European Journal of
Applied
Eur. J. Appl. Physiol. 42, 35--40 (I979)
Physiology
and Occupational Physiology 9 Springer-Verlag 1979
Age-related Differences in Lactate Distribution Kinetics Following Maximal Exercise Stephen P. Tzankoff and Arthur H. Norris Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore City Hospitals, Baltimore, MD 21224, USA
Summary. Lactate concentrations were determined at 3, 5, and 7 min of recovery following maximal, continuous, multi-stage treadmill work in 180 men, aged 2 0 - 8 0 years, who were participants of the Baltimore Longitudinal Study of Aging. Each subject was placed into one of six age groups, e.g., 20-29, 30-39, etc. As expected, average concentrations decreased consistently with age. All three sampling times were similar in characterizing maximal lactates for the youngest men. For each older group, except for the oldest, the later values were significantly (p < 0.01) higher than the 3-rain values. For subjects in their 50's and 60's mean concentrations continued to rise through the 7th min. These data suggest that in man there is a progressive, age-related diminution of ability to diffuse lactate from muscle and/or distribute it into its space. This may result in decreased endurance and work capacity and a prolongation of recovery. As an alternative to multiple sampling and analyses for maximal lactate, single blood samples should be obtained no sooner than 5 min of recovery for men up to age 50, and at 7 min for those between 50 and 70 years. Variabifity among the men over 70 years of age was large enough to preclude single-sample alternatives.
Key words: Human aging -- Anaerobic work - Vasomotor control - Peripheral circulation - Maximal ~-Oz - Gerontology
In man, energy transformation for the performance of maximal muscular work is largely derived via the aerobic pathway. A smaller proportion of the energy demand derives from anaerobic glycolysis with the concomitant production of lactic acid. The substance diffuses rapidly out of muscle, and distributes, via the circulatory system, into a space roughly equivalent to the total body water. Production and distribution of lactate, under conditions of maximal exercise, occurs over a short time, usually a few minutes. Its uptake by various tissues and eventual disappearance from the circulation requires several hours at rest. Thus, after diffusion and distribution are complete, usually in the first few minutes of
0301-5548/79/0042/0035/$ 01.20
36
S.P. Tzankoff and A. H. Norris
recovery, lactate concentration in blood is expected to be high and relatively stable, (Margaria et al., 1933). This concentration has been termed the "maximal lactate". There is general agreement that high maximal lactates following maximal exercise objectively demonstrate high perseverance and appropriate tolerance to muscular fatigue by subjects who performed the test. Extensive experimental evidence shows that the maximal lactate is generally higher in those who are physically fit. Healthy sedentary men who undergo physical training for several weeks or a few months exhibit higher posttraining maximal lactate concentrations when compared with their pretraining values. There is, however, less agreement on when in recovery, and how blood should be obtained for the determination of maximal lactate. For example, Robinson (1938), in a comprehensive study of physical fitness in relation to age, reported maximal lactates determined on venous blood drawn 5 min after exhausting treadmill runs. P. O. Astrand (1952), I. Astrand (1958), and Saltin et al. (1969) sampled fingertip blood, respectively, in the 1st and at 3 - 4 min, at approximately 1 and 2 min, and in the 1st, 3rd, and 6th min of recovery. All reported only the highest concentrations. Shephard et al. (1968) sampled fingertip blood at 2 and 4 min of recovery in 24 men aged 2 0 - 4 0 years. Their finding, confirmed by retest, was that most of their subjects (n = 22) could be characterized as exhibiting higher values at either 2 or 4 rain. However, in a more recent report on elderly men and women, Sidney and Shephard (1977) sampled blood for maximal lactate at only 2 min recovery. Review of the literature has made it obvious that defensible choices for time of sampling blood for maximal lactate determination vary between 1 and 6 min. Most importantly, however, there has been no information as to whether older subjects reach maximal lactate values at the same time as young ones. Clearly, if lactate distribution kinetics differ in some systematic fashion with age, no single time will adequately characterize maximal lactate in men of different ages or in the same men as they age. Our experimental protocol was therefore designed to include multiple sampling during recovery from maximal treadmill exercise.
