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The Physiology of Deep Water Running as a Training Program

Proposition for Debate - by Robin Horne

Contents

Statement of the Topic

The Physiology of Deep Water Running as a Training Program

Introduction

Running related injuries are common and frequently due to overuse. The prescription of an appropriate training protocol to maintain an injured athlete-s cardiovascular and muscular fitness is a major challenge for the treating clinician. Often part of the treatment program involves reducing or discontinuing training. This inactivity can result in a significant loss of cardiovascular fitness (Coyle 1984). Research has shown that a six- week break from training can result in a 14-16% decrease in maximal oxygen uptake (VO2max), a significant indicator of aerobic performance (Coyle 1984).

When athletes have been required to avoid full weight-bearing activities often forms of non-weight bearing exercise, such as swimming or cycling, is prescribed to maintain fitness levels. Such activities lack specificity to running. Deep water running (DWR) however, involves the simulation of running while being suspended in deep water by the use of a floatation device. This essentially weightless environment eliminates the ground reaction force associated with heel strike. It has gained popularity in the rehabilitation of injured runners as it is seen to have high specificity by simulating the same muscle groups in a similar movement pattern to running on land (Hamer and Morton 1990). The research to support this theory has often been of poor experimental design with low subject numbers. This paper aims therefore to examine the available literature in an attempt to evaluate the efficacy of DWR as an alternative to running on land. Parameters such as frequency, intensity and duration of training are examined with regard to their effect on maintaining cardiovascular fitness and strength.

Aerobic Performance

Following injury most athletes are concerned regarding their loss of aerobic fitness during the recovery process. If DRW is to be prescribed as an alternative to land running it is important to examine the effect of this exercise on maintaining or improving aerobic ability.

Hamer and Morton (1990) performed a study that examined DRW with regard to aerobic, anaerobic and muscular parameters. Twenty untrained subjects were randomly allocated into a DWR and a control group. The DRW group underwent an eight-week interval- training program with 20-45 minutes per session three times per week. Aerobic performance parameters measured were maximum O2 consumption (VO2max), maximal oxygen pulse (O2 pulse max), maximal ventilation (VEmax) and sub-maximal and maximum heart rate (HRmax). These were measured on an incremental treadmill test to volitional exhaustion. Muscular endurance was examined by measuring knee flexor and extensor torque output on a Cybex II. A graded exercise test was performed by the DWR group to determine VO2max and the relationship between HR and oxygen consumption during running in water. Training was performed three times per week and target HR's increased from 60% (wks 1-2) to 70% (wks 3-6) to 80%VO2max (wk 6-8).

Significant increases in VO2max and O2pulse occurred in the DWR group that were not found in the control group. Significant decreases occurred in HRmax of the DWR group compared to the control. The DWR group also demonstrated a 13% increase in anaerobic peak power, anaerobic mean power and anaerobic total work. As in other studies they found lower heart rates (6-12b/min) at VO2max and O2pulsemax measured while DWR compared with treadmill running. Hamer and Morton (1990) concluded that the six-week training protocol used demonstrated DWR to effectively increase both aerobic and anaerobic fitness.

Physiological responses when exercising to maximal aerobic capacity were compared between twenty male subjects while DWR and TR (Nakanishi et al 1999). Oxygen consumption (VO2), ventilation, respiratory quotient (RQ), HR, rate of perceived exertion (RPE) and blood lactate were measured. Responses to DWR compared with TR indicated significantly lower VO2max (2.68 vs 3.4 ml/kg/min), HRmax (171 vs 190 b/min) maximal minute ventilation and peak blood lactate levels. It was suggested that the hydrostatic effects of immersion in water and altered muscle recruitment patterns of DWR attributed to the lower VO2max and HRmax values compared with TMR. These responses were found to be similar in young and middle aged subjects.

In a similar study, maximal physiologic responses were compared between DWR and TMR using 24 subjects (Butts et al 1991). Again, VO2max and HRmax were found to be significantly lower with DRW, with similar responses found in both sexes. RQ was not found to be significantly different. The observation was made that these differences were similar in magnitude to those found between TMR and cycling ergometry. As such, it was recommended that DWR should still be considered a useful training technique. Again caution was advised in using land based HR's to determine training intensity for a DWR program.

