Exercise intensity-related responses of beta-endorphin and catecholamines

Ten men and 10 women exercised on a bicycle ergometer for 20 min at 40, 60, and 80% maximal oxygen uptake (VO2max) to determine the relationship between plasma beta-endorphin, catecholamines, and exercise intensity. Compared to rest, plasma beta-endorphins were not significantly elevated during the 40 and 60% workloads (4.8 +/- 1.0 pmol.l-1 vs 3.8 +/- 0.7 and 6.3 +/- 0.9, respectively). In contrast, the 80% exercise significantly elevated endorphins to 16.1 +/- 4.0 pmol.l-1. Plasma norepinephrine concentrations were 0.30 +/- 0.04 ng.ml-1 at rest and increased with exercise intensity (40% = 0.60 +/- 0.05, 60% = 0.93 +/- 0.07, 80% = 2.00 +/- 0.14, VO2max = 2.55 +/- 0.14 ng.ml-1). Plasma epinephrine followed the same trend (rest = 0.07 +/- 0.01, 40% = 0.33 +/- 0.03, 60% = 0.49 +/- 0.02, 80% = 0.88 +/- 0.07, VO2max = 0.95 +/- 0.06 ng.ml-1). Norepinephrine was found to significantly correlate to endorphins (r = 0.499; P less than 0.02). Conversely, epinephrine was not correlated with beta-endorphin (r = 0.309; P greater than 0.05). The low correlation suggests a weak relationship between beta-endorphin and catecholamine responses during exercise. The results of this investigation suggest that the relationship between beta-endorphin and exercise intensity is curvilinear, with anaerobic activity producing the most significant endorphin response. It was also noted that the beta-endorphin response was not related to gender, but the amine response to exercise was gender-related, being greater for the men.     

Plasma beta-endorphin immunoreactivity during graded cycle ergometry

The present study was undertaken to define the response of plasma beta-endorphin immunoreactivity (ir-BE) to exercise of increasing intensity. Nineteen healthy males performed continuous exercise for 32 min on a cycle ergometer, comprised of 8-min bouts at %VO2max approximating 25, 50, and 75% of maximal exercise. Venous blood samples were collected before exercise (T = -20 and 0 min), during exercise (T = 8, 16, 24, and 32 min), and in recovery (T = +15, +30 min). Ir-BE in plasma was measured by radioimmunoassay using Immuno Nuclear assay kits. Plasma ir-BE level (pg X ml-1) was not altered from pre-exercise (18.3 +/- 1.3) after 8 min of exercise at 25 and 50% VO2max intensity; however, ir-BE rose significantly after 8 min of 75% VO2max work intensity (27.1 +/- 2.4) and was further elevated at maximal exercise (74.1 +/- 8.6). Ir-BE level remained elevated 15 min (60.9 +/- 8.1) and 30 min (35.2 +/- 5.2) post-exercise. The response pattern was further characterized by a significant (P less than 0.05) inter-individual variation, both at rest and during exercise; also, regression analysis indicated the ir-Be levels attained at maximal exercise were inversely related to the relative VO2max (ml X kg-1 X min-1) of the subject (predicted ir-BE = 248.2 - 3.39 VO2max; r = -0.397, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise intensity and erythrocyte 2,3-diphosphoglycerate concentration

The present study examines the acute effects of two different exercise intensities on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) concentration. Thirty-one females (X +/- SD age = 23.7 +/- 3.37 yr; VO2max = 44.3 +/- 5.40 ml X kg-1 X min-1) completed 2 separate 15-min constant load cycling tests at exercise intensities representing 35 and 75% of VO2max. Venous blood was obtained pre-exercise (PRE), immediately post-exercise (POST), 15 min post-exercise (POST15), and 30 min post-exercise (POST30) to determine lactic acid, 2,3-DPG, and hemoglobin concentrations and hematocrit. Significant increases (P less than 0.01) in lactic acid concentration (1.1 +/- 0.14 at PRE to 6.2 +/- 0.48 m X mol-1 X l-1 at POST), 2,3-DPG concentration (1.9 +/- 0.06 at PRE to 2.1 +/- 0.06 mumol X ml-1 at POST), and 2,3-DPG corrected for plasma volume shift (PVC 2,3-DPG) (1.9 +/- 0.06 at PRE to 2.4 +/- 0.07 mumol X ml-1 at POST15) were observed only following the 75% submaximal exercise. At POST30 (75% VO2max) PVC 2,3-DPG and lactic acid remained 5.3 and 97% (P less than 0.05) above baseline, respectively. An exercise intensity effect was observed only in lactic acid response (P less than 0.05) but not in 2,3-DPG (mumol X ml-1 and mumol X g-1 hemoglobin or PVC 2,3-DPG. A significant time-intensity interaction (P less than 0.05) for PVC 2,3-DPG suggests that PVC 2,3-DPG response over time was different between the two exercise intensity levels, with the 75% intensity eliciting a greater increase in PVC 2,3-DPG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between %HRmax, %HR reserve, %VO2max, and %VO2 reserve in elite cyclists