Methods Subjects included for this study were 180 men selected from among participants of the Baltimore Longitudinal Study of Aging, which has previously been described (Stone and Norris, 1966; Rowe et al., 1976). None suffered from significant cardiovascular disease as assessed from medical history and examination which included a 12-lead ECG. In addition, those who for the first time showed exerciseinduced ECG changes indicative of myocardial ischemia while participating in the present study were excluded from the analyses. For most subjects, particularly the older ones, the current stay at the Gerontology Research Center (GRC) represented a repeat visit. They were thus familiar with the surroundings, personnel, and the treadmill testing procedure. In the morning of their arrivals at GI/.C they were asked to undergo a multi-stage treadmill test designed to include measurements of maximal aerobic capacity. Informed consent was obtained. After an initial warm-up lasting 2--3 rain at 5.6 km/h on the level, the treadmill grade was raised by 3% grade increments every 2 rain until subjects reached self-def'medexhaustion. Apart from reassurances that the continuously monitored ECG and heart rate appeared within normal limits, there was no systematic attempt to encourage the men to perform beyond what they perceived as a maximal effort. As the end of the test approached, experienced observers rated the performance as either maximal or submaximal
Lactate Distribution Kinetics and Age
37 MEAN
N
27.2
IB
100
~ 90
~B 29 F 8o
~ 7Q ~
54.5
38
N s Fig. 1. Blood lactate concentrations (means + SE) as a function of time in recovery from maximal treadmill exercise for each of the six age groups. Mem,a age and n for each group is shown to the right of the figure
I 4
5
@
7
TIMEIN RECOVERY(rnin)
based on a combination of heart rate, apparent effort, profusion of sweating, and to some extent, spontaneous comments by the subject. Blood for the lactate analyses was obtained only on those rated as maximal performers. Immediately on finishing the walk, the subject was helped onto a cushioned chair mounted at the rear of the treadmill where he recovered until heart rate returned to near resting, pre-exercise levels. Venipuncture of an antecubital vessel was performed, without stasis, early in the 3rd rain of recovery. Blood samples were drawn into evacuated, heparinized tubes at the end of 3, 5, and 7 rain. Each aliquot was immediately mixed by inversion and placed in an ice-water slurry. Deproteination in 10% (w/v) trichloroacetic acid was done within 10 rain of sampling. Supernatants were separated after centrifugation and saved for later lactate analyses in duplicate using the Strom (1949) modification of the BarkerSummerson (1941) method. Each assay included a set of standards and a control. Subjects were grouped by age into categories spanning 10 years, e.g., 20-29, 30-39, 40-49, and so on. Group N's are given in Fig. 1. All subjects had lactate determinations for each of the specified times in recovery from maximal treadmill exercise. Age and sampling-time related differences were tested for statistical significance using a 2-way analysis of the variance (ANOVA). The largest mean concentration differences for each age group were tested for statical significance using the studentized range method (Ferguson, 1971).
