Chan et al. BMC Musculoskeletal Disorders (2017) 18:313 DOI 10.1186/s12891-017-1674-2
RESEARCH ARTICLE
Open Access
The effects of therapeutic hip exercise with abdominal core activation on recruitment of the hip muscles Mandy KY Chan, Ka Wai Chow, Alfred YS Lai, Noble KC Mak, Jason CH Sze and Sharon MH Tsang*
Abstract Background: Core stabilization has been utilized for rehabilitation and prevention of lower limb musculoskeletal injuries. Previous studies showed that activation of the abdominal core muscles enhanced the hip muscle activity in hip extension and abduction exercises. However, the lack of the direct measurement and quantification of the activation level of the abdominal core muscles during the execution of the hip exercises affect the level of evidence to substantiate the proposed application of core exercises to promote training and rehabilitation outcome of the hip region. The aim of the present study was to examine the effects of abdominal core activation, which is monitored directly by surface electromyography (EMG), on hip muscle activation while performing different hip exercises, and to explore whether participant characteristics such as gender, physical activity level and contractile properties of muscles, which is assessed by tensiomyography (TMG), have confounding effect to the activation of hip muscles in enhanced core condition. Methods: Surface EMG of bilateral internal obliques (IO), upper gluteus maximus (UGMax), lower gluteus maximus (LGMax), gluteus medius (GMed) and biceps femoris (BF) of dominant leg was recorded in 20 young healthy subjects while performing 3 hip exercises: Clam, side-lying hip abduction (HABD), and prone hip extension (PHE) in 2 conditions: natural core activation (NC) and enhanced core activation (CO). EMG signals normalized to percentage of maximal voluntary isometric contraction (%MVIC) were compared between two core conditions with the threshold of the enhanced abdominal core condition defined as >20%MVIC of IO. Results: Enhanced abdominal core activation has significantly promoted the activation level of GMed in all phases of clam exercise (P < 0.05), and UGMax in all phases of PHE exercise (P < 0.05), LGMax in eccentric phases of all 3 exercises (P < 0.05), and BF in all phases of all 3 exercises except the eccentric phase of PHE exercise (P < 0.05). The %MVIC of UGMax was significantly higher than that of LGMax in all phases of clam and HABD exercises under both CO and NC conditions (P < 0.001) while the %MVIC of LGMax was significantly higher than UGMax in concentric phase of PHE exercise under NC condition (P = 0.003). Gender, physical activity level and TMG parameters were not major covariates to activation of hip muscles under enhanced core condition. Conclusions: Abdominal core activation enhances the hip muscles recruitment in Clam, HABD and PHE exercises, and this enhancement is correlated with higher physical activity and stiffer hip muscle. Our results suggest the potential application of abdominal core activation for lower limb rehabilitation since the increased activation of target hip muscles may enhance the therapeutic effects of hip strengthening exercises. Keywords: Hip muscles, Electromyography, Abdominal core activation
* Correspondence: [email protected] Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hunghom, Hong Kong SAR, China © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Chan et al. BMC Musculoskeletal Disorders (2017) 18:313
Background Over past two decades, core stabilization has been popular in rehabilitation and sports training program to prevent musculoskeletal injuries and enhance performances [1, 2]. Both the lumbar spine and pelvis can be stabilized by the passive and active subsystems of the neuromusculo-skeletal system [3]. The integrity and interaction of the bony structures and soft tissues of the vertebral column contribute to the role and function of the passive subsystem. Muscles which embrace the abdominal wall, the intersegmental muscles and the para-spinal muscles form the active subsystem. By promoting the activation of the abdominal core muscles, the composite function of the active subsystem in promoting the spinal stability could therefore be enhanced. Previous studies have used pressure biofeedback unit (PBU) to indirectly monitor the magnitude of abdominal core activation and examined its effect on hip muscles activity in the isometric phases of side-lying hip abduction and prone hip extension exercises [4–6]. It remains questionable if this method warrants the validity of the abdominal core recruitment because the value shown in the PBU is primarily from the changes in pressure that the body segment exerts upon the transducer. Factors