Deep water running (DWR) is a mode of exercise utilized by athletes (both injured and healthy) as well as many special populations (e.g. pregnant women, lower back pain and cardiac patients). Exercising with the body submerged in water presents some interesting physiological changes that complicate the method of prescribing exercise intensity. A person involved in an exercise program that utilizes DWR should be aware of the changes in HR and VO2 in order to set an effective level of intensity.
It is well documented that heart rate (HR) and oxygen consumption (VO2) are lower during deep water running (DWR) compared to treadmill running (TMR) at peak exercise (2, 3, 6, 9, 10, 12, 16, 17). The metabolic responses during submaximal DWR, however, are not well understood.
During submaximal exercise, Svedenhag and Seger reported that for a given VO2, the corresponding HR was lower during DWR compared to TMR (16). In contrast, Michaud and colleagues reported that there was no significant difference in HR at an equivalent submaximal VO2 (3.3 L/min) between modes (12). Similarly, Demaere and Ruby observed that VO2 was not different during DWR and TMR when subjects exercised at an equivalent submaximal HR (4). In a comparison of values relative to peak responses, Mercer, Jensen, and Fromme reported that VO2 was lower during DWR than TMR at 61% and at 82% of the corresponding VO2peak for each mode (10). This is in agreement with Michaud and colleagues who reported that VO2 was lower during DWR compared to TMR at 70% of the VO2peak for the respective modes of exercise (12). It was also reported that HR was lower during DWR at 82% but not at 61% of the HR peak for the corresonding mode (10).
The purpose of this study was to examine the submaximal HR and VO2 responses during DWR and TMR graded exercise tests to volitional fatigue. The observations of this study will facilitate a better understanding of the physiological responses to exercise while submerged in water and will lead to an effective means of prescribing exercise intensity during DWR.
A continuous graded exercise test (GXT) was completed during DWR and TMR by each subject (15 males, 13 females). Test order was randomized with at least 24 hours between tests. All subjects but one were inexperienced in DWR, however, each subject was allowed time to acclimatize to the mode of exercise prior to testing. The study was approved by the University of North Texas Institutional Review Board, and all subjects signed a waiver in accordance with the American College of Sports Medicine guidelines for protection of human subjects.
The DWR test was performed in a tank 1.8m x 1.8m x 1.8m. The water temperature ranged from 25° to 28° C. During the test, the subject wore an Aqua Jogger around the waist to aid in flotation. A tether was attached to the back of the Aqua Jogger and ran through a series of pulleys with the opposite end attached to a bucket suspended 0.75m above the deck (Mercer and Jensen, submitted for review).
The protocol for the DWR GXT consisted of 1 minute stages. To provide for a graded exercise response, a 0.57 kg weight was added to the bucket at the beginning of each stage. The added weight had the effect of increasing the intensity of exercise. Weight was added to the bucket each stage until the subject could not keep the bucket from touching the ground (see Figure 1).
Figure 1 about hereThe protocol for the treadmill test consisted of 1 minute stages, with the first stage requiring the subject to exercise at 80.4 mmin-1 at a 3% grade. Elevation was increased to 7.5% grade for the second stage and remained constant for all subsequent stages. The next three stages consisted of speeds of 93.8 mmin-1, 107.2 mmin-1, and 134 mmin-1. The speed of all subsequent stages was increased by 13.4 mmin-1. Air temperature ranged from 21° C to 24°C.
VO2 was determined via Med Graphics CPMax cart (St. Paul, MN) and recorded every 15 seconds during both tests. HR was monitored through radiotelemetry (Polar, CIC Accurex, Hempstead, NY) and recorded 10 seconds prior to the end of each stage. The criteria for peak responses of HR and VO2 was the highest observed response with a respiratory equivalent ratio greater than 1.05. The submaximal VO2 selected from the data collected during the GXT for each category per subject was the VO2 nearest in magnitude to the category. For instance, if a subject had a VO2 of 18 and 23 mlkg-1min-1, the 18 mlkg-1min-1 chosen for the 20 mlkg-1min-1 category. There were instances where the nearest measured VO2 was beyond ±5.0 mlkgmin-1 of a category. In these cases, the data was not included, and the corresponding data of that category for that subject was dropped from the analysis for both modes of exercise. For example, if a subject had a VO2 of 15 and 26 mlkg-1min-1 during DWR, the 20 mlkg-1min-1 category was not included in the subsequent analysis for that subject for DWR as well as TMR regardless if the subject had a VO2 during TMR that met the criteria for inclusion of data for the 20 mlkg-1min-1 TMR category. The actual VO2 values which represent each category were not different betwen modes (p>.05) and are presented in Table 1.
Subject characteristics and peak values for VO2 and HR during DWR and TMR are reported in Table 2 for males and females. A Repeated Measures Analysis of Variance was used to test for differences in HR and VO2 by test condition (either DWR or TMR). The peak values were significantly different between tests regardless of gender (p<.01). The comparison of the submaximal responses indicate that the corresponding HR at a VO2 of 20, 30, and 40 mlkg-1min-1 for males and 20 and 30 mlkg-1min-1 for females were not different (p>.05). Thus, at an equivalent submaximal VO2, HR did not differ during DWR and TMR. Submaximal data is presented in Table 3.
