Q: I’M A RUNNER WHO IS INTERESTED IN TRYING SOME WATER-BASED EXERCISE AS A REFRESHING OPTION TO BEAT THE SUMMER HEAT. UNFORTUNATELY, I AM ONLY A MARGINAL SWIMMER AND THUS I DON’T FEEL LIKE I GET A GOOD WORKOUT WITH SWIMMING. A FRIEND USES AQUA RUNNING. COULD YOU GIVE SOME BACKGROUND ON THIS FORM OF TRAINING? WILL THIS TYPE OF EXERCISE BE OF VALUE FOR MY RUNNING PROGRAM? DO YOU HAVE ANY SUGGESTIONS ON HOW TO MAXIMIZE BENEFITS WITH THIS TYPE OF EXERCISE?
A: Heading into the water does sound like a refreshing summer option. Although swimming is a great aerobic activity, having sufficient swimming skills is a prerequisite to maximize the usefulness of this mode of exercise. The American College of Sports Medicine classifies various aerobic activities based on the skill requirement and the prerequisite fitness level (see Table) (1). Swimming is in group “C” and thus would not appear to be the best option until sufficient swimming skills are attained.
As you have already identified, aqua running (also referred to as deep-water running [DWR]) is a water-based option that gets around the issue of being a skilled swimmer, although it does require some attention to technique to maximize effectiveness. Thus, DWR might also be classified as a group “C” activity, but not at the same skill level as swimming. DWR involves simulating the running motion while in the deep end of a swimming pool or in a body of water where the runner cannot touch the bottom. Wearing a flotation device (e.g., vest or belt) is recommended to ensure that body position is maintained (8); without a flotation device, exercisers often resort to circular arm and leg motions similar to treading water to keep their heads above water rather than to running motions (5). The DWR technique is outlined in Box 1 and pictured in the Figure.
WHAT ARE SOME OF THE DIFFERENCES BETWEEN DWR AND ON-LAND RUNNING?
Although the intent of DWR is to replicate on-land running (OLR), differences do exist between the two exercise modes. With OLR, gravity must be overcome to move over the ground. In essence, runners must elevate themselves from earth to move forward and then control the resulting return to earth caused by gravity’s pull. In contrast, with DWR, the buoyancy of the water helps move the body (or limbs) toward the surface and resists movements away from the surface (6). This necessitates different muscle recruitment; overall, there appears to be a reduction in activity of the weight-bearing muscles (6). The viscosity and drag forces of water provide resistance in proportion to the runner’s effort (8).
In addition to biomechanical differences, there are physiological differences. Maximal oxygen uptake (V˙O2max) and maximal heart rate (HR) tend to be lower with DWR than with OLR (4). Some researchers suggest that different muscle recruitment patterns may be the underlying factor responsible for the lower V˙O2max during DWR versus OLR (4). Water density is approximately 800 times that of air and, therefore, exercising in water presents a greater viscosity friction, resulting in differences in recruitment of motor units within the active muscles (4).
The lower HR typically found with DWR compared with OLR has been attributed to the central shift in blood volume caused by the hydrostatic pressure exerted by the water on the submerged body (4). The pressure of the water on the limbs results in improved blood return to the heart (venous return), thus increasing the amount of blood in the heart before contraction (preload), and, in turn, the amount of blood moved from the heart with each beat (stroke volume). Because the heart is able to move more blood with each beat, the number of heartbeats per minute is lower to achieve the same cardiac output. Lower levels of sympathetic hormones (epinephrine and norepinephrine) also have been observed with higher intensity DWR, which may be another factor contributing to the lower HR typically observed (4).
When considering maximal exercise in the water compared with on land, familiarity with DWR may play a role (2). One study specifically compared runners who were adapted to DWR (defined as using DWR training at least two sessions per week for at least two months) with runners who had not previously used DWR (2). For the runners adapted to DWR, V˙O2max was still lower compared with that of OLR, but the difference was less than that found for the novice DWR runners. Specifically, the runners previously adapted to DWR had a V˙O2max that was almost 90% of their treadmill V˙O2max (for the nonadapted runners, the DWR V˙O2max was only 80% of their treadmill V˙O2max) (2). Thus, it appears that attention to proper form, along with a willingness to practice the technique, is important. The time frame needed for familiarization has not been quantified, although some have suggested that a minimum of 2 to 3 weeks, including 2 to 3 sessions per week, may be needed (4).
HOW USEFUL IS DWR FOR AEROBIC TRAINING AND PERFORMANCE?
For untrained individuals, DWR may actually allow improvements in fitness (as would be expected caused by any increase in physical activity). When studies of trained runners are examined, DWR appears to provide a sufficient stimulus to maintain OLR performance (6).
Two studies illustrating this included trained runners with high fitness levels, as evidenced by average V˙O2max measures of 58.6 mL·kg−1·min−1 and 63.4 mL·kg−1·min−1 (3,7). One of the studies was a 6-week training study in which runners engaged in either DWR or treadmill running (7). Both groups followed a similar workout schedule, including high-intensity interval sessions and moderate-intensity recovery sessions. No differences were found between the groups for any of the variables measured during posttraining treadmill tests, including V˙O2max, running economy, or maximal HR. The authors concluded that DWR was as effective as OLR for maintaining aerobic performance during a 6-week period for trained runners.
These conclusions were supported by another study of trained runners who engaged in DWR training for 4 weeks, including long and short intervals and constant-intensity long-duration sessions (3). The Brennan scale (a perceived exertion scale created for use with DWR) was used to gauge the intensity. The scale, from 1 to 5, ranged from very light to very hard; with each level equated to OLR intensities (level 1, light jog; level 2, long steady run; level 3, 5- or 10-km race; level 4, 400- to 800-m intervals; level 5, 100- to 200-m sprint) (8). After 4 weeks of DWR training, this group of runners was able to match their baseline V˙O2max, lactate threshold, and running economy. In addition, 5-km performance times were similar after the 4 weeks of DWR training as before.
Therefore, DWR appears to be an effective training tool to maintain OLR performance and aerobic fitness. Both of these training studies used interval sessions within the DWR training (3,7). Examples of two of the interval sessions used in the 4-week training study are shown in Box 2 (3). Examples include the number of repetitions, the time of each interval, and the Brennan exertion scale level. Subjects in the 4-week training study included DWR on 5 to 6 days per week (typically 2 days of longer intervals, 2 days of shorter intervals, and 1 to 2 constant-intensity longer duration sessions that included 45 minutes at an exertion level of 2 to 3). As with OLR, endless possibilities are available with manipulation of the interval number, time, and intensity. Although the research studies described used DWR exclusively, DWR can potentially be used in combination with OLR as a cross-training mode (4).
Based on current research, it would appear that DWR can be a valuable mode of exercise within a running program. Beginners should focus on workout intensity and DWR form. Avoid becoming a human buoy floating in the water instead of an athlete in training! A slight shift in mindset is required because increasing the speed of movements will increase drag, so gauging the intensity by horizontal movement through the water is not appropriate. Instead, consider charting leg turnover (also referred to as cadence); a higher cadence reflects a higher intensity. Intensity can subjectively be assessed with a perceived exertion scale, like the Brennan scale. Using interval training has been found to be beneficial in studies with trained runners (3,7). In addition to workout intensity, attention to running form appears to be key. Given the combination of buoyancy and the increased density of water (compared with air), realize that muscle recruitment will be somewhat different, but the intent is to mimic OLR form while in the water. Some time may be needed to adjust to this new mode of exercise, but attention to form and intensity will help maximize the potential training benefits.
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