like body weight and displacement of the center of mass during exercises would have therefore limited the comparisons between participants and exercises [7]. Furthermore, the effect of abdominal core activation was only examined during the isometric phase of exercises. In studies conducted by Chance-Larsen et al. [4] and Oh et al. [5], the activity of gluteus maximus (GMax) was assessed as a single unit in which the functional differences of the subdivisions of GMax were not considered [8]. Therefore, the present study was designed to monitor the abdominal core activation directly over the bilateral internal oblique muscles (IO) using the surface EMG method. The effect of abdominal core activation was also examined more comprehensively with the inclusion of analysis of muscle activity of the subdivisions of GMax and additional exercises and phases. This study aimed to examine the effects of abdominal core activation on hip muscles activity during therapeutic hip exercises with regards to the concentric, isometric and eccentric phases. Furthermore, selected factors which included the gender and physical activity level of the participants and the contractile properties of hip muscle assessed by the tensiomyography (TMG) were also examined for the possible confounding effects these factors may have on the activation of the hip muscles during the therapeutic hip exercises. Methods Study design
This was a cross-sectional study. The independent variables were two condition of abdominal core activation:
Page 2 of 11
1) natural core activation (NCA) and 2) enhanced core activation (ECA). The ECA condition was defined as at least 20% of the normalized percentage of maximum voluntary isometric contraction (%MVIC) of the contralateral and ipsilateral internal obliques (CIO & IIO) of the dominant leg (the side used to kick a ball). A target of 20% of MVIC of the IO was adopted in this study based on the level of abdominal core activation which could offer optimal spinal stability as suggested in previous research [9, 10]. The dependent variables were the activity of gluteus medius (GMed), upper part of gluteus maximus (UGMax), lower part of gluteus maximus (LGMax) and biceps femoris (BF) of the dominant leg measured by the surface electromyography (EMG). Participants
Twenty healthy participants (10 F and 10 M) were recruited from the Hong Kong Polytechnic University using convenient sampling. Participants with any musculoskeletal or neurological disorder over their lower back or lower limbs were excluded. Explanation of objectives, procedures, benefits and potential risks of the study was given before participants signed an informed consent approved by the Ethics Committee of the Hong Kong Polytechnic University. Demographic data, including the physical activity level, measured by International Physical Activity Questionnaire Short Form (IPAQ-SF) [11], and the contractile properties of GMax (maximal radial displacement [Dm] and contraction time [Tc]), measured by TMG system (TMG S1 system, TMG-BMC Ltd., Slovenia), was shown in Table 1. The TMG measurement enables the assessment of the muscle mechanical response towards an electrical stimulus using an noninvasive approach [12]. Both the Dm and Tc values provide an objective and reliable measure of the contractile property of the muscle. Due to the inaccessibility of the deep gluteal muscles, only the GMax was measured in this study. Experimental procedures and measurements
For monitoring of the muscle activity of the transverse abdominal wall, EMG activity of the transverse fibres of Table 1 Characteristics of participants with mean (SD) Age (years)
21.10 (1.70)
Height (cm)
166.75 (7.90)
Weight (kg)
58.10 (9.20)
Dominant leg (n)
Left = 0
Right = 20
Physical activity level (n)
Low = 0
Moderate = 10
Contractile properties Maximal radial displacement, Dm (mm)
9.72 (3.15)
Contraction time, Tc (ms)
42.42 (5.32)
Vigorous = 10
Chan et al. BMC Musculoskeletal Disorders (2017) 18:313
the internal obliques and the underlying transverse abdominis, which was named as IO in this study, was measured using the surface EMG methods [9, 13, 14]. Before placing EMG electrodes, skin preparation including hair removal, light abrasion with sandpaper and cleaning with isopropyl alcohol was completed to lower the skin impedance to 0.05). In LGMax, activation in ECA condition was significantly higher than that in NCA condition in the eccentric phase of all 3 exercises (P < 0.05), and in the isometric phase of PHE (P = 0.013). BF showed significantly greater activations (P < 0.05) in ECA condition when compared to that in NCA condition in all phases of the 3 hip exercises except in the eccentric phase of PHE (P = 0.074).
