Ⅰ. Introduction
The core muscles of the human body are explained by the concept of a cylinder or box, as the abdominal muscles are responsible for the front and side walls of the trunk, the spine and hip muscles for the back wall, and the diaphragm and pelvic floor muscles for the top and bottom wall, respectively (Dougherty, 2011). Therefore, all movements of the body starts from the core muscles, that is, it indicates that the stronger the core, the more the body's energy can be effectively controlled (Kibler, Press & Sciascia, 2006). Energy production was clearly affected according to the force level of core muscles (Jamison, McNally, Schmitt & Chaudhari, 2013). For example, if the force level was insufficient during gait, the trunk became unstable since all forces for gait performance started from only the hip muscles and were not balanced properly (Ketelhut, Kindred, Manago, Hebert & Rudroff, 2015). Also, core muscles have been considered as a protective structure that reduce on spinal stresses caused by all forces ocurred during functional movements (Guo, Guo & Ren, 2021).
For this core stability, core strengthing training in the abdominal, lumbar and pelvic muscles has been generally conducted during rehabilitation, which leads to improve lumbar stability and postural alignment (Ghasemi, Goharjoo & Faizi, 2020). Interestingly, Improvement in pulmonary function would be accompanied since strengthening of the diaphragm of core muscles is included(Jun, Kim, Nam & Kim, 2016).
Cigarettes are a representative favorite dainty that has a harmful effect on pulmonary function in modern society, causing chronic bronchitis and chronic obstructive pulmonary disease (Aravamudan et al., 2014). Previous studies have reported that these pulmonary diseases not only impaired the pulmonary ventilation function, but also altered the thoracic movement mechanism ( Alter, Aboussouan & Mireles-Cabodevila, 2017). Furthremore, respiratory muscle weakness not only reduced functions of the entire core muscle, but also directly caused dyspnea during sports exercises to reduce performance, so efficient therapeutic intervention is required to care respiratory muscle (Lee, Cho, Hwang & Lee, 2018). Futhremore, according to previous studies, in general, most young smokers have 1-3 years of smoking experience with lower overall lung function than non-smokers during this period (Tantisuwat & Thaveeratitham, 2014).
To date, many previous studies on core muscle training have demonstrated its effectiveness in terms of improving motor performance and balance ability after intervention, but not considered its effect on respiratory function (Akuthota & Nadler, 2004). Therefore, in this study, the effect of core training on pulmonary function as well as balance ability was observed for smokers to investigate the complex effects of core strengthening traing.
Ⅱ. Methods
1. Participants
The sample size was calculated according to th result of a previous study (Pengel, Refshauge & Maher, 2004Pengel, Refshauge & Maher, 2004) with an effect size of 1.6, assuming α =0.05, power of 80%, so a sample size of 8 patients per group would be required by G Power 3.1.9.7. Eight healthy males (age: 24.75±6.60), smoking for more than three years participated in this study. All participants voluntarily agreed to participate after the explanation of experimental procedure before participating in the experiment.
2. Experimental precedure
All participants conducted baseline measurement of balance ability and pulmonary function before intervention, and post-measurement was conducted after 4-week intervention period. Core training intervention was consisting of plank and leg raise exercise, and was conducted twice a week for a total of 4 weeks.
3. Intervention
Plank exercise (Byrne et al., 2014) was performed as follows; in prone position, they lie down with wrists and elbows on the floor shoulder width. Then, the elbows and shoulders were vertically supported, feet were supported by toes and pelvis was lifted. During exercise, the trunk was kept in a straight line from the side view. In the first week, 30-second exercise and 25-second rest per set were performed in a total of three sets, and the exercise time per set was increased by 10 seconds every week. After Plank exercise, Leg raise exercise (Ifeyinwa et al., 2021) was immediately performed as follows; in supine position, they lie down comfortably with both arms were placed next to your waist. They flexed knees 10 degrees, lifted legs to 90 degrees, and slowly lower their legs. In the first week, 10-time exercise per set and 30-second rest in a total of 3 sets were performed. It was progresively performed by increasing the number of exercises by 5 times per week.
4. Outcome measurements
1) Balance ability
Good Balance System (Metitur, Finland) was used to evaluate balance ability (Ha, Cho & Lee, 2014). The center of gravity (COG) of the body was measured by performing the task, standing on the force plate in a natural and comfortable position and maintaining the posture for 30 seconds during the gaze fixed to the mark on the front wall with 5-cm distance between heels.
