1. Introduction

Low Back Pain (LBP) is one of the most common musculoskeletal health problems in society today and has reached an epidemic level [1,2]. It is estimated to affect at least 70% of the general population at some point in their lives^2-4 and 5-10% of American adults will experience chronic LBP [3,4]. LBP is defined as non-specific pain between the 12^th rib and the inferior gluteal folds that can be accompanied by leg pain [1]. Most cases recover quickly, however some are at risk of becoming chronic cases of pain and disability [2]. The strain on the health care system from LBP is significant as it is a common reason why individuals seek medical attention [2]. In addition, if early detection and treatment for LBP is not done, the effects on the individual could be severe as disability may occur[5]resulting in many consequences, including an inability to work or care for oneself [6].

1.1.  Data Reduction

 A second investigator calculated the TrA and LM activation ratio by dividing the contracted muscle thickness by the resting muscle thickness. Use of the activation ratio standardizes the activation observed to the resting level and allows for comparison across participants [22].

The timing of activation was calculated by dividing the number of image frames that were collected over the 10-second interval. The frame where the TrA or LM started to contract was multiplied by the number of seconds each frame was collected at. This was the reported time that the muscle started contracting. The ultrasound software was used to convert the time of that frame into seconds [22]. The images were coded so that they did not indicate LBP status.

1.2.  Statistical Analysis

Statistical analysis was performed using SPSS (IBM SPSS Statistics for Windows, version 21.0; IBM Corp, Armonk, NY). Separate 2 x 2 analysis of variances (ANOVA) were applied to compare muscle activation ratios and timing of activation between the healthy and LBP patients. Paired samples t-tests where used to assess differences in VAS and ODI scores between the LBP group. Alpha was set a priori at 0.05. Effect sizes were calculated by Cohen’s d to be interpreted for meaningfulness and clinical significance. 

2. Results

There were no significant differences between groups for TrA (p>.101) and LM (p>.437) timing and activation after 4 weeks of yoga. ODI was significantly different (p=.049), but the effect size confidence interval crossed zero (CI -0.55-0.94). VAS was not significantly different (p=.239), but the effect size was strong (0.87 (0.11-1.63)). Results are presented in Tables 2-4.

Activation (mean ± SD) is the ratio of the muscle thickness change from a resting to a contracted position during the abdominal draw in maneuver and calculated as a contracted state/resting rate ratio

Timing was calculated as the point when the muscle began to contract when the arm was brought overhead after a three second wait period. 

3. Discussion

This controlled laboratory study was conducted to evaluate the effectiveness of a 4-week yoga intervention on core musculature, pain and functional disability among healthy and LBP participants.In particular, we were interested in determining if and how yoga may be effective at improving LBP outcomes.The results found that participants with LBP experienced pain relief, but there was no changes found with functional disability, muscle activation and muscle timing.No serious adverse events were reported from the yoga sessions from any of the participants. 

While the difference in ODI scores were significant, the effect size confidence interval crossed zero, and as such the change may not be meaningful. The average baseline ODI scores were less than 10%, indicating a population with minor disability.The minimal detectable change has been reported as 15-16% [23,24]. Since the average ODI scores at baseline were less than 10% and are below the minimal detectable change, this indicates that a change in the scores would not cause a significant difference in a clinical setting.A floor effect may have resulted, where there was not much room for improvement in scores. 

Pain on the other hand, showed a strong effect size. Pain decreased by about half in our LBP participants. However, this should be taken with caution. The average baseline VAS scores were below 20mm (2 out of 10). Our population was not in considerable pain during the study and may not be generalizable to a more painful population.

Core muscle ultrasound imaging of the TrA and LM showed no significant changes over the 4-week intervention. Neural changes may have occurred causing an increase in muscle fiber recruitment.Short-term strength training increases the output of motor neurons to the targeted muscles of the training [25]. The neural transmission is altered by strength training through motor neurons controlling the muscles therefore facilitating undetectable strength changes [26]. Before force generation or muscle thickness is observed there needs to be more efficacy of the motor neural junctions (synapses) and more excitability of the motor neurons [25] which may have occurred in our study. More time may have been needed for the body to adapt to the neural changes and increase muscle thickness.

Adherence to the yoga intervention was excellent at 96% with all but one participant completing the minimum of 7 of the 8 classes conducted (68% completed all 8 sessions).The high attendance rate to each of the eight sessions may be attributed to the sense of community that was developed over the 4 weeks among participants. Slade et al., [27] demonstrated that individuals are more likely to engage in exercise programs and activity that consider their fitness levels, health status and exercise experience. The yoga classes in this study were beginner level targeted to participants who never performed yoga before and was tailored to participants having LBP.This may be the reason we saw an increased adherence to the yoga intervention.The yoga classes were instructed in a group setting, which afforded participants to become familiar with each other and to the instructor of the class.The small class size and intimate and personal setting was conducive for participants to develop a sense of accountability, which increased adherence to participation. Participants were able to gain socialization and support from the group intervention providing them a positive experience to manage their LBP. 

Prior yoga studies for LBP have used a variety of yoga styles.The use of hatha yoga is the most common practiced type for LBP in real-world environments, as well as therapeutic setting [28]. Our study was conducted at the discretion of the yoga instructor to mimic everyday yoga classes addressing the needs of the participants.In this case the classes had a LBP treatment focus using a passive hatha yoga style initially then progressed the class to become more active style of yoga, with one breath associated to each movement, if the participants were responding well.The yoga teacher began the 4-week intervention with two weeks (4 sessions) of gentle hatha yoga to introduce the first-time participants to the foundations of yoga including posture, breathing, mobility, stretching, core engagement, relaxation and listening to one’s body.The last two weeks (4 sessions) were more active yoga classes incorporating standing postures and sun salutations linking one breath to one movement.Currently there has been no research to suggest one type of yoga is more effective than another for providing relief of LBP.The yoga sessions involved total body activity and not isolated core muscle training.All of yoga postures performed were instructed the focus on correct posture and alignment and participants were not specifically cued to activate their core muscles during all poses.The lack of repetitive cueing to activate the TrA and LM or use of specific core muscle exercises may explain the lack of change observed in the TrA and LM muscles.

A unique aspect of this study was the use of ultrasound imaging to examine the coremusculature of the TrA and LM to see if we could provide reasoning to why participants may be seeing improvements in their LBP symptoms and daily functioning.A potential limitation to the lack of change seen in the musculature or effect on outcome measures was that the classes were only 30 minutes in total.The 30-minute classes included a mindfulness and breathing warm-up for 5 minutes and resting corpse pose called savasana, used for relaxation and meditation, at the end of each session for 5 minutes allowing for approximately 20 minutes of yoga postures including instructional demonstrations.The short duration of the classes may have influenced the inactivity of the core tonot show any significant changes in the timing or activation of the musculature.Ward, et al., [28] found large variation in frequency and duration of yoga classes from 40 to 120 minutes with the average being 75 minutes and the frequency being 1 to 6 times per week.Higher frequencies of classes were reported with shorter duration of 60 minutes or less.It was most common for yoga classes to be conducted one time per week in most intervention protocols [28]. Duration of the yoga intervention varied from 2 weeks to 24 weeks with the most common being 12 weeks, occurring in 5 studies [3,29-32]. This suggests that a longer duration study may be required to see benefits on core musculature and outcome measures.

Research conducted has demonstrated that individuals with LBP possess a delay in core activation of the TrA and LM that may lead to spinal instability.In the participants of this study a delayed timing of activation was not observed in the LBP group which may be explained by the age of the target population and the low-grade LBP that they were experiencing.The ODI scores were (6.02 ± 3.83%) placing them in the minimal disability category allowing them to go about daily activities where no treatment or conservative treatment can be used.The LBP baseline scores on the ODI and VAS indicated that the symptomatic participants did not experience LBP to a severe enough level to cause large alterations in their daily activities to be reflected in their subjective measures.Utilizing a young population did not demonstrate differences either, however in future studies a more functionally disabled population would be recommended. 

We may compare the results of this study to the 6-week study by Galantino et al., [12]. who had 22 participants undergo 60-minute hatha yoga classes twice weekly. This study was similar to our study however was two-weeks longer and focused only on hatha yoga. Galantino et al., [12] found no statistical significance in their ODI (p=0.170) or flexibility measures (p=.534) between the control and intervention groups.They did find that the depression outcome (Beck Depression Inventory) improved significantly (p=.008).Their improvements in the ODI score were from 24.98% to 21.15% among the yoga group (n=11) showing that their LBP group was more symptomatic then the participants in our study (n= 14) whose ODI scores decreased 6.0% to 5.2%.

Some limitations that may have affected the results of our study could have been the small sample size of 25 participants, where only half had LBP. The youthful age of the participants in our study was the target to see if LBP could be intervened from a younger age as a prevention tool for re-occurrence.All previous literature utilized adults older than our target age range, in their mid-40’s [12,30-33]. Also, the location of the yoga classes (off campus) and the timing of the yoga class (middle of the day at 11:30 am) may have limited the number of participants able to participate.

Future studies should examine flexibility measures as well as psychological outcomes regarding depression (Beck depression inventory), mood or journaling (best part of the experience, look forward to most about yoga, difficult thing to be involved with the group, impact of the instructor) to provide a more comprehensive examination of the effects of yoga. The intervention should be of longer duration and the follow-up periods should be extended to see the long-term effects if LBP returned or was prevented among the affected participants.The outcome measures for future studies should examine all dimensions of health surrounding LBP addressing the mind, body and spirit that is affected by LBP.

4. Conclusion

This controlled laboratory study, despite its limitations, demonstrated promising results for a 4-week yoga intervention for individuals with LBP.It provides potential for long-term effects on core musculature to be examined alongside LBP outcomes to prevent recurrence if timing and activation can be improved.Future studies should examine all dimensions of human wellness, including mind, body and spirit.Group exercise has demonstrated success through a strong adherence when all individuals were beginners to yoga, and the classes were targeted for younger individuals with LBP.The improvements in the report of subjective pain should support more studies to examine the objective reasons for yoga effectiveness, and be included as a complimentary method to traditional exercise or physical therapy treatment. 

Table 1: Demographics of Participants.

Appendix A: Yoga Postures Performed.

Table 2: ODI and VAS Scores Following a 4-week Yoga Program Among LBP Participants.

Table 3: Transverse Abdominis Activation and Timing Following a 4-week Yoga Program.

Table 4: Lumbar Multifidus Activation and Timing Following a 4-week Yoga Program.

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