Dr. Tanaka’s Research Publications and Presentations
Influence of acupuncture on muscle coordination revealed by dynamic electromyographic evaluation
Tim Hideaki Tanaka, Ph.D.
Part of this paper was presented at the symposium: Status of Acupuncture and Moxibustion during the 53rd Annual Meeting of the Japan Society of Acupuncture and Moxibustion, held at Makuhari Messe in Chiba, Japan, June 2004.
Over the past thirty years in particular, acupuncture has been widely used in Europe and North America especially for the management of musculo-skeletal conditions.1,2 The most widely reported effects of acupuncture for these conditions are analgesia3 and the reduction of hypertonicity.4 However, the efficacy of acupuncture on musculo-skeletal conditions has not been well documented using objective evaluation indices. Furthermore, there is a paucity of data available on how acupuncture actually influences muscular function.
The neuromuscular activity, manifested as myoelectric signal, can be recorded through electromyography (EMG) by means of surface or needle electrodes. EMG objectively reveals the fine interplay or coordination of muscles through the observation of the changes in motor unit action potential which emanate from the contracting muscle.
Lumbar paraspinal EMG activity recorded on the surface or intramuscularly, becomes silent spontaneously somewhere between 45 to 90 degrees forward flexion. This phenomena, referred to as ‘flexion-relaxation’, was first reported by Floyd and Silver in 1951,5 and has been studied extensively since then. Flexion-relaxation can be frequently observed in healthy normal subjects5-14 regardless of the speed of trunk flexion.7 Patients with lower back pain, however, often exhibit continuous EMG activity throughout the movements without eliciting the flexion-relaxation response.6,9,12,14 Diminished flexion-relaxation among lower back pain patients is considered to be due to the protective guarding reaction.6 Flexion-relaxation seen among normal healthy subjects is thought to be caused by an inhibitory reflex due to the stimulation of stretch receptors in the posterior vertebrae ligaments.5Figures 1 and 2 illustrate examples of lumbar paraspinal EMG activity during trunk flexion on normal and back pain subjects.
Flexion-relaxation can also be seen under load conditions (lifting up 10 kg or 13 kg objects).10,12 The erector spinae muscles participate very little in initial extension from a fully flexed position. Instead the initial action is caused by the rebound of stretched connective tissue and the hip extensor muscles. The lumbar paraspinal muscle activity cannot be observed during the initial phase of extension movement. In circumstances such as this, the lumbar vertebrae are not protected by the contracted paraspinal muscles, thus spinal facet joints and ligaments are exposed to the load directly. This could be one of the main reasons why acute lower back strain can occur when picking up even light objects from the floor (Fig. 3).
Acupuncture treatment for lumbar strain injury: Dynamic lumbar paraspinal EMG pattern during acute and recovery phase
A 50 year old male was complaining of acute lumbar pain and radiating pain down the right posterior leg. Postural analysis indicated right concave functional lumbar scoliosis (Fig. 4a). A flexion-relaxation phenomenon was not observed on his lumbar paraspinal integrated EMG tracings (Fig. 5). In addition, there was noticeable asymmetrical left and right lumbar paraspinal activity. Trunk flexion return movement is a symmetrical movement and therefore, under normal circumstances, left and right paraspinal muscles should synergistically fire at an approximate 1:1 ratio. In this case, however, there is substantial asymmetry between the left and right sides possibly due to the painful inhibition on the right side creating a compensatory additional load on the left lumbar paraspinal muscles. The lateral bending-return movement is an asymmetrical movement, and with normal healthy subjects, it should show asymmetrical left and right side muscle recruitment pattern. On this particular subject, there was a contralateral muscle firing pattern (co-contraction) without reciprocal inhibition (Fig. 6).
