Effect of work duration on physiological and rating scale of perceived exertion responses during self-paced interval training

This study compared running velocity, physiological responses, and perceived exertion during self-paced interval training bouts differing only in work bout duration. Twelve well-trained runners (nine males, three females, 28+/-5 years, VO2 max 65+/-6 mL min(-1) kg(-1)) performed preliminary testing followed by four "high-intensity" interval sessions (Latin squares, 1 session week(-1) over 4 weeks) consisting of 24 x 1, 12 x 2, 6 x 4, or 4 x 6-min running bouts with a 1:1 work-to-rest interval (total session duration 48 min). The average running velocity decreased (93%, 88%, 86%, 84% vVO2 max, P < 0.01) with increasing work duration. Peak VO2 averaged about 92+/-4% of VO2 max for 2-, 4-, and 6-min intervals compared with only 82+/-5% for 1-min bouts (P < 0.001). Six of 12 athletes achieved their highest average VO2 and heart rate during 4-min intervals. The average RPEpeak (rating scale of perceived exertion) was approximately 17+/-1 for all four interval sessions. RPE increased by 2-4 U during an interval training session. The mean lactate concentration was similar across sessions (4.3+/-1.1-4.6+/-1.5 mmol L(-1)). Under self-paced conditions, well-trained runners perform "high-intensity" intervals at an RPE of approximately 17, independent of interval duration. The optimal interval duration for eliciting a high physiological load is 3-5 min under these training conditions. Increases in RPE during an interval bout are not associated with increasing blood lactate concentration.     

Changing the number of submaximal exercise bouts effects calculation of MAOD

The aim of this present study was to evaluate the effect of the number of submaximal exercise bouts used to construct the power-VO2 regression, on calculations of MAOD through the sequential and systematic removal of the highest and lowest submaximal VO2 values from the standard ten point regression line. Eight trained male cyclists participated in this study. The mean (+/- SD) age, height, weight and VO2max for the subjects were 25+/-7 yr, 178.2+/-3.0 cm, 69.9+/-4.9 kg and 57.5+/-6.9 ml x kg(-1) x min(-1). After VO2max testing each subject undertook ten submaximal exercise bouts at between 30% and 90% VO2max and one supramaximal bout calculated to elicit 100% VO2max. Expired gases were measured via open circuit spirometry. The mean power output of the supramaximal bout was 336.5+/-442.5 W and the mean duration was 269.4+/-42.9 s. The correlation coefficients ranged from 0.981 to 0.996 while the MAOD values ranged from 29.6+/-15.7 ml O2 eq x kg(-1) to 61.3+/-44.7 ml O2 eq x kg(-1). When compared to the standard ten points, as a percentage difference, this difference ranged from 4.1+/-3.6% to 83.7+/-54.9%. The main finding of this study is that inaccuracies occur in the measurement of MAOD when less than ten points are used in the calculation. Further study is required for the development of a standardised protocol for the accurate, valid and reliable measurement of MAOD.     

Recovery kinetics throughout successive bouts of various exercises in elite cyclists

PURPOSE: In the present study we investigated whether a high volume of cycling training would influence the metabolic changes associated with a succession of three exhaustive cycling exercises. METHODS: Seven professional road cyclists (VO2max: 74.3 +/- 3.7 mL.min.kg; maximal power tolerated: 475 +/- 18 W; training: 22 +/- 3 h.wk) and seven sport sciences students (VO2max: 54.2 +/- 5.3 mL.min.kg; maximal power tolerated: 341 +/- 26 W; training: 6 +/- 2 h.wk) performed three different exhaustive cycling exercise bouts (progressive, constant load, and sprint) on an electrically braked cycloergometer positioned near the magnetic resonance scanner. Less than 45 s after the completion of each exercise bout, recovery kinetics of high-energy phosphorylated compounds and pH were measured using P-MR spectroscopy. RESULTS: Resting values for phosphomonoesters (PME) and phosphodiesters (PDE) were significantly elevated in the cyclist group (PME/ATP: 0.82 +/- 0.11 vs 0.58 +/- 0.19; PDE/ATP: 0.27 +/- 0.03 vs 0.21 +/- 0.05). Phosphocreatine (PCr) consumption and inorganic phosphate (Pi) accumulation measured at end of exercise bouts 1 (PCr: 6.5 +/- 3.2 vs 10.4 +/- 1.6 mM; Pi: 1.6 +/- 0.7 vs 6.8 +/- 3.4 mM) and 3 (PCr: 5.6 +/- 2.4 vs 9.3 +/- 3.9 mM; Pi: 1.5 +/- 0.5 vs 7.7 +/- 3.3 mM) were reduced in cyclists compared with controls. During the recovery period after each exercise bout, the pH-recovery rate was larger in professional road cyclists, whereas the PCr-recovery kinetics were significantly faster for cyclists only for bout 3. DISCUSSION: Whereas the PDE and PME elevation at rest in professional cyclists may indicate fiber-type changes and an imbalance between glycogenolytic and glycolytic activity, the lower PCr consumption during exercise and the faster pH-recovery kinetic clearly suggest an improved mitochondrial function.     

