of water temperature
Body temperature is the balance between heat production and heat loss.
Changes in body temperature of subjects immersed in aquatic environments,
as well as, those of aquatic instructors in the deck of indoor swimming-pools
When immersed, body heat is lost mainly by conduction and convection.
Water has a thermal conductivity about 26 times greater than air and body
loses heat four times faster, for the same temperature (Wilmore and Costill,
The rate of heat loss is further accelerated, due to convection, if water
is moving around the subject as it happens during aquatic exercises (Data
et al., 2006).
Heat lost to the water has a linear relationship with water temperature
and the immersion duration (Craig, 1983).
Cold water (i.e., 14 ºC) promotes a decrease of rectal temperature and
an increase in HR of 5%, systolic BP of 7 % and diastolic BP of 8 %, when
compared to controls at air temperature (Srámek et al., 2000).
It has been reported that immersion at neutral temperature (i.e., 32 ºC)
did not change rectal temperature and metabolic rate, but promoted a bradycardia
of 15 %, systolic BP decrease of 11 % and diastolic BP decrease of 12
%. Physiological adaptations are mediated by humoral control mechanisms,
while responses induced by cold water are mainly due to an increased activity
of the sympathetic nervous system (Srámek et al., 2000).
Immersed subjects at 40 ºC present an increased HR and an increased index
of the cardiac parasympathetic system in comparison to a 25 ºC immersion
and a control condition on land (Nahimura et al., 2008).
For the 40 ºC environment, during and post exercise HR increased, although
the index of the cardiac parasympathetic system decreased during exercise
(Nahimura et al., 2008).
While exercising, the slowed enzymatic processes and slowed nerve conduction
that impair the rate of force development reduce local muscular endurance
during dynamic contractions and impair manual dexterity until 35 ºC (Drinkwater,
Both the voluntary and evoked force development capacities of muscle are
unimpaired until cooling is quite severe, such as, less than 27 ºC (Drinkwater,
At least during submaximal swimming significant changes in metabolic responses
were reported according to water temperature. Comparing one hour breaststroke
swim at 21 ºC, 27 ºC and 33 ºC, HR increased throughout the bouts; VO2
was lowest at the warmest temperature; respiratory exchange ratio (RER)
declined with time and was inversely related with temperature; [La-]
was higher in the coldest temperature and; no significant effect of temperature
in insulin and glucose was reported (Houston et al., 1978).
Once again, during light swimming VO2 was about 0.7 L·min-1
in a 28-35 ºC water temperature, but increased in a 24-26 ºC temperature
So, body temperature can be controlled by: (i) an increase of exercise
work rate in order to promote heat production (Craig, 1983);
(ii) an increase of body fat to decrease the heat lost and; (iii) the
wear of wetsuits which reduced the decrease of the core temperature (e.g.,
Kang et al., 1983;
Wakabayashi et al., 2006).
Even so, most of head-out aquatic exercises are performed in water temperatures
of approximately 27 ºC. This temperature selection seems to be based in
the knowledge gathered in competitive swimming and not in head-out aquatic
exercises. Moreover, the water temperature selected for competitive swimming
is not based on experimental results but in empirical decisions. Nonetheless,
water temperatures around 27 ºC seem to be the most suitable for appropriate
acute physiological responses during head-out aquatic exercises as well.
However, different head-out aquatic exercise programs will induce different
exercise intensities and, therefore, a need of appropriate water temperatures
to stay comfortable and/or preventing thermo-regulation stress. For example,
if the aim of the activity is the relaxation, the improvement of range
of motion and/or flexibility workout, the water temperature should be
increased to a thermo neutral value. Appropriate water temperature should
also be considered according to the population special characteristics.
Subjects should stay comfortable throughout the onset of exercise bout.
For example, older subjects will need a higher water temperature in comparison
to younger adults. In this sense, Aquatic Exercise Association (2008)
state in their standards and guidelines water temperature ranging from
28-30 ºC for aquatic fitness programs.
When conducting head-out aquatic exercise sessions, most instructors are
also exercising. Evaporation is the main way for heat dissipation during
exercise (Wilmore and Costill, 1994).
