The importance of gluteal muscle strength in dynamic pelvic stability of fatigued female endurance road runners

Abstract

BACKGROUND:

Recently there has been a rise in female participation in running yet the female population is under-researched in sport specific research. Locally, many female athletes annually compete in numerous ultra-marathons ( $>$ 42 km).

OBJECTIVE:

This study investigated the importance of Gluteal muscle strength in dynamic pelvic stability of fatigued female endurance road runners.

METHODS:

Fourteen female endurance runners (age: 38.0 $\pm$ 10.12 years, BMI: 21.99 $\pm$ 2.37 kg/m ${}^{2}$ , and VO ${}_{\text{2max}}$ : 40 $\pm$ 5.34 ml/min/kg) volunteered for the participation of this study. Through isokinetic testing, muscle strength and fatigability of the Gluteus Maximus, Medius and Minimus was determined. Sign tests compared pelvis stability (unilateral Trendelenburg, Pelvic Bridge test and pelvic stability through a gait analysis) before and after an endurance run on a cambered and flat surface. Participants were divided into two groups based on change in pelvic stability after the fatigue intervention.

RESULTS:

The unaffected group was moderately younger; lighter in weight and had a lower BMI. Additionally, this group was largely more experienced ( $p=$ 0.61, $d=$ 1.341); aerobically fit and ran significantly longer weekly distances ( $p=$ 0.002, $d=$ 3.4). There was no statistical difference in isokinetic testing of strength and endurance hip flexion/extension and abduction/adduction between the two groups ( $p>$ 0.05).

CONCLUSION:

In conclusion, the group that was more experienced and ran longer weekly distances showed no change in pelvic stability after an endurance run. However, the group that showed changes in pelvic stability suggests that fatigue could be a contributing factor to pelvic compensation. It is recommended that female endurance runners incorporate strength training to strengthen the Gluteal and Hip Flexor muscle groups to reduce pelvic compensation.

Keywords

Female endurance runners gluteal muscle strength pelvic instability road running

1. Introduction

Running is a popular sport that is vastly researched world-wide where there are various distances from half marathons to ultra-marathons, but the female population is under-researched and under-represented in sport specific research [1]. Recently, there has been a rise in female participation in running. In South Africa, many female athletes compete annually, in ultra-marathons ( $>$ 42 km). A recent analysis of ultra-marathon events reported that the number of female competitors has dramatically increased in recent years [2]. Specific to the Comrades ultramarathon, a South African race of 89 km, female participation increased by 2396 between 1980 and 2014 [3].

As part of Ultra Marathon training programs, athletes compete in timed half and standard marathon distances, in addition to their normal weekly training distances. Training on roads is a popular mode of training for endurance runners where it is common for these athletes to use road edges to avoid traffic, when paved pedestrian are not available. Due to the engineering of the roads being cambered for water drainage, it may influence running kinematics of the hip and pelvis [4]. This is due to running on the right-hand side of the road in South Africa, where the cambered surface causes a difference in lateral elevation where the right foot strikes slightly downhill compared to the left. Due to road camber, the orientation of the pelvis may be affected potentially resulting in changes to muscle strength, pelvic range of motion and muscle imbalances.

Female recreational runners showed adjustments of the pelvis and hip when analysing frontal plain mechanics when running on a cambered road [4]. It is important to research pelvic stability in female runners due to having a larger Q-angle than that of males which causes greater pelvic instability and weakness, ultimately leading to knee and hip injury [5]. Previous research concludes that female athletes have a unique anatomic and functional considerations, female athletes may have a potential predisposition to specific injuries of the hip. Due to the growing population of female athletes, they need specialised care and consideration [6]. This warrants that further research in pelvic compensation in female endurance roadrunners is of great importance.

Hip instability can be accurately determined in healthy individuals using the Trendelenburg test which has a high accuracy level [7]. The reliability of transverse plane pelvic alignment measurement during the pelvic bridge test with unilateral knee extension showed substantial inter-rater reliability and excellent intra-test reliability [8]. The reliability of isokinetic hip flexor and extensor strength measurements in healthy subjects and athletes showed that the estimated mean reliability of hip extension was good (ICC $=$ 0.88; 95% CI: 0.83–0.93) and hip flexion was moderate (ICC $=$ 0.73; 95% CI: 0.51–0.94) [9].

