Acute effects of centrally- and unilaterally-applied posterior-anterior mobilizations of the lumbar spine on lumbar range of motion,hamstring extensibility and muscle activation

Abstract

BACKGROUND:

Lumbar mobilizations are used to clinically treat the lumbar and hamstring region. However, evidence is limited regarding the effectiveness of specific mobilization methods.

OBJECTIVE:

To compare central and unilateral posterior-anterior mobilizations (CPA, UPA) of the lumbar spine on lumbar and hamstring range of motion (ROM), and muscle activity (sEMG).

METHODS:

Twenty participants received CPA, UPA, or no mobilization (CON) on separate occasions (crossover design). Post-treatment outcome measures were ROM during active lumbar flexion (ALF) and active knee extension (AKE), as well as sEMG of the Erector Spinae (ES) and Biceps Femoris (BF) during these movements.

RESULTS:

sEMG was possibly to very likely lower following CPA (mean difference range $=$ $-$ 5% to $-$ 21%) and UPA ( $-$ 7% to $-$ 36%), while ROM was most likely greater ( $-$ 12% to 25% and $-$ 17% to 24%, respectively). Most sEMG measures were possibly to likely lower following UPA versus CPA ( $-$ 18% to $-$ 11%), while AKE ROM was possibly greater ( $-$ 5.5%). Differences in ES sEMG ( $-$ 2.5%) and ROM ( $-$ 1.4%) during ALF were unclear and most likely trivial, respectively.

CONCLUSIONS:

CPA and UPA mobilizations increase lumbar and hamstring ROM whilst reducing local muscle activity. These effects appear to be greater for UPA mobilizations when compared with CPA.

Keywords

Manipulation spinal lumbar vertebrae hamstring muscles

1. Introduction

Low back pain causes more disability worldwide than any other condition and the cost to the National Health Service in the UK exceeds 1000 million pounds per year [1, 2]. Lumbar mobilizations have been used to decrease spinal pain and stiffness whilst increasing range of motion [3]. Recent National Institute of Clinical Excellence [2] guidelines suggested this type of manual therapy can be used to treat patients with lower back pain as part of an overall treatment plan. In Northern Ireland, of 157 physiotherapists surveyed, approximately 42% chose to treat patients with lumbar pathology with mobilizations [4].

The lumbar spine is widely considered to have an indirect impact on the hamstring complex due to its anatomical and functional relationship [5, 6, 7]. The origin of the neural supply and neurodynamics of the hamstring complex implicates the lumbar spine as a potential source of pain referral and impacts on the biomechanical function of the muscle group [8]. Restricted hamstring extensibility has been demonstrated to directly decrease lumbar flexion range [9]. Furthermore, back pain is associated with changes in the mechanical characteristics of the hamstring lowering muscle activity within the complex, whilst increasing its stiffness [10, 11, 12].

Hamstring strains continue to be one of the most common musculoskeletal injuries in athletes of all age ranges, genders, sports, and levels of competition [13]. Reduced extensibility of the hamstring remains an associated risk factor for injury as well as impinging on lumbar mobility [9, 14, 15, 16]. Recent evidence suggests that lumbar mobilizations can increase the hamstring tissue extensibility, as measured by the active knee extension test, and reduce muscle electromyography activity of the hamstring and Erector Spinae (ES) during active movements in the immediate term [17, 18]. Given excessive ES activity has been reported in patients with low back pain [19], assessing muscle activity may provide valuable mechanistic information related to spinal mobilizations. The Biceps Femoris (BF), as the most commonly injured hamstring muscle [20], and the ES with, its role to compensate the net moment caused by external load and body weight, are key muscles to quantify EMG activity [21] in response to spinal mobilizations.

Mobilizations have been reported to provide both biomechanical benefits and neurophysiological effects on symptom modulation; although the mechanisms behind this are relatively poorly understood [22, 23]. Mobilizations are reported to decrease pain by activating the central pain modulating areas of the brain including the descending periaqueductal grey (dPAG). The side specific changes reported by Perry and Green [24] might suggest activation of the dPAG together with stimulation of the descending pain inhibitory systems, though further investigation to establish this theory is required. Authors have proposed that the activation of dPAG and descending pain inhibitory systems results in hypoalgesic and sympathoexcitatory responses extending beyond the spinal segment mobilized [22, 25].

