A pilot study on the influence of exercising on unstable training machine on balance control and trunk muscles activity

Abstract

BACKGROUND:

The main position of the working population is becoming sitting. Immobile prolonged sedentary time may cause negative effects including reduced intervertebral discs nutrition. Main ways of mitigating them are regular position changes and exercising.

OBJECTIVE:

To evaluate influence of the short term training on unstable training machine on balance control and trunk muscles activity in patients with lower back pain.

METHODS:

Participants ( $n=$ 16) experiencing lower back pain were trained on an unstable sculling machine “Rehabili”. Their balance tested by (Biodex Balance System) and rectus abdominis, externus oblique, transverse abdominis, multifidus and erector spine muscles activity (measured by surface electromyography) while sitting and standing with usual and aligned body postures both before and after six weeks of training (three 15 minutes sessions per week) were compared in between.

RESULTS:

Balance control improved after the training program. Besides, more symmetrical activation of both sides rectus and transversus abdominis muscles, as well as increased transversus abdominis muscle activation of 19% ( $p<$ 0.05), were observed.

CONCLUSIONS:

Six weeks short sessions training on unstable training machine improved balance control and increased trunk muscles activity especially in aligned body posture when standing or sitting on unstable surface.

Keywords

Prolonged sitting balance trunk muscles activity unstable training

1. Introduction

Poor postural control is observed in sitting for patients suffering from lower back pain [1, 2]. In 37% of all cases, back pain results from all the risk factors related to work environment [3]. Studies show that sitting as an action does not damage our spine, however, the posture dominant in this position induces lower back pain [4]. Experts have analysed four sitting positions: flat back, long lordosis, short lordosis and slump sitting positions [5]. It was determined that deep multifidus muscles and abdominal (internal oblique and transverse) muscles had higher activity during sitting in short lordosis. The lowest activity of the same muscles was during the sitting position with a flat back. To restore the multifidus muscle, exercises should be performed in a neutral lordosis position using isometric activity, which would result in the tonic muscle mode. It is a very important action for stopping lower back pain recurrence and onset [6]. Systematic review has shown that it is more difficult to perform work-tasks at the time when patients feel low back pain at work that requires physical efforts and mental concentration [7]. For this reason, they lose a lot of time for important tasks implementation, and this is the result, but not the reason, why they experience the onset of low back pain.

Physical activity is one of the ways to reduce musculoskeletal diseases, type two diabetes, cardio – pulmonary diseases, and early mortality [8, 9]. The United States of America Federation guidelines recommend 30 minutes of moderate physical activity 5 times per week [9], which could reduce the diseases mentioned above.

It was also stated that one of the main consequences of sedentary lifetime and work environment in Western countries is lower back pain [10]. The first onset of low back pain appears in young adults, and symptoms repeat constantly [11, 12]. Lower back pain is divided into that of specific origin (about 5–15%) and nonspecific (causes are unknown) origin, about 85–95% of all cases of lower back pain [11, 13]. Lower back pain treatment is widely analysed, however, there is no optimal treatment and it is still being discussed by most physiotherapy scientists. Systematic review has shown that one of the possible treatments is multidisciplinary biopsychosocial attitude towards low back pain [14]. This approach is based on physical, psychological, and social dysfunctions that cause low back pain. The treatment requires different specialists’ competency, patients’ education and solutions of the problem. Moreover, it is important to mention that back schools also have a positive impact on correct motion and daily activities that are inevitable in lifetime [7].

One of the aims during the systematic review was to assess the training influence on neuromuscular control and functional exercise effect [15]. Results showed that balance training for an interventional group had a positive effect on improving the postural sway and functional balance compared with the control group. Longer balance training had a stronger effect than short-period. Jump, agility and neuromuscular control improved after the balance training program. Another systematic review studied the dose-response relationships of balance training in healthy young adults aged 16–40 [16]. This review revealed that balance training for 11–12 weeks, three or six training sessions per week, 11–15 minutes long for a single training session, improved the steady-state balance for recreational athletes. However, a six-week training period helped sub-elite athletes reach almost the same results as recreational athletes. We chose this duration of balance training because we have exploratory population with lower back pain to see if there are any physiological changes after a six-week training period.

