Table 2 Included studies per outcome measurement

Notzel et al. 2011 [28]

Modified Posturomed, Biovision

Participants stood barefoot in a static weight bearing position on the posturomed plate for 10 s while it that vibrated.

Activity level

Fatigability

Time to onset

Time of peak

Patients with LBP demonstrated statistically significant less gluteus medius muscle activity compared to controls. This could be associated with reduced hip stability.

LBP: 56.29 μV (±39.63)

nLBP: 96.42 μV (±64.77), p < .05

Normalisation: not performed, raw EMG values used

Not measured

Not measured

Not measured

Farahpour et al. 2018 [17]

BTS FREE EMG300

Participants walked for 8 steps in standardised shoes.

RMS

LBP: 111.8% (±48.6%)

nLBP: 48.4% (±27.3%), p < .05

Normalisation: % of MVIC in single leg stance while maintaining the pelvis level

Not measured

Not measured

Not measured

Participants with LBP showed statistically significant more gluteus medius muscle activity compared to controls.

Larsen et al. 2018 [38]

Noraxon EMG

Participants performed 10 ascent and 10 descent step tasks at self-selected speed, separated by 3 min of rest.

RMS

Specific values not reported, p > .05

Normalisation: % of sub maximum voluntary contraction during standing hip abduction with manual external resistance

Not measured

Not measured

Not measured

No statistically significant differences in gluteus medius activity during ascent and descent between those with and without LBP.

Penney et al. 2014 [29]

Biopac EMG system

Participants stood in a single leg stance position for 30 s, with the non-weight bearing limb flexed between 60 and 90 degrees at the hip. One minute rest between each of the 3 reps per side, with a 5 min rest between sides.

RMS

LBP: 5.8% (± 2.6%)

nLBP: 4.2% (± 2.3%), p = .05

iEMG

LBP: 122% (± 55%)

nLBP: 87.8% (± 49%), p = .03

Normalisation: % of MVIC in side-lying hip abduction with manual resistance

Not measured

LBP: 461.7 ms (±286.5) nLBP: 493.4 ms (±292.8), p = .73

Not measured

There was no statistically significant difference in onset time of the gluteus medius when moving to unipedal stance between the groups. However, the LBP group demonstrated statistically significant more gluteus medius activation.

Santos et al. 2013 [18]

EMG810C, EMG System do Brasil®

Participants started kneeling and then were asked to flex their R hip and extend their R knee until the R foot contacted the ground (the L knee remained on the ground). The same process was then repeated on the L limb.

R peak amplitude, MED (IQR_1–3)

LBP: 1.25 (1.00–2.16)

nLBP: 1.60 (1.00–2.10), p = .007

L peak amplitude, MED (IQR_1–3)

LBP: 1.19 (1.04–2.31)

nLBP: 1.81 (1.02–2.11), p < .001

R iEMG, MED (IQR_1–3)

LBP: 0.66 (0.17–1.00)

nLBP 1.00 (0.35–1.48), p = .004

L iEMG, MED (IQR_1–3)

LBP: 1.00 (0.57–1.00)

nLBP 1.00 (0.87–2.00), p = .001

Normalisation: % of average activity during the kneeling task.

Not measured

Not measured

R, % of duration of task, MED (IQR_1–3)

LBP: 0.68 (0.11–0.94)

nLBP: 0.44 (0.07–0.74), p = .001

L, % of duration of task, MED (IQR_1–3)

LBP: 0.86 (0.13–1.00)

nLBP: 0.21 (0.05–0.83), p < .001

Participants with LBP demonstrated statistically significant lower amounts of glutues medius muscle activity, and later times of peak activation compared to those without LBP.

Ringheim et al. 2015 [31]

EMG TeleMyo 2400 (Noraxon)

Participants stood barefoot for 15 min.

Start RMS (%Max)

LBP: 10.4 (6.3–36.5)

nLBP 8.3 (4.9–11.6), p = .19

Slope RMS (%Max)

LBP: − 1.5 (− 9.1–7.7)

nLBP: − 0.6 (− 1.7–3.5), p = .66

Normalisation: % of maximum voluntary contraction during standing hip flexion and extension in an isokinetic device.

Coefficient of variation LBP: 27.4 (23.4–48.5)

nLBP: 31 (17.5–39.7), p = .62

Slope MDF (Hz/min) LBP: 12.9 (− 9.0–21.3)

nLBP: 2.5 (− 8.0–21.3), p = .28

Not measured

Not measured

No statistically significant differences in the amount of gluteus medius muscle activity or variability of muscle activity over time between those with and without LBP.

Embaby et al. 2013 [24]

Myomonitor® Wireless EMG System

Participant stood shod for 30 min.

