Sports Medicine 16 (6): 374-380, 1993 0112-1642/93/0012-0374/$03.50/0 © Adis International Limited. All rights reserved.

Physiological Responses to Deep Water Running in Athletes Robert P. Wilder! and David K. Brennan 2 Department of Physical Medicine and Rehabilitation, Division of Sportsmedicine, Baylor University Medical Center, and the Tom Landry Center for Sportsmedicine and Research, Dallas, Texas, USA 2 Department of Physical Medicine and Rehabilitation, Baylor College of Medicine, and the Houston International Running Center, Houston, Texas, USA

Deep water running is a popular form of cardiovascular conditioning for injured athletes as well as for other athletes who desire a low impact aerobic workout. Deep water running, or aqua running, consists of simulated running in the deep end of a pool aided by a flotation device (vest or belt) that maintains the head above water. The form of running in water follows as closely as possible the pattern used on land. The participant may be held in I location by a tether cord, essentially running in place, or may actually run through the water the width of the pool. The tether may serve to increase resistance, assist maintenance of a near vertical posture, and facilitate monitoring of exercise. No contact is made with the bottom of the pool, thus eliminating impact. Significant differences exist in the physiological responses to deep water running and land based running. An understanding of these differences will assist the athlete, coach, or healthcare provider in developing optimum exercise prescriptions and rehabilitative protocols.

1. Maximal Physiological Responses Several studies have compared maximal physiological responses to deep water running and land

based running (Butts et al. 199Ia,b; Navia 1986; Svedenhag & Seger 1992; Town & Bradley 1991). Important measures of response to exercise of maximal intensity include maximum oxygen uptake (\'02max) and maximal heart rate. Maximal \'02 values during supported deep water running (with a flotation device) have ranged from 83 to 89% of those values obtained during land based running. Heart rates during deep water running have ranged from 89 to 95% of those values obtained during land based running. Butts and colleagues (1991b) reported results obtained during maximal graded exercise tests (GXT) of deep water running in 12 female high school cross-country runners. The average \'02max was 86% of the average \,02max obtained during a treadmill GXT. Peak heart rates averaged 91 % of those values obtained on the treadmill. No significant difference was noted in maximal perceived exertion. In a similar study, Butts et al. (1991a) examined maximal responses in 24 trained men and women. The average \'02max values measured during a GXT of deep water running were 84% of those values obtained during treadmill running for women and 89% for men. Peak heart rates during deep water running averaged 95% of those values obtained on land. Ventilation volumes were also

Physiological Responses to Deep Water Running

375

running (12.4 mmollL vs 10.0 mmollL). Maximal oxygen pulse was slightly lower during deep water running (23.4 ml 02/beat vs 24.5 ml 02/beat) [table I]. Maximal oxygen uptakes during a symptomlimited deep water running GXT averaged 83% and peak heart rates averaging 89% of those values attained during maximal treadmill running (Navia 1986). However, the RER reported during deep water running averaged 0.95, insufficient to qualify as a true maximal test. During unsupported deep water running (without a flotation device), Town and Bradley (1991) reported V02max values averaging 73.5% and peak

noted to be significantly lower during deep water running. Examining gender differences, men had significantly greater ventilation volumes and maximal oxygen uptakes (as has been shown with land based exercise); however, no significant difference between the sexes was noted for respiratory exchange ratio (RER) or peak heart rate. During deep water running at maximal exertion in 10 trained runners, Svedenhag and Seger (1992) recorded V02max values averaging 88% and peak heart rates averaging 91 % of those values obtained during treadmill running. Blood lactate levels tended to be higher following maximal deep water

Table I. Maximal physiological responses [mean (standard deviation)] to deep water running Physiological measure

Reference Butts et al.

Butts et al.

Butts et al.