The aim of the research was to evaluate influence of the short term periodical trainings on unstable training (sculling) machine for six weeks on the balance control ability and trunk muscles activity in patients with lower back pain.

2. Methods

2.1 Subjects

Twenty adults of both sexes who have experienced low back pain in the last 6 months were included in this study. Individuals who volunteered to participate in this study responded to the announcement. Four participants were excluded from this case because they did not end training sessions and did not participate in the second testing. For this reason data obtained on sixteen volunteers of both sexes were included in this study. The study subjects’ average ( $\pm$ SD) age was 30 ( $\pm$ 10), height was 176.5 ( $\pm$ 12.5) cm, mass was 76 ( $\pm$ 19) kg. The inclusion criteria of participants were: low physical activity, a sitting position at work, low or moderate back pain. Exclusion criteria were: pain in the thoracic spine, vestibular disorders and age more than forty years. All the participants were verbally informed of the protocol, read and signed a consent form. Ethical approval was obtained from the local research ethics committee (Lithuanian University of Health Sciences). The study participants were interviewed with a special questionnaire about lower back pain and physical activity.

2.2 Procedures

Testing before and after the training programme was carried out according to the protocol showed on Fig. 1.

First of all the static body balance maintenance was tested on Biodex Balance System (BBS). BBS uses a circular balance platform able to tilt up to 20 ${}^{\circ}$ about the anterior-posterior and medial-lateral axes, which is controlled by a microprocessor-based actuator. The actuator controls the manually preset degree of surface instability, which ranges from a completely stable surface (stability level 12) to a very unstable surface (stability level 1). The degree to which the platform tilts during a balance assessment is dictated by the subject’s balance ability [17, 18].

Figure 1.

Methodology protocol.

Body balance using BBS was measured in the usual and aligned body posture in sitting (on stool placed on the platform) and standing positions on a stable and unstable platform for 40 seconds, three times each, with 10 seconds rest between the trials (Fig. 2). The participants were informed about the balance maintenance and their center of mass positioning in the right direction. The participants were verbally informed to keep their usual body posture and after that – the aligned body posture during the balance testing. The aligned body position was set manually with verbal instructions.

Moreover, the trunk muscles activity was measured during the balance testing by surface electromyograph (sEMG) (Noraxon MR3.6). Before the surface electrodes placement the skin was shaved, swabbed and rubbed with alcohol to reduce skin impedance. Bipolar EMG electrodes were affixed on the skin and measurement were recorded during balance testing. Signal was fixed for 40 seconds with the same protocol as balance measurement (40 seconds, three times each, with 10 seconds rest between the trials). EMG data were collected from 3 abdominal wall muscles bilaterally: rectus abdominis, externus oblique, transverse abdominis, and 2 back wall muscles bilaterally: multifidus and erector spine [19, 20, 21]. The Noraxon electrodes have adhesive area of 4 $\times$ 2.2 cm; diameter of the two circular adhesive areas was 1 cm; distance to inter-electrode was 2 cm.

Figure 2.

(a) Experimental environment. Patient performs balance tests on stable and unstable surface in standing position. (b) Experimental environment. Patient performs balance tests on stable and unstable surface in sitting position.

An isokinetic dynamometer (Humac NORM) was used for the evaluation of maximal voluntary isometric contraction (MVIC). The participants did trunk flexion, extension, and lateral trunk flexion of the right and left sides in an upright standing position. The protocol was set according to [22], however, the participants did MVIC in an erect standing position, not leaned forward 30 ${}^{\circ}$ as in the previously mentioned research, because of the purpose to keep a neutral spine position. Each trial was performed three times for five seconds of MVIC with 30 second between the trials. Ten minutes rest period was provided between the MVICs and because of the fatigue protocol.