Results and Discussion M e a n values for age, b o d y mass, m a x i m a l % grade o f treadmill, heart rate, a n d m e a s u r e d R ( V C O / I Y O 2 ) are s h o w n in T a b l e 1. These values are in g o o d a g r e e m e n t with the previously cited studies o n m a x i m a l w o r k performed b y healthy, non-athletic m e n in the adult age range. F i g u r e 1 shows the m e a n blood lactate c o n c e n t r a t i o n s plotted against time of recovery for each of the six age groups. As expected, inspection shows that c o n c e n trations decrease progressively with increased age. Both the decrease in lactate conc e n t r a t i o n with age a n d the increase in lactate c o n c e n t r a t i o n with time were statistically significant (p < 0.01) b y 2-way A N O V A . The interaction b e t w e e n sampling time a n d age was statistically significant (p < 0.01). M e a n values for the y o u n g e s t m e n showed n o significant differences with sampiing time, suggesting that diffusion o u t o f muscle a n d distribution t h r o u g h the
38
S.P. Tzankoff and A. H. Norris
Table 1. Characteristics (mean + SE) of the subjects by age group Mean age (year)
Weight (kg)
Max. grade (%)
Max. HR (b/re.in)
Max. R P'COJ~'O2
27.2
75.2 + 1.7
18.2 _+0.51
192.8 • 1.8
1.20 + 0.002
34.9
79.8 + 1.3
16.5 + 0.40
184.1 + 1.4
1.15 + 0.009
45.2
84.3 + 2.1
13.3 + 0.70
172.9 + 2.2
1.17 + 0.017
54.5
78.1 + 1.6
12.9 + 0.42
167.3 • 2.0
1.15 +_0.015
64.9
79.4 _+2.5
12.0 + 0.73
154.9 • 3.1
1.14 i 0.020
75.2
74.4 _+5.0
12.3 • 1.14
149.5 _+5.4
1.10 • 0.030
lactate space were complete by the 3rd min of recovery. For the older men, beginning with those in their 30's, mean blood lactate concentrations at 3 min of recovery were lower than at 5 rain. While concentrations for those in their 30's and 40's tended to plateau by the 5th min, those in their 50's and 60's exhibited continued increments through the 7th rain of recovery. For those in their 30's through 60's, the highest mean lactate concentrations were significantly different (p < 0.01) from their respective lowest concentrations. Interestingly, the pattern for those in their 70's, was similar to that of the youngest. An appealing, though naive, interpretation of this similarity is that these very select old men have managed to retain some youthful qualities consistent with healthy longevity, e.g., sound vasomotor control. That their maximal lactate concentrations reached only about half of the values shown by the youngest men reflects the insidious, age-related decrement in skeletal muscle mass (Tzankoff and Norris, 1977, 1978). Clearly, maximal lactate concentrations are best quantified by serial sampling during recovery which involves multiple analyses for determination of the plateau value. For most studies this protocol would be prohibitive in terms of personnel and other expense. The alternative is to choose an appropriate time, based on age, when lactate concentrations are most likely to have reached a maximal value. In Fig. 2 each subject's lactate concentrations were calculated as percentages of the highest value measured. These were averaged by age group and are shown as connected points for each of the blood sampling times in recovery. As compared with the later sampling times, the 3-min sample is inadequate in representing the highest lactate concentrations except for the youngest and oldest men. Although both the 5- and 7-min samples are about equivalent in characterizing maximal lactate concentrations across the adult ages up to age 70, the suggestion of continued increments past the 7th rain in those over 50 years of age (Fig. 1) justifies sampling at 5 rain for men up to age 50 and at 7 min for those aged 50 to 70 years. For men over 70 years of age the present data are so variable as to suggest no recourse except multiple sampling during recovery. The present findings pertain directly to data from samples obtained by antecubital venipuncture. By the time lactate reaches uniform distribution throughout its space capillary blood samples obtained by puncture of a prewarmed fingertip should
Lactate Distribution Kinetics and Age
39 16
6'8
100
9 9o
Fig. 2. Blood lactates (expressed as percent of highest value for each subject) as a function of age for each of the three sampling times during recovery from maximal treadmill exercise
\o
o/\
TIME IN RECOVERY: o 3 MIN. 9 5 MIN.
80
25
,~ 7 MIN.
