Electromyographic analysis of VMO and VL across straight leg raise,short arc quad,medial tibial rotation and hip adduction in normal individuals

Abstract

BACKGROUND:

The lateral malalignment of patella is considered to be the main cause of patellofemoral pain syndrome (PFPS). PFPS, in an occupational setup, is aggravated by prolonged sitting, climbing stairs, squatting, and kneeling. Strengthening of vastus medialis oblique (VMO) opposes the lateral force produced by vastus lateralis (VL) and helps in stabilizing patella.

OBJECTIVE:

The main objective was to compare six common rehabilitation exercises (REs) and to identify those which could possibly activate VMO selectively to alleviate PFPS of occupational workers.

METHODS:

Ten subjects, having no history of PFPS, performed six REs, namely, straight leg raise with neutral hip position (SLRN), straight leg raise with externally rotated hip position (SLRER), short arc quad with neutral hip position (SAQN), short arc quad with externally rotated hip position (SAQER), medial tibial rotation and hip adduction (HA). REs were compared on the basis of integrated electromyographic activity of VMO and VL.

RESULTS:

Results demonstrated that VMO activity was more than that of VL during all REs. However, this difference was not statistically significant in any of the six REs. HA produced significantly higher VMO activity than SLRN, SLRER and SAQN.

CONCLUSIONS:

The results provided a wider range of options for selecting apposite REs for treating patients diagnosed with PFPS.

Keywords

Patellofemoral pain syndrome rehabilitation exercises electromyography vastus medialis oblique vastus lateralis

1 Introduction

An effective occupational safety and health system promotes safe work environment for all individuals in the work field [1, 2]. Traditional as well as innovative methods have been suggested to reduce risk of occupational hazards [3 –6]. Patellofemoral pain syndrome (PFPS), a syndrome characterized by knee pain, has been studied in the present paper. PFPS has been reported to be the most common cause of knee pain in the United States [7 –9]. Vastus medialis oblique (VMO) and vastus lateralis (VL) muscles are the part of the quadriceps femoris, which work together to stabilize patella during dynamic knee extension. However, the role of VMO is important in stabilizing patella as it opposes the lateral force produced by VL. The lateral malalignment of the patella resulting from an imbalance between VMO and VL is considered to be the main cause of PFPS [10]. Several studies have demonstrated that rehabilitation exercises (REs) causing preferential activation of VMO are able to alleviate PFPS of patients [11, 12].

It is generally agreed upon that the REs producing overall strengthening of the whole quadriceps femoris do not help in improving lateral muscle imbalance, and therefore VMO should be selectively strengthened to increase dynamic stabilization of the patella using REs which stimulate a discriminatory training effect on VMO over other quadriceps muscles [13]. The present work focuses on comparing six rehabilitation exercises on individuals having no history of PFPS. These REs were chosen on the basis of concerning literature [7, 8 , 12] and experiential knowledge of our research team. Occupational workers involved in activities like prolonged sitting, climbing stairs, squatting and kneeling are exposed to the risk of PFPS [14]. As such the results of present work in the form of selected REs can possibly be used to alleviate PFPS of occupational workers having PFPS.

Electromyography (EMG) is an established tool to measure the electrical potentials associated with muscle activity [15, 16]. EMG has been used in the present work to measure the VMO and VL activities during all REs. However, the exact relationship between EMG and muscle tension is still argued [10]. Ratio of VMO activity over VL activity (VMO/VL) represents relative EMG activity. Researchers have compared VMO and VL activities as well as VMO/VL ratio across different rehabilitation exercises [7 , 17]. REs, in general, aim to achieve a ratio which is significantly higher than one. Therefore, treatment of PFPS involves selective strengthening of the VMO and improving the timing of the VMO and VL contractions for their simultaneous occurrence. Researchers have found no difference in the muscle recruitment during rehabilitation exercises between subjects with and without PFPS [8, 13]. Therefore, a number of studies have examined REs on subjects having no history of PFPS to strengthen VMO selectively [7 , 18].

Many studies have demonstrated that VMO could not be selectively activated during various REs, however, some studies have reported otherwise. EMG activity of VMO has been found significantly higher than that of VL during hip adduction [10]. Medial tibial rotation (MTR) has strengthened VMO selectively compared to VL [19]. Six REs were evaluated in this work for selective strengthening of VMO (Figs. 1–6), which were numbered as per the sequence given to subjects: (1) straight leg raise with neutral hip position (SLRN), (2) straight leg raise with externally rotated hip position (SLRER), (3) short arc quad with neutral hip position (SAQN), (4) short arc quad with externally rotated hip position (SAQER), (5) MTR and (6) hip adduction (HA). A rest period of 5 minute between exercises may allow any random sequence of these exercises. VMO and VL activities as well as VMO/VL ratio were compared across all REs.

