Factors which alter the relationship between ventilation and carbon dioxide production during exercise in normal subjects

The slope of the linear relationship between ventilation and carbon dioxide production has been thought to indicate that is one of the major stimuli to . A group of 15 normal subjects undertook different incremental treadmill exercise protocols to explore the relationship between and . An incremental protocol using 1 instead of 3-min stages of exercise resulted in an increase in the to ratio [26.84 (SEM 1.23) vs 31.08 (SEM 1.36) (P < 0.008) for the first stage, 25.24 (SEM 0.86) vs 27.83 (SEM 0.91) (P < 0.005) for the second stage and 23.90 (SEM 0.86) vs 26.34 (SEM 0.81) (P = 0.001) for the third stage]. Voluntary hyperventilation to double the control level of during exercise resulted in an increase in the to slope [from 21.3 (SEM 0.71) for the control run to 35.1 (SEM 1.2) for the hyperventilation run (P < 0.001)]. Prolonged hyperventilation (5 min) during exercise at stage 2 of the Bruce protocol resulted in a continuted elevation of and the slope. A steady state of and metabolic gas exchange can only be said to have been present after at least 3 min of exercise. Voluntary hyperventilation increased the slope of the relationship between and . End-tidal carbon dioxide fell, but remained within the normal range. These results would suggest that a non-carbon dioxide factor may have been responsible for the increase we found in during exercise, and that factors other than increased dead space ventilation can cause an increased ventilation to slope, such as that seen in some pathophysiological conditions, such as chronic heart failure.     

Aerobic power and pubertal peak height velocity in Belgian boys

Summary To determine the cardiorespiratory response to maximal exercise before, during and after the pubescent growth spurt, thirty boys were tested at yearly intervals over a period of six consecutive years. For each individual, peak height velocity (PHV) was determined. The age at PHV (¯X= 13.6 years) was taken as a standard of maturation. The results from all subjects at 1.5 and 0.5 years before and 0.5 and 1.5 years after PHV are presented. The highest oxygen uptake ( ) obtained during an incremental bicycle ergometer test to voluntary exhaustion was taken as peak oxygen uptake ( peak). Across each of the four years studied, mean peak (min=49.6; max=52.5 ml·kg^–1·min^–1) and mean heart rate (HR) at peak (min=190; max=192) did not change significantly as a function of PHV. On the other hand, the respiratory quotient at peak increased considerably from mean minima and maxima of 0.99 and 1.01 before PHV to 1.07 and 1.10 after PHV. Ventilatory equivalent for ( ), taken as an indicator of ventilatory economy, seemed to be unaffected by the maturation process. The steepest increase in circumpubertal oxygen pulse was found one year after PHV. Average stability coefficients (¯r), calculated from the inter-years correlations were high for height (¯r=0.95), weight (¯r=0.92), HR at peak (¯r=0.74), peak in 1/min (¯r=0.71), oxygen pulse (¯r=0.68) and tidal volume (¯r=0.64).     

Use of oxygen uptake recovery curve to predict peak oxygen uptake in upper body exercise

A group of 18 well-trained white-water kayakers performed maximal upper body exercise in the laboratory and during.a field test. Laboratory direct peak oxygen uptake ( ) values were compared, firstly by a backward extrapolation estimation and secondly by an estimation calculated from measured during the first 20 s of exercise recovery. Direct peak correlated with backward extrapolation (r=0.89), but the results of this study showed that the backward extrapolation method tended to overestimate significantly peak by [0.57 (SD 0.31) 1·min^–1 in the laboratory, and 0.66 (SD 0.33) 1·min^–1 in the field,P<0.001]. The measured during the first 20 s of recovery, whether the exercise was performed in the laboratory or in the field, correlated well with the laboratory direct peak (r=0.92 andr=0.91, respectively). The use of the regression equation obtained from field data _2f20s, that is peak ₂=0.23+1.08 _2f20s, gave an estimated peak ₂, the mean difference of which compared with direct peak was 0.22 (SD 0.13) 1·min^–1. In conclusion, we propose the use of a regression equation to estimate peak from a single sample of the gas expired during the first 20 s of recovery after maximal exercise involving the upper part of the body.     

