Plank exercise improves respiratory capacity through positive changes in body composition, abdominis function, and autonomic nerves' activities

Abstract

This research aimed to explore the impact of plank exercise training (PET) on respiratory function, body composition, abdominis performance, and autonomic nervous system (ANS). Sixty‐one young adults participated and were divided into a control group (CG, n = 31) and an exercise group (EG, n = 30), wherein PET was administered 3 days per week for 12 weeks. After the experiment, the body composition of the CG deteriorated, whereas that of the EG improved (p < 0.001). The EG exhibited a reduction of ∼34% in the mean maximum displacement and a rise of ∼20% in the mean contraction time of the abdominis. The sit‐up in the EG demonstrated a significant increase of ∼55%. In the EG, there was a substantial increase in peak expiratory force by ∼24% and forced expiratory volume in 1 s by ∼14%, accompanied by a reduction in resting respiratory rate by ∼ −9%. When compared to the CG, these alterations were significant between the two groups (p = 0.001). In the EG, there was a significant decrease in resting heart rate by ∼2%, accompanied by a decrease in sympathetic nervous activity by ∼ −5% and by an increase in parasympathetic nervous activity by ∼5%. When compared to the CG, these alterations were significant between the two groups (p = 0.001). The findings of this study revealed that implementing PET in young adults, while controlling for dietary intake and physical activity, resulted in noteworthy changes in respiratory capacity. These changes were coupled with improvements in body composition, abdominal functions, and the ANS.

INTRODUCTION

Respiration encompasses a set of vital processes that are essential for the survival of all living creatures on Earth. From a physiological perspective, respiration involves the intricate procedure of drawing oxygen from the surrounding environment into cells within the human body while simultaneously expelling carbon dioxide in the opposite direction. The lungs, serving as the primary organs for respiration, consist of fibrous structures that, by themselves, cannot intake oxygen or expel carbon dioxide (Hsia et al., ). Instead, the task of drawing air into the lungs for oxygen and facilitating the removal of carbon dioxide is carried out by the muscles surrounding the rib cage and the diaphragm (Bott et al., ). Moreover, the neck muscles, including the sternocleidomastoid and scaleni, along with the rectus abdominis muscle located below the diaphragm, are also crucial contributors to the breathing process (Lissens, ).

It can be suggested that engaging in daily exercises to strengthen respiratory muscles has the potential to enhance breathing function (Evans & Whitelaw, ; Man et al., ). In recent times, the plank exercise training (PET) has garnered significant attention due to its effectiveness in rapidly burning calories and strengthening the core muscles in the abdominal regions (Byrne et al., ; Cho et al., ; Park et al., ). It's a simple exercise to learn, demands minimal time, space, and financial investment. The PET involves supporting the body trunk by assuming a rigid position with forearms and both feet in contact with the ground (Calatayud et al., ). This exercise notably enhances the activity of core muscles and promotes the stabilization of the core by maintaining the body's neutral posture (Ekstrom et al., ). Importantly, it's recognized that increasing abdominal muscle endurance through a PET contributes to improved overall body mobility (Byrne et al., ).

Nonetheless, it's important to note that while studies have shown the positive impact of PET on strengthening core muscles, there has been a limited exploration of the broader physiological context, including the involvement of the nervous system and the contribution of the abdominal muscles as a respiratory muscle through PET. Hence, the objective of this study was to examine the impact of PET on respiratory function and explore its effects on body composition, abdominal muscles, and the nervous system.

