Effects of whole body vibration exercise on lumbar-abdominal muscles activation for patients with chronic low back pain | BMC Sports Science, Medicine and Rehabilitation | Full Text
This study aimed to identify the effect of WBV on lumbar abdominal muscle activities in patients with CLBP. Using different combinations of vibration parameters, this study could provide important ideas for clinical treatment or research to attention on the interaction effects of exercise and frequencies.
Effect of WBV on lumbar-abdominal muscle activation
Results of our study powerfully supported the first hypothesis that adding WBV to exercises could increase muscle activation in MF (the total average, 208.7%), ES (the total average, 190%), AOE (the total average, 206.8%) and RA (the total average, 247.1%). In general, our study showed that muscle activation of patients with CLBP was similar to that of previous studies on healthy adults [9, 26]. For example, the authors evaluated the trunk muscle activation in different static exercises on the vibrating platform, and their results revealed that WBV led to increased muscle activation by 1.6% ± 1.4% maximal voluntary contraction (MVC) in MF and 46.4% ± 14.9% MVC in RA . These data showed that WBV could induce lumbar–abdominal muscle activity. Other factors would affect the degree of muscle activation . For example, healthy individuals performed single bridge exercise with WBV training, resulting in higher degree of ES activation than MF activation . This result differed from the findings of our study, in which CLBP patients conducting single bridge exercise induced the highest AOE activation.
Considering all the evidence gathered from these findings and previous studies, WBV training could be popular among individuals with poor muscle strength, and long-term training would result in more gains . Second, the effect of WBV on muscle activation depends on the body position, types of participants and vibration frequency . Third, we should be rigorous on comparing different populations. The EMG presents individual differences, such as skin interference, body posture and electrode position. Given these uncontrollable factors, we should conduct data standardisation according to certain reference values, such as the value of sEMG in no-WBV condition or MVC. This design uses the value of sEMG in no-WBV condition as reference to ensure reliable conclusions .
Effect of different frequencies on lumbar-abdominal muscle activation
The results of this study revealed that a higher frequency (15 Hz) induces higher neuromuscular activity than lower WBV frequencies (5 and 10 Hz), thus supporting the second hypothesis.
During WBV, the body of an individual is stimulated by appropriate mechanical stimuli. The related mechanism possibly utilises mechanical vibration and external resistance loads to stimulate muscle spindles; this training method improves neuromuscular function by inducing elevated muscle contractile activities and central nervous system adaptation . These study findings were similar to those of several previous studies. For example, Brigitte et al. reported that vibration led to increased RMS value of MF by 26% when compared with that under no vibration . Xueqiang et al. performed a clinical study about the effect of different platforms on lumbar–abdominal muscle activation. They reported that unstable platforms could induce higher activation than stable ones when healthy subjects performed various kinds of exercise . Desai et al. studied the rate of lumbar–abdominal muscle activation (RMS% MVC) in patients with CLBP and healthy people; the results demonstrated that the unstable platform is a good choice for inducing muscle activation . The above evidence all suggest that stimulation of unstable planes or vibration platform increases muscle activity. The practical significance of RMS is as a statistical characteristic of EMG showing muscle activities . When the body is on the vibration platform, the muscle induces more muscle spindles to resist external loads and maintain body balance. To a certain extent, a higher RMS value indicates more muscle activity. Our results showed that high vibration frequency is better for lumbar–abdominal muscle in patients with CLBP than low vibration frequency.
