Force-velocity test: effect of a heavy-load start on maximal anaerobic power and blood lactate levels

The purpose of this study was to determine the effect of starting the force-velocity test with a heavy load on both maximal anaerobic power and blood lactate concentration. Nine male subjects aged 23.4 +/- 1.3 yr (mean +/- sem) participated in a first force-velocity test (FV1) which had an initial load of 1 kg (classical protocol). Then a week later in a second force-velocity test (FV2) which had an initial load corresponding to maximal power developed during FV1 (W1). The increase in load was of 1 kg for FV1 and FV2. Our results show that during FV2, compared to FV1: 1) maximal anaerobic power developed (W2) is superior to W1 (W1 = 1,165.2 +/- 70.4 W; W2 = 1,278.6 +/- 92.3 W; p less than 0.02); 2) blood lactate concentration after the first load is inferior (p less than 0.001); 3) blood lactate concentration is not significantly different at the peak of power. Thus, starting the force-velocity test with a heavy load allows an increase of maximal anaerobic power until a blood lactate concentration which may be compared to the one obtained during the classic force-velocity test. In conclusion, maximal anaerobic power measured during the force-velocity test seems to depend on protocol used.     

Ratings of perceived exertion in individuals with varying fitness levels during walking and running

It was the purpose of this investigation to: 1) compare the ratings of perceived exertion (RPEs) in high and low fit individuals when walking and running at comparable exercise intensities and 2) to determine if ventilation (VE) provides a central signal for RPEs. Nine high fit and nine low fit male subjects completed two exercise bouts on a treadmill, one uphill walking and the other level running. Workloads for each bout were set at 90% of each subject's ventilatory threshold (VT) as determined from a graded exercise test. Oxygen consumption (Vo2), heart rate (HR), and VE were all similar between the walk and run trials for the low fit subjects (P greater than 0.05). HR were found to be significantly greater during the walk trial vs. the run trial (P less than 0.05) for the high fit subjects, whereas, VE was significantly greater during the run trial. Oxygen consumption was similar for the high fit subjects during both trials (P greater than 0.05). During the walk and run trials, central (12.1 +/- 1.6 vs. 11.4 +/- 1.5), local (14.0 +/- 1.3 vs. 13.9 +/- 1.1) and overall (12.8 +/- 1.2 vs. 12.4 +/- 1.4) RPEs were not found to be significantly different for the low fit group (P greater than 0.05). In contrast, during the walk vs. the run trial there was a significant increase in central (10.7 +/- 2.0 vs. 9.2 +/- 1.9), local (11.5 +/- 2.0 vs. 9.8 +/- 1.8) and overall (11.2 +/- 2.4 vs. 9.6 +/- 2.3) RPEs for the high fit group (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Maximal oxygen consumption test during arm exercise--reliability and validity.

The reliability and validity of a continuous progressive arm test, in which maximal 02 consumption (V02 max arm) is determined, were analyzed. Forty-one men (28.2 +/- 8.8 yr) performed the test twice. Eighteen additional men (22.6 +/- 5.6 yr) performed the arm test, as well as the treadmill run, in which maximal O2 consumption VO2max leg) was determined. The validity of the VO2 max arm test was computed, using VO2 max leg as a criterion for the individual's aerobic capacity. The reliability coefficients of VO2 max arm, VEmax arm, and HRmax arm were 0.94, 0.98, and 0.76, respectively, indicating a high reliability of the testmthe validity coefficient of VO2max arm was only 0.74. The regression equation of VO2max leg on VO2max arm was y = 24.4 + 0.9 +/- 4.4 (Syx). These findings indicate that, following the suggested protocol, the individual repeatedly uses the same muscles and does reach an all-out stage. However, different individuals apparently are aided by their trunk and leg muscles to different degrees, which lowers the validity of this test as a predictor of aerobic capacity.     