Reliability of EMG Recordings
The test-retest ICCs (3,1) for the EMG recordings of the hip muscles during Clam, HABD and PHE in concentric, isometric and eccentric phases were summarized in ranges. Good to excellent reliability [24] was observed in Clam in NCA (0.698–0.977) and ECA (0.681–0.967). Similarly, good to excellent reliability was observed in Table 3 Number of participants with invalid trials Exercise
Condition
Phase
Number of subjects with invalid trials (n/20)
Clam
ECA
Concentric
2
ECA
Eccentric
6
NCA
Concentric
1
NCA
Isometric
4
ECA
Concentric
2
ECA
Eccentric
5
NCA
Isometric
1
ECA
Eccentric
4
HABD
PHE
HABD Hip abduction, PHE Prone hip extension, ECA Enhanced core activation, NCA Natural core activation
Difference in the activation of UGMax & LGMax
In Clam and HABD, the %MVIC of UGMax was significantly greater than that of LGMax in all phases for both ECA and NCA conditions (P < 0.01). In PHE, there were no significant difference between %MVIC of UGMax and that of LGMax in most phases for both NCA and ECA conditions, except in the concentric phase of the PHE under NCA condition, the %MVIC of LGMax was significantly greater than that of UGMax (P = 0.003) (Table 6). Difference in change of activation of hip muscles between exercises
The change of EMG activities of GMed in isometric phase (F = 5.900, P = 0.005), BF in concentric (P = 0.024) and isometric phases (P = 0.017) after enhanced core activation significantly differed between the three hip exercises. With respect to GMed, post hoc analysis revealed that enhancement of EMG activity in PHE was significantly greater than that in HABD (P = 0.009). There was no statistical difference for the comparisons between PHE and Clam, HABD and Clam.
Chan et al. BMC Musculoskeletal Disorders (2017) 18:313
Page 6 of 11
Table 4 EMG activity in terms of %MVIC with mean (SD) of internal oblique muscle over the contralateral side (CIO) and ipsilateral side (IIO) of the exercising hip Exercise
Phase
CIO NCA
ECA
P-value
NCA
ECA
P-value
Clam
Concentric
2.45 (0.51)
47.08 (4.98)
RESEARCH ARTICLE
Open Access
The effects of therapeutic hip exercise with abdominal core activation on recruitment of the hip muscles Mandy KY Chan, Ka Wai Chow, Alfred YS Lai, Noble KC Mak, Jason CH Sze and Sharon MH Tsang*
Abstract Background: Core stabilization has been utilized for rehabilitation and prevention of lower limb musculoskeletal injuries. Previous studies showed that activation of the abdominal core muscles enhanced the hip muscle activity in hip extension and abduction exercises. However, the lack of the direct measurement and quantification of the activation level of the abdominal core muscles during the execution of the hip exercises affect the level of evidence to substantiate the proposed application of core exercises to promote training and rehabilitation outcome of the hip region. The aim of the present study was to examine the effects of abdominal core activation, which is monitored directly by surface electromyography (EMG), on hip muscle activation while performing different hip exercises, and to explore whether participant characteristics such as gender, physical activity level and contractile properties of muscles, which is assessed by tensiomyography (TMG), have confounding effect to the activation of hip muscles in enhanced core condition. Methods: Surface EMG of bilateral internal obliques (IO), upper gluteus maximus (UGMax), lower gluteus maximus (LGMax), gluteus medius (GMed) and biceps femoris (BF) of dominant leg was recorded in 20 young healthy subjects while performing 3 hip exercises: Clam, side-lying hip abduction (HABD), and prone hip extension (PHE) in 2 conditions: natural core activation (NC) and enhanced core activation (CO). EMG signals normalized to percentage of maximal voluntary isometric contraction (%MVIC) were compared between two core conditions with the threshold of the enhanced abdominal core condition defined as >20%MVIC of IO. Results: Enhanced abdominal core activation has significantly promoted the activation level of GMed in all phases of clam exercise (P < 0.05), and UGMax in all phases of PHE exercise (P < 0.05), LGMax in eccentric phases of all 3 exercises (P < 0.05), and BF in all phases of all 3 exercises except the eccentric phase of PHE exercise (P < 0.05). The %MVIC of UGMax was significantly higher than that of LGMax in all phases of clam and HABD exercises under both CO and NC conditions (P < 0.001) while the %MVIC of LGMax was