Fig.1

Straight leg raise with neutral hip position (SLRN).

Fig.2

Straight leg raise with externally rotated hip position (SLRER).

Fig.3

Short arc quad with neutral hip position (SAQN).

Fig.4

Short arc quad with externally rotated hip position (SAQER).

Fig.5

Medial tibial rotation (MTR).

Fig.6

Hip adduction (HA).

2 Methods

2.1 Subjects

Experiments were performed on 10 male occupational workers (age range: 18–43 years). Subjects were selected on the following criteria: (1) physically active in their day to day life, and (2) having no history of PFPS. The subjects were a mix of naïve (four) and experienced (six) occupational workers. Naive workers had a work-experience of less than six months, whereas experienced workers had a work-experience of atleast four years.

It was ascertained through a questionnaire given to subjects that they did not have any history of PFPS, lower-limb musculoskeletal injury, and neurological impairment. Healthy workers as subjects provided a homogeneous population for the protocol of this study. The dominant leg was used for all subjects for electrode placement. It was determined by observing dominating arm of each subject, the preferred arm when performing writing tasks. Name, age, height, and weight of all subjects were recorded and body mass index (BMI) was calculated. Means and standard deviations for these data are shown inTable 1.

Table 1
Demographic data

No. of subjects Age (yrs) Weight (Kgs) Height (cm) BMI (Kg/m²)

10 30. 7 66.9 168.1 23.63

SD ±4.8 ±7.7 ±4.8 ±2.2

No. of subjects	Age (yrs)	Weight (Kgs)	Height (cm)	BMI (Kg/m²)
10	30. 7	66.9	168.1	23.63
SD	±4.8	±7.7	±4.8	±2.2

2.2 Equipment

EMG is the collective electric signal from muscles, which is produced during muscle contraction. For recording the EMG, the non-invasive surface electrodes were applied to the skin of the subjects in this work. Biopac MP 150 with AcqKnowledge 4.1 software (Biopac System, Inc., USA) was used to acquire useful information from EMG signal. It recorded multiple channels with differing sample rates at speed up to 400 kHz. Shielded electrode lead assembly (SS2, Biopac MP 150, Biopac System, Inc., USA) was used to connect Tel 100 M-C portable amplifier/transmitter. Bipolar adhesive surface electrodes (Ag-AgCl) were used over the muscle bellies of the VMO and VL. A goniometer (TSD 130E, Biopac MP 150, Biopac System, Inc., USA) was employed to measure knee joint angle.

2.3 Procedure

An informed consent was obtained prior to experiments from each subject. A brief demonstration of EMG equipment and six rehabilitation exercises was given to each subject. Thereafter, a testing session was taken up by each participant for all exercises. During REs at supine position, a 2.2 kg weight was taped at the upper side of the heel, which provided the required resistance during rehabilitation exercises to enhance EMG activity of knee muscles. Weight of 2.2 kg was decided based on initial experiments ensuring that subjects were not over-stressed during exercises. The room temperature was fixed at about 30°C based on a commonly observed local temperature in different occupational setups. The dominant leg of each subject was used for electrode placement by shaving and cleaning (with spirit and towel) the designated areas. The electrodes were placed parallel to the direction of the muscle fibres on the VMO and VL following standard norms [20, 21]. A rest period of 3 to 5 minutes between exercises has been widely used by researchers [11, 13]. As such, subjects were given a five minute rest period in between each exercise in the present study. This in turn would minimise the possibility of cross effects among all exercises.

2.4 EMG analysis

The normalization of the dynamic movements of each exercise was done to a dynamic maximum. Therefore, each muscle data was normalized with respect to the maximum integrated (iEMG) activity recorded during an experimental test for that muscle. This type of normalization helps in assuring constancy for normalization within each muscle, and assures that the reliability of normalization is based on a dynamic movement [7 , 22]. Kellis and Baltzopoulos [23] have analyzed EMG signals of dynamic and static methods of normalization, and have supported a dynamic method of normalization for performing dynamic testing of subjects.

