile in patients suffering from shoulder disorders to guide rehabilitation. It is possible that joint loading does not depend only on the maximal capacity of each muscle to produce force independently; it also depends on the magnitude of the force that both muscles produce at the same time. It would be interesting to study if asymptomatic athletes with increased physical activity show different ratio values of ER/IR shoulder rotators and higher torques per 10 degrees of isokinetic ROM than individuals who do not participate in sports activities.

Purpose: The purpose of our study was to examine the shoulder ER/IR ratio by using the maximum values per 10° of ROM, in a functional range of motion totaling 90° signaling a more detailed observation.

Methods: Fifteen swimmers and 15 non-athletes participated in the study. Subjects were measured in the seated position with 45° of shoulder abduction. Isokinetic unilateral concentric shoulder ER and IR peak moments (PM) per 10° of ROM were assessed isokinetically at 120°/s at a range of motion of 90°.

Results: Statistically significant differences were found between the external rotators' moment at 0°–10° (p=0.03) and at 40°–50° (p=0.044). In the internal rotators moment, statistically significant differences were observed at 40°–80° (p=0.020 to p=0.038), but also in the mean peak moment measurement. However, ER/IR ratio per 10° of isokinetic velocity did not present significant differences between the two groups(p=0.082 to p=0.630). Except for the angles 0–10, athletes have a lower ER/IR ratio in the 90° ROM than non-athletes.

Conclusions: The 2 antagonist muscle groups are highly dependent on the angular position examined as the ratio decreases (indicating lower values of ER and higher IR values in shoulder joint degrees approaching external rotation). Our results indicate that athletes and control individuals have no significant ER/IR ratio differences.

Implications: Implications are important as the main peak moment is not present in the degrees that usually an athlete is injured. A rehabilitation program must emphasize to the ROM the injury takes place for better results.

Funding acknowledgements: This research received no external funding.

Keywords:
Shoulder rotators ratio
Isokinetic evaluation
Muscle balance

Topics:
Musculoskeletal: upper limb
Musculoskeletal
Sport & sports injuries

Did this work require ethics approval? Yes

Institution: School of Health Sciences, University of Thessaly

Committee: Research Ethics Committee of Department of Physiotherapy

Ethics number: 646/9-9-2021