3'5
4'5
5'5 AGE (yrs)
65
7'5
yield comparable data. However, even with careful measurement of the microliter volumes required for this technique, contamination of the sample with lactate-rich fluid secreted by the numerous and very active sweat glands on fingers is difficult to control. The present data do not provide insight about the many mechanisms which might mediate the age-related damping of lactate distribution kinetics during recovery from maximal muscular work. Distribution of lactate might be delayed as a result of age-related changes in vasomotor control which mediates redistribution of blood flow during recovery. Slower diffusion out of blood and into tissues which comprise the lactate space may also contribute to the delay. On the other hand, compared with the young men, lactate production during recovery may continue at a higher rate or for a longer time in older men. The rapid removal of lactate out of working muscle might contribute to longer endurance and greater work capacity. To the extent that this process is delayed, the older subjects are at a disadvantage. In summary, the present study shows that diffusion and/or distribution of lactate from muscle recovering from maximal work requires progressively longer times as mean ages of subjects increase. Samples obtained in the first 1 - 4 rain of recovery will systematically underestimate mean maximal lactates in groups of older subjects. When limitations require that determinations of maximal lactate be done on single samples obtained during recovery, the appropriate, age-dependent time for sampling should be chosen: 5 min for men up to age 50, 7 min for men between 50 and 70 years. For men over 70 years of age, intersubject variability precludes the choice of an appropriate time for a single-sample determination.
Acknowledgements. We wish to express our sincere appreciation to the participants in the Baltimore Longitudinal Study of Aging who have, over many years, enthusiasticallygiven their time and patience to the study of Gerontology. We are indebted to Mrs. Carolyn Eames who performed the more than 1,000 lactate determinations, Mrs. Catherine Dent who assisted in stress testing, and to Dr. Leonard Giambra for statistical consultations.
40
S.P. Tzankoff and A. H. Norris
References Astrand, I.: The physical work capacity of workers 50-64 years old. Acta Physiol. Scand. 42, 73-86 (1958) Astrand, P.-O.: Experimental studies of physical working capacity in relation to sex and age. Copenhagen: Munksgaard 1952 Barker, S. B., Summerson, W. H.: The colorimetric determination of lactic acid in biological material. J. Biol. Chem. 138, 535-554 (1941) Ferguson, G. A.: Statistical analysis in psychology and education. New York: McGraw-Hill 1971 Margaria, R., Edwards, H. T., Dill, D. B.: The possible mechanisms of contracting and paying the oxygen debt and the role of lactic acid in muscular contraction. Am. J. Physiol. 106, 689-715 (1933) Robinson, S.: Experimental studies of physical fitness in relation to age. Arbeitspiaysiologie 10, 251-323 (1938) Rowe, J. W., Andres, R., Tobin, J. D., Norris, A. H., Shock, N. W.: The effect of age on creatinine clearance in men: a cross-sectional and longitudinal study. J. Gerontol. 31, 155-163 (1976) Saltin, B., Hartley, L. H., Kilbom, A., Astrand, I.: Physical training in sedentary middle-aged and older men. II: Oxygen uptake, heart rate, and blood lactate concentration at submaximal and maximal exercise. Scand. J. Clin. Lab. Invest. 24, 323--334 (1969) Shepard, R. J., Allen, C., Benade, A. H. S., Davies, C. T. M., diPrampero, P. E., Hedman, R., Merriman, J. E., Myhre, K., Simmons, R.: The maximum oxygen intake. An international reference standard of cardio-respiratory fitness. Bull WHO 38, 757-764 (1968) Sidney, K. H., Shephard, R. J.: Maximum and submaximum exercise tests in men and women in the seventh, eighth, and ninth decades of life. J. Appl. Physiol.: Respir. Environ. Exercise Physiol. 43, 280-287 (1977) Stone, J. L., Norris, A. H.: Activities and attitudes of participants in the Baltimore Longitudinal Study. J. Gerontol. 21, 575-580 (1966) Strom, G.: The influence of anoxia on lactate utilization in man after prolonged muscular work. Acta Physiol. Scand. 17, 440-451 (1949) Tzankoff, S. P., Norris, A. H.: Effect of muscle mass decrease on age-related BMR changes. J. Appl. Physiol.: Respir. Environ. Exercise Physiol. 43, 1001-1006 (1977) Tzankoff, S. P., Norris, A. H.: Longitudinal changes in basal metabolism in man. J. Appl. Physiol.: Respir. Environ. Exercise Physiol. 45, 536-539 (1978)
Accepted May 30, 1979
Applied
Eur. J. Appl. Physiol. 42, 35--40 (I979)
Physiology
and Occupational Physiology 9 Springer-Verlag 1979