Svedenhag &

Town & Bradley

(1991b)

(1991a)

(1991a)

Seger (1992)

(1991)

[females]

[males]

Max V02 TM (Umin)

3.0(0.3)

3.321 (0.317)

4.550 (0.368)

4.60 (0.14)

Max V02 DWR (Umin)

2.6 (0.5)

2.786 (0.367)

4.086 (0.405)

4.03 (0.13)

Max V02 TM (mf/kg/min)

54.7 (7.0)

55.7 (4.8)

64.5 (2.8)

58

Max '1102 DWR (mf/kg/min)

46.8 (9.1)

46.8 (5.9)

58.4 (3.9)

48

'il02 DWRlTM (%)

86

84

89

87.8 (2.4)

HR max TM (beats/min)

197.9 (9.4)

188.7 (9.3)

193.3 (5.8)

188 (2)

HR max DWR (beats/min)

180.3 (6.0)

179.5 (7.5)

183.4 (5.9)

172 (3)

HR DWRlTM (%)

91

95

95

91

RERTM

1.05 (0.03)

1.13 (0.03)

1.15 (0.04)

1.2 (0.03)

1.09 (0.04)

1.11 (0.03)

1.1 (0.04)

RERDWR

1.01 (0.08)

RPETM

19.1 (0.3)

RPEDWR

19.3 (0.6)

73.50

Navia (1986)

83 197 175

90

89 0.95 19.2 19.1

Lactate TM (mmol/L)

10.0(0.6)

Lactate DWR (mmof/L)

12.4 (1.3)

Lactate DWRITM (%)

124

02 pulse max TM

24.5

81

(ml 02lbeat) 02 pulse max DWR

23.4

(ml O2lbeat) 02 pulse max DWRITM

0.96

Ventilation TM (Umin)

111.6 (7.0)

150.0 (11.6)

Ventilation DWR (Umin)

97.7 (10.9)

140.8 (17.8)

Abbreviations: DWR = deep water running; HR = heart rate; RER = respiratory exchange ratio; RPE = ratings of perceived exertion; TM = treadmill.

376

heart rates averaging 90% of those values obtained on land. Blood lactate levels after maximal deep water running were lower than those levels after maximal treadmill running. However, the water test lasted only 4 minutes (two I-minute submaximal stages and a 2-minute stage at maximal intensity). Treadmill stages lasted 3 minutes each. In our experience, I-minute stages are insufficient to effect a complete response to a particular exercise intensity during deep water running.

2. Submaximal Physiological Responses and Perceived Exertion Important relationships have been shown during deep water running at submaximal intensities. It appears that for a given level of perceived exertion, heart rates and oxygen uptake levels tend to be lower during deep water running than during treadmill running. During graded exercise testing, Svedenhag and Seger (1992) demonstrated higher central and peripheral perceived exertion ratings during deep water running at any given \T02 or heart rate than during treadmill running at the same intensity. Navia (1986) reported a similar relationship between rating of perceived exertion (RPE) and physiological responses during graded exercise. Higher RPE values were expressed during deep water running at any given heart rate than during treadmill running. A similar relationship was noted for RPE and \T02. These differences are important if perceived exertion is used as the sole measure of exercise intensity (table I). During submaximal deep water running for 45 minutes, Bishop et al. (1989) recorded lower mean \T02 and ventilation values than during a 45-minute treadmill run at a comparable perceived exertion (\T02: 29.8 vs 40.6 mllkg/min; ventilation: 58.1 vs 79.1 Llmin). Heart rates were also lower during deep water running (122 vs 157 beats/min); however, this was not deemed statistically significant with the small sample (n = 7) involved. Two of the participants described as the most accomplished runners and enthusiastic deep water runners did achieve similar responses during both deep water running and treadmill running, suggest-

