In the past years, researchers have focused on the cardiorespiratory responses to maximal effort during aquatic incremental tests, often comparing these with dry-land measurements. Activities such as exercise on aquatic cycle ergometers (14,15,17,23,31), water-walking (19,32,36), and deep-water running (9,13,19,20,24–26,35,36) have been widely investigated in the literature. From these studies, it is well-established that the maximal heart rate (HRmax) in the aquatic environment is lower than it is on dry land, as a result of the hydrostatic effects of water (34,38). However, comparisons of maximal oxygen uptake (V[Combining Dot Above]O2max) between aquatic and dry-land exercises are not consistent with some studies showing similar values (14,15,31,32) and others showing lower values during aquatic exercise (9,19,20,26,36). Likewise, studies that compared the maximal ventilation (VEmax) between environments reported similar (20,35), greater (32), or lower responses (9,13,19,26) in aquatic protocols compared with those performed on dry land. Potential reasons for these divergences are differences in the protocols used, the muscle groups recruited, and the exercise patterns performed during the tests. For this reason, these values cannot be directly applied to different water aerobic exercises, and the literature is sparse regarding the maximum cardiorespiratory responses during this type of aquatic exercise (2,18).
In the study of water aerobics, many experiments have investigated the submaximal cardiorespiratory responses when different exercises were performed at different cadences (3–5,10,11,28,30). Significant differences have been observed in oxygen uptake (V[Combining Dot Above]O2) and heart rate (HR) when comparing different types of water aerobic exercises, and increases in these responses were verified as the cadence increased. To examine the effects of different intensities, studies by Alberton et al. (4) and Pinto et al. (28) investigated stationary running (SR) performed at submaximal cadences of 60, 80, and 100 b·min−1 and reported intensities ranging from 24 to 46% of V[Combining Dot Above]O2max. To compare water aerobic exercises, a study by Raffaelli et al. (30) investigated the cardiorespiratory responses during different exercises at cadences ranging from 110 to 140 b·min−1. The authors reported intensities ranging from 20 to 59% of V[Combining Dot Above]O2max for SR, jumping jacks, and cross-country skiing (CCS), and from 40 to 84% of V[Combining Dot Above]O2max for frontal kick (FK) and sideways kick exercises. It should be noted that the cadences selected in the previously mentioned studies resulted in low relative intensities, evidenced by the percentage of V[Combining Dot Above]O2max achieved. Notwithstanding, it is important to highlight that these values for the percentage of V[Combining Dot Above]O2max for the above-mentioned studies were based on maximum tests performed on dry land.
The different maximum cardiorespiratory responses between aquatic and dry-land exercises are well known; thus, when analyzing these responses during submaximal cadences, these values should be determined relative to the maximum values obtained during aquatic tests performed during specific water aerobic exercises. However, as mentioned above, the literature is sparse regarding HR, V[Combining Dot Above]O2, and ventilation (VE) responses to these exercises at maximum effort (MAX). Alberton et al. (2) analyzed V[Combining Dot Above]O2 responses during aquatic incremental tests performed during 3 water aerobic exercises (FK, SR, and jumping jacks) compared with a treadmill on land (TL). In addition to the V[Combining Dot Above]O2 at MAX, these values were also determined at the intensities corresponding to the first ventilatory threshold (VT1) and second ventilatory threshold (VT2). Lower V[Combining Dot Above]O2 values were found for the aquatic exercises at all intensities with approximately 50% of V[Combining Dot Above]O2max observed at VT1 and 70% of V[Combining Dot Above]O2max at VT2 for all aquatic exercises. However, other cardiorespiratory parameters such as the HR and VE were not evaluated in this study.
Because water aerobics is a popular physical activity for improving health and well-being, it is important to understand the cardiorespiratory responses to different water exercises compared with dry land exercises during maximum tests. Currently little has been reported in the literature regarding these parameters. In addition, it is important to determine the ventilatory thresholds because these intensities demarcate the predominantly aerobic training zone and can be used to adjust the aquatic fitness training sessions to achieve this intensity. Additionally, it is particularly important to further explore changes in HR at these intensity levels because HR is an indicator of intensity control that is widely used to optimize a water aerobics program. Therefore, the purpose of the present study was to compare the cardiorespiratory responses of young women at VT1, VT2, and MAX between incremental tests using water aerobic exercises and TL. It was hypothesized that HR, V[Combining Dot Above]O2 and VE values would be similar among the water aerobic exercises and greater with TL at all intensities. Furthermore, when expressed as percentages of the maximum, these variables were expected to be similar at VT1 and VT2 during the 4 different protocols.