Study have shown the effect of different vibration frequencies on the activation of lumbar and abdominal muscles, revealing no significant differences between different vibration frequencies during bridge exercise . The effect of WBV training (less than 20 Hz) on lumbar and abdominal muscles could increase the muscle strength of the extensor muscle, whereas 40 Hz would decrease the extensor muscle endurance . Moreover, the Iα inhibitory neurons in the drafting state could be activated by WBV (Less than or equal to 5 Hz), which could promote the reduction of single synaptic reflexes and relax tensed muscles . High-intensity vibration would forcefully expose the muscle spindles to vibration stimulation, producing an inhibitory reflex, blocking muscle spindle transmitters, reducing the sensitivity of muscle spindle and causing muscle fatigue [32, 33]. The vibration frequency of lumbar abdomen is mostly below 20 Hz, and the results showed that such value could relieve pain in patients with CLBP and reduce the dysfunction index [16, 34]. In current studies, 15 Hz induces higher neuromuscular activity compared with 5 Hz and 10 Hz. Considering the overall evidence, 15 Hz vibration frequencies can lead to enhanced exercise benefits.
Effect of different exercises on lumbar-abdominal muscle activation
Among the various exercises selected in this study, the optimum routines included plank for MF and ES, single bridge for AOE and V crunch for RA. Different muscles perform differently during exercises considering their own anatomical characteristics.
MF and ES are kinds of back muscles that maintain the spinal stability and balance. During plank exercise, the muscles are in static equal-length contraction, which would activate as many muscles, especially the deep stabilizing muscles such as the MF, as possible to maintain the stability of the spine . MF contains rich proprioceptive receptors that enable the performance of delicate movements. When the spine suddenly becomes imbalanced, the MF would contract before the larger muscle groups adjust the displacement of individual vertebral segments. MF is a fundamental part to maintaining the normal biometric lines of the spine and enhancing lumbar stability [35, 36]. ES covers the lumbar and thoracic region; it is a large muscle group that maintains the stability of the spine. ES is a primary muscle for plank; both sides of ES contract to resist body gravity and keep the spine in a stable condition . Previous studies showed that side stay and bridge exercises are good for back muscles, such as MF and ES, in WBV condition . The most possible explanation for the conflicting results of this experiment could be the interaction effects between vibration frequencies and exercises on muscles. In general, WBV induced the greatest back muscle activation during plank training.
RA and AOE are both lumbar–abdominal muscles. During V crunch exercise, both ends of the body leave the ground, and all the gravity is concentrated on the abdominal muscles. These muscles require more muscle spindles to resist the load. On the other hand, the action of the V crunch is a centripetal contraction, whereas the RA is an active muscle requiring more strength. Atsushi et al. observed the effects of different platforms on trunk muscles during core stability training. The results showed that V crunch induced the highest RA activities on an unstable platform . Vera-Garcia et al. observed that the degree of RA activation reached more than 10% of that of AOE under the V crunch exercise with unstable conditions . Our findings were similar to those of previous studies. AOE is a large, thin and irregularly quadrilateral muscle located on the side of abdomen. During single bridge, one side of the upper limb and lower limb was off the ground; the AOE would then undertake more tasks to prevent the body from tilting. Furthermore, single bridge exercise induces more activities on AOE when compared with other exercises . Therefore, in the case of WBV training, RA in the action of V crunch and AOE in the action of single bridge showed the highest value of RMS, implying that the V crunch and single bridge could better activate abdominal muscles.
Some clinical implications were provided in our study. First, WBV can effectively induce muscle activation in patients with CLBP, indicating that it could be an effective assisted intervention to improve muscle performance, such as muscle strength, proprioception and flexibility [40, 41]. Second, the different WBV parameters have different effects on the lumbar-abdominal sEMG. Exercise, frequency and their interactions should be considered during WBV training of CLBP patients. We determined the best combination of WBV intensity at 15 Hz and 2 mm and plank or single bridge or V crunch exercises. If you want to improve back muscle performance, Plank or single bridge should be the more preferred choice for these individuals. If you want to improve abdominal muscle performance, V crunch would be a good choice.
First, the results of this study could only be generalised to younger CLBP patients and could not represent all age groups with CLBP. Second, the selection of exercise featured certain limitations. Future research can expand the range of movements and observe the effect of different frequencies on the muscles in the case of dynamic movements. Third, amplitudes and frequencies are important factors for the effect of WBV training. Thus, future studies should include different amplitudes and additional frequencies.
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