J

. Puman Ergol., 8: 83-90,1979

EFFECT OF PROLONGED RUNNING ON PHYSIOLOG-ICAL RESPONSES TO SUBSEQUENT EXERCISE

Michael N. SAWKA, Ronald G. KNOWLTON,* Roger M. GLASER,

Stephen W. WILDS and Daniel S. MILES

Department of Physiology, School of Medicine, Wright State University, Dayton, Ohio 45435 U.S.A.

*Physical Education Research Laboratory , Southern Illinois University, Carbondale, Illinois 62901 U.S.A.

The purpose of this study was to compare metabolic and cardiopulmonary responses for submaximal and maximal exercise performed several days

preceding (pre-test) and 45 min after (post-test) 21 miles of high intensity (70% VO2 max) treadmill running. Seven aerobically trained subjects' oxygen uptake, oxygen pulse, respiratory exchange ratio, heart rate,

pulmonary ventilation, ventilatory equivalent of oxygen, and blood lactate concentration were determined for exercise during the pre-and

post-test sessions. No differences were found for submaximal oxygen uptake, oxygen pulse, pulmonary ventilation and ventilatory equivalent of oxygen between the pre-and post-test values. Generally, submaximal heart rate responses were higher, and respiratory exchange ratio values were lower during the post-test. Reductions of maximal work time

(12%), maximal oxygen uptake (6%) and maximal blood lactate concen-tration (47%) Were found during the post-test. Thermal stress and

glycogen depletion are possible mechanisms which may be responsible for these observed differences.

During prolonged high intensity exercise, individuals may experience moderate dehydration (GISOLFI and COPPING, 1974) and lowered muscle glycogen stores

(COSTILL et al., 1973). These two alterations are believed to be partially responsible for the well documented increased body temperature, increased heart rate, de-creased stroke volume, increased pulmonary ventilation and lowered respiratory exchange ratio values that occur during the course of prolonged exercise (DEMPSEY et 41.,1977; SAWKA et al., 1979a; SMITH et al.,1976). These two alterations could also influence physiological responses and performance during subsequent exercise. Little is known, however, of changes in metabolic responses and cardiopulmonary responses during submaximal and maximal exercise performed shortly following

Received for publication, September 12, 1979.

83

84 M. N. SAWKA et a!.

participation in prolonged high intensity exercise. Previous investigations have only examined one submaximal exercise level (AsMUSSEN et at., 1974; SALTIN and STENBERG, 1964), or studied a limited number of physiological variables (KARLSSON et at., 1975; MoSTARDI et at., 1974). Likewise, limited data have been reported for metabolic responses and physical work capacity to subsequent maximal effort exercise (ASTRAND 1963; COSTILL et at., 197la; KARLSSON et al., 1975).

The purpose of this investigation was to compare metabolic and cardiopul-monary responses for submaximal and maximal exercise performed several days

preceding and 45 min after 21 miles of high intensity (70% Vo2 max) treadmill running.

METHODS

The subjects for this investigation were seven males who were running a

minimum of 50 miles per week and had all completed marathon races in less

than three hours during the preceding 12 months. The subjects had a mean

(•}SD) age of 28+4.0 yrs, stature of 175•}5.8 cm, weight of 68•}7.9 kg and

maximal oxygen uptake of 66+5.3 ml/kg.min. Previous to all testing, the purpose

and risks involved in this study were explained to each subject. Each expressed

understanding by signing a statement of informed consent. The protocol and

procedures used for this study have been approved by the Human Subjects Com-

mittee at Southern Illinois University.

All exercise tests were conducted in an air conditioned laboratory with a room

temperature that ranged from 22•‹ to 25•Ž and a relative humidity between 45

and 60%. Several days prior to, and 45 min following 21 miles of high intensity

treadmill running, subjects were tested for selected physiological responses to

submaximal and maximal treadmill running. It was anticipated that a 45 min

rest period would allow sufficient time for the return of blood lactate concentration

to resting levels and the repayment of the oxygen debt. The pre-and post-test

protocol consisted of the subjects running continuously on a motor driven tread-

mill at a constant velocity of 8 mph. The initial work grade was 0%, and grade

was increased by 3 % every 2.5 min. All tests were terminated by exhaustion.

