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BIO DESIGN

pISSN 1225-8962
eISSN 2287-982X

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Phys. Ther. Korea 2023; 30(3): 237-244

Published online August 20, 2023

https://doi.org/10.12674/ptk.2023.30.3.237

© Korean Research Society of Physical Therapy

Enhancing Shoulder External Rotator Electromyography Activity During Sitting External Rotation Exercise: The Impact of Biofeedback Training

Il-young Yu1 , PT, PhD, Min-joo Ko2 , PT, PhD, Jae-seop Oh2 , PT, PhD

1Department of Rehabilitation Center, DangDang Korean Medicine Hospital, Changwon, 2Department of Physical Therapy, College of Healthcare Medical Science and Engineering, Inje University, Gimhae, Korea

Correspondence to: Jae-seop Oh
E-mail: ysrehab@inje.ac.kr
https://orcid.org/0000-0003-1907-0423

Received: August 1, 2023; Revised: August 11, 2023; Accepted: August 12, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: The external rotation (ER) exercise in performed at a 90° abduction of the shoulder joint is an effective to strengthen the infraspinatus. However, failure of the humeral head to control axial rotation during exercise can be increased the posterior deltoid over activity. Biofeedback training is an effective method of promoting motor learning and control it could look forward to activate the infraspinatus selectively by controlling the humeral head during exercise. Objects: The aim of this study was investigated that whether biofeedback for axial rotation was effective to activate selectively the infraspinatus during ER exercise.
Methods: The 15 healthy males participated, and all subjects performed both ER exercise in a sitting position with shoulder abducted 90° under conditions with and without axial rotation biofeedback. Exercise was performed in a range of 90° ER, divided into three phases: concentric, isometric, and eccentric. The infraspinatus and posterior deltoid muscle activity were observed using surface electromyography.
Results: Both infraspinatus activity (p < 0.01) and infraspinatus to posterior deltoid activity ratio (p = 0.01) were significantly higher with biofeedback however, posterior deltoid activity was significantly lower with biofeedback (p = 0.01). The infraspinatus muscle activity and muscle activity ratio were the highest in the isometric contraction type, and there were significant differences for all contraction types (p < 0.05). Whereas, the posterior deltoid activity was the lowest in the isometric contraction type, and showed a significant difference between isometric and other two contraction types (p < 0.05), but no significant different between concentric and eccentric contraction.
Conclusion: Our results indicate that the axial rotation biofeedback during sitting ER exercise might be effective method to activating selective infraspinatus muscle and recommended to enhance the dynamic stability of the shoulder joint.

Keywords: Biofeedback, Humeral head, Rotator cuff, Shoulder joint

Article

Original Article

Phys. Ther. Korea 2023; 30(3): 237-244

Published online August 20, 2023 https://doi.org/10.12674/ptk.2023.30.3.237

Copyright © Korean Research Society of Physical Therapy.

Enhancing Shoulder External Rotator Electromyography Activity During Sitting External Rotation Exercise: The Impact of Biofeedback Training

Il-young Yu1 , PT, PhD, Min-joo Ko2 , PT, PhD, Jae-seop Oh2 , PT, PhD

1Department of Rehabilitation Center, DangDang Korean Medicine Hospital, Changwon, 2Department of Physical Therapy, College of Healthcare Medical Science and Engineering, Inje University, Gimhae, Korea

Correspondence to:Jae-seop Oh
E-mail: ysrehab@inje.ac.kr
https://orcid.org/0000-0003-1907-0423