significantly higher than UGMax in concentric phase of PHE exercise under NC condition (P = 0.003). Gender, physical activity level and TMG parameters were not major covariates to activation of hip muscles under enhanced core condition. Conclusions: Abdominal core activation enhances the hip muscles recruitment in Clam, HABD and PHE exercises, and this enhancement is correlated with higher physical activity and stiffer hip muscle. Our results suggest the potential application of abdominal core activation for lower limb rehabilitation since the increased activation of target hip muscles may enhance the therapeutic effects of hip strengthening exercises. Keywords: Hip muscles, Electromyography, Abdominal core activation
* Correspondence: [email protected] Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hunghom, Hong Kong SAR, China © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Chan et al. BMC Musculoskeletal Disorders (2017) 18:313
Background Over past two decades, core stabilization has been popular in rehabilitation and sports training program to prevent musculoskeletal injuries and enhance performances [1, 2]. Both the lumbar spine and pelvis can be stabilized by the passive and active subsystems of the neuromusculo-skeletal system [3]. The integrity and interaction of the bony structures and soft tissues of the vertebral column contribute to the role and function of the passive subsystem. Muscles which embrace the abdominal wall, the intersegmental muscles and the para-spinal muscles form the active subsystem. By promoting the activation of the abdominal core muscles, the composite function of the active subsystem in promoting the spinal stability could therefore be enhanced. Previous studies have used pressure biofeedback unit (PBU) to indirectly monitor the magnitude of abdominal core activation and examined its effect on hip muscles activity in the isometric phases of side-lying hip abduction and prone hip extension exercises [4–6]. It remains questionable if this method warrants the validity of the abdominal core recruitment because the value shown in the PBU is primarily from the changes in pressure that the body segment exerts upon the transducer. Factors like body weight and displacement of the center of mass during exercises would have therefore limited the comparisons between participants and exercises [7]. Furthermore, the effect of abdominal core activation was only examined during the isometric phase of exercises. In studies conducted by Chance-Larsen et al. [4] and Oh et al. [5], the activity of gluteus maximus (GMax) was assessed as a single unit in which the functional differences of the subdivisions of GMax were not considered [8]. Therefore, the present study was designed to monitor the abdominal core activation directly over the bilateral internal oblique muscles (IO) using the surface EMG method. The effect of abdominal core activation was also examined more comprehensively with the inclusion of analysis of muscle activity of the subdivisions of GMax and additional exercises and phases. This study aimed to examine the effects of abdominal core activation on hip muscles activity during therapeutic hip exercises with regards to the concentric, isometric and eccentric phases. Furthermore, selected factors which included the gender and physical activity level of the participants and the contractile properties of hip muscle assessed by the tensiomyography (TMG) were also examined for the possible confounding effects these factors may have on the activation of the hip muscles during the therapeutic hip exercises. Methods Study design
This was a cross-sectional study. The independent variables were two condition of abdominal core activation:
Page 2 of 11
1) natural core activation (NCA) and 2) enhanced core activation (ECA). The ECA condition was defined as at least 20% of the normalized percentage of maximum voluntary isometric contraction (%MVIC) of the contralateral and ipsilateral internal obliques (CIO & IIO) of the dominant leg (the side used to kick a ball). A target of 20% of MVIC of the IO was adopted in this study based on the level of abdominal core activation which could offer optimal spinal stability as suggested in previous research [9, 10]. The dependent variables were the activity of gluteus medius (GMed), upper part of gluteus maximus (UGMax), lower part of gluteus maximus (LGMax) and biceps femoris (BF) of the dominant leg measured by the surface electromyography (EMG). Participants