Exercise-induced blood prolactin variations in trained adult males: a thermic stress more than an osmotic stress

Blood prolactin (PRL) variations have been linked to temperature and osmotic changes in several species. The latter factors are here explored to better understand blood PRL responses frequently induced during physical exercise. Since body heat generated by exercise can lead to marked body fluid shifts, it was postulated that PRL changes observed during exercise could be associated with variations in body temperature and/or blood osmolality (OSM). A wide range (38.5-40.5 degrees C) of rectal temperatures (Tr; used here to appreciate core temperatures) were theoretically selected and randomly assigned as targets to male runners. Measured by thermistor probe, target Tr were obtained by a combination of factors: (a) increases heat production by treadmill running, and (b) decreases heat losses by appropriate clothing (decreases evaporation) in warmed (decreases radiation) and hypoventilated (decreases convection) laboratory conditions. For each subject, target Tr was attained not prior to 30 min after initiation of running, and had to be maintained for at least 10 min, for a mean (+/- SD) running time of 52.6 +/- 10.0 min. In a first protocol, hypohydration was provoked in 26 runners (23.9 +/- 4.7 years) by total restriction of water intake. In a second protocol (10 different runners: 22.3 +/- 3.3 years), euhydration was maintained by water intake (20 ml/kg body weight). Venous blood was sampled at rest before and immediately after the run. PRL was assayed by RIA; OSM was measured by freezing point depression; sodium was analyzed by flame photometry. At rest, before the heat-producing exercise, mean PRL values were 9.4 +/- 3.4 ng/ml for both eu/hypohydrated groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prediction of maximal VO2 from a submaximal StairMaster test in young women

The StairMaster 4000 PT is a popular step ergometer which provides a submaximal test protocol (SM Predicted VO(2)max) for the prediction of VO(2)max (ml.kg(-1).min(-1)). The purpose of this study was to evaluate the SM Predicted VO(2)max protocol by comparing it to results from a VO(2)max treadmill test in 20 young healthy women aged 20-25 years. Subjects were 10 step-trained (ST) women who had performed aerobic activities and exercised on a step ergometer for 20-30 minutes at least 3 times per week for the past 3 months, and 10 non-step-trained (NST) women who had performed aerobic activities no more than twice a week during the past 3 months and had no previous experience on a step ergometer. The SM Predicted VO(2)max protocol used 2 steady state heart rates between approximately 115-150 b.min(-1) to estimate VO(2)max. The Bruce maximal treadmill protocol (Actual VO(2)max) was used to measure VO(2)max by open circuit spirometry. Each subject performed both tests within a 7-day period. The means and standard deviations for the Actual VO(2)max tests were 39.8 +/- 6.1 ml.kg(-1).min(-1) for the ST group, 37.6 +/- 6.3 ml.kg(-1).min(-1) for the NST group, and 38.7 +/- 6.2 ml.kg(-1).min(-1) for the Total group (N = 20); and for the SM Predicted VO(2)max tests, means and standard deviations were 40.78 +/- 14.0 ml.kg(-1).min(-1), 30.9 +/- 4.8 ml.kg(-1).min(-1) and 35.9 +/- 11.4 ml.kg(-1).min(-1). There was no significant difference (p > 0.05) between the means of the Actual VO(2)max and SM Predicted VO(2)max test for the Total group (N = 20) or the ST group (n = 10), but a significant difference (p < 0.05) was shown for the NST group. The coefficient of determination (R(2)) and standard error of estimate (SEE) for the SM Predicted VO(2)max and Actual VO(2)max tests were R(2) = 0.18, SEE = 5.72 ml.kg(-1).min(-1) for the Total group; R(2) = 0.00, SEE = 6.68 ml.kg(-1).min(-1) for the NST group; and R(2) = 0.33, SEE = 5.32 ml.kg(-1).min(-1) for ST group. In conclusion, the SM Predicted VO(2)max test has acceptable accuracy for the ST group, but significantly underpredicted the NST group by almost 7 ml; and, as demonstrated by the high SEEs, it has a low level of precision for both ST and NST subjects.     

