PHYSIOLOGICAL RESPONSES TO FITNESS ACTIVITIES

Journal of Strength and Conditioning Research, 2004, 18(4), 719–722 q 2004 National Strength & Conditioning Association

PHYSIOLOGICAL RESPONSES TO FITNESS ACTIVITIES: A COMPARISON BETWEEN LAND-BASED AND WATER AEROBICS EXERCISE PIERO BENELLI,1 MASSIMILIANO DITROILO,1

AND

GIUSEPPE DE VITO2

1 Istituto di Ricerca sull’Attivita` Motoria—Facolta` di Scienze Motorie, Universita` degli Studi di Urbino ‘‘Carlo Bo,’’ Italia; 2Applied Physiology Department, Strathclyde Institute for Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom.

ABSTRACT. Benelli, P., M. Ditroilo, and G. De Vito. Physiological responses to fitness activities: A comparison between land-based and water aerobics exercise. J. Strength Cond. Res. 18(4):000– 000. 2004.—This study compared the heart rate (HR) and blood lactate (BL) responses in young healthy women performing the same routine of aerobics exercise in 3 different conditions: on land, in shallow water (0.8 m), and in deep water (1.4 m). The average age and body mass index (BMI) of the group were 27.4 years and 22.6 kg·m22, respectively. The highest HR and BL values were reached during land aerobics (median HR values were 138.0 and 161.5 b·min21, and lactate values were 3.10 and 5.65 mmol·L21 at slow and at faster pace, respectively). These parameters were progressively reduced going from shallow water (121.5 and 154.0 b·min21, 1.75 and 3.15 mmol·L21) to deep water (97.5 and 113.5 b·min21, 1.70 and 1.75 mmol·L21). The HR measured as percentage of maximum HR varied from 48.43% to 77.53% depending on the water depth and the pace. These data indicate that exercise in water significantly reduces HR and BL production compared with the same exercise performed on land. KEY WORDS. shallow water exercise, deep water exercise, physical fitness, heart rate, blood lactate

INTRODUCTION ater aerobics (WA) is among the most popular and widely prescribed fitness activities because it appears to be suitable for different groups: older, injured, and even healthy people. This can be related to the peculiarity of the water environment, which is characterized, in fact, by a condition of reduced gravity acceleration associated to an increased density (compared with air). As a result in the water environment the movements become rather slow, making WA less demanding and traumatic than a similar activity practiced on land (8). Different studies have investigated the different physiological responses comparing land-based running and water running (4, 8, 11) or walking performed on land and in water (14). Most studies showed higher HR (about 10–15 b·min21) during exercise on land compared with exercise in water performed at the same relative intensity (4, 8, 11, 13–15, 16). Few studies that focused specifically on WA considered heart rate (HR), blood lactate (BL; 3, 7, 10), and oxygen uptake (7) found a reduction of values of the mentioned parameters during WA compared with exercise on land. The HR-dampened response during exercise performed in deep water has been attributed to the following factors: (a) a redistribution of blood volume (‘‘cephalad shift’’) due to the action of hydrostatic pressure on the

W

thoracic and abdominal areas (2, 8); and (b) an increase in atrial blood volume associated with a reduction of systemic vascular resistances (5, 8, 12, 13). In addition, these differences have been found to be higher at maximal, rather than submaximal, exercise (8). Concerning BL response to water exercise, some studies have observed a reduction (8, 15), whereas others have observed an increase (8, 13), compared with land-based exercise. These discrepancies have been attributed to the different study protocols that involved different muscles and different speed of movements (6, 8). Furthermore, it has been shown that the observed modifications in physiological responses to WA could be attenuated in subjects fully familiarized with this exercise (16). Previous research has usually compared exercise on land and in water at the same depth (7, 10, 14), but to our knowledge no studies have investigated the effect of different depths of water during a standardized exercise like that proposed in the present investigation. The only 2 studies that adopted a similar approach used running protocols comparing dry running with water running at different depths (9, 15). Therefore, the purpose of the present study was to compare the HR and BL responses in young healthy women performing the same routine of aerobic exercise in 3 different conditions: on land, in shallow water, and in deep water. This information has the potential to provide a better insight about the general physiological responses of subjects who regularly participate in WA training.

METHODS Experimental Approach to the Problem

In the present study the experimental design comprised a within-subjects protocol in which a group of 10 women completed 3 different exercises (on land, in shallow water, and in deep water) on consecutive occasions within 6 days’ time. The rhythm of the exercises, the temperature of the water, and the time of the sessions were kept under control, whereas the order of the sessions was randomized. Subjects

Ten healthy women volunteered and gave their written informed consent for participating in the study. Each subject underwent a medical examination before inclusion. The study design was approved by the human ethics committee of the University of Urbino, Italy. Subjects were 719

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familiar with the aerobic routine requested, both on land and in the water. They were all practicing WA 2 or 3 times per week for at least 1 year before the study began. The average age, height, body mass, and body mass index (BMI) are shown in Table 1. Tasks and Equipment

Table 1. Age and physical characteristics of the subjects. n 5 10 Age (y) Height (m) Mass (kg) BMI (kg·m22)