Twenty healthy participants (10 F and 10 M) were recruited from the Hong Kong Polytechnic University using convenient sampling. Participants with any musculoskeletal or neurological disorder over their lower back or lower limbs were excluded. Explanation of objectives, procedures, benefits and potential risks of the study was given before participants signed an informed consent approved by the Ethics Committee of the Hong Kong Polytechnic University. Demographic data, including the physical activity level, measured by International Physical Activity Questionnaire Short Form (IPAQ-SF) [11], and the contractile properties of GMax (maximal radial displacement [Dm] and contraction time [Tc]), measured by TMG system (TMG S1 system, TMG-BMC Ltd., Slovenia), was shown in Table 1. The TMG measurement enables the assessment of the muscle mechanical response towards an electrical stimulus using an noninvasive approach [12]. Both the Dm and Tc values provide an objective and reliable measure of the contractile property of the muscle. Due to the inaccessibility of the deep gluteal muscles, only the GMax was measured in this study. Experimental procedures and measurements
For monitoring of the muscle activity of the transverse abdominal wall, EMG activity of the transverse fibres of Table 1 Characteristics of participants with mean (SD) Age (years)
21.10 (1.70)
Height (cm)
166.75 (7.90)
Weight (kg)
58.10 (9.20)
Dominant leg (n)
Left = 0
Right = 20
Physical activity level (n)
Low = 0
Moderate = 10
Contractile properties Maximal radial displacement, Dm (mm)
9.72 (3.15)
Contraction time, Tc (ms)
42.42 (5.32)
Vigorous = 10
Chan et al. BMC Musculoskeletal Disorders (2017) 18:313
the internal obliques and the underlying transverse abdominis, which was named as IO in this study, was measured using the surface EMG methods [9, 13, 14]. Before placing EMG electrodes, skin preparation including hair removal, light abrasion with sandpaper and cleaning with isopropyl alcohol was completed to lower the skin impedance to 0.05). In LGMax, activation in ECA condition was significantly higher than that in NCA condition in the eccentric phase of all 3 exercises (P < 0.05), and in the isometric phase of PHE (P = 0.013). BF showed significantly greater activations (P < 0.05) in ECA condition when compared to that in NCA condition in all phases of the 3 hip exercises except in the eccentric phase of PHE (P = 0.074).
Reliability of EMG Recordings
The test-retest ICCs (3,1) for the EMG recordings of the hip muscles during Clam, HABD and PHE in concentric, isometric and eccentric phases were summarized in ranges. Good to excellent reliability [24] was observed in Clam in NCA (0.698–0.977) and ECA (0.681–0.967). Similarly, good to excellent reliability was observed in Table 3 Number of participants with invalid trials Exercise
Condition
Phase
Number of subjects with invalid trials (n/20)
Clam
ECA
Concentric
2
ECA
Eccentric
6
NCA
Concentric
1
NCA
Isometric
4
ECA
Concentric
2
ECA
Eccentric
5
NCA
Isometric
1
ECA
Eccentric
4
HABD
PHE
HABD Hip abduction, PHE Prone hip extension, ECA Enhanced core activation, NCA Natural core activation
Difference in the activation of UGMax & LGMax
In Clam and HABD, the %MVIC of UGMax was significantly greater than that of LGMax in all phases for both ECA and NCA conditions (P < 0.01). In PHE, there were no significant difference between %MVIC of UGMax and that of LGMax in most phases for both NCA and ECA conditions, except in the concentric phase of the PHE under NCA condition, the %MVIC of LGMax was significantly greater than that of UGMax (P = 0.003) (Table 6). Difference in change of activation of hip muscles between exercises
The change of EMG activities of GMed in isometric phase (F = 5.900, P = 0.005), BF in concentric (P = 0.024) and isometric phases (P = 0.017) after enhanced core activation significantly differed between the three hip exercises. With respect to GMed, post hoc analysis revealed that enhancement of EMG activity in PHE was significantly greater than that in HABD (P = 0.009). There was no statistical difference for the comparisons between PHE and Clam, HABD and Clam.
Chan et al. BMC Musculoskeletal Disorders (2017) 18:313
Page 6 of 11
Table 4 EMG activity in terms of %MVIC with mean (SD) of internal oblique muscle over the contralateral side (CIO) and ipsilateral side (IIO) of the exercising hip Exercise
Phase
CIO NCA
ECA
P-value
NCA
ECA
P-value
Clam
Concentric
2.45 (0.51)
47.08 (4.98)