Maximum oxygen uptake in healthy nonathletic males

Summary Maximum oxygen uptake ( max), maximum heart rate (MHR), blood lactic acid (LA) and pH were measured during bicycle ergometer exercise in 52 men, 22 to 60 years old, engaged in clerical and light manual work (prison personnel and prisoners in the Netherlands). max decreases with, age, but less than expected from previous studies in which the data on young subjects were probably biased in favor of well-trained individuals. The data provide provisional standard values for max in healthy untrained males, derived from a population in which physical activity was similar irrespective of age. MHR and LA decrease significantly with age after elimination of as a variable. In 20 subjects, max was measured with the steady-state method and with a single increasing load test; the differences were small for practical purposes. The increasing load method is useful to estimate aerobic capacity in a single test, even in subjects unaccustomed to exercise tests.This study was supported, in part, by a grant from the Medical Research Committee of the American Thoracic Society, the Medical Division of the National Tuberculosis Association.     

A model for studying the distortion of muscle oxygen uptake patterns by circulation parameters

Summary The transmission of muscle oxygen uptake patterns to the pulmonary site is a basically nonlinear process during unsteady state exercise. We were mainly interested in three questions concerning the dynamic relationship between power input and pulmonary output: 1. To what extent can linear system analysis be applied? 2. What is the relative influence of muscle on pulmonary as compared to other parameters such as muscle perfusion kinetics? 3. To what extent does pulmonary reflect muscle ? Investigations were performed by means of a mathematical model including a muscle compartment and two serial, flow-varying time delays. The non-exercising parts of the body were. incorporated as one term for perfusion and one for . Parameters were adjusted so as to represent a reference state of aerobic exercise while monofrequent sinusoidal changes in aerobic metabolism were used as forcing signals. The following answers were derived from the simulations: 1. Non-linear distortions of the signals are negligible provided that analyses are not driven too far into the higher frequency range (periods shorter than about 1 min). 2. Variations of muscle kinetics have greater effects on pulmonary than changes of perfusion kinetics or venous volume. This finding applies irrespective of whether or not pulmonary closely reflects muscle 3. Small differences in the time constants for muscle perfusion and muscle are a major prerequisite if pulmonary , kinetics are to be taken as correct estimates of muscle kinetics. High basal muscle perfusion, small perfusion changes and small venous volumes between muscle and lungs are further factors reducing dynamic distortions of the muscle signal.     

Times to exhaustion at 100% of velocity at\dot V{\text{O}}_{\text{2}} max and modelling of the time-limit / velocity relationship in elite long-distance runners

The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits _{max max} in 38 elite male long - distance runners _max = 71.4 ± 5.5 ml.kg^–1.min^–1 and _max = 21.8 ± 1.2 km.h^–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in _max. Tlim value was negatively correlated with _max (r = -0.362, p< 0.05) and _max (r = –0.347, p< 0.05) but positively with LT (%v _max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at _max in a homogeneous group of elite male long-distance runners was inversely related to _max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) .     

Association between heart rate variability and training response in sedentary middle-aged men

The effect of exercise training on heart rate variability (HRV) and improvements in peak oxygen consumption ( _peak) was examined in sedentary middle-aged men. The HRV and absolute and relative _peak of training (n = 19) and control (n = 15) subjects were assessed before and after a 24-session moderate intensity exercise training programme. Results indicated that with exercise training there was a significantly increased absolute and relative _peak (P < 0.005) for the training group (12% and 11% respectively) with no increase for the control group. The training group also displayed a significant reduction in resting heart rate; however, HRV remained unchanged. The trained subjects were further categorized into high (n = 5) and low (n = 5) HRV groups and changes in _peak were compared. Improvements in both absolute and relative _peak were significantly greater (P > 0.005) in the high HRV group (17% and 20% respectively) compared to the low HRV group (6% and 1% respectively). The groups did not differ in mean age, pretraining oxygen consumption, or resting heart rate. These results would seem to suggest that a short aerobic training programme does not alter HRV in middle-aged men. Individual differences in HRV, however, may be associated with _peak response to aerobic training.     

Effects of previous exercise on the ventilatory determination of the aerobic threshold

Summary To study the effects of previous submaximal exercise on the ventilatory determination of the Aerobic Threshold (AeT), 16 men were subjected to three maximal exercise tests (standard test = ST, retest = RT, and test with previous exercise = TPE) on a cycle ergometer. The protocol for the three tests consisted of 3 min pedalling against 25 W, followed by increments of 25 W every minute until volitional fatigue. TPE was preceded by 10 min cycling at a power output corresponding to the AeT as determined in ST, followed by a recovery period pedalling against 25 W until returned to values consistent with the initial response to 25 W. AeT was determined from the gas exchange curves (ventilatory equivalent for O₂, fraction of expired O₂, excess of , ventilation, and respiratory gas exchange ratio) printed every 30 s. The results showed good ST×RT reliability (r=0.89). TPE showed significantly higher AeT values (2.548±0.44 l·min^–1) when compared with ST (2.049±0.33 l·min^–1) and RT (2.083±0.30 l·min^–1). There were no significant differences for the sub-threshold respiratory gas exchange ratios among the trials. The sub-threshold response showed significantly higher values for TPE at power outputs above 50 W. It was concluded that the performance of previous exercise can increase the value for the ventilatory determination of the AeT due to a faster sub-threshold response.Supported by fellowship number 3660/80-3, CAPES, Brazil     

The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man

Summary This study examined the effects of dietary manipulation upon the respiratory exchange ratio ( ) as a predictor of maximum oxygen uptake ( ). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45±5% carbohydrate (CHO)) for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3±2% CHO), and again after three days of a high CHO diet (61±5% CHO). Respiratory gases were continuously monitored during each test using an online system. No significant changes in mean exercise oxygen uptake ( ), or maximum functional heart rate (FHR_max) were found between tests. Mean exercise carbon dioxide output ( ) and R were significantly lower than normal after the low CHO diet (bothp<0.001) and significantly higher than normal after the high CHO diet (bothp<0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p<0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p<0.05) over the final 5 min of exercise, after the high CHO diet. As a result, predictions of based on the R-time relationship were similar to recorded after the normal CHO dietary condition (-1.5±1.9%), but higher after the low CHO diet (+14.8±3.9%,p<0.001) and lower after the high CHO diet (–7.0±4.5%,p<0.01). These results indicate that dietary manipulation can significantly affect respiratory gas exchanges during fixed term maximal incremental exercise, and by doing so can significantly influence predictions of based on R.     

Respiratory frequency and the oxygen cost of exercise

Summary Although many studies indicate that the spontaneous breathing frequency minimizes breathing work, the consequences of this for exercise energetics have never been investigated. To see if the spontaneous exercise breathing frequency minimizes oxygen uptake, we compared during treadmill walking (2/3 max) at several alternative frequencies. The alternative frequencies ranged from the lowest sustainable to a frequency twice the spontaneous value. All eight subjects adjusted tidal volume to comfort. Exercise oxygen uptake was constant, independent of breathing frequency. At the same time, minute ventilation rose to be 65% greater at the highest frequency than at the lowest (P<0.01). We then reproduced the various exercise frequencies, tidal volumes, and ventilations during seated isocapnic hyperpnea to measure with locomotory muscles at rest. Once again, oxygen uptake was constant, independent of breathing frequency. We conclude that the spontaneous exercise breathing frequency fails to minimize during either exercise or resting reproduction of exercise ventilation.Supported in part by NIH Grant HL 26351     

Cardiorespiratory and metabolic adaptations to hyperoxic training

This study examined the effects of hyperoxic training on specific cardiorespiratory and metabolic responses. A group of 19 male subjects trained for 5 weeks on a cycle ergometer at 70% of hyperoxic or normoxic maximal heart rate, the hyperoxic group (HG) breathing 70% O₂, the normoxic group (NG) breathing 21% O₂. The subjects were tested pre- and post-training under both hyperoxia and normoxia. Measurements included cardiac output , stroke volume (SV), heart rate (HR), pulmonary ventilation , oxygen consumption , partial pressure of oxygen (PO₂), partial pressure of inspired carbon dioxide (PCO₂), blood lactate concentration [L], and fiber type composition. The was significantly lower at submaximal work rates (P < 0.05) and maximal increased after training in both groups for both test conditions; hyperoxic was lower than normoxic (P < 0.05). The maximal increased significantly (P < 0.05) in both groups for both tests and was 11%–12% higher during hyperoxia. Post-training maximal heart rate (HR_max) was significantly decreased (P < 0.05) at the same absolute work rate regardless of the training group or test type. The SV was increased at each work rate and was unchanged. The maximal increased significantly (P < 0.05) for both groups and types of test: for normoxia: NG 27.3–30.4 l · min^–1 and HG 30.3–32.31 · min^–1 and for hyperoxia: NG 24.7–25.6 and HG 27.9–31.2 l · min^–1. Although working at the same intensity relative to HR_max, HG showed significantly lower [L] following a single training session, yet maximal values were unchanged after training. Both groups showed a significant increase in the percentage of type IIA fibers post-training but HG retained a larger percentage of HB fibers. Mitochondrial enzymes; citrate kinase, 3-hydroxyacyl CoA dehydrogenase, and cytochrome c-oxidase were increased in the normoxic trained subjects (P < 0.05). In summary, training induced adaptive responses in maximal aerobic power, HR, SV, , [L], and muscle fiber type composition, independent of inspired PO₂. Intramuscular data suggested there may be some differences between hyperoxic and normoxic training and these were substantiated by mitochondrial enzyme and lactate findings. Our data would suggest that transport mechanisms may limit the ability to increase aerobic power.     

Ventilation studied with circulatory occlusion during two intensities of exercise

Summary Our purpose was to study the possible role of a pulmonary chemoreceptor in the control of ventilation during exercise. Respiratory gas exchange was measured breath-by-breath at two intensities of exercise with circulatory occlusion of the legs. Eight male subjects exercised on a cycle ergometer at 49 and 98 W for 12 min; circulation to the legs was occluded by thigh cuffs (26.7 kPa) for two min after six min of unoccluded exercise. PETCO₂ and decreased and PETO₂ increased significantly during occlusion at both workloads. Occlusion elicited marked hyperventilation, as evidenced by sharp increases in , and . A sudden sharp increase in PETCO₂ was seen 12.3±0.5 and 6.5±1.2 s after cuff release in all subjects during exercise at 49 and 98 W, respectively. At 49 W a post-occlusion inflection in was seen in 7 subjects 21.1±5.8 s after the PETCO₂ inflection. Three subjects showed an inflection in at 98 W 23.3±7.5 s after the PETCO₂ inflection. There were significant increases in PETCO₂, and after cuff release. mirrored better than , post occlusion. On the basis of a significant lag time between inflections in PETCO₂ and following cuff release, it is concluded that the influences of a pulmonary CO₂ receptor were not seen.     

Central hypoxic-hypercapnic interaction in mild hypoxia in man

Hypoxic-hypercapnic interaction in mild hypoxia was studied in 12 healthy males. Steady state ventilatory responses to hypercapnic-hypoxia were obtained as the difference in ventilation between hypoxia (mean values ± S.D. of =7.36±0.20 kPa or of 7.10 ±0.41 kPa) and hyperoxia ( >26.7 kPa) with the same degree of hypercapnia ( 6.12±0.22 kPa). On the other band, withdrawal responses were obtained as the magnitude of depression in ventilation caused by two bicaths of O₂ from the above mentioned hypoxic hypercapnia. Averaged and were 9.57±5.45 and 6.45 ±4.90l/min, respectively, the difference being statistically significant (P<0.01). Furthermore, if we assume the presence of ventilatory depression to be due to tissue fall resulting from an increase in cerebral blood flow caused by hypoxia, the magnitude of central hypoxic-hypercapnic interaction was estimated to be as great as the value of .     

Validity of a new portable indirect calorimeter: the AeroSport TEEM 100

The purpose of this study was to compare oxygen uptake ( ) values collected with a new portable indirect calorimeter (AeroSport TEEM 100 Metabolic Analysis System) against a more traditional large calorimeter system that has been reported to be valid and reliable (SensorMedics 2900 Metabolic Measurement Cart). Minute ventilations ranging from rest up to heavy exercise were compared with simultaneous measurements from a 120-1 Tissot gasometer. Each of the three TEEM 100 pneumotachs were tested. Three hundred and sixty-one separate ventilation tests were performed using the low-flow, medium-flow, and high-flow heads of the portable calorimeter. For each of the pneumotachs, the correlation between the portable calorimeter values and the gasometer values exceededr = 0.94. The standard error of estimate for the low-, medium- and high-flow pneumotach were 5.96, 4.89 and 9.0%, respectively, expressed relative to the mean gasometer value. Simultaneous measurements of using the portable calorimeter and the SensorMedics 2900 unit were compared during rest and at work rates starting at zero watts, increasing by 25 W to 150 W. Each work rate was of 4 min duration. The average of data from minutes 3 and 4 were used in all analyses. There was very close agreement between the two metabolic measurement systems. Except at the 100-W work rate, where the difference was small (3.9%), yet statistically significant, all of the other differences in were small and non-significant. The scatter plot of for the SensorMedics versus the portable Aero-Sport calorimeter revealed close agreement; the correlation wasr = 0.96, (SEE = 3.95%). It was concluded that the AeroSport TEEM 100 portable calorimeter system produces valid data at rest and at low to moderate work rates compared to a criterion, large system.     

Prediction of individual oxygen uptake on-step transients from frequency responses

Power-oxygen uptake ( ) frequency responses can be used to predict responses to arbitrary exercise intensity patterns. It is still an open question for which range of exercise intensities such computed response patterns yield valid predictions. In the present study, we determined the power- frequency response of nine sports students by means of pseudo-randomised switching between 20 W and 80 W during upright and supine cycle exercise. Starting from a baseline of 20 W each subject also performed sustained step increases to 40 W, 80 W, 120 W, and 160 W in both positions. The individual step responses were then compared with the expected time-courses predicted on the basis of the individual frequency responses. The comparison showed a close agreement for the 20 W–40 W and 20 W–80 W steps in both positions. With larger step amplitudes the kinetics became increasingly slower than the predicted time course in both positions. During additional ramp tests (10 W · 30 s^–1) whole blood lactic acid concentration [1a^–]_b tended to be higher in the supine position at exercise intensities higher than 160 W. The mean power at 4 mmol · 1^–1 [la^–]_b amounted to 234 (SD 32) W and 253 (SD 44) W (P<5%) in the supine and the upright position, respectively. The maximal oxygen uptake relative to body mass was not found to be significantly different [upright, mean 57 (SD 10) ml · (min · kg)^–1;supine, mean 54 (SD 10) ml · (min · kg)]. These findings would suggest that for a range of mild exercise intensities kinetics are not appreciably influenced by the step amplitude or by cardiovascular changes associated with the upright and the supine position.     

The energy cost of level cross-country skiing and the effect of the friction of the ski

Summary Oxygen consumption [( ) in ml·kg^–1·min^–1], blood lactate concentration ([La] in mM) and dynamic friction of the skis on snow [(F) inN] were measured in six athletes skiing on a level track at different speeds [(v) in m·min^–1] and using different methods of propulsion. The increased withv andF, the latter depending mostly on snow temperature, as did [La]. The was very much affected by the skiing technique. Multiple regression equations gave the following results: with diagonal stride (DS), =–23.09+0.189v+0.62N; with double pole (DP), =–30.95+0.192v+0.51N; and with the new skating technique (S), =–32.63 +0.171+0.68N. In terms of DS is the most expensive technique, while S is the least expensive; however, asF increases, S, at the highest speed, tends to cost as much as DP. At speeds from 18 to 22 km·h^–1, the speeds measured in the competitions, theF for DS and DP can represent from 10% to 50% of the energy expenditure, withF ranging from 10 to 60N; with S this range increases to 20%–70%. This seems to depend on the interface between the skis and the snow and on the different ways the poles are used.     

Metabolic responses to light arm and leg exercise when sitting

Summary Seven male subjects performed progressive exercises with a light work load on an upper limb or bicycle ergometer in the sitting position. At any comparable work load above zero, arm exercise induced higher oxygen uptake, ventilation, heart rate, oxygen pulse, respiratory rate and tidal volume than leg exercise. At similar levels of above 0.45 1 · min^–1, heart rate and ventilation were higher during arm exercise. A close linear relationship between carbon dioxide output and oxygen uptake was observed during both arm and leg exercises, the slope for arm work being steeper. The ventilatory equivalent for gradually decreased during both types of exercise. The ventilatory equivalent for remained constant (arm) while it rose (leg) to a peak at 9.8 W and then gradually decreased. Ventilation in relation to tidal volume had a linear relationship with leg exercise, but became curvilinear with arm exercise after tidal volume exceeded 1100ml. The observed differences in response between arm and leg exercises at a given work load appear to be influenced by differences in sympathetic outflow due to the greater level of static contraction of the relatively small muscle groups required by arm exercise.     

Some simple multiple linear regression equations for estimation of maximal aerobic power in healthy indian males

Summary An attempt has been made to evolve some simple multiple linear regression equations for the prediction of max from body weight, time for 3.2 km run and exercise dyspnoeic index (DI_std Ex%). The predictor variables have been selected by examining the product moment correlations of body weight, relative body weight indices, time for 3.2 km run, chest expansion, height, and DI_std Ex% with max, based on data collected on 320 healthy Indian males (17–22 years). It has been observed that body weight, time for 3.2 km run and DI_std Ex% attained maximum correlations with max. Thus, two regression equations with two and three predictor variables have been established in this paper to predict max. The first regression equation yielded a multiple correlation of 0.608 (P<0.001) with a standard error of 0.214 l·min^–1. In this equation, body weight and time for 3.2 km run were considered as significant predictors. To increase the precision of this equation, another multiple linear regression equation based on body weight, time for 3.2 km run and DI_std Ex% as predictors has been developed. This equation yielded a multiple correlation of 0.658 (P<0.001) with a standard error of 0.204 l·min^–1. Applications of these regression equations will be of practical importance to biomedical scientists engaged in the development of a simple procedure for indirect assessment of max, and may serve well as preliminary screening procedures for personnel selection.     

Precision of ventilatory and gas exchange alterations as a predictor of the anaerobic threshold

Summary Anaerobic threshold has been defined as the oxygen uptake ( ) at which blood lactate (La) begins to rise systematically during graded exercise (Davis et al. 1982). It has become common practice in the literature to estimate the anaerobic threshold by using ventilatory and/or gas exchange alterations. However, confusion exists as to the validity of this practice. The purpose of this study was to examine the precision with which ventilatory and gas exchange techniques for determining anaerobic threshold predicted the anaerobic threshold resolved by La criteria. The anaerobic threshold was chosen using three criteria: (1) systematic increase in blood La (AT_La), (2) systematic increase in ventilatory equivalent for O₂ with no change in the ventilatory equivalent for CO₂ ( ), and (3) non-linear increase in expired ventilation graphed as a function of ( ). Thirteen trained male subjects performed an incremental cycle ergometer test to exhaustion in which the load was increased by 30 W every 3 minutes. Ventilation, gas exchange measures, and blood samples for La analysis were obtained every 3rd min throughout the test. In five of the thirteen subjects tested the anaerobic threshold determined by ventilatory and gas exchange alterations did not occur at the same as the AT_La. The highest correlation between a gas exchange anaerobic threshold and AT_La was found for and was r=0.63 (P<0.05). These data provide evidence that the AT_La and do not always occur simultaneously and suggest limitations in using ventilatory or gas exchange measures to estimate the AT_la.     

Effect of glucose polymer diet supplement on responses to prolonged successive swimming,cycling and running

Summary Fifteen male endurance athletes were studied to determine the effect of a glucose polymer (GP) diet supplement on physiological and perceptual responses to successive swimming, cycling and running exercise. Thirty min of swimming, cycling and running at 70% , followed by a run to exhaustion at 90% was performed after one week of training under two dietary conditions: 1) GP (230 g of GP consumed daily) and 2) placebo (P, saccharin-sweetened supplement consumed daily). During GP, daily carbohydrate (CHO) intake was higher (p<0.05) by 173 g or 14% of energy intake than during P, but total energy intake was not significantly different. During 90 min of exercise, CHO utilization and blood glucose were significantly higher under GP than P by an average of 20.2% and 14.5%, respectively, but heart rate, ventilation, oxygen uptake, ratings of perceived exertion, and plasma lactate were not different. Run time to exhaustion at 90% was significantly longer by 1.2 min (23%) under GP. The results suggest that a GP diet supplement may be of value during endurance exercise by increasing the availability of CHO.