A Novel Wall Touch-Single Limb Stance Exercise for Dynamic Activation o f Gluteus Maximus - A Cross Sectional Study

Abstract

Objective

Gluteus maximus (GM) dysfunction is associated with spinal/lower extremity musculoskeletal conditions. Studies on weightbearing GM exercises that can be used earlier in rehabilitation is limited. Utilizing GM isometric contraction and load transmission to thoracolumbar fascia during trunk straightening under unilateral stance, we for the first time describe Wall Touch Single Limb Stance (WT-SLS) exercise. Specific exercise prescription may be rationalised using knowledge of how upper and lower fibres of GM (UGM, LGM) respond during novel WT-SLS.

Methodology

Surface EMG signals from UGM and LGM were compared among WT-SLS, Step up (SU) and Unilateral wall squat (UWS) in healthy subjects (N = 24). Raw data was normalized and expressed as percentage of maximum voluntary isometric contraction (%MVIC). Relative easiness in performing the exercises was scored using Borg's CR10 scale. Statistical significance was defined as p < 0.05.

Results

WT-SLS had the highest %MVIC for both UGM and LGM (p < 0.0001), suggesting maximum activation of GM in healthy adults by our novel exercise. WT-SLS generated more motor unit action potentials, and had significantly greater activity for UGM than LGM (p = 0.0429). Remaining exercises had no differential activation of UGM and LGM. WT-SLS was perceived as only ‘slight’ exertion.

Conclusions

WT-SLS depicted the greatest muscle activation, suggesting possible better clinical and functional outcomes considering GM activation and strengthening. UGM was preferentially activated during WT-SLS, but not during SU and UWS. Therefore, targeting GM with our novel exercise may improve gluteal weakness and dysfunction in lumbar radiculopathy, knee ligament injuries; as preventive measure for injury; or for postural correction.

1. Introduction

Gluteus maximus (GM) is considered to be one of the most important lower limb muscles for maintaining both static and dynamic postural stability. Upper GM (UGM) is more active during activities incorporating hip abduction owing to its attachment with tensor fascia lata, while lower GM (LGM) is better suited for hip extension.¹ GM has been reported to be underactive or weak functional and more fatigable in majority of the musculoskeletal and sports conditions involving spine &/or lower limb,² thus contributing to underperformance and injury risk.³ The contribution of GM can not be underestimated due to its significant role in providing stability to the lumbopelvic structures and load transfer between trunk and lower extremities, through its attachment with thoracolumbar fascia (TLF) and also in taking the pressure off of the underlying neuromuscular structures.⁴ The saggy/sleepy glutes, commonly associated with sedentary lifestyle and posterior pelvic tilt, is a risk factor for compression of the underlying nerve and muscle, thus causing pain, paresthesia and neurological deficits in the lower limb. Also, the muscular imbalance of stabilisers around the lumbopelvic region has been reported to be associated with origin and/or worsening of low back pain and radicular symptoms, and other lower extremity ligamentous injury symptoms.³

GM has been recognized as the primary muscle accountable for hip extension, in various loaded exercises like squat and leg press which involves concurrent knee and hip extension thus minimizing the activation of hamstrings.5, 6, 7, 8 Comparative assessment using surface electromyography (sEMG) studies has been used to measure muscle's activation patterns, fatigue and also in the field of strength and conditioning for exercise selection and intensity progression.^9,10 It is important to consider these patterns while prescribing the exercises for the purpose of physical fitness or for rehabilitation from an injury, as the number of motor units recruited would regulate the force of muscle contraction.¹¹

Gluteus maximus has also been stated to be the global stabiliser for the hip extension movement, thus contributing towards the proper recruitment pattern for movement.^4,12 So the inappropriate activation of this muscle can result in a failed load transfer system, wherein the hamstrings will fire early trying to compensate for the inactive/weak GM.^13,14

It is a common practice among clinicians worldwide to prescribe strengthening exercises for GM in both weight bearing (WB) and non-weight bearing (NWB) positions, with previous research stating that lower extremity muscle activity is greater in unilateral WB, followed by bilateral WB and then NWB.15, 16, 17, 18, 19 The WB strengthening exercises are preferred more in chronic or functional rehabilitation phase as they simulate the functional pattern more closely.

