Comparison of Physiological and Perceptual Responses Between Continuous and Intermittent Cycling

The present study tested the hypothesis that the exercise protocol (continuous vs. intermittent) would affect the physiological response and the perception of effort during aquatic cycling. Each protocol was divided on four stages. Heart rate, arterial blood pressure, blood lactate concentration, central and peripheral rate of perceived exertion were collected in both protocols in aquatic cycling in 10 women (values are mean ± SD): age=32.8 ± 4.8 years; height=1.62 ± 0.05 cm; body mass=61.60 ± 5.19 kg; estimated body fat=27.13 ± 4.92%. Protocols were compared through two way ANOVA with Scheffé’s post-hoc test and the test of Mann- Whitney for rate of perceived exertion with α=0.05. No systematic and consistent differences in heart rate, arterial blood pressure, double product and blood lactate concentration were found between protocols. On the other hand, central rate of perceived exertion was significantly higher at stage four during continuous protocol compared with intermittent protocol (p=0.01), while the peripheral rate of perceived exertion presented higher values at stages three (p=0.02) and four (p=0.00) in the continuous protocol when compared to the results found in intermittent protocol. These findings suggest that although the aquatic cycling induces similar physiologic demands in both protocols, the rate of perceived exertion may vary according to the continuous vs. intermittent nature of the exercise.


Introduction
Physical training is often based on continuous and/or intermittent methods with the purpose of improving cardio respiratory ability (Barbosa et al., 2009). Studies have compared the effect of those methods on heart rate (HR) (Arngrimsson et al., 2003;Roecker et al., 2002), on arterial blood pressure (Mourot et al., 2004;Crisafulli et al., 2004), on double product (Forjaz et al., 1998), on blood lactate concentration (Gharbi et al., 2008;Sabapathy et al., 2004) and on the rate of perceived exertion (Borg and Kaijser, 2006;Lagally et al., 2002). However, these studies have not addressed the aquatic cycling. Cycling is one of the most popular means of exercise for general and specific physical conditioning and industry experts have adapted cycling equipments to the aquatic environment. Due to the nature of the equipment and of the aquatic environment, this type of exercise stands out as one more option for cardio respiratory training, applicable to different age groups and fitness levels by adapting the postures and grips the indoor stationary cycling.
According to Barbosa et al. (2009), the use of aquatic cycling has been reported in literature for three decades, though its findings are still contradictory. Alberton et al. (2010) suggest that © Editorial Committee of Journal of Human Kinetics HR in the water could be similar or higher as compared with dry land measurements. Barbosa et al. (2010) analyzed the relationships between musical cadence and the physiological adaptations to basic head-out aquatic exercises. The study included an intermittent and progressive protocol and the main conclusion was that increasing musical cadence imposed an increase in the physiological response. In this context, several physiologic indicators have been used in order to quantify the intensity of exertion in those environments, such as: the HR (Sheldahl et al., 1984;Reilly et al., 2003); double product (Veloso et al., 2003), and blood lactate concentration (Di Masi et al., 2007).
In water, resting or exercising induces different physiological responses when compared with those achieved in dry-land conditions (Shono et al., 2000;Reilly et al., 2003) and are affected by a number of factors, such as buoyancy, thermal conductivity of the water (Choukroun and Varene, 2000), hydrostatic pressure (Goodall and Howatson, 2008), among others. Those responses depend also on the body positioning in the water (Millet et al., 2002;Egaña et al., 2006) and on the type of exercise (Barbosa et al., 2009). Kang et al. (2005) compared the responses of HR between intermittent (130 ± 2 bpm) and continuous cycling (127 ± 2 bpm) on land and did not found significant differences between both methods. The lactate concentration was significantly higher at the end of the intermittent exercise with a mean value above 7 mmol in the final stage of the IP. Contrarily, Sabapathy et al. (2004), have examined the physiological responses in 10 subjects who performed a continuous and intermittent land cycling protocol and observed that the intermittent protocol was associated to significantly lower values of HR. Unfortunately, no previous study examined the type of physiological response induce by continue or intermittent exercise in water environment. Therefore, the present study tested the hypothesis that the type of exercise (continuous vs. intermittent) would affect the physiological response and the perception of effort during aquatic cycling.

Participants
Ten women (values are mean ± SD: age=32.8 ± 4.8 years; height=1.62 ± 0.05 cm; body mass=61.60 ± 5.19 kg; estimated body fat=27.13 ± 4.92%) of low risk, practicing regular classes of cycling in water for at least six months, participated in the study. All of them signed a written informed consent to participate in the study and in accordance with the norms for accomplishment of research with humans established in the Helsinki Declaration of 1975. The experimental procedures were approved by the Ethics Committee of the Institution.

