Aging, Ventilation and Cycle Exercise Time to Exhaustion
12
JEPonline
Journal of Exercise Physiologyonline
Official Journal of The American
Society of Exercise Physiologists (ASEP)
ISSN 1097-9751
An International Electronic Journal
Volume 6 Number 1 February 2003
Systems Physiology: Cardiopulmonary
AGE ASSOCIATED DECLINES IN EXERCISE TIME TO EXHAUSTION AND
VENTILATORY PARAMETERS IN TRAINED CYCLISTS
FRANK B. WYATT, JASON P. McCARTHY
Department of Health, Human Performance, and Recreation, Baylor University
ABSTRACT
AGE ASSOCIATED DECLINES IN EXERCISE TIME TO EXHAUSTION AND VENTILATORY
PARAMETERS IN TRAINED CYCLISTS. Frank B. Wyatt, Jason P. Mccarthy. JEPonline. 2002;6(1):1217. The purpose of this study was to investigate the cardiopulmonary parameters in a cross section of fit, aging
cyclists to determine the associations between age, heart rate and ventilation on exercise time to exhaustion.
Subjects were twenty-seven (N=27) males age 21 to 74 yrs. Each subject performed a maximal test on a cycle
ergometer to volitional fatigue. Cardiopulmonary measures included; maximal oxygen consumption (VO2max,
mL/kg/min, L/min), expired minute ventilation (VE, L/min), carbon dioxide production (VCO2, L/min),
respiratory rate (RR) in breaths per minute (b/min), percent (%) O2 expired and % CO2 expired, ventilatory
equivalents for O2 (VE/VO2) and CO2 (VE/VCO2), maximal heart rate (MHR, beats/min), ventilatory threshold
(VT), heart rate threshold (HRT) and time to exhaustion (TE) in minutes (min). Through regression analyses
with age as the independent variable, the following measures significantly declined with age: VO2, VE, VCO2,
RR, MHR, VT, HRT and TE. Expired percent O2 and CO2, along with VE/VO2 and VE/VCO2 showed low
coefficient values indicating little change between subjects with age. In conclusion, age decrements in
cardiopulmonary related variables appear to be caused by diminished exercise capacities causing lowered
maximal exercise intensities. The poor correlation between VE/VO2 and VE/VCO2 and age reveal that
ventilatory capacities and function contribute little to the diminished exercise tolerance due to aging.
Key Words: Aging, Exercise Tolerance, Hypercapnea, Ventilatory Threshold, Chemoreceptor
INTRODUCTION
With an increase in exercise intensity, there is an increased rate of ventilation (hyperpnea) facilitated by
numerous neural and chemical mediators (1). The primary humoral mediators associated with exercise-induced
increases in ventilation are increases in the arterial partial pressure of carbon dioxide (PaCO2) and decreases in
blood pH (2). Whipp (3) has reported three phases of exercise hyperpnea. The initial phase is generally
considered neurally mediated, while phases II and III are highly influenced by blood PaCO2 and H+
Aging, Ventilation and Cycle Exercise Time to Exhaustion
13
concentrations during prolonged and/or increased exercise intensity. This mechanism of ventilatory stimulation
is a respiratory response to regulate acid/base balance (4). An increase in extracellular PCO2 decreases pH. By
adjusting the PCO2 through increased ventilation the pulmonary system can effectively regulate the H+
concentration of the extracellular fluid (5). The onset of an exponential increase in ventilation during exercise
in response to this regulation of H+ has been identified as the ventilatory threshold.
During incremental exercise, the ventilatory threshold is sometimes detected through an exponential increase in
expired volumes of carbon dioxide (VCO2) relative to VO2 (6). This is explained by the increase in arterial H+
and PaCO2, stimulating ventilation via the chemoreceptors in the carotid and aortic bodies (7). This
hyperventilatory response dampens the extent of acidosis primarily through the reversal of the carbonic
anhydrase reaction, resulting in proton (H+) and bicarbonate (HCO3-) conversion to carbon dioxide (8). With
hyperventilation, there is a decrease in alveolar PCO2 and thus a compensatory fall in blood H+. Brooks et al.
(5) notes that the hyperventilatory response increases pH in two ways: 1) by eliminating CO2 and thereby
lowering blood PCO2, HCO3- and H+, and 2) by reducing CO2 as a denominator in the Henderson-Hasselbalch
equation as follows:
pH= 6.1+ log ([HCO3-] / [CO2])
Respiratory compensation due to metabolic acidosis allows for a decline in PaCO2, thus dampening the decrease
in blood pH and offsetting fatigue. When elimination of CO2 becomes difficult through ventilatory constraints,
alveolar and PaCO2 rise abruptly in spite of hyperventilation. There is a resultant accumulation of CO2 in the
body (hypercapnea), which in turn further lowers blood pH and contributes to arterial hypoxemia and
limitations in systemic oxygen (O2) transport and aerobic capacity (9). Should ventilatory constraints exist as
with specific diseases and/or aging, resultant systemic limitations would facilitate decreased endurance and
premature fatigue.