Experimental Approach to the Problem
To verify the V[Combining Dot Above]O2, VE, and HR responses to different water aerobic exercises compared with TL, data were collected over a 5-day period for each participant. On the first day, anthropometric measures were taken and the subjects were familiarized with the protocols. At the following 4 sessions, the protocol was performed with the execution of one of the aquatic exercises (SR, FK, or CCS) or TL exercise to maximal exertion in a randomized order. The participants' V[Combining Dot Above]O2, VE, and HR were measured during all protocols, and the values corresponding to VT1, VT2, and MAX were determined.
Twenty physically active and healthy women volunteered to take part in this study (mean ± SD: age, 24.0 ± 2.5 years; height, 163.3 ± 6.7 cm; body mass, 60.0 ± 6.7 kg; and fat mass, 29.3 ± 5.0%). The participants had engaged in water aerobics for at least 3 months; aged between 18 and 28 years; had a regular menstrual cycle; were free of any musculoskeletal, bone and joint, or cardiac and pulmonary diseases; and were not taking any medication. To participate in the study, all participants were required to read and sign a written informed consent containing all information about the procedures and potential risks involved in participation. The study was approved by the Local Research Ethics Committee (2008097), and is in accordance with the Declaration of Helsinki.
During the initial session, participants' physical characteristics were assessed. Body mass and height measurements were obtained using an analogic medical scale and a stadiometer (Filizola, Sao Paulo, Brazil). To estimate body density, skinfolds were measured using a plicometer (Lange, Cambridge, United Kingdom), according to the protocol proposed by Jackson et al. (22). Body fat was subsequently calculated using the Siri equation (33). Each subject performed a familiarization session for the 3 water aerobic exercises at increasing cadences while wearing the gas analyzer mask. In addition, all details that needed to be considered when performing the exercises were explained, including the range of movement and other considerations.
Stationary running, FK, and CCS exercises, which are commonly used during water aerobics classes and have been previously investigated in the literature (2–5,28–30) were selected for the study. All exercises were divided into 2 phases with each segmental action (flexion or extension) performed in 1 beat. Stationary running (Figure 1A) is an exercise performed with a single support and flight phase. The first phase corresponds to flexion of the right hip and knee to 90° angle, starting the flight phase, followed by right hip and knee extension until the support phase. Frontal kick (Figure 1B) is also characterized by a single support and flight phase. The first phase corresponds to flexion of the right hip to 45° angle, knee extension, and ankle plantar flexion, starting the flight phase, followed by extension of the right hip and ankle dorsiflexion until the support phase. In contrast, CCS (Figure 1C) is characterized by bipedal support, without a flight phase, and the changes in the foot-support phases are performed by sliding the feet. The first phase corresponds to flexion of the right hip to 60° angle, knee semi-flexion, and ankle dorsiflexion, followed by extension of the right hip and knee while maintaining the ankle dorsiflexion. For all exercises, the upper limbs performed a slight shoulder flexion followed by extension with the elbow flexed to 90° angle for the maintenance of balance. The upper and lower limbs performed these movements in an alternating manner. An elastic band was fixed in lateral support to control the range of movement and to limit the amplitude of movement to adequate values.
The 4 incremental maximum tests were performed in a randomized order with HR, V[Combining Dot Above]O2, and VE being measured. A 48-hour interval was allowed between sessions. Participants were asked not to eat for 3–4 hours before testing and not to consume stimulants or perform intense physical activity for 12 hours before the experimental protocol. Furthermore, sessions were performed between the eighth and 20th day after the start of the last menstruation to control the hormonal period (12) and at the same time of the day to avoid variations related to circadian rhythms.
