Effect of low- intensity continuous training on lung function and cardiorespiratory fitness in both cigarette and hookah smokers.

Background: The decline in cardiorespiratory fitness and lung function was higher in smokers. Training method could mitigate some of the negative consequences of smoking among smokers unable or unwilling to quit. Objective: To examine the effects of continuous training on lungs functional capability and cardiorespiratory fitness in smokers. Methods: Fifteen cigarette smokers, 14 hookah smokers, and 14 nonsmokers were assigned to low-intensity continuous training (20-30 minutes of running at 40% of maximum oxygen uptake (O 2 max)). Lung function and cardiorespiratory fit ness parameters were determined using respectively spirometer and treadmill maximal exercise test. Results: Continuous training improved forced expiratory volume in one second (FEV 1 ) and forced expiratory flow at 50% of FVC (FEF50 %) in all participants, smokers and nonsmokers (p < 0.05). In contrast, forced vital capacity (FVC) im provement was significant only among cigarette smokers (CS) (+1.7±2.21%, p < 0.01) and hookah smokers (HS) (+1.3±1.7 %, p < 0.05). Likewise, an improvement in cardiorespiratory fitness in both smokers groups without significant changes in diastolic blood pressure (DBP) for CS group and in velocity at maximum oxygen uptake (vO 2 max) for HS group. Conclusion: The low-intensity continuous training improves cardiorespiratory fitness and reduces lung function decline in both cigarette and hookah smokers. It seems to be beneficial in the prevention programs of hypertension. It could have important implications in prevention and treatment programs in smokers unable or unwilling to quit. et al. Effect of low- intensity continuous training on lung function and cardiorespiratory fitness in both cigarette and hookah smokers.


Introduction
The decline in fitness and lung function was significantly higher in smokers than in nonsmokers and could not be explained by differences in age and physical activity 1 . stances and harmful effects on cardiopulmonary function and antioxidant defense capacity and produced in some cases, the same effects as the cigarettes. Many previous studies suggest that smoking hookah has adverse effects similar to cigarettes [6][7][8] .
The findings of Saetta et al. 9 indicate that cigarette smoke affects not only the airways, but also the lung parenchyma and pulmonary arteries, causing irreversible obstruction of the branches. The main risk factor for this obstruction is smoking. Thus, and according to a Swedish study that was interested in subjects aged over 76 years, nearly 66.7% of smokers presented with a chronic obstructive pulmonary disease (COPD). This data suggests that COPD is a disease that affects the majority of smokers when they live long enough 10 . This pathology, according to WHO statistics 11 , is the cause of death that will increase more in industrialized countries and will become the third leading cause of death in 2020. In Tunisia, the death rate from smoking-related COPD is 84 % in men and 35% in women 12 .
Undoubtedly, the inhalation of cigarette or hookah smoke is associated with hypertension (HT), an increase in resting heart rate (HR) and at exercise and a decreased tolerance to the effort 13 . These effects are important firstly via the nicotine which causes an increase in myocardial oxygen demand and, secondly, by the functional anemia induced by the increased uptake of carbonmonoxide on the hemoglobin 14 . Therefore an increased tachycardia, decreased maximal oxygen consumption and harmful effect on peripheral muscle 15,16 with early anaerobic threshold 17 . These different effects result in reduced of effort tolerance 18,19 .
In order to prevent and slow the progression of hypertension and improve health and cardiorespiratory performance, several previous studies have suggested that physical activity can play a central role [20][21][22][23] . In this context, the Canadian medical association indicated that regular moderate physical activity (40% to 60% of O 2 max) for 50 to 60 minutes, 3-4 times a week was rec-ommended in the prevention or treatment of hypertension 24 . Fagard et al. 22 confirm these results, showing a significant reduction in systolic blood pressure (SBP) and diastolic blood pressure (DBP) for a repeated exercise 3-5 times per week for 30 to 60 min and 40% to 50% of O 2 max. In addition, other studies using different training periods showed significant improvements in O 2 max and in the rate of spontaneous walking 20 and a significant decrease in fatigue, and an improvement of physical ability and life quality 21 .
Exercise may have the potential to mitigate some of the negative consequences of smoking. Some studies, suggest that training at vigorous exercise intensity (60-85% of reserve heart rate) can be a useful aid to stop smoking 25,26 . To our knowledge there's lack of empirical evidence documented that such a method of physical activity has beneficial effects on physiological symptoms of smokers. Therefore, there is a need to expand the range of potentially effective harm reduction strategies among smokers unable or unwilling to quit smoking.
We would like discover a physical activity method to become a strategy so that it can improve cardiopulmonary performance and delay the lung function decline caused by smoking.
It seems therefore important to assess through a cohort study, the low-intensity continuous training effects on cardiorespiratory performance and lung function in sedentary adults, cigarette and hookah smokers.