An indoor swimming pool is characterized by a high level of humidity,
which affects the heat loss by evaporation. The already high quantity
of water molecules in the environment affects the evaporation of sweat
from the body. Consequently, body is under a thermoregulation stress.
Moreover, indoor swimming pools also present a high temperature. When
exercising, the aquatic instructor will present changes in the cardiovascular
function, such as a reduction of stroke volume, since there is a reduction
of returning blood volume to the heart. Hot environments sets up a competition
between active muscles and skin for blood supply. The former to deliver
oxygen, nutrients and remove metabolites; the latter to facilitate heat
loss (Wilmore and Costill, 1994).
Both phenomena, hot and humid environment, can explain the increase of
acute response to exercise for aquatic instructors in what concerns to
RPE, HR and VO2 (Barbosa et al., 2007).
Therefore, new highlights about physiological adaptations of aquatic instructors
should be a priority in head-out aquatic exercises research in a near
of water depth
There are several investigations about the influence of body immersion
level during head-out aquatic exercises. Rate of perceived exertion is
higher when exercising immersed by the hip, comparatively with immersion
up to the breast (Barbosa et al., 2007).
This perceived differences can be related to: (i) the higher intensity
of drag forces acting in the lower limbs, as compared to those acting
in the trunk and upper limbs, when partially immersed; (ii) an increasing
ground reaction force, due to a reduction of the buoyancy (Nakazawa et
and; (iii) changes in neuromuscular patterns of active muscles at different
levels of body immersion (Fujisawa et al. 1998;
Poyohnen et al., 1999;
It has been observed that the HR decreased significantly with the increase
of body immersion (Barbosa et al., 2007;
Benelli et al., 2004;
Town and Bradley, 1991).
The lower HR with higher immersions during aquatic activities is a well-
documented phenomenon and is believed to be related with: (i) the diving
bradycardia with, or without, the face immersion (Andersson et al., 2003;
Shono et al., 2001);
(ii) a higher volume of blood distribution in the trunk (Sheldahl et al.,
(iii) the improved conditions for heart filling during diastole, due to
hydrostatic pressure and buoyancy, thereby promoting a higher stroke volume
and; (iv) in some exercises, a horizontal body position, which improves
the conditions for heart filling during diastole (Benelli et al., 2004;
Bjertnaes et al., 1984;
Benelli et al., 2004
reported a decrease of the median value from land-based to shallow-water
exercises of 7.5 b·min-1 and to deep-water exercises of 48
b·min-1. Barbosa et al., 2007
described a decrease of the mean heart rate from land-based to the breast
immersion exercise of 21. 2 and 9.3 b·min-1 for women and men,
respectively. Yun et al., 2004
compared HR during rest on land, rest in water and exercising in water,
in several groups. They reported a decrease from rest on land to rest
immersed of 1.9 b·min-1 for young women and 4.7 b·min-1
for middle age women and 1.1 b·min-1 for professional women
divers. So, it is questionable if the deduction of 11-17 b·min-1
when monitoring HR suggested by the Aquatic Exercise Association can be
adjusted in order to increase prescription's accuracy.
Oxygen uptake and EE are lower at breast immersion when compared with
hip immersion (Barbosa et al., 2007).
The reduction of VO2 and EE with increasing body immersion
can be explained by: (i) the decrease of cardiovascular workout and the
increase of hydrostatic pressure; (ii) the buoyancy force, as when totally
immersed it reduces the neuromuscular activity of antigravitical/postural
muscles (Butts et al., 1991)
and; (iii) the extra difficulty to transfer body heat to the environment
when exercising immersed to the hip, with subsequent increase in HR (Fink
et al., 1975).
On the other hand, VO2 was reported as being higher during
shallow water, compared with deep water running (Town and Bradley, 1991).
When comparing shallow-water versus deep-water exercises, the physiological
demand seems to be lower for the second conditions. Indeed, HR and [La-]
(Benelli et al., 2004);
VO2max and HR (Dowzer et al., 1999;
Town and Bradley, 1991)
are higher during shallow-water exercitation. However, RER and [La-]
present non-significant differences between both depth conditions (Town
and Bradley, 1991).
While shallow-water practice is presumably an efficient method of maintaining
cardiovascular fitness, some questions must be raised about the efficiency
of deep-water exercises (Frangolias and Rhodes, 1996;
Dowzer et al., 1999;
Chu and Rhodes, 2001).