Not measured

R first 5 min, MDF

LBP: 172.40 (±48.96)

nLBP: 171.41 (±38.87), p > .05

R Last 5 min, MDF

LBP: 158.91 (±49.03) nLBP: 195.19 (±34.74), p < .05

L First 5 min, MDF

LBP: 159.29 (±48.81) nLBP: 173.12 (±41.36), p > .05

L Last 5 min, MDF

LBP: 177.18 (±53.95) nLBP: 185.04 (±48.04), p > .05

Not measured

Not measured

Participants with LBP demonstrated statistically significant less gluteus medius muscle activity on the R during the last 5 min compared to those without LBP (indicating greater fatigue). Differences in the first 5 min on both sides, and the last 5 min on the L side, were not statistically significant.

Hungerfor-d et al. 2003 [26]

Noraxon Telemyo 8 EMG

Participants stood on one leg then flexed the contralateral hip and knee to 90 degrees. Five trials per side were conducted.

Peak amplitude Specific values for gluteus medius not reported, p > .05

Normalisation: % of maximal activity during the single leg standing task.

Not measured

Specific values (in ms) for gluteus medius not reported, p > .05

Not measured

No statistically significant differences in the amount of activity or time of onset of the gluteus medius muscle in those with and without LBP.

Sutherin et al. 2015b [34]

EMG100C Biopac

Participants performed 5 consecutive isometric hip abduction contractions, in a side-lying position at zero degrees of hip abduction, each lasting 30 s. This was done on both sides, separated by 15 min of rest.

RMS

No specific values reported, p > .05

Normalisation: % of MVIC during side-lying hip abduction with manual resistance.

MDF

No specific values reported, p > .05

Not measured

Not measured

No statistically significant differences in the amount or duration of gluteus medius muscle activity between those with and without LBP.

Nelson-Wong et al. 2013 [6]

Biopac MP150

Participants performed the active hip abduction (AHAbd) test in a side-lying position. Note: A positive value indicates the first listed muscle activates first and a negative value indicates the second listed muscle activates first.

Not measured

Not measured

REO-RGMd

LBP: − 0.18 s (±0.28) nLBP: 0.10s (±0.31), p = .015

LEO-RGMd

LBP: − 0.03 s (±0.37) nLBP: 0.03 s (±0.37), p = .65

RIO-RGMd

LBP: − 0.11 s (±0.33)

nLBP: 0.14 s (±0.33), p = .033

LIO-RGMd

LBP: 0.02 s (±0.37)

nLBP: 0.08 s (±0.40), p = .62

RES-RGMd

LBP: 0.05 s (±0.34)

nLBP: 0.06 s (±0.33), p = .94

LES-RGMd

LBP: − 0.11 s (±0.29)

nLBP: 0.07 s (±0.36), p = .15

REO-LGMd

LBP: 0.17 s (±0.38)

nLBP: 0.05 s (±0.30), p = .35

LEO-LGMd

LBP: 0.04 s (±0.39)

nLBP: 0.12 s (±0.35), p = .55

RIO-LGMd

LBP 0.01 s (±0.42)

nLBP: 0.19 s (±0.28), p = .15

LIO-LGMd

LBP: − 0.04 s (±0.32)

nLBP: 0.17 s (±0.35), p = .049

RES-LGMd

LBP: − 0.24 s (±0.33)

nLBP: 0.09 s (±0.39), p = .014

LES-LGMd

LBP: 0.01 s (±0.34)

nLBP 0.10 s (±0.38), p = .44

Not measured

During the R AHAbd test, participants with LBP demonstrated statistically significant earlier activation of the R gluteus medius muscle relative to the ipsilateral trunk flexors (RIO and REO), compared to controls. During the L AHAbd test, participants with LBP statistically significantly activated the LGMd prior to the contralateral trunk extensors (RES) and ipsilateral IO, compared to controls.

Rabel et al. 2013 [30]

Noraxon Telemyo 2400 T EMG

Participants performed the active hip abduction (AHAbd) test in a side-lying position. Note: the larger the number, the longer it took for that muscle to activate.

Not measured

Not measured

LBP: 1629 ms (±1715) nLBP: 648 ms (±150), p = .115

Not measured

No statistically significant differences in time to onset for the gluteus medius muscle in those with and without LBP.

Hides et al. 2016 [25]

Power Trak II handheld dynamometer

Participants were positioned supine with hip in neutral. A strap was used to stabilise pelvis. Participants abducted their hip against the dynamometer at a maximal effort for 5 s with examiner resistance applied. Three trials with a 15 s rest between each trial.

Those with LBP had statistically significantly less gluteus medius muscle strength on the stance limb, but significantly more on the kicking limb.

Kendall et al. 2010 [5]

Lafayette manual muscle tester

The test limb was positioned parallel to the treatment table, directly in line with the hip. 3 maximal voluntary isometric strength contractions with a 30s rest period between trials was performed

LBP participants had statistically significantly less gluteus medius muscle strength compared to those without LBP.