Participants
A total of forty-three sedentary and healthy male smokers and non-smokers from the general community of Tunisia, which belongs to the public function (profession does not require physical exertion), volunteered to participate in this study and were recruited within pharmacology laboratory of the Faculty of Medicine, University of Sfax, Tunisia. The anthropometric characteristics of participant are shown in [ Table 1]. Participants were admitted to the training program after approval by a cardiologist physician. They were normolipidemic (fasting triglycerides < 1.7 mmol/L), nonobese. No subject used nutritional supplements or medications. Presence of any kind of disease (based on history, medical examination, and exercise stress testing), or FEV 1 / FVC% < 70% 27,28 , or involvement in regular physical activity or exercise program for the 12-month period preceding the visit day, were also exclusion criteria. On the basis of these criteria, 9 subjects from 52 were excluded. Eventually, 43 subjects were included in subsequent tests and they were admitted to the training program.
After receiving a complete verbal description of protocol, risks and benefits of the study, subjects provided written consent to an experimental protocol approved by the Research Ethics Committee of the Faculty of Medicine, University of Sfax, Tunisia. Smokers were instructed to refrain from smoking at least one hour prior to reporting to the laboratory as suggested by Dietrich et al. 29 Cigarette and hookah smokers were recruited according to the number of cigarettes and hookah per day and how long they had been smoking. We considered cigarette smokers all subjects with consumption greater or equal to 10 pack-years (PY) and an average score of tobacco dependence of 8.12 ±1.41, measured by the Fagerström nicotine dependence test 30 . We quantified hookah consumption, as in the study of Kiter et al. 31 , in hookah-years (HY) and kg of cumulative tobacco. The tobacco used in a single hookah session weighs between 10 and 25 grams 32 . Regular hookah smokers are those having tobacco consumption greater or equal to 5 hookah-years (HY) 33 .
Participants were divided into three groups, and they performed a low-intensity continuous training program 3 times a week for 12 weeks. A cigarette smokers group (CS) (n= 15); a hookah smokers group (HS) (n = 14) and another nonsmokers group (NS) (n = 14). All subjects were subjected to a spirometric assessment and physical test session before and after the training program. The session includes lung function and treadmill maximal exercise test. All these measurements were performed by the same examiners to avoid methodological errors.

Anthropometric measurements
Body weight was measured to the nearest 100 grams with a calibrated electronic scale (TANITA TBF.350 model), and height was measured to the nearest 1mm with a fixed stadiometer. Body mass index (BMI) was calculated with the formula: [BMI (kg.m -2 ) = Weight (kg) / Height 2 (m 2 )].

Calculation of recovery index
Heart rate was recorded every minute during 5 minutes after the exercise test. Calculation of recovery index is based on two data: Calculation of the regression index and the correlation index.

Recovery index = Regression index x correlation Index
Lung function assessments A portable spirometer (MIR Spirobank G USB Spirometer, Rome, Italy) was used to assess smokers lung function. Standard procedure requires forced vital capacity (FVC) and forced expiratory volume in one second (FEV 1 ) and should be measured from a series of at least three forced expiratory curves 34 . This study requiredparticipants to perform three correct manoeuvres. Participants completed the spirometry assessment seated with a nose clip attached, the mouthpiece is placed into the mouth, lips and teeth around the mouthpiece to form a tight seal and breathe out hard and quickly until all air is expelled. It is vital that participants inhale completely, to total lung capacity, and continue to exhale until they have fully emptied their lungs (to residual volume). Pulmonary function variables included: FVC, FEV 1 , FEV 1 /FVC ratio, FEF 50% and FEF 25-75% . Results were expressed as percentages of the predicted value to allow comparison of results across participants.
Physical fitness assessment V̇ O 2 max and max heart rate measurements during exercise were examined through treadmill maximal exercise test (COSMED Pulmonary-Function Equipment 37 Via dei Piani di monte Savello I-00040 Rome ITALY). This dynamic and maximum test, untilfatigue, consists in increasing the speed of 1kmh -1 every 2 min, after warm up of 5 min with a 6 kmh -1 speed until the participant could no longer continue. V̇ O 2 max is reached when oxygen consumption remains at steady state despite an increase in workload. Heart rate using (Polar Electro Oy, Kempele, Finland) was monitored throughout the test and was recorded at the conclusion of every two-minute stage. The oxygen consumption (V̇ O 2 ) was continually recorded and measured in real time using oxygen analyzer (Fitmate, version 1.2 PRO COSMED). At the end of the test a detailed report will be printed. Verbal encouragement was provided throughout the test to ensure that the maximal effort was achieved.