Davidson (2000) examined the ability of deep water running training to improve cardiovascular fitness in a young sedatory population. Ten untrained female subjects were allocated into a DRW and road running (RR) group. They each underwent a four- week training program consisting of progressive aerobic interval training, three days a week. A ten-week detraining program followed this training. A four-week training program in the alternate exercise was then completed. Subjects underwent pre-test VO2max testing which was repeated after each training program. Results indicated both methods produced a significant increase in VO2max compared with the pre-test without a significant difference between the two. The finding that a DWR regime may be equally as effective as road running in improving cardiovascular fitness in an untrained population has important clinical implications. Specifically for those with musculoskeletal disorders that may exclude the possibility of RR, it is important to be able to prescribe exercise in a non-impact environment, which produces similar physiological effects.

During a long rehabilitation phase it may be useful to compare current aerobic fitness with pre-injury levels. A sub-maximal DWR test could be used if it was able to provide a valid VO2max estimate. Decisions regarding training intensity based on comparisons between the water and land tests could then be safely made. In order to develop a DWR field test for estimating VO2max a study was performed by Sherman and Mitchaud (1997). A maximal treadmill test was used to determine VO2max in thirty subjects. A 15-minute sub-maximal DWR test was then performed at a self-selected cadence. A regression model using cadence, PPE, body weight and gender was developed which was found to accurately predict VO2max. Therefore, based on the results of this study, and using a similar young healthy population, the model developed could be used to accurately determine VO2max during a rehabilitation phase. Adjustments to the intensity of the athlete's current training regime could be made accordingly.

Frequency and Intensity of Exercise

Intensity of training is an important parameter in exercise prescription. Commonly target HR ranges are used as an indicator of intensity in road running (RR). The relationship therefore between the parameters of HR, cardiac output (Q) and stroke volume (SV) while DWR and RR need to be examined if accurate prescription of intensity of exercise in water is to be achieved.

McClung et al (1998) performed a study on five endurance athletes to examine Q and SV at a similar HR and VO2 when DWR and treadmill running (TMR). Results indicated Q and SV to be significantly higher in TMR as compared to DWR (15.6 l/min and 17.7 l/min respectively). It was concluded that while HR was lower while DWR compared with TMR other physiologic parameters must be examined in order to prescribe intensity.

Eyestone et al (1993) compared the effectiveness of DWR, cycling and running in maintaining VO2max and 2 mile run performance using a six-week training protocol.

Thirty-two trained athletes underwent a 4-week pre-training course of 30 minutes running three days per week. VO2max and 2-mile run performance was measured after the pre-training and post intervention. VO2max criteria was expiratory ratio > 1.0, plateau of VO2 and achievement of HRmax. Following the two-mile run subjects were stratified into low, medium and high performance levels and randomly allocated into a cycling, DWR or LR group and trained for six weeks. Training frequency was 3x/week (wk 1), 4x/week (wks 2-5) and 5x/week (wk 6). Length of training was increased from 20mins to 30mins and the intensity from 70% to 80% HRmax.

All groups showed a slight decrease in 2-mile run times though this was statistically insignificant. A sight decrease in VO2max also occurred in all groups with insignificant differences between groups.

This study would indicate that an injured runner who adopted a DWR or cycling protocol at an intensity, duration and frequency similar to pre-injury could maintain near normal VO2max and 2-mile run times over a six-week period. While this study maintained frequency and duration of training other research found that if training intensity was maintained frequency could be reduced by 67% for up to 15 weeks with no loss of performance (Hickson et al 1995).

Rate of Perceived Exertion

Often while exercising athletes will estimate their intensity by using perceived exertion rather than a HR. A scale that correlates rate of perceived exertion (RPE) and HR has been developed. Borg (1982) demonstrated a strong linear relationship between RPE and HR with incremental exercise intensity.

Hamer and Slocombe (1997) examined the relationship between HR and RPE for DWR and TMR. Twelve subjects were used and performed six sub-maximal incremental work intensities running on the treadmill and in water. At each incremental exercise level the subject provided a RPE between 6 (very, very light) and 20 (very, very hard) to reflect total body fatigue. This scale was developed to correspond approximately to HR's ranging from 60 to 200 beats/min. Results indicated that running in water with an RPE the same as on the treadmill produced a HR which was on average 17 beats/min lower. It was suggested this was due to increased cardiac output via an increased stroke volume produced by shunting of blood from the periphery. This occurred due to the hydrostatic pressure of the water increasing venous return and in turn stroke volume. Therefore, at similar sub-maximal exercise levels HR's were lower in the water due to an increase in cardiac output.

