(Chest. 2003;124:2377-2383.)
© 2003
American College of Chest Physicians
Adaptation of Pulmonary Oxygen Consumption Slow Component Following 6 Weeks of Exercise Training Above and Below the Lactate Threshold in Untrained Men*
Jeffrey V. Ocel, PhD;
Larry E. Miller, MA;
Lee M. Pierson, MS;
David F. Wootten, PhD;
Brian J. Hawkins, MS;
Jonathan Myers, PhD and
William G. Herbert, PhD
* From Beth Israel Deaconess Medical Center (Dr. Ocel), Boston, MA; Virginia Polytechnic Institute and State University (Mr. Miller, Mr. Pierson, and Mr. Hawkins), Blacksbury, WV; Univer-sity of Memphis (Dr. Wootten), Memphis, TN; Veterans Affairs Palo Alto Health Care System (Dr. Myers), Palo Alto, CA; and Health Research Group (Dr. Herbert), Blacksburg, VA.
Correspondence to: Jeffrey V. Ocel, PhD, Clinical Physiologist, Department of Cardiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02081; e-mail: jocel{at}bidmc.harvard.edu
 |
Abstract
|
|---|
Study objectives: To examine the effects of 6 weeks of exercise training above or below the lactate threshold (LT) on the slow component (SC) of pulmonary oxygen consumption (
O2).
Design: Randomized controlled trial.
Setting: University human performance laboratory.
Participants: Apparently healthy, untrained men (n = 18).
Interventions: Subjects were randomized to one of three groups: high-intensity exercise training (HI) [above the LT], moderate-intensity exercise training (MOD) [below the LT], or no exercise training (CON). Exercise groups performed cycle ergometry 4 d/wk for 6 weeks. Total work throughout training was constant between groups.
Measurements and results. Maximal cycle ergometry was performed at baseline and after training to assess power output at the LT (WLT), O2 at the LT (O2LT), and peak O2 (O2PK). High-intensity, constant-load cycling was performed at baseline and weeks 1, 2, 4, and 6 to assess SC adaptations. WLT, O2LT, and O2PK increased after 6 weeks in both exercise groups compared to the CON group (p < 0.05), although there were no differences between the training groups. SC of O2 decreased 44% in the HI group following 1 week of exercise training vs MOD (20%, p < 0.05) and CON (12%, p < 0.01) groups. The SC attenuation was more prominent at all time points in the HI group compared to the MOD group. Total SC attenuation over the 6-week training period did not differ between the HI (71%) and MOD (57%) groups.
Conclusions: Training at HI or MOD produced similar improvements in the LT, O2, and power output at peak exertion when total work output was held constant. Attenuation of the SC with training above and below the LT were similar, although above-LT training promoted faster SC adaptations.
Key Words: constant load • cycle ergometry • lactate threshold • pulmonary oxygen consumption • slow component
|
Introduction
|
|---|
Pulmonary oxygen consumption (O2) increases rapidly during the first 3 min of constant-load exercise. From 3 min until the end of exercise, O2 response is dependent on exercise intensity. With exercise below the lactate threshold (LT), which is defined as the workload where blood lactate concentration [La] is 
2 mM,1
steady-state conditions are achieved and no further rises in O2 are observed. However, with constant-load exercise above the LT, O2 continues to rise after 3 min. This O2 increase is termed the slow component (SC) of O2.2
3
During severe exercise, the steady state in O2, which is seen with low- to moderate-intensity exercise, may be delayed or not attained at all due to the SC rise.4
5
If, however, a steady state is attained above the LT, the O2 response is often greater per unit work than below the LT.4
The SC may exceed 1 L of O2 per minute,5
and may even increase O2 to maximal levels.6
A reduction of the SC with exercise is highly desirable, as this adaptation may allow one to undertake longer periods of physical activity and increase physical work tolerance before fatigue. Endurance training of 2 to 8 weeks has been shown to attenuate the SC.7
8
9
10
The SC of O2 during cycle ergometry has been demonstrated to be 90 to 250 mL greater vs treadmill running.11
12
Furthermore, SC response is inversely related to aerobic fitness.13
Thus, constant-load, high-intensity cycle ergometry in untrained subjects may result in substantial SC responses, thereby allowing room for improvement due to long-term exercise training. The purpose of this study was to examine both the time course and magnitude of SC change following 6 weeks of cycle ergometry training above or below the LT in untrained male subjects.