PURPOSE: To evaluate the relations between %HRmax, %HRR, %VO2max, and %VO2R in elite cyclists and to check whether the intensity scale recommended by ACSM in its 1998 position stand is also applicable to this specific population. METHODS: Twenty-six male elite road cyclists (25.1 +/- 0.7 yr, 71.0 +/- 1.2 kg, 70.9 +/- 1.2 mL x kg(-1) x min(-1), 433.9 +/- 9.8 W) performed an incremental maximal exercise test (50 W x 3 min(-1)). Individual linear regressions based on HR and VO2 values measured at rest, end of each stage, and maximum, were used to calculate slopes and intercepts, and to predict %HRmax, %HRR, %VO2max, or %VO2R for a given exercise intensity. RESULTS: Below 85% VO2max or VO2R, predicted %HRmax values were significantly higher (P < 0.001) than the ACSM intensity scale (58, 65, 73, and 87% vs 55, 62, 70, and 85% HRmax at 40, 50, 60, and 80% VO2max, and 48, 61, 74% vs 35, 55, and 70% HRmax at 20, 40, and 60% VO2R). The %HRR versus %VO2max regression mean slope (1.069 +/- 0.01) and intercept (-5.747 +/- 0.80) were significantly different (P < 0.0001) from 1 and 0, respectively. Conversely, the %HRR versus %VO2R regression was indistinguishable from the line of identity (mean slope = 1.003 +/- 0.01; mean intercept = 0.756 +/- 0.7). Predicted %VO2R values were equivalent to %HRR in the 35-95%HRR range. %VO2max was equivalent to %HRR at and above 75%HRR, and it was significantly higher at (P < 0.05) and below 65%HRR (P < 0.001). CONCLUSION: The intensity scale recommended by ACSM underestimates exercise intensity in elite cyclists. Prediction of %HRR by %VO2R is better than by %VO2max. Thus, elite cyclists should use %HRR in relation to %VO2R rather than in relation to %VO2max.     

Pre-exercise glucose ingestion at different time periods and blood glucose concentration during exercise

The purpose of this study was to investigate the effects of glucose ingestion (GI) at different time periods prior to exercise on blood glucose (BG) levels during prolonged treadmill running. Eight subjects (X+/-SD), age 20+/-0.5yr, bodymass 70.7+/-4.1 kg, height 177+/-4 cm, VO2max 52.8+/-7.8 ml x kg(-1) x min(-1) who underwent different experimental conditions ingested a glucose solution (1 g/kg at 350 ml) 30 min (gl-30), 60 min (gl-60), 90 min (gl-90), and a placebo one 60 min (pl-60) prior to exercise in a counterbalanced design. Afterwards they ran at 65% of VO2max for 1 hour and then at 75 % of VO2max till exhaustion. Fingertip blood samples (10 microl) were drawn every 15 min before and during exercise for the determination of BG levels. Oxygen uptake (VO2), heart rate (HR), and blood lactate (La) were also measured every 15 min during exercise. Peak BG values were reached within 30 min after GI but were different (p < 0.01) at the onset of exercise (gl-30: 147+/-22, gl-60: 118+/-25, gl-90: 109+/-22, pl-60: 79+/-5mg/dl). The two-way ANOVA repeated measures and the Tukey post-hoc test revealed a higher BG concentration (p < 0.05) for the gl-30 and the pl-60 as compared to the gl-60 and gl-90 during running (e.g. 15min run: 82+/-11, 68+/-5, 64+/-3, 78+/-7, and 60min run: 98+/-12, 85+/-12, 83+/-11, 94+/-11 mg/dl for gl-30, gl-60, gl-90, and pl-60, respectively). However, this did not significantly affect the duration of treadmill running. The La levels were higher (p < 0.05) after GI as compared to placebo throughout exercise (values at exhaustion: 4.6+/-0.2, 5.0+/-1.5, 4.8+/- 1.7 mmol/l for gl-30, gl-60, gl-90, and 3.5+/-0.8 mmol/l for placebo). The gl-30 and the placebo fluctuated closer to normoglycaemic levels. The glucose ingestion (60 to 90 min) prior to exercise lowered the blood glucose levels without affecting the duration of running performance at 75% VO2max. Thus, in order to maintain normoglycaemic levels, pre-exercise glucose supplementation should be given 30 min before the onset of exercise.     