MATERIALS AND METHODS

Participants

The study included male and female college students with ages spanning from 20 to 24 years. We enlisted male and female students who were in good health and had no prior experience with plank exercises. Furthermore, all participants were chosen based on their responses to a brief questionnaire (with “Yes” or “No” options) to ascertain their smoking status, presence of back pain, and drinking alcohol. Individuals responding with “Yes” to any of these criteria were then excluded from participating in the study. Individuals were disqualified from participating if they had undergone any treatment or were taking medication known to have an impact on physical or psychological conditions, or if they had undergone significant surgery within the year preceding the commencement of this study. The sample size for this study was determined using GPower (version 3.1.9.7, Heinrich-Heine-University Software). It was calculated by summing the required number of subjects for the analysis of variance, taking into consideration the following parameters: an effect size of f² (V) = 0.25, an alpha error probability of 0.05, a power of 0.95, the presence of two groups, and a numerator difference of 2. According to GPower's calculations, the optimal sample size for this experimental design was determined to be 54 participants. This study decided to select 67 participants in consideration of the dropout rate. Out of the 67 participants initially recruited for the study, 3 individuals were excluded. A total of 64 participants were assigned unique identification numbers before being randomly assigned to one of two groups using random number tables. To ensure a truly random allocation, we employed the Research Randomizer program (Urbaniak & Plous, ). Each participant selected a numbered ticket from a container was input as individual sets into the program. Subsequently, they were assigned at random to either the control group (CG) or the exercise group (EG), with each group consisting of 32 participants. In order to uphold separation and avoid communication between the two groups, the CG attended laboratory sessions in the morning, while the EG did so in the afternoon. This measure ensured that the groups did not interact during the study. Over the course of the 12-week experiment, 1 participant from the CG and 1 participant from the EG dropped out, resulting in the final analysis of data from 31 in the CG and 30 in the EG, after one participant was removed due to an analysis error.

Experimental design

This study was a randomized controlled trial that conducted quantitative research to investigate the impact of plank exercises on body composition, respiratory capacity, abdominal function, and the autonomic nervous system (ANS) in university students. All data in this study were acquired from March 6, 2023 to May 30, 2023. This study was registered with the Clinical Research Information Service, reference KCT0005931. Before the commencement of the study, the principal investigator provided detailed explanations of all procedures to the participants. Subsequently, all participants read and signed an informed consent form. After receiving approval from the IRB (HS22-05-03) which approved by the Health Science Human Studies Committee of *** University, the experiment was carried out. To uphold the principle of double-blindness in this study, the roles of the measurer and exercise instructor were kept separate. Essentially, these two individuals were not acquainted with each other throughout the experiment. Specifically, neither the researcher nor the participants were aware of the group assignments during the test phase. The state of double-blindness persisted until all measurements and experiments were concluded, and the confidentiality of the assigned groups was rigorously maintained. At the same time, steps were taken to reduce external factors by daily recording and assessing the dietary intake and physical activity of all participants in both groups. The plank exercise program for the EG was performed 3 days a week for 12 weeks.

Measurement methods

All measurements were conducted twice, both at the baseline and at the end of the 12-week period. Essentially, participants reconvened in the laboratory after 12 weeks to undergo measurements in the same location. The detailed measurement methods are outlined as follows.

Measurement for demographics and body composition

The study inquired about the age and sex while also evaluating the body composition of all participants. Height (cm) measurements were taken using an automatic height meter (BMS 330, BioSpace), with participants wearing lightweight gowns. Body weight (kg), fat mass (kg), and muscle mass (kg) were determined via DEXA whole-body scan (TSX-303A, Toshiba Medical Systems Corporation) while participants lay in the supine position following a 10-h fasting period. The DEXA whole-body scan was performed quickly to reduce radiation exposure (Jee, ; Smith-Bindman, ). The body mass index (BMI) was computed using the weight-to-height ratio formula (kg/m²). In terms of waist-to-hip ratio (WHR), waist circumference was measured at the level of the navel while participants stood comfortably. Hip circumference (cm) was measured at the point of greatest protrusion when viewed from the side.

Measurement for controlled variables (calorie input and output)

During the pre-experiment session, all participants were instructed on how to use a dietary camera AI system (DoingLab Inc.) to photograph the meals they prepared for consumption each day. The system automatically computed the calorie intake from the images, and these calculated data were transmitted to a designated researcher daily for evaluation. Afterward, the data was analyzed on a weekly basis, and the data accumulated over the final 12 weeks was averaged for analysis. Meanwhile, the participants' daily physical activity levels were recorded and quantified using the International Physical Activity Questionnaire—shortened form version (Cheng, ). Participants completed questionnaires based on their physical activity records for each week throughout the experimental period. The daily calorie expenditure was calculated using metabolic equivalent-minutes. Following that, the data was utilized to calculate the average weekly levels of physical activity, and these averages were subsequently analyzed based on the accumulated data.