All subjects performed eight repetitions (or trials) of each exercise. EMG data during middle five trials were considered for the analysis, and the remaining trials were excluded. The speed of the repetitions was controlled by a computerized metronome set to 45 beats per minute. Standard EMG procedures were followed as per norms [20]. Sampling of the EMG data was done at 1,000 samples per second. EMG data were amplified 2,000 times by the Tel-100 system of Biopac MP 150. The EMG signals were band-pass filtered with cut off frequency as 20 to 500 Hz using AcqKnowledge 4.1 Software, Biopac Systems, Inc. USA. These signals were then full-wave rectified and integrated using MATLAB Software, The Mathworks, Inc. (Fig. 7). The process of obtaining iEMG signals was repeated for each muscle.

Fig.7

Rectification and integration of EMG activities in Vastus Medialis Oblique.

2.5 Statistical analysis

One-way analysis of variance (ANOVA) was used to test iEMG differences among the exercises for statistical significance using an alpha level of 0.05 for each muscle. If a statistical significance was found, then post hoc analysis using least significant difference (LSD) test (having equal samples) was performed to compare exercises using p≤0.05 for the level of significance. Means and standard deviations were computed for the normalized EMG readings of the VMO and the VL for all exercises.

3 Results

Tables 2 and 3 show the normalized mean iEMG (% MVC) data of VL and VMO respectively during six REs. Normalizing was done with respect to the peak iEMG value of each muscle.

Table 2
Normalized mean iEMG (% MVC) data in VL for six rehabilitation exercises

SLRN SLRER SAQN SAQER MTR HA

Mean 31.96 29.54 36.79 43.38 38.42 53.15

±SD ±11.58 ±9.06 ±20.9 ±16.18 ±11.22 ±21.81

	SLRN	SLRER	SAQN	SAQER	MTR	HA
Mean	31.96	29.54	36.79	43.38	38.42	53.15
±SD	±11.58	±9.06	±20.9	±16.18	±11.22	±21.81

Table 3

Normalized mean iEMG (% MVC) activity of VMO in six rehabilitation exercises

	SLRN	SLRER	SAQN	SAQER	MTR	HA
Mean	34.09	31.89	45.38	50.34	43.49	60.58
±SD	±12.97	±10.74	±12.67	±12.49	±23.9	±20.81

Higher VL activity leads to a lateral force on patella which in turn may cause PFPS. Therefore, REs resulting in a VMO/VL ratio lower than one are not used, in general, to alleviate PFPS. In the present study, this ratio was found greater than one for all REs (Table 4). However, one-way ANOVA with repeated measures indicated that VMO activity was not significantly higher than VL activity for each RE.

Table 4

VMO/ VL ratio among six rehabilitation exercises

	SLRN	SLRER	SAQN	SAQER	MTR	HA
Mean	1.12	1.1	1.49	1.27	1.15	1.21
±SD	±0.41	±0.23	±0.68	±0.41	±0.63	±0.37

4 Discussion and conclusion

Subjects having no symptoms of PFPS were selected to provide a homogeneous population for the protocol of this study. VMO and VL activities were recorded across six REs to identify exercise(s) which could strengthen VMO selectively. Selective strengthening of VMO results in a VMO/VL ratio higher than one. Several researchers have evaluated REs in the past for their usefulness in terms selective strengthening of VMO [7 , 24–26].

It was notable in the present study that VMO/VL ratio was more than one (ranging from 1.1±0.23 for SLRER to 1.49±0.68 for SAQN) for all six REs. Therefore, all REs resulted in higher VMO activity in comparison to VL activity. This is important because higher VL activity may lead to a lateral force on the patella [11].

However, a statistical analysis using ANOVA showed that VMO activity was not significantly higher than VL activity for each of six REs. There are many studies in the literature which reported similar result, i.e. not achieving selective VMO activity over VL during different rehabilitation exercises, e.g., straight leg and short quad exercises [7], medial tibial rotation [10], lower extremity exercises [27] etc.

VMO/VL ratio of all REs was also inter-compared (Table 4). There was no significant difference in the VMO/VL ratios across all REs. As such performance of all exercises was equal in terms of selective strengthening of VMO. Livecchi et al. [28] compared VMO/VL ratio across four REs namely SLRN, SLRER, SAQN and SAQER, and reported no significant difference among them.