Effects of sodium bicarbonate ingestion on prolonged intermittent exercise

PURPOSE: The aim of this study was to determine the effects of sodium bicarbonate ingestion on prolonged intermittent exercise and performance. METHODS: Eight healthy male subjects (mean +/- SD: age 25.4 +/- 6.4 yr, mass 70.9 +/- 5.1 kg, height 179 +/- 7 cm, VO(2max) 4.21 +/- 0.51 L.min-1) volunteered for the study, which had received ethical approval. Subjects undertook two 30-min intermittent cycling trials (repeated 3-min blocks; 90 s at 40% VO(2max), 60 s at 60% VO(2max), 14-s maximal sprint, 16-s rest) after ingestion of either sodium bicarbonate (NaHCO(3); 0.3 g.kg-1) or sodium chloride (NaCl; 0.045 g x kg(-1). Expired air, blood lactate (BLa), bicarbonate (HCO(3)-), and pH were measured at rest, 30 and 60 min postingestion, and during the 40% VO(2max) component of exercise (4, 10, 16, and 29 min). RESULTS: After ingestion, pH increased from rest to 7.46 +/- 0.03 and 7.40 +/- 0.01 for NaHCO(3) and NaCl, respectively (main effect for time and trial; P < 0.05). Values decreased at 15 min of exercise to 7.30 +/- 0.07 and 7.21 +/- 0.06, respectively, remaining at similar levels until the end of exercise. BLa peaked at 15 min (12.03 +/- 4.31 and 10.00 +/- 2.58 mmol.L-1, for NaHCO(3) and NaCl, respectively; P > 0.05) remaining elevated until the end of exercise (P < 0.05). Peak power expressed relative to sprint 1 demonstrated a significant main effect between trials (P < 0.05). Sprint 2 increased by 11.5 +/- 5% and 1.8 +/- 9.5% for NaHCO(3) and NaCl, respectively. During NaHCO(3), sprint 8 remained similar to sprint 1 (0.2 +/- 17%), whereas a decrease was observed during NaCl (-10.0 +/- 16.0%). CONCLUSION: The results of this study suggest that ingestion of NaHCO(3) improves sprint performance during prolonged intermittent cycling.     

Cardiovascular drift is related to reduced maximal oxygen uptake during heat stress

INTRODUCTION/PURPOSE: This study investigated whether the progressive rise in heart rate (HR) and fall in stroke volume (SV) during prolonged, constant-rate, moderate-intensity exercise (cardiovascular drift, CVdrift) in a hot environment is associated with a reduction in VO(2max). METHODS: CVdrift was measured in nine male cyclists between 15 and 45 min of cycling at 60% VO(2max) in 35 degrees C that was immediately followed by measurement of VO(2max). VO(2max) also was measured after 15 min of cycling on a separate day, so that any change in VO(2max) between 15 and 45 min could be associated with the CVdrift that occurred during that time interval. This protocol was performed under one condition in which fluid was ingested and there was no significant body weight change (0.3 +/- 0.4%), and under another in which no fluid was ingested and dehydration occurred (2.5 +/- 1%, P < 0.05). RESULTS: Fluid ingestion did not affect CVdrift or change in VO(2max). A 12% increase in HR (151 +/- 9 vs 169 +/- 10 bpm, P < 0.05) and 16% decrease in SV (120 +/- 12 vs 101 +/- 10 mL.beat(-1), P < 0.05) between 15 and 45 min was accompanied by a 19% decrease in VO(2max) (4.4 +/- 0.6 vs 3.6 +/- 0.4 L.min(-1), P < 0.05) despite attainment of a higher maximal HR (P < 0.05) at 45 min (194 +/- 5 bpm) vs 15 min (191 +/- 5 bpm). Submaximal VO(2) increased only slightly over time, but VO(2max) increased from 63 +/- 5% at 15 min to 78 +/- 8% at 45 min (P < 0.05). CONCLUSION: We conclude CVdrift during 45 min of exercise in the heat is associated with decreased VO(2max) and increased relative metabolic intensity. The results support the validity of using changes in HR to reflect changes in relative metabolic intensity during prolonged exercise in a hot environment in which CVdrift occurs.     