The lactate minimum test protocol provides valid measures of cycle ergometer VO(2)peak

AIM: The aim of the present study was to investigate the validity of the Lactate Minimum Test (LMT) for the determination of peak VO(2) on a cycle ergometer and to determine the submaximal oxygen uptake (VO(2)) and pulmonary ventilation (VE) responses in an incremental exercise test when it is preceded by high intensity exercise (i.e., during a LMT). METHODS: Ten trained male athletes (triathletes and cyclists) performed 2 exercise tests in random order on an electromagnetic cycle ergometer: 1). Control Test (CT): an incremental test with an initial work rate of 100 W, and with 25 W increments at 3-min intervals, until voluntary exhaustion; 2). LMT: an incremental test identical to the CT, except that it was preceded by 2 supramaximal bouts of 30-sec (approximately 120% VO(2)peak) with a 30-sec rest to induce lactic acidosis. This test started 8 min after the induction of acidosis. RESULTS: There was no significant difference in peak VO(2) (65.6+/-7.4 ml x kg(-1) x min(-1); 63.8 +/- 7.5 ml x kg(-1) x min(-1) to CT and LMT, respectively). However, the maximal power output (POmax) reached was significantly higher in CT (300.6+/-15.7 W) than in the LMT (283.2+/-16.0 W). VO(2) and VE were significantly increased at initial power outputs in LMT. CONCLUSION: Although the LMT alters the submaximal physiological responses during the incremental phase (greater initial metabolic cost), this protocol is valid to evaluate peak VO(2), although the POmax reached is also reduced.     

Exercise-induced effects on growth hormone levels are associated with ghrelin changes only in presence of prolonged exercise bouts in male athletes

AIM: The aim of this study was to evaluate growth hormone (GH) and ghrelin levels in response to physical exercise in athletes. METHODS: Two different exercise workloads were administered in two different groups of athletes. Group A athletes (19 males, 18 females; mean age +/- standard deviation: 25+/-6.7 years), performing a 60-90 min training session at approximately 80% of VO2max, were sampled for GH and ghrelin determinations before and immediately at the end of a training session on-the-field. Group B athletes (4 males; mean age: 28.2+/-7.2 years) performed two consecutive 30-min cycling sessions at 80% of individual VO2max at different time intervals between bouts (2 and 6 h) in two different days. GH and ghrelin concentrations were determined in blood samples collected at 15-min intervals during exercise and following 1 h of recovery. RESULTS: In group A athletes, GH levels increased after the training session (P<0.0001), with no differences between males and females. In male athletes, ghrelin levels significantly decreased after the training session (from 1 506.4+/-859 to 1 254.8+/-661.7 pg/mL, P<0.05), while no significant changes were found in females. No correlations were observed between GH and ghrelin levels at rest and after training. In group B athletes, GH levels significantly increased after the first exercise bouts (peak: 26.8+/-11.2 and 17.3+/-3.5 ng/mL, respectively), while the pattern of GH response was different after the second bout of exercise performed at 2-h or 6-h interval. In fact, peak GH concentration in response to the second bout (4.3+/-1.6 ng/mL) was lower (P<0.01) than that of the first bout when the interval elapsed was only 2 h, while a recovery of GH responsiveness was evident after the 6-h interval between the two exercise bouts (11.9+/-3.3 ng/mL). As far as ghrelin levels are concerned, no significant changes were observed during and after the two exercise bouts performed at the different time intervals. CONCLUSION: GH responses to prolonged exercise bouts (60-90 min) are associated with changes in ghrelin levels only in male athletes, while repeated exercise bouts of lower duration (30 min), capable to determine marked GH responses, are divorced from changes in ghrelin concentrations.     