Oxygen uptake (Vo2), respiratory exchange ratio (R), pulmonary ventilation (VE)

and heart rate (HR) were monitored at each work grade, and maximal blood lactate

(LA) concentration was determined at the completion of the test. To obtain

reliable pre-test data, and control for habituation, this test protocol was repeated

on three separate dates. Since there were no significant differences in responses

between the second and third pre-test runs, data from the third session were

considered valid and used. The prolonged run consisted of the subjects exercising

on the treadmill for 160 min at 8 mph. Work grade was set so that each subject

was running at 70% of their Vo2 max.

All respiratory and metabolic determinations were obtained by open circuit

SUBSEQUENT EXERCISE 85

spirometry. Ventilation was measured with a Parkinson-Cowan (CD-4) dry gas meter, calibrated against a 350/ Tissot gasometer, and recorded on a Beckman Dynograph. The respiratory gases were continually analyzed for concentrations of carbon dioxide and oxygen from a Plexiglas mixing chamber. Mean gas con-centrations during the last 30 seconds of each collection period were used for the metabolic calculations. Carbon dioxide concentration was determined by an infrared CO2 analyzer (Godert Capnograph) and oxygen concentration by a

polarographic 02 analyzer (Beckman OM-11). The electronic analyzers were calibrated immediately before all gas collection periods with room air and reference

gases which were analyzed by the Scholander technique (SCHOLANDER,1947). Five min following maximal exercise, samples of arterialized capillary blood

were collected from free flowing digit punctures. It is at this time that blood LA concentration peaks during passive recovery (DIAMANT et al., 1960. Blood LA was determined by an enzymatic technique previously described (SAWKA et al., 1979b), and automatic pipets were used for all micropipeting. The spectrophoto-meter (Spectronic 20) absorbance value from each sample was plotted on a standard LA curve to obtain the appropriate concentrations. Heart rate was determined from the electrocardiogram (R-R interval) using a bipolar chest electrode place-ment.

The student's dependent t test was used to compare the data obtained during the pre-test several days preceding, and the post-test 45 min after 21 miles of treadmill running. Each null hypothesis was tested at the P<0.05 level for statistical significance.

RESULTS

During the prolonged running mean body weight significantly decreased from 69.2 kg to 66.4 kg. This approximated a 4% weight loss. Table 1 presents the submaximal metabolic responses to the pre- and post-prolonged run tests. During both tests V02 and respiratory exchange ratio (R) increased linearly with work grade. No differences between the pre-and post-tests for Vo2 responses were found at any of the submaximal work grades. R values were significantly lower at 0%, 3% and 9% grades during the post-than pre-test. Oxygen pulse responses remained fairly constant at each work grade, with no differences found between the two tests.

Table 2 presents the submaximal cardiopulmonary responses to the pre-and

post-prolonged run tests. During both tests HR and VE increased linearly with work grade. Although significance was not demonstrated for VE, the HR re-sponses were significantly higher at the 3 % and 6 % grades during the post-than

pre-test. Ventilatory equivalent of oxygen (VE/Vo2) increased gradually with work grade, and no differences were found between the two tests for this variable.

Table 3 presents the data obtained for maximal work time, V02 max and maxi-

86 M. N. SAWKA et al.

Table 1. Submaximal metabolic responses to a multistage treadmill test administered several days before (pre) and 45 min

after (post) 21 miles of high intensity running.

NS, not significant.

Table 2. Submaximal cardiopulmonary responses to a multistage treadmill test administered several days preceding (Pre) and 45 min after

(Post) 21 miles of high intensity running.

NS, not significant.

mal blood lactate concentrations during the pre-and post-prolonged run tests. Significant reductions of work time (12%), Yo2 max (6 %) and blood lactate (47%) were found during the post-than pre-test.

DISCUSSION

Previous studies examining the effects of high intensity exercise on subsequent

SUBSEQUENT EXERCISE 87

Table 3. Data obtained on a maximal treadmill test administered several days before (Pre) and 45 min after (Post) 21 miles

of high intensity running.

exercise performance generally have not focused on submaximal physiological responses. It has been speculated that as runners fatigue they may alter their

gait and become less efficient (R®WELL, 1971). This change in gait would most likely elevate submaximal Vo2 responses. The present study's runners had similar submaximal Vo2 responses during the pre-and post-tests. This finding for subse-

quent exercise is supported by data indicating that subjects maintain relatively constant submaximal V02 responses during prolonged high intensity exercise

(CasTILL et al., 1971b; SAWKA et al., 1979a). KOYAL et al. (1976), have reported that when energetics are predominately

aerobic, VE is linear with V02, and VE/ V®2 values approximate 25. They suggest

that marked increases in VE/Vo2 may be indicative of respiratory compensation in response to a metabolic acidosis. GLASER et al. (1979), have reported a high

correlation (r=0.86) between blood lactate concentration and VE/Vo2 values during exercise at intensities above anaerobic threshold. For both tests, evidence of elevated anaerobic glycolysis with increased work grade was provided by the

increasing VE/Vo2 values. The present study's similar VE/Vo2 data during sub-maximal running for the pre-and post-tests suggests that our subjects may have had comparable blood lactate concentrations.