Some explanations can be addressed for these results (Reilly et al., 2003):
(i) the short duration of the water exercise protocols; (ii) the reliance
on the subjects to control exercise intensity up to a perceived maximum;
(iii) the changes in the kinematical and neuromuscular characteristics
of the technique to be performed.
To understand differences in the physiological response according to the
water depth, data comparing head-out aquatic with land-based exercises
may also be considered. Most of the researches devoted their analysis
to tasks performed in a gym (e.g., Benelli et al., 2004;
Green et al., 1990;
Shono et al., 2001).
RPE is described as being higher during aquatic exercises than on land
(Butts et al., 1991;
DeMaere and Ruby, 1997;
Hall et al., 1998; Yu
et al., 1994).
On the other hand, HR (Barbosa et al., 2007;
Benelli et al., 2004; Eckerson and Anderson, 1992;
Town and Bradley, 1991;
Yu et al., 1994)
and [La-] (Di Masi at al., 2007)
are lower during aquatic exercises for the same reasons presented for
its reduction with increasing body immersion. A conflicting issue is the
bioenergetical profile. Several investigations reported that when exercising
on land, VO2 or EE were significantly higher comparatively
with aquatic exercises (Barbosa et al., 2007;
Butts et al., 1991;
Hall et al., 1998;
Yu et al., 1994).
Contrarily, other studies observed that those parameters during aquatics
were significantly lower or non-different from land-based exercises (e.g.,
Darby and Yackle, 2000;
Green et al., 1990).
However, it is known that environmental conditions have a significant
influence in the thermoregulation system and, therefore, in the physiological
response to exercise (cf. "effects of water temperature" sub-chapter).
That is why at least one paper compared aquatic exercises with land-based
exercises performed in the pool-side, as done by aquatic instructors (Barbosa
et al., 2007).
of type of exercise
There are several types of exercises, drills and routines that can be
performed during an aerobic head-out aquatic exercise session. From a
technical point of view, those exercises are categorized in six main groups:
(i) walking; (ii) running; (iii) rocking; (iv) kicking; (v) jumping and;
(vi) scissors (Sanders, 2000).
Each one of these exercises can be performed in several variants according
to some guidelines described by the same author. In comparison to other
aerobic aquatic activities, such as swimming, one of the main advantages
of head-out aquatic exercises is the variety of exercises, drills and
routines that can be performed throughout a session or a program. Even
so, the question whether these exercises promote similar acute physiological
adaptations is an issue that must be addressed.
Most of the studies on this issue devoted their attention to the differences
between immersed walking vs. running. Typically, an incremental protocol
from a slow to a maximal speed was applied (e.g., Kato et al., 2001;
Yu et al., 1994).
Transition speed from walking to running in water happens at 1.67 m·s-1
(Kato et al., 2001).
It was reported that speed had a significant effect in several physiological
parameters, such as RPE, HR and VO2 (Shono et al., 2001;
Yu et al., 1994).
Speed is related to drag force. So, as speed increases, subjects are submitted
to an increasing drag force as well, and need a higher metabolic power
to overcome such external force. By consequence, all physiological parameters
increase as well. Moreover, it seems to exist a significant relationship
between physiological and kinematical variations for immersed locomotion
(Kato et al., 2001).
Physiological and even biomechanical assessment of the remaining types
of head-out aquatic exercises is scarce. Some few exceptions are the works
evaluating the squat jump (Hoshijima et al., 1999),
single leg jump (Triplett et al., 2009),
the rocking horse (Barbosa et al., 2007),
the kicking (Poyhonen et al., 1999)
and the arm's horizontal adduction and abduction (Colado et al., 2009a).
No data is present in the literature about the physiological adaptations
of other types of head-out aquatic exercises.
There are several equipments and apparatus commercially available for
head-out aquatic exercise users. These equipments can be used in a given
part of the session or throughout all session itself. Bench-stepping platforms,
ergo- bicycles, rubber bands, flotation vests, ankle cuffs, treadmills,
hydro-flumes or dumb-belts are some examples of such equipments. So, the
question to be answered is what kind of acute physiological adaptations
this apparatus promote during head-out aquatic exercises.