Each testing session started with the collection of cardiorespiratory variables at rest. Initially, participants remained in a supine position for 30 minutes and then in an orthostatic position for 3 minutes to evaluate HR, V[Combining Dot Above]O2, and VE. For the aquatic tests, these variables were also measured at rest while in an orthostatic position and immersed in water for 3 minutes. The incremental maximal test on dry land was carried out using a treadmill (10,200 ATL; Inbramed, Porto Alegre, Brazil) with an initial velocity of 5 km·h−1 and a 1% slope for 2 minutes. After this warm up, the velocity was increased by 1 km·h−1 every minute, maintaining the slope, until the participants reached their MAX. The room temperature ranged between 22 and 26° C. The aquatic incremental maximal tests were conducted with an initial cadence of 80 b·min−1 for 2 minutes with 10 b·min−1 increases in cadence every minute until MAX was reached. The cadences were set by a digital metronome (MA-30; Korg, Tokyo, Japan). Tests were performed barefoot in a shallow swimming pool with a depth between 0.95 and 1.30 m, allowing submersion of the participants to the depth of the xiphoid process. Water temperature was maintained at 32° C.
Tests were stopped when participants indicated their exhaustion using a hand signal or if they were unable to maintain the stage's cadence or velocity. The assessment was considered valid when at least one of the following criteria were met at the end of the test (21): a plateau in V[Combining Dot Above]O2 despite an increase in exercise intensity; a respiratory exchange ratio (RER) >1.15; a rate of perceived exertion (RPE) >17 (the RPE 6–20 Borg scale was used); or the estimated HRmax was reached (only for TL). Descriptive results for RER, RPE, and duration at the end of the incremental maximal tests are presented in Table 1, demonstrating that all protocols provided acceptable values. To evaluate V[Combining Dot Above]O2 and VE data during the tests, a mixing-box-type portable gas analyzer (VO2000; MedGraphics, Ann Arbor, MI, USA), previously calibrated according to the manufacturer's specifications, was used. The sampling rate was 10 seconds and data were acquired using Aerograph software. Heart rate was measured using a HR monitor (S610; Polar, Kajaani, Finland).
Values for the cardiorespiratory variables at rest were calculated based on the mean values for HR, V[Combining Dot Above]O2, and VE that were collected during the last minute spent in the orthostatic position on dry land and during water immersion. First and second ventilatory thresholds were determined using the first and second break points on the VE-by-intensity graph and confirmed using the slopes of the ventilatory equivalents for oxygen (VE/V[Combining Dot Above]O2) and carbondioxide (VE/V[Combining Dot Above]CO2), respectively (37). Three independent, experienced physiologists who were blinded to test condition determined the corresponding break points by visual inspection and identified the corresponding HR, V[Combining Dot Above]O2, and VE values. The break points were considered valid if at least 2 physiologists were in accordance. When the 3 points were discordant, the median value was identified and used for the analysis.
The V[Combining Dot Above]O2max value was defined as the plateau in V[Combining Dot Above]O2 that was observed at the end of the test, specifically an alteration in V[Combining Dot Above]O2 <50 ml·min−1 in response to an increase in intensity (8). When the plateau was not observed, the peak V[Combining Dot Above]O2 was considered to be V[Combining Dot Above]O2max (21). The HRmax was defined as the greatest value recorded during the test. Likewise, the highest value of VE was defined as VEmax. Finally, the HR and V[Combining Dot Above]O2 values corresponding to the VT1 and VT2 were expressed as a percentage of the maximal effort based on the HRmax and V[Combining Dot Above]O2max values obtained from each incremental maximal test (%HRmax and %V[Combining Dot Above]O2max, respectively).
Results are reported as the mean ± SD. The normality of the distribution was assessed using a Shapiro-Wilk test. Statistical comparisons were assessed using repeated measures analysis of varience with Bonferroni post hoc tests. The significance level was set at α = 0.05, and the SPSS statistical software package (version 19.0) was used for all analyses.
Resting HR, V[Combining Dot Above]O2, and VE values showed no significant differences between the 4 sessions in orthostatic position on dry land (p > 0.05) or between the 3 sessions in water immersion (p > 0.05). This suggests that participants initiated all incremental maximal tests at similar levels of cardiorespiratory activity; therefore, the magnitude of the alterations found in these variables during the protocols can be attributed to the effort made during their execution.
