AEROBIC RESPONSES OF FEMALE DISTANCE RUNNERS TO SUBMAXIMAL AND MAXIMAL EXERCISE* Jack Daniels Physical Education Department The University of Texas Austin, Texas 78712
Gary Krahenbuhl Arizona State University Tempe, Arizona 85281
Carl Foster Ball State University Muncie, Indiana 47303
Jimmy Gilbert National Aeronautics and Space Administration Houston, Texas 77001
Sylvia Daniels Lunier High School Austin, Texas 78758
Introduction
That males outperform females in distance running has been readily observed for as long as performances have been recorded. Standards are about 10% slower for women in 1500- and 3000-meter races and nearly 25% slower over the marathon distance. It has been suggested that the female possesses an architecture less efficient for running. Pelvis width, obliquity of the femur, and length of the female leg and stride have all received attention as possible mechanical deficiencies.** These structural characteristics, however, may not accurately describe the accomplished female distance runner, who has been shown to possess a more masculine build with respect to hip width and leg lex~gth.~-~ Females in a wide variety of sports are generally reported as having more body fat than do male^,^ a factor that could harm performance in medium endurance events where the body weight is supported. Still, Wilrnore and Brown* have found values as low as 6% among female distance runners. Another possibility is that females possess lower hemoglobin concentrations than do males,g resulting in a lower oxygen-carrying capacity of the blood. In recent years the importance of the aerobic demands of running at submaximal speeds has received increased attention.l0, '' It appears that considerable individual differences may exist,'* but whether the factor of running
* Supported in part by
The Canadian Track and Field Association.
726
Daniels et al.: Female Aerobic Responses
727
“efficiency,” or economy, can be used to differentiate among nearly equal competitors is not at all clear. Previous studies 13. 1 have explored male/ female differences during either treadmill walking or work on a bicycle ergometer. On these tasks the absolute oxygen demands of work at submaximal loads are lower in females than in males, but this is basically a function of the lower average body weight of females. Also, since women possess a lower maximum aerobic power ( Vo,),,, ,O* they are usually working at a higher percentage of their Vo,mnY during exercise involving a standard workload,, and since blood lactate accumulation is determined largely by the percent V,,,mnx used during this disparity may contribute to sex differences in running performance. Studies directly measuring sex differences in the aerobic demands of submaximal running have often been complicated by the difficulty of locating female subjects capable of submaximal runs at speeds that are more routine for male runners. If the aerobic demands of running can be shown not to differ between trained male and female runners, then the existing erformance differences may be essentially just a function of differences in The purpose of this study was to compare the aerobic demands of submaximal running in highly trained and talented male and female runners. Additionally, an attempt was made to exp1a.h differences that might be found to exist between men and women regarding Vo, during submaximal running when the subjects either are not tested over, or are not capable of submaximal work over, a common range of speeds.
8,,,,,.
Methods and Procedures The initial phase of this investigation involved 20 highly-trained runners (10 men and 10 women) who were tested during submaximal and maximal runs on a treadmill. The “submax” test session consisted of four 6-8-minute treadmill runs at approximately 202, 215, 241, and 268 mlmin. Belt revolutions were counted to determine the exact.pace and expired air was collected for the last 90 seconds of each run. The Vo, calculated for each corresponding run was taken as representative of the aerobic demands of running at that speed. The “max” test required the subjects to run on a treadmill with speed and/or grade increments added each minute. Speed was increased up to 10 mph, then 2% grade increments were added each minute until voluntary exhaustion. In each case, exhaustion was reached after 6 to 8 minutes of work. Consecutive 30- to 60-second expired gas samples were collected in meteorological balloons through a low resistance breathing valve and collection valve systern,l8 starting at the end of the third minute of exercise. Gas samples were analyzed for C 0 2 y d O2 content with a Lloyd Gallenkamp volumetric analyzer. The highest Vo,reached during each run was considered Vo, mnx. To further examine the comparison of the aerobic demands of running. between males and females and among a common group of runners when Vo,/ speed regression equations are derived from different speed ranges, an additional series of submaximal runs were completed by five male and five female runners. In this second series of tests the same procedures and methods as described above were employed except the speeds used ranged from 150 to 250 m/min. Five speeds, distributed approximately equally apart, were used and separate
Annals New York Academy of Sciences
728