Costa et al., 2008
compared the same basic head-out aquatic exercise in young, healthy and
physically active women: (i) only with legs actions; (ii) with simultaneous
legs and arms actions and (iii) with simultaneous legs and arms actions
using buoyancy dumb-belts. Practicing with dumb-bells promoted an increase
in RPE, [La-] and HR when compared with the remaining conditions
(Costa et al., 2008).
Authors suggested that practicing head-out aquatic exercises with both
simultaneous legs and arms actions, matched with the American College
of Sports Medicine guidelines (2000).
However, when practicing with dumb-bells, the acute response was consistently
above the target zone often suggested by this same organization (Costa
et al., 2008).
On the other hand, some research groups intended to analyze the neuromuscular
effect of the head- out aquatic exercise with dumb-belts (e.g., Colado
et al., 2009a).
It can be suggested significant relationships between the physiological
and the biomechanical adaptations during this kind of exercise. However,
at least to our knowledge, there is no research about this interplay.
The bench-stepping platform (also known as aqua-step) is equipment often
used. Evans and Cureton, 1996
performed a physiological assessment of bench-stepping at the same cadence
(0.48 Hz) in water and on land. HR and VO2 were lower during
water exercise, although RPE had no significant variation. Adding the
arms to leg actions increased VO2 demand as well. Therefore,
the authors suggested that bench-stepping with the use of arms in water
meets the American College of Sports Medicine guidelines (2000)
for the improvement of aerobic capacity. In one other paper, this same
group (Evans and Cureton, 1998)
compared bench-stepping with platforms at different heights on land and
in water (0.18 and 33 cm) using climbing movement with no arms (traditional
step pattern) and straddle jumping involving arms and legs (modified step
pattern). The intensity of traditional stepping in water was less than
or equal to 50 % VO2max recommended by the American College
of Sports Medicine (2000)
to increase fitness. The intensity for modified stepping in water was
less than or equal to 50 % VO2max recommended by the same organization
at all bench heights (Evans and Cureton, 1998).
Although the re-new interest that ergo-bicycle is having, these types
of equipments are not novel in the aquatic context. Indeed, since three
decades ago there are some reports about the modification of standard
ergo-bicycles for aquatic programs (e.g., Morlok and Dressendorfer, 1974).
It seems to exist contradictory data about the effect of the ergo-bicycles
in the acute adaptation: (i) after a maximal bout, there was no significant
difference in VO2max between aquatic and land-based exercise,
but HR and ventilation exchange decreased significantly when exercising
immersed (Dressendorfer et al., 1976);
(ii) at similar ergometric workload, VO2, tidal volume, breathing
frequency and [La-] levels were significantly higher in water
than on land (Bréchat et al., 1999);
(iii) at moderate intensity, there was no significant difference in HR,
but systolic BP was significantly lower during water exercitation (Matsui
et al., 1999).
Di Masi et al., 2007
describe a faster [La-] removal during immersed cycling when
compared with land cycling. However, the amount of [La-] during
submaximal exercise was no different in the two conditions. Others have
compared several aquatic ergo-bicycles models and verified significant
differences in some physiological parameters (e.g., VO2 and
HR) according to the model evaluated (Giacomini et al., 2007).
Due to the commercial success that this equipment has, new highlights
should be obtained about the physiological response with its use, such
as the effects of: (i) the level of body immersion; (ii) several body
postures; (iii) different pedalling rates; (iv) different resistance mechanics
of the models used or; (v) aquatic resistance exercises, for arms and
trunk, performed in the ergo-bicycle.
The flume is an ergo-meter where the subjects exercise stationary against
a water flow. This apparatus has been developed in the late sixties and
early seventies for competitive swimming (e.g., Holmér, 1972;
Nowadays this apparatus has been also used for head-out aquatic exercises.
At least free and flume swims presented similar values for VO2max,
R and VE (Bonen et al., 1980).
However, significant differences between these two conditions of exercise
have been reported other authors. Indeed, D'Acquisto et al. (1991)
verified that flume swimming required higher VO2max, HR and
[La-] than free swim. It can be speculated that the type of
fluid flow around the subject in the ergometer is different from that
in free swimming. This phenomenon has repercussions in the transfer of
kinematical energy to the water and, therefore decreases the movement
efficiency. Although there is no systematic study about physiological
adaptations in a flume during head-out aquatic exercises, it can be hypothesized
that data will be very similar. A single study about walking in a flume
presented data quite similar (Yu et al., 1994).