The descriptive values (mean ± SD) corresponding to the cadences (SR, FK, and CCS) or velocities (TL) at the VT1, VT2, and MAX intensities are presented in Table 2. The cardiorespiratory responses at the MAX, VT2, and VT1 intensities are shown in Table 3. Maximal heart rate and V[Combining Dot Above]O2max did not differ significantly between the water aerobic exercises SR, FK, and CCS. However, the values found for the aquatic tests were significantly lower compared with TL (HRmax: p < 0.001; V[Combining Dot Above]O2max: p < 0.001). Maximal ventilation was not significantly different between the 4 protocols (p > 0.05). Likewise, HR, V[Combining Dot Above]O2 and VE at the VT2 intensity were significantly higher for the TL test compared with the other tests with no significant differences between the 3 water aerobic exercises (HR: p < 0.001; V[Combining Dot Above]O2: p < 0.001; VE: p < 0.001). At the VT1 intensity, only HR had significantly greater values for TL compared with the water aerobic exercises (HR: p = 0.001), whereas V[Combining Dot Above]O2 and VE values were similar for the 4 protocols (V[Combining Dot Above]O2: p > 0.05 and VE: p > 0.05).
In the analysis of the %HRmax values, no significant differences were found between the 4 protocols at VT2 (p > 0.05) and VT1 (p > 0.05). However, the %V[Combining Dot Above]O2max presented a distinct pattern between intensities. Although no significant differences were observed between the 4 protocols at VT2 (p > 0.05), lower values were found in the TL condition compared with the water aerobic exercises at VT1 (p = 0.01) (Figure 2).
The main finding of this study was the similar cardiorespiratory patterns between the 3 water aerobic exercises for all variables analyzed. Furthermore, HR at VT1, VT2, and MAX was significantly greater within the TL condition compared with the water aerobic exercises and V[Combining Dot Above]O2 values at the MAX and VT2 intensities, confirming our hypothesis. When these variables were expressed as percentages of the maximum at the VT1 and VT2 intensities, no significant differences were found between the 4 protocols, with the exception of the TL at VT1, which is partially in agreement with our hypothesis.
According to the data found in this study, HR values at MAX, VT2, and VT1 were significantly lower for the 3 water aerobic exercises compared with the TL protocol. The HR response during water immersion is widely described in the literature with studies showing reduced values in the aquatic environment at rest (16,26,27,34,38) and during exercise, independent of the water exercise type. The lower HRmax found for the 3 water aerobic exercises compared with exercise on dry land in this study concurs with studies examining deep-water running (9,13,19,20,24,26,35,36), shallow-water walking, (19,36) and using an aquatic cycle ergometer (14,15,31). In addition, the few authors who have analyzed the HR response in aquatic tests at VT1 during deep-water running (9,20) also observed lower values in water compared with dry land.
These reduced values for HR in the aquatic environment compared with dry land at maximal and submaximal intensities can be attributed to a central shift in blood volume, caused by the hydrostatic pressure and the different thermal conditions of the aquatic environment (38). Immersion in water exposes the body to a hydrostatic pressure (1,7) that is the main reason for the decreased HR during immersion (14,15,31,38). The theory explaining this phenomenon states that during water immersion, central blood volume is increased through the redistribution of venous blood and extracellular fluid from the lower to the upper part of the body. As a result, the heart and central circulation are distended, leading to the stimulation of volume and pressure receptors in these tissues, which in turn leads to a readjustment of the cardiovascular system. The consequent increases in the central venous pressure, the cardiac output, and the stroke volume lower the HR (38). Moreover, the change in thermal conditions offered by the water also seems to contribute to the reduction in HR because the heat exchange between the body and the environment is facilitated during water immersion (23,34). Consequently, the need to distribute blood from the central region (i.e., chest and abdomen) to the extremities decreases, concentrating the plasmatic volume in the central region of the body. It is important to note that the magnitude of these alterations is directly related to the water temperature (16,17,23,27,34).
However, when the HR values were expressed as percentages of the maximum, no significant differences were observed between all protocols (water aerobic exercises and TL) at the VT1 and VT2 intensities. For SR, FK, CCS, and TL, %HRmax values of 66, 68, 66, and 70% were found at VT1 and of 86, 86, 86, and 90% at VT2, respectively. This indicates that the relationship between the points at which VT1 or VT2 and maximum exertion occurred is the same for the 4 exercises analyzed. The values found for the %HRmax at VT2 are consistent with the study by Barbosa et al. (11) that identified values of approximately 86% of the theoretical HRmax estimated for the intensity corresponding to 4 mmol·L−1 of blood lactate during the rocking horse water aerobic exercise.