The effect of warm-up on high-intensity, intermittent running using nonmotorized treadmill ergometry

The aim of this study was to investigate the effect of previous warming on high-intensity intermittent running using nonmotorized treadmill ergometry. Ten male soccer players completed a repeated sprint test (10 x 6-second sprints with 34-second recovery) on a nonmotorized treadmill preceded by an active warm-up (10 minutes of running: 70% VO2max; mean core temperature (Tc) 37.8 +/- 0.2 degrees C), a passive warm-up (hot water submersion: 40.1 +/- 0.2 degrees C until Tc reached that of the active warm-up; 10 minutes +/- 23 seconds), or no warm-up (control). All warm-up conditions were followed by a 10-minute static recovery period with no stretching permitted. After the 10-minute rest period, Tc was higher before exercise in the passive trial (38.0 +/- 0.2 degrees C) compared to the active (37.7 +/- 0.4 degrees C) and control trials (37.2 +/- 0.2 degrees C; p < 0.05). There were no differences in pre-exercise oxygen consumption and blood lactate concentration; however, heart rate was greater in the active trial (p < 0.05). The peak mean 1-second maximum speed (MxSP) and group mean MxSP were not different in the active and passive trials (7.28 +/- 0.12 and 7.16 +/- 0.10 m x s(-1), respectively, and 7.07 +/- 0.33 and 7.02 +/- 0.24 m x s(-1), respectively; p > 0.05), although both were greater than the control. The percentage of decrement in performance fatigue was similar between all conditions (active, 3.4 +/- 1.3%; passive, 4.0 +/- 2.0%; and control, 3.7 +/- 2.4%). We conclude that there is no difference in high-intensity intermittent running performance when preceded by an active or passive warm-up when matched for post-warm-up Tc. However, repeated sprinting ability is significantly improved after both active and passive warm-ups compared to no warm-up.     

A comparison of VO2max and metabolic variables between treadmill running and treadmill skating

The purpose of this study was to determine differences in VO2max and metabolic variables between treadmill running and treadmill skating. This study also examined VO2max responses during a continuous skating treadmill protocol and a discontinuous skating treadmill protocol. Sixteen male high school hockey players, who had a mean age of 16 +/- 1 years and were of an above-average fitness level, participated in this study. All subjects completed 4 exercise trials: a 1-hour skating treadmill familiarization trial, a treadmill running trial, and 2 randomized skating treadmill trials. Minute ventilation (VE), oxygen consumption VO2), carbon dioxide production VCO2), respiratory exchange ratio (RER), and heart rate were averaged every 15 seconds up to VO2max for each exercise test. The results showed that there was a significant difference (P < 0.05) for VO2max (mL.kg.min) and maximal VCO2 (L.min) between the running treadmill protocol and discontinuous skating treadmill protocol. There was also a significant difference for maximal RER between the discontinuous and continuous skating treadmill protocol and between the discontinuous skating treadmill protocol and running treadmill protocol. In conclusion, the running treadmill elicited a greater VO2max (mL.kg.min) than the skating treadmill did, but when it comes to specificity of ice skating, the skating treadmill may be ideal. Also, there was no significant difference between the discontinuous and continuous skating treadmill protocols. Therefore, a continuous protocol is possible on the skating treadmill without compromising correct skating position and physiologic responses. However, the continuous skating treadmill protocol should undergo validation before other scientists, coaches, and strength and conditioning professionals can apply it correctly.     

Maximal aerobic capacity for repetitive lifting: comparison with three standard exercise testing modes

A multi-stage, repetitive lifting maximal oxygen uptake (VO2max) test was developed to be used as an occupational research tool which would parallel standard ergometric VO2max testing procedures. The repetitive lifting VO2max test was administered to 18 men using an automatic repetitive lifting device. An intraclass reliability coefficient of 0.91 was obtained with data from repeated tests on seven subjects. Repetitive lifting VO2max test responses were compared to those for treadmill, cycle ergometer and arm crank ergometer. The mean +/- SD repetitive lifting VO2max of 3.20 +/- 0.42 l.min-1 was significantly (p less than 0.01) less than treadmill VO2max (delta = 0.92 l.min-1) and cycle ergometer VO2max (delta = 0.43 l.min-1) and significantly greater than arm crank ergometer VO2max (delta = 0.63 l.min-1). The correlation between repetitive lifting oxygen uptake and power output was r = 0.65. VO2max correlated highly among exercise modes, but maximum power output did not. The efficiency of repetitive lifting exercise was significantly greater than that for arm cranking and less than that for leg cycling. The repetitive lifting VO2max test has an important advantage over treadmill or cycle ergometer tests in the determination of relative repetitive lifting intensities. The individual curves of VO2 vs. power output established during the multi-stage lifting VO2max test can be used to accurately select work loads required to elicit given percentages of maximal oxygen uptake.     