Specifically, centrally applied posterior-anterior (PA) mobilizations at L4 have been shown to produce a sympathoexcitatory increase, measured via skin conduction, which initiates the sympathetic nervous system cascade of neurophysiological reaction associated with mobilization related hypoalgesia [26]. Furthermore, side-specific peripheral sympathetic nervous system changes, assessed by skin conductance and measured via electrodes, have been reported following unilateral lumbar mobilizations [24]. Mobilizations can also increase the neurodynamics of the posterior lower limb, evaluated by the straight leg raise test, both immediately and at a 24-hour follow-up [27, 28]. Recently, Mendiguchia et al. [29] have included lumbar facet mobilizations as part of a multi-factorial approach to hamstring rehabilitation and a return to play algorithm.

Despite the ability of mobilizations to decrease spinal pain and improve hamstring extensibility, a lack of understanding regarding the effects of specific technique selection remains. Numerous variables are included with technique selection, with an evidence base existing to support clinician choice for mobilization force, duration and amplitude [30, 31]. Patient position, spinal level, force direction, grade, rate, rhythm and duration are also key considerations. Importantly, no research exists supporting which specific technique to apply either a central posterior-anterior (CPA) mobilization on the spinous process or a unilateral posterior-anterior (UPA) technique on the transverse process or facet joint [32]. Decisions generated by clinicians regarding the type of mobilization to be applied must be based on theoretical concepts and empirical evidence. The lack of research into mobilization techniques and the comparison of their effects prevents clinician’s from making evidence based decisions [30].

Traditionally, mobilization choice has been dependent on biomechanical limitations identified at a specific spinal level or the primary spinal level associated with symptom presentation [23]. Central mobilizations are applied for central pain presentation whilst side specific unilateral mobilizations are used for pain which radiates laterally [32]. However, to our knowledge, the magnitude of the effects of CPA versus UPA selection on distal anatomical structures including the hamstring complex has yet to be elucidated. Comparing the effectiveness of specific locations on outcome measures related to lumbar spine range, hamstring extensibility and muscle electrical activity will enable clinicians to make informed decisions on appropriate technique selection.

Therefore, we aimed to quantify the effect of CPA versus UPA on lumbar spine range, hamstring extensibility and muscle electrical activity of the ES and BF. Through this study it is aimed to provide clinicians with evidence on which to generate evidence based reasoning.

2. Methodology

2.1 Experimental design and protocol

This report is conducted with recommendations from CONSORT for publishing non-pharmacologic intervention studies [33]. We utilized a counterbalanced, post-only crossover design to compare the acute effects of CPA and UPA lumbar mobilizations on measures of lumbar and hamstring range of motion and muscle activity. Participants visited a biomedical sciences laboratory on three separate occasions, each separated by one week, and received either a) CPA lumbar mobilization, b) UPA lumbar mobilization, or c) no mobilization (i.e. control condition, CON). To improve test validity, participants were instructed to refrain from caffeine at least 4 hours prior to testing, and avoid strenuous exercise at least 24 hours prior [34]. Mobilization treatment order was counterbalanced using the Latin square method to mitigate any potential order effects. On recruitment, participants ( $n=$ 24, details below) were randomized to one of six possible subsets of treatment sequences to ensure every treatment followed every other treatment the same number of times ( $n=$ 4).

All testing sessions were performed at the same time of day for each participant to reduce the influence of diurnal effects and laboratory temperature (21.5 degs) and humidity conditions (29% humidity; 1002 barametric pressure) were maintained constant throughout and between assessment visits. Following each treatment (CPA, UPA or CON), participants immediately performed a test of active knee extension (AKE) and active lumbar flexion (ALF), during which measures of range of motion and muscle electrical activity of the ES group and BF were taken. Tests of AKE and ALF, along with the collection of outcome measures, were performed and recorded by a practitioner who was blinded to the mobilization allocation. Outcome measures were recorded immediately after each other, approximately one minute apart, to allow for the participant to reach the correct position. We also counterbalanced the order of ALF and AKE assessments within each treatment sequence subgroup to mitigate assessment order having adverse influences on outcome measures. As per previous studies [17, 18] four ALF and AKE were conducted prior to final assessment of the outcome measures to counteract against variations in tissue extensibility.