Abdominal muscle tone measures

This research employed the tensiomyography (TMG) to investigate alterations in the rectus abdominis muscle after performing plank exercises. The TMG (TMG100, TMG-BMC Ltd.) includes a stimulator responsible for generating electrical stimulation, a sensor that transmits the muscle's response to a computer, and a software program designed to monitor and assess the muscle's reaction (Dahmane et al., ). It assesses muscle response to a single electrical stimulus by quantifying the displacement of the muscle belly in a radial direction. The primary variables under consideration are the maximum displacement of the muscle (Dm), which measures the maximum distance (in millimeters) the muscle moves during contraction, and the contraction time (Tc), which represents the time (in milliseconds) it takes for the muscle to contract from 10% to 90% of Dm. To assess the muscle tone of the rectus abdominis muscles, electrodes were affixed at intervals of roughly 5 cm on both the left and right sides of the navel, spanning from the proximal to the distal regions. Additionally, a sensor was securely positioned at the abdominal center. Stimulation commenced at an initial intensity of 20 mA and was incrementally raised by 10 mA steps until the maximum Dm value was achieved. Before conducting the measurements, participants were instructed to rest in a bed for 5 min to ensure muscle relaxation. Subsequently, the recorded values were documented and subjected to analysis.

Abdominal muscle endurance test

Sit-ups were utilized to assess the endurance of abdominal muscles. Participants were asked to recline on a raised platform tilted at a 15-degree angle. They were instructed to position their feet 30 cm apart, bend their knees at a 90-degree angle, and rest their feet on the platform's footrest. With their hands crossed over their chests, they reclined on their backs at the inclined angle. During the assessment, participants lifted their upper bodies, making sure both elbows touched their knees, and then returned to the lying position with their backs against the floor. This movement was measured once, and the maximum number of repetitions performed per minute was recorded for subsequent analysis.

Respiratory capacity measures

Lung capacity denotes the volume of air that can be rapidly exhaled following inhalation. Respiratory function assessment was conducted using a Spirovit SP-1 spirometer from SCHLLER AG in Switzerland. The following parameters were measured: Forced expiratory volume in 1 s (FEV₁), and peak expiratory flow (PEF) by a single researcher. To perform the tests, participants sealed their noses with a stopper and inserted a disposable mouthpiece into their mouths by one examiner with more than 10 years of clinical experience. They then exhaled their maximum breath for the above variables through their mouths following maximal inhalation. Before the actual experiment, the participants were given practice sessions to familiarize themselves with the spirometry measurement technique. The spirometry test was performed three times for each subject, and the highest recorded value among the three attempts was utilized for statistical analysis, as detailed in Sutbeyaz et al., . The established norm for lung capacity in adults is typically between 3.5 and 4.8 L for males and 2.5–3.1 L for females. In the meantime, this research assessed the resting respiratory rate (rRR) of every participant for a 60-s. All individuals were prompted to shut their eyes and breathe at ease. A single researcher determined the respiratory rate by observing the participant's chest movements in a relaxed state and counting the occurrences.

HRV measures

To gauge ANS activity, we determined heart rate variability (HRV) utilizing uBiomacpa (Biosensecreative Co. Ltd.). The participants were requested to avoid engaging in exercise or consuming alcohol on the day prior to the experiment. Additionally, they were instructed not to eat or consume caffeine for a period of 3 h leading up to the HRV measurement. On the measurement day, HRV assessments were conducted twice, at 10:00 a.m. and 3:00 p.m., and the resulting mean values were analyzed. To ensure accurate measurements, participants were instructed to sit comfortably for a duration of 2–3 min, while pulse waves were non-invasively recorded using a sensor inserted into the index finger. All participants were encouraged to avoid factors that could potentially impact the measurements, including talking, coughing, and deep breathing.

In domain analysis, the measurement focuses on the time intervals between normal QRS complexes or the instantaneous heart rate at specific points to calculate what's known as the normal-to-normal interval (NN interval) between consecutive normal QRS complexes. The standard deviation (SD) of these NN intervals (SDNN) can be determined. SDNN encompasses all the cycle elements contributing to HRV. Another parameter, the square root of mean squared differences of successive NN intervals (RMSSD). Frequency domain analysis of HRV delves into the spectral components of HRV, including the high-frequency (HF) and low-frequency (LF) ranges. These spectral components provide insights into the sympathetic activity through LF and the parasympathetic activity through HF (Lane et al., ; White & Raven, ). The evaluation of the ANS was conducted in accordance with the guidelines outlined by the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology ().