Regarding V[Combining Dot Above]O2, the aquatic protocols resulted in significantly lower V[Combining Dot Above]O2max values compared with TL. These results corroborate several studies that reported reduced V[Combining Dot Above]O2max responses during deep-water running compared with TL (9,13,19,20,24–26,35,36). Furthermore, the studies by Town and Bradley (36) and Dowzer et al. (19) compared TL; deep-water running; and shallow-water walking (1.2–1.3 m), and found significant differences between these 3 exercise types. Their results showed that deep-water running resulted in V[Combining Dot Above]O2max values corresponding to 74 (36) and 75.3% (19) of those obtained on dry land, whereas the shallow-water walking resulted in values corresponding to 90 and 83.7%. In this study, the SR, FK, and CCS exercises resulted in V[Combining Dot Above]O2max values that were 84, 86, and 83% of those obtained during TL. These results suggest that the movement pattern is primarily responsible for the reductions in V[Combining Dot Above]O2max rather than solely the aquatic environment.
The similarities in V[Combining Dot Above]O2max between the environments increase with the similarities in the exercise techniques. This is confirmed by studies showing no differences in the V[Combining Dot Above]O2max responses during identical exercises, such as using a cycle ergometer (14,15,31) and walking on a treadmill (32) in the water or on dry land. In this study, the exercise on dry land that was used as reference was running on a treadmill, which has been described as a type of physical exercise that places a very high demand on the cardiovascular system because of the weight support required during the effort and the level of muscle recruitment required for the performance of the movement (19,36). This explains the significantly higher V[Combining Dot Above]O2max during TL than during the 3 water aerobic exercises. Otherwise, significant differences were not observed in this variable at the MAX intensity between the aquatic tests (SR, FK, and CCS). These data corroborate the study by Alberton et al. (2) who evaluated the V[Combining Dot Above]O2max in aquatic tests similar to the water aerobic exercises investigated in this study (SR and FK), and reported no significant difference between the exercises. However, these authors investigated a different water aerobic exercise (i.e., jumping jacks) and observed significantly lower V[Combining Dot Above]O2max values than those obtained with the other water exercises. This is because it is performed with a smaller range of motion, lower angular velocity, and less muscle recruitment.
Regarding the ventilatory thresholds, the V[Combining Dot Above]O2 corresponding to VT2 was higher for the TL compared with the water aerobic exercises, without significant differences between SR, FK, and CCS; these results were similar to the results found for V[Combining Dot Above]O2max. These data also corroborate the study by Alberton et al. (2) that identified higher V[Combining Dot Above]O2 values at VT2 in TL than water aerobic exercises (SR, FK, and jumping jacks). When V[Combining Dot Above]O2 values were expressed as percentages of the maximum, no significant differences at VT2 were observed between the 4 protocols with values of %V[Combining Dot Above]O2max of 73, 73, 77, and 80% found for the exercises SR, FK, CCS, and TL, respectively. This indicates that the relationship between the points at which VT2 and maximum exertion occurred is the same for the 4 exercises analyzed. This pattern is similar to that observed by Alberton et al. (2) who found values of 72, 72, and 69% of V[Combining Dot Above]O2max for the SR, FK, and jumping jacks exercises at this intensity with no significant differences between them and the TL.
No significant differences were found in the V[Combining Dot Above]O2 values at VT1 in this study between the 4 protocols. Frangolias and Rhodes (20) and Azevedo et al. (9) analyzed V[Combining Dot Above]O2 at the VT1 intensity during deep-water running compared with TL. Likewise, Alberton et al. (2) compared the V[Combining Dot Above]O2 responses at the VT1 intensity during 3 water aerobic exercises compared with TL. In contrast to the present results, these authors reported lower values of V[Combining Dot Above]O2 at the VT1 intensity in the aquatic environment compared with dry land. These differences between the present results and those observed in the studies mentioned above can be caused by the different protocols used for the incremental maximal tests performed in the different studies. Furthermore, Butts et al. (13) suggest that the main limiting factors for V[Combining Dot Above]O2max in activities, such as deep-water running, are the restrictions evoked by the water in the attempt to reach the MAX. Accordingly, these differences between protocols in water and on dry land become more evident as the exercise intensity increases, i.e., as the effort approaches the maximum, such as at the VT2 intensity, and are influenced less at lower intensities, such as VT1. Thus, at high intensities, the difficulty of displacing the limbs in water is greater because of the increase in the drag forces because the increase in the velocity of motion in water is squared and directly proportional to this force (6). The literature is still sparse regarding V[Combining Dot Above]O2 responses at the VT1 and VT2 intensities during different water exercises. Thus, future studies are needed to better understand these responses.