regression equations were calculated using the three slowest speeds, the middle three speeds, and the three fastest speeds. In both phases of the investigation, the males and females were considered to be of comparable ability based on the average departure from current world records displayed by the two groups. Results and Discussion
TABLE 1 presents the descriptive data for the 20 subjects used in phase 1 of the study. The men were clearly larger and had greater values for VO,max (both in absolute terms and when expressed in ml/kg.min), Qx, and 0, pulse at VO,,,,. Maximum heart rates were higher among the women, but the difference was not significant ( p > 0.05). These results are all as would be expected and are generally a function of the size difference between mcn and women. In regard to running performance, it appears that the greater VO,max displayed by the male runners would give them a clear advantage in endurance events, a not surprising fiqding in light of the performance differences that do exist (19% difference in VO,mnxin this study as opposed to the typical 10%25% difference generally voted in distance running performances between the sexes) and that a greater V,,,,, by trained males is widely accepted. The p ~ values ,from the ~ phase~1 tests ~are presented ~ in~ TABLE ~2. Although the women were characterized by slightly greater 3 , ,,ubmax values at the speeds used, none of the differences was significant. The women also showed somewhat greater variability in po, at all speeds (the lowest and highest values were also recorded by females at all test speeds) ; the men were characterized by a tendency to become less variable as speed increased. These findings strongly suggest that there are no sex differences in the aerobic demands of running when the range of speeds used is common to both groups of runners and when all subjects are similar in ability. Interestingly,
TABLE1 DESCRIPTIVE DATA:TRAINED DISTANCE RUNNERS Variable Height (cm) Weight (kg)
64te skin fold (mm) t jml/kg min) Vs at , V O ~ ~ . ~
-
R at Voprn..
Heart rate maximum Odpulse (ml/beat) Vent/Or
Males (n=10) Mean SD * 179.3 65.7 39.6 73.7 166.1 1.11 180.3 26.9 34.3
* SD, standard deviation.
6.1 5.6 6.8 5.1 17.5 0.07 7.2 2.7 3.4
Females (n=10) Mean SD 166.2 % 52.1 % 48.1 % 59.6 % 107.8 % 1.08 190.8 16.3 % 34.7
t Tricep, subscapular, suprailiac, umbilical, pectoral, mid-thigh (anterior). % Significantly different from males (p
< 0.01).
4.7 3.7 4.4 4.4 12.0 0.03 10.7 1.7 3.0 -
Daniels et al.: Female Aerobic Responses
729
TABLE2 COMPARISON OF MALE AND FEMALE DISTANCE RUNNERSON THE AEROBIC OF RUNNINGAT FOURSELECTED S U E M A X M f i SPEEDS
Speed (m/min) 202
to,*(ml/kg.min) Males (n=10)
Females (n= 10)
36.2
38.0 (31-42) 40.7 (34-45) 46.0 (40-50) 51.5 (4655)
( 32-39 )
215 24 1 268
DEMANDS
39.0 (35-42) 44.6 (41-47) 50.5 (47-53)
* Go2 values were calculated for common speeds from individual regression equations. Ranges are shown in parentheses below mean values. the subject with the lowest polmax ( a female) who would presumably be working at the greatest percent of her p,,, at all submax speeds, recorded the lowest ~o,,,,ma, at every running speed. It appears that her ability to perform equally against other women with higher is a function of her greater “efficiency” as demonstrated in the sybmax tests. FIGURE 1 presents a plot of the Vo, data collected at all submax speeds used in the first series of tests. @so shown are the combined linear and quadratic regression curves and the Volmar mean values for the men and women. Although the linear regression equation proved very satisfactory in describing the relationship between running speed and to,, the second-order curve fit the data significantly better. Higher order polynomials were unsuccessful in reducing the deviation about the regression. If the curvilinear relationship displayed is a function of higher speeds demanding increasingly gre.ater energy, as the work represents a higher and higher fractional utilization of Vo, max, then the women would show a greater Vo, than the men at any given speed (which was only a nonsignificant tendency in the present study), based on the lower VOlmaxof the women. It would seem an appropriate follow-up to the present work to compare males and females who have equal VOlmaxvalues and who are equally well trained. This would eliminate the possibility that differences in fractional utilization may be a contributing factor. The results of phase 2 of the investigation are summarized in FIGURE2. Since there were again no differences between the male and female runners in Vo, at any of the five submax speeds, the data were combined and used to construct three separate regression curves based on the three slowest speeds, the middle three speeds, and the three fastest speeds. If Vo, values were calculated through extrapolation of one regression equation to determine the Vo2related to a speed outside the confines of the data from which that particular curve was constructed (for example, 300 m/min running speed) then differences in the aerobic demands of running became evident. This was true whether men and women were compared or if either separate group or a combination of
65
70
0
200
220
2bo
280
Speed (ddd
260
Linear and quadratic regression curves calculated from individual values for 10 females and 10 males.