Yet another possibility is to exercise in aquatic treadmill. Comparing
submaximal walking in underwater and land treadmills, VO2 and
RPE were significantly higher in water (Hall et al., 1998). Thus, walking in chest-deep water yields a higher energy
cost than walking at similar speeds on land. On the other hand, some data
suggest that when exercising in underwater treadmill, EE (e.g., Shono
et al., 2000) and VO2, RPE, BP (Dolbow et al., 2008) are considerably lower than in free exercising. Migita
et al., 1996 proposed that one half of the speed would be necessary
in underwater treadmill to achieve the same physiological responses that
land treadmill. Walking in an underwater treadmill inserted in a flume,
no significant differences in the VO2-HR relationships was
found between land and water performances (Shono et al., 2007).
When exercising in deep-water the use of flotation vests and ankle cuffs
is common. These equipments enable the subject to submerge still maintaining
an upright position. Without the flotation vest, the subjects must relay
in their ability to perform the skills, as well as their ability to maintain
buoyancy. VO2, VE, HR and RPE were significantly lower when
running with the flotation vest than without it for a group of non-expert
runners; however the same tendency was verified for expert runners but
with no statistical meaning (Gehring et al., 1997). It seems that expert runners are able to elicit higher
exercise intensities, both when practicing with or without the flotation
vest. Contrarily, non-expert runners seem to rely in the buoyancy of the
equipment rather than in the running technique during the bouts. On the
other hand, when comparing tethered running with and without a flotation
vest, evidences revealed that some kineanthropometrical parameters related
to buoyancy force (e.g., fat-mass), to drag force (e.g., body surface
area and height), to weight force (e.g., body mass) and to propulsive
force (e.g., segmental strength) predicted (R2 = 0.57, P =
0.01) the maximal horizontal propulsive force (Vila-Chã et al., 2007). This means that, besides physical fitness and technical
level, often described in the literature, kineanthropometrical characteristics
of the subject also affect significantly his performance during aquatic
The scarce number of investigations about the utility of these equipments
does not matched the variety of apparatus commercially available and its
uses on regular basis in head-out aquatic exercise sessions. Therefore,
the true repercussions in the acute physiological during head-out aquatic
routines with such apparatus should be assessed.
of segmental action
Acute response of aquatic exercises can be dependent from the number of
body segments in action. Each head-out aquatic exercise has several variants.
Some of those variants are based on the number of body segments in action
during exercise (legs movement only, arms movement only and both arms
and legs simultaneous movements). For a given basic movement, at the same
music cadence, RPE, HR and [La-] were significantly higher
when exercising with simultaneous arms and legs actions, compared with
leg exercise (Darby and Yaeckle, 2000;
Costa et al., 2008). The same phenomenon was described for metabolic parameters,
e.g., METs values during bench-stepping performed by women (Evans and
Cureton, 1996). Therefore, it seems that increasing limbs in action
will induce a significant increase in the acute response to exercise.
This effect may be explained by: (i) the mechanical work done, once drag
force also increases and therefore the RPE (Yu et al., 1994); (ii) the number of muscles in activity promotes a
higher oxygen and nutrients demand, increasing HR and metabolite production
Besides the arm actions, also hand and fingers positions may influence
the biomechanical and physiological. Different hand position, e.g., attack
and sweep angle (Silva et al., 2008a) and different finger's spread, e.g., fingers close together,
little spread and large spread, leads to several drag force intensities
(Marinho et al., in press) and therefore influences the physiological
response. Drag force evaluated with "computer fluid dynamic"
approach (e.g., Silva et al., 2008b) presented the minimum value near angles of attack of
0º and 180º and the maximum value was obtained near to 90º, when the hand
is almost perpendicular to the flow (Silva et al., 2008a). Using the same methodology, for attack angles higher
than 30º, as used in head-out aquatic exercises, when little distance
between fingers is adopted higher values of drag coefficient are verified,
rather than with fingers close together and with large finger spread (Marinho
et al., in press).