|
Materials and Methods
|
|---|
Subjects
Subjects were recruited from the campus of Virginia Polytechnic Institute and State University. Inclusion criteria for study participation included male gender, age 18 to 30 years, nonparticipation in regular physical activity (
2 d/wk and 40 min/d) during the 3 months prior to enrollment, and lack of contraindications to vigorous exercise determined with a medical history questionnaire. Eighteen subjects volunteered for the study and gave written informed consent after a thorough explanation of the study protocol. The procedures used in this study were in accordance with the recommendations of the Helsinki Declaration of 1975, and were approved by the Institutional Review Board for Research Involving Human Subjects at Virginia Polytechnic Institute and State University.
Maximal Cycle Ergometry Testing
Subjects performed a maximal cycle ergometry test prior to and following the 6-week intervention period. Each test was performed in a 4-h postabsorptive state at the same time of day on a calibrated, electronically braked cycle ergometer (CardiO2; Medical Graphics Corporation; St. Paul, MN). The cycling protocol started with no resistance on the flywheel and increased 20 W/min. The test was terminated on subject request or the inability to maintain a cadence > 40 revolutions per minute. O2 was measured with a calibrated metabolic cart (CPX/D; Medical Graphics Corporation). Peak O2 (O2PK) was defined as the highest O2 (20-s average) achieved during the final minute of exercise. Blood (1 mL) was drawn at rest and after each minute of exercise through an indwelling catheter in the antecubital vein. Blood samples were collected in glass tubes containing potassium oxalate to prevent further glycolysis and sodium fluoride to prevent ex vivo coagulation, and immediately analyzed for [La] with an automated analyzer (YSI 1500 Sport Lactate Analyzer; YSI; Yellow Springs, OH). LT was calculated by three blinded investigators and defined as the breakpoint in the linear relationship of blood [La] to O2.10
14
An increase in [La] of at least 0.2 mM was required for the determination of LT. When disparities existed among investigators, the average [La] was reported. Interobserver reliability for determination of LT using this method was 0.98.
Constant-Load Exercise Testing
Subjects performed a high-intensity constant-load cycle ergometry test at a power output calculated as follows:
where WLT is the power output (watts) at the LT, and WPK is the power output (watts) at O2PK. Subjects cycled at the designated power output for up to 15 min. If the subject was unable to complete the entire 15 min of exercise, the time was noted and the end points for all subsequent constant-load testing with that subject were held constant. Blood was drawn and analyzed for [La] at rest, after 3 min of exercise, and at test termination. O2 was measured throughout the constant-load tests. These trials were repeated at weeks 1, 2, 4, and 6 throughout the intervention period. The SC of O2 was calculated by subtracting the O2 at the third minute of exercise from the end-exercise O2.5
10
Exercise Training
Following initial testing, subjects were randomly assigned to either high-intensity exercise training (HI), moderate-intensity exercise training (MOD), or a no exercise training (CON) control group. The training program consisted of supervised cycle ergometry (Monark E818; Monark Exercise AB; Vansbro, Sweden) 4 d/wk, in addition to the constant-load tests performed on the first day of weeks 1, 2, 4, and 6. Workload and test duration were held constant for each subject throughout the training period. Subjects in the HI group trained at an intensity of WLT + 0.75 (WPK – WLT) for 25 ± 2 min per session. Subjects in the MOD group trained at 90% of WLT for 60 min per session. Total work performed was equal between exercise groups. All subjects were asked to refrain from physical activity outside of the study.
Data Analysis
Two-way (time x treatment) repeated-measures analysis of variance was used to determine the effects of training on physiologic parameters at the LT and at peak exercise, as well as on SC changes. When significant main effects were found, the Tukey post hoc test was applied to identify pairwise differences. Pearson product-moment correlations were used to assess the relationships between training-induced changes in the SC and changes in [La], minute ventilation (E), and heart rate during constant-load testing. Statistical significance was set at p < 0.05. All values are reported as mean ± SEM unless noted otherwise.