Plank exercise program

The PET was conducted 3 days per week, with sessions scheduled on alternate days for 12 weeks. Before and after the plank exercise routine, participants engaged in 5 min of lying stretches. The term “lying down stretching” typically denotes stretching exercises carried out in a reclined position. In the context of this study, participants engaged in stretches such as hamstring stretch, quadriceps stretch, chest opener stretch, child's pose, and supine spinal twist. During the workout phase, participants performed three different types of plank exercises. The participants were directed to assume the standard plank exercise position, with their arms fully extended and hands on the floor directly beneath their shoulders, resembling the initial posture of a push-up. It was emphasized to maintain a straight body alignment, avoiding any sagging or lifting of the hips. Their ankles should be dorsiflexed, which means their toes pointed into the floor, providing support for their body weight. In the elbow plank exercise, participants should maintain a straight and rigid alignment from their head to their toes, ensuring there's no raising of the hips. The shoulders and elbows should be flexed at a 90-degree angle. Similarly, in the side plank exercise, participants should sustain a straight and firm alignment from head to toe, avoiding any dipping or elevation of the hips. The shoulder was abducted to a 90-degree angle and the elbow was flexed to a 90-degree angle. This exercise is performed with participants lying on one side, supporting their torso using one arm while looking towards the side.

In the initial 4 weeks, the exercise regimen included three variations of plank exercises: standard plank (1 min of exercise followed by 1 min of rest), elbow plank (1 min of exercise followed by 1 min of rest), and side plank (1 min of exercise followed by a 1-min rest). Each of these exercises was performed for a total of three sets, resulting in a cumulative exercise time of 9 min. Between the 5th and 8th weeks, an additional set was incorporated into each exercise, thereby prolonging the overall exercise duration to 12 min. From the 9th to the 12th week, an additional set was introduced to each exercise, resulting in the extension of the exercise routine to a total duration of 15 min. All participants in this study engaged in plank exercise programs under the guidance of an instructor, facilitating effective supervision. Moreover, a daily attendance check method was consistently implemented throughout the 12-week duration of the study.

Statistical analyses

Statistical analysis was performed with GraphPad Prism 10.0.2 software (Graph Pad Software), and the significance level was set to α = 0.05. The normality of all measured variables was analyzed using the D'Agostino & Pearson omnibus normality test. Before the experiment, the study conducted a comparison of the variables in the two groups using the Mann–Whitney U-test. Comparisons of normally distributed quantitative data were estimated through ANOVA. When the sample was not normally distributed, the Mann–Whitney U-test was performed to analyze two independent groups and the Wilcoxon signed rank test was performed to analyze two different times. To compare the change over time, a delta percentage (Δ%) analysis was performed, and the significance was tested for this value by the Mann–Whitney U-test. Partial eta squared (η²) effect size was employed to gauge the extent of the difference within each group, with the benchmarks for small, moderate, and large effects set at 0.01, 0.06, and 0.14, respectively (Cohen, ).

RESULTS

Demographic and physical characteristics before the experiment

Before the commencement of the study, the participants had an average age of 20.98 ± 2.17 years. Specifically, the CG had an average age of 20.84 ± 1.92 years, and the EG had an average age of 21.13 ± 2.43 years. Notably, there was no significant difference observed between these two groups (Z = −0.452, p = 0.651). Within the CG (n = 31), there were 15 females (48.4%) and 16 males (51.6%). In the EG (n = 30), there were 14 females (46.7%) and 16 males (53.3%). The CG had a height of 1.71 ± 0.08 m and a weight of 67.62 ± 13.39 kg. Meanwhile, the EG had a height of 1.70 ± 0.08 m and a weight of 67.72 ± 12.28 kg. Importantly, there were no significant differences observed between the two groups (Z = −0.745, p = 0.456 for height; Z = −0.079, p = 0.937 for weight). The CG exhibited a muscle mass of 30.82 ± 4.94 kg and a fat mass of 17.56 ± 6.28 kg. In contrast, the EG had a muscle mass of 30.81 ± 5.25 kg and a fat mass of 17.16 ± 3.34 kg. Notably, no statistically significant differences were found between these two groups (Z = −0.274, p = 0.784 for muscle mass; Z = −0.520, p = 0.603 for fat mass). Furthermore, the WHR for both CG and EG was 0.87 ± 0.06 and 0.87 ± 0.04, respectively, with no statistically significant difference observed between the two groups (Z = −0.269, p = 0.788). Additionally, the BMI for both CG and EG was 22.85 ± 3.03 and 23.17 ± 2.80 kg/m², respectively, with no significant difference detected between the groups (Z = −0.447, p = 0.655).