Several research groups compared the acute response to exercises performed
only with the legs or the arms. RPE was reported as being higher for arm's
exercises, at least for land-based routines (Borg et al., 1987; Butts et al., 1995; Kang et al., 1999). One single study evaluated the MET's level for aquatic
exercises performed either with arms or legs only. For both genders, MET
value's for callisthenics exercises, were higher for legs actions (Cassady
and Nielsen, 1992). Indeed, at least for terrestrial and other types of
aquatic tasks, it was already reported that an increasing number of limbs
in action leads to a concomitant increase of the acute response (Butts
et al., 1995; Robert et al., 1996;
Darby and Yaeckle, 2000).
of music cadence
For some aquatic instructors, one of the most important aspects when conducting
their sessions is to include music in the routines with the aim to: (i)
motivate practitioners during the session; (ii) maintain the synchronization
of the practitioners during specific routines and; (iii) achieve a given
intensity of exertion. In fact, some aquatic instructors plan their sessions
according to the music characteristics. They choose a given music for
a specific part of the session, according to its cadence or rhythm, in
order to achieve a pre-determinate intensity of exertion. In this sense,
the countdown of one musical beat in each two beats is synchronized with
the execution of a given segmental action of the full exercise being performed
(this is know as "water tempo"). So, movement frequency is related
to music cadence. However, only a couple of papers attempted to understand
the relationship between music cadence and acute physiological response
in head-out aquatic exercises. Increases in the music cadence imposed
significant increases in the acute physiological adaptation (RPE, HR,
and [La-]) of the subjects (Hoshijima et al., 1999;
Barbosa et al., in press). Indeed, other researches reported that in several
kinds of head-out aquatic tasks, increasing physiological responses were
observed during incremental protocols (Darby and Stallman et al., 2006;
The increased physiological response may be explained by the fact that
increasing music cadence will also increase movement velocity and frequency.
Since drag force has a quadratic relationship with movement speed, an
increased drag induces a larger energy demand.
Therefore, an issue that must be addressed is the understanding of the
appropriate music cadence is in order to achieve the desired intensity
of exertion. Usually, aquatic instructors adopt the physical fitness guidelines
for land-based activities. However, it is questionable if those guidelines
are suitable for aquatic exercise programs also. Head-out aquatic programs
are moderate-vigorous activities, where it is presumable that [La-]
must be under or very close to its onset accumulation. Some researchers
set a 4 mmol of lactate per liter as a reference value, expressing V4
as the exercise intensity (displacement speed) corresponding to that threshold
(e.g., Heck et al., 1985).
Barbosa et al. (in press) adapted the concept of V4 to head-out aquatic
exercises, and defined it as being the music cadence achieved at a 4 mmol·l-1
of blood lactate concentration (R4), i.e., the rhythm in which is achieved
the 4 mmol·l-1 of [La-]. For young and active women
R4 evaluated after an intermittent and progressive test was 148.13 ± 17.53
b·min-1 (Barbosa et al., in press).
However, these values are quite individual and hardly applicable to all
subjects of an aquatic class group. So, the determination of a range of
intensity (target zone) for young and active women was developed based
in the 25 and 75 quartiles of the subjects' evaluated (Barbosa et al.
in press). With that aim, the RPE at R4 (RPE@R4), the HR at R4 (HR@R4)
and the percentage of the maximal theoretical HR at R4 (%HRmax@R4) were
computed. Authors reported that R4 ranged from 136.03 b.min-1
(quartile 25) to 158.28 b·min-1 (quartile 75), RPE@R4 ranged
from 13.25 to 16.75, HR@R4 from 162.25 b·min-1 to 178.50 b·min-
1 and %HRmax@R4 from 82.00 % to 89.75 %. Comparing these data with
the American College of Sports Medicine guidelines (2000)
they are appropriated but can be slightly adjusted for aquatic activities
in order to promote a more accurate exercise prescription of young, healthy
and physically active subjects.
Although these results may come as an advance in head-out aquatic exercises
knowledge, this data is only suitable for young, healthy and active women.
New investigations should be developed in order to determinate more accurately
target zones for other specific populations. For instance, to evaluate
it according to gender, physical activity level, age, mode or type of