Effect of abdominal muscle training

Original article Arch Argent Pediatr 2016;114(5):434-440 / 434 a. Exercise Biology Effect of abdominal muscle training on Lab (Laboratorio de respiratory muscle strength and forced Biología del Ejercicio, expiratory flows in sedentary, healthy adolescents LBE), School of Kinesiology, School Iván Rodríguez-Núñez, Kinesiologista,b,c,d,e, Ximena Navarro, Kinesiologistb, of Health Sciences, Darwin Gatica, Kinesiologistc,d,e and Carlos Manterola, M.D.e,f,g Universidad San Sebastián, Concepción, ABSTRACT It has been observed that Chile. Introduction. Respiratory muscle training is respiratory muscle training (RMT) the most commonly used method to revert may be effective to mitigate the b. Master Program in respiratory muscle weakness; however, the deterioration in muscle strength and Cardiorespiratory effect of protocols based on non-respiratory endurance,5-7 and peak cough flow Kinesiology, School of maneuvers has not been adequately studied in the (PCF) in children with neuromuscular Kinesiology, School pediatric population. The objective of this study disorders.6 However, there is still of Health Sciences, was to establish the effect of abdominal muscle no consensus on which are the most Universidad San training on respiratory muscle strength and effective training protocols to achieve Sebastián, Concepción, forced expiratory flows in healthy adolescents. function targets.8 In the clinical Chile. Methods. This was a quasi-experiment. The setting, RMT using a threshold valve sample was made up of healthy adolescents (Threshold®) is the most widely used c. School of Kinesiology, divided into two groups: an experimental group modality;7 however, it is an indirect School of Health, who completed eight weeks of active abdominal and non-specific method to achieve Universidad Santo muscle training, and an equivalent control muscle strengthening. Tomás, Concepción, group. The following indicators were measured: Chile. abdominal muscle strength, maximal inspiratory From a physiological perspective, pressure, maximal expiratory pressure (MEP), the performance of respiratory d. Research Task Force peak expiratory flow, and peak cough flow, muscles is affected by both chest and in Cardiovascular before and after protocol completion. A value abdominal muscles. Thus, it has been and Respiratory of p < 0.05 was considered significant. demonstrated that several exercise Health IDEAS-CVR, Results. All studied outcome measures increased modalities focused on abdominal Concepción, Chile. significantly in the experimental group but only muscles and upper and lower limbs MEP increased in the control group. In addition, stimulate the diaphragm, increase e. Doctoral Program a higher MEP was observed in the experimental transdiaphragmatic pressure, and in Medical Sciences, group compared to the control group at the end induce different levels of abdominal School of Medicine, of the protocol, together with a greater increase muscle fatigue.9,10 Universidad de La in MEP and peak expiratory flow. Finally, the Frontera, Temuco, increase in MEP was associated with an increase This precedent underscores the Chile. in cough peak flow in the experimental group potential effect of training protocols but not in the control group. based on non-respiratory exercises f. Department of Conclusion. After eight weeks of abdominal on muscle strength and pulmonary Surgery and Center muscle training, MEP and peak expiratory flow function parameters. Hence, several of Excellence for increased in healthy (sedentary) adolescents. studies conducted in adults have Morphological and Such effects were associated with intervention- demonstrated that non-respiratory Surgical Studies induced increases in cough peak flow. maneuvers, e.g. sit-ups, may increase (Centro de Excelencia Key words: respiratory muscle training, peak respiratory muscle strength.11 In en Estudios expiratory flow, respiratory muscle, abdominal addition, it has been observed that Morfológicos y training, cough. abdominal muscle training protocols, Quirúrgicos, CEMyQ), both passive (based on electrical Universidad de La http://dx.doi.org/10.5546/aap.2016.eng.434 stimulation)12,13 and active, may be Frontera, Chile. effective to improve respiratory INTRODUCTION muscle strength and forced expiratory g. Center for Bioscience Respiratory muscle weakness flows.14 However, the effect of this Research, Universidad type of training strategy has not been Autónoma de Chile, is one of the major functional adequately studied in the pediatric Chile. consequences suffered by children population.14 with chronic respiratory disease E-mail address: (CRD).1-3 It leads to alveolar Iván Rodríguez Núñez, hypoventilation, microatelectases, Kinesiologist, and failure of the cough mechanism, [email protected] and these factors increase the risk for Funding: respiratory failure.4 This study was funded by the School of Kinesiology of Universidad San Sebastián, Concepción, Chile. Conflict of interest: None. Received: 11-15-2015 Accepted: 04-20-2016