Continuous training protocol
Subjects of three groups underwent a continuous training program during a 3-months period. Training was performed continuously for 20 minutes (first month), 25 minutes (second month) and 30 minutes (third month), three times per week at an intensity of 40% of V̇ O 2 max, on race track of 400 m at the Institute of Sport of Sfax, Tunisia. The cones placed and spaced 20 meters on a race track. At each beep, the subject must reach the following cone. All warm-ups before training should be between 50% and 60% of maximum heart rate for a period of about 10 minutes. It was asked of participants to run with a continuous rhythm respecting sound beeps and the requested time throughout the training session. The training load was insured by time and traveled distance and controlled by sound beeps. (T: the time between two cones; d: distance between two cones; V: proposed velocity). The load increase during the training period was provided by the increase in working time and the distance covered in each session. All participants successfully completed the training period and no absences were recorded during all sessions. In addition, we have verified that there was no involvement in physical activity or exercise program throughout the 12-week training period.

Statistical analysis
All statistical tests were processed using STATISTICA Software (StatSoft, France). The data was expressed as mean ± SD (standard deviation). After normality verification with the Shapiro-Wilk's w test, and homogeneity of variances with Levene's test, parametric tests were performed. One-way ANOVA was used to indicate inter group differences in the baseline subjects' characteristics. Inter and intra-group comparisons of the variables were made by two-way ANOVA (group vs. training) with repeated measurements. Least Significant Different (LSD) post-hoc analysis was used to identify significant group differences that were indicated by one-way and two-way ANOVA. A probability level of 0.05 was selected as the criterion for statistical significance.

Results
Before and after training, we did not observe any significant difference in body-weight and BMI values between the nonsmoker and smoker groups ( Table 2). However, most of the spirometric values were higher in all of non-smokers subjects and significantly different to those of cigarette and hookah smokers before our training program. We reported in table 3 the spirometric values in percentages of the predicted value of our entire population before training. Furthermore, the FEV 1 of CS group tends to be lower than of NS group, but the difference was not significant. The HS group also showed a low level of FEF 50% compared to the two groups CS (P < 0.05) and NS (P < 0.01).

Training effect on lung function
The improvement rate in the respiratory functional exploration results after the training period, is summarized in  The three-month continuous training period, induces changes in respiratory parameters, however, they vary according to the group. This change did not show significant differences in PEF, FEV 1 /FVC and FEF 25-75% measured after the training period.
The training period produces an increase in FVC of all our participants; however, this improvement was significant only among smokers. It is of the order of +1.7 ± 2.21% (p <0.01) for CS group and +1.3 ± 1.7% (p <0.05) for HS group. In addition, all our subjects ben-efited a significant increase in FEV 1 after the training program (Table 3). Thus, the improvement was +1.83 ± 2.69% of NS group (p <0.05), +1.9 ± 2.13% (p <0.05) in CS group and +1.7 ± 2% (p <0.05) for the HS group. The FEF 50% of the three groups NS, CS and HS follows the same trend as the FEV 1 , with significant differences (p <0.05), representing increases of +1.08 ± 2.19%, +1 ± 2.36% and +1.6 ± 2.5%, respectively.
The (LSD) post-hoc test showed that the two groups CS and HS had resting HR, SBP and DBP similar and significantly higher than those of nonsmokers (p < 0.001). Similarly, no significant difference in these values was revealed between the two smoker groups.
Regarding the V̇ O 2 max, v V̇ O 2 max and recovery index, the statistical analysis showed significant differences between the two smoking groups (p < 0.001, p < 0.001 and p < 0.01, respectively). Similarly, we have registered in the values of v V̇ O 2 max and V̇ O 2 max, significant differences between smoker and nonsmoker groups (p < 0.001). The recovery index was better in nonsmokers compared to cigarette smokers (p < 0.001) and in cigarette smokers versus hookah smokers (p < 0.01).