Table 2 & 3 about here
Discussion
The results indicate that the peak responses for HR and VO2 were lower during DWR compared to TMR. This observation is in agreement with other studies (2,3,6,9,10,12,16,17). The observation that for a given submaximal VO2, the corresponding HR was not different during DWR and TMR is in agreement with the results reported by Michaud and colleagues (12) as well as Demaere and Ruby (4). In contrast, Svedenhag and Seger reported that the HR for a given submaximal VO2 (2.5 and 3.5 Lmin) was lower during DWR compared to TMR (16). The cause for the discrepancy between the results reported by Svedenhag and Seger and the present study is not known. Svedenhag and Seger compared HR and VO2 levels that were calculated via a linear regression model calculated from five data points. Where as the HR and VO2 comparisons made in the present study were based on measured data.
Previously, the authors reported that VO2 was lower during DWR than TMR at 61% and at 82% of VO2peak of the respective mode of exercise (10). It was also reported that HR was lower during DWR than TMR at 82% of the HRpeak of the corresponding mode of exercise (10). The data from the present study (Figure 2 and 3) illustrate that comparing percentages of HRpeak and VO2peak would yield a lower VO2 and HR during DWR because the peak responses during DWR are lower than during TMR.
The question remains, however, if the HR - VO2 relationship is similar during DWR and TMR, why are peak values lower during DWR? One possible explanation is that DWR skill level is a factor responsible for the lower VO2peak and HRpeak during DWR compared to TMR. However, Town and Bradley (17) reported that trained runners regularly exposed to water running achieved 74% of TMR VO2peak during DWR (without the use of a flotation device). Svedenhag and Seger (16) reported subjects who were trained runners as well as experienced water runners, achieved 87.8% of the TMR VO2peak during DWR. Likewise, Michaud and colleagues (12) reported that well trained runners inexperienced in DWR achieved 88% of TMR VO2peak during DWR. Therefore, the lower HRpeak and VO2peak during DWR compared to TMR may not be dependent on skill or level of experience with DWR. Interestingly, different protocols for eliciting peak responses during DWR and TMR have been utilized in previous investigations (2, 3, 10, 12, 16, 17, 21) with no effect in the magnitude of difference between modes of exercise.
One reason DWR has increased in popularity with runners over the years has been the concept that the running action during DWR is similar to TMR. Therefore a carry over training effect of DWR may be transferable to land based running. Running is a high impact activity that can result in overuse injuries (8). DWR offers the advantage of mimicking running technique while eliminating the impact nature of running.
There are a limited number of studies which have examined the training responses elicited from a DWR training program (1, 5, 7, 11, 13, 14, 18). Whether or not training responses can carry over from DWR to land based running has yet to be conclusively determined. There is the question of whether an individual should train at a level of intensity relative to the peak responses during a DWR GXT, or, because land based results are a common goal of utilizing DWR, at a level of intensity relative to TMR. Further research on the training effects during DWR are needed. The results of the present study indicate that a HR measurement taken during DWR will equate to a VO2 that would be equivalent to the VO2 at the same HR during TMR. However, the relative level of intensity during DWR is higher for a given percent of the peak responses because VO2peak and HRpeak are lower during DWR.
In order to determine an effective method for determining exercise intensity, training studies which base the exercise intensity during DWR on a DWR GXT, as opposed to a TMR GXT, are needed. Also, further biomechanical analyses of DWR are needed to determine the similarity of DWR and TMR. The results of this study indicate that HR was not different for a VO2 when comparing DWR and TMR. VO2peak and HRpeak are, however, lower during DWR compared to TMR.
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Table 2: Subject Characteristics and peak values for HR and VO2
MALESn=15 FEMALESn=13
Age (years) 24.3 4.7 21.0 1.3
Stature (cm) 179 7.8 166 5.9
Mass (kg) 79.5 10.8 58.9 7.0
DWR TMR DWR TMR
VO2peak 49.9 9.9 60.3 13.9 37.6 5.3 46.3 5.7
HRpeak 173 10.1 191 6.3 180 8.3 185 9.3
Table 3: Heart Rate Response at a given Oxygen Consumption
VO2 MALES FEMALES
(mlkgmin-1) DWR TMR DWR TMR
20 122 9.4 124 21.5 131 13.6 140 16.6
n=12 n=13
30 142 17.2 144 18.2 166 11.7 164 10.4
n=15 n=13
40 159 20.0 161 16.8
n=13
Note: No difference between conditions for either gender (p>.05)
Table 1: Actual VO2 Measurements
VO2 MALES FEMALES
(mlkgmin-1) DWR TMR DWR TMR
20 21.50 1.51 19.45 1.50 18.48 2.66 20.31 1.80
n=12 n=13
30 29.67 2.21 30.15 1.75 30.45 1.77 30.45 3.18
n=15 n=13
40 40.97 2.13 41.22 1.93
n=13
Note: No difference between conditions for either gender (p>.05)