Effect of abdominal muscle training on respiratory muscle strength and forced expiratory flows in sedentary, healthy adolescents / 435 Therefore, the goal of this study was to assess pressure (MIP), measured during a maximum the effect of abdominal muscle training on inspiratory effort, from residual volume, and respiratory muscle strength and forced expiratory maintained for at least one second, and maximal flows in sedentary, healthy adolescents. expiratory pressure (MEP), measured during a maximum expiratory effort, from total lung MATERIAL AND METHODS capacity, and maintained for at least one second. This was a quasi-experimental study with an An aneroid vacuum/pressure gauge NS 120- TRS, calibrated in centimeters of water (from 0 equivalent control group. Preliminary results ttoak-e12m0,eaansudrfermomen0tst.oM+I1P20ancdmMH2EOP) was used to from the experimental group were reported in a values were previously published pilot study.14 expressed as habpseoalukteexvpaliuraetso(rcymfHlo2Ow).(1P5 E Also, bot F) and Sample: Healthy adolescents attending a peak cough flow (PCF) were measured using public school from the city of Concepción, Chile a flow meter (Mini-Wright®; Clement Clarke were selected by convenience, with no gender International, Essex, England). PEF was measured restrictions. Inclusion criteria included sedentary, with the subject standing and wearing a nose clip, healthy adolescents (who did physical activity and the indication was given to blow with the for less than 60 minutes twice a week) and who greatest possible force from total lung capacity. had not done any muscle training in the past The test was performed at least three times month. Exclusion criteria were the presence of and a maximum of eight times; the highest cardiorespiratory or musculoskeletal disease reproducible value in three attempts with a and smoking. Eligibility criteria were verified difference no greater than 10% between each during an interview with every study participant, value was recorded.16 PCF was measured with and using a checklist completed by parents the subject seated, and the indication was given to before their children were enrolled in the study. inhale as deeply as possible and then to perform No cardiovascular health checks, such as an a maximum coughing effort through the flow echocardiogram or stress test, were done before meter. Results were expressed in liters/minute.17 the experimental protocol. Both study participants In addition, as a measure of effectiveness of and their parents signed an informed assent abdominal muscle training (AMT), abdominal and consent, respectively, and the study was muscle strength (AMS) was established. AMS was authorized by the Institutional Ethics Committee. measured using the sit-up test, a functional test The study was conducted between June 2014 and that has been widely used in both healthy subjects May 2015. and patients with chronic respiratory disease.14,18 The subject initially lies supine with knees bent at The sample size was estimated based on the 90°, feet on the floor, and hands on the side of the previously published methodology.14 An 80% head. An assistant helps the subject keep his/her statistical power and a 5% type I error were feet on the mat. At this time, the examiner gives considered; therefore, the minimum sample the indication to start the test, which consists needed for this study was 17 subjects per group. in performing the maximum number of trunk In this context, the experimental group was first flexion-extension repetitions in 30 seconds. selected as per inclusion criteria, and then the Training protocol: AMT was conducted as per control group was established. Both groups were Rodríguez et al.14 Briefly described, the protocol paired based on biodemographic characteristics consisted in training each abdominal muscle (weight, height, age, and gender) and pulmonary group during eight weeks. During each exercise function