|
Results
|
|---|
Physical characteristics of the subjects are presented in Table 1 . No baseline differences were noted among the three groups. Details of the 6-week exercise training programs are provided in Table 2
. Although exercise intensity and duration/session varied between groups, total work (watts x minute) was similar between training groups. Compliance, defined as the number of training sessions attended divided by total possible training sessions, was 92% and 91% in the HI and MOD groups, respectively, over the 6-week training period. The effects of the cycle ergometry training program on O2 and power output at maximal exercise and the LT are reported in Table 3
. Power output (16 to 18%), O2 (15 to 19%), and ventilation (19 to 23%) at peak exercise significantly increased in both training groups. However, more dramatic positive effects were noted in power output (43 to 51%) and O2 (33 to 35%) at the LT. These changes were all significant vs CON, although no differences were noted between the training groups.
The effects of cycle ergometry training on physiologic markers during the constant-load tests are shown in Table 4
. Both training groups experienced a significant reduction in heart rate (p < 0.01), O2 (p < 0.05), E (p < 0.01), and [La] (p < 0.001) from the pretraining constant-load test. The HI group experienced greater reductions in all these variables vs MOD, although only heart rate and [La] significantly differed. SC changes over the 6-week training period are presented in Figure 1
. The HI group experienced a 44% SC reduction (p = 0.03) after 1 week of exercise training, which was greater than MOD (p < 0.05) and CON (p < 0.01). Between week 2 and week 4, SC decreased another 51% (p < 0.01). By week 6, SC in the HI group decreased approximately 0.5 L from baseline (p = 0.004), a 71% overall reduction. A significant time effect was also observed in the MOD group (p < 0.001). A 36% decline in SC (p = 0.04) was noted after 2 weeks of exercise training, which was greater than CON (p < 0.05). No further significant changes in SC were noted in the MOD group from weeks 2 to 6, although slight reductions continued and remained lower than CON (p < 0.05) at each interval. Over the 6-week intervention period, SC decreased 57% from baseline in the MOD group. No SC changes were noted in the CON group.
Significant correlations were found between the decline in SC and decreases in [La] (r = 0.76, p < 0.01) and ventilation (r = 0.59, p < 0.05) with constant-load testing in the exercise groups. The relationship between SC and [La] change over the 6-week training period are presented in Figure 2
.
|
Discussion
|
|---|
The current study reports similar improvements in O2, WLT, and WPK in groups who trained above and below the LT for 6 weeks. Furthermore, SC responses from high-intensity, constant-load cycling were attenuated over the 6-week training period in both exercise groups. However, significant SC changes were observed after only 1 week of HI and 2 weeks of training at 90% of WLT. To our knowledge, this is the first report to show SC reductions in as little as 1 week.
Previous studies7
8
15
16
have reported SC alterations in 2 to 8 weeks of exercise training. Most recently, Saunders et al16
reported slight decreases in end-exercise O2 (58 mL/min, p < 0.05) with high-intensity constant-load cycling after 4-week of cycle ergometry training in young men and women. End-exercise O2 with moderate-intensity (15% below LT) constant-load cycling was unchanged. This is in contrast to SC reductions in the present study of 429 mL and 216 mL in the HI and MOD groups, respectively. Maximal O2 increases were approximately three times greater for the HI group in the present study despite similar subject fitness levels and training protocols.
Womack and colleagues10
reported significant declines in SC after 2 weeks of cycle ergometry training at 70% O2PK, which continued through 6 weeks. However, there was no control group in this study, which diminishes the confidence in the results. When accounting for changes in the CON group, the HI group in the present study showed a similar decrease in SC after 1 week of exercise training than Womack and colleagues10
after 2 weeks. Interestingly, the MOD group reduced SC in 2 weeks as well, but at a much reduced exercise intensity (approximately 45% O2PK).
Casaburi et al15
reported on 10 subjects who participated in an 8-week, high-intensity, endurance training program (5 d/wk, 45 minutes per session). Before and after the training period, subjects completed a series of four constant-load cycle ergometry bouts of 15 min at the following exercise intensities: 90% of the ventilatory threshold, and 25%, 50%, and 75% of the difference between the ventilatory threshold and O2PK. Maximum O2 increased 15%, and although small SC reductions (approximately 70 mL) were seen in the constant-load bouts below the ventilatory threshold, much greater reductions (approximately 150 to 250 mL) were observed at all workloads above the ventilatory threshold.