Rossi, Ganassini, Tantucci and Grassi (10) reported that aging reduces lung elastic recoil , forced expiratory
volume in the first second (FEV1) and increases residual and closing volume. Babb and Rodarte (11) studied
aging subjects with normal pulmonary function and found reduced maximal expiratory flow indicating a loss of
lung recoil. A reduced expiratory flow would hinder CO2 blow off, leading to a hypercapnic state and an
earlier onset of fatigue.
While evidence does indicate declines in myocardial function and an earlier time to fatigue with aging,
questions remain as to the role specific ventilatory parameters and threshold measures play in this decline. In
addition, while declines are evident, the rate of decline may vary in specific aging populations (i.e., fit versus
unfit). Therefore, it is the purpose of this study to investigate the role of cardiopulmonary parameters in a fit,
aging population on time to fatigue.
METHODS
Participants
Subjects consisted of twenty-seven (N=27) male cyclists, age 21 y to 74 y. Prior to testing, each subject
completed a medical/health questionnaire, the PAR-QTM Fitness Readiness questionnaire and signed an
informed consent. The university Internal Review Board for Humans as Subjects approved all testing. The
inclusion criteria required the subjects to utilize cycling as the primary mode of training. A minimum of four
(4) days per week of cycle training was required with the stipulation that the training was being done for an
"event". An event was defined as an organized cycling occurrence requiring formal registration. The subjects
selected for inclusion were considered fit. Baseline values of height (cm), weight (kg), heart rate (beats/min),
blood pressure (mmHg) and body-fat (3-site skinfold, %) were collected prior to exercise testing with the
subjects in a rested state.
Aging, Ventilation and Cycle Exercise Time to Exhaustion
14
Testing Procedures
Subjects began the exercise testing with a warm-up on their bicycle set up on a cycle ergometer (VelodyneTM).
Prior to testing, the ergometer was calibrated for power output measures. This was followed by an incremental
workload test with the initial workload set at 50 watts (W), increasing 50 W every 3 min to volitional fatigue.
Time to exhaustion (TE, min.) for each subject was recorded. The subjects were then allowed to cool down
prior to de-briefing.
Ventilatory and gas measures were collected continuously during the cycling protocol and data were averaged
every 20 s utilizing a QuintonTM metabolic cart. Gas measures included the following: maximal oxygen
consumption (VO2max, L/min, mL/kg/min), expired volume of minute ventilation (VE, L/min), expired minute
volume of carbon dioxide (VCO2,L/min), breathing rate (RR, breaths/min), percent (%) O2 and %CO2 expired
and the ventilatory equivalents for O2 (VE/VO2) and CO2 (VE/VCO2). Heart rate (beats/min) was continuously
recorded and averaged every minute through electronic telemetry utilizing a PolarTM heart rate monitor.
Ventilatory threshold (VT) was determined as the increase in VE/VO2 when ventilation outstrips oxygen
consumption. This method showed high association with increased lactate and decreased pH during exercise
(11). Ventilatory threshold was reported as VO2 in absolute terms (L/min) and in relative terms as a percentage
of VO2max. Heart rate threshold (HRT) was identified as the point of disproportionate change in heart rate as
the level of work expressed as VO2 increased proportionately.
Statistical Analyses
Descriptive statistics included mean, standard deviation, median and range. Simple regression analyses were
utilized to determine correlations with age as the independent variable with myocardial and ventilatory
parameters as the dependent variables. Through regression analyses, the slope or rate of change in measured
variables across age was determined. Power analysis of the design indicated that an n-sample size of 15-22
yields high power of 0.8 to 0.95, respectively (13). Statistical significance was set a priori at p≤0.05.
RESULTS
Table 1: Descriptive data of the Subjects.
Data for the mean, standard deviation (SD),
Variable
Median Range
Mean±
± SD
median and range of demographic information
42.5
21-74
Age (yr)
46.1±14.9
can be seen in Table 1. Ventilatory and heart
178
161.5-189
Height (cm)
178.3±7.7
rate measures across age with regression slopes
75.4
60.2-111.8
Weight (kg) 75.7±10.8
can be seen in Table 2. Maximal oxygen
11.5
4.8-19
Body
fat
(%)
11.5±3.6
consumption (VO2max), VCO2, VE, RR, MHR,
VT (L/min), HRT (beats/min) and TE declined
significantly (p≤0.05) across age. The measured variables of % O2 and % CO2 expired, VE/VO2, VE/VCO2, VT
(%VO2max) and HRT (%MHR) were not significantly different across age.
Ventilatory parameters measured within this study showed significant declines across age from 21 to 74 years
(Table 2). However, the slope of decline in selected cardiopulmonary parameters was varied and did not
necessarily profile the decline shown in TE (Figure 1). The ventilatory parameters of oxygen consumption and
carbon dioxide production in absolute terms declined with age at a similar rate (Figure 2). Yet the rate of
decline in expired ventilation (VE) was considerably greater (Figure 3).