Among the control variables, the daily dietary intake was 2322.32 ± 369.35 kcal for the CG, whereas it was 2258.37 ± 415.39 kcal for the EG, showing no significant difference between the two groups (Z = −0.404, p = 0.686). Furthermore, the daily physical activity levels were 1784.71 ± 259.32 MET · min/week for the CG and 1724.87 ± 249.06 MET · min/week for the EG, indicating no significant difference between the two groups (Z = −0.188, p = 0.851).

Changes and differences of body composition and abdominis function

As indicated in Table , the CG experienced an increase in body weight, whereas the EG witnessed a reduction. These outcomes were observable in the interactions. Likewise, fat mass, BMI, and WHR displayed parallel trends to those observed in body weight. On the contrary, muscle mass decreased in the CG, whereas it showed an increasing trend in the EG with a large effect size, and this trend was significantly evident in the interaction effect.

TABLE 1 Changes and differences of body composition and abdominis variables.

Variables	Times	Groups	p
CG	EG	G	T	G*T
Body composition factors
Weight (kg)	Pre	67.62 ± 13.39	67.72 ± 12.28	0.569	0.003	0.001
Post	68.72 ± 13.06	64.97 ± 11.06
Muscle mass (kg)	Pre	30.82 ± 4.94	30.81 ± 5.25	0.044	0.010	0.001
Post	27.00 ± 6.26	32.34 ± 4.70
Fat mass (kg)	Pre	17.56 ± 6.28	17.16 ± 3.34	0.123	0.264	0.002
Post	19.38 ± 4.72	16.27 ± 3.71
BMI (kg/m2)	Pre	22.85 ± 3.03	23.17 ± 2.80	0.784	0.152	0.001
Post	23.24 ± 2.99	22.52 ± 2.57
WHR	Pre	0.87 ± 0.06	0.87 ± 0.04	0.081	0.574	0.001
Post	0.89 ± 0.05	0.85 ± 0.04
Abdominis capacities
Dm of right side (mm)	Pre	5.54 ± 2.59	5.79 ± 3.06	0.005	0.472	0.001
Post	7.06 ± 3.04	3.67 ± 1.60
Dm of left side (mm)	Pre	5.34 ± 2.49	5.55 ± 2.92	0.002	0.076	0.001
Post	6.43 ± 2.45	3.07 ± 1.61
Tc of right side (ms)	Pre	33.10 ± 8.11	33.34 ± 9.40	0.020	0.694	0.005
Post	28.38 ± 9.85	36.93 ± 8.90
Tc of left side (ms)	Pre	32.66 ± 7.52	32.53 ± 8.35	0.020	0.884	0.006
Post	28.10 ± 8.33	37.59 ± 14.79
Sit-ups (reps)	Pre	22.68 ± 8.75	22.60 ± 6.54	0.001	0.001	0.001
Post	19.29 ± 8.53	35.60 ± 13.75

As depicted in Table , the Dm of the right abdominis exhibited an inclining pattern in the CG but displayed a decreasing tendency in the EG. These changes were similarly observed in the Dm of the left abdominis. Conversely, the right abdominis Tc displayed a declination in the CG while demonstrating a tendency to incline in the EG. These trends were likewise noticeable in the Tc of the left abdominis. These results were evident in the interactions across all variables. Moreover, there was a notable increase in all post-variables observed in the EG compared to the CG, and this increase was characterized by a large effect size (≥0.14).

Figure  presents the delta percent differences in the primary components of body composition. In the CG, muscle mass displayed a decrease of −12.54 ± 13.56%, while in the EG, it exhibited an increase of 5.88 ± 9.28%. This difference was statistically significant (Z = −4.776, p = 0.001, η² = 0.392) between the two groups. Within the CG, there was a notable increase in fat mass by 21.20 ± 44.25%, whereas in the EG, fat mass displayed a decrease of 4.48 ± 16.42%. This discrepancy was statistically significant (Z = −2.418, p = 0.016, η² = 0.131) between the two groups (Figure ). Likewise, WHR experienced a rise of 2.01 ± 3.05% in the CG, while it declined by 2.35 ± 3.68% in the EG, signifying a notable distinction (Z = −4.283, p = 0.001, η² = 0.301) between the two groups (Figure ).