2.2 Participants

Twenty-four participants (proportion of males: 55%, age [mean $\pm$ SD]: 26 $\pm$ 4 y, body weight: 75 $\pm$ 12 kg, stature: 173 $\pm$ 10 cm) were recruited from a population of students at Teesside University, United Kingdom, between April 2015 and December 2015. Participants were included if they were aged over eighteen and without current spinal or lower limb pathology. Those with current symptomatic low back pain, neurological symptoms, hamstring or hip pathology were excluded. A history of lumbar surgery or any contraindication to spinal mobilization also prevented participation [32]. Four participants were excluded from the study based on current lumbar or hip pain. Written informed consent was obtained from all participants prior to testing and the study received ethical approval via Teesside University’s ethics committee (Ethics Number: SSSBLREC250415), in accordance with the Declaration of Helsinki.

2.3 Lumbar mobilizations

Participant’s laid prone on a plinth placed upon force plates, which measured the mobilization force. The CPA group received central posterior-anterior lumbar mobilizations to the L5 vertebrae segment. We selected this segmental level due to the relationships between L5 and both hamstring pain and flexibility [35]. UPA lumbar mobilizations were administered to the unilateral zygapophyseal L4/5 joint to the ipsilateral side as the dominant limb, determined by preferred kicking foot. Grade three mobilizations, defined as large amplitude oscillations into resistance [32], were applied to both groups by a physiotherapist with ten years’ clinical experience and postgraduate qualifications in spinal mobilization. Mobilizations for both test conditions were applied as a large-amplitude oscillatory movement for two minutes, three times at the relevant spinal level [32, 36]. Spinal level was determined by passive physiological intervertebral movement and spinal palpation by two independent physiotherapists blinded to group allocation. CPA mobilizations were applied via the ulnar border of the hand, with the area between the pisiform and hook of hamate in contact with the spinous process. The same hand position was maintained for UPA mobilizations, with the contact area immediately adjacent to the spinous process, on the identified transverse process [32]. Both CPA and UPA mobilizations were applied at a frequency of 1 Hz maintained by a metronome. Force plate data was recorded at 500 Hz above the frequency of the mobilizations preventing sampling errors.

Following initial baseline outcome measures the control group laid prone, the time it took for the clinician to explain, identity and perform the lumbar mobilizations. Following this ten-minute period, the relevant outcome measures were re-tested.

2.4 Outcome measures

Active lumbar flexion range was measured by the modified Schober (mSchober) test [37, 38]. Each participant stood on a wooden box, 60 cm in height, with their feet positioned 8 cm apart as indicated by tape (Fig. 1). A blinded assessor identified, via a skin marker, 5 cm below and 10 cm above the lumbosacral junction, determined by a passive physiological intervertebral movement and lumbar palpation [32, 38]. Each participant was instructed to actively flex forward as far as possible, with the knees extended, until instructed to return to neutral. Test performance (range of motion) was recorded as the change in distance between the two skin markers, measured by a tape measure (seca Germany) in centimeters. The test-retest correlation coefficient ( $r$ ) for lumbar range of motion measured via the mSchober is reported to be 0.88 [39]; making this a highly reliable assessment.

Figure 1.

The active lumber flexion test position.

The active hamstring extensibility of the dominant leg was measured by the AKE. During the test, participants laid supine on a plinth with one mobilization belt placed across the anterior superior iliac spine preventing pelvic and lumbar movement. Another belt was placed 20 cm above the tibial tuberosity of the non-dominant/non-testing leg to prevent motion [40]. The belt positions were marked for re-measurement purposes. The hip was held at a 9 ${}^{\circ}$ flexed angle by a wooden wedge (Fig. 2). Participants were instructed to extend the knee of the testing leg until the end of maximal range perceived as discomfort, determined by the participant [41]. An inclinometer (Dr Rippstein, Zurich, Switzerland), positioned on the anterior tibial border halfway between the inferior pole of the patella and the line between the malleoli measured positional change [42]. Throughout testing the ankle was maintained in plantigrade by a medical brace. Test performance (range of motion) was measured as the degrees from full active knee extension, where full active knee extension would equal 0 ${}^{\circ}$ . The test-retest intraclass correlation coefficient (ICC) for hamstring extensibility measured via AKE is reported to be 0.86 [41]; making this a highly reliable assessment.