Received: August 1, 2023; Revised: August 11, 2023; Accepted: August 12, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: The external rotation (ER) exercise in performed at a 90° abduction of the shoulder joint is an effective to strengthen the infraspinatus. However, failure of the humeral head to control axial rotation during exercise can be increased the posterior deltoid over activity. Biofeedback training is an effective method of promoting motor learning and control it could look forward to activate the infraspinatus selectively by controlling the humeral head during exercise. Objects: The aim of this study was investigated that whether biofeedback for axial rotation was effective to activate selectively the infraspinatus during ER exercise.
Methods: The 15 healthy males participated, and all subjects performed both ER exercise in a sitting position with shoulder abducted 90° under conditions with and without axial rotation biofeedback. Exercise was performed in a range of 90° ER, divided into three phases: concentric, isometric, and eccentric. The infraspinatus and posterior deltoid muscle activity were observed using surface electromyography.
Results: Both infraspinatus activity (p < 0.01) and infraspinatus to posterior deltoid activity ratio (p = 0.01) were significantly higher with biofeedback however, posterior deltoid activity was significantly lower with biofeedback (p = 0.01). The infraspinatus muscle activity and muscle activity ratio were the highest in the isometric contraction type, and there were significant differences for all contraction types (p < 0.05). Whereas, the posterior deltoid activity was the lowest in the isometric contraction type, and showed a significant difference between isometric and other two contraction types (p < 0.05), but no significant different between concentric and eccentric contraction.
Conclusion: Our results indicate that the axial rotation biofeedback during sitting ER exercise might be effective method to activating selective infraspinatus muscle and recommended to enhance the dynamic stability of the shoulder joint.

Keywords: Biofeedback, Humeral head, Rotator cuff, Shoulder joint

Fig 1.

Figure 1.Sitting external rotation exercise with axial rotation biofeedback. (A) Starting position and (B) ending position.
Physical Therapy Korea 2023; 30: 237-244https://doi.org/10.12674/ptk.2023.30.3.237

Fig 2.

Figure 2.Comparison of infraspinatus muscle activity between muscle contraction types with and without biofeedback. %MVIC, percentage of maximal voluntary isometric contraction. *p < 0.05.
Physical Therapy Korea 2023; 30: 237-244https://doi.org/10.12674/ptk.2023.30.3.237

Fig 3.

Figure 3.Comparison of posterior deltoid muscle activity with and without biofeedback. %MVIC, percentage of maximal voluntary isometric contraction. *p < 0.05.
Physical Therapy Korea 2023; 30: 237-244https://doi.org/10.12674/ptk.2023.30.3.237

Fig 4.

Figure 4.Comparison of posterior deltoid muscle activity between muscle contraction types. %MVIC, percentage of maximal voluntary isometric contraction. *p < 0.05.
Physical Therapy Korea 2023; 30: 237-244https://doi.org/10.12674/ptk.2023.30.3.237

Fig 5.

Figure 5.Comparison of infraspinatus to posterior deltoid muscle activity ratios between muscle contraction types with and without biofeedback. *p < 0.05.
Physical Therapy Korea 2023; 30: 237-244https://doi.org/10.12674/ptk.2023.30.3.237

Table 1 . Mean ± standard deviation muscle activity and muscle activity ratio during concentric, isometric, and eccentric contraction, with and without biofeedback.

VariableMuscle contractionWithout biofeedbackWith biofeedbackMean difference (95% CI)p-value
Infraspinatus (%MVIC)Concentric20.39 ± 5.6528.86 ± 4.463.04 (0.45–5.63)0.025
Isometric28.15 ± 10.7636.94 ± 11.861.71 (0.44–3.86)0.001
Eccentric15.87 ± 4.5118.20 ± 4.893.13 (0.74–5.51)0.014
Posterior deltoid (%MVIC)Concentric11.29 ± 6.607.97 ± 4.813.31 (1.41–5.21)0.002
Isometric8.24 ± 3.426.01 ± 2.262.23 (0.93–3.53)0.002
Eccentric10.19 ± 4.199.10 ± 3.571.08 (0.05–2.11)0.040
Activity ratioConcentric2.38 ± 1.304.68 ± 2.47–2.30 (–3.51 to –1.09)0.002
Isometric3.81 ± 1.726.50 ± 2.02–2.69 (–4.03 to –1.33)0.002
Eccentric1.83 ± 1.112.23 ± 1.00–0.39 (–0.85 to 0.06)0.080

Values are presented as mean ± standard deviation. %MVIC, percentage of maximal voluntary isometric contraction; CI, confidence interval..