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Ratanapinunchai J1, Madeeyoh I1
1Faculty of Associated Medical Sciences, Chiang Mai University, Physical Therapy, Chiangmai, Thailand
Background: Winged scapula are associated with the serratus anterior weakness. Wide origin (1st-8th ribs) and insertion (scapula: medial border) of the serratus anterior creates different directions of muscle fibers thus generating different actions for movement. If we can identify the different actions of this muscle in more detail, the movement impairment and subsequent treatment approach will be more accurately identifiable. The present study explored action of the serratus anterior which was divided into the middle (MSA) (rib 5th) and the lower serratus anterior (LSA) (rib 8th) fibers.
Purpose: To determine the differences in muscle activation between MSA and LSA during three exercises.
Methods: Fifteen healthy males were recruited for the study. Three exercises, that is, the bench push-up plus (BPUP) with hands on a bench, the unstable bench push-up plus (UPUP) with hands on a balance cushion, and the resisted shoulder flexion (RSF) with 10 repetition maximum weight were tested. The push-up and adding a small movement of pushing the upper back toward the ceiling at the end of movement is called the push-up plus whereas, raising the upper limb with hand held a load toward the ceiling is called the RSF. These closed and open kinematics exercises, i.e. with hand attached to the floor and hand freely moved in space were selected because they required the different movement of the scapula. A normalized EMG activity of MSA and LSA were recorded using the Power Lab® (ADInstruments, Australia) during isometric scapular protraction for BPUP and UPUP or at 150° shoulder flexion for RSF. Normalization was calculated using the maximum voluntary isometric scapular protraction activity (%EMG). The order of measurement was randomly selected.
Results: The results showed that the ratio of %EMG of MSA: LSA was greater than one in BPUP (1.41 ± 0.36) and UPUP (1.81 ± 0.47), but less than one (0.86 ± 0.27) in RSF. These ratios were statistically significant different (one-way ANOVA, p 0.05). %EMG of MSA was different from LSA in each exercise (repeated measures ANOVA, p 0.05). Activity of MSA and LSA in RSF was significantly (LSD, p 0.001) higher than those of BPUP and UPUP (%EMG of the MSA = 80.53 ± 26.07, 64.75 ± 23.19 and 55.62 ± 25.56 for the RSF, BPUP, and UPUP respectively and %EMG of LSA = 95.54 ± 24.15, 50.71 ± 26.32, and 32.26 ± 16.14 for the RSF, BPUP, and UPUP respectively). However, there was no difference (LSD, p=0.095) in %EMG of MSA and LSA between BPUP and UPUP.
Conclusion(s): The MSA worked more than LSA in the push-up plus exercise but the opposite was found in a RSF exercise. The RSF required more activities of MSA and LSA than push-up plus exercises.
Implications: This information may be useful for strengthening the serratus anterior. Different exercises should be used, that is, a push-up plus for the MSA and RSF exercise for the LSA or combination of these exercises to emphasize both parts of the serratus anterior. Further study in females or subjects with serratus anterior weakness is required.
Keywords: Electromyogram, Scapular, Upper limb exercise
Funding acknowledgements: Department of Physical Therapy, Faculty of Associated Medical Sciences
Purpose: To determine the differences in muscle activation between MSA and LSA during three exercises.
Methods: Fifteen healthy males were recruited for the study. Three exercises, that is, the bench push-up plus (BPUP) with hands on a bench, the unstable bench push-up plus (UPUP) with hands on a balance cushion, and the resisted shoulder flexion (RSF) with 10 repetition maximum weight were tested. The push-up and adding a small movement of pushing the upper back toward the ceiling at the end of movement is called the push-up plus whereas, raising the upper limb with hand held a load toward the ceiling is called the RSF. These closed and open kinematics exercises, i.e. with hand attached to the floor and hand freely moved in space were selected because they required the different movement of the scapula. A normalized EMG activity of MSA and LSA were recorded using the Power Lab® (ADInstruments, Australia) during isometric scapular protraction for BPUP and UPUP or at 150° shoulder flexion for RSF. Normalization was calculated using the maximum voluntary isometric scapular protraction activity (%EMG). The order of measurement was randomly selected.
Results: The results showed that the ratio of %EMG of MSA: LSA was greater than one in BPUP (1.41 ± 0.36) and UPUP (1.81 ± 0.47), but less than one (0.86 ± 0.27) in RSF. These ratios were statistically significant different (one-way ANOVA, p 0.05). %EMG of MSA was different from LSA in each exercise (repeated measures ANOVA, p 0.05). Activity of MSA and LSA in RSF was significantly (LSD, p 0.001) higher than those of BPUP and UPUP (%EMG of the MSA = 80.53 ± 26.07, 64.75 ± 23.19 and 55.62 ± 25.56 for the RSF, BPUP, and UPUP respectively and %EMG of LSA = 95.54 ± 24.15, 50.71 ± 26.32, and 32.26 ± 16.14 for the RSF, BPUP, and UPUP respectively). However, there was no difference (LSD, p=0.095) in %EMG of MSA and LSA between BPUP and UPUP.
Conclusion(s): The MSA worked more than LSA in the push-up plus exercise but the opposite was found in a RSF exercise. The RSF required more activities of MSA and LSA than push-up plus exercises.
Implications: This information may be useful for strengthening the serratus anterior. Different exercises should be used, that is, a push-up plus for the MSA and RSF exercise for the LSA or combination of these exercises to emphasize both parts of the serratus anterior. Further study in females or subjects with serratus anterior weakness is required.
Keywords: Electromyogram, Scapular, Upper limb exercise
Funding acknowledgements: Department of Physical Therapy, Faculty of Associated Medical Sciences
Topic: Human movement analysis; Musculoskeletal: upper limb
Ethics approval required: Yes
Institution: Chiang Mai University
Ethics committee: Ethics Committee of the Faculty of Associated Medical Sciences
Ethics number: AMSEC-60EX-087
All authors, affiliations and abstracts have been published as submitted.