Figure 2.

The active knee extension test position.

Muscle electrical activity of the ES and BF was measured via surface electromyography (sEMG) during both ALF and AKE assessments. Prior to the electrode application, the participants skin was prepared to minimize any interference in the signal, by shaving and cleaning the area with a 70% isopropyl alcohol wipe. Noraxon self-adhesive Ag/AgCl snap electrodes (Noraxon, USA) were used throughout the investigation. These electrodes have an inter-electrode placement of 20 mm and were placed on the relevant muscle in accordance to the Surface Electromyography for the Non-Invasive Assessment of Muscles (SENIAM) recommendations [43, 44]. The inter-electrode method of data collection substantially removes far-field potentials such as crosstalk signals [45]. Electrodes remained in position throughout the testing procedure, including mobilizations, to eliminate placement error and allow immediate reassessment of the outcome measures. No recording of sEMG activity occurred during mobilization. Superficial muscles were chosen to provide a clearer sEMG signal and reduce cross talk [46].

To assess BF muscle activity, an electrode was placed half way between the ischial tuberosity and the lateral epicondyle of the tibia, on the participant’s dominant side. The electrode for the ES (longissimus) was placed two finger widths lateral to L1, on the muscle belly, to the participants dominant side [44, 47, 48]. We recorded muscle electrical activity for 10 seconds at rest (lying prone) and at end ranges of the ALF and AKE assessments, with the mean values for the 10 seconds used for analysis. Since ALF and AKE inherently involve low-level sEMG, normalizing values against a maximum voluntary contraction was not deemed appropriate or necessary [49, 50]. Data were collected using a wireless sEMG system (Cometa) sampling at 2000 Hz. The sEMG signal was then processed and filtered (Cometa v1.6 software) using a high pass Butterworth filter, with a cut off frequency of 20 Hz [44, 48, 51]. Data were then rectified and smoothed using a root-mean-square filter with a floating window of 20 ms [52, 53, 54]. While there are limitations of sEMG to isolate muscles, and avoid cross-talk [44], sEMG has been shown to accurately assess myoelectrical activity of the ES [55] and BF muscles [56].

Table 1

Descriptive (mean $\pm$ SD) post-mobilization data for each condition

Outcome measure	Condition
	CON	CPA	UPA
Active knee extension
BF electric activity ( $\mu$ V)	12.4 $\pm$ 8.1	9.4 $\pm$ 6.0	8.3 $\pm$ 5.5
ES electric activity ( $\mu$ V)	8.8 $\pm$ 6.4	6.5 $\pm$ 3.5	5.0 $\pm$ 1.8
Range of motion ( ${}^{\circ}$ )*	54 $\pm$ 14	47 $\pm$ 12	46 $\pm$ 14
Active lumbar flexion
BF electric activity ( $\mu$ V)	7.3 $\pm$ 5.4	6.3 $\pm$ 5.5	5.6 $\pm$ 4.4
ES electric activity ( $\mu$ V)	6.0 $\pm$ 1.3	5.7 $\pm$ 1.4	5.6 $\pm$ 1.3
Range of motion (cm)**	5.6 $\pm$ 1.4	6.9 $\pm$ 1.5	6.9 $\pm$ 1.5

*degrees from full active knee extension, where full active knee extension $=$ 0 ${}^{\circ}$ . **change in lumbar surface length. Abbreviations: BF $=$ biceps femoris; CON $=$ no mobilization; CPA $=$ centrally applied posterior anterior mobilizations; ES $=$ erector spinae (longissimus); UPA $=$ unilaterally applied posterior anterior mobilizations.