Oxidative stress in athletes during extreme endurance exercise

Despite the many known health benefits of exercise, there is a body of evidence suggesting that endurance exercise is associated with oxidative stress. To determine whether extreme endurance exercise induces lipid peroxidation, 11 athletes (3 females, 8 males) were studied during a 50 km ultramarathon (trial 1) and during a sedentary protocol (trial 2) 1 month later. The evening before each trial, with dinner, subjects consumed 75 mg each d(3)-RRR and d(6)-all rac-alpha-tocopheryl acetates. Blood was obtained at baseline, 30 min pre-race, mid-race, post-race, 1 h post-race, 24 h post-race, and at corresponding times during trial 2. All 11 subjects completed the race; average run time was 391 +/- 23 min. Plasma F(2)-isoprostanes increased from 75 +/- 7 pg/ml at pre-race to 131 +/- 17 (p <.02) at post-race, then returned to baseline at 24 h post-race; F(2)-isoprostanes were unchanged during trial 2. Deuterated alpha-tocopherol disappearance rates were faster (2.8 x 10(-4) +/- 0.2 x 10(-4)) during the race compared to the sedentary trial (2.3 x 10(-4) +/- 0.2 x 10(-4); p <.03). These data suggest that extreme endurance exercise results in the generation of lipid peroxidation with a concomitant increase in vitamin E disappearance.     

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

This study examined the effects of dietary manipulation upon the respiratory exchange ratio (R = VCO2/VO2) as a predictor of maximum oxygen uptake (VO2max). 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 on-line system. No significant changes in mean exercise oxygen uptake (VO2), VO2max or maximum functional heart rate (FHRmax) were found between tests. Mean exercise carbon dioxide output (VCO2) and R were significantly lower than normal after the low CHO diet (both p less than 0.001) and significantly higher than normal after the high CHO diet (both p less than 0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p less than 0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p less than 0.05) over the final 5 min of exercise, after the high CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Blood lactate production and recovery from anaerobic exercise in trained and untrained boys

Blood lactate production and recovery from anaerobic exercise were investigated in 19 trained (AG) and 6 untrained (CG) prepubescent boys. The exercises comprised 3 maximal test performances; 2 bicycle ergometer tests of different durations (15 s and 60 s), and running on a treadmill for 23.20 +/- 2.61 min to measure maximal oxygen uptake. Blood samples were taken from the fingertip to determine lactate concentrations and from the antecubital vein to determine serum testosterone. Muscle biopsies were obtained from vastus lateralis. Recovery was passive (seated) following the 60 s test but that following the treadmill run was initially active (10 min), and then passive. Peak blood lactate was highest following the 60 s test (AG, 13.1 +/- 2.6 mmol.1-1 and CG, 12.8 +/- 2.3 mmol.1-1). Following the 15 s test and the treadmill run, peak lactate values were 68.7 and 60.6% of the 60 s value respectively. Blood lactate production was greater (p less than 0.001) during the 15 s test (0.470 +/- 0.128 mmol.1-1.s-1) than during the 60 s test (0.184 +/- 0.042 mmol.1-1.s-1). Although blood lactate production was only nonsignificantly greater in AG, the amount of anaerobic work in the short tests was markedly greater (p less than 0.05-0.01) in AG than CG. Muscle fibre area (type II%) and serum testosterone were positively correlated (p less than 0.05) with blood lactate production in both short tests. Blood lactate elimination was greater (p less than 0.001) at the end of the active recovery phase than in the next (passive) phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of training on muscle metabolism during treadmill sprinting