Procedures
All volunteers attended the test venue on three different days, with an interval of seven days. The volunteers were instructed not to workout exhaustively in the previous 24 hours; to remain well hydrated in the previous 24 hours and to avoid eating, smoking, drinking alcohol or caffeine three hours before the tests, as well as to sleep between 6 and 8 hours in the night before testing.
The volunteers were submitted to an anthropometrical evaluation, consisting of body mass and height measures (Filizola, PL150-Personal Line, Brazil). The same technician obtained all anthropometric measurements, on the right side of the subject's body. Skinfold thickness was obtained with a Lange skinfold caliper. A 3-site skin fold equation for woman was used to estimate body density (Jackson and Pollock, 1978) and body fat was subsequently calculated using the Siri equation (Heyward and Stolarczyz, 2001).
To evaluate the cardio respiratory capacity, the individuals were submitted to the Balke protocol (1959) accomplished in a standard cycloergometer (Monark 868E, Monark-Crescent, Varberg, Sweden) in a laboratory setting. It was applied progressive loads of 25 W every two minutes, until reaching the maximum voluntary exhaustion (Balke, 1959). The volunteers were submitted randomly to two cycling sessions using the aquatic bicycle (Hydrorider, A1S1316, Italy). Both sessions had a total duration of 31 minutes with a seven days interval in between, and were always carried out at the same time of the day. The temperature of the pool water was between 30 and 31ºC and 50% of relative humidity. The level of the immersion in water on sitting position was at the xifoid process.
The exercise protocols had a total Journal of Human Kinetics Special Issue 2011, http://www.johk.pl duration of 31 minutes and were divided in five stages. Tables 1 and 2 present respectively the characteristics of the Continuous Protocol (CP) and the Intermittent Protocol (IP). The pedaling cadence was controlled by a metronome (Yamaha, QT-1, USA). In position 1 the individuals remained seated with hands on the base of the bicycle handlebar; in position 2, standing up with hands on the base of the bicycle handlebar; and in position 3 and standing up with hands on the extremity of the bicycle handlebar. Cycling cadence was maintained throughout all testing between 80 and 100 revolutions per minute.

Data Collection
Absolute heart rate (HR) was continuously measured with a cardio-frequency meter (POLAR®, A1, Finland) device and Rate of Perceived Exertion (RPE) was measured at the end of each minute of exercise (Borg Scale-CR10). Blood pressure (BP) and blood Lactate concentration (BLC) were also assessed in the last minute of each stage. For BP, was measured by auscultation technique, non-invasive, using a sphygmomanometer (Tycos®, CE0050, USA) and professional stethoscope (Marshall®, Omrow Health Care, USA). Capillary (finger) blood sample were collected for BLC with an YSI 1500 analyzer (Yellowsprings, OH, USA). Prior to each testing, the lactate analyzer was calibrated with standard lactate solutions of 2.5, 5.0, 10.0 and 15.0 mmol·L-1 (Yellowsprings, OH, USA).

Statistical Analysis
After identification of data normality (Shapiro-Wilk test), a two-way analysis of variance (protocol type; stages) was applied to check the effect in the variables selected. A post-hoc Scheffé test was used to describe possible differences among the variables. The Mann-Whitney test was used to compare the rate of perceived exertion between the respective stages. The study admitted a significance level = 0.05. The data were processed using Statistical software (Statsoft, version 6.0, USA). Data s presented as mean ± standard deviation (SD).

Results
The figure 1 shows the time on-response of HR response during both. Despite slightly higher values for continuous stages, most of the differences were not significant. In the second stage, when the individuals were pedaling standing up, the mean HR values during IP (149.00 ± 9.00 bpm) were significantly lower when compared with HR values during CP (158.00 ± 10.00 bpm).   Figure 2 presents lactate concentration in the blood. The mean values observed at Stage I was significantly lower when compared with those at Stage IV in the continuous and intermittent protocols. Figure 3 and 4 show the mean rate of perceived exertion. In Figure 6 (Evertsen et al., 2001;Billat et al., 2003;Kang et al., 2005). Although not measured in our study, such factors could have also influenced our subjects and help to explain the differences between our study and that by Edwards et al. (1973).
The RPE was also addressed in the study by Kang et al. (2005), and it showed mean values of 8.90 0.50 in the IP and of 9.70 0.70 in CP. These values are higher than the findings of the present study, though they did not found significant differences between IP and CP. Contrarily we have found significant differences in RPE between the two protocols in stages III and IV. Several factors are believed to influence RPE, such as the exercise intensity (Alberton et al., 2010), the water depth (Di Masi et al., 2007), the water temperature (Fujishima and Shimizu, 2003) and the stimulation of peripheral receptors located on members and trunk (Robertson et al., 1995). The lower mean value for RPE in our study compared with those found in dry-land cycling. Kang et al. (2005) confirm that the aquatic environment may serve as a lowering factor in the perception of effort. Moreover, the fact that we found lower RPE mean values in IP when compared with CP suggests that the aquatic environment may enhance the effects of the short recovery periods involved in the intermittent exercise. It is important to consider on future studies could be performed with other population, other intensities, different aquatic environment such as temperature and depth.
The hypothesis that the intermittent protocol would offer a lower physiologic demand was only partially confirmed. HR, DP and RPE were higher during the CP. Plus, SBP and DBP and BLC presented higher mean values in the IP. The IP induced a more pronounced HR reduction and BLC during the recovery periods, suggesting a faster recovery in the intermittent protocol. More studies are recommended with other possible exercise intensity and volume combinations, as well as with different gender and conditioning level of the individuals.