2.5 Statistical analysis

Raw data showed no evidence of non-normal distribution, and are therefore presented as the mean $\pm$ SD. Before analysis, data were log transformed and then back-transformed to obtain the difference in outcome measures between each condition (CPA, UPA and CON) as accurate percentages [57]. Percent differences are presented with 90% confidence limits (CL) as markers of uncertainty in the estimates [58]. In sports medicine research, null hypothesis significance testing fails to provide information about the effect size or the range of feasible values in relation to clinically important threshold values [57, 59]. The use of P values therefore provides inadequate information to the practitioner who is concerned with real-world effects and their likelihood of substantiality. Accordingly, we used magnitude-based inferences to examine the acute effects of CPA and UPA mobilizations of the lumbar spine on hamstring lumbar range of motion, hamstring extensibility and muscle activation. In the absence of well-established minimum clinically significant differences for our outcome measures, we used standardized threshold values of 0.2, 0.6, and 1.2 multiplied by the pooled between-participant SD to represent small, moderate and large effects, respectively [57]. Subsequently, inference was based on the disposition of the CL for the mean difference in relation to these thresholds and the probability (percent chances) that the true population effect was the observed magnitude that was estimated per the magnitude-based inference approach [58]. Percent chances were qualified via probabilistic terms assigned using the following scale: 25–75%, possibly; 75–95%, likely or probably; 95–99.5%, very likely; and 99.5%, most likely [58]. Since there is no direct link between measures of range of motion and muscle electrical activity during AKE with outcomes (e.g. health, performance), inferences were evaluated mechanistically and deemed clear if the CL did not overlap both substantially positive and negative thresholds by $\geqslant$ 5% [58].

3. Results

The mean ( $\pm$ SD) force applied during CPA and UPA mobilizations was 99.5 $\pm$ 4.6 N and 74.5 $\pm$ 5.0.

Table 2
Acute effects of centrally- and unilaterally-applied posterior-anterior mobilizations of the lumbar spine on hamstring lumbar range of motion, hamstring extensibility and muscle activation

Outcome measure	CPA compared with CON		UPA compared with CON		Mobilization comparison (UPA compared with CPA)
	%; $\pm$ 90% CL	Inference	%; $\pm$ 90% CL	Inference	%; $\pm$ 90% CL	Inference***
Active knee extension
BF muscle activity	$-$ 21; $\pm$ 11	Likely small $\downarrow$	$-$ 30; $\pm$ 12	Very likely small $\downarrow$	$-$ 11.2; $\pm$ 8.0	Possibly lower following UPA
ES muscle activity	$-$ 21; $\pm$ 10	Likely small $\downarrow$	$-$ 36; $\pm$ 16	Possibly moderate (very likely small) $\downarrow$	$-$ 18; $\pm$ 15	Likely lower following UPA
Range of motion*	$-$ 12.1; $\pm$ 1.8	Most likely small $\uparrow$	$-$ 17.0; $\pm$ 3.4	Possibly moderate (most likely small) $\uparrow$	$-$ 5.5; $\pm$ 3.8	Possibly greater following UPA
Active lumbar flexion
BF muscle activity	$-$ 16.0; $\pm$ 5.1	Very likely small $\downarrow$	$-$ 24.8; $\pm$ 6.6	Possibly moderate (most likely small) $\downarrow$	$-$ 10.5; $\pm$ 5.9	Possibly lower following UPA
ES muscle activity	$-$ 4.7; $\pm$ 2.8	Possibly small $\downarrow$	$-$ 7.1; $\pm$ 7.5	Possibly small $\downarrow$	$-$ 2.5; $\pm$ 7.8	Unclear
Range of motion**	25.4; $\pm$ 7.8	Likely moderate $\uparrow$	23.6; $\pm$ 8.2	Likely moderate $\uparrow$	$-$ 1.4; $\pm$ 2.5	Most likely trivial

*degrees from full active knee extension, where full active knee extension $=$ 0 ${}^{\circ}$ . A reduction therefore implies greater range of motion. **change in lumbar surface length. An increase therefore implies greater range of motion. ***the magnitude of all substantial differences were small. Abbreviations: $\downarrow$ $=$ reduction; $\uparrow$ $=$ increase; BF $=$ biceps femoris; CL $=$ confidence limits; CON $=$ no mobilization; CPA $=$ centrally applied posterior anterior mobilizations; ES $=$ erector spinae (longissimus); UPA $=$ unilaterally applied posterior anterior mobilizations.