Belman and Gaesser7
reported a slight reduction in end-exercise O2 for a 6-min, high-intensity treadmill run following 8 weeks of exercise training. O2PK (p = 0.02) and peak LT (p < 0.01) increased with training, although no differences were observed between groups training above vs below the LT.
The rapid attenuation of the SC in the current study vs previous studies may be due to several factors. First, only one study10
reported week-by-week changes in SC due to exercise training. Thus, the SC changes reported with exercise training in other studies may actually be explained by the changes that occur in the first 1 to 2 weeks based on the results of the present study and the work of Womack et al.10
Second, the HI group trained at 75% of the difference between LT power output and peak exertion (approximately 80% O2PK). Thus, these high training intensities may have been responsible for the rapid attenuation in SC. Finally, the initial SC was higher than previous reports.10
16
17
Thus, as anticipated, there may have been greater room for improvement after exercise training.
The results in the MOD group demonstrate SC attenuation in response to long-term exercise training, although a significant reduction was not noted until after 2 weeks of training. In addition, the magnitude of reduction was smaller than that found for our HI group at the 2-week interval, and is comparable to that reported by others15
after 5 weeks of training at a slightly lower training intensity. The pretraining exercise intensities for both the HI and MOD training groups appear to meet the guidelines for the threshold stimulus for training effects.18
Although exercise intensity was prescribed as a percentage of initial O2PK, increases in O2 with training actually resulted in slight decreases in relative intensity although the absolute workload remained constant. For example, the HI and MOD groups initially trained at 81% and 48% of O2PK, respectively. After the 6-week training period, the relative training intensity was 73% and 43% of O2PK in the HI and MOD groups, respectively. Both groups experienced similar improvements in O2 and power output at peak exercise and at the LT, with no significant differences noted between the training groups. In addition, both training groups significantly improved these parameters vs CON. These results are similar to other reported investigations of the effects of high- vs low-intensity training on O2PK and peak LT.7
8
14
Thus, when controlling total work, exercise training at levels below the LT may produce similar adaptations as training at intensities above the LT.
A moderate relationship between both the change in SC over the training period and end-exercise [La] and the change in ventilation over the training period were noted. Although no consensus exists, several variables have been identified as predictors of SC change with exercise training including alterations in [La],8
10
15
ventilation,10
15
19
plasma epinephrine concentration,10
and motor-unit recruitment patterns.5
However, most evidence points toward motor unit recruitment patterns in the etiology of the SC. The SC of O2 is greater when cycling at 100 revolutions per minute vs 50 revolutions per minute,20
the former requiring recruitment of more fast-twitch muscle fibers. Furthermore, cyclists with a greater proportion of fast-twitch muscle fibers have a higher O2 during high-intensity constant-load exercise.21
Poole et al22
demonstrated that augmented leg O2 during severe exercise explained approximately 86% of the SC and suggested a minor role for ventilatory, cardiac, auxiliary muscle work, or metabolic stimulation outside the working muscle. Thus, the observed relationships of [La] and ventilation with SC are likely causal.
|
Conclusions
|
|---|
The results of the current study suggest that HI and MOD result in similar improvements in O2 and power output at peak exercise and the LT. Although SC reductions after long-term exercise training are similar between exercise intensities above and below the LT, reductions occur in as little as 1 week with above-LT training intensities and may continue for up to 4 weeks.
|
Footnotes
|
|---|
Abbreviations: CON = no exercise training; HI = high-intensity exercise training; [La] = blood lactate concentration; LT = lactate threshold; MOD = moderate-intensity exercise training; SC = slow component; E = minute ventilation; O2 = pulmonary oxygen consumption; O2LT = pulmonary oxygen consumption at the lactate threshold; O2PK = peak pulmonary oxygen consumption; WLT = power output (watts) at the lactate threshold; WPK = power output (watts) at peak oxygen consumption
All research was performed at Virginia Polytechnic Institute and State University.
Received for publication May 6, 2003.