Sixteen subjects volunteered for the study and were divided into a control (4 males and 4 females) and experimental group (4 males and 4 females, who undertook 8 wk of sprint training). All subjects completed a maximal 30-s sprint on a nonmotorized treadmill and a 2-min run on a motorized treadmill at a speed designed to elicit 110% of maximum oxygen uptake (110% run) before and after the period of training. Muscle biopsies were taken from vastus lateralis at rest and immediately after exercise. The metabolic responses to the 110% run were unchanged over the 8-wk period. However, sprint training resulted in a 12% (P less than 0.05) and 6% (NS) improvement in peak and mean power output, respectively, during the 30-s sprint test. This improvement in sprint performance was accompanied by an increase in the postexercise muscle lactate (86.0 +/- 26.4 vs. 103.6 +/- 24.6 mmol/kg dry wt, P less than 0.05) and plasma norepinephrine concentrations (10.4 +/- 5.4 vs. 12.1 +/- 5.3 nmol/l, P less than 0.05) and by a decrease in the postexercise blood pH (7.17 +/- 0.11 vs. 7.09 +/- 0.11, P less than 0.05). There was, however, no change in skeletal muscle buffering capacity as measured by the homogenate technique (67.6 +/- 6.5 vs. 71.2 +/- 4.5 Slykes, NS).     

Energy expenditure and influence of physiologic factors during marathon running

This study examined energy expenditure and physiologic determinants for marathon performance in recreational runners. Twenty recreational marathon runners participated (10 males aged 41 +/- 11.3 years, 10 females aged 42.7 +/- 11.7 years). Each subject completed a V(.-)O2max and a 1-hour treadmill run at recent marathon pace, and body composition was indirectly determined via dual energy X-ray absorptiometry. The male runners exhibited higher V(.-)O2max (ml x kg(-1) x min(-1)) values (52.6 +/- 5.5) than their female counterparts (41.9 +/- 6.6), although ventilatory threshold (T-vent) values were similar between groups (males: 76.2 +/- 6.1 % of V(.-)O2max, females: 75.1 +/- 5.1%). The male runners expended more energy (2,792 +/- 235 kcal) for their most recent marathon as calculated from the 1-hour treadmill run at marathon pace than the female runners (2,436 +/- 297 kcal). Body composition parameters correlated moderately to highly (r ranging from 0.50 to 0.87) with marathon run time. Also, V(.-)O2max (r = -0.73) and ventilatory threshold (r = -0.73) moderately correlated with marathon run time. As a group, the participants ran near their ventilatory threshold for their most recent marathon (r = 0.74). These results indicate the influence of body size on marathon run performance. In general, the larger male and female runners ran slower and expended more kilocalories than smaller runners. Regardless of marathon finishing time, the runners maintained a pace near their T-vent, and as T-vent or V(.-)O2max increased, marathon performance time decreased.     

The impact of different pacing strategies on five-kilometer running time trial performance

The purpose of this study was to determine the optimal 1.63-km (1-mile) pacing strategy for 5-km running performance in moderately trained women distance runners. Eleven women distance runners (20.7 +/- 0.8 years, 163.8 +/- 2.0 cm, 57.0 +/- 2.2 kg, 51.7 +/- 1.0 ml.kg(-1).min(-1), 18.9 +/- 0.8% fat, 78.1 +/- 1.4% VO(2)max at lactate threshold) performed 2 preliminary 5-km time trials on a treadmill to establish baseline 5-km times. The average 1.63-km split pace of the fastest preliminary trial was manipulated for the first 1.63 km of the experimental trials and run either equal to (EVEN), 3% faster than (3%), or 6% faster than (6%) the current baseline average 1.63-km pace for each subject. Ventilation (V(E)), oxygen consumption VO(2)max )), respiratory exchange ratio, and heart rate were measured continuously. Overall 5-km times were not different (p > 0.05) for the EVEN, 3% and 6% trials finishing in 21:11 (minutes/seconds) +/- 29 seconds, 20:52 +/- 36 seconds and 20:39 +/- 29 seconds, respectively. The fastest time for 8 subjects resulted from the 6% trial and the other 3 subjects' fastest times resulted from the 3% trial. The overall exercise intensity (%VO(2)max , %VO(2)max above lactate threshold, V(E), and respiratory exchange ratio) of the first 1.63-km split was not different between the 3 and 6% trials, despite the 6% trial being 13 seconds faster than the 3% trial. Based on these findings, initial 1.63-km starting paces of a 5-km race can be 3 to 6% greater than current average race pace without negatively impacting performance. In order to optimize 5-km performance, runners should start the initial 1.63 km of a 5-km race at paces 3-6% greater than their current average race pace.     