Muscle glycogen depletion alters oxygen uptake kinetics during heavy exercise

PURPOSE: To test the hypothesis that muscle fiber recruitment patterns influence the oxygen uptake (VO2) kinetic response, constant-load exercise was performed after glycogen depletion of specific fiber pools. METHODS: After validation of protocols for the selective depletion of Type I and II muscle fibers, 19 subjects performed square-wave exercise at 80% VT (moderate) and at 50% of the difference between VT and VO2max (heavy) without any prior depleting exercise (CON), after HIGH (10 x 1-min exercise bouts at 120% VO2max), and after LOW (3 h of exercise at 30% VO2max) exercise. RESULTS: Differences in VO2 kinetic parameters were only observed in heavy exercise AFTER HIGH: the VO2 primary component was higher (1.75 +/- 0.12 L x min) compared with CON (1.65 +/- 0.11 L x min, P < 0.05), and the VO2 slow component was lower (0.18 +/- 0.03 L x min) compared with CON (0.24 +/- 0.04 L x min, P < 0.05). CONCLUSIONS: The results indicate that the VO2 response to heavy constant-load exercise can be altered by depletion of glycogen in the Type II muscle fibers, lending support to the theory that muscle fiber recruitment influences both the VO2 primary and slow component amplitudes during heavy intensity exercise.     

Effects of exercise intensity, duration and recovery on in vitro neutrophil function in male athletes

The aim of the present study was to compare the effects of exercise at 80% VO2max (resulting in fatigue within 1 h) with more prolonged exercise at a lower work rate (55% VO2max for up to 3 h) on blood neutrophil function and plasma concentrations of cortisol, glutamine and glucose. Eighteen healthy male subjects (mean+/-SD age 22.5+/-3.7 yrs, VO2max 60.1+/-6.6 ml x kg(-1) x min(-1)) cycled on an electrically braked ergometer at 80% VO2max to fatigue (37+/-19 min). On another occasion, separated by at least one week, subjects performed exercise on the same ergometer at 55% VO2max for 3 h or to fatigue, whichever was the sooner. Mean exercise time was 164+/-23 min. The order of the trials was randomised. Both exercise bouts caused significant (p<0.05) elevations of the blood leucocyte count and plasma cortisol concentration and reductions in the in vitro neutrophil degranulation response to bacterial lipopolysaccharide and oxidative burst activity. After exercise at the lower work rate for a longer duration, plasma cortisol concentration was higher, blood leucocyte and neutrophil counts were higher, blood lymphocytes, plasma glucose and indices of neutrophil function were lower than those observed at 80% VO2max. Plasma glutamine only fell significantly during recovery after the more prolonged exercise. We conclude that when exercise is very prolonged, the diminution of innate immune function is greater, or at least as great as that observed after fatiguing exercise at higher work rates. Furthermore, reductions in neutrophil function after exercise at 80% VO2max were not related to changes in the plasma glutamine concentration, although both plasma glutamine and neutrophil function were decreased at 1 and 2.5 h post-exercise in the long duration exercise trial.     

The menstrual cycle and exercise: performance, muscle glycogen, and substrate responses

Six eumenorrheic females (age = 26.3 +/- 2.4 yrs; X +/- SE) exercised until exhaustion (EE; 70% VO2max) at the midluteal (LP, 7-8 days after ovulation) and midfollicular (FP, days 7-8) phases of their menstrual cycles. Phases were confirmed by estradiol and progesterone concentrations. Each EE test was preceded by a depletion exercise bout (DE; 90 min, 60% VO2max and 4 x 1 min, 100% VO2max) and 3 days of rest/diet control. Muscle biopsies 1% (vastus lateralis) were taken post-DE, pre-EE, and post-EE and then analyzed for glycogen content. There was a strong tendency (P less than 0.07) for EE duration to be greater during LP (139.2 +/- 14.9 min) than FP (126 +/- 17.5 min). Glycogen repletion (pre-EE minus post-DE) following DE was greater (P = 0.05) during the LP than FP (88.2 +/- 4.7 vs 72.8 +/- 5.7 mumol/g w. w. muscle). However, EE glycogen utilization (pre-EE minus post-EE/EE time) did not differ between phases (LP = 0.41 +/- 0.08 mumol/g w. w. muscle/min vs FP = 0.33 +/- 0.11 mumol/g w. w. muscle/min; P = 0.17). The results suggest that exercise performance and muscle glycogen content are enhanced during the LP of the menstrual cycle. These findings imply athletic performance may be affected by the phases of the menstrual cycle.     