Ritchie and Hopkins (1991) performed a similar study that compared several physiologic parameters at a similar RPE while DWR and TMR. Eight subjects were required to exercise at an intensity which they perceived as hard for 30 minutes in deep water and on the treadmill at hard and normal. This was also compared to road running at a normal training pace. Physiological indices of intensity including oxygen consumption (VO2), respiratory quotient (RQ), HR and RPE were used to compare the two groups. Using these parameters it was found that hard DWR produced similar VO2 (73% of VO2max) to the treadmill hard run (78%) but significantly higher than the treadmill normal run (62%). The findings for RQ were similar. Heart rates during hard DWR however were similar to normal training and significantly lower than hard treadmill running. This was a similar finding to Hamer and Slocombe (1997). It was hypothesised that the lower HR at high RPE measured while DWR was due to the increased venous return or peripheral cooling produced by immersion in water. It was concluded that based on the intensity and duration used in the study, DWR could be used to maintain or improve aerobic power. Further work was needed though to verify that competitive performance could be enhanced with this technique. It was also recommended that caution should exercise in prescribing DWR training intensity based on HR's measured while land running.

The above findings were again reinforced in another study comparing RPE when DWR (Brown et al 1996). Heart rates and VO2 measurements were taken continuously while subjects performed DWR in three-minute stages to VO2 peak at leg speeds controlled by a metronome. RPE was measured on the Borg scale. This was compared to similar leg speeds measured while running on a treadmill. Results again demonstrated significantly higher RPE's during DWR at equal leg speeds to TMR. RPE's measured at each stage for either exercise mode did not show significant differences between men and women.

Wilder et al (1993) agrees that conventional methods of exercise prescription on land using heart rate and RPE may need to be modified for aqua running. Several reasons were provided for the need to alter the method of prescription including:

Also at similar RPE's, a comparison of DWR and TMR produced lower:

A study was performed to investigate if a correlation existed between cadence and heart rate (Wilder et al 1993). It was assumed that as HR and O2 uptake are linearly related and that to produce a training effect an exercise level between 55% and 90% of HRmax was desirable. Twenty subjects underwent an exercise test that matched running rhythm in the deep water to a cadence set by a metronome. Twelve incremental cadences were used and heart rates at each increment taken. It was demonstrated that a high correlation existed between cadence and heart rate. The conclusion drawn was that cadence could be used as a standard measure for exercise prescription for deep water running.

Age and Gender Physiologic Variations

Brown et al (1997) investigated the physiological responses to DWR and TMR between males and females. Twenty-four subjects (12 males and 12 females) performed tethered DWR at incremental leg speeds matched to metronome cadences. VO2 peak was recorded when the subject could no longer match the cadence. Subjects then performed a treadmill running test with cadences matched to the DWR test. When the final DWR cadence was reached the treadmill grade was incrementally increased 5% every two minutes until VO2max was reached. Significant gender differences averaged across all DWR occurred for VO2 l/min and VO2 ml/kg/min. These variations were not found for HR, VO2 ml/kg/LBW/min or RER. Gender differences for TMR were not found. TMR compared with DWR showed significant difference for HR, VE, VO2 ml/kg/min, VO2 ml/kg/LBW/min and RER. This appeared consistent with the other studies comparing the two exercise mediums. These results would indicate that when DRW is matched to TMR by stride cadence the physiological responses during DWR are significantly greater. Women appear to respond with less physiologic stress to DWR compared with males though are similar during TMR.

Brown et al (1998) also explored physiological parameters in older adults while DWR. The relationship between HR as a percentage of HRpeak and VO2 as a percentage of VO2peak were examined in twenty-three healthy older adults aged 50 to 70 years. The protocol involved DRW at three-minute incremental stages at leg speeds matched to a cadence. Oxygen uptake and HR were monitored continuously during the task until VO2peak was reached. Using linear regression the relationship between %VO2peak and %HRpeak was found to be significantly different. Similar differences were also found between males and females and would appear to support the gender differences revealed in the previous study by Brown et al (1997).

Conclusion

Deep water running has become an extensively used training option for the rehabilitation of runners. The research presented would suggest that a water-based running programme could be confidently implemented in the short or long term as a substitution for land running. DWR appears to satisfy the principles of specificity of training for running as effective maintenance and improvement of both aerobic and anaerobic fitness have been demonstrated. It appears submaximal DWR tests can be used to accurately determine current fitness levels. Target HR's should be set on average 17 b/min. lower to account for the effect of the water. If land RPE scores are used to set intensity, expect HR's to be lower compared to land running. It is suggested the athlete use a similar training frequency and intensity to pre-injury to maintain fitness though there is the indication that frequency may be reduced if the intensity is maintained.

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Exercise Physiology Educational Resources 2000