2) Pulmonary function
Quark Spiro (COSMED, USA) was used to evaluate pulmonary function (Pellegrino et al., 2021). The overall pulmonary function was evaluated by measuring the amount, speed, and air components during inhalation and exhalation. Each participant bit the mouthpiece with lips and took a breath comfortably. Then, they inhaled as much as possible and exhaled with the utmost effort at once. The total measurement was conducted three times, and the highest value was selected.
5. Statistcial anlaysis
To compare the differences in balance ability and pulmonary function before and after the experiment, paired t-test was used using SPSS Ver 23.0, and the statistical significance level was set to α=0.05.
Ⅲ. Results
1. Balance ability
For balance ability, there was no significant changes in extent in mediolateral direction, anterioposterial direction and total sway area of COG after 4-week intervention as shown in Table 1.
2. Pulmonary function
For pulmonary function, there was only significant change in expiratory minute ventilation (VE, P<.001), while expiratory vital capacities (EVC), expiratory and inspiratory reserve volume (ERV and IRV, respectively), inspiratory minute ventilation (VI) and tidal volume (VT) were not significantly changed as shown in Figure 1.
Ⅳ. Discussion
This study was conducted to investigate the effects of 4-weeks core strengthening training on balance ability and pulmonary function for healthy adult males with more than 3 years of smoking experience. As a result, there was no significant change in balacne ability, but a significant change in part of pulmonary function was confirmed.
As reported in previous studies, diaphragm breathing is linked to functional movements in terms of mobility and stability (Bradley & Esformes, 2014). With regard to the biomechanical aspect of breathing, the expiratory function promotes active recruitment of abdominal muscles in contrast to the natural elevation of rib cage. In agreement with these evidences, our study also showed a improved expiratory minute ventilation after 4-week abdomianl core strengthening training (Carvalho & Assini, 2008).
Generally, during exhalation, the thoracic spine returns to a neutral position (against hyperlordosis), and the diaphragm is positioned horizontal without pelvic tilting (Leong, Lu, Luk & Karlberg, 1999). Neutralization of these spines can reduce hyperlordosis and spinal pain caused by excessive muscle tension, and further promotes spinal stabilization by restoring breathing patterns (Izzo, Guarnieri, Guglielmi & Muto, 2013). Therefore, this study confirmed that abdominal core training have a positive effect on respiratory function by restoring this breathing pattern rather than directly affecting the lungs.
Core training exercises provides several other benefits. First, the recruitment of deep abdominal muscles increases intra-abdominal pressure and co-activation of the entire abdominal wall, which plays a fundamental role in providing adequate support for the spine and trunk (Neumann & Gill, 2002). Second, accurate core training does not produce repetitive flexion movements that would be harmful to the spine. Third, the abdominal could be trained in a neutral posture, maintaning the spine alignment consistently.
In this study, there were no significant results of balance ability after 4 weeks of core training. This is believed to be because the balancing ability is too insignificant to be improved only by training abdominal muscles, and the balancing ability is neurologically affected as well as the recruitment of other core muscles (Pollock, Durward, Rowe & Paul, 2000). In other words, even if the strengthening of abdominal muscles slightly increases spinal stabilization, short-term intervention could not have changed the overall balance ability because it was produced by the combination of visual, vestibular, and proprioceptive functions (Grace Gaerlan, 2012). In addition, the ceiling effect would have appeared because participants of this study did not have any muscle or neurological problems.
Although the sole effect of 4-week plank and leg raise exercises in this study was not statistically significant, plank and leg raise exercises has been commonly used as one of exercise methods to strengthen core muscles in sports rehabilitation program, which has the effect of improving athletic performance. For example, Gatz (2009) stated that running speed of track-and-field athletes could be improved in long-term core training rather than short-term training, and Kim & Chung (2009) reported that core exercise for 10 weeks for golf players improved flexibility and back muscle strength. Therefore, plank exercise will be essentially used to improve performance as well as the balance ability of trinee in the field of sports rehabilitation.
This study was limited in generalizing the effects of core programs because the sample size was small and the exercise program was relatively simple. In addition, since the intervention period was relatively short, it is difficult to make sure that this study significantly showed exercise effects. Therefore, in future studies, it is necessary to supplement these limitations to investigate more various effects of core training exercise.
Ⅴ. Conclusion
In this study, it was conducted to investigate the effects of abdominal core training on balance ability and pulmonary function of smokers. As a result, it was confirmed that abdominal core training had a preferential effect on respiratory function over balance ability, and in particular, a preferential change was found in exhalation rather than inhalation. Therefore, it was concluded that abdominal core training would be useful in patients with pulmonary disease, and further studies need to reveal the hidden effects of core exercise with sufficient sample size.