Descriptive (mean $\pm$ SD) post-mobilization data for each outcome measure are presented in Table 1. The acute effects of CPA and UPA mobilizations of the lumbar spine on measures of lumbar and hamstring range of motion and muscle activity during AKE and ALF are presented in Table 2. When compared with no mobilization, CPA and UPA mobilizations incurred small to moderate reductions in muscle electrical activity (BF and ES) during AKE; with these reductions being lower for UPA. Both mobilizations caused small to moderate improvements to AKE range of motion, respectively; with the improvement in range of motion being greater following UPA. During ALF, CPA and UPA mobilizations incurred small to moderate reductions in BF muscle electrical activity, respectively, and these reductions were lower for UPA when compared with CPA. There was a possibly small reduction in ES electrical activity for both mobilizations compared with no mobilization and the difference between mobilizations was unclear. There was a moderate increase in ALF range of motion following both CPA and UPA mobilizations and the difference between mobilizations was trivial.

4. Discussion

Lumbar mobilizations continue to form an integral part of therapeutic management of the lumbar region. Furthermore, the ability to utilise lumbar mobilizations to alter the extensibility and muscle activity of the hamstring complex has recently been reported [17, 18, 24, 27]. Despite this, the effectiveness of several variables associated with lumbar mobilizations have yet to be investigated including the role of specific locations. We therefore aimed to investigate the acute effects of CPA and UPA of the lumbar spine in relation to lumbar and hamstring outcome measures. The main findings from our investigation were that both CPA and UPA increase lumbar range of motion and hamstring extensibility whilst also reducing local muscle activity, yet UPA mobilizations provide greater effects on hamstring extensibility and muscle activity when compared with CPA.

Previously, the effectiveness of the two most clinically popular spinal mobilizations, central and unilateral posterior-anterior mobilizations, on range of motion and muscle electrical activity of the lumbar and hamstring were unknown. Our data show that both CPA and UPA mobilizations elicit at least a possibly small effect on the measures we assessed. These results are also comparable to other investigations which found improvements in lumbar range post mobilization [60, 61]. Against the control CPA range increased by 25.4% and UPA 23.6%. This is consistent with results from previous studies demonstrating an average increase of 18.6% [17], 17.8% [62] and 7.1% [63] respectively. Chesterton and Payton [17] also reported an increase of 22.8% in AKE range. However, Petty [64], Chiradejnant et al. [65, 66], and Stamos-Papastamos et al. [36] all found no significant effect of lumbar mobilizations on range of motion. Although, this study did not investigate the mechanism by which these increases in range occurred, it is conceivable that the mechanical and neurophysiological mechanisms described to improve mobility were present. Passive motion has been reported to selectively stretch contracted tissues [67]. Additionally, mobilizations have been found to activate the periaqueductal gray and inhibit temporal summation which decreases the excitability of dorsal horn cells [25, 66]. Following mobilization, the Hoffman reflex has demonstrated a transient attenuation of alpha motor neuron excitability decreasing protective muscle guarding, which may result in gains in joint range [69].

In our investigation, UPA reduced the muscle electrical activity of the BF during both ALF and AKE. A proposed benefit of mobilization is the reduction of muscle activation which has been reported at the lumbar spine [31, 54]. Against the control CPA mobilizations also had a likely small (AKE) and very likely small (ALF) effect on reducing BF activity. These results support previous work suggesting that distal structures, including the hamstring, could be treated more proximally [17, 70]. This is likely due to the direct relationship between sympathetic excitation and pain modulation [71, 72, 73]. Several specific mechanisms for this decrease in sEMG activity have been proposed. Joint afferent activity itself can cause reduction in muscle excitability [74, 75] as can the hypoalgesic effect of mobilizations [25, 76, 77]. Mobilizations can increase muscle spindle activity [69, 78, 79, 80], stimulate golgi tendon organ activity [77], which leads to a reflex inhibition of muscle. The exact neurophysiological mechanisms of both CPA and UPA mobilizations is beyond the scope of this study. UPA mobilizations may stimulate overlying musculature and cutaneous tissues in a different manner when compared to CPA mobilization techniques and therefore the proposed mechanisms may be different [22, 72]. An investigation of cervical spinal mobilizations reported that UPA applied mediolateral forces are less compared to CPA mediated forces [81]. Changing the angle of applied force will affect the magnitude of vertical force potentially impacting on the physiological responses recorded. Future research investigating this effect at the lumbar spine may be warranted.