Prior heavy exercise enhances performance during subsequent perimaximal exercise

PURPOSE: To test the hypothesis that prior heavy exercise increases the time to exhaustion during subsequent perimaximal exercise. METHODS: Seven healthy males (mean +/- SD 27 +/- 3 yr; 78.4 +/- 0.7 kg) completed square-wave transitions from unloaded cycling to work rates equivalent to 100, 110, and 120% of the work rate at VO2peak (W-[VO2peak) after no prior exercise (control, C) and 10 min after a 6-min bout of heavy exercise at 50% Delta (HE; half-way between the gas exchange threshold (GET) and VO2peak), in a counterbalanced design. RESULTS: Blood [lactate] was significantly elevated before the onset of the perimaximal exercise bouts after prior HE (approximately 2.5 vs approximately 1.1 mM; P < 0.05). Prior HE increased time to exhaustion at 100% (mean +/- SEM. C: 386 +/- 92 vs HE: 613 +/- 161 s), 110% (C: 218 +/- 26 vs HE: 284 +/- 47 s), and 120% (C: 139 +/- 18 vs HE: 180 +/- 29 s) of W-VO2peak, (all P < 0.01). VO2 was significantly higher at 1 min into exercise after prior HE at 110% W-VO2peak (C: 3.11 +/- 0.14 vs HE: 3.42 +/- 0.16 L x min(-1); P < 0.05), and at 1 min into exercise (C: 3.25 +/- 0.12 vs HE: 3.67 +/- 0.15; P < 0.01) and at exhaustion (C: 3.60 +/- 0.08 vs HE: 3.95 +/- 0.12 L x min(-1); P < 0.01) at 120% of W-VO2peak. CONCLUSIONS: This study demonstrate that prior HE, which caused a significant elevation of blood [lactate], resulted in an increased time to exhaustion during subsequent perimaximal exercise presumably by enabling a greater aerobic contribution to the energy requirement of exercise.     

Effect of short-term fat adaptation on high-intensity training

PURPOSE: To determine the effect of short-term (3-d) fat adaptation on high-intensity exercise training in seven competitive endurance athletes (maximal O2 uptake 5.0 +/- 0.5 L x min(-1), mean +/-SD). METHODS: Subjects consumed a standardized diet on d-0 then, in a randomized cross-over design, either 3-d of high-CHO (11 g x kg(-1)d(-1) CHO, 1 g x kg(-1) x d(-1) fat; HICHO) or an isoenergetic high-fat (2.6 g CHO x kg(-1) x d(-1), 4.6 g FAT x kg(-1) x d(-1); HIFAT) diet separated by an 18-d wash out. On the 1st (d-1) and 4th (d-4) day of each treatment, subjects completed a standardized laboratory training session consisting of a 20-min warm-up at 65% of VO2peak (232 +/- 23W) immediately followed by 8 x 5 min work bouts at 86 +/- 2% of VO2peak (323 +/- 32 W) with 60-s recovery. RESULTS: Respiratory exchange ratio (mean for bouts 1, 4, and 8) was similar on d-1 for HIFAT and HICHO (0.91 +/- 0.04 vs 0.92 +/- 0.03) and on d-4 after HICHO (0.92 +/- 0.03) but fell to 0.85 +/- 0.03 (P < 0.05) on d-4 after HIFAT. Accordingly, the rate of fat oxidation increased from 31 +/- 13 on d-1 to 61 +/- 25 micromol x kg(-1) x min(-1) on d-4 after HIFAT (P < 0.05). Blood lactate concentration was similar on d-1 and d-4 of HICHO and on d-1 of HIFAT (3.5 +/- 0.9 and 3.2 +/- 1.0 vs 3.7 +/- 1.2 mM) but declined to 2.4 +/- 0.5 mM on d-4 after HIFAT (P < 0.05). Ratings of perception of effort (legs) were similar on d-1 for HIFAT and HICHO (14.8 +/- 1.5 vs 14.1 +/- 1.4) and on d-4 after HICHO (13.8 +/- 1.8) but increased to 16.0 +/- 1.3 on d-4 after HIFAT (P < 0.05). CONCLUSIONS: 1) competitive endurance athletes can perform intense interval training during 3-d exposure to a high-fat diet, 2) such exercise elicited high rates of fat oxidation, but 3) compared with a high-carbohydrate diet, training sessions were associated with increased ratings of perceived exertion.     