35
40
45
50
55
are mean Vo,,.,
FIGURE.^.
.g”
Y
3 3
‘ 6 0
2
7
75
320
340
PO,and speed values for
)(M
20 runners. Also shown
360
v)
8
xg-
4
w 0
P)
u
U
$ L .. i
4
8
OOE
*
I
082
8
8
09Z I
I
OtZ
. I
OIL I
(rrp/=) P d S
I
ooz 1
I
081 I
091 0
09
09
OE
0
8 N
Annals New York Academy of Sciences
732
both was used in the comparisons. Also, this phenomenon was most evident when use of the slowest speeds was made. This could quite often lead to the mistaken conclusion that the aerobic demands of running differ between men and women since it is not unexpected that a slower range of speeds would be employed in testing women than those used with trained male runners. It is interesting to note that two of the female vnners in this study are sub-3-hour marathoners and both displayed very low VOxsubmnX values over the range of speeds at which they train most often, a finding that is in agreement with earlier research reported by Costill, Thomason, and Roberts.1° Compared with other runners who competed more successfully at shorter distance faces, however, the present marathon subjects did show a more rapid rise in Vo, as speeds increased. That the regression curve constructed from the slowest speeds appears to be much flatter than those calculated from higher speeds is likely a function of the difficulty the subjects had in running comfortably at the very slow speeds. There appeared to be a tendency to displace the body more vertically at the slower speeds, a finding that has been reported by Dillman? and Rapp,'@ and which may lead to a correspondingly greater expenditure of energy at the slower speeds. Once a more comfortable speed is reached (generally expressed by the subjects as being about 200 m/min and above) the changing workload appears to be more linearly related to changes in the aerobic demands of the work. Although the slope of the regression curve describing all the present data appears steeper than that calculated from data describing young girls reported by Astrand,13 the regression equation calculated from his data (y = 10.547 0.157~)is remarkably similar to what was calculated from the three slowest speeds in the present study (y =7.86 + 0.147x, FIGURE2). The range of speeds was similar in the two instances.
+
Conclusions (1) There appear to be no differences in the aerobic demands of running at submaximal speeds between males and females who are of relatively equal ability and fitness. That the effects of fractional utilization during submaximal running may produce measurable differences in VO,aubmnx at given speeds of running is not clear and should be-investigated using trained males and females of both equal and widely different Vo, values. (2) It tppears that the comparison of regression curves relating running speed and V,, for different speed ranges is clearly a hazardous practice. This is true whether subjects are of the same or opposite sex. The data presented in FIGURE 2 indicate that the use of speeds below 200 m/min produces a particularly flat regression curve and calculation of the energy demands of running at higher speeds based on data collected at very slow speeds would greatly underestimate the energy requirements of the faster running. A quadratic regression equation should be used when sufficient data are available. The following regression equatioF best fit the present data: y = 14.77 0 . 0 5 9 ~ 0.000279~2,where y = Vo, (ml/kg*min) and x = speed (m/min), and y = 83.74 2.798~ 0.014288~2,where y = speed (m/min) and x = (ml/ kg-min) (3) The differences in male and female running performances at middle
+
+
.