A variety of exercises have been reported previously in the literature for training GM, including the multi-directional step ups, lunges, deadlifts, squats, prone hip extension etc.²⁰ but none of these incorporate any functional exercise for the dynamic activation purpose which can be used in the acute or subacute conditions. Also, the previous literature analysing the upper and lower portions of GM during various functional exercises is highly limited. Here, we describe a novel exercise for GM activation, utilizing the specific isometric contraction of GM in unilateral stance, coupled with load transmission to thoracolumbar fascia during trunk straightening, and coined the exercise as Wall touch Single Limb Stance (WT-SLS). Knowledge of how upper and lower fibres of GM (UGM, LGM) respond during novel WT-SLS, may provide a scientific rationale for specific exercise prescription. So, this study is an attempt to examine the electromyography of upper and lower GM to study the dynamic activation of the muscle using our novel exercise vis-a vis traditional exercises.

2. Methodology

This was a cross-sectional study designed to compare the influence of WT-SLS on Gluteus maximus activation, in comparison with unilateral wall squat (UWS)²¹ and step up (SU)²² exercises. The latter two were chosen for comparison in view of their high activity level,²⁰ unilateral weight bearing nature of exercise and feasibility.

2.1. Participants

Purposive sampling was used to recruit healthy adult volunteers of both the genders and 18-30 years of age after obtaining the informed consent for this study. The study was approved by the institute's ethical committee (IEC-INT/2022/Study-10), and conducted in accordance with Declaration of Helsinki.

The subjects were enrolled if they were otherwise healthy and not involved in any kind of resistance training or sport activity on regular basis. Exclusion criteria included professional athletes, pregnant or lactating females, pain while performing any test-exercise, history of any injury/surgery/deformity of lower limb or spine that could limit the performance of any of the testing session exercises, history of patellofemoral pain syndrome, any neuromuscular disorder.

2.2. Protocols

Anthropometric measurements of height and body mass were taken to calculate subjects’ BMI. Subjects were asked to refrain from participating in any resistance training for 72 h before the test session, and to wear loose clothing (preferably vest and shorts) and comfortable shoes for the test session. Testing was performed at the same time of the day for all subjects, to rule out any effects of time and/or temperature change.

On the test day, all the participants performed a 10-min warm-up session that included dynamic stretches for the lower limb followed by practice repetitions of all the three exercises to ensure the correct technique performance. The subjects were then asked to perform the three exercises in a random sequence. The order of randomness was created using random pattern generator (http://www.psychicscience.org/random), so as to avoid any sequence bias. All exercises were repeated in triplicates with 5–6 s of contraction followed by 3 min of rest between change of exercise (Fig. 1). All EMG data was sampled from the dominant lower extremity, defined as the extremity which can kick a ball at the maximum distance.

Fig. 1.

Study protocol.

Step-up (SU) was performed in standing. the subject started from the non-dominant rear leg in 100° hip extension and was asked to step up with posterior border of leading dominant leg heel touching the edge of the 10” box, by extending the leading hip and knee. The exercise terminated when the rear leg gets placed on the box (Fig. 2A).

Fig. 2.

A) Step Up Exercise B) Unilateral wall Squat C) Wall touch SLS D) MVIC test- Standing Glute Squeeze.

Unilateral Wall Squat (UWS) was performed with subject standing against a wall, with a unilateral stance on the dominant leg (heel placed 1’ away from the wall), and non-dominant hip in flexion and knee fully extended to keep it off the floor. Subject was instructed to squat down as far as possible without losing the balance, and then getting back to start position, all the while keeping the head and trunk upright and against the wall (Fig. 2B).

Wall Touch-SLS exercise (WT-SLS) was performed with the subject standing upright, facing 45° to the wall, with the weight bearing on the target/dominant limb in external rotation, and the other lower extremity at hip and knee 90° flexion, with the knee touching the wall. The subject was then instructed to elongate the trunk as if trying to appear taller but without heel raise, simultaneously maximally contracting the glutes isometrically, with a hold for 5-6 s (Fig. 2C).

2.3. Electromyographic analysis

The electrode site skin preparation included removing excess hair with razor (if needed), and cleaning the skin with isopropyl alcohol swab. The self adhesive surface electrodes of 1 cm diameter and interelectrode distance of 2 cm, were used for measuring the EMG activity of UGM and LGM. A line was marked from posterior superior iliac spine (PSIS) to Greater trochanter (GT) of dominant lower limb. Electrodes for UGM were placed 5 cm above this line and parallel to the orientation of the muscle fibres, and 5 cm below the line for LGM. To ensure consistent electrode placement throughout the test session, electrodes were secured using surgical tape. The EMG measurements for Gluteus maximus activity were then recorded during the exercises.

EMG data was collected and exported using Nihon Kohden II machine (Nihon-Kohden Co., Japan). Upper fibres of gluteus maximus (UGM) were recorded above the level of an imaginary line between PSIS and GT; lower fibres (LGM) were recorded below that. The surface electrode was applied over the maximum bulk felt on active extension of ipsilateral hip joint. The recording electrode was applied 3-4 cm distal and lateral to the surface electrode. The ground electrode was applied over the contralateral lower limb.

Motor unit action potentials (MUAPs) were recorded at 200-500 μV and 10 ms, with high-cut filter at 3 kHz and low-cut filter at 50Hz. Data was smoothed using a root-mean-square algorithm with a 200 μV gain. Activity of GM during the three exercises were denoted utilizing the average percent MVIC peak activity for each.

2.4. MVIC testing and %MVIC calculation

Maximal voluntary isometric contraction (MVIC) test was performed using Standing Glute Squeeze technique²³ in which the participants were asked to stand with feet slightly wider than shoulder width apart and hips slightly externally rotated. Each subject was then instructed to squeeze the glutei and focus on externally rotating and extending the hips (Fig. 2D).

Five minutes after completion of all three exercises, MVIC of GM was established as a reference value, so as to state each exercise in the test session as a percentage of MVIC, thus allowing a standardized comparison across the subjects. Three 5-s MVICs for GM were performed in order to normalize the muscle activation data obtained during the above three exercises. The mean amplitude were calculated for the 3 MVIC trials per muscle.

2.5. Subjective force estimation

Subjective force estimation was reported by the subjects. After the test session was over, each subject was asked to report the level of exertion as perceived for exercise performance using Borg's CR10 scale. The scores on the Borg's CR10 scale range from zero to ten, with zero being ‘no perceived exertion’ and ten being ‘very, very heavy’.

2.6. Statistical analysis

The sample size was calculated with reference to relevant previous studies.^16,21,24,25 A-Priori power analysis was performed using G*Power software, for a null hypothesis to be rejected with a two-tailed test at significance level (α) of 0.05 and power (1-β) of 0.95. Previous reports on wall touch single limb stance exercise are lacking. Therefore, we decided to use an effect size (d) of 0.8, following which the required sample size was estimated at a minimum of 23. Normalized mean EMG signal amplitudes (as percentage of MVIC scores) were expressed as mean and standard deviation for all three exercises. Effect size (Cohen's d) was calculated between the groups with the formula of mean differences divided by the pooled standard deviations,²⁶ using Excel® spreadsheet (Microsoft 365®, MA, USA). A d value less than 0.2 were considered to have small effect; 0.2–0.5 as medium effect and 0.6–0.8 as large effect.²⁷

Activity of UGM and LGM was compared among exercises using a repeated-measures one-way analysis of variance (ANOVA). Tukey's analysis was done for multiple comparisons test among the three exercises. Statistical analyses were performed using GraphPad Prism 9.4.1. (San Diego, CA), with a statistical significance defined as a p < 0.05.

3. Results

3.1. Subjects

Of total 31 healthy volunteers who participated in this study, 7 females were excluded from the study due to difficulty in recording sEMG activity owing to higher gluteal fat. Data obtained from remaining 24 subjects (17 M, 7F) was analysed. The participants had a mean age of 21.8 ± 2.22 years (range:19-27) and mean BMI of 20.89 ± 2.006 kg/m²(Range: 17.58–26.23).

3.2. %MVIC of three exercises for LGM and UGM

For all three exercises, the pairwise comparisons revealed significantly higher activity for UGM than LGM, with the difference being maximum for WT-SLS (Table 1). The one-way ANOVA with repeated measures indicated a significant main effect across exercise for UGM (F_2,69 = 17.09, p < 0.0001), and LGM (F_2,69 = 15.08, p < 0.0001).

Table 1.

Pairwise comparisons for UGM and LGM.

	LGM	UGM	Mean difference with 95% CI	p
SU	65.25 ± 29.04	70.4 ± 30.6	5.11 (−9.754, 19.99)	0.4837
UWS	80.23 ± 31.51	93.2 ± 33.5	13.00 (−1.29, 27.30)	0.0726
WT-SLS	112.5 ± 30.68	137 ± 52.7	24.58 (0.86, 48.31)	0.0429*

*p < 0.05.