Sports Medicine 16 (6) 1993

ing that motivation or familiarity may play a role in attaining levels of physiological response. Ritchie and Hopkins (1991) noted that perceived exertion and perceived pain during a 30minute deep water run at a 'hard' pace were comparable to those ratings obtained during 'hard' treadmill running. These ratings were significantly greater than perceived exertions during treadmill running or road running at a 'normal' training pace. Examining the relationship between heart rate and \T02 during submaximal graded exercise, Svedenhag and Seger (1992) reported lower heart rates during deep water running than treadmill running at any given level of oxygen uptake. Oxygen pulse was also higher in the water during sub maximal exercise. A similar relationship between heart rate and \T02 was noted by N avia (1986) at higher work loads. These results suggest that an aerobic training effect may occur at lower heart rates during deep water running than during treadmill running. Yamaji et al. (1990) noted significant interindividual variability in heart rate (HR) responses as a function of \T02 during unsupported deep water running. Although group data revealed a similar HR- \T02 relationship for both deep water running and treadmill running, 2 of the more skilled participants did have lower heart rate values during deep water running than during treadmill running at comparative \T02. Ritchie and Hopkins (1991) showed heart rate values during the 30-minute session of hard deep water running that were lower than those during hard treadmill running (159 vs 176 beats/min). Oxygen uptake values, however, were similar (49 ml/kg/min vs 53 ml/kg/min). The heart rate values obtained during hard deep water running were similar to those obtained during treadmill running at a normal training pace. However, corresponding oxygen uptake was greater during hard deep water running. The Ritchie and Hopkins (1991) study also supports the contention that deep water running may result in a greater overall aerobic response if heart rate is used as the measure of exercise intensity.

Physiological Responses to Deep Water Running

377

3. Long Term Training Effects Two studies have reported the long term effects of a deep water running training programme (Brennan et al. 1992; Eyestone et al. 1993; Michaud et al. 1992). Ten volunteers who underwent an 8week training programme of deep water running showed improvements in V02max during both water based and land based graded exercise testing (19.6 and 10.7% respectively), thus demonstrating a training effect as well as a crossover effect to land based exercise (Brennan et al. 1992; Michaud et al. 1992). Eyestone et al. (1993) demonstrated that deep water running was comparable to land based running and cycling for preserving levels of fitness during a 6-week training period at maintenance duration (20 to 30 min) and frequency (3 to 5 times/week). Although a small decrease in V02max was noted for each group, this was much less than the 16 to 17% loss previously reported during a 6-week rest period.

4. Deep Water Running Compared with Land Based Running Several possible explanations exist for the differences in metabolic response to deep water running and land based running. Differences in muscle use and activation patterns contribute to these differences in exercise response. Furthermore, owing to the elimination of weight bearing and the addition of resistance, less work is likely to be performed by the larger muscle groups of the lower extremities, and a comparatively increased proportion of work is done by the upper extremities than during land based exercise. This may contribute to the lower maximal oxygen uptakes recorded during deep water running. Lower perfusion pressures in the legs during immersion with resultant decreases in total muscle blood flow have also been proposed to influence a higher anaerobic metabolism during deep water running (Svedenhag & Seger 1992). Hydrostatic pressure is postulated to assist cardiac performance by promoting venous return;

Fig. 1. The form of running in water closely resembles movement patterns used on land. A greater physiological response in terms of maximum oxygen uptake and heart rate response can be obtained by strict adherence to proper technique (with permission, Houston International Running Center, Inc. 1993). (Top) lateral view (close-up): note that the arm carry is identical to that used with land based running; (middle) anterior view; (bottom) lateral view.

Sports Medicine 16 (6) 1993

378

thus the heart does not have to beat as fast to maintain cardiac output. This may contribute to the lower heart rates observed during both submaximal and maximal deep water running. Temperature has also been demonstrated to have an effect on heart rate during exercise, with higher temperatures correlating with higher heart rates. Familiarity with this form of exercise also appears to be an important factor in maximising physiological response to deep water running when measured at a particular level of perceived exertion. Our experience has indicated that strict adherence to proper form and technique ensures higher physiological responses as measured by \T02 and heart rate (Brennan & Wilder 1990) [see fig. 1]. We have also found 3 methods useful for grading exercise intensity and maximising physiological responses during deep water exercise: heart rate, rating of perceived exertion, and cadence (Wilder & Brennan 1993). Workout programmes are typically designed to reproduce the work an athlete would do on land, and incorporate long runs as well as interval/speed training (see fig. 2).