Accepted for publication May 7, 2003.
|
References
|
|---|
- Davis, JA, Caiozzo, VJ, Lamarra, N, et al (1983) Does the gas exchange anaerobic threshold occur at a fixed blood lactate concentration of 2 or 4 mM? Int J Sports Med 4,89-93[ISI][Medline]
- Saunders, MJ, Evans, EM, Arngrimsson, SA, et al Muscle activation and the slow component rise in oxygen uptake during cycling. Med Sci Sports Exerc 2000;32,2040-2045[CrossRef][ISI][Medline]
- Lucia, A, Rivero, JL, Perez, M, et al Determinants of VO(2) kinetics at high power outputs during a ramp exercise protocol. Med Sci Sports Exerc 2002;34,326-331[Medline]
- Whipp, BJ The slow component of O2 uptake kinetics during heavy exercise. Med Sci Sports Exerc 1994;26,1319-1326[ISI][Medline]
- Gaesser, GA, Poole, DC The slow component of oxygen uptake kinetics in humans. Exerc Sport Sci Rev 1996;24,35-71[Medline]
- Barstow, TJ, Mole, PA Linear and nonlinear characteristics of oxygen uptake kinetics during heavy exercise. J Appl Physiol 1991;71,2099-2106[Abstract/Free Full Text]
- Belman, MJ, Gaesser, GA Exercise training below and above the lactate threshold in the elderly. Med Sci Sports Exerc 1991;23,562-568[ISI][Medline]
- Casaburi, R, Storer, TW, Sullivan, CS, et al Evaluation of blood lactate elevation as an intensity criterion for exercise training. Med Sci Sports Exerc 1995;27,852-862[Medline]
- Poole, DC, Ward, SA, Whipp, BJ The effects of training on the metabolic and respiratory profile of high-intensity cycle ergometer exercise. Eur J Appl Physiol Occup Physiol 1990;59,421-429[Medline]
- Womack, CJ, Davis, SE, Blumer, JL, et al Slow component of O2 uptake during heavy exercise: adaptation to endurance training. J Appl Physiol 1995;79,838-845[Abstract/Free Full Text]
- Billat, VL, Richard, R, Binsse, VM, et al The V(O2) slow component for severe exercise depends on type of exercise and is not correlated with time to fatigue. J Appl Physiol 1998;85,2118-2124[Abstract/Free Full Text]
- Jones, AM, McConnell, AM Effect of exercise modality on oxygen uptake kinetics during heavy exercise. Eur J Appl Physiol Occup Physiol 1999;80,213-219[Medline]
- Russell, A, Wadley, G, Snow, R, et al Slow component of [V]O(2) kinetics: the effect of training status, fibre type, UCP3 mRNA and citrate synthase activity. Int J Obes Relat Metab Disord 2002;26,157-164[CrossRef][ISI][Medline]
- Weltman, A, Wood, CM, Womack, CJ, et al Catecholamine and blood lactate responses to incremental rowing and running exercise. J Appl Physiol 1994;76,1144-1149[Abstract/Free Full Text]
- Casaburi, R, Storer, TW, Ben-Dov, I, et al Effect of endurance training on possible determinants of O2 during heavy exercise. J Appl Physiol 1987;62,199-207[Abstract/Free Full Text]
- Saunders, MJ, Evans, EM, Arngrimsson, SA, et al Endurance training reduces end-exercise O2 and muscle use during submaximal cycling. Med Sci Sports Exerc 2003;35,257-262[Medline]
- Casaburi, R, Storer, TW, Wasserman, K Mediation of reduced ventilatory response to exercise after endurance training. J Appl Physiol 1987;63,1533-1538[Abstract/Free Full Text]
- American College of Sports Medicine position stand: the recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness in healthy adults. Med Sci Sports Exerc 1990;22,265-274[ISI][Medline]
- Gaesser, GA Influence of endurance training and catecholamines on exercise O2 response. Med Sci Sports Exerc 1994;26,1341-1346[ISI][Medline]
- Gaesser, GA, Cooper, RJ, Wilson, LA Blood [lactate] and "excess" O2 uptake during high intensity cycling at slow and fast cadences [abstract]. Physiologist 1992;35,210
- Coyle, EF, Sidossis, LS, Horowitz, JF, et al Cycling efficiency is related to the percentage of type I muscle fibers. Med Sci Sports Exerc 1992;24,782-788[ISI][Medline]
- Poole, DC, Schaffartzik, W, Knight, DR, et al Contribution of excising legs to the slow component of oxygen uptake kinetics in humans. J Appl Physiol 1991;71,1245-1260[Abstract/Free Full Text]
TOP
Abstract
Introduction