[IMAGE OMITTED. SEE PDF]

Within the CG, there was a notable increase in mean Dm values by 35.50 ± 67.29%, whereas in the EG, mean Dm values displayed a decrease of 33.53 ± 51.81%. This discrepancy was statistically significant (Z = −4.790, p = 0.001, η² = 0.254) between the two groups (Figure ). Within the CG, there was a notable decrease in mean Tc values by 12.53 ± 19.21%, whereas in the EG, mean Tc values displayed an increase of 19.85 ± 42.48%. This discrepancy was statistically significant (Z = −3.434, p = 0.001, η² = 0.201) between the two groups (Figure ). When examining the delta percent differences in sit-up performance, the CG exhibited a decrease of −12.87 ± 26.82%, while the EG displayed an increase of 55.04 ± 45.53%. This difference was statistically significant (Z = −5.420, p = 0.001, η² = 0.463) between the two groups (Figure ).

Changes and differences of respiratory capacity and nervous system

As demonstrated in Table , in the CG, there was a tendency for PEF and FEV₁ to decrease, accompanied by a significant increase in rRR. Conversely, in the EG, PEF and FEV₁ exhibited significant increases, coupled with a significant decrease in rRR. These results were evident in the interactions within every variable. Additionally, it's worth noting that there was a significant increase in all post-variables observed in the EG when compared to the CG, and this increase was characterized by a large effect size. The sympathetic nerve activation (SNA) displayed an inclination to increase in the CG, whereas in the EG, there was a tendency for SNA to decrease. These observations indicated a significant interaction between the two groups. The PNA exhibited contrasting results compared to SNA. As depicted in Table , there was a significant increase in the rHR for the CG, while the EG exhibited a tendency for rHR to decrease. In other words, there was a significant improvement in all post-variables observed in the EG when compared to the CG, and this improvement was characterized by a large effect size.

TABLE 2 Changes and differences of respiratory capacity and autonomic nervous activation.

Variables	Times	Groups	p
CG	EG	G	T	G*T
Respiratory factors
PEF (L/s)	Pre	4.07 ± 1.22	4.04 ± 0.73	0.050	0.002	0.001
Post	3.86 ± 1.25	4.97 ± 1.26
FEV₁ (L)	Pre	3.16 ± 0.69	3.26 ± 0.75	0.020	0.187	0.001
Post	2.92 ± 0.67	3.66 ± 0.76
rRR (reps/min)	Pre	17.23 ± 3.17	17.70 ± 3.27	0.046	0.699	0.001
Post	18.87 ± 2.39	15.67 ± 4.05
Nervous activation
SNA	Pre	7.52 ± 0.71	7.64 ± 0.73	0.017	0.404	0.001
Post	8.11 ± 0.57	7.23 ± 0.91
PNA	Pre	7.04 ± 0.73	7.11 ± 0.79	0.067	0.619	0.028
Post	6.87 ± 0.61	7.37 ± 0.64
rHR (bpm)	Pre	81.17 ± 11.62	81.16 ± 12.69	0.056	0.033	0.001
Post	88.65 ± 9.07	78.86 ± 9.66

When analyzing the delta percentages for PEF, the CG showed a decrease of 4.52 ± 14.64%, whereas the EG demonstrated an increase of 23.80 ± 27.56%. These changes were statistically significant (Z = −4.113, p = 0.001, η² = 0.301) between the two groups (Figure ). In the delta percentages for FEV₁, the CG exhibited a decrease of 6.83 ± 12.51%, while the EG displayed an increase of 14.29 ± 19.54%. These changes were statistically significant (Z = −4.344, p = 0.001, η² = 0.301) between the two groups (Figure ). Regarding the delta percentages for rRR, the CG demonstrated an increase of 11.67 ± 16.90%, while the EG exhibited a decrease of 8.64 ± 28.56%. These changes were statistically significant (Z = −3.408, p = 0.001, η² = 0.163) between the two groups (Figure ).

[IMAGE OMITTED. SEE PDF]

In the delta percentages for SNA, the CG exhibited an increase of 8.88 ± 13.25%, while the EG displayed a decrease of 5.16 ± 10.33%. These changes were statistically significant (Z = −4.005, p = 0.001, η² = 0.264) between the two groups (Figure ). Concerning the delta percentages for PNA, the CG demonstrated a decrease of 1.80 ± 9.40%, while the EG exhibited an increase of 4.61 ± 12.18%. These changes were statistically significant (Z = −1.985, p = 0.047, η² = 0.083) between the two groups (Figure ). When examining the delta percentages for rHR, the CG displayed an increase of 10.90 ± 16.34%, while the EG demonstrated a decrease of 1.95 ± 9.42%. These changes were statistically significant (Z = −3.666, p = 0.001, η² = 0.192) between the two groups (Figure ).