outcome measures (respiratory muscle session, all muscle groups were trained actively, strength and forced expiratory flows) before the with no external aid, reaching between 200 and 300 protocol. repetitions per session. Sessions took place twice weekly, each lasting 45 minutes. On their side, Outcome measures: Age, gender, height, subjects in the control group were asked to do their and body weight were recorded before study normal activities and were monitored during the initiation. Weight and height were measured eight weeks that the experimental protocol lasted. using an analog scale and a tape measure, and In the end, both pulmonary function and AMS expressed in kilograms (kg) and centimeters (cm), were measured one day before and one day after respectively. the training protocol in both study groups. Outcome measures of interest included respiratory muscle strength and forced respiratory flows. Respiratory muscle strength was established based on maximal inspiratory

436 / Arch Argent Pediatr 2016;114(5):434-440 / Original article Analysis schedule: The MedCalc Statistical RESULTS Software, version 14.12.0 (MedCalc Software bvba, General characteristics of the sample: Ostend, Belgium; http://www.medcalc.org, 2014) was used to do an exploratory data analysis, and The experimental group was made up of normality was measured using the Shapiro-Wilk 17 subjects (8 boys) and the control group test. Once the normal distribution of data was included 23 subjects (9 boys). Age, gender and verified, descriptive statistics were established anthropometric characteristics are detailed in using average and standard error of the mean Table 1, and were similar in both study groups. (SEM). Also, no significant difference was observed The absolute value of pulmonary function in terms of respiratory muscle strength (MIP and parameters was compared between study groups MEP), forced expiratory flows (PEF and PCF), using the t test for independent samples and also and AMS between groups before starting the for paired samples, to assess differences between training protocol (Table 2). absolute values before and after the intervention. Effect of training: All subjects completed the In addition, the Mann-Whitney U test was protocol without incidents. No subject from used to compare the size of variations in outcome either group was excluded from the protocol measures of interest between the control and the due to non-adherence or health conditions. experimental groups. The association between Following the training program, only subjects in dichotomous outcome measures was assessed the experimental group increased the number of using a χ² test. sit-ups done in 30 seconds by 21.7% (p= 0.0001). Finally, a linear regression analysis was done Both respiratory muscle strength and forced to establish the association between the size of the expiratory flows increased significantly from effect on MEP and forced expiratory flows (PEF baseline in the experimental group. Thus, MIP and PCF). increased 16.8% (p= 0.006) and MEP, 50.2% (p < 0.0001). PEF rose 8.4% (p = 0.003) and PCF, A value of p < 0.05 was considered significant. 9.1% (p= 0.015). On their side, these outcome Table 1. Baseline characteristics of the sample Outcome measures Control group (n= 23) Experimental group (n= 17) p value Gender (M/F) 9/14 8/9 0.8588 Age (years old) 15.4 ± 0.1 15.2 ± 0.1 0.1609 Height (cm) 161.4 ± 1.9 162.9 ± 1.7 0.5601 Weight (kg) 61.6 ± 2.3 56.6 ± 2.4 0.1537 M: male; F: female. Results are described as average ± standard error of the mean. Table 2. Respiratory muscle strength and forced expiratory flows before and after training Outcome measures Control group (n= 23) Experimental group (n= 17) p value Pre-MIP (cmH2O) 99.6 ± 5.9 96.5 ± 4.3 0.6828 Post-MIP (cmH2O) 108.1 ± 4.1 112.8 ± 4.3** 0.4051 Pre-MEP (cmH2O) 84.5 ± 3.9 0.0799 Post-MEP (cmH2O) 93.5 ± 2.0*** 69.4 ± 3.8 0.0125 Pre-PEF (L/min) 416.5 ± 19.9 104.3 ± 3.3*** 0.4379 Post-PEF (L/min) 424.5 ± 15.8 424.3 ± 22.6 0.0759 Pre-PCF (L/min) 382.2 ± 18.5 457.0 ± 19.0** 0.4898 Post-PCF (L/min) 410.3 ± 13.7 401.2 ± 19.0 0.2520 Pre-sit-up test (n° reps/30 s) 23.3 ± 1.4 437.6 ± 19.2* 0.4592 Post-sit-up test (n° reps/30 s) 23.4 ± 1.7 0.0039 23.5 ± 1.0 28.6 ± 0.8*** MIP: maximal inspiratory pressure, MEP: maximal expiratory pressure, PEF: peak expiratory flow, PCF: peak cough flow, sit-up test: number of repetitions done in 30 seconds. Results are described as mean ± standard error of the mean. * < 0.05, ** < 0.01, *** < 0.001.