Age-related Differences in Lactate Distribution Kinetics Following Maximal Exercise Stephen P. Tzankoff and Arthur H. Norris Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore City Hospitals, Baltimore, MD 21224, USA
Summary. Lactate concentrations were determined at 3, 5, and 7 min of recovery following maximal, continuous, multi-stage treadmill work in 180 men, aged 2 0 - 8 0 years, who were participants of the Baltimore Longitudinal Study of Aging. Each subject was placed into one of six age groups, e.g., 20-29, 30-39, etc. As expected, average concentrations decreased consistently with age. All three sampling times were similar in characterizing maximal lactates for the youngest men. For each older group, except for the oldest, the later values were significantly (p < 0.01) higher than the 3-rain values. For subjects in their 50's and 60's mean concentrations continued to rise through the 7th min. These data suggest that in man there is a progressive, age-related diminution of ability to diffuse lactate from muscle and/or distribute it into its space. This may result in decreased endurance and work capacity and a prolongation of recovery. As an alternative to multiple sampling and analyses for maximal lactate, single blood samples should be obtained no sooner than 5 min of recovery for men up to age 50, and at 7 min for those between 50 and 70 years. Variabifity among the men over 70 years of age was large enough to preclude single-sample alternatives.
Key words: Human aging -- Anaerobic work - Vasomotor control - Peripheral circulation - Maximal ~-Oz - Gerontology
In man, energy transformation for the performance of maximal muscular work is largely derived via the aerobic pathway. A smaller proportion of the energy demand derives from anaerobic glycolysis with the concomitant production of lactic acid. The substance diffuses rapidly out of muscle, and distributes, via the circulatory system, into a space roughly equivalent to the total body water. Production and distribution of lactate, under conditions of maximal exercise, occurs over a short time, usually a few minutes. Its uptake by various tissues and eventual disappearance from the circulation requires several hours at rest. Thus, after diffusion and distribution are complete, usually in the first few minutes of
0301-5548/79/0042/0035/$ 01.20
36
S.P. Tzankoff and A. H. Norris
recovery, lactate concentration in blood is expected to be high and relatively stable, (Margaria et al., 1933). This concentration has been termed the "maximal lactate". There is general agreement that high maximal lactates following maximal exercise objectively demonstrate high perseverance and appropriate tolerance to muscular fatigue by subjects who performed the test. Extensive experimental evidence shows that the maximal lactate is generally higher in those who are physically fit. Healthy sedentary men who undergo physical training for several weeks or a few months exhibit higher posttraining maximal lactate concentrations when compared with their pretraining values. There is, however, less agreement on when in recovery, and how blood should be obtained for the determination of maximal lactate. For example, Robinson (1938), in a comprehensive study of physical fitness in relation to age, reported maximal lactates determined on venous blood drawn 5 min after exhausting treadmill runs. P. O. Astrand (1952), I. Astrand (1958), and Saltin et al. (1969) sampled fingertip blood, respectively, in the 1st and at 3 - 4 min, at approximately 1 and 2 min, and in the 1st, 3rd, and 6th min of recovery. All reported only the highest concentrations. Shephard et al. (1968) sampled fingertip blood at 2 and 4 min of recovery in 24 men aged 2 0 - 4 0 years. Their finding, confirmed by retest, was that most of their subjects (n = 22) could be characterized as exhibiting higher values at either 2 or 4 rain. However, in a more recent report on elderly men and women, Sidney and Shephard (1977) sampled blood for maximal lactate at only 2 min recovery. Review of the literature has made it obvious that defensible choices for time of sampling blood for maximal lactate determination vary between 1 and 6 min. Most importantly, however, there has been no information as to whether older subjects reach maximal lactate values at the same time as young ones. Clearly, if lactate distribution kinetics differ in some systematic fashion with age, no single time will adequately characterize maximal lactate in men of different ages or in the same men as they age. Our experimental protocol was therefore designed to include multiple sampling during recovery from maximal treadmill exercise.