+
+
vo,
Daniels et al.: Female Aerobic Responses
733
vo,max.
and long distance races are mainly attributable t o differences in This being the case, and in the absence of other yet-to-be-detected sex differences that might be important particularly in marathon running, females of the caliber presently competing in middle distance races should be capable of marathon times in the range of 2 hours 20 minutes t o 2 hours 30 minutes. References L. J. & C. E. BRUBAKR. 1973. Biomechanical and neuromuscular as1. STANLEY, 2. 3. 4. 5. 6. 7. 8.
9. 10.
11. 12. 13. 14. 15. 16. 17. 18.
19.
pects of running. 111 Exercise and Sport Sciences Reviews. J. H. Wilmore, Ed. Vol. 1: 189-216. Academic Press. New York, N.Y. DILLMAN, C. J. 1975. Kinetic analyses of running. In Exercise and Sport Sciences Reviews. J. H. Wilmore & J. F. Koegh, Eds. Vol. 3. Academic Press. New York, N.Y. OYSTER,N. & E. P. WOOTEN.1971. The influence of selected anthropometric measures on the ability of college women to perform the 35-yard dash. Med. Sci. Sports. 3: 130-134. MALINA, R. M., A. B. HARPER, H. H. AVENT& D. E. CAMPBELL. 1971. Physique of female track and field athletes. Med. Sci. Sports 3: 32-38. SILLS,F. D. 1960. Anthropometry in relation to physical performance. I n Science and Medicine of Exercise and Sports. W. R. Johnson, Ed. Harper. New York, N.Y. TANNER, J. M. 1964. The Physique of the Olympic Athlete. Allen and Ulwin. London, England. S. 1974. Physiological characteristics of female athletes. Res. Quart. PLOWMAN, 45: 349-362. WILMORE, J. H. & C. H. BROWN.1974. Physiological profiles of women distance runners. Med. Sci. Sports 6: 178-181. ASTRAND, P.-O., T. E. CUDDY,B. SALTIN & J. STENBERG.1964. Cardiac output during submaximal and maximal work. J. Appl. Physiol. 19: 268-274. COSTILL,D. L., H. THOMASON & E. ROBERTS.1973. Fractional utilization of the aerobic capacity during distance running. Med. Sci. Sports 5: 248-252. DANIELS, J. & N. OLDRIDGE.1971. Changes in oxygen consumption of young boys during growth and running training. Med. Sci. Sports 3: 161-165. DANIELS, J. 1974. Physiological characteristics of champion male athletes. Res. Quart. 45: 342-348. ASTRAND, P.-0. 1952. Experimental Studies of Physical Working Capacity in Relation to Sex and Age. Ejnar Munksgaard. Copenhagen, Denmark. HERMANSEN, L. & K. L. ANDERSON.1965. Aerobic work capacity in young Norwegian men and women. J. Appl. Physiol. 20: 425-431. SALTIN,B. & P.-0. ASTRAND.1967. Maximum oxygen uptake in athletes. J. Appl. Physiol. 23: 353-358. COSTILL, D. L. 1970. Metabolic responses during distance running. 3. Appl. Physiol. 28: 251-255. NACLE,F., D. ROBINHOLD, E. HOWLEY,J. DANIELS, G. BAPTISTA & K. STOEDEFALKE. 1970. Lactic acid accumulation during running at submaximal aerobic demands. Med. Sci. Sports 2: 182-1 86. DANIELS, J. 1971. Portable respiratory gas collection equipment. J. Appl. Physiol. 31: 164-167. RAPP,K. E. 1963. Running velocity: body-rise and stride-length. Unpublished Master's Thesis. State University of Iowa. Ames, Iowa.