Arab et al. 2010 [4]

Pressure meter

Side lying hip abduction test. Three maximal voluntary isometric contractions, held for 5 s with 15 s rest between trials.

LBP participants had statistically significantly less gluteus medius muscle strength compared with subjects without LBP.

Cai et al. 2015 [23]

Isokinetic dynamometer

Three standing concentric muscle contractions (torque) measured with leg secured to dynamometer

No statistically significant differences in gluteus medius strength between those with and without LBP.

Penney et al. 2014 [29]

Lafayette Manual Muscle Tester

Participants were laid on their side and abducted their hip whilst the examiner resisted with their hand just superior to the ankle. Two maximal resisted voluntary contractions for a 3s max voluntary contraction with 1 min rest in-between.

LBP participants had statistically significantly less gluteus medius muscle strength on both sides compared to those without LBP.

Nourbakh-sh et al. 2002 [3]

Pressure meter

Side lying hip abduction test. Three maximal voluntary isometric contractions, held for 5 s

LBP participants had statistically significantly less gluteus medius muscle strength compared to those without LBP.

Sutherlin et al. 2015a [33]

Isokinetic dynamometer

Side lying hip abduction, three maximal voluntary isometric contraction (torque). Hip-abduction trials lasting 5 s were recorded, with 30 s of rest between trials.

No statistically significant differences in gluteus medius strength between those with and without LBP.

Cooper et al. 2016 [16]

Subjective Measure

Gluteus medius strength was tested by placing subject in side-lying and having the subject abduct and slightly extend the hip while keeping the pelvis rotated slightly forward. Resistance was applied at the ankle. Graded 1–5.

LBP participants had statistically significantly less gluteus medius muscle strength compared to those without LBP.

Cooper et al. 2016 [16]

Subjective observation

While standing one hip is flexed. Trendelenburg sign considered present if the subject was unable to maintain the pelvis level or had to shift the trunk to keep the pelvis level.

LBP participants were statistically significantly more likely to demonstrate a trendelenburg sign, indicating gluteus medius muscle weakness.

Kendall et al. 2010 [5]

Treadmill and Vicon

Subjects performed a baseline standing trial, 2 static Trendelenburg trials, and a 30s walking trial on a treadmill at a speed of 1.34 m/s.

No statistically significant differences in presence of Trendelenburg sign between those with and without LBP, indicating no difference in dynamic strength provided by the gluteus medius.

Farasyn et al. 2005 [35]

Fischer pressure algometer

Lying prone the rate of pressure increase was maintained at a constant rate of on average 1Kg/sec. Three short consecutive PPT measurements with 10 s in between were performed.

Participants with LBP had a statistically significant lower threshold for pain than those without LBP.

Cooper et al. 2016 [16]

Palpation

Gluteus medius was palpated from its insertion, muscle belly and origin. Tenderness was defined as pain reported by patient and when using enough pressure to blanch the examiner’s nail.

Participants with LBP had a statistically significant greater number of trigger points in the gluteus medius muscle compared to those without LBP, as well as, more on the affect side compared to the unaffected side (for unilateral LBP suffers).

Iglesias-Gonzalez et al. 2013 [27]

Palpation

The gluteus medius was palpated by an experience clinician. No other details reported.

Participant with LBP had a statistically significant greater number of latent trigger points in both the painful and less painful sides compared to those without LBP. The number of active trigger points on either side in those with LBP was not statistically significant.

Njoo et al. 1994 [36]

Palpation

Lying prone the gluteus medius was palpated and number of trigger graded as present or absent.

Participants with LBP had a statistically significant greater number of trigger points in the gluteus medius muscle compared to those without LBP.

Aboufazeli et al. 2018 [39]

Ultrasound (GE, Model GE LOGIQ S6, MA, USA), 5.0 MHz curvilinear transducer

Side-lying at rest and during resisted hip abduction (0.5Kg weightused for resistance). Only painful side measured in LBP group. In the control group, the thicknesses of both sides were measured and then averaged. Thickness was measured as the distance between the superior and inferior hyperechoic muscle fascias, at the middle of each image.

Participants with LBP demonstrated a statistically significant smaller change in gluteus medius muscle thickness, from rest to during resisted hip abduction, compared to those without LBP.

Mendis et al. 2016 [37]

1.5 T Siemens Magnetom SonataMR

Lying supine on the imaging table with knees and hips supported in neutral position.

No statistically significant differences between the thickness of the gluteus medius muscle between those with and without LBP.

Skorupska et al. 2016 [32]

1.5 Tesla Signa HDe system (GE)

Lying supine

No statistically significant differences between each side. Note: No comparisons made between groups.