Influence of plasma catecholamines on the lactate threshold during graded exercise

This investigation examined the relationship among plasma catecholamines, the blood lactate threshold (TLa), and the ventilatory threshold (TVE) in highly trained endurance athletes. Six competitive cyclists and six varsity cross-country runners performed a graded exercise test via two different modalities: treadmill running and bicycle ergometry. Although maximal oxygen consumption (VO2 max) did not differ significantly for the cyclists for treadmill running and cycling (64.6 +/- 1.0 and 63.5 +/- 0.4 ml O2.kg-1-min-1, respectively), both TLa and TVE occurred at a relatively earlier work load during the treadmill run. The opposite was true for the runners as TLa and TVE appeared at an earlier percent of VO2max during cycling compared with treadmill running (60.0 +/- 1.7 vs. 75.0 +/- 4.0%, respectively, TLa). The inflection in plasma epinephrine shifted in an identical manner and occurred simultaneously with that of TLa (r = 0.97) regardless of the testing protocol or training status. Although a high correlation (r = 0.86) existed for the shift in TVE and TLa, this relationship was not as strong as was seen with plasma epinephrine. The results suggest that a causal relationship existed between the inflection in plasma epinephrine and TLa during a graded exercise test. This association was not as strong for TVE and TLa.     

Lovastatin use and muscle damage in healthy volunteers undergoing eccentric muscle exercise.

We did a double-blind, placebo-controlled crossover study of 10 healthy young men taking no medications to determine if ingesting lovastatin is associated with more severe muscle damage after exercise. Five men in the first group took 40 mg of lovastatin daily for 30 days while those in the second group took an identical-appearing placebo. Each volunteer then walked downhill on a -14-degree incline on a treadmill at 3 km per hour for an hour. After a 2-week rest, the subjects were crossed over. Serial serum creatine kinase activity was measured immediately before and 8, 24, 48, 72, 120, and 144 hours after each treadmill session. With each subject serving as his own control, peak mean serum creatine kinase activity (/+- SEM) following treadmill after lovastatin therapy was similar to that following placebo (168.4 +/- 25.8 U per liter versus 146.7 +/- 14.7 U per liter, respectively [P = .9]). With an alpha value of .05, we had greater than a 99% chance of detecting a difference in the rise of serum creatine kinase activity of 200 U per liter between groups. Our data suggest that lovastatin is not an independent risk factor for developing exercise-induced muscle damage using this model of exercise in our study population.     

Validity of the heart rate deflection point as a predictor of lactate threshold during running.

During an incremental run test, some researchers consistently observe a heart rate (HR) deflection at higher speeds, but others do not. The present study was designed to investigate whether differences in test protocols could explain the discrepancy. Additionally, we sought to determine whether the HR deflection point accurately predicts lactate threshold (LT). Eight trained runners performed four tests each: 1) a treadmill test for maximal O(2) uptake, 2) a Conconi test on a 400-m track with speeds increasing approximately 0.5 km/h every 200 m, 3) a continuous treadmill run with speeds increasing 0.5 km/h every minute, and 4) a continuous LT treadmill test in which 3-min stages were used. All subjects demonstrated an HR deflection on the track, but only one-half of the subjects showed an HR deflection on the treadmill. On the track the shortening of stages with increasing speeds contributed to a loss of linearity in the speed-HR relationship. Additionally, the HR deflection point overestimated the LT when a continuous treadmill LT protocol was used. In conclusion, the HR deflection point was not an accurate predictor of LT in the present study.     

Repeated exercise paired with "imperceptible" dead space loading does not alter VE of subsequent exercise in humans.