Number 01 repellbons

t

(37:00) .,

I

Durabon 01 repeubons (in mln:sec)

! x 2:00 0

APE SH (30), 8 x 5 x 2:00 0 APE SH (30),

I

!oo 0

APE H (30)

I

WOfkou1 number Total workou1llme

exertion level, APE

Aecovery penod In sec

Fig. 2. Sample workout protocol (from Brennan & Wilder 1990). In the case shown the workout protocol (#1) would call for 5 repetitions of 2 minutes (2:00) duration each at a perceived exertion (RPE) level of somewhat hard (SH), followed by 8 repetitions of 1 minute (1 :00) duration each at a perceived exertion level of hard (H), followed by 5 repetitions of 2 (2:00) minutes duration each at a perceived exertion level of SH with a 3D-second (30) recovery period consisting of easy deep water jogging after each interval.

6 7 8 9 10

Very, very light Very light

11 12 13 14 15

FaIrlY light

17

Very han:!

16

18 19 20

Somewhat hard Hard

very, very hard

Fig. 3. Borg Scale of perceived exertion (Borg 1982).

4.1 Heart Rate A high correlation exists between heart rate and oxygen uptake. The American College of Sports Medicine (1991) guidelines recommend that for a training effect exercise should be at a level between 55 and 90% of the maximum heart rate (the target heart rate range). The maximum heart rate can be estimated (220 minus age) or can be based upon heart rate levels attained during exercise of maximum effort. Although heart rate levels in the water tend to be lower than those attained on land, it is possible to approach land based values by adherence to proper technique. Heart rate can be monitored by a waterproof heart rate monitor or periodically monitored by palpation. 4.2 Ratings of Perceived Exertion The most commonly used scale of perceived exertion is the Borg Scale, a I5-point scale with verbal descriptors ranging from very, very light to very, very hard (see fig. 3). We have been using the Brennan Scale (Brennan & Wilder 1990), a 5-point scale designed for deep water running with verbal descriptors ranging from very light to very hard (see fig. 4). We further instruct the athletes that level 1 (very light) corresponds to a light jog or recovery run, level 2 (light) to a long steady run, level 3 (somewhat hard) to a 5 to lOkm road race pace, level 4 (hard) to a 400 to 800m track speed, and levelS (very hard) to sprinting (a 100 to 200m

Physiological Responses to Deep Water Running

379

track speed). The Brennan scale facilitates the incorporation of both speed and distance work into workouts in a manner easily understood by both coaches and athletes.

1

V~I!lLht

2 3

light Somewhat hard Hard Very hard

4

5

Fig. 4. Brennan Scale of perceived exertion (from Brennan & Wilder 1990).

4.3 Cadence We have demonstrated a significant correlation between cadence and heart rate, with intraindividual correlations averaging 0.98 (Wilder et al. 1993). The competitive athletes studied underwent a graded test of aqua running following our standard protocol (see fig. 5). Cadence is controlled through the use of an auditory metronome, thus providing an external cue to regulate exercise intensity. By recording heart rate responses to varying levels of cadence we can anticipate an expected physiological response to a particular cadence level. Workouts using timed intervals can be designed at particular cadence levels.

Heart rate is used primarily during long runs, prolonged periods of exercise at a specified rate (target heart rate). Rating of perceived exertion and cadence are most often used for interval sessions. RPE is most useful in group settings, while cadence is most appropriate for individual sessions.

