Received: 16 August 2017
Revised: 5 December 2017
Accepted: 16 February 2018
DOI: 10.1002/pri.1717
RESEARCH ARTICLE
Influence of water depth on energy expenditure during aquatic walking in people post stroke Hyosok Lim
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Daniel Azurdia
Department of Kinesiology, California State University, Northridge, Northridge, CA, USA Correspondence Hyosok Lim, Center of Achievement in the Department of Kinesiology, California State University, Northridge, 18111 Nordhoff street, Northridge, CA 91330, USA. Email:
[email protected]
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Brenda Jeng
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Taeyou Jung
Abstract Background and Purpose:
This study aimed to investigate the metabolic cost during
aquatic walking at various depths in people post stroke. The secondary purpose was to examine the differences in metabolic cost between aquatic walking and land walking among individuals post stroke. Design:
A cross‐sectional research design is used.
Methods:
Twelve participants post stroke (aged 55.5 ± 13.3 years) completed 6 min
of walking in 4 different conditions: chest‐depth, waist‐depth, and thigh‐depth water, and land. Data were collected on 4 separate visits with at least 48 hr in between. On the first visit, all participants were asked to walk in chest‐depth water at their fastest speed. The walking speed was used as a reference speed, which was applied to the remaining 3 walking conditions. The order of remaining walking conditions was randomized. Energy expenditure (EE), oxygen consumption (VO2), and minute ventilation (VE) were measured with a telemetric metabolic system. Results:
Our findings showed statistically significant differences in EE, VO2, and VE
among the 4 different walking conditions: chest‐depth, waist‐depth, and thigh‐depth water, and land (all p < .05). The participants demonstrated reduction in all variables as the water depth increased from thigh depth to chest depth. Significantly higher values in EE and VO2 were found when the water depth increased from waist depth to chest depth. However, no significant difference was found in all variables between thigh‐ depth and waist‐depth walking. Only thigh‐depth walking revealed significant differences when compared with land walking in all variables. Conclusions:
People post stroke consume less energy in chest‐depth water, which
may allow them to perform prolonged duration of training. Thigh‐depth water demonstrated greater EE compared with other water depths; thus, it can be recommended for time‐efficient cardiovascular exercise. Waist‐depth water showed similar EE to land walking, which may have been contributed by the countervailing effects of buoyancy and water resistance. KEY W ORDS
cardiorespiratory responses, pool floor walking, stroke, water immersion
Physiother Res Int. 2018;e1717. https://doi.org/10.1002/pri.1717
wileyonlinelibrary.com/journal/pri
Copyright © 2018 John Wiley & Sons, Ltd.
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However, the water depth at waist level and above revealed an opposite trend. It has been reported that metabolic cost reduced as the
Gait impairment is one of the major motor characteristics of people
water depth increased from the waist level (Alkurdi et al., 2010;
post stroke. Although 65–85% of individuals post stroke learn to walk
Benelli et al., 2014).
independently by 6 months through rehabilitation, gait abnormalities
The metabolic cost during aquatic treadmill walking was reported
persist through the chronic stages of stroke (Wade, Wood, Heller,
to be significantly different among various water depths in healthy
Maggs, & Langton Hewer, 1987). Gait impairment, such as hemiparetic
adults. However, no studies examined the influence of water depth
gait, demonstrates increased energy expenditure (EE) among people
in people post stroke. In addition, to our knowledge, only one study
post stroke when compared with an efficient symmetric gait
have attempted to use pool floor walking as a form of aquatic walking
(Zamparo, Francescato, De Luca, Lovati, & Di Prampero, 1995). More-
(Nishiyori, Lai, Lee, Vrongistinos, & Jung, 2016). Most previous
over, the amount of increased energy cost has been reported to be
aquatic gait research utilized an aquatic treadmill, which tends to pro-
twice that of normal gait (Platts, Rafferty, & Paul, 2006). The high‐
vide convenient experimental control but is not readily available in
energy demand while walking has a profoundly negative impact on
clinical or community settings. Therefore, the purpose of this study
functional independence, mobility, and community participation in
was to investigate the influence of different water depths on meta-
individuals post stroke (Eng & Tang, 2007).
bolic cost during pool floor walking in people post stroke. It was
People post stroke often experience increased physical inactivity
hypothesized that participants post stroke would demonstrate lower
due to the high‐energy demand of walking, resulting in poor cardio-
metabolic cost as the water depth increases to the chest depth during
vascular fitness (Lee & Blair, 2002). Poor cardiovascular fitness is
pool floor walking. The secondary purpose was to examine differ-
related to a higher risk of recurrent stroke and stroke mortality
ences in metabolic cost between land walking and pool floor walking
(Salonen et al., 2003). In addition, up to 75% of people who
at three water depths among individuals post stroke. It was hypothe-
experienced a stroke have some form of cardiovascular disease
sized that participants post stroke would show higher metabolic cost
(Roth, 1993). Therefore, improving cardiovascular fitness is an essen-
during land walking when compared with pool floor walking in three
tial component in stroke rehabilitation.
water depths.
Treadmill walking has been widely utilized as a method of stroke rehabilitation. Walking on a treadmill has shown a substantial and progressive reduction on the EE in people post stroke (Macko et al.,
2
METHODS
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1997). The reduced EE during walking is considered to be an indicator of improved cardiovascular fitness (Macko et al., 2005). Body‐weight‐ supported treadmill (BWST) walking creates a safer walking environ-
2.1
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Participants
ment for people post stroke in the early stage of rehabilitation by
Twelve individuals post stroke (6 males/6 females, mean age
reducing the amount of body mass they need to carry. In addition,
55.5 ± 13.3 years) participated in this study. Participant's mean height
the metabolic cost of BWST walking was reported to be lower when
and weight were as follows: height (165.7 ± 9.6 cm), weight
compared with unsupported treadmill walking in individuals post
(79.2 ± 15.1 kg). All participants were minimum of 6‐month post‐
stroke (Danielsson & Sunnerhagen, 2000). However, BWST tends to
stroke after their diagnosis (Table 1). Participants were (a) able to walk
be cumbersome because it often requires an instrumented treadmill
independently without a walking aid for a minimum of 10 min, (b)
and increases the level of discomfort due to the harness system.
cooperate with the testing procedures, and (c) had no surgery within
Buoyancy allows an individual to experience partial weight bear-
the last 6 months. Participants were excluded if they had (a) an acute
ing effect in an aquatic setting. The effect of buoyancy reduces the
injury, (b) cardiovascular complication, (c) uncontrolled seizure,
vertical ground reaction force on the lower extremities, which contrib-
(d) cognitive impairment that interferes the participant to follow the
utes to less body weight bearing during aquatic walking (Nakazawa,
procedures, or (e) fear of water. The study was approved by an
Yano, & Miyashita, 1994). A recent study found lower EE during
institutional review board in the university. All participants were
aquatic treadmill walking when compared with overground treadmill
required to provide written permission from their primary physicians
walking in individuals post stroke (Jung, Ozaki, Lai, & Vrongistinos,
to participate in the study. Written informed consent was acquired
2014). Moreover, the body weight support effect from the buoyancy
from each participant prior to data collection.
allows people with gait impairment to exercise in the early stage of rehabilitation, even though they may lack postural control and balance
TABLE 1
Characteristics of the 12 participants post stroke
(Barbeau, Wainberg, & Finch, 1987). The effectiveness of aquatic exercise in people post stroke has been well documented in previous literature (Chu et al., 2004; Yoo, Lim, Lee, & Kwon, 2014).
Characteristics Gender (M/F)
Stroke (n = 12) 6/6
Previous studies reported that aquatic treadmill walking at various
Age (years)
water depths affects the metabolic cost in healthy adults
Height (cm)
(Alkurdi, Paul, Sadowski, & Dolny, 2010; Benelli et al., 2014; Gleim &
Weight (kg)
Nicholas, 1989; Pohl & McNaughton, 2003). When the water depth
Years post stroke
4.4 ± 2.4
was below waist level, metabolic cost increased as the water depth
Affected side (R/L)
5/7
increased (Gleim & Nicholas, 1989; Pohl & McNaughton, 2003).
55.5 ± 13.3 165.7 ± 9.6 79.3 ± 15.2
Note. M = male; F = female; R = right; L = left. Mean ± standard deviation.
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2.2
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Experimental design
remaining walking conditions was randomized. A metronome and ver-
A movable floor pool (KBE Bauelemate, GmbH & Co., Wilhelmshaven, Germany) was used for aquatic walking and an open carpeted room
bal prompts were utilized to match cadence and lap time among the four walking conditions.
for land walking at the university‐based aquatic therapy centre (Figure 1). Participants were required to complete four walking ses-
2.4
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Analysis
sions in different conditions: chest‐depth, waist‐depth, and thigh‐ depth water, and land on separate days. Chest depth was defined as the level of xiphoid process, waist depth was defined as the level of umbilicus, and thigh depth was defined as the level of greater trochanter. The water depths were adjusted using the movable floor pool. Dependent variables such as EE, oxygen consumption (VO2), and minute ventilation (VE) were measured during the 6‐min walk test using
The mean EE, VO2, and VE values based on the 6‐min walk tests in four walking conditions were calculated. Separate repeated measures analysis of variance was used to observe the difference among four walking conditions. P values were adjusted by using Bonferroni method. Data analyses were performed using SPSS software, version 22.0 (IBM SPSS Statistics 22, Armonk, NY, USA).
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the telemetric metabolic system (K4b , Cosmed Inc., Rome, Italy, 1998) at each water depth. The telemetric metabolic system captured breath‐by‐breath gas exchange and was kept in a waterproof container during aquatic walking sessions. The water temperature was maintained constant at 34–35 °C (93.2–95.0 °F).
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RESULTS
Twelve participants post stroke met the inclusion criteria. All participants successfully completed the research procedures without injuries or falls. Participant information is summarized in Table 1. Statistical
2.3
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Procedure
analysis revealed significant differences among four walking conditions in EE, VO2, and VE (all p < .05). The means and standard devia-
All participants completed four walking sessions on a separate day
tions of all dependent variables at four different walking conditions
with at least 48 hr in‐between. Each walking session consisted of
are displayed in Table 2.
10‐min seated rest, followed by 6‐min walking on a 20‐m oval‐shaped
Post hoc analysis showed a significant reduction in EE, VO2, and
walkway while wearing a telemetric metabolic system. Participants
VE as the water depth increased from thigh‐depth to chest‐depth
were asked not to consume any caffeine or alcohol at least 3 hr prior
water. The participants significantly decreased EE by approximately
to each session.
33% from thigh depth to chest depth (5.03 to 3.38 kcal/min;
During the first session, participants were instructed to walk at
p = .009) and 17% from waist depth to chest depth (4.09 to
their fastest speed for 6 min at chest‐depth water. Lap time was
3.38 kcal/min; p = .009). They significantly decreased VO2 by 33%
recorded to identify participants' walking speed. A metronome was
from thigh depth to chest depth (12.42 to 8.27 ml·kg−1·min−1;
also used to measure the participants' cadence. The lap time and
p = .008) and 19% from waist depth to chest depth (10.20 to
cadence were averaged to determine the reference walking speed.
8.27 ml·kg·min−1; p = .020). Significant reduction in VE by 30% was
Participants performed walk tests at the speed determined from the
noted from thigh depth to chest depth (29.66 to 20.70 L/min;
first session in the remaining three walking conditions such as waist‐
p = .036). However, no significant difference in VE was identified
depth and thigh‐depth water, and land. The order of the three
between waist depth and chest depth (Figure 2). Our results
FIGURE 1
Movable floor pool
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TABLE 2
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Physiological responses in different walking conditions Water depth Chest
Measures
b,c
EE (kcal/min)
3.38 ± 1.36
VO2 (ml·kg−1·min−1)
8.27 ± 2.26b,c 20.70 ± 9.64b
VE (L/min)
Waist 4.09 ± 1.68
Thigh d
5.03 ± 1.87
p value
Land a,d
3.95 ± 1.48
b
.010
10.20 ± 3.15d
12.42 ± 4.18a,d
10.15 ± 3.17b
.014
24.28 ± 10.79
29.66 ± 11.51a,d
22.75 ± 9.02b
.028
Note. EE = energy expenditure; VO2 = oxygen consumption; VE = minute ventilation. Mean ± standard deviation. a
Significantly different than land (p < .05).
b
Significantly different than thigh (p < .05).
c
Significantly different than waist (p < .05).
d
Significantly different than chest (p < .05).
FIGURE 2
Differences in (a) energy expenditure, (b) oxygen consumption, and (c) minute ventilation among four walking conditions
demonstrated no significant differences between thigh‐depth and
4
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DISCUSSION
waist‐depth walking in all variables. When comparing aquatic and land walking, statistical significance
The study aimed to investigate metabolic cost to pool floor walking at
was only found on thigh‐depth water in all variables. EE, VO2, and VE
different water depths in individuals post stroke. Our findings showed
in thigh‐depth walking showed 22%, 18%, and 23% increases, respec-
decreased metabolic cost during chest‐depth walking as compared
tively, when compared with land walking (3.95 to 5.03 kcal/min,
with waist depth and thigh depth, respectively. Thigh‐depth walking
p = .018; 10.15 to 12.42 ml·kg−1·min−1, p = .015; 22.75 to
demonstrated the highest metabolic cost among the three water
29.66 L/min, p = .009). We found no significant differences on
depths. The secondary purpose was to identify differences in meta-
chest‐depth and waist‐depth walking when compared with land
bolic cost between land walking and walking in three water depths
walking in all variables.
in individuals post stroke. Significantly higher physiological responses
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during thigh‐depth walking were observed when compared with land
inconsistent findings. The definition of thigh‐depth water was differ-
walking. In addition, waist‐depth walking expended similar energy to
ent in the previous studies. We defined the thigh‐depth water at the
land walking at a matched walking speed.
level of the greater trochanter while previous studies used the midpoint between the anterior superior iliac spine and the central patella
4.1
Water depth
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(Gleim & Nicholas, 1989; Pohl & McNaughton, 2003). Although the difference in the water depth was relatively small (upper thigh vs.
4.1.1
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Chest depth
Our results demonstrated that significantly less energy was spent as
midthigh), it might have affected our findings inconsistent with two previous studies.
the water depth increased from thigh depth to chest depth and waist depth to chest depth. When the water depth increased to chest‐depth water, it enhanced the effect of body weight support during pool floor walking due to increased buoyancy. Approximately 50% of body
4.2
Aquatic versus land walking
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Thigh‐depth versus land walking
weight is supported at the waist depth, 70–75% at the chest depth,
4.2.1
and 90% at the neck‐depth water (Koury, 1996). The increased effect
Individuals post stroke showed significantly higher metabolic cost in
of buoyancy at chest‐depth water appears to reduce the workload and
thigh‐depth walking compared with land walking at a matched speed.
results in reduced metabolic cost in people post stroke.
This result is consistent with the previous studies that found higher
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Our findings are consistent with what has been reported in the
metabolic cost during thigh‐depth treadmill walking compared with
previous literature. Benelli et al. (2014) reported significantly lower
land treadmill walking in healthy adults (Gleim & Nicholas, 1989; Pohl
VO2 and heart rate in chest‐depth walking as compared with waist‐
& McNaughton, 2003). The effect of water resistance applied on the
depth walking, regardless of the step frequency. A nonmotorized
lower extremities is significant, which creates drag force in thigh‐
treadmill was used in the previous study. Greater friction and
depth walking, as water is approximately 800 times denser than air
increased muscle activation are reported in a nonmotorized treadmill
(Dowzer & Reilly, 1998). It is interesting to find consistent outcomes
when compared with the conventional motorized treadmill (Snyder,
even though two previous studies used different methods including
Myatt, Weiland, & Bednarek, 2011). A nonmotorized treadmill some-
the sample of participants (healthy adults vs. people post stroke) and
how shares similar characteristics to pool floor walking, which may
the mode of ambulation (aquatic treadmill vs. pool floor walking). As
have contributed to our consistent outcomes. Comparison between
discussed earlier, the slower walking speed of people post stroke is
chest‐depth walking and thigh‐depth walking in physiological
associated with decreased drag force; thus, less metabolic cost is
responses has never been investigated in the previous studies. Most
expected than healthy adults. However, in our present study, partici-
previous studies were limited to assessing the water depths in either
pants were asked to walk on the pool floor, which is considered for-
above or below the waist level.
ward locomotion. Forward locomotion in water may require additional energy in order to travel through water when compared
4.1.2
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Waist depth
with stationary walking on an aquatic treadmill. Also, higher push‐off
There was no statistical significance found between waist‐depth and
force is required during forward locomotion, unlike stationary walking
thigh‐depth walking in the current study. However, our results
on a treadmill (Brouwer, Parvataneni, & Olney, 2009). Therefore,
showed a trend of decreased physiological responses on waist‐depth
despite the methodological differences, we found consistent results.
walking when compared with thigh‐depth walking. Waist‐depth water may have allowed the participants to benefit from the effect of buoyancy, whereas thigh‐depth water did not provide sufficient body
4.2.2
weight support to observe the significant reduction in metabolic cost.
Our results demonstrated no significant difference between waist‐
In the thigh‐depth water, drag force from the water resistance seems
depth walking and land walking in participant post stroke. Physiologi-
to affect the propelling motion of the legs during pool floor walking,
cal values were rather similar to each other. Waist‐depth water, in
whereas decreased buoyancy provides less weight support.
which
|
Waist‐depth versus land walking
50%
body
weight
support
is
expected,
may
have
Previous studies reported significantly lower metabolic cost to
counterbalanced the added resistance to the movement imposed by
waist‐depth walking when compared with thigh‐depth walking in
water (Conti, Minganti, Magini, & Felici, 2015). In contrast, other stud-
healthy adults (Gleim & Nicholas, 1989; Pohl & McNaughton, 2003).
ies reported that waist‐depth jogging or running showed a higher met-
Differences in walking speed appear to be associated with this dis-
abolic cost to that of land (Gleim & Nicholas, 1989; Pohl &
crepancy. Drag force is greatly affected by movement velocity in
McNaughton, 2003). Different modes of ambulation on these studies
water, in addition to surface area, water density, and drag coefficient,
can be related to the discrepancy. Again, speed of movement in water
Fd = ½CDρAv (Alexander, 1977). People post stroke demonstrates
appears to be a main factor for this inconsistent outcome. Faster leg
slower walking speed than healthy adults in water similar to land walk-
movement propelling through water during jogging or running may
ing (Jung et al., 2014). The slower walking speed in participants post
have produced greater drag force compared with walking in the pres-
stroke can substantially reduce drag force while walking in water. This
ent study, particularly slower walking among people post stroke.
reduced drag force associated with slower walking speed of partici-
Greater drag force applied on the leg requires the people to move with
pants post stroke may have contributed to the inconsistent results.
greater mechanical and physiological energy cost, which results in
In addition, different methodology may be associated with our
increased oxygen uptake.
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4.2.3
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Chest‐depth versus land walking
ET AL.
stroke can still benefit from the various characteristics of water for
Our findings demonstrated no significant differences between chest‐
their training, such as pain reduction, decreased fear of fall, and free-
depth and land walking at a matched speed. However, our results
dom of movement.
revealed a trend of decreased physiological responses to chest‐depth walking compared with land walking. This finding indicates that energy
ACKNOWLEDGEMENT
consumption in chest‐depth walking was similar to that of land walking
The authors would like to thank all participants and research staff
in individuals post stroke. Even with 70–75% body weight support in
members who were involved in the study. This research did not
chest‐depth water, participants had to carry their bodies through the
receive any specific grant from funding agencies in the public, com-
water with increased surface area. The influence of buoyancy appeared
mercial, or not‐for‐profit sectors.
to countervail the effects of water resistance. As a result of countervailing effects, we may have not found significant differences
CONFLIC T OF INT E RE ST
in physiological responses. Our results are inconsistent with previous
The authors declare that they have no financial conflicts of interest.
research findings, which reported higher physiological responses during chest‐depth treadmill walking compared with overground treadmill walking in healthy adults (Alkurdi et al., 2010; Hall, Macdonald,
ORCID Hyosok Lim
http://orcid.org/0000-0001-7147-8026
Maddison, & O'Hare, 1998). The fast movement speed in healthy adults appears to generate greater drag force, which made them to use greater energy. Again, differences in walking speed is considered to be one of the affecting factors for these inconsistent results.
4.3
|
Limitations and future studies
There are several limitations in this study to be considered. First, the sample size in this study (N = 12) was relatively small, which limits our ability to generalize the outcomes in this population. Future studies with a larger sample size are warranted. Additionally, our study recruited individuals post stroke with high functional mobility. It is recommended to investigate individuals post stroke with a lower level of functional mobility. Similar methodology may be applied to examining other disability population with gait impairment. Another limitation is that we were limited to using one speed throughout the different water depths during pool floor walking. Further research is suggested to observe the influence of various speeds, in different water depths, on physiological responses during pool floor walking. Lastly, the order of four walking conditions was not completely randomized. Chest‐ depth test was performed on the first visit, and only the remaining walking conditions were randomized. Our rationale behind this method was to obtain reference walking speed from the chest‐depth test that is also viable in other walking conditions. Fastest walking speed acquired from land or shallow water would be difficult to use as a matched speed in chest‐depth water due to the drag force.
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C O N CL U S I O N
Our results indicate that metabolic cost of individuals post stroke during pool floor walking are significantly influenced by water depth. These findings suggest that people post stroke may sustain a longer duration of exercise, such as gait training, in chest‐depth water. Thigh‐depth water may be recommended as an ideal environment for time‐efficient cardiovascular exercise. Our results also demonstrated that walking in waist‐depth water does not change the metabolic cost as compared with land walking. Thus, this finding suggests that energy conservation may not be expected during walking in the waist‐depth water among people post stroke. However, people post
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How to cite this article: Lim H, Azurdia D, Jeng B, Jung T. Influence of water depth on energy expenditure during aquatic walking in people post stroke. Physiother Res Int. 2018;e1717. https://doi.org/10.1002/pri.1717