We employed an associative learning paradigm to test the hypothesis that exercise hyperpnea in humans arises from learned responses forged by prior experience. Twelve subjects undertook a "conditioning" and a "nonconditioning" session on separate days, with order of performance counterbalanced among subjects. In both sessions, subjects performed repeated bouts of 6 min of treadmill exercise, each separated by 5 min of rest. The only difference between sessions was that all the second-to-penultimate runs of the conditioning session were performed with added dead space in the breathing circuit. Cardiorespiratory responses during the first and last runs (the "control" and "test" runs) were compared for each session. Steady-state exercise end-tidal PCO(2) was significantly lower (P = 0.003) during test than during control runs for both sessions (dropping by 1.8 +/- 2 and 1.4 +/- 3 Torr during conditioning and nonconditioning sessions, respectively). This and all other test-control run differences tended to be greater during the first session performed regardless of session type. Our data provide no support for the hypothesis implicating associative learning processes in the ventilatory response to exercise in humans.     

Examining the influence of hydration status on physiological responses and running speed during trail running in the heat with controlled exercise intensity

The purpose of this study was to determine the effects of dehydration at a controlled relative intensity on physiological responses and trail running speed. Using a randomized, controlled crossover design in a field setting, 14 male and female competitive, endurance runners aged 30 ± 10.4 years completed 2 (hydrated [HY] and dehydrated [DHY]) submaximal trail runs in a warm environment. For each trial, the subjects ran 3 laps (4 km per lap) on trails with 4-minute rests between laps. The DHY were fluid restricted 22 hours before the trial and during the run. The HY arrived euhydrated and were given water during rest breaks. The subjects ran at a moderate pace matched between trials by providing pacing feedback via heart rate (HR) throughout the second trial. Gastrointestinal temperature (T(GI)), HR, running time, and ratings of perceived exertion (RPE) were monitored. Percent body mass (BM) losses were significantly greater for DHY pretrial (-1.65 ± 1.34%) than for HY (-0.03 ± 1.28%; p < 0.001). Posttrial, DHY BM losses (-3.64 ± 1.33%) were higher than those for HY (-1.38 ± 1.43%; p < 0.001). A significant main effect of T(GI) (p = 0.009) was found with DHY having higher T(GI) postrun (DHY: 39.09 ± 0.45°C, HY: 38.71 ± 0.45°C; p = 0.030), 10 minutes post (DHY: 38.85 ± 0.48°C, HY: 38.46 ± 0.46°C; p = 0.009) and 30 minutes post (DHY: 38.18 ± 0.41°C, HY: 37.60 ± 0.25°C; p = 0.000). The DHY had slower run times after lap 2 (p = 0.019) and lap 3 (p = 0.025). The DHY subjects completed the 12-km run 99 seconds slower than the HY (p = 0.027) subjects did. The RPE in DHY was slightly higher than that in HY immediately postrun (p = 0.055). Controlling relative intensity in hypohydrated runners resulted in slower run times, greater perceived effort, and elevated T(GI), which is clinically meaningful for athletes using HR as a gauge for exercise effort and performance.     

Growth hormone responses to repeated maximal cycle ergometer exercise at different pedaling rates.

The present study examined the growth hormone (GH) response to repeated bouts of maximal sprint cycling and the effect of cycling at different pedaling rates on postexercise serum GH concentrations. Ten male subjects completed two 30-s sprints, separated by 1 h of passive recovery on two occasions, against an applied resistance equal to 7.5% (fast trial) and 10% (slow trial) of their body mass, respectively. Blood samples were obtained at rest, between the two sprints, and for 1 h after the second sprint. Peak and mean pedal revolutions were greater in the fast than the slow trial, but there were no differences in peak or mean power output. Blood lactate and blood pH responses did not differ between trials or sprints. The first sprint in each trial elicited a serum GH response (fast: 40.8 +/- 8.2 mU/l, slow: 20.8 +/- 6.1 mU/l), and serum GH was still elevated 60 min after the first sprint. The second sprint in each trial did not elicit a serum GH response (sprint 1 vs. sprint 2, P < 0.05). There was a trend for serum GH concentrations to be greater in the fast trial (mean GH area under the curve after sprint 1 vs. after sprint 2: 1,697 +/- 367 vs. 933 +/- 306 min x mU(-1) x l(-1); P = 0.05). Repeated sprint cycling results in an attenuation of the GH response.