Biomechanics and Medicine in Swimming XI

BiomechanicsandmedicineinswimmingXi
Heart Rate Responses During Gradually Increasing
and Decreasing Exercise in Water
nishimura, K. 1 , nose, Y. 2 , Yoshioka, A. 2 , Kawano, h. 3 , onodera,
s. 4 , takamoto, n. 1
1Hiroshima Institute of Technology, Hiroshima, Japan
2Graduate School of Kawasaki University of Medical Welfare, Kurashiki,
Japan
3Waseda University, Tokorozawa, Japan
4Kawasaki University of Medical Welfare, Kurashiki, Japan
The purpose of this study was to determine the heart rate (HR)
responses during and after gradually increasing and decreasing
exercise in water and on land. Eight healthy Japanese males volunteered
for this study. Subjects performed arm cranking exercise
(calibration and triangular tests) for 32 -min and recovered for
1 -min. HR and cardiac autonomic nervous system activity were
continuously measured. The amplitude and phase lags at the top
and bottom of the work rate were measured in each cycle. The
results were as follows; 1) the HR phase response was shorter in
water than on land, but there were no differences in amplitude,
2) reactivation in cardiac parasympathetic nerve was greater in
water. Thus, exercise and recovery in water may enhance the stability
of autonomic nervous activity, not only during exercise but
also after exercise.
Key words: arm cranking exercise, gradually increasing and decreasing
exercise, water immersion, heart rate response, recovery after excise
IntroductIon
In water, humans have different physiological responses than on land
due to the influence of the physical characteristics of water, such as water
temperature (hydrostatic), water pressure, buoyancy and viscosity. Venous
return is greater in water than on land, which causes increased
stroke volume and cardiac output, decreased heart rate, and increased
cardiac parasympathetic nervous system modulation.
During arm cranking exercise, there are no significant differences of
oxygen uptake between in-water and on-land conditions, despite water
immersion-induced bradycardia (Kimura et al., 2001). In addition, the
high frequency component in heart rate variability, an index of cardiac
autonomic nervous system, is enhanced at the onset of arm cranking
exercise in water compared with the on land response. These data suggest
that during exercise at the same work-load, heart rate responses
including heart rate variability are different between on-land and inwater
conditions. Heart rate kinetics (i.e., phase response and amplitude)
during sinusoidal exercise are affected by cardiopulmonary fitness
(Fukuoka et al., 2002), physical fitness status (Fukuoka et al., 2002) and
low intensity aerobic training (Nabekura et al., 2007). In fact, the time
delay of heart rate in response to sinusoidal exercise is shorter in highly
fit individuals, suggesting that heart rate kinetics in response to sinusoidal
exercise may reflect physical fitness. However, the effects of environmental
factors, in particular water immersion, on heart rate kinetics in
response to gradually increased and decreased exercise workload, such as
in sinusoidal or gradually increasing and decreasing exercise, are largely
unknown.
It has been shown that the time constant of heart rate decline for the
first 30 second (T30) after exercise can serve as a specific index to assess
post-exercise reactivation of cardiac parasympathetic nerve activity
(Imai et al., 1994). Nishimura et al. suggested that supine floating after
exercise induced a greater activation in the cardiac parasympathetic nervous
system, via increase of central venous pressure and cardiac output,
and the subsequent arterial baroreflex response caused by greater venous
208
return, leading to bradycardia (Nishimura et al., 2006).
Therefore, it was hypothesized that 1) the phase response and amplitude
of heart rate during gradually increasing and decreasing arm
cranking exercise in water exercise is higher than on land, and 2) the
activation of the cardiac parasympathetic nervous system after exercise
in the water is greater than after on-land exercise. To test these hypotheses,
the present study was designed to determine the effects of heart
rate response during and after gradually increasing and decreasing arm
cranking exercise in the water and on land.
Methods
Eight healthy Japanese males volunteered for this study. Their mean (±
SD) age, height, body weight, and % body fat were 20.9 ± 0.6 years,
175.3 ± 4.2 cm, 66.9 ± 4.7 kg, and 13.9 ± 2.8 %, respectively. All subjects
signed an informed consent form prior to participation in this study.
Subjects performed arm cranking exercise for 32 -minutes and recovered
for 1 -minute in a standing position. Subjects performed two
types of exercise, a calibration test and a triangular test. The calibration
test consisted of three 4-minute bouts of exercise at 20, 60 and 40% of
peak oxygen uptake (VO2peak) with a total duration of 12 -minutes.
The triangular test consider of 4-minute bouts of gradually increasing
and decreasing work load exercise between 20 and 60%VO2peak for
20 -minutes. Both experimental tests were performed on land (L-condition)
and in water (W-condition). Water temperature was 30 ºC and
water level was at the height of the iliac crest.
Heart rate and cardiac autonomic nervous system activity were
continuously measured under both conditions. Heart rate maximal and
minimal values, amplitude (difference between maximal and minimal
values), and phase lags at the top and bottom of the work rate were
measured in each exercise cycle. The cardiac autonomic nervous system
activity was calculated using the Maximum Entropy Calculation (Mem-
Calc) methodology. The heart rate variability frequency domain spectrum
was divided into two parts: high frequency (HF; 0.15-0.40Hz)
and low frequency (LF; 0.04-0.15Hz). The cardiac autonomic nervous
system activity was transformed into natural logarithmic values to obtain
a statistically normal distribution. The natural logarithm of HF was
taken as an index of cardiac parasympathetic nervous system modulation.
T30 reflected reactivation of cardiac parasympathetic was calculated
by decrease of heart rate calculated from RR intervals 30 seconds
after exercise. All experiments were performed at the same time. All
subjects fasted during three hours prior to the experiments, and caffeine
intake was not allowed either during that time. Room temperature and
humidity were 27.3 ± 1.2ºC and 64.9 ± 5.0%, respectively.
All data are expressed as mean ± standard deviation. Two-way analysis
of variance for repeated measurements (condition × time course)
and paired t-tests were used to compare values obtained during the Lcondition
and the W-condition trials. The level of significance was set
up at p< 0.05.
Table 1. Changes in heart rate during each work load both in the Wcondition
and on the L-condition.
work load(watt) L-condition(bpm) W-condition(bpm)
Rest on land 59.3±7.8 57.0±13.5
Calibration 20 93.0±7.0 84.3±9.4 *
Calibration 60 129.1±13.8 119.2±16.2 *
Calibration 40 115.8±15.6 102.7±14.5 *
Increasing 40 114.7±16.1 99.6±14.5 *
Increasing 45 117.8±14.9 102.2±15.5 *
Increasing 50 120.7±14.9 104.9±15.0 *
Increasing 55 123.9±15.1 108.1±15.3 *
Increasing 60 128.1±14.4 110.8±15.3 *
Decreasing 55 130.6±15.3 112.6±15.3 *