Inverse relationship between VO2max and economy/efficiency in world-class cyclists

PURPOSE: To determine the relationship that exists between VO2max and cycling economy/efficiency during intense, submaximal exercise in world-class road professional cyclists. METHODS Each of 11 male cyclists (26+/-1 yr (mean +/- SEM); VO2max: 72.0 +/- 1.8 mL x kg(-1) x min(-1)) performed: 1) a ramp test for O2max determination and 2) a constant-load test of 20-min duration at the power output eliciting 80% of subjects' VO2max during the previous ramp test (mean power output of 385 +/- 7 W). Cycling economy (CE) and gross mechanical efficiency (GE) were calculated during the constant-load tests. RESULTS: CE and GE averaged 85.2 +/- 2.3 W x L(-1) x min(-1) and 24.5 +/- 0.7%, respectively. An inverse, significant correlation was found between 1) VO2max (mL x kg(-0.32) x min(-1)) and both CE (r = -0.71; P = 0.01) and GE (-0.72; P = 0.01), and 2) VO2max (mL x kg(-1) x min(-1)) and both CE (r = -0.65; P = 0.03) and GE (-0.64; P = 0.03). CONCLUSIONS: A high CE/GE seems to compensate for a relatively low VO2max in professional cyclists.     

Anaerobic exercise induces moderate acute phase response

PURPOSE: It was intended to compare the immune reaction after single and repeated short bouts of anaerobic exercise. METHODS: Twelve unspecifically trained male subjects (27 +/- 2 yr, 75 +/- 2 kg, VO(2peak) 52 +/- 2 mL x min(-1) x kg(-1)) performed one 60-s all-out test (SMT) on a cycling ergometer and the same test followed by eight 10-s all-out tests every 5 min (AN-TS). These tests and one control day (Co-Day) were applied in randomized order. At rest and 15 min, 2 h, and 24 h after cessation of exercise the following venous blood parameters were determined: concentration of neutrophils and (CD16(+ -)) premacrophages (both flow-cytometrically), interleukin 6 and 8 (IL-6, IL-8), C-reactive protein (CRP) and cortisol. RESULTS: Two hours after cessation of exercise the neutrophils increased stronger after AN-TS than after SMT (P < 0.01). The peak in the number of premacrophages occurred earlier after SMT (15 min post; P < 0.01 to Co-Day) than after AN-TS (2 h post; P < 0.05 to Co-Day). IL-6 was elevated at 15 min and 2 h after AN-TS (P < 0.01 to SMT and Co-Day) but only slightly 2 h after SMT (P < 0.01 to Co-Day). There were no significant changes in IL-8. CRP was the only elevated parameter 24 h postexercise exclusively after AN-TS (P < 0.05 to Co-Day). CONCLUSIONS Repeated short anaerobic bouts of cycling lead to an acute phase response, which is more pronounced than after a single bout. Athletes should take care in performing such training sessions several times a week because signs of inflammation are detectable even 24 h after cessation of exercise.     

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.     

Increased inflammatory response of blood cells to repeated bout of endurance exercise

PURPOSE: The aim of the present study was to assess the effects of two 30-min consecutive exercise bouts on a treadmill at 80% VO2max separated by a 4-h rest interval, on blood cell counts and the production of tissue factor, cytokines, and eicosanoids in lipopolysaccharide (LPS)-stimulated blood. METHODS: Blood samples were taken from eight endurance athletes (mean+/-SD: age, 23.4+/-1.6 yