Steady-rate Exercise Research Articles

Comment on Point:Counterpoint: The lactate paradox does/does not occur during exercise at high altitude”

POINT-COUNTERPOINT COMMENTSComment on Point:Counterpoint: The lactate paradox does/does not occur during exercise at high altitude”George A. BrooksGeorge A. BrooksPublished Online:01 Jun 2007https://doi.org/10.1152/japplphysiol.00287.2007This is the final version - click for previous versionMoreSectionsPDF (29 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat The following letter is in response to the Point:Counterpoint “The lactate paradox does/does not occur during exercise at high altitude” that appears in this issue.To the Editor: The exchange between Drs. West and van Hall (8, 9) is unsatisfying. West's (9) paper is classic, but incomplete. And while anachronism may explain Dr. van Hall's (8) dire response, his behavior should not be supported by the Journal of Applied Physiology. So far as I know, there has been only one attempt to determine the effects of acute and chronic altitude exposure on lactate kinetics that imposed appropriate dietary controls to distinguish between hypoxia and cachexia (2). West did not reference any of the papers, whereas van Hall cited some of the body of work, but chose to ignore the results. Seemingly, van Hall ignored the results because he has no understanding of the Lactate Shuttle (1), a concept that has received cross-disciplinary support (7). Hence, he cannot understand our findings that working muscle beds can simultaneously produce and consume lactate (3), diverse tissues can produce lactate for consumption by working muscle (4), and the sympathetic nervous system greatly influences carbohydrate metabolism at altitude (5). As summarized previously by Reeves (6), our results are (and should be) different from those of van Hall et al. because they gave no consideration to the necessity of controlling diet and body mass, which is essential (2), rendering their data uninterpretable. We showed by means of tracers and (a-v) measurements that lactate flux is increased on acute altitude because sympathetic nervous system (SNS) activity is increased and that with time at altitude lactate flux and SNS activity decrease.REFERENCES1 Brooks GA. Lactate shuttles in nature. Biochem Soc Trans 30: 258–264, 2002.Crossref | PubMed | ISI | Google Scholar2 Brooks GA, Butterfield GE. Metabolic response of lowlanders to high altitude exposure: malnutrition vs. the effect of hypoxia. In: Lung Biology in Health and Disease, High Altitude, edited Hornbein T and Schoene B. New York: Dekker, 2001, p. 569–600.Google Scholar3 Brooks GA, Butterfield GE, Wolfe RR, Groves BM, Mazzeo RS, Sutton JR, Wolfel EE, Reeves JT. Decreased reliance on lactate during exercise after acclimatization to 4,300 m. J Appl Physiol 71: 333–341, 1991.Link | ISI | Google Scholar4 Brooks GA, Wolfel EE, Butterfield GE, Cymerman A, Roberts AC, Mazzeo RS, Reeves JT. Poor relationship between arterial [lactate] and leg net release during steady-rate exercise at 4,300 m altitude. Am J Physiol Regul Integr Comp Physiol 275: R1192–R1201, 1998.Link | ISI | Google Scholar5 Mazzeo RS, Bender PR, Brooks GA, Butterfield GE, Groves BM, Sutton JR, Wolfel EE, Reeves JT. Arterial catecholamine responses during exercise with acute and chronic high-altitude exposure. Am J Physiol Endocrinol Metab 261: E419–E424, 1991.Link | ISI | Google Scholar6 Reeves JT, Wolfel EE, Green HJ, Mazzeo RS, Young AJ, Sutton JR, Brooks GA. Oxygen transport during exercise at high altitude and the lactate paradox: lessons from Operation Everest II and Pikes Peak. In: Exercise and Sport Sciences Reviews, vol. 20. New York: Williams and Wilkins, 1992, p. 275–296.Google Scholar7 Schurr A. Lactate: the ultimate cerebral oxidative energy substrate. J Cereb Blood Flow Metab 26: 142–152, 2006.Crossref | PubMed | ISI | Google Scholar8 Van Hall G. Counterpoint: The lactate paradox does not occur during exercise at high altitude. J Appl Physiol. In press.Google Scholar9 West J. Point: The lactate paradox does occur during exercise at high altitude. J Appl Physiol. In press.Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformationCited ByRegulation of human metabolism by hypoxia-inducible factor28 June 2010 | Proceedings of the National Academy of Sciences, Vol. 107, No. 28The lactate paradox revisited in lowlanders during acclimatization to 4100 m and in high-altitude natives27 February 2009 | The Journal of Physiology, Vol. 587, No. 5 More from this issue > Volume 102Issue 6June 2007Pages 2408-2408 Copyright & PermissionsCopyright © 2007 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00287.2007PubMed17379751History Published online 1 June 2007 Published in print 1 June 2007 Metrics