For this study, the unstable training machine “REHABILI” (Fig. 3) was used for training in the sitting position. The principle of this device is based on simulation of sculling, but involves not only the movements’ and resistance patterns, but also instability of the seat in frontal plane, thus the participants had to do exercises and to keep the balance at the same time. Besides, this machine had an integrated computer, which captures the number of cycles, rate, time, heart rate, energy expenditure; and seat tilt angle indication and registration system. The resistance on oars of the unstable training machine are adjustable, but in this study minimal hydrodynamic resistance (generated by hydraulic cylinders) was used, because the point of research was training of the balance for patients with low back pain. Thus the maximal resistance force value was $\sim$ 90 N during the drive phase, but usually the force participants of research applied on oars was about 60 N during the drive phase. Special feature of this training machine is the possibility to adjust its instability, or to be precise – intensity of assistance in keeping balance when sitting on it. During this research, the participants had a different ability to keep their balance, for this reason instability was selected individually according to the individuals’ ability to keep their balance at the first time when they sat on this machine. The intensity of the exercising during all training sessions was twenty rowing cycles per minute; each session lasted 15 minutes.

Figure 3.

Training on unstable training machine.

The training on an unstable training machine lasted six weeks, three times per week for 15 minutes per training. At the first meeting, the instability level of training machine was set for each individual according to his ability to keep the balance (zero tilt) while sitting still without leaning to the sides. The instability level was gradually increased when the patients felt comfortable and did not lean to the sides even during the training. Every person was trained individually with trainer instructions about the action, exercises and aligned body posture maintenance. During the training session, patients had to keep their posture aligned with neutral pelvis and with body segments alignment considering the vertical line projection above the base of support [23] at all phases of the exercise. The patients were trained to do trunk flexion/extension, arms extension/flexion and legs flexion/extension on an unstable training device in sitting positions (Fig. 4). The training dose was selected on the basis of systematic review of balance training [24]. The patients were tested after six weeks of training the same way, as before training program.

Figure 4.

The base of training program on unstable training machine REHABILI.

2.3 Data and statistical analysis

sEMG signal normalization was done using (Noraxon MR 3.6) Myomuscle software. sEMG data were band-pass filtered (the frequency range 5–500 Hz) then rectified and smoothened. The non-reproducible part of the signal was minimized by applying digital smoothing algorithms that outline the mean trend of signal development. The steep amplitude spikes were cut away; the signal receives a “linear envelope”. The amplitude of sEMG data was normalized using the mean dynamic activity method [25]. For further calculations and results comparison between patients, maximum voluntary isometric contraction (MVIC) was performed for each muscle and the sEMG amplitude recorded at the same time.

The overall stability index (OSI) was used for the evaluation of balance keeping; it was calculated automatically by Balance System (Biodex). OSI represents the variance of the foot platform tilt, from the horizontal position Eq. (1). High OSI score means significant displacements of the patient’s center of gravity and is indicative low ability to keep balance during static test.

$\displaystyle\text{(OSI)}=\sqrt{\frac{\Sigma(0-X)+\Sigma(0-Y)^{2}}{\text{% number of samples}}}$ (1)

$X$ – motion in frontal plane (anterior – posterior); $Y$ – motion in sagittal plane (medial – lateral).

The data were analysed with statistical package SPSS version 23.0. For a small sample, the nonparametric Wilcoxon test was used. The data level for statistical significance was set at $p<$ 0.05. The data were presented as arithmetic mean $\bar{x}$ ( $\pm$ SD).

3. Results

3.1 Body balance in two different postures

When testing patients before and after the training program their body balance was measured on two different bases of support, stable and unstable. Patients kept their balance in standing and sitting positions and in two different postures, usual and aligned (Table 1).