Further, individual activity of VMO and VL were compared during all six REs. One way ANOVA and LSD post hoc analysis at (p≤0.05) level of significance revealed the following. HA produced significantly higher activity in comparison to SAQN SLRER, and SLRN in VL. Although VMO/VL ratio was more than one during HA, yet VMO activity was not significantly higher than VL activity. Similar result was obtained by other studies [17, 25]. However, some studies supported hip adduction as a means of strengthening the VMO selectively. For instance, Hanten and Schulthies [10] observed selective strengthening of VMO during HA. The difference in the results may be attributed to difference in method of study, e.g., (i) using different types of electrodes, i.e., surface electrodes Vs needle electrodes (surface electrodes were used in the present study to ensure that EMG readings were specific to the VMO and VL), (ii) performing experiments with no resistance or with maximal-effort isometric contractions etc.

HA activity was significantly higher than SLRN, SLRER, and MTR for VMO. Hip adduction serves two tasks in the rehabilitation of patients having PFPS symptoms. Firstly, HA minimizes the lateral pull on the patella by activating the VMO selectively. Secondly, strong hip adductors provide stable origin to the VMO. Mean normalized iEMG (% MVC) activity of VMO activity during HA was observed as 60.58 (Table 3), which was the highest value across all REs. The effect of simultaneous knee extension and hip adduction on electrical activity of VMO and VL was reported in Andriacchi et al. [29]. A decrease in the VMO activity was reported, which may be attributed to the followings facts: (1) testing of submaximal values, (2) small sample size, and (3) the abduction torque is applied to the lower leg.

Another inference of the present study was that SAQN and SAQER produced significantly higher iEMG activities than SLRN and SLRER for VMO. This result is in line with the result of another study [7].

Many researchers experimented with MTR exercise to strengthen VMO selectively [10, 19]. Engle [19] demonstrated that MTR produced higher VMO activity when knee was in slight extension. Hanten and schulthles [10] tested MTR at 30° of flexion and concluded that VMO could not be selectively strengthened. Also, the results of the present study showed that VMO activity was not significantly higher than VL activity during MTR with no resistance. Surface electrodes were used in the present study to record iEMG signals, whereas wire electrodes were used in Hanten and schulthles [10].

Standard EMG procedures were followed as per norms [25]. Same day recording was used to reduce variability in the results. Crosstalk interference was minimized by bipolar placement of electrodes.

Limitations of the present study are as follows. Smaller sample size was used which might not be representing a normal population. The age range was quite large for the sample size selected. The study did not include female subjects. Resistance exercises were not experimented to observe selective strengthening of VMO. The results provided a wider range of options for choosing appropriate REs to treat individuals diagnosed with PFPS. Future research should involve a larger sample size including both genders and a range of resistance exercise.

Conflict of interest

None to report.

Footnotes

Acknowledgments

This work is supported by UGC, New Delhi, under Grant F. No. 3-38/2012(SAP-II) dated 02/10/2012; and by DST, New Delhi, under Grant Dy. No. 100/IFD/2563/2012-2017 dated 20/07/2012. Both authors acknowledge the help of Dr. Shellyka Ratnakar, Physiotherapist, Saran Ashram Hospital, Dayalbagh, Agra, India.

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Electromyographic analysis of VMO and VL across straight leg raise,short arc quad,medial tibial rotation and hip adduction in normal individuals

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1 Introduction

2.1 Subjects

Table 1 Demographic data No. of subjects Age (yrs) Weight (Kgs) Height (cm) BMI (Kg/m2) 10 30. 7 66.9 168.1 23.63 SD ±4.8 ±7.7 ±4.8 ±2.2

2.3 Procedure

2.4 EMG analysis

3 Results

Table 2 Normalized mean iEMG (% MVC) data in VL for six rehabilitation exercises SLRN SLRER SAQN SAQER MTR HA Mean 31.96 29.54 36.79 43.38 38.42 53.15 ±SD ±11.58 ±9.06 ±20.9 ±16.18 ±11.22 ±21.81

Conflict of interest

Footnotes

Acknowledgments

References

Table 1
Demographic data

No. of subjects Age (yrs) Weight (Kgs) Height (cm) BMI (Kg/m²)

10 30. 7 66.9 168.1 23.63

SD ±4.8 ±7.7 ±4.8 ±2.2

Table 2
Normalized mean iEMG (% MVC) data in VL for six rehabilitation exercises

SLRN SLRER SAQN SAQER MTR HA

Mean 31.96 29.54 36.79 43.38 38.42 53.15

±SD ±11.58 ±9.06 ±20.9 ±16.18 ±11.22 ±21.81