Exercise intensity and duration affect blood soluble HSP72

Soluble heat shock protein 72 (sHSP72) is suggested to play a role as a signalling molecule in the immune response to exercise. We were interested in whether duration and intensity of endurance running affect the level of inducible sHSP72 in the plasma/serum of endurance athletes. In the first part of the study, the influence of a continuous treadmill run of 60 min (CR) with an intensity of 75 % VO2max, a long treadmill run of 120 min (LR) with an intensity of 60 % VO2max, an extensive interval training program (IT; 10 x 1000 m, ca. 35 min, VO2max 88 %), and a competitive marathon run (MA) within 260 +/- 39 min (VO2max ca. 65 %) on the release of sHSP72 into the peripheral blood was tested. Blood samples were drawn before and directly after exercise, as well as 0.5, 1, 3, 24 h after exercise to determine sHSP72 levels. Secondly, we compared the effects of two exercise bouts with identical duration (23.7 +/- 7 min) but different intensities (Exhaustive exercise (ET) at 80 % VO2max vs. moderate exercise (MT) at 60 % VO2max) on sHSP72 concentration. The sHSP72 levels in plasma/serum were analyzed using an enzyme immunoassay specific for inducible HSP72 (Stressgen,Victoria, Canada). Early, significant increases of sHSP72 were detected immediately after all types of exercise with highest levels after MA. ET induced significantly higher levels of sHSP72 compared with MT. Long-lasting, competitive endurance exercise induced a more pronounced response of sHSP compared with more intensive but shorter exercise. Exercise intensity was also an important influencing factor. A duration- and intensity-dependent role for sHSP72 in the exercise-induced changes of the immune response may be assumed.     

Effects of acute cold exposure on submaximal endurance performance

The purposes of this study were to assess VO2max and submaximal endurance time to exhaustion (ET) during acute cold-air exposure. Eight male subjects (means age = 19.9 yr) were alternately exposed in groups of four to chamber temperatures of +20 degrees C and -20 degrees C for 30 h each. A week was allowed between exposures. Maximum oxygen uptake was measured using a mechanically-braked cycle ergometer, and ET was determined on the same ergometer using a 17-min/3-min exercise/rest schedule until the subject was unable to maintain pedal rate. Maximum oxygen uptake was not significantly different between conditions: 3.43 +/- 0.09 l X min-1 at +20 degrees C and 3.35 +/- 0.10 l X min-1 at -20 degrees C. During endurance exercise, intensities equaled 77.1 +/- 1.4% and 78.9 +/- 2.0% of VO2max at +20 degrees C and -20 degrees C, respectively. Heart rate and VO2 values obtained between 8 and 10 min of the endurance run were not significantly different (156 +/- 2 bpm and 2.63 +/- 0.08 l X min-1 at +20 degrees C and 158 +/- 3 bpm and 2.65 +/- 0.11 l X min-1 at -20 degrees C). Endurance time to exhaustion however, decreased 38% (P less than 0.05) from 111.9 +/- 22.8 min at +20 degrees C to 66.9 +/- 13.6 min at -20 degrees C. The data support the contention that aerobic capacity is not altered by cold exposure but suggest a marked decrease in submaximal endurance performance.     

Effect of high-intensity submaximal work, with or without rest, on subsequent VO2max

PURPOSE: In practice, tests of maximal oxygen uptake (.VO2max) are often preceded by a lactate profile, a highly intense but submaximal exercise bout. The .VO2max response to preceding high-intensity submaximal exercise, with or without a rest period, has not been determined. If .VO2max is limited after a lactate profile, exercise-induced hypoxemia (EIH) may explain the deficit. The purposes of this study were to: 1) examine the effects of high-intensity submaximal exercise, with or without rest, on subsequent .VO2max; and 2) evaluate the role of EIH in causing any observed changes. METHODS: Ten healthy, well-trained, male cross-country skiers (age = 20.5 +/- 4.7 yr, height = 181.6 +/- 6.0 cm, mass = 72.1 +/- 5.7 kg) completed three exercise trials: an incremental run to fatigue (MAX), MAX preceded by a high-intensity submaximal run (lactate profile) and a 20-min rest period (discontinuous protocol [DC]), and MAX preceded by a high-intensity submaximal exercise run with no rest (continuous protocol [C]). .VO2max, minute ventilation, and arterial oxygen saturation were measured throughout, and diffusion capacity was evaluated 2 min postexercise.RESULTS No significant between trial differences were observed, although the difference between .VO2max determined during the MAX trial (62.7 +/- 6.7 mL.kg-1.min-1) and during the DC trial (58.3 +/- 4.4 mL.kg-1.min-1) approached significance (P = 0.059). DC .VO2max responses could be separated into two groups: five responders whose .VO2max suffered during the DC trial (decreased >7.5% from MAX) and five nonresponders, whose .VO2max was unaffected by preceding submaximal exercise and a rest period. Responders showed greater aerobic capacity during the MAX trial. CONCLUSION: .VO2max is significantly reduced in approximately 50% of cross-country skiers when a maximal exercise test is preceded by high-intensity submaximal exercise and a 20 min rest period; the role of EIH in causing these reductions is unclear.     

Plasma beta-endorphin concentration: response to intensity and duration of exercise

Twelve college-age men exercised on a bicycle ergometer to VO2max and at 60, 70, and 80% VO2max for 30 min to determine the effects of exercise intensity on plasma beta-endorphin (B-EP). The time course for alterations in B-EP and the relationship to lactate were also examined. Following the VO2max test, the three submaximal intensities were completed on separate days using a counter-balanced design. Blood was sampled from an indwelling venous catheter at rest during exercise and recovery to assess the time course response. B-EP content was determined by radioimmunoassay (Immunonuclear) with less than 5% cross-reactivity to B-LPH. At rest, B-EP content was similar across visits, 4.34 +/- 0.36 pmol.l-1. The 60% intensity did not elevate B-EP at any time measured. B-EP content increased by 15 min at 70% VO2max with a further increase at 30 min. B-EP remained elevated during the 20 min recovery. At 80% VO2max B-EP content increased by 5 min. B-EP continued to increase during the exercise and peaked at 21.91 +/- 2.03 pmol.l-1 5 min into the recovery. Lactate showed a mild correlation with B-EP (r = 0.43) at 80% VO2max. A significant correlation (r = 0.78) between lactate and B-EP did occur with the VO2max test. It is concluded that an exercise intensity of at least 70% VO2max for 15 min is needed to increase plasma B-EP. Furthermore, the higher the exercise intensity the more rapid the onset for increases in plasma B-EP.     

Inspiratory muscle training fails to improve endurance capacity in athletes

PURPOSE: The purpose of this study was to examine the effects of specific inspiratory muscle training (IMT) on respiratory muscle strength and endurance and whole-body endurance exercise capacity in competitive endurance athletes. METHODS: Seven collegiate distance runners (5 male/2 female; VO2max = 59.9 +/- 11.7 mL.kg-1.min-1) were recruited to participate in this study. Initial testing included maximal oxygen consumption (VO2max), sustained maximal inspiratory mouth pressure (MIP), breathing endurance time (BET) at 60% MIP, and endurance run time (ERT) at 85% VO2max. Heart rate (HR), minute ventilation (VE), oxygen consumption (VO2), and ratings of perceived dyspnea (RPD) were recorded at 5-min intervals and during the last minute of the endurance run. Blood lactate concentration (BLC) was also obtained immediately before and at 2 min after the endurance run. All testing was repeated after 4 wk of IMT (50-65% MIP, approximately 25 min x d(-1), 4-5 sessions/week, 4 wk). RESULTS: After 4 wk of IMT, MIP and BET were significantly increased compared with pretraining values (P < 0.05). No significant differences between pre and post values were observed in VO2max or ERT at 85% VO2max after IMT. No significant differences between pre and post values were detected in HR, VE, VO2, or RPD during the endurance run as measured at steady state and end of the test after IMT. BLC was not significantly different before or at 2 min after the endurance run between pre and post IMT. CONCLUSION: These results suggest that IMT significantly improves respiratory muscle strength and endurance. However, these improvements in respiratory muscle function are not transferable to VO2max or endurance exercise capacity as assessed at 85% VO2max in competitive athletes.     