DISCUSSION

This study verified that engaging in plank exercises over a 12-week period can enhance respiratory function. Notably, the findings indicated that, beyond respiratory improvements, PET positively influences body composition, abdominal muscle strength and endurance, and induces changes in the ANS following exercise.

The plank exercise entails maintaining a straight body posture while supporting oneself on the ground (Calatayud et al., ). Recently, not only in homes and fitness centers but also in hospitals and other settings, the plank exercise is being adapted and utilized in various ways (Lee et al., ; Park et al., ). This PET is recognized for its ability to enhance the strength of the abdominal muscles within the core muscle group, thereby benefiting overall body movement (Byrne et al., ). Similar to the results of several other studies (Chase et al., ; Lee et al., ), the PET observed in this study demonstrated outstanding changes in indicators related to the body composition. Specifically, concerning body fat, both the CG and EG exhibited a statistically significant interaction effect after the 12-week experiment. Moreover, clear patterns of change were also evident in BMI and WHR. In contrast, muscle mass in the CG decreased by ∼13% after 12 weeks, while in the EG, it increased by ∼6%. Similarly, Ekstrom et al. () conducted electromyography tests on 19 male and 11 female participants after performing nine different exercises. Among these exercises, the side-bridge exercise was found to strengthen the participants' gluteus medius and external oblique abdominis muscles. In essence, the results of this study align with our study's application of three variations of plank exercises, showing an increase in the strength and endurance exerted on the abdominal muscles (Kim & Park, ). Kim et al. () proposed that incorporating isometric hip adduction into plank exercises could serve as an effective method to boost abdominal muscle activity. Additionally, Cortell-Tormo et al. () illustrated the impact of scapular and pelvic positions on the electromyography response of core muscle groups, underscoring their significant contribution to postural stabilization, particularly in posterior pelvic tilt positions. Core exercises like the roll-out plank (Cugliari & Boccia, ) and the suspended front plank (Calatayud et al., ) were also suggested as effective approaches for achieving heightened activation of the rectus abdominis (Oliva-Lozano & Muyor, ). To be specific, in the sit-up test conducted in this study, the CG exhibited a decrease of ∼13%, while the EG demonstrated an increase of ∼55%. This indicates a substantial improvement in abdominal muscle endurance over the 12 weeks of PET. Furthermore, when assessing the mean Dm of the rectus abdominis using TMG, the CG exhibited an increase of ∼36%, whereas the EG demonstrated a decrease of ∼34% after the 12-week experiment. On the other hand, the mean Tc of the rectus abdominis in the CG decreased by ∼13%, whereas in the EG, it increased by ∼20% after the 12-week experiment. In a related context, Wiewelhove et al. () found that Tc was extended, and there was a trend towards a decrease in Dm following 6 days of high-intensity interval training. Additionally, García-Manso et al. () reported a reduced Dm value following high-load resistance exercise. These results are consistent with our own findings. In other words, Tc was shorter in the CG, but it became prolonged in the EG after 12 weeks’ PET.

The plank exercises can be characterized as an exercise that heightens the engagement of core muscles and fosters core stabilization by preserving the body's neutral posture (Ekstrom et al., ). In particular, the development of abdominal muscles through the plank exercises develops the respiratory muscles around the abdominal cavity as well as the chest cavity, ultimately providing high-quality breathing ability during resting or exercise. This implies that the EG's increase of ∼24% in PEF, as well as the ∼14% increase in FEV₁ observed in our study, align with that interpretation. According to the results of this study, the PET for abdominis caused significant changes in the rRR. Specifically, the rRR of CG showed a tendency to increase (∼12%), whereas it showed a tendency to decrease (∼9%) in the EG. The plank exercises heightened activation is especially noteworthy not just in the deep muscles but also in the more superficial muscles. Kim et al. () similarly demonstrated a noteworthy increase in the thickness of both the oblique abdominal muscles and the gluteus maximus as a result of plank exercises. Interestingly, the increase in the thickness of the external oblique muscle was more pronounced compared to other exercise methods as indicated by Snarr and Esco () and Stevens et al. (). It suggests a more pronounced effect on trunk stabilization by augmenting the active muscular stiffness of the core, which is particularly relevant for bearing weight and maintaining stability in the trunk (Akuthota et al., ; Stanton & Kawchuk, ). In the previous study by Pettersen (), it was reported that during forced inhalation, in addition to the contraction of the diaphragm and intercostal muscles, auxiliary respiratory muscles such as the abdominal muscles and muscles around the spine also come into play. Paillard () even suggested that, in activities such as walking, respiratory muscles' involvement not only contributes to generating respiratory pressure but also influences postural stability. This suggests that exercises involving the abdominal muscles can have an impact on increasing forced vital capacity. The major muscles involved in forced inhalation and exhalation, as well as auxiliary muscles, are distributed throughout the torso. These muscles, in addition to their respiratory functions, continually interact through mutual neuromuscular control to maintain core stability in response to both internal and external environmental factors (Hull et al., ). Meanwhile, the pulmonary function test outcomes for the CG in this study indicated a decline in the younger subset without pre-existing diseases or a history of smoking. These findings align with prior research proposing that elements like a sedentary lifestyle, inadequate regular exercise, environmental influences, and genetic predisposition could impact lung function (Booth et al., ; Garcia-Aymerich et al., ). The results of this study hold significant significance as they essentially suggest that even individuals considered healthy may undergo alterations in lung function over time if they lack physical activity or are exposed to specific environmental factors.