The aim of this study was to assess gluteal strength of female endurance runners through pelvic compensation following an endurance run. The objective of this study was to assess isokinetic muscle strength and fatigability of the Gluteus Maximus, Medius and Minimus; pelvic stability through functional strength tests before and after an endurance run; pelvic stability before and after an endurance run on a flat and cambered surface; and evaluate the relationship between strength and pelvic stability.

2. Method

2.1 Participants

A sample of 14 healthy female endurance runners (age: 38.0 $\pm$ 10.12 years, height: 164.14 $\pm$ 7.21 cm, mass: 59.0 $\pm$ 7.87 kg, BMI: 21.99 $\pm$ 2.37 kg/m ${}^{2}$ ) volunteered for participation in this study. Participants were required to complete a demographic questionnaire (running history and previous injuries) an informed consent (see below) and PAR-Q ${}^{+}$ forms (Physical Activity Readiness Questionnaire for Everyone) [10]. A certificate of ethical clearance was granted by the University of Johannesburg, Faculty of Health Science (REC-1389-2022). The participants received an information letter prior to the study explaining the purpose of the research, and individual expectations. Informed consent was completed by each participant before starting testing.

2.2 Procedure

Measurements and evaluations were conducted before proceeding to test the participants which included weight (Elektra Care scale, South Africa) in kilograms to the nearest second decimal place, and height (Seca 213 Portable Stadiometer, Germany) in centimetres to the nearest half centimetre. A postural analysis was conducted by assessing the anterior, posterior, and lateral views before continuing with further testing.

On day 1 of testing participants performed a Trendelenburg test [11], a Single Leg Pelvic Bridge test, and a double-leg pelvic bridge [12]. These tests recorded any pelvic compensations and instability. Specifically, the Trendelenburg test required participants to stand in a neutral position and lift one leg assuming a single leg stance. If the PSIS falls on the non-weight-bearing side, the test is regarded as positive and indicates pelvic instability [11]. For the single Leg Pelvic Bridge test participant lay supine with knees flexed at 90-degrees with feet flat on the ground. Participant were instructed to fully extend the non-weight-bearing leg and raise the pelvis in an upward motion forming a straight line from the raised ankle through the hips and to the shoulders [12]. If the participant can keep the ASIS bilaterally at an even height, the test is regarded as negative indicating pelvic stability. If the participant is unable to keep the ASIS bilaterally at an even height, the test is regarded as positive pelvic instability [12]. Similar to the single leg pelvic bridge, the double leg pelvic bridge was used to evaluate pelvic stability. The pelvic stability evaluation (double leg pelvic bridge) followed the same protocol as the single leg tests. Participants were required to elevate the pelvis so that a straight line was established from shoulders through the pelvis terminating at the knees. If the participant can keep the anterior superior iliac spine (ASIS) bilaterally at an even height, the test is regarded as negative pelvic stability. If the participant in unable to keep the ASIS bilaterally at an even height, the test is regarded as positive pelvic instability [12]. To ensure inter-rater reliability, there was an agreement established by the observers.

The participants were required to complete an endurance run over a standardised 28 km club time trial route. Following which, the participants completed the required stability tests (Trendelenburg test and a Single Leg Pelvic Bridge test). Sign tests compared unilateral pre and post run of Trendelenburg, Pelvic Bridge test and pelvic stability. This allowed for the 14 participants to be split into two different groups. This included one group with 8 participants that showed no change in pelvic stability and labelled the “Unaffected Group”, and one group with 6 participants that showed change in pelvic stability after the run and labelled the “Affected Group”.

A minimum of 48-h after day 1 of testing, day 2 of testing was conducted. Prior to aerobic capacity and isokinetic testing, all participants completed a 5-minute moderate-intensity warm up run on a treadmill (Woodway 4front, USA) at a rate of perceived exertion of 12 on the 6–20 Borg RPE scale. Additionally, for equipment familiarisation, participants wore the oxygen consumption mask during the warm-up. Following which, the participants completed a maximal oxygen consumption (VO ${}_{\text{2max}}$ ) test as a laboratory fatigue intervention using an oxygen and carbon dioxide analyser (Cortex Metalyzer 3B, Germany) which was calibrated before each test. Specifically, participants completed the Heck VO ${}_{\text{2max}}$ Protocol. An incremental stepped protocol with a fixed grade inclination of 3%. The participants warmed up for 3-min at 6 km $\cdot$ h ${}^{-1}$ . The test then began at 8.4 kmh, and the velocities increased with increments of 1.2 kmh every 1-min and 15-s [13]. Verbal encouragement was provided throughout the test, until termination at volitional fatigue. The maximal oxygen consumption was determined in millilitres of oxygen per kilogram of weight per minute (ml/kg/min) where the change in respiratory exchange ratio (RER) was at 1.15.

Figure 1.

Participant positioning for isokinetic testing of A. Abduction and adduction. B. Flexion and extension.

Table 1

Sign tests comparisons of functional stability tests pre- and post-run including Trendelenburg, Single leg Pelvic Bridge and Pelvic Stability tests

	Negative differences	Positive differences	Ties	$P$ value
Trendelenburg left	4	0	10	0.125
Trendelenburg right	4	1	9	0.375
Pelvic bridge left	4	1	9	0.375
Pelvic bridge right	2	0	12	0.5
Pelvic stability	6	0	8	0.031

Negative differences indicate that the stability declined or test failure following the fatiguing run. Positive differences indicate that stability was improved following the fatiguing run. Ties indicate no change in stability test following the fatiguing run.

Table 2

Comparing demographic data, running mileage, experience and aerobic capacity of two groups of female recreational endurance athletes

	Unaffected group (Group 1) ( $n=$ 8)	Affected group (Group 2) ( $n=$ 6)	$P$ value	Cohen’s $d$
Age (years)	35.75 $\pm$ 11.57	41.00 $\pm$ 7.72	0.357	0.571
Height (cm)	163.63 $\pm$ 7.41	164.83 $\pm$ 7.57	0.770	0.902
Mass (kg)	57.75 $\pm$ 6.45	60.67 $\pm$ 9.85	0.515	0.713
BMI (kg/m ${}^{2}$ )	21.74 $\pm$ 2.46	22.33 $\pm$ 2.42	0.661	0.825
Weekly running mileage ${}^{*}$	70.00 $\pm$ 16.04	42.50 $\pm$ 7.58	0.002	3.400
Running experience (years)	6.88 $\pm$ 3.44	5.92 $\pm$ 3.32	0.610	1.341
VO ${}_{2}$ max (ml/min/kg)	41.38 $\pm$ 5.80	38.17 $\pm$ 4.45	0.283	1.681

${}^{*}$ Significant difference $p<$ 0.05.

The participants then completed isokinetic testing on the Humac Norm Isokinetic Dynamometer (version 15000.0103 USA). The dynamometer was calibrated on the day of testing, as per the instructional guide. Adjustments of the dynamometer range of motion stops, height, axis of rotation, and position on monorail were done accordingly to the participant. Specifically, the greater trochanter was aligned to the axis of rotation on the dynamometer [14, 15]. For abduction/adduction tests (Fig. 1a), participant lay on their side, secured at the waist and torso, to a fully reclined seat, and their distal thighs were stabilised by adjusting straps on the hip pad appendage [14]. Good reliability has been reported for testing hip abduction/adduction in this position [9]. Similarly, hip flexion/extension was tested with the participants in a supine position (Fig. 1b), securing their waist and torso to the fully reclined seat, and stabilising their distal thighs [14, 15]. Hip flexion/extension tests in this position have been shown to be reproducible [16]. Participants were afforded five submaximal practice attempts to familiarise themselves with the protocol prior to each testing condition. Strength tests (60/60 ${}^{\circ}$ /s) consisted of five repetitions at maximal effort for hip flexion/extension and hip abduction/adduction. Following the strength tests, participants were granted no more than five minutes for passive recovery. Endurance tests (180/180 ${}^{\circ}$ /s) consisted of 15 repetitions at maximal effort for hip flexion/extension and hip abduction/adduction. Visual feedback and verbal encouragement were provided by the researchers throughout the duration of the tests. The peak moment for each test was recorded.

2.3 Data analysis

All data was tested for normality using a Shapiro-Wilk test. Data was summarised and presented using mean $\pm$ sd. Sign ranked tests were used to assess ranked data from the functional stability tests (Trendelenburg, Single leg Pelvic Bridge and Pelvic Stability tests). Independent $T$ -tests were used to quantify differences between continuous data (demographic, physiological and isokinetic variables). Finally, effects sizes (Cohen’s $d$ ) using Hopkins (2002) descriptors, were calculated to quantify size differences between groups. Statistical Package for the Social Sciences (SPSS version 27.0, IBM) was used with significance set at $p<$ 0.05.

3. Results

Fourteen female endurance runners (weekly mileage: 58.21 $\pm$ 18.97 km, running experience: 6.46 $\pm$ 3.30 years, and VO ${}_{\text{2max}}$ : 40 $\pm$ 5.34 ml/min/kg) participated in this study.

Table 3
A comparison of isokinetic peak moments (Nm) of left and right concentric hip extension, flexion, and abduction in two groups of female endurance runners

	Combined ( $n=$ 14)	Unaffected group ( $n=$ 8)	Affected group ( $n=$ 6)	$P$ value	Cohen’s $d$
Strength tests (60/60 ${}^{\circ}$ /s)
Extension right	98.93 $\pm$ 36.06	106.25 $\pm$ 44.38	89.17 $\pm$ 20.57	0.402	0.469
Extension left	106.07 $\pm$ 36.11	107.50 $\pm$ 45.28	104.17 $\pm$ 22.64	0.872	0.089
Flexion right	91.00 $\pm$ 16.80	92.00 $\pm$ 20.56	89.67 $\pm$ 11.74	0.809	0.134
Flexion left	88.14 $\pm$ 20.28	91.38 $\pm$ 26.64	83.83 $\pm$ 6.05	0.513	0.364
Abduction right	100.79 $\pm$ 29.16	102.63 $\pm$ 36.19	98.33 $\pm$ 19.10	0.797	0.142
Abduction left	99.21 $\pm$ 27.79	97.75 $\pm$ 27.21	101.17 $\pm$ 31.03	0.830	$-$ 0.118
Endurance tests (180/180 ${}^{\circ}$ /s)
Extension right	46.96 $\pm$ 24.82	49.38 $\pm$ 28.92	43.73 $\pm$ 20.22	0.691	0.220
Extension left	51.75 $\pm$ 20.57	54.43 $\pm$ 22.37	48.18 $\pm$ 19.30	0.594	0.295
Flexion right	58.48 $\pm$ 12.19	59.58 $\pm$ 13.83	57.02 $\pm$ 10.69	0.714	0.202
Flexion left	57.40 $\pm$ 14.56	60.20 $\pm$ 17.05	53.67 $\pm$ 10.72	0.428	0.443
Abduction right	59.39 $\pm$ 10.51	61.51 $\pm$ 13.01	56.56 $\pm$ 5.77	0.405	0.467
Abduction left	59.68 $\pm$ 20.13	59.85 $\pm$ 23.32	59.46 $\pm$ 17.10	0.973	0.019

Pre- and post-endurance run stability test results are reported in Table 1. The Trendelenburg test on the left side showed 4 participants had a negative difference (change from stable pelvis before the run to unstable pelvis after the run) and 10 of the participants showed no change. The Trendelenburg test on the right showed 4 participants had a negative difference, 1 participant had a positive difference (change from unstable pelvis before the run to stable pelvis after the run), and 9 participants showed no change. The Single Leg Pelvic Bridge test on the left showed 4 participants had a negative difference, 1 participant had a positive difference, and 9 participants had no change. The Single Leg Pelvic Bridge test on the right showed 2 participants had a negative difference, and 12 participants had no change. There was little statistical significance indicating pelvic muscular fatigue based on the functional tests. However, a large difference was noticed when assessing pelvic stability through a visual gait analysis as 6 participants had a negative difference, and 8 participants showed no change. This indicates a trend that pelvic compensation occurs after an endurance run comparing pre-run flat surface to post-run cambered surface gait analysis.

Following, these results, participants were divided into two groups based on the sign test as seen in Table 1. Group 1, the unaffected group, included 8 individuals with no change in pelvic stability before and after an endurance run when testing a gait analysis on a flat surface. Group 2, the affected group, included 6 individuals with a negative difference noted in pelvic stability before and after an endurance run when testing a gait analysis on a flat surface. Demographic and physiological data for the two groups is shown in Table 2.

When comparing the unaffected group to the affected group, although not significant, the unaffected group was moderately younger, lighter in weight and had a lower BMI. Additionally, the unaffected group was largely more experienced and aerobically fit, ran significantly longer weekly distances.

Table 3 compares isokinetic peak moment differences between the two groups through concentric strength (60/60 ${}^{\circ}$ /s) and endurance (180/180 ${}^{\circ}$ /s) tests of hip flexion, extension, and abduction.

There was no statistical significance noted between the two groups however there were moderate differences noted in the strength test (60/60 ${}^{\circ}$ /s) of hip extension concentric on the right as well as in the endurance test (180/180 ${}^{\circ}$ /s) of hip flexion concentric on the left and hip abduction concentric on the right.

4. Discussion

The aim of this study was to determine the relationship of gluteal muscle strength and dynamic pelvic stability in fatigued endurance runners following cambered road running. When comparing the unaffected group to the affected group, although not significant, the unaffected group was moderately younger; lighter in weight and had a lower BMI. Additionally, the unaffected group was largely more experienced; aerobically fit and ran significantly longer weekly distances. No statistical isokinetic differences were noted between the groups. A trend was noted in the Isokinetic test results showing that the unaffected group was stronger in hip extension strength on the right, stronger in hip flexion endurance on the left and stronger in hip abduction endurance on the right. Overall, the unaffected group was stronger in all isokinetic tests besides hip abduction strength on the left.

Previous research had similar demographics of adult female endurance runners [2, 3, 18]. The results of 80 participants showed the mean age of 40.92 ( $\pm$ 9.61) years, a height of 163.60 ( $\pm$ 6.41) cm, a weight of 62.24 ( $\pm$ 10.05) kg, running experience of 10 ( $\pm$ 8.37) years and weekly mileage of 27.62 ( $\pm$ 11.69) miles/week (44.45 km per week) [17]. The age of peak performance in 50 km Ultra Marathon runners was 41 years in women [18]. Our sample size has a mean age of 38.0 $\pm$ 10.12 years which indicates that this research sample is relative to other sample ages in previous studies of competitive female endurance runners.

When comparing aerobic capacity, further research assessed the mean VO ${}_{\text{2max}}$ , results found the athletic group had a VO ${}_{\text{2max}}$ of 39.62 $\pm$ 2.80 ml/kg/min [19]. It has been seen elite female long distance runners had an average VO ${}_{\text{2max}}$ of 64 ml/min/kg [20]. This puts our sample in a recreational athlete category in terms of aerobic capacity at a VO ${}_{\text{2max}}$ of 40 $\pm$ 5.34 ml/min/kg. It would be expected that our sample size would have a lower VO ${}_{\text{2max}}$ due to a higher altitude in Johannesburg, South Africa where there is an elevation of 1753 m.

The physiological demands for endurance runners include: VO ${}_{\text{2max}}$ , lactate threshold and energy demand while running at a given pace. An increase in intensity of exercise requires an increase of maximal oxygen uptake to maintain performance levels. Individuals with a higher lactate threshold can perform better in endurance running as well as expend less energy if they perform with a better running economy [21]. It is seen that the unaffected group presents with a higher VO ${}_{\text{2max}}$ and showed no changes in pelvic compensation after an endurance run. This research suggests that the unaffected group showed a better running economy due to having better pelvic stability and aerobic capacity.

Assessing the results in the current study, the unaffected group has slightly stronger Gluteus Medius on the right seen in the hip abduction endurance Isokinetic test. This group may have adapted to the camber being on the right side which has strengthened Gluteus Medius and therefore showed no pelvic compensation after the endurance run. Female recreational runners showed adjustments of the pelvis and hip when analysing frontal plane mechanics when running on a cambered road [4]. Gluteus Medius is a main pelvic stabiliser [22] which is why there may be a direct correlation between a stronger right Gluteus Medius shown during the Isokinetic strength test and no pelvic compensation shown during the gait analysis after the run. This may indicate that the unaffected group was able to maintain pelvic stability after the fatigue intervention. The affected group showed a slightly weaker Gluteus Medius on the right during the isokinetic endurance test, as well as pelvic compensation after the fatigue intervention. Considering this group has not been running for as long and has less mileage per week compared to the unaffected group; the pelvic stabilising muscles may not have yet adapted to the camber during their road running training. The unaffected group has possibly adapted to the camber of the road or fatigue as they have more running experience and weekly mileage. The Isokinetic test for hip extension strength on the right indicates that they have a stronger Gluteus Maximus as compared to the affected group. This was also seen with hip flexion endurance on the left indicating that Rectus Femoris, Psoas Major and Iliacus is stronger on the left. This may be due to running on the right-hand side of the road with the camber being on the right side. It is a possibility that the left leg may need more range of motion through hip flexion due to being on the higher surface of the road. Previously it has been observed that the right pelvic range of motion was significantly greater than the left pelvic range of motion when analysing frontal plane kinematics [4]. These results were seen in participants who ran on the left-hand side of the road. The affected group was stronger in the hip abduction isokinetic strength test on the left. However, the results were not the same with the isokinetic hip abduction endurance test. This is possibly the reason pelvic compensation was still displayed after the fatigue intervention as Gluteus Medius endurance can be improved. Although trends were seen with the Isokinetic testing, there was no statistical difference in relation to running economy. This was seen in previous research when analysing Isokinetic strength of the knee and ankle joint in relation to running economy [23].

The current study is limited by the fatigue intervention mode. Participants were free to run a distance between 15 and 30 kilometres at their own pace. As such, it is unlikely that participants experience true physiological fatigue [24]. Additionally, the exact occurrence of pelvic muscle fatigue for each participant could not be measured in this pre-post study design. The isokinetic test used to test muscle strength and endurance based off peak moment data analysed only one joint movement whereas running uses multi-joint movements [25]. Further research could use different multi-joint tests to analyse strength and endurance of the full kinetic chain. To be more objective with pelvic compensation, the use of an EMG to analyse muscle activation while running and with the functional tests used in this research. Leg length discrepancy played a limiting factor in this study as it was not included in the method. Further research could analyse the link between leg length discrepancy and pelvic compensation. Additional research could include a postural stability test on the Biodex Biosway Balance System (950-460 USA) to analyse the ability to maintain balance as well as a stability index [26].

5. Conclusion

In conclusion the group that was more experienced showed no changes in pelvic stability after an endurance run. However, the group that showed changes in pelvic stability suggests that fatigue could be a contributing factor to pelvic compensation. There was no statistical difference in isokinetic strength between the two groups suggesting that years of running experience and weekly mileage may play an important role in pelvic stability. A bigger sample size may find more conclusive evidence between Gluteal muscle strength through isokinetic testing.

In light of the findings, to reduce pelvic instability, female endurance runners should strengthen Gluteus Medius, Gluteus Maximus, Rectus Femoris, Psoas Major and Iliacus. Exercises that may improve pelvic stability include Resistance Band Abductor Side-walks, Fire-hydrants, Clamshells, and Lateral Step-down Squats [27]. Additional exercises that we suggest are Single Leg Romanian Deadlift, Weighted Back Squats and Resistance Band Hip Flexion. This should be performed at an intensity of 50–70% of 1RM, 20–25 reps and 3 sets. This focuses on endurance strengthening which we believe is beneficial for female endurance athletes.

Author contributions

CONCEPTION: Michelle de Meillon, Molly Keegan, Darren Kwong and Andrew Green.

PERFORMANCE OF WORK: Michelle de Meillon, Molly Keegan, Darren Kwong and Andrew Green.

INTERPRETATION/ANALYSIS OF DATA: Michelle de Meillon, Molly Keegan, Darren Kwong and Andrew Green.

PREPARATION OF THE MANUSCRIPT: Michelle de Meillon, Molly Keegan, Darren Kwong and Andrew Green.

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Michelle de Meillon, Molly Keegan, Darren Kwong and Andrew Green.

SUPERVISION: Darren Kwong and Andrew Green.

Ethical considerations

A certificate of ethical clearance was granted by the University of Johannesburg, Faculty of Health Science (REC-1389-2022). The participants received an information letter prior to the study explaining the purpose of the research, and individual expectations. Informed consent was completed by each participant before starting testing.

Funding

The authors report no funding.

Footnotes

Acknowledgments

The authors would like to thank the participants for their time.

Conflict of interest

The authors have no conflicts of interest to report.

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