Fig. 7 shows lumbar paraspinal EMG activity on the same subject after two weeks. Acupuncture treatment was done on two occasions during this period using Dynapuncture approach (simultaneous application of acupuncture and passive and active lumbar pelvic mobilization) with moxibustion treatment. An integrated EMG tracing during flexion-return movements indicated both the normal appearance of flexion-relaxation as well as left and right lumbar paraspinal muscles showing a very symmetrical recruitment pattern. The patient noticed a substantial diminution of pain and as such, functional scoliosis was corrected as seen in Fig. 4b. EMG activity during left lateral bending-return, co-contraction disappeared. During right flexion and return movement, there was also the appearance of normal reciprocal inhibition on the ipsilateral side, although there was an increase of EMG activity after the patient returned to neutral position (post-movement irritability) (Fig. 8). Overall, there was a substantial improvement in the lumbar EMG pattern. The degree of influence of acupuncture cannot be determined in this one case considering the natural course of this type of injury. We have however, clinically observed remarkable improvements of lumbar paraspinal EMG activity patterns in many cases as pain decreased during the course of acupuncture treatments.
Determination of the source of pain or injury, and interpretation of dynamic EMG recruitment patterns can be complex. In general, EMG activity is often inhibited in the injured side during flexion-return movement, and elevated activity can be seen in the healthy side as a result of compensation. However, if there is a spasm in the injured muscle, the opposite EMG activity pattern can be observed as a result of nerve irritation. Lower EMG activity on one side may be due to the protective inhibition from ipsilateral pain or weakened muscle strength. Higher EMG on the other side may be due to compensation from the contralateral injury or reflex spasm due to ipsilateral pain.
In clinical practice, in situations where the location of pain or injury is not clearly identified, it is important to determine the possible cause behind the specific EMG pattern in order to develop an appropriate treatment approach and specific exercise protocol.
Immediate effect of acupuncture on lumbar paraspinal EMG symmetry pattern
We have conducted a study investigating the immediate effect of acupuncture on muscle synergistic pattern.15 Healthy subjects who have exhibited more than a 20 % difference between left and right lumbar paraspinal EMG activity during a trunk flexion-return movement were administered acupuncture stimulation on one side of LP muscles.
Acupuncture needles were inserted in the B23 and B25 acupuncture point to a depth of approximately 1 to 1.5 inches, until the tip of the needle reached the mid-valley of the paraspinal muscle. Following the needle insertion, each point was stimulated by gently manipulating the needle for 60 seconds using a twitching movement of the fingers.
Significant reduction in lumbar EMG asymmetry was observed immediately following acupuncture stimulation (p=0.049, Fig. 9). A clear reduction in EMG asymmetry was observed in 9 out of the 10 subjects (Fig. 10). The response was a very consistent reduction in EMG asymmetry with no significant individual differences. This was with the exception of one subject, in which asymmetrical dynamic EMG activity increased after stimulation (from 24% to 33%). In this particular instance, acupuncture was re-administered on the contralateral side and reevaluation revealed that the degree of asymmetry decreased to a minimum range (4 percent difference). The reason for the increase after the first acupuncture administration may be attributed to either an EMG assessment error or because the acupuncture site and/or method was unsuitable for this occasion. Possible variation in dynamic EMG responses depending on the type or site of stimulation remains as a future research objective.
The data was further analyzed comparing integrated EMG amplitude value (absolute EMG) before and after acupuncture. On the stimulated side, absolute EMG values did not change significantly after acupuncture (Fig. 11). However, on the non-stimulated side, the absolute EMG values significantly decreased for subjects with high baseline absolute EMG readings (p=0.037), and significantly increased for subjects with low baseline absolute EMG readings (p=0.0185) (Fig. 12). This intriguing data suggests that acupuncture may influence the sensitivity of muscle spindles and the centrifugal regulatory system. The exact mechanism is not certain from this study, however acupuncture stimulation seems to be transmitted through not only a single pathway but through a complex interaction of the central and peripheral systems.
A previous study suggests that asymmetrical Dynamic EMG activity is more frequently observed in the pain population.16 It is conceivable that prolonged asymmetrical use of muscles may eventually lead to pain and functional musculo-skeletal disorders.
For prevention of injury and enhancement of sports performance, it is important to emphasize not only the strengthening of muscle, but also the crucial role of proper muscle coordination. This includes the coordination of synergistic muscles and the correspondingly appropriate reciprocal inhibitory pattern.
In conclusion, the available research data suggests that acupuncture can be a beneficial method for decreasing functional muscular distortion and enhancing synergistic coordination. Further study is necessary to explore what types of acupuncture are most effective in creating better coordination of muscles according to various muscle recruitment patterns based on the findings of surface EMG assessments.
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