Methods Subjects included for this study were 180 men selected from among participants of the Baltimore Longitudinal Study of Aging, which has previously been described (Stone and Norris, 1966; Rowe et al., 1976). None suffered from significant cardiovascular disease as assessed from medical history and examination which included a 12-lead ECG. In addition, those who for the first time showed exerciseinduced ECG changes indicative of myocardial ischemia while participating in the present study were excluded from the analyses. For most subjects, particularly the older ones, the current stay at the Gerontology Research Center (GRC) represented a repeat visit. They were thus familiar with the surroundings, personnel, and the treadmill testing procedure. In the morning of their arrivals at GI/.C they were asked to undergo a multi-stage treadmill test designed to include measurements of maximal aerobic capacity. Informed consent was obtained. After an initial warm-up lasting 2--3 rain at 5.6 km/h on the level, the treadmill grade was raised by 3% grade increments every 2 rain until subjects reached self-def'medexhaustion. Apart from reassurances that the continuously monitored ECG and heart rate appeared within normal limits, there was no systematic attempt to encourage the men to perform beyond what they perceived as a maximal effort. As the end of the test approached, experienced observers rated the performance as either maximal or submaximal
Lactate Distribution Kinetics and Age
37 MEAN
N
27.2
IB
100
~ 90
~B 29 F 8o
~ 7Q ~
54.5
38
N s Fig. 1. Blood lactate concentrations (means + SE) as a function of time in recovery from maximal treadmill exercise for each of the six age groups. Mem,a age and n for each group is shown to the right of the figure
I 4
5
@
7
TIMEIN RECOVERY(rnin)
based on a combination of heart rate, apparent effort, profusion of sweating, and to some extent, spontaneous comments by the subject. Blood for the lactate analyses was obtained only on those rated as maximal performers. Immediately on finishing the walk, the subject was helped onto a cushioned chair mounted at the rear of the treadmill where he recovered until heart rate returned to near resting, pre-exercise levels. Venipuncture of an antecubital vessel was performed, without stasis, early in the 3rd rain of recovery. Blood samples were drawn into evacuated, heparinized tubes at the end of 3, 5, and 7 rain. Each aliquot was immediately mixed by inversion and placed in an ice-water slurry. Deproteination in 10% (w/v) trichloroacetic acid was done within 10 rain of sampling. Supernatants were separated after centrifugation and saved for later lactate analyses in duplicate using the Strom (1949) modification of the BarkerSummerson (1941) method. Each assay included a set of standards and a control. Subjects were grouped by age into categories spanning 10 years, e.g., 20-29, 30-39, 40-49, and so on. Group N's are given in Fig. 1. All subjects had lactate determinations for each of the specified times in recovery from maximal treadmill exercise. Age and sampling-time related differences were tested for statistical significance using a 2-way analysis of the variance (ANOVA). The largest mean concentration differences for each age group were tested for statical significance using the studentized range method (Ferguson, 1971).