Buffering of lactic acid by the bicarbonate system increases venous PCO2, and results in increased respiratory compensation and elevated R values (IssEKUTz et al., 1962). The lower R values during submaximal running for the post-test, however, probably do not indicate a decreased respiratory compensation. The lower R values during the post-test were probably indicative of a shift in metabolic substrate from predominately carbohydrate to lipid. COSTILL et al. (1971b) found decreased submaximal exercise R values to be associated with depleted muscle

glycogen stores. HR responses to submaximal running were found to be generally higher during

the post-than pre-test. MOSTARDI et al. (1974), have observed increased submaxi-mal HR responses in 10 subjects when bench stepping after a 60 to 70 min treadmill walk. They speculated that the elevated HR responses may have resulted from an elevated body temperature and subsequently increased cardiac output and cutaneous circulation. SAWKA et al. (1977) found that a masters age runner's

88 M. N. SAWKA et al.

submaximal HR, stroke volume and cardiac output responses did not differ from

pre-marathon values when tested 24 hours after a marathon race. Their subject,

however, probably did not have an increased thermal load after the 24-hour rest.

Although rectal temperature (Tr) was not measured during the pre- and

post-maximal tests, the present study's subjects did have very high Tr's (X=40.3•}

0.05•Ž) after prolonged running. This probably resulted in greater thermal stress

during the post-than pre-test. The data of ROWELL et al. (1969) have demonstrated

an increased cardiac output and HR above control values at moderate intensity

exercise during increased thermal stress. However, at a greater exercise intensity

during thermal stress, an increased HR with a decreased stroke volume and cardiac

output were found in comparison to control values (ROWELL et al., 1966). For

the present study, it is uncertain what combination of circulatory adjustments

accounted for the increased submaximal heart rate during the post-test.

Other investigators have reported a decreased maximal exercise blood lactate

concentration (ranging from 31 % to 76 %) after prolonged exercise (AsTRAND

et ale, 1963; AsMussEN et al., 1974; COSTILL et al., 1971a; SAWKA et al., 1977).

A decreased LA concentration after maximal exercise has been associated with

a lowering of muscle glycogen stores (COSTILL et al., 1.973), but the actual mecha-

nism(s) are not substantiated. COSTILL et al. (197lb) have observed a continued

reduction of muscle glycogen stores in five-trained runners after each of three

16.1 km runs (at 80 % Vo2 max) spaced by a 24-hour rest. The same trend of

decreased glycogen stores may have occurred in the present subjects, who only

had 90-rein of rest, and accounted for the decreased maximal LA concentration.

The validity of both maximal work time and VV02 max are to a large extent

dependent on the subject's motivation and cooperation. The subjects for this study

were paid volunteers and highly motivated to perform well on the maximal tests.

It was anticipated that because of the subjects' running experience and motivation,

the shorter maximal work times implied decreased physiological ability to perform

strenuous exercise. The present study found Vat max to be reduced by 6 % after

prolonged high intensity exercise. Similarly, A5TRAND et al. (1963) found an 11

reduction of Vat max for 5 members of the Swedish National Cross Country Ski

team when tested two hours after an 85 km race, and COSTILL et al. (1971a) found

an 8 % reduction of Vat max for 5 runners when tested 45 min after a 16.1 km race.

These lowered V®2 max values following exertion indicate that prolonged exercise

may reduce an individual's ability to deliver and/or utilize oxygen.

The results of this study suggest that prolonged high intensity exercise does

not influence trained runners' VE, Vo2, VE/Vo2 and 02 pulse responses to subse-

quent submaximal exercise. During subsequent submaximal exercise, elevated

HR responses are probably elicited by increased thermal stress, and lowered R

values are probably indicative of a shift in metabolic substrate from predominately

carbohydrate to lipid. For maximal effort exercise, aerobic power and anaerobic

capacity are reduced by prolonged running. This reduced metabolic potential

SUBSEQUENT EXERCISE 89

results in a decreased work time during subsequent exercise.

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