As this is the first study to investigate the effects of technique selection on measures of both the lumbar and hamstring region, evidence is presented to support specific mobilization selection. This study suggests clinicians who wish to target unilateral tissue from the spinal column could utilise UPA techniques over CPA mobilizations, due to the ability to influence both range of motion and muscle activity of unilateral tissues. However, both mobilizations improved ALF and reduced sEMG activity of ES. The trivial effects found for ALF between both mobilizations suggest that either technique can increase range and clinicians should consider this in their clinician reasoning when selecting appropriate lumbar mobilizations techniques.

4.1 Limitations and future research

We acknowledge several limitations in our present investigation that are worthy of discussion. First, only the acute effects of the mobilizations were investigated in our crossover trial, which may limit the application of our data to medium- and long-term effects. A second limitation of our current work is the recruitment of asymptomatic individuals and therefore the effect of assessing CPA versus UPA in a symptomatic population remains unclear. Future research should investigate how variables are influenced within a symptomatic population over the short-, medium- and long-term. We based our four pre-measures of AKE and ALF on recommendations from pilot tests in the methodology of previous research [17], yet no formal reliability trial has been conducted to determine the appropriateness of this arbitrary cut-off value (e.g. a pairwise analysis of consecutive trials, Hurst et al. [82]). We acknowledge that without this, changes in ROM may have been influenced by a decrease in passive stiffness of the soft tissue. Our treatment order was counterbalanced using the Latin Square method, yet we lost four participants to follow-up. This ultimately resulted in treatment sequences being disproportionate – a clear limitation of the Latin Square method.

The application of sEMG has limitations with signal influenced by external noise, electrical activity of adjacent muscle, the depth of adipose tissue the signal is required to travel and the number of active motor units at the time of recording [83]. Despite the reliability of sEMG in both the ES [55] and BF [56] being previously reported this has not been established within our laboratory for these outcome measures, therefore the precision of the measurement is currently unknown. Lastly, our data were restricted to a traditional group-level comparison, which is unlikely to reflect the true responses on an individual level. The individual responses to CPA or UPA mobilizations remains unknown and warrants further investigation.

5. Conclusions

The evidence base for mobilizations to form part of treatment programmes for the lumbar spine is established whilst its ability to influence the hamstring region is still in its infancy. As part of a wider multifactorial approach to lumbar and hamstring management, clinicians can incorporate mobilizations which have the potential to produce positive effects on local range of motion and muscular activity. Our results demonstrated that UPA and CPA mobilizations can be applied to increase lumbar range of motion and reduce local Erector Spinae muscle activity. UPA mobilizations have a greater ability to increase hamstring extensibility whilst reducing Biceps Femoris muscle activity compared with CPA mobilizations. This data adds to the current literature aiding clinical reasoning of the management of the lumbar and hamstring region using lumbar mobilizations.

Footnotes

Conflict of interest

None to report.

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Acute effects of centrally- and unilaterally-applied posterior-anterior mobilizations of the lumbar spine on lumbar range of motion,hamstring extensibility and muscle activation

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Methodology

2.1 Experimental design and protocol

2.2 Participants

2.3 Lumbar mobilizations

2.4 Outcome measures

3. Results

Table 2 Acute effects of centrally- and unilaterally-applied posterior-anterior mobilizations of the lumbar spine on hamstring lumbar range of motion, hamstring extensibility and muscle activation

4.1 Limitations and future research

5. Conclusions

Footnotes

Conflict of interest

References

Table 2
Acute effects of centrally- and unilaterally-applied posterior-anterior mobilizations of the lumbar spine on hamstring lumbar range of motion, hamstring extensibility and muscle activation