Gary Krahenbuhl Arizona State University Tempe, Arizona 85281
Carl Foster Ball State University Muncie, Indiana 47303
Jimmy Gilbert National Aeronautics and Space Administration Houston, Texas 77001
Sylvia Daniels Lunier High School Austin, Texas 78758
Introduction
That males outperform females in distance running has been readily observed for as long as performances have been recorded. Standards are about 10% slower for women in 1500- and 3000-meter races and nearly 25% slower over the marathon distance. It has been suggested that the female possesses an architecture less efficient for running. Pelvis width, obliquity of the femur, and length of the female leg and stride have all received attention as possible mechanical deficiencies.** These structural characteristics, however, may not accurately describe the accomplished female distance runner, who has been shown to possess a more masculine build with respect to hip width and leg lex~gth.~-~ Females in a wide variety of sports are generally reported as having more body fat than do male^,^ a factor that could harm performance in medium endurance events where the body weight is supported. Still, Wilrnore and Brown* have found values as low as 6% among female distance runners. Another possibility is that females possess lower hemoglobin concentrations than do males,g resulting in a lower oxygen-carrying capacity of the blood. In recent years the importance of the aerobic demands of running at submaximal speeds has received increased attention.l0, '' It appears that considerable individual differences may exist,'* but whether the factor of running
* Supported in part by
The Canadian Track and Field Association.
726
Daniels et al.: Female Aerobic Responses
727
“efficiency,” or economy, can be used to differentiate among nearly equal competitors is not at all clear. Previous studies 13. 1 have explored male/ female differences during either treadmill walking or work on a bicycle ergometer. On these tasks the absolute oxygen demands of work at submaximal loads are lower in females than in males, but this is basically a function of the lower average body weight of females. Also, since women possess a lower maximum aerobic power ( Vo,),,, ,O* they are usually working at a higher percentage of their Vo,mnY during exercise involving a standard workload,, and since blood lactate accumulation is determined largely by the percent V,,,mnx used during this disparity may contribute to sex differences in running performance. Studies directly measuring sex differences in the aerobic demands of submaximal running have often been complicated by the difficulty of locating female subjects capable of submaximal runs at speeds that are more routine for male runners. If the aerobic demands of running can be shown not to differ between trained male and female runners, then the existing erformance differences may be essentially just a function of differences in The purpose of this study was to compare the aerobic demands of submaximal running in highly trained and talented male and female runners. Additionally, an attempt was made to exp1a.h differences that might be found to exist between men and women regarding Vo, during submaximal running when the subjects either are not tested over, or are not capable of submaximal work over, a common range of speeds.
8,,,,,.
Methods and Procedures The initial phase of this investigation involved 20 highly-trained runners (10 men and 10 women) who were tested during submaximal and maximal runs on a treadmill. The “submax” test session consisted of four 6-8-minute treadmill runs at approximately 202, 215, 241, and 268 mlmin. Belt revolutions were counted to determine the exact.pace and expired air was collected for the last 90 seconds of each run. The Vo, calculated for each corresponding run was taken as representative of the aerobic demands of running at that speed. The “max” test required the subjects to run on a treadmill with speed and/or grade increments added each minute. Speed was increased up to 10 mph, then 2% grade increments were added each minute until voluntary exhaustion. In each case, exhaustion was reached after 6 to 8 minutes of work. Consecutive 30- to 60-second expired gas samples were collected in meteorological balloons through a low resistance breathing valve and collection valve systern,l8 starting at the end of the third minute of exercise. Gas samples were analyzed for C 0 2 y d O2 content with a Lloyd Gallenkamp volumetric analyzer. The highest Vo,reached during each run was considered Vo, mnx. To further examine the comparison of the aerobic demands of running. between males and females and among a common group of runners when Vo,/ speed regression equations are derived from different speed ranges, an additional series of submaximal runs were completed by five male and five female runners. In this second series of tests the same procedures and methods as described above were employed except the speeds used ranged from 150 to 250 m/min. Five speeds, distributed approximately equally apart, were used and separate
Annals New York Academy of Sciences
728