Results and Discussion M e a n values for age, b o d y mass, m a x i m a l % grade o f treadmill, heart rate, a n d m e a s u r e d R ( V C O / I Y O 2 ) are s h o w n in T a b l e 1. These values are in g o o d a g r e e m e n t with the previously cited studies o n m a x i m a l w o r k performed b y healthy, non-athletic m e n in the adult age range. F i g u r e 1 shows the m e a n blood lactate c o n c e n t r a t i o n s plotted against time of recovery for each of the six age groups. As expected, inspection shows that c o n c e n trations decrease progressively with increased age. Both the decrease in lactate conc e n t r a t i o n with age a n d the increase in lactate c o n c e n t r a t i o n with time were statistically significant (p < 0.01) b y 2-way A N O V A . The interaction b e t w e e n sampling time a n d age was statistically significant (p < 0.01). M e a n values for the y o u n g e s t m e n showed n o significant differences with sampiing time, suggesting that diffusion o u t o f muscle a n d distribution t h r o u g h the
38
S.P. Tzankoff and A. H. Norris
Table 1. Characteristics (mean + SE) of the subjects by age group Mean age (year)
Weight (kg)
Max. grade (%)
Max. HR (b/re.in)
Max. R P'COJ~'O2
27.2
75.2 + 1.7
18.2 _+0.51
192.8 • 1.8
1.20 + 0.002
34.9
79.8 + 1.3
16.5 + 0.40
184.1 + 1.4
1.15 + 0.009
45.2
84.3 + 2.1
13.3 + 0.70
172.9 + 2.2
1.17 + 0.017
54.5
78.1 + 1.6
12.9 + 0.42
167.3 • 2.0
1.15 +_0.015
64.9
79.4 _+2.5
12.0 + 0.73
154.9 • 3.1
1.14 i 0.020
75.2
74.4 _+5.0
12.3 • 1.14
149.5 _+5.4
1.10 • 0.030
lactate space were complete by the 3rd min of recovery. For the older men, beginning with those in their 30's, mean blood lactate concentrations at 3 min of recovery were lower than at 5 rain. While concentrations for those in their 30's and 40's tended to plateau by the 5th min, those in their 50's and 60's exhibited continued increments through the 7th rain of recovery. For those in their 30's through 60's, the highest mean lactate concentrations were significantly different (p < 0.01) from their respective lowest concentrations. Interestingly, the pattern for those in their 70's, was similar to that of the youngest. An appealing, though naive, interpretation of this similarity is that these very select old men have managed to retain some youthful qualities consistent with healthy longevity, e.g., sound vasomotor control. That their maximal lactate concentrations reached only about half of the values shown by the youngest men reflects the insidious, age-related decrement in skeletal muscle mass (Tzankoff and Norris, 1977, 1978). Clearly, maximal lactate concentrations are best quantified by serial sampling during recovery which involves multiple analyses for determination of the plateau value. For most studies this protocol would be prohibitive in terms of personnel and other expense. The alternative is to choose an appropriate time, based on age, when lactate concentrations are most likely to have reached a maximal value. In Fig. 2 each subject's lactate concentrations were calculated as percentages of the highest value measured. These were averaged by age group and are shown as connected points for each of the blood sampling times in recovery. As compared with the later sampling times, the 3-min sample is inadequate in representing the highest lactate concentrations except for the youngest and oldest men. Although both the 5- and 7-min samples are about equivalent in characterizing maximal lactate concentrations across the adult ages up to age 70, the suggestion of continued increments past the 7th rain in those over 50 years of age (Fig. 1) justifies sampling at 5 rain for men up to age 50 and at 7 min for those aged 50 to 70 years. For men over 70 years of age the present data are so variable as to suggest no recourse except multiple sampling during recovery. The present findings pertain directly to data from samples obtained by antecubital venipuncture. By the time lactate reaches uniform distribution throughout its space capillary blood samples obtained by puncture of a prewarmed fingertip should
Lactate Distribution Kinetics and Age
39 16
6'8
100
9 9o
Fig. 2. Blood lactates (expressed as percent of highest value for each subject) as a function of age for each of the three sampling times during recovery from maximal treadmill exercise
\o
o/\
TIME IN RECOVERY: o 3 MIN. 9 5 MIN.
80
25
,~ 7 MIN.