The effect of prolonged cycling on pedal forces

The aim of this study was to determine whether cyclists modify the pattern of force application to become more effective during a prolonged ride to exhaustion. Twelve competitive male cyclists completed a steady-rate exercise ride to exhaustion at 80% of their maximum power output at 90 rev · min−1 on a cycle ergometer. Pedal force, pedal and crank angle data were collected from an instrumented bicycle for three pedalling cycles at the end of the first and final minutes of the exercise test with simultaneous video recording of the lower limbs. Kinematic and force data were combined to compute hip, knee and ankle joint moments. There were changes in the pattern of force application, joint kinematics and joint moments of force. Comparison of the first minute and the final minute ride revealed significantly increased peak effective force (340±65.0 and 377±74.8 N for the first and final minute, respectively; F 1,11=7.44, P= 0.02), increased positive (28.4±4.5 and 30.5±4.8 N · s for the first and final minute, respectively; F 1,11=7.80, P= 0.02) and negative angular impulses (−1.5±1.6 and −2.4±1.5 N · s for the first and final minute, respectively; F 1,11=4.50, P= 0.06). Contrary to our initial assumptions, it would appear that riders became less effective during the recovery phase, which increased the demand for forces during the propulsive phase. Training the pattern of force application to improve effectiveness may be a useful strategy to prolong an endurance ride.

The effects of pre-warming on the metabolic and thermoregulatory responses to prolonged submaximal exercise in moderate ambient temperatures.

To determine the effects of pre-warming on the human metabolic and thermoregulatory responses to prolonged steady-rate exercise in moderate ambient temperatures and relative humidities [means (SD) 21.7 (2.1) degrees C and 36.7 (5.4)%, respectively], six healthy men each ran at a steady-rate (70% maximal oxygen uptake) on a treadmill until exhausted after being actively pre-warmed (AH), passively pre-warmed (PH), and rested (Cont). Exercise time to exhaustion was significantly reduced following both AH and PH compared to Cont [AH 47.8 (14.0) min, PH 39.6 (16.0) min, Cont 62.0 (8.8) min; P<0.05]. During exercise there were no significant differences in oxygen uptake, total sweat loss, mean skin temperature (T(sk)) and the thermal gradient ( T(re)-T(sk), where T(re) is rectal temperature) following the three conditions. Serum prolactin, plasma catecholamine and plasma free fatty acid concentrations were also similar between all three trials. In contrast, T(re), mean body temperature, heart rate and ratings of perceived exertion were significantly greater during the initial 25 min of exercise following both AH and PH, compared with Cont ( P<0.05). At exhaustion, there were no significant differences in the metabolic and thermoregulatory responses to exercise between the trials. The current findings demonstrate that AH and PH promote a reduction in prolonged submaximal endurance performance under moderate environmental temperatures compared with pre-exercise rest. Such observations appear likely to have been mediated through mechanisms associated with the earlier development of high internal body temperature which resulted in changes in the capacity for heat storage.

EFFECTS OF EXTERNAL AUDITORY QUANTUM BEHAVIORS ON SELECTED CARDIO-RESPIRATORY AND METABOLIC VARIABLES DURING STEADY-RATE EXERCISE

Research on human psychosomatic relationship acknowledges that changes in the physiological state are accompanied by appropriate changes in the psychological state, conscious or unconscious, and conversely. This research has focused on simple movement tasks and/or cognitive processing and not on physical exercise. The purpose of this study was to examine the effects of an external auditory quantum behavior on selected cardio-respiratory, metabolic, and perceptual variables during steady-rate exercise. Participants (n = 17) exercised on a treadmill for 9 min at a steady-rate (40% VO2MAX). At min 4, 6, and 8 of the exercise, auditory stimuli (music, tone, & crowd) were randomly introduced to participants via head phones for 30 s. Results were analyzed by a series of one-way ANOVA's with repetitions across three levels of time (pre-during-port auditory stimulus) on relative VO2, HR (bpm), respiratory rate (_f), and VE (1/min). Heart rate during crowd stimulus decreased (p ≤ .05) from steady-rate and increased (p ≤ .05) during post stimulus to near steady-rate levels (p ≥ .05). Results illustrate that perception of an auditory stimulus may influence physiological state via HR and thus influence exercise performance.

Physiological responses to laboratory-based soccer-specific intermittent and continuous exercise

The aim of this study was to devise a laboratory-based protocol for a motorized treadmill that was representative of work rates observed during soccer match-play. Selected physiological responses to this soccer-specific intermittent exercise protocol were then compared with steady-rate exercise performed at the same average speed. Seven male university soccer players (mean - s : age 24 - 2 years, height 1.78 - 0.1 m, mass 72.2 - 5.0 kg, VO 2max 57.8 - 4 ml·kg -1 ·min -1 ) completed a 45-min soccer-specific intermittent exercise protocol on a motorized treadmill. They also completed a continuous steady-rate exercise session for an identical period at the same average speed. The physiological responses to the laboratory-based soccer-specific protocol were similar to values previously observed for soccer match-play (oxygen consumption approximately 68% of maximum, heart rate 168 - 10 beats·min -1 ). No significant differences were observed in oxygen consumption, heart rate, rectal temperature or sweat production rate between the two conditions. Average minute ventilation was greater ( P ≪ 0.05) in intermittent exercise (81.3 - 0.2l·min -1 ) than steady-rate exercise (72.4 - 11.4l·min -1 ). The rating of perceived exertion for the session as a whole was 15 - 2 during soccer-specific intermittent exercise and 12 - 1 for continuous exercise ( P ≪ 0.05). The physiological strain associated with the laboratory-based soccer-specific intermittent protocol was similar to that associated with 45 min of soccer match-play, based on the variables measured, indicating the relevance of the simulation as a model of match-play work rates. Soccer-specific intermittent exercise did not increase the demands placed on the aerobic energy systems compared to continuous exercise performed at the same average speed, although the results indicate that anaerobic energy provision is more important during intermittent than during continuous exercise at the same average speed.

Circadian variation in blood pressure responses to muscular exercise.

Abstract The physiological responses to strenuous steady-rate exercise are known to vary with time of day. Less well understood are the acute reactions to abrupt short-term all-out muscular efforts. This study examined circadian variation in blood pressure responses to short-term intense exercise. Twelve males participated in an experiment that involved performance of maximal muscular efforts at six times of the day. The time points were equally spaced throughout the day and for each subject the tests were conducted within a 2-week period. Systolic and diastolic blood pressures were measured pre-exercise using sphygmomanometry and body temperature was recorded with a rectal probe. Muscle function tests consisted of (1) three slow and three fast isokinetic movements, knee extensions performed under both concentric and eccentric conditions; (2) a 20s maximal isometric contraction, and (3) a 60s fatigue loading with concentric and eccentric contractions. Blood pressures were again measured immediately after ...

Lactate and ventilatory thresholds: disparity in time course of adaptations to training.

We tested the hypothesis that the lactate threshold (Tlac) during incremental exercise could be increased significantly during the first 3 wk of endurance training without any concomitant change in the ventilatory threshold (Tvent). Tvent is defined as O2 uptake (VO2) at which ventilatory equivalent for O2 [expired ventilation per VO2 (VE/VO2)] increased without a simultaneous increase in the ventilatory equivalent for CO2 (VE/VCO2). Weekly measurements of ventilatory gas exchange and blood lactate responses during incremental and steady-rate exercise were performed on six subjects (4 male; 2 female) who exercised 6 days/wk, 30 min/session at 70-80% of pretraining VO2max for 3 wk. Pretraining Tlac and Tvent were not significantly different. After 3 wk of training, significant increases (P less than 0.05) occurred for mean (+/- SE) VO2max (392 +/- 103 ml/min) and Tlac (482 +/- 135 ml/min). Tvent did not change during the 3 wk of training, despite significant (P less than 0.05) reductions in VE responses to both incremental and steady-rate exercise. Thus ventilatory adaptations to exercise during the first 3 wk of exercise training were not accompanied by a detectable alteration in the ventilatory "threshold" during a 1-min incremental exercise protocol. The mean absolute difference between pairs of Tlac and Tvent posttraining was 499 ml/min. Despite the significant training-induced dissociation between Tlac and Tvent a high correlation between the two parameters was obtained posttraining (r = 0.86, P less than 0.05). These results indicate a coincidental rather than causal relationship.(ABSTRACT TRUNCATED AT 250 WORDS)

The lactate shuttle during exercise and recovery.

Most (75%+) of the lactate formed during sustained, steady-rate exercise is removed by oxidation during exercise, and only a minor fraction (approximately 20%) is converted to glucose. Significant lactate extraction occurs during net lactate release from active skeletal muscle; the total lactate extraction approximates half the net chemical release. Of the lactate which appears in blood, most of this will be removed and combusted by oxidative (muscle) fibers in the active bed and the heart. The "shuttling" of oxidizable substrate in the form of lactate from areas of high glycogenolytic rate to areas of high cellular respiration through the interstitium and vasculature appears to represent an important means by which substrate is distributed, metabolic "waste" is removed, and the functions of various tissues are coordinated during exercise. During recovery from sustained exhausting exercise, most of the lactate accumulated during exercise will continue to be removed by direct oxidation. However, as the muscle respiratory rate declines in recovery, lactate becomes the preferred substrate for hepatic gluconeogenesis. Practically all of the newly formed liver glucose will be released into the circulation to serve as a precursor for cardiac and skeletal muscle glycogen repletion. Liver glycogen depots will not be restored, and muscle glycogen will not be completely restored until refeeding. This is because the diversion of lactate carbon to oxidation during exercise and recovery represents an irreversible loss of gluconeogenic precursor and because the processes of protein proteolysis and gluconeogenesis from amino acids are insufficient to achieve complete glycogen restitution after exhausting exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient VO2 characteristics in children at the onset of steady-rate exercise.

Abstract The transient oxygen uptake (VO2) response during the initial phase of exercise was investigated in 28 children (mean age ± SD = 10.2 ± 2.28 years) during constant load submaximum bicycle ergometer exercise (mean power output ± SD = 56 ± 4.0 watts; mean VO2 ± SD = .92 ± .141 [mdot] min-1). The VO2 half-time (VO2 - t½) averaged (± SD) 34.8 (± 12.70) sec which is similar to that observed in adults. Examination of the VO2-t ½ response as it related to age (7 to 14 years) showed that younger children attained steady-rate VO2 more quickly than older children (r = .77 between age and VO2-t½, P < .05). Body size, maturational level, exercise intensity, cardiorespiratory factors, and anaerobic potential are suggested as possible factors accounting for the positive age vs VO2-t ½ relationship.

Muscular efficiency during steady-rate exercise. II. Effects of walking speed and work rate.

A comparison of walking against vertical (gradient) and horizontal (trailing weight) forces was made during steady-rate exercise at 0.250, 500, and 750 kg-m/min with speeds of 3,0, 4.5, and 6.0 km/h. In all cases exponential relationships between energy expenditure (calculated from the steady-rate respiration) and increasing work rate and speed were observed which indicated that muscular efficiency during walking is inversely related to speed and work rate. "Work" (level, unloaded walking as the baseline correction), "delta" (measured work rate as the baseline correction), and "instantaneous" (derived from the equation describing the caloric cost of work) efficiencies were computed. All definitions yielded decreasing efficiencies with increasing work rates. At work rates above 250 kg-m/min the curves describing the relationship between energy expenditure and work rate were parallel for vertical and horizontal forces, indicating equivalent efficiencies in this range. Only the delta and instantaneous definitions accurately described these relationships for vertical and horizontal work. Determinations of combined work loads (gradient plus trailing weight) were made and the energy costs of both types of work found to be additive.

Muscular efficiency during steady-rate exercise: effects of speed and work rate.

In a comparison of traditional and theoretical exercise efficiency calculations male subjects were studied during steady-rate cycle ergometer exercises of "0," 200, 400, 600, and 800 kgm/min while pedaling at 40, 60, 80, and 100 rpm. Gross (no base-line correction), net (resting metabolism as base-line correction), work (unloading cycling as base-line correction), and delta (measurable work rate as base-line correction) efficiencies were computed. The result that gross (range 7.5-20.4%) and net (9.8-24.1%) efficiencies increased with increments in work rate was considered to be an artifact of calculation. A LINEAR OR SLIGHTLY EXPONENTIAL RELATIONSHIP BETWEEN CALORIC OUTPUT AND WORK RATE DICTATES EITHER CONSTANT OR DECREASING EFFICIENCY WITH INCREMENTS IN WORK. The delta efficiency (24.4-34.0%) definition produced this result. Due to the difficulty in obtaining 0 work equivalents, the work efficiency definition proved difficult to apply. All definitions yielded the result of decreasing efficiency with increments in speed. Since the theoretical-thermodynamic computation (assuming mitochondrial P/O = 3.0 and delta G = -11.0 kcal/mol for ATP) holds only for CHO, the traditional mode of computation (based upon VO2 and R) was judged to be superior since R less than 1.0. Assuming a constant phosphorylative-coupling efficiency of 60%, the mechanical contraction-coupling efficiency appears to vary between 41 and 57%.