After the continuous training period, participants
showed different improvements (Table 6). Significant changes in resting HR for the three groups NS, CS and HS were observed after training, with declines of -1.75 ± 2 bpm (P <0.05), 2.5 ± 3 4 bpm (P <0.01) and -2.2 ± 3.1 bpm (P <0.05), respectively. Similarly, there was a decrease of SBP for both smoker groups (P <0.05).
In contrast, the decrease in DBP was significant only for the HS group (P <0.01), by a decrease of -2.4 ± 3.4 (mm Hg).
The low-intensity continuous training induced also significant increases of vO 2 max for subjects of NS and CS groups and O 2 max for the subjects of the CS and HS groups. Finally, the recovery index results showed most improved recoveries for the subjects of the three groups (NS: + 0.44 ± 0.4; CS: + 0.47 ± 0.6; HS: + 0 98 ± 0.8). Table 6. Improvement rate (Δ) of cardiorespiratory values in Pre vs. Post training program Parameters HR = heart rate; bpm = beats per minute; SBP = systolic blood pressure; DBP = diastolic blood pressure; vO2max = velocity at maximum oxygen uptake; O2max = maximum oxygen uptake; ns = not significant; †, † †, † † † = significant differences in Pre vs. Post training program at p < 0.05, p < 0.01, p < 0.001, respectively.  On the other hand, low-intensity continuous training induced a significant decrease in blood pressure and resting HR. The result is a significant reduction in SBP of -2% for CS group and -1.8% for the HS group, and only significant decrease of -2.5% of DBP in HS group (Fig.1)

Fig 2. Improvement rate in percentage (Δ%) of lung function parameters in Pre vs. Post program
Exercise is an important component of pulmonary rehabilitation and may be associated with physiological and psychological benefits 49 . Although the respiratory rehabilitation programs improve the quality of life and some physiological measures, the improvements in FEV 1 levels were not reported consistently 2 . In our study, all participants, smokers and nonsmokers had higher levels of FEV 1 and FVC after this continuous training program. The improvement was about +2% and from +0.9% to +2%, respectively (Fig.2). Our results confirm the findings of Mehrotra et al. 50 , who reported that lung function was better in most active subjects than sedentary subjects. However, there was no significant difference of FEV 1 /FVC in Pre vs. Post program. This is explained by the pulmonary efficiency weakness of our participants. These results are consistent with the findings of Cheng et al. 51 .
The cigarette smoker participants who had the lowest FVC before training protocol, tended to have the best improvement among the three groups after training (≈ +2%). This may suggest that the respiratory system response to physical activity among CS group is higher than in HS or NS groups.
In summary, our analysis suggests that a low-intensity continuous training program was associated with an improved cardiorespiratory fitness and aspect of physiological wellness. This improvement was more marked in smokers than in nonsmokers, but the respiratory func-

Conclusion
The present study demonstrates that low-intensity continuous training improves cardiorespiratory fitness.
Intensity and training volume have been closely monitored to demonstrate the continuous exercise importance in reducing lung function decline in cigarette and hookah smokers. Likewise, physical training with continuous exercises seems to be beneficial in hypertension prevention. Finally, these results could have important implications in prevention and treatment programs in both cigarette and hookah smokers unable or unwilling to quit.
Practical implications -Smokers before training have a reduced lung function and worst cardiorespiratory fitness compared with no smokers.
-Significant improvements in FEV 1 and FEF50 % among smokers and nonsmokers after training.
-Significant improvements in FVC only in smokers -Improvement in cardiorespiratory capacity is significantly higher in smokers than in nonsmokers.
-Smokers unable to quit smoking could focus at practicing leisure time physical activity regularly to reduce the decline of lung function and cardiorespiratory capacity.

Limitations of the study
The lack of a control group may be considered a limitation of the present study (smokers group follow the same daily activity during the same training period). I also think that future research should include a group of passive smokers. Likewise, the relatively small sample size could have limited our ability to detect group differences in the chosen parameters. This is indeed a limitation of this work, and should be considered relative to our findings.