Effect of abdominal muscle training on respiratory muscle strength and forced expiratory flows in sedentary, healthy adolescents / 437 measures increased mildly in the control group; the control group: 0.7, 95% CI: -1.7 to 3.18) (Table 3 only MEP showed a significant rise (+16%, - Figure 2). No association was observed between p= 0.0004). MEP and PEF gains (p= 0.12). The inter-group analysis following the DISCUSSION intervention showed a greater respiratory muscle The main findings of this study revealed that strength and higher forced expiratory flows in the experimental group; however, a statistically AMT was effective to increase respiratory muscle significant difference was observed only for MEP strength, especially, expiratory muscle strength (+14.2%, p = 0.0125). (MEP) and PEF. In turn, training-induced MEP gains were associated with increases in cough Also, the analysis of the effect size on function in the experimental group. studied outcome measures indicated, for the experimental group, a greater functional gain These results are consistent with those across all outcome measures compared to the obtained in studies that assessed the effect of control group; for the latter, functional gain was non-respiratory maneuvers on respiratory muscle statistically significant only in terms of MEP performance. Strongoli et al. demonstrated that (p < 0.0001) and PEF (p= 0.02) (Figure 1). maneuvers such as standing and trunk flexion from a sitting and supine position involve the The linear regression analysis of gains in respiratory muscles and significantly increase MEP and forced expiratory flows (PEF and PCF) diaphragmatic pressure to such a level as showed a positive correlation between MEP to induce a training stimulus.9 DePalo et al. and PCF (r= 0.66, r2= 0.44, p= 0.0038) in the showed that training biceps and trunk flexion experimental group. This was not observed in the for 16 weeks was associated with significant control group (slope for the experimental group: increases in MIP (+27.6%) and MEP (+36.9%).11 2.4, 95% confidence interval (CI): 0.9-3.9; slope for Figure 1. Effect size induced by abdominal muscle training compared to the control group D MIP D MEP Control Control Experimental Experimental D PEF D PCF Control Control Experimental Experimental A shows the effect on maximal inspiratory pressure (MIP); B shows the effect on maximal expiratory pressure (MEP); C shows the effect on peak expiratory flow (PEF); and D shows the effect on peak cough flow (PCF). * p < 0.05, ** p < 0.0001

438 / Arch Argent Pediatr 2016;114(5):434-440 / Original article Our study evidenced that doing specific exercises In addition, AMT significantly increased PEF to strengthen abdominal muscles would mainly and PCF in the experimental group; however, favor muscles involved in active exhalation; the effect size was meaningfully superior to the however, results were not conclusive regarding control group only in terms of PEF. Nevertheless, the effects on inspiratory muscles. a significant association was observed between MEP and PCF gains. In this setting, it has been Similar results have also been reported previously observed that six weeks of abdominal with conventional respiratory muscle training muscle electrical stimulation together with protocols, which have proven to be effective voluntary cough maneuvers may be effective to to improve respiratory muscle strength and increase PCF and abdominal and gastric pressures physical fitness in healthy, untrained subjects during forced expiration.13 On their side, Gollee and athletes.19,20 In the clinical setting, it has et al. observed that superficial abdominal muscle been reported that inspiratory muscle training functional stimulation increased PCF and tidal improves both respiratory muscle strength and volume in tetraplegic subjects.21 The linear endurance in children with neuromuscular regression analysis done in our study estimated disorders,5 and even that home-based that per every Lcm/mHi2nO, of increase in MEP, PCF (unsupervised) training protocols induce increased 2.4 and this confirms both increased respiratory muscle strength and have outcome measures are closely dependent on positive effects on force expiratory flows.6 Table 3. Linear regression analysis between the size of the effect on maximal expiratory pressure and peak cough flow Group Slope* Intercept r r2 P value Experimental group 2.5 (de 0.9 a 3.9) -49.5 (de -107.3 a 8.4) 0.66 (de 0.27 a 0.87) 0.43 0.0038 22.1 (de -20.3 a 64.4) 0.13 (de -0.29 a 0.51) 0.02 0.5486 Control group 0.72 (de -1.7 a 3.2) Results are described as absolute value and 95% confidence interval. Figure 2. Linear regression between the size of the effect on peak cough flow and maximal expiratory pressure D PCF Experimental Control D MEP PCF: peak cough flow; MEP: maximal expiratory pressure. *Y axis outcome measure: gain in peak cough flow induced by training; X axis outcome measure: gain in maximal expiratory pressure induced by training.

Effect of abdominal muscle training on respiratory muscle strength and forced expiratory flows in sedentary, healthy adolescents / 439 each other. In biomechanical terms, during cough Acknowledgments mechanism, expiratory muscles play a critical We would like to thank all adolescents and role both during relaxation in the inspiratory phase and during isometric contraction in the their parents for agreeing to participate in this compression phase, which allows raising intra- study and the school for letting us conduct this abdominal pressure up to 300 mmHg.22 project. One of the limitations of this study is that arbitrarily establishing an equivalent control Also, to the Kinesiology students who helped group with no randomization may be a us with this research line. potential source of bias. In this context, pairing was attempted based on relevant parameters REFERENCES (anthropometric outcome measures and respiratory function); however, it is not possible 1. 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