It's important to highlight that the abdominal muscles are primarily under the control of the somatic nervous system, whereas the muscles involved in respiration around the abdomen are mainly regulated by the ANS originating from the medulla oblongata. Indeed, the ANS and the hypothalamic-pituitary-adrenal axis are two major systems that respond to stress, including stress induced by exercise (Ulrich-Lai & Herman, ). This study delved into the impact of plank exercises on these systems, exploring how they influence heart rate and abdominal muscles. Consequently, it is hypothesized that regular exercise may have a potentially positive impact on breathing capacity by affecting not only somatic nerves but also autonomic nerves activation. However, it is important to highlight that there have been no studies conducted to investigate these specific changes. Hence, the secondary objective of this study was to examine respiratory capacity and abdominal nervous tone in relation to the development of abdominis. In essence, this research sought to determine whether engaging in regular plank exercises would lead to a beneficial alteration in respiratory capacity through the development of rectus abdominisae muscles. Furthermore, it aimed to ascertain whether any observed changes in respiratory capacity could be attributed to ANS-related alterations. According to the findings of this study, after 12 weeks of PET, the sympathetic nervous system activity in the CG increased by ∼9%, whereas in the EG, it decreased by ∼5%. In contrast, the parasympathetic nervous system activity in the CG decreased by ∼2%, while in the EG, it increased by ∼5%. These results led to an approximately 11% increase in the rHR in the CG, while that of EG showed a decrease of about 2%. This observation is supported by the significant increases in SDNN and RMSSD following plank exercise. The plank exercise examined in this study demonstrated various benefits not only for lung function but also for overall physical function in healthy individuals. This suggests potential positive effects on lung function and physical performance in individuals with cardiopulmonary diseases (Cavaggioni et al., ), although further research is needed to substantiate this. Even if not following a standardized plank exercise, actively incorporating exercises to strengthen respiratory muscles, such as modified plank positions (e.g., adopting the pushup position with knees on the floor), could be considered post lung disease or lung-related surgery (Mereles et al., ; Yun et al., ). Such exercises may prove beneficial in enhancing cardiorespiratory function, lung compliance, and overall activity levels by improving abdominal muscle endurance and stiffness, as observed in this study.

CONCLUSIONS

The implementation of plank exercises for 12 weeks among young adults aimed at abdominis development yielded substantial modifications in body composition and abdominal functionality. These outcomes indicate that such exercises might bring about advantageous enhancements in respiratory capacity through adaptations in the ANS. Nonetheless, it is essential to recognize that this study has certain limitations, notably a small sample size and a lack of diversity in participants' demographic backgrounds. To enhance the validity and relevance of the findings, future researchers are urged to incorporate more extensive and diverse participant groups.

ACKNOWLEDGMENTS

This research did not receive support from an external grant.

CONFLICT OF INTEREST STATEMENT

No potential conflict of interest was reported by the authors.

References

Akuthota, V., A. Ferreiro, T. Moore, and M. Fredericson. 2008. “Core Stability Exercise Principles.” Current Sports Medicine Reports 7(1): 39–44. [DOI: https://dx.doi.org/10.1097/01.CSMR.0000308663.13278.69].