regression equations were calculated using the three slowest speeds, the middle three speeds, and the three fastest speeds. In both phases of the investigation, the males and females were considered to be of comparable ability based on the average departure from current world records displayed by the two groups. Results and Discussion
TABLE 1 presents the descriptive data for the 20 subjects used in phase 1 of the study. The men were clearly larger and had greater values for VO,max (both in absolute terms and when expressed in ml/kg.min), Qx, and 0, pulse at VO,,,,. Maximum heart rates were higher among the women, but the difference was not significant ( p > 0.05). These results are all as would be expected and are generally a function of the size difference between mcn and women. In regard to running performance, it appears that the greater VO,max displayed by the male runners would give them a clear advantage in endurance events, a not surprising fiqding in light of the performance differences that do exist (19% difference in VO,mnxin this study as opposed to the typical 10%25% difference generally voted in distance running performances between the sexes) and that a greater V,,,,, by trained males is widely accepted. The p ~ values ,from the ~ phase~1 tests ~are presented ~ in~ TABLE ~2. Although the women were characterized by slightly greater 3 , ,,ubmax values at the speeds used, none of the differences was significant. The women also showed somewhat greater variability in po, at all speeds (the lowest and highest values were also recorded by females at all test speeds) ; the men were characterized by a tendency to become less variable as speed increased. These findings strongly suggest that there are no sex differences in the aerobic demands of running when the range of speeds used is common to both groups of runners and when all subjects are similar in ability. Interestingly,
TABLE1 DESCRIPTIVE DATA:TRAINED DISTANCE RUNNERS Variable Height (cm) Weight (kg)
64te skin fold (mm) t jml/kg min) Vs at , V O ~ ~ . ~
-
R at Voprn..
Heart rate maximum Odpulse (ml/beat) Vent/Or
Males (n=10) Mean SD * 179.3 65.7 39.6 73.7 166.1 1.11 180.3 26.9 34.3
* SD, standard deviation.
6.1 5.6 6.8 5.1 17.5 0.07 7.2 2.7 3.4
Females (n=10) Mean SD 166.2 % 52.1 % 48.1 % 59.6 % 107.8 % 1.08 190.8 16.3 % 34.7
t Tricep, subscapular, suprailiac, umbilical, pectoral, mid-thigh (anterior). % Significantly different from males (p
< 0.01).
4.7 3.7 4.4 4.4 12.0 0.03 10.7 1.7 3.0 -
Daniels et al.: Female Aerobic Responses
729
TABLE2 COMPARISON OF MALE AND FEMALE DISTANCE RUNNERSON THE AEROBIC OF RUNNINGAT FOURSELECTED S U E M A X M f i SPEEDS
Speed (m/min) 202
to,*(ml/kg.min) Males (n=10)
Females (n= 10)
36.2
38.0 (31-42) 40.7 (34-45) 46.0 (40-50) 51.5 (4655)
( 32-39 )
215 24 1 268
DEMANDS
39.0 (35-42) 44.6 (41-47) 50.5 (47-53)
* Go2 values were calculated for common speeds from individual regression equations. Ranges are shown in parentheses below mean values. the subject with the lowest polmax ( a female) who would presumably be working at the greatest percent of her p,,, at all submax speeds, recorded the lowest ~o,,,,ma, at every running speed. It appears that her ability to perform equally against other women with higher is a function of her greater “efficiency” as demonstrated in the sybmax tests. FIGURE 1 presents a plot of the Vo, data collected at all submax speeds used in the first series of tests. @so shown are the combined linear and quadratic regression curves and the Volmar mean values for the men and women. Although the linear regression equation proved very satisfactory in describing the relationship between running speed and to,, the second-order curve fit the data significantly better. Higher order polynomials were unsuccessful in reducing the deviation about the regression. If the curvilinear relationship displayed is a function of higher speeds demanding increasingly gre.ater energy, as the work represents a higher and higher fractional utilization of Vo, max, then the women would show a greater Vo, than the men at any given speed (which was only a nonsignificant tendency in the present study), based on the lower VOlmaxof the women. It would seem an appropriate follow-up to the present work to compare males and females who have equal VOlmaxvalues and who are equally well trained. This would eliminate the possibility that differences in fractional utilization may be a contributing factor. The results of phase 2 of the investigation are summarized in FIGURE2. Since there were again no differences between the male and female runners in Vo, at any of the five submax speeds, the data were combined and used to construct three separate regression curves based on the three slowest speeds, the middle three speeds, and the three fastest speeds. If Vo, values were calculated through extrapolation of one regression equation to determine the Vo2related to a speed outside the confines of the data from which that particular curve was constructed (for example, 300 m/min running speed) then differences in the aerobic demands of running became evident. This was true whether men and women were compared or if either separate group or a combination of
65
70
0
200
220
2bo
280
Speed (ddd
260
Linear and quadratic regression curves calculated from individual values for 10 females and 10 males.