Table 1
Individuals body balance in standing and sitting on stable and unstable surfaces in two different postures. Values represents overall stability index (OSI). Data is presented as mean ( $\pm$ SD)

Position	Standing on unstable surface in usual body posture	Standing on unstable surface in aligned body posture	STD of standing on unstable surface in aligned body posture	Sitting on stable surface in aligned body posture	Sitting on unstable surface in aligned body posture	STD of sitting on unstable surface in aligned body posture
Before training	2.86 ( $\pm$ 1.35)*	2.41 ( $\pm$ 0.94)*	2.41 ( $\pm$ 1.09)*	1.59 ( $\pm$ 1.06)*	1.81 ( $\pm$ 0.65)*	1.28 ( $\pm$ 0.91)*
After training	1.97 ( $\pm$ 1.28)*	1.89 ( $\pm$ 0.84)*	1.64 ( $\pm$ 0.85)*	0.86 ( $\pm$ 0.33)*	1.51 ( $\pm$ 0.7)*	0.96 ( $\pm$ 0.43)*
Significant level	$p<$ 0.05	$p<$ 0.05	$p<$ 0.05	$p<$ 0.05	$p<$ 0.05	$p<$ 0.05

${}^{*}$ Statistically significant differences $p<$ 0.05.

3.2 Trunk muscles activity in two different postures

Transverse abdominis muscle activity for the participants with a usual body posture in standing on an unstable surface before the training was 45.22% ( $\pm$ 28.40), after training 65.18% ( $\pm$ 42.49), there was a statistically significant difference ( $Z=$ $-$ 2.172, $p=$ 0.03) (Table 2).

Table 2
Trunk muscles activity in different postures and surfaces before and after trainings

Muscles	Values		Symmetry
	Before	After	Right	Left	Right	Left
Transversus abdominis	Standing on unstable surface in usual body posture		Standing on unstable surface in aligned body posture
	45.22% ( $\pm$ 28.40)*	65.18% ( $\pm$ 42.49)*	80.10% ( $\pm$ 60.56)*	65.56%( $\pm$ 50.54)*	74.83% ( $\pm$ 52.52)	76.43% ( $\pm$ 55.7)
Externus obliques	62.69% ( $\pm$ 54.18)*	49.48%( $\pm$ 31.72)*	–		–
Externus obliques	Sitting on stable surface in aligned body posture
	58.55%( $\pm$ 47.11)*	43.18% ( $\pm$ 31.72)*	–		–
	Sitting on unstable surface in aligned body posture
	82.74% ( $\pm$ 72.24)*	55.66%( $\pm$ 45.02)*	–		–
Rectus	Sitting on stable surface in aligned body posture
abdominis	–	–	21.33%( $\pm$ 20.54)*	31.72%( $\pm$ 32.81)*	23.34% ( $\pm$ 22.62)	25.17%( $\pm$ 21.24)

Data is presented as mean ( $\pm$ SD). ${}^{*}$ Statistically significant differences $p<$ 0.05.

However, externus obliques muscle activity in aligned body posture in standing on unstable surface before the training was 62.69% ( $\pm$ 54.18), after training became lower 49.48% ( $\pm$ 31.72). The difference was statistically significant ( $Z=$ $-$ 2.045, $p=$ 0,04). Standing on an unstable surface in an aligned body posture, the right side transverse abdominis muscle activity was 80.10% ( $\pm$ 60.56), the left side – 65.56% ( $\pm$ 50.54), the differences were statistically significant ( $Z=$ $-$ 2.045, $p=$ 0.04). After training sessions, the right side transverse abdominis muscle activity was 74.83% ( $\pm$ 52.52), the left side – 76.43% ( $\pm$ 55.7), the differences were not statistically significant ( $Z=$ $-$ 0.362, $p=$ 0.72), the transverse abdominis muscle symmetry after training became better. When sitting on a stable surface in an aligned body posture, the externus oblique muscle activity before the training was 58.55% ( $\pm$ 47.11), after training became lower 43.18% ( $\pm$ 31.72). The difference was statistically significant ( $Z=$ $-$ 2.276, $p=$ 0.02). However, sitting on a stable surface in an aligned body posture the right side rectus abdominis muscle activity before the training was 21.33% ( $\pm$ 20.54), the left side – 31.72% ( $\pm$ 32.81), the differences were statistically significant ( $Z=$ $-$ 2.508, $p=$ 0.01). After the training program, the right side rectus abdominis muscle activity was 23.34% ( $\pm$ 22.62), the left side – 25.17% ( $\pm$ 21.24), the differences were not statistically significant ( $Z=$ $-$ 0.534, $p=$ 0.59). When sitting on an unstable surface in an aligned body posture, the externus obliques muscle activity before the training was 82.74% ( $\pm$ 72.24), after training became lower 55.66% ( $\pm$ 45.02). The difference was statistically significant ( $Z=$ $-$ 2.857, $p=$ 0.004).