不同湿度高温环境下机体有氧运动能力相关指标比较

目的:探讨不同湿度高温环境对有氧运动能力的影响。方法:随机选取10名男性大学生为对象,设定环境温度为33℃,相对湿度分别为20%、40%、60%、80%作为模型,实验时间4周,两次测试之间间隔1周。测试时受试者进行递增负荷跑台运动,以8 km/h为起始速度,每分钟增加0.8 km/h到16 km/h为止,然后逐级加坡度,0.5%为起始坡度,每分钟递增0.5%直至受试者不能坚持,运动过程中监测心率、摄氧量、每分钟通气量(VE)以及主观用力感觉指数(RPE),测试前及结束后无名指采血测试血乳酸。结果:不同湿度高温环境下运动VE、最大心率(HRmax)、最大摄氧量(VO2max)无显著性差异,60%相对湿度下运动时VO2max(3831.7±313.16 ml/min)、VE(137.5±9.38 L/min)、HRmax(199.1±8.29 beat/min)均较其余相对湿度大。20%相对湿度组运动后3 min及5 min血乳酸较80%湿度组显著升高(P<0.05),60%相对湿度组运动后3 min血乳酸亦显著高于80%湿度组(P<0.05)。80%相对湿度组运动后1 min RPE仍显著高于40%相对湿度组(P<0.05),20%相对湿度组RPE值增加较缓慢,运动至第7和10 min时RPE值显著低于60%相对湿度组(P<0.05)。结论:与其余湿度相比,33℃高温环境下,80%相对湿度中机体有氧运动能力并未得到充分发挥。     

Effects of leg press training on cycling, leg press, and running peak cardiorespiratory measures

Six males and seven females trained 3 d per wk (30 min at 80 to 85% heart rate reserve) for 20 wk on a leg press apparatus. A progressive exercise test was administered on a cycle ergometer, leg press apparatus, and treadmill before and after training. Before training, peak oxygen consumption (VO2, ml X kg-1 X min-1) during the leg press test was higher for the males (23.9 +/- 1.60, mean +/- SE) compared to the females (19.5 +/- 2.40, P less than or equal to 0.05). Peak VO2 during the cycling (males = 36.6 +/- 2.65, females = 28.5 +/- 2.35) and treadmill (males = 39.8 +/- 2.04, females = 33.2 +/- 2.64) tests was also different between the sexes, and 30 to 40% higher than during the leg press test (P less than or equal to 0.05). Peak heart rate (beats X min-1) was not different between the sexes (P greater than 0.05), yet was 11% lower during the leg press test (165 +/- 3.5) compared to the cycling (184 +/- 2.8) and treadmill (187 +/- 1.3) tests (P less than or equal to 0.05). After training, peak VO2 during the cycling and treadmill tests increased 10 to 15%, compared to 35% during the leg press test (P less than or equal to 0.05). The only change in peak heart rate was a 6% increase during the leg press test (P less than or equal to 0.05). Although peak VO2 on the leg press apparatus was lower than on the cycle ergometer and treadmill, leg press exercise elicited a sufficient stimulus for increasing peak VO2 on the three testing modes.     

Effect of a prior intermittent run at vVO2max on oxygen kinetics during an all-out severe run in humans

BACKGROUND: The purpose of this study was to examine the influence of prior intermittent running at VO2max on oxygen kinetics during a continuous severe intensity run and the time spent at VO2max. METHODS: Eight long-distance runners performed three maximal tests on a synthetic track (400 m) whilst breathing through the COSMED K4 portable telemetric metabolic analyser: i) an incremental test which determined velocity at the lactate threshold (vLT), VO2max and velocity associated with VO2max (vVO2max), ii) a continuous severe intensity run at vLT+50% (vdelta50) of the difference between vLT and vVO2max (91.3+/-1.6% VO2max)preceded by a light continuous 20 minute run at 50% of vVO2max (light warm-up), iii) the same continuous severe intensity run at vdelta50 with a prior interval training exercise (hard warm-up) of repeated hard running bouts performed at 100% of vVO2max and light running at 50% of vVO2max (of 30 seconds each) performed until exhaustion (on average 19+/-5 min with 19+/-5 interval repetitions). This hard warm-up speeded the VO2 kinetics: the time constant was reduced by 45% (28+/-7 sec vs 51+/-37 sec) and the slow component of VO2 (deltaVO2 6-3 min) was deleted (-143+/-271 ml x min(-1) vs 291+/-153 ml x min(-1)). In conclusion, despite a significantly lower total run time at vdelta50 (6 min 19+/-0) min 17 vs 8 min 20+/-1 min 45, p=0.02) after the intermittent warm-up at VO2max, the time spent specifically at VO2max in the severe continuous run at vdelta50 was not significantly different.     

Effect of exercise intensity on relationship between VO2max and cardiac output

PURPOSE: The purpose of this study was to determine whether the maximal oxygen uptake (VO2max) is attained with the same central and peripheral factors according to the exercise intensity. METHODS: Nine well-trained males performed an incremental exercise test on a cycle ergometer to determine the maximal power associated with VO2max (pVO2max) and maximal cardiac output (Qmax). Two days later, they performed two continuous cycling exercises at 100% (tlim100 = 5 min 12 s +/- 2 min 25 s) and at an intermediate work rate between the lactate threshold and pVO2max (tlimDelta50 +/- 12 min 6 s +/- 3 min 5 s). Heart rate and stroke volume (SV) were measured (by impedance) continuously during all tests. Cardiac output (Q) and arterial-venous O2 difference (a-vO2 diff) were calculated using standard equations. RESULTS: Repeated measures ANOVA indicated that: 1) maximal heart rate, VE, blood lactate, and VO2 (VO2max) were not different between the three exercises but Q was lower in tlimDelta50 than in the incremental test (24.4 +/- 3.6 L x min(-1) vs 28.4 +/- 4.1 L x min(-1); P < 0.05) due to a lower SV (143 +/- 27 mL x beat(-1) vs 179 +/- 34 mL x beat(-1); P < 0.05), and 2) maximal values of a-vO2 diff were not significantly different between all the exercise protocols but reduced later in tlimDelta50 compared with tlim100 (6 min 58 s +/- 4 min 29 s vs 3 min 6 s +/- 1 min 3 s, P = 0.05). This reduction in a-vO2 diff was correlated with the arterial oxygen desaturation (SaO2 = -15.3 +/- 3.9%) in tlimDelta50 (r = -0.74, P = 0.05). CONCLUSION: VO2max was not attained with the same central and peripheral factors in exhaustive exercises, and tlimDelta50 did not elicit the maximal Q. This might be taken into account if the training aim is to enhance the central factors of VO2max using exercise intensities eliciting VO2max but not necessarily Qmax.     

Prolonged exercise in highly trained female endurance runners

The effects of prolonged exercise in a 21 degree C dry bulb and 15 degree C wet bulb environment at 65%-70% VO2max were examined in seven highly trained females. The subjects, aged 22-35 years, underwent an initial incremental treadmill test to exhaustion, with assessment of VO2max and related cardiorespiratory variables. One week later, under similar environmental conditions, subjects ran at approximately 65% VO2max for 80 min on a motor-driven treadmill. Approximately 10 ml of venous blood was withdrawn 10 min prior and immediately prior to the onset of prolonged exercise, and at 20, 40, 60, and 80 min, and 20 min post-exercise. Venous blood was analyzed for glucose, lactate, osmolality, Na+, K+, protein, and hemoglobin (Hb). Hematocrit was measured and changes in plasma volume calculated. VO2, VE, respiratory exchange ratio, and heart rate were recorded at 17, 37, and 77 min. The percent body fat estimated from skinfold thicknesses was 19 +/- 1%. The mean VO2max was 59.3 +/- 1.0 ml . kg-1 . min-1, with a mean max VE STPD and heart rate of 78.75 +/- 3.10 1 . min-1 and 175 +/- 4 beats . min-1, respectively. No significant changes occurred in VO2, VE, % VO2max, heart rate, venous lactate, plasma glucose, or plasma protein during the prolonged exercise. A significant decrease in respiratory exchange ratio was noted. Significant changes also occurred in hematocrit, Hb, Na+, K+, and osmolality. An interesting finding was the pre-exercise expansion of the plasma volume.