5. Conclusions In spite of the differences between deep water running and land based running, aqua running does

Name: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

Date: _ _ _ _ _ __

Predicted 90% max heart rate : ________________

TMI _ _ _ _ _ ___

Stage

End-point

Cadence

Heart rale

RPE

Comments

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Fig. 5. Houston International Running Center Data Collection Sheet, Wilder graded exercise test for aqua running (©1990, Houston International Running Center, with permission).

380

elicit the physiological responses necessary to promote a training effect as defined by the American College of Sports Medicine (1991) [40 to 85% V02max or 55 to 90% maximum heart rate]. These responses can be maximised by adherence to proper technique and by the use of environmentspecific means of exercise prescription (established specifically for deep water exercise). Deep water running also offers additional benefits, most notably the maintenance of quick turnover (rapid gait cycling) as well as coordinated movements between the arms and legs. These aspects facilitate return to land based training. Maintaining conditioning is a challenge for injured athletes. Deep water running provides an effective means to continue training during rehabilitation. Deep water running may then be incorporated into a regular training programme, providing a low stress form of additional cardiovascular exercise.

References American College of Sports Medicine. Guidelines for graded exercise testing and exercise prescription, 4th ed., p. 96, Lea & Febiger, Philadelphia, 1991 Bishop PA, Frazier S, Smith J, Jacobs D. Physiologic responses to treadmill and water running. Physician and Sportsmedicine 17: 87-94, 1989 Borg GY. Psychophysical basis of perceived exertion. Medicine and Science in Sports and Exercise 14: 377-387, 1982 Brennan DK, Wilder RP. Aquarunning: an instructors manual, Houston International Running Center, Houston, 1990

Sports Medicine 16 (6) 1993

Brennan DK, Michaud TJ, Wilder RP, Sherman NW. Gains in aquarun peak oxygen consumption after eight weeks of aquarun training. Abstract. Medicine and Science in Sports and Exercise 24 (Suppl.): S23, 1992 Butts NK, Tucker M, Greening C. Physiologic responses to maximal treadmill and deep water running in men and women. American Journal of Sports Medicine 19: 612-614, 1991a Butts NK, Tucker M, Smith R. Maximal responses to treadmill and deep water running in high school female cross country runners. Research Quarterly for Exercise and Sport 62: 236-239, 1991b Eyestone ED, Fellingham G, George J, Fisher AJ. Effect of water running and cycling on maximum oxygen consumption and 2-mile run performance. American Journal of Sports Medicine 21: 41-44, 1993 Michaud TJ, Brennan DK, Wilder RP, Sherman NW. Aquarun training and changes in treadmill running maximal oxygen consumption. Abstract. Medicine and Science in Sports and Exercise 24 (Suppl.): S23, 1992 Navia AM. Comparison of energy expenditure between treadmill running and water running. Thesis, University of Alabama at Birmingham, 1986 Ritchie SE, Hopkins WG. The intensity of exercise in deep water running. International Journal of Sports Medicine 12: 27-29, 1991 Svedenhag J, Seger J. Running on land and in water: comparative exercise physiology. Medicine and Science in Sports and Exercise 24: 1155-1160, 1992 Town GP, Bradley SS. Maximal metabolic responses of deep and shallow water running in trained runners. Medicine and Science in Sports and Exercise 23: 238-241, 1991 Wilder RP, Brennan DK, Schotte DE. A standard measure for exercise prescription for aqua running. American Journal of Sports Medicine 21: 45-48, 1993 Wilder RP, Brennan DK. Aqua running for athletic rehabilitation. In Buschbacher & Braddom (Eds) State of the art reviews in physical medicine and rehabilitation: sportsmedicine, in press, 1993 Yamaji K, Greenley M, Northey DR, Hughson RL. Oxygen uptake and heart rate responses to treadmill and water running. Canadian Journal of Sports Sciences 15: 96-98,1990

Correspondence and reprints: Dr Robert P. Wilder, The Tom Landry Center for Sportsmedicine and Research, 411 N. Washington, Suite 4000, Dallas, TX 75246, USA.