4. Discussion

After training on an unstable machine, the results of balance in sitting and standing positions became better. In sitting and standing positions with an aligned body posture on an unstable surface, the stability index and standard deviation of stability index after the training were statistically significantly decreased ( $p<$ 0.05), it means that the sway was lower after the training procedures. Balance training has a significant influence on balance improvement and trunk muscles activity increment [26]. Patients suffering from low back pain have poorer posture control and balance maintenance, also, a strong correlation was found [26] between poor balance maintenance in sitting and prolonged muscle activity, when balance was suddenly disturbed. Patients with non-specific low back pain have poorer balance maintaining, higher swaying, especially in the anterior-posterior directions, when compared with healthy people [27].

Posture is of great importance for balance maintenance [28], balance is kept worst by patients who spend most of their time in a wrong sitting position. Posture and balance maintenance connections were also analysed during this research. It was found, that after the training sessions, patients kept their balance better in an aligned body posture, and just in one case balance was better in the usual body posture, when the patients’ standing on an unstable surface stability index score was lower, however, the standard deviation of this stability index did not change. It means that the sway did not become better after the training sessions.

After the training, the externus obliques muscles activation became lower in the usual standing position on an unstable surface and in an aligned body posture in sitting and standing positions on stable and unstable surfaces ( $p<$ 0.05). According to other authors, lower muscles activation show effective and productive trunk strategies’ usability [29]. Training on an unstable surface increases muscle adaptation; because of it, the muscle activity could be lower than before the training sessions [29]. Besides, muscle activity after the training could be lower because of attentiveness, increased self-esteem and reduction of tiredness.

Asymmetry of deep abdominal muscle transverse abdominis could also be seen from the results of research. According to other authors [30], transverse abdominis activation depends on the mechanical disturbance importance and the direction of the trunk. However, the author’s results are based on surface electromyography as our research results. The asymmetry of rectus abdominis muscle activity to the front surface conversion is asymmetrical for patients suffering from low back pain [30]. Our research has shown the same results: before the training, patients felt low back pain, and the activity of rectus abdominis was asymmetrical, however, after the training sessions, the activity of this muscle became more symmetrical than before the training.

5. Conclusions

This study examines the influence of the personalised short-term periodical trainings on unstable training machine on the body balance control ability and trunk muscles activity (in two different body postures and positions) in patients with lower back pain. Research revealed that balance trainings have positive influence on trunk muscles activity (transversus abdominis muscle increased about 19%), and balance maintenance ability, especially in an aligned body posture, about 33% increased postural control. Increased Transversus abdominis muscles activity and symmetry showed better postural control in balance maintenance and reduced swaying parameters. Trainings on unstable training machine leaded to increment of the activity of deep muscles, which are responsible for spine stabilisation, and decreased activity of superficial muscles (externus obliques muscles activity decreased 13%). This important fact shows that training on unstable machine makes deep muscles to work more efficiently. Nevertheless, there is still a need of further research, considering larger sample sizes, control group.

Footnotes

Conflict of interest

None to report.

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A pilot study on the influence of exercising on unstable training machine on balance control and trunk muscles activity

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Methods

2.1 Subjects

2.2 Procedures

3.1 Body balance in two different postures

Table 1 Individuals body balance in standing and sitting on stable and unstable surfaces in two different postures. Values represents overall stability index (OSI). Data is presented as mean ( ± SD)

Table 2 Trunk muscles activity in different postures and surfaces before and after trainings

5. Conclusions

Footnotes

Conflict of interest

References

Table 1
Individuals body balance in standing and sitting on stable and unstable surfaces in two different postures. Values represents overall stability index (OSI). Data is presented as mean ( $\pm$ SD)

Table 2
Trunk muscles activity in different postures and surfaces before and after trainings