35
40
45
50
55
are mean Vo,,.,
FIGURE.^.
.g”
Y
3 3
‘ 6 0
2
7
75
320
340
PO,and speed values for
)(M
20 runners. Also shown
360
v)
8
xg-
4
w 0
P)
u
U
$ L .. i
4
8
OOE
*
I
082
8
8
09Z I
I
OtZ
. I
OIL I
(rrp/=) P d S
I
ooz 1
I
081 I
091 0
09
09
OE
0
8 N
Annals New York Academy of Sciences
732
both was used in the comparisons. Also, this phenomenon was most evident when use of the slowest speeds was made. This could quite often lead to the mistaken conclusion that the aerobic demands of running differ between men and women since it is not unexpected that a slower range of speeds would be employed in testing women than those used with trained male runners. It is interesting to note that two of the female vnners in this study are sub-3-hour marathoners and both displayed very low VOxsubmnX values over the range of speeds at which they train most often, a finding that is in agreement with earlier research reported by Costill, Thomason, and Roberts.1° Compared with other runners who competed more successfully at shorter distance faces, however, the present marathon subjects did show a more rapid rise in Vo, as speeds increased. That the regression curve constructed from the slowest speeds appears to be much flatter than those calculated from higher speeds is likely a function of the difficulty the subjects had in running comfortably at the very slow speeds. There appeared to be a tendency to displace the body more vertically at the slower speeds, a finding that has been reported by Dillman? and Rapp,'@ and which may lead to a correspondingly greater expenditure of energy at the slower speeds. Once a more comfortable speed is reached (generally expressed by the subjects as being about 200 m/min and above) the changing workload appears to be more linearly related to changes in the aerobic demands of the work. Although the slope of the regression curve describing all the present data appears steeper than that calculated from data describing young girls reported by Astrand,13 the regression equation calculated from his data (y = 10.547 0.157~)is remarkably similar to what was calculated from the three slowest speeds in the present study (y =7.86 + 0.147x, FIGURE2). The range of speeds was similar in the two instances.
+
Conclusions (1) There appear to be no differences in the aerobic demands of running at submaximal speeds between males and females who are of relatively equal ability and fitness. That the effects of fractional utilization during submaximal running may produce measurable differences in VO,aubmnx at given speeds of running is not clear and should be-investigated using trained males and females of both equal and widely different Vo, values. (2) It tppears that the comparison of regression curves relating running speed and V,, for different speed ranges is clearly a hazardous practice. This is true whether subjects are of the same or opposite sex. The data presented in FIGURE 2 indicate that the use of speeds below 200 m/min produces a particularly flat regression curve and calculation of the energy demands of running at higher speeds based on data collected at very slow speeds would greatly underestimate the energy requirements of the faster running. A quadratic regression equation should be used when sufficient data are available. The following regression equatioF best fit the present data: y = 14.77 0 . 0 5 9 ~ 0.000279~2,where y = Vo, (ml/kg*min) and x = speed (m/min), and y = 83.74 2.798~ 0.014288~2,where y = speed (m/min) and x = (ml/ kg-min) (3) The differences in male and female running performances at middle
+
+
.
+
+
vo,
Daniels et al.: Female Aerobic Responses
733
vo,max.
and long distance races are mainly attributable t o differences in This being the case, and in the absence of other yet-to-be-detected sex differences that might be important particularly in marathon running, females of the caliber presently competing in middle distance races should be capable of marathon times in the range of 2 hours 20 minutes t o 2 hours 30 minutes. References L. J. & C. E. BRUBAKR. 1973. Biomechanical and neuromuscular as1. STANLEY, 2. 3. 4. 5. 6. 7. 8.
9. 10.
11. 12. 13. 14. 15. 16. 17. 18.
19.
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