Mean 6 SD 27.4 1.64 60.7 22.63

6 6 6 6

3.6 0.06 7.3 3.33

Each participant was asked to perform 30 minutes of standardized exercise: the first 15 minutes at a slow pace (performed at a pace of 1.15 Hz), and the second 15 minutes at twice the original pace (2.3 Hz). The 3 exercise routines were held in a gym (land aerobics [LA]), in a swimming pool of shallow water (SWA; about 0.8 m), and in deep water (DWA; about 1.4 m). The temperature of the water was kept at about 27.58C in all experimental sessions. Each of the sessions was conducted at least 2 days apart between the hours of 6 and 7 PM, and the order of the tests was randomized. The same experienced instructor lead the exercise during the 3 routines. The subjects were equipped with a Polar Vantage heart rate monitor (Polar Electro, Kempele, Finland) in order to measure the HR (b·min21) throughout the exercise. Furthermore, capillary blood was taken from the finger tip after 15 and 30 minutes of exercise. BL (mmol·L21) was analyzed by a portable lactate analyzer (Lactate Pro; Arkray Inc., Kyoto, Japan). Statistical Analyses

All statistical analyses were conducted by means of the SPSS software (10.1; SPSS, Chicago, IL). Physical data characteristics are presented as mean 6 standard deviation (SD). Since the data were not normally distributed, a nonparametric test (the Friedman test) was used to determine the significance of the differences between LA, SWA, and DWA data at the 2 considered paces. Afterward, an unplanned multiple comparison based on Bonferroni criterion was used. The significance was fixed at an alpha level of 0.05.

FIGURE 1. Box-and-whisker graph of heart rate (HR) values: Slow pace exercise.

RESULTS Figures 1–4 are box and whisker graphs of the HR and BL values. Figure 1 shows the HR trend of the exercise performed in 3 different environments at a slow pace. The median HR values were 138.0, 121.5, and 97.5 b·min21 for LA, SWA, and DWA, respectively. Figure 2 shows the HR trend (median values 161.5, 154.0, 113.5 b·min21) of the exercise performed in 3 different environments at a faster pace. Table 2 lists the HR values as a percentage of predicted maximum HR (HRmax, 220 2 age). These HR values corresponded to 71.85% (slow pace) and 84.55% (fast pace) of predicted HRmax during LA, to 61.88% (slow pace) and 77.53% (fast pace) during SWA, to 48.43% (slow pace) and 58.50% (fast pace) during DWA. Figures 3 and 4 show the BL values measured during LA, SWA, and DWA at both slow (3.10, 1.75, 1.70 mmol·L21) and fast pace (5.65, 3.15, 1.75 mmol·L21). Not surprisingly the highest HR and BL values (for both the slow and faster pace routines) were reached when the exercise was performed on land. The HR values decrease steeply, especially from SWA to DWA and during the faster pace session. On the other hand, the BL values decrease from LA to SWA and during slow pace session.

FIGURE 2. Box-and-whisker graph of heart rate (HR) values: Fast pace exercise.

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WATER AEROBICS EXERCISE 721

DISCUSSION

FIGURE 3. Box-and-whisker graph of blood lactate (BL) values: Slow pace exercise.

Our data indicate that WA results in a significantly lower HR and BL production compared with exercise on land. In addition, the deeper the water, the less the physiological demand. These results are in agreement with those of Town and Bradley (15) who compared running on a treadmill with deep and shallow water running. These results are probably due to the different responses of the cardiovascular apparatus; as a result of hydrostatic chest compression and central hypervolemia (5, 8, 12); and to the different response of the muscular apparatus as a result of the much higher density and viscosity friction of the water environment (8), which lessened the mechanical work performed by the subjects. This means that the involvement of anaerobic metabolism during water exercise, and WA in particular, is quite reduced. Thus, this kind of activity could be considered an ideal low-impact activity, safe even for a frail population. Moreover, when observing Figures 3 and 4, it is apparent that the data variability drops considerably when moving from the land to the water environment. This fact might be of great importance for the aim of fitness activities, where people are often different in age and abilities, and WA could be an effective mean for a controlled physiological response in heterogeneous groups. The American College of Sport Medicine (ACSM) recommendations for adults’ fitness activities (1) provides the guidelines for improving physical fitness level in both young and middle-aged people. In the present study, the intensity of WA (percent predicted HRmax), as shown in Table 2, falls within the recommended intensity range for cardiorespiratory fitness improvement (1). Similar results have been reported also in older women practicing WA (10). However, it is important to stress that the intensity of DWA is at the lower limit of the intensity range recommended by ACSM. Therefore, more studies are needed in order to gain a better understanding of brief and longterm physiological adaptations of water exercise, especially WA.

PRACTICAL APPLICATIONS

FIGURE 4. Box-and-whisker graph of blood lactate (BL) values: Fast pace exercise.

The results obtained from this study put into evidence that exercise performed in water is less demanding than exercise on land carried out at the same level of intensity, as shown by the reduced HR and blood lactate production. Therefore, this kind of exercise can be a valid alternative to the more traditional land-based exercise, especially when applied to special populations. This is particularly true for older people, injured athletes, and all subjects with impairment in their physical capability. Since exercise performed in water has been shown to induce specific and peculiar physiological responses, the traditional recommendations (e.g., ACSM) for adults’ fitness activi-

Table 2. Percent of HRmax values reached during land aerobics (LA), shallow water aerobics (SWA), and deep water aerobics (DWA). SWA

LA mean (%) SD

DWA

Slow pace

Fast pace

Slow pace

Fast pace

Slow pace

Fast pace

71.85 10.25

84.55 7.94

61.88 8.68

77.53 10.55

48.43 7.09

58.50 7.24

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ties should be revised to include specific directions for water-based exercise.

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Address correspondence to Piero Benel, pierobenelli@ uniurb.it.