3'5
4'5
5'5 AGE (yrs)
65
7'5
yield comparable data. However, even with careful measurement of the microliter volumes required for this technique, contamination of the sample with lactate-rich fluid secreted by the numerous and very active sweat glands on fingers is difficult to control. The present data do not provide insight about the many mechanisms which might mediate the age-related damping of lactate distribution kinetics during recovery from maximal muscular work. Distribution of lactate might be delayed as a result of age-related changes in vasomotor control which mediates redistribution of blood flow during recovery. Slower diffusion out of blood and into tissues which comprise the lactate space may also contribute to the delay. On the other hand, compared with the young men, lactate production during recovery may continue at a higher rate or for a longer time in older men. The rapid removal of lactate out of working muscle might contribute to longer endurance and greater work capacity. To the extent that this process is delayed, the older subjects are at a disadvantage. In summary, the present study shows that diffusion and/or distribution of lactate from muscle recovering from maximal work requires progressively longer times as mean ages of subjects increase. Samples obtained in the first 1 - 4 rain of recovery will systematically underestimate mean maximal lactates in groups of older subjects. When limitations require that determinations of maximal lactate be done on single samples obtained during recovery, the appropriate, age-dependent time for sampling should be chosen: 5 min for men up to age 50, 7 min for men between 50 and 70 years. For men over 70 years of age, intersubject variability precludes the choice of an appropriate time for a single-sample determination.
Acknowledgements. We wish to express our sincere appreciation to the participants in the Baltimore Longitudinal Study of Aging who have, over many years, enthusiasticallygiven their time and patience to the study of Gerontology. We are indebted to Mrs. Carolyn Eames who performed the more than 1,000 lactate determinations, Mrs. Catherine Dent who assisted in stress testing, and to Dr. Leonard Giambra for statistical consultations.
40
S.P. Tzankoff and A. H. Norris
References Astrand, I.: The physical work capacity of workers 50-64 years old. Acta Physiol. Scand. 42, 73-86 (1958) Astrand, P.-O.: Experimental studies of physical working capacity in relation to sex and age. Copenhagen: Munksgaard 1952 Barker, S. B., Summerson, W. H.: The colorimetric determination of lactic acid in biological material. J. Biol. Chem. 138, 535-554 (1941) Ferguson, G. A.: Statistical analysis in psychology and education. New York: McGraw-Hill 1971 Margaria, R., Edwards, H. T., Dill, D. B.: The possible mechanisms of contracting and paying the oxygen debt and the role of lactic acid in muscular contraction. Am. J. Physiol. 106, 689-715 (1933) Robinson, S.: Experimental studies of physical fitness in relation to age. Arbeitspiaysiologie 10, 251-323 (1938) Rowe, J. W., Andres, R., Tobin, J. D., Norris, A. H., Shock, N. W.: The effect of age on creatinine clearance in men: a cross-sectional and longitudinal study. J. Gerontol. 31, 155-163 (1976) Saltin, B., Hartley, L. H., Kilbom, A., Astrand, I.: Physical training in sedentary middle-aged and older men. II: Oxygen uptake, heart rate, and blood lactate concentration at submaximal and maximal exercise. Scand. J. Clin. Lab. Invest. 24, 323--334 (1969) Shepard, R. J., Allen, C., Benade, A. H. S., Davies, C. T. M., diPrampero, P. E., Hedman, R., Merriman, J. E., Myhre, K., Simmons, R.: The maximum oxygen intake. An international reference standard of cardio-respiratory fitness. Bull WHO 38, 757-764 (1968) Sidney, K. H., Shephard, R. J.: Maximum and submaximum exercise tests in men and women in the seventh, eighth, and ninth decades of life. J. Appl. Physiol.: Respir. Environ. Exercise Physiol. 43, 280-287 (1977) Stone, J. L., Norris, A. H.: Activities and attitudes of participants in the Baltimore Longitudinal Study. J. Gerontol. 21, 575-580 (1966) Strom, G.: The influence of anoxia on lactate utilization in man after prolonged muscular work. Acta Physiol. Scand. 17, 440-451 (1949) Tzankoff, S. P., Norris, A. H.: Effect of muscle mass decrease on age-related BMR changes. J. Appl. Physiol.: Respir. Environ. Exercise Physiol. 43, 1001-1006 (1977) Tzankoff, S. P., Norris, A. H.: Longitudinal changes in basal metabolism in man. J. Appl. Physiol.: Respir. Environ. Exercise Physiol. 45, 536-539 (1978)
Accepted May 30, 1979