Regarding the VE responses, the 4 maximal tests resulted in similar VEmax values, a pattern distinct from those obtained for the HRmax and V[Combining Dot Above]O2max variables. This finding agrees with previous studies that found similar VEmax values during exercises performed in water (deep-water running) or on dry land (TL), despite lower V[Combining Dot Above]O2max values in the aquatic environment (20,35). According to Agostoni et al. (1), the hydrostatic pressure during immersion compresses the abdomen and maintains the diaphragm in a position that is close to full expiration. This increases the effort required to inspire, once pulmonary compliance and vital capacity are reduced. In addition, the increased central blood volume has been reported to contribute to the pulmonary compliance during aquatic immersion (1,7). Together with previous studies, the similar VEmax values between environments found in this study suggest that VE is not restricted by increased intrathoracic blood volume and hydrostatic compression of the chest during immersion. Nevertheless, some authors have reported greater (32) and lower VE values (9,13,19,26) in aquatic protocols compared with those performed on dry land.
Although the 3 water aerobic exercises resulted in lower values of VE at the VT2 intensity than those observed with TL, there was no significant difference in VE at the VT1 intensity between the 4 protocols. This pattern is similar to that observed for V[Combining Dot Above]O2. To the authors' knowledge, only the studies by Frangolias and Rhodes (20) and Azevedo et al. (9) compared the VE responses at ventilatory threshold between environments, but in these studies, only the VT1 intensity was investigated. In contrast to our findings, these authors observed significantly lower VE responses at VT1 in the deep-water running condition compared with TL. Future studies analyzing the VE at the VT1 and VT2 intensities during different water exercises, using different incremental protocols, are still needed to clarify this issue.
The present results highlight the importance of using a specific maximal incremental test performed in the aquatic environment for prescription of water aerobics exercises. This prevents the overestimation of the training intensities, which could happen if they were based on results obtained from a maximal test performed on TL. Furthermore, the cardiorespiratory responses to the 3 water aerobic exercises were similar at all intensities, indicating that the results of a maximal test for 1 exercise are sufficient to determine the intensity of other exercises for young women during water aerobics classes.
Because V[Combining Dot Above]O2max is costly and impractical to measure, the HRmax could be used to determine the intensity of training during aquatic programs instead. Thus, an individual maximal incremental test using one of the 3 water exercises analyzed, similar to the protocol developed for this study, should be performed to directly measure the HRmax. From this value, different ranges of %HRmax can be calculated for each individual according to the goals of the program to adequately individualize the intensity of training for both individual aquatic programs and collective water aerobics classes.
For an aerobic program, the target training zone should be based on intensities between VT1 and VT2. According to the findings of this study, referencing the %HRmax that corresponds to these intensities, it is recommended that the prescription of the aquatic program for young active women be adjusted to maintain a HR between 65% (VT1) and 86% (VT2) of the HRmax. For example, based on these values, at the beginning of the aquatic program, intensities that result in a HR of approximately 65% of the HRmax are recommended, and as the program progresses, this intensity could be increased until values of approximately 86% of the HRmax are reached. Other types of progression can be used, such as those used in the study by Pinto et al. (29) during water-based concurrent training. The present results are valid for young women, and additional studies should be developed to investigate these responses in other groups of participants and during other water aerobic exercises.
This study was supported by CAPES and CNPq, Brazil. The authors thank the INBRAMED company for their invaluable contribution to this study. The authors confirm that they have no conflicts of interest associated with this publication.
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Keywords:Copyright © 2014 by the National Strength & Conditioning Association.
immersion; oxygen consumption; ventilation; heart rate