Aging, Ventilation and Cycle Exercise Time to Exhaustion
15
Table 2: Regression Analyses Between Age and
Multiple Dependent Variables Pertaining to
Ventilation, Heart Rate and Time to Exhaustion
Variable
R
p
Slope
VO2max (mL/kg/min)
-0.76
<0.0001
-.66
VO2 max (L/min)
-0.73
<0.0001
-.05
VCO2 (L/min)
-0.73
<0.0001
-.06
VE (L/min)
-0.57
<0.002
-1.56
RR (beats/min)
-0.58
<0.001
-.33
TE (min)
-0.74
<0.0001
-.26
O2 expired (%)
-0.19
=0.32
-.01
CO2 expired (%)
-0.08
=0.70
-.002
VE/VCO2
0.29
=0.13
+.08
VE/VO2
0.29
=0.13
+.05
VT absolute (L/min)
-0.63
<0.0004
-.04
VT relative (%VO2max)
0.16
=0.43
+.09
MHR (beats/min)
-0.84
<0.0001
-.78
HRT absolute (beats/min)
-0.72
<0.0001
-.75
HRT relative (%MHR)
-0.13
=0.52
-.05
contributing factor to decreased TE with age.
The reduced VO2 and VCO2 points to peripheral
decline in oxygen consumption and carbon
dioxide production, respectively. In addition, the
MHR and absolute HRT measures allow for
cardiovascular limitations with increased age
(Figure 4). Higginbotham et al. (16) investigated
the physiologic mechanisms of decline in aerobic
capacity with an aging population. They found
the age related decline in aerobic work
performance resulted primarily from a reduced
exercise heart rate when compared to peripheral
oxygen utilization. This is consistent with the
current research showing a greater rate of decline
in MHR (-.78) and absolute HRT (-.75) than in
relative VO2max (-.66) and absolute VT (-.04).
DISCUSSION
The current research indicates specific
cardiopulmonary parameters decline with age.
With the decline in these parameters there is an
associated decline in time to exhaustion. The
data indicate that that volume of gas exhaled is
a contributing factor in time to exhaustion.
McClaran, Wetter, Pegelow and Dempsey (14)
examined expiratory flow limitation and it's
effects on the ventilatory response during
heavy exercise. They concluded expiratory
flow limitations result in increased endexpiratory lung volume, reduced tidal volume,
and inhibit respiratory motor output and
ventilation. In the current study, the
significant declines seen in VE and RR would
reduce the effects of isocapnic buffering
resulting in lowered pH, increased muscle
fatigue and reduced time to exhaustion. Babb
(15) concluded, in an investigation of
mechanical ventilatory limitations with aging
subjects, that at higher workloads mechanical
ventilatory constraints inhibit VE. However,
the non-significant changes in VE/VO2 and
VE/VCO2 in the current study would indicate
that ventilatory constraints were not the only
100
80
60
40
20
0
20
30
40
50
60
70
80
Age (y)
VO2max (ml/kg/min)
RR (b/min)
TE (min)
Figure 1. Mximal oxygen consumption, respiratory rate and
time to exhaustion across age.
Aging, Ventilation and Cycle Exercise Time to Exhaustion
16
7
6
240
5
200
4
3
160
2
120
1
80
0
20
30
40
50
60
70
80
40
Age (y)
VO2 (L/min)
0
20
VCO2 (L/min)
30
40
50
60
70
80
Age (y)
Figure 2. Asolute maximal oxygen consumption and
carbon dioxide production across age.
VE (L/min)
TE (min)
Figure 3. Expired minute ventilation and time to exhaustion across
age.
CONCLUSIONS
220
It is apparent that across the ages of this group
(21-74 yrs), the cardiopulmonary variables
200
measured and time to exhaustion are shown to
diminish. With aging it has been shown that
180
ventilation, cardiovascular and neuromuscular
components are affected. Maharam et al. (17) in
160
studying the masters’ athlete found changes in
140
skeletal muscle, heart function and aerobic
capacity. However, they note that declines with
120
aging may be attenuated with exercise. In the
current study utilizing a fit population the rate of
100
20
30
40
50
60
70
80
decline varied across measures with significant
slopes of decline highest in VE at –1.56 to a low
Age (y)
of –0.04 with absolute VT. This varies from past
research indicating an overall approximate decline
MHR (bpm)
HRT (bpm)
of 5% per decade (18). Yet studies to date have
not compared different systems rate change across
age. The current study utilizes a multi-variable
Figure 4. Maximal heart rate and heart rate threshold across
age.
approach to physiologic declines associated with
reduced time to exhaustion. Further studies are
warranted to determine specific systems rate change related to the aging process and exercise performance. In
conclusion, this study confirms the cardiopulmonary declines with fit, aging subjects and the associated effect
on time to exhaustion.
Aging, Ventilation and Cycle Exercise Time to Exhaustion
17
Address for Correspondence: Frank B. Wyatt, Ed.D., Department of Health, Human Performance, and
Recreation, 500 Speight, P.O. Box 97313, Baylor University, Waco, TX 76798; Phone: (254) 710-3504; FAX:
(254) 710-3527; Email: Frank_Wyatt@baylor.edu.
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