We found significantly higher activity during WT-SLS relative to SU and UWS exercises (ANOVA, p < 0.0001) for both UGM and LGM. For LGM, WT-SLS exercise showed 1.7- and 1.3-fold higher activity compared to SU and UWS exercise respectively. Similar results were found for UGM. The UGM showed the greatest mean amplitude when analysed with WT-SLS [137 ± 52.7% (95% CI: 115, 159)] compared to the other two exercises (ANOVA, p < 0.0001). In fact, the UGM had higher %MVIC than LGM (137 ± 52.7% vs. 112.5 ± 30.68%, p < 0.05; d = 0.55), suggesting that this exercise is best in involving the activity of UGM.

For LGM and UGM, multiple comparisons test revealed a significant difference between WT-SLS and SU (p < 0.0001) and between UWS and WT-SLS (p = 0.0014, 0.0010 respectively), while there was an insignificant difference between SU and UWS (p = 0.21, 0.12 respectively).

3.3. Subjective force estimation

For the Subjective force estimation, Borg's score for three test session exercises was rated by the subjects according to the perceived level of exertion during the exercise performance (Fig. 3). The SU was easiest (0.48 ± 0.09), and UWS being the hardest to perform (4.75 ± 0.23). The subjects perceived ‘slight’ exertion while performing WT-SLS (2.35 ± 0.15).

Fig. 3.

Borg's CR 10 score.

4. Discussion

Quantifying the muscle activation during an exercise helps a clinician/therapist to make the right choice to improve the subject's athletic performance or for functional rehabilitation. This study examined the peak sEMG amplitude for Gluteus maximus (upper and lower) during three different functional closed kinetic chain exercises (SU, UWS, WT-SLS), without any additional load. The tested exercises were chosen as they simulate the functional muscle recruitment patterns. One can infer about strengthening the muscle with a particular exercise by deducing the activity's EMG amplitude in form of percentage MVIC. All three exercises were reported to have very high activity of >60% for both UGM and LGM, according to a general classification suggested by DiGiovine et al.²⁸ The muscle activation for both UGM and LGM followed a trend of lowest to highest during SU, UWS, WT-SLS. The UGM showed higher activity for all three exercises, relative to LGM. These results are in partial agreement with previous research reporting preferential activation for superior GM during exercises incorporating hip abduction &/or external rotation.²⁵

In agreement with our hypothesis, the WT-SLS exercise demonstrated the highest activity in terms of maximum amplitude MUAPs in both LGM (112.5 ± 30.68% of MVIC) and UGM (137 ± 52.7% of MVIC). Significant difference for peak amplitude in GM activity between WT-SLS and SU, WT-SLS and UWS (p < 0.01) could be attributed to the test position with hip in external rotation which is anatomically an action of Gluteus maximus as a global mobilizer. When the lower extremities are fixed to the ground (i.e., in closed chain movement), the GM can straighten the trunk and prevent forward lean of the trunk to keep the body in balance. The fascial linkage between GM and TLF permits tension generated with GM's isometric contraction during WT-SLS, to reach TLF through GM fascia, thereby stretching the trunk.^29,30 Tensioning the TLF further adds to the spinal stability, by inducing a decrease in superficial muscle activity.³¹ Additionally, verbal instructions specific for muscle's contraction during the performance of exercise could have also contributed to the higher activity. Amplitude greater than maximal effort contraction for MVIC testing can possibly be because of co-contraction of core muscles while performing WT-SLS, thus contributing to the additional requirement of stability. These co-activations are usually characteristic of the excessive demand, for instance, from an instability of supporting base, where body needs to be more in control from the lumbopelvic core musculature. Another likely explanation for the higher than MVIC amplitude, could be the unilateral weight bearing nature of exercise superimposed over the similarity in the technique, as it is already established that the neuromuscular activation for a muscle (in this case, gluteus maximus) is higher during unilateral stance exercises relative to bilateral ones.^19,32,33 Therefore, the authors of this study recommend WT-SLS exercise over UWS and SU for dynamic activation of Gluteus maximus.

Although all the exercises had average peak MUAP amplitude greater than the otherwise stated ‘40-60%’ threshold required for strengthening a muscle,³⁴ so either can be used for the said purpose. But whether these exercises can be used in all stages of recovery was the question of interest to the authors. While many exercises (including SU, and UWS alongwith all their variations) are commonly used for strengthening GM as part of functional rehabilitation in later stage of recovery, little is known for any effective exercise that can be used for activating/strengthening the GM, in patients with acute or subacute stage of pain. As detected on sEMG in our subjects, the recruitment (number of MUAP generated at any specific force) recorded while performing the test-exercises were much higher in number for wall touch SLS as compared to the other two exercises. Higher recruitment implies greater number of fibres of the muscle being activated at a specific level of force. Furthermore, as reflected by Borg's score, WT-SLS was experienced as only slight level of exertion, hence is easy to perform too. Therefore, the authors suggest the use of Wall Touch-SLS exercise not only for strengthening, but also for dynamic activation leading to pain reduction in early recovery stage, provided the patient is able to maintain unilateral stance comfortably. It may be interesting to check for its effectiveness in pain reduction in subjects with low back or sacroiliac joint pain, patellofemoral pain syndrome or knee/ankle ligament injuries where the TLF and GM dysfunction is usually seen.^30,35

Ayotte et al.²¹ reported an activation of 86 ± 43%MVIC for the gluteus maximus during the UWS. This value is in close proximity with our values for both lower (80.23 ± 31.51%MVIC) and upper (93.2 ± 33.5%MVIC) gluteus maximus. Despite of the difference in techniques for MVIC testing in the two studies, the GM activation values on the EMG are quite similar for UWS. The findings of this study are in contrast to that of Distefano et al.²⁴ and Boudreau et al.,³⁶ who reported an activity of 59% and 35.2%MVIC respectively for single limb squat. This variation in values could be because of methodological differences in the MVIC position and squat technique. It is likely that an altered ground reaction force relative to body position contributed to the higher GM activity when the foot was placed anterior to the centre of mass.²¹

SU involves force generation by hip and knee extensors to vertically accelerate the body against gravity, with greater ground reaction force for the concentric phase relative to bilateral squat.³⁷ Contrarily, as noted in our EMG data, the activity for both UGM and LGM was lower for step-up than squat. Difference in loading may account for this variation in results of two studies, for unilateral squat requires higher torque generation and neuromuscular activation. Moreover, the demand on GM is higher to produce greater hip extensor thrust during unilateral squat with a favourable length-tension relationship. Our recorded values for step-up are comparable to those by Ayotte et al. for forward step-up.²¹ However, despite the similarity in technique of step-up in study by Simenz et al.,²² the muscle activation recorded are quite distinctive for the two studies. Different technique for MVIC testing and use of 6RM technique during step-up may attribute to this.

5. Conclusion & clinical implication

Training the Gluteus maximus utilizing the wall touch SLS exercise, can possibly help to both dynamically activate and strengthen the muscle, thus avoiding the unwanted pressure over the underlying sciatic nerve and also correcting the altered hip mechanics owing to inadequate gluteal musculature motor control. Also, its effects can possibly prevent/rehabilitate the ligamentous instability in the knee and ankle, or degenerative changes in knee, by providing better dynamic control and by co-activating the core muscles thus adding to stability.

Since this study was performed on healthy individuals, and we found that WT-SLS had the best result in healthy volunteers, we anticipate using this exercise in patients cohort in future. It would be interesting to determine the efficacy of the wall touch SLS exercise in subjects with spinal/lower limb mechanical dysfunctions (for instance, lumbar radiculopathy, patellofemoral pain, sports injuries like hamstring strain, iliotibial band friction syndrome etc), as preventive measure for injury, or for postural correction.

Limitation of this study would include the use of surface EMG, instead of needle EMG, as sEMG data can have artefacts, and the presence of overlying fat and crosstalk from surrounding muscles can make it difficult to perform.

Source of funding

No funding was received for this study at any stage.

Informed consent

Informed consent was obtained from all subjects prior to enrolment into the study.

Institutional ethical committee approval

Institutional ethical committee approval was obtained from Institute's ethical committee vide ref No. IEC-INT/2022/Study-10.

Authors’ contribution

BR: conceptualization, Data curation; Formal analysis; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Roles/Writing - original draft; Writing - review & editing. SS: Data curation; Investigation; Methodology; Project administration; Roles/Writing - original draft. PB: Data curation; Investigation; Methodology; Project administration; Roles/Writing - original draft. RS: Data curation; Project administration; Resources; Roles/Writing - original draft; Writing - review & editing. MSD: conceptualization; Project administration; Resources; Supervision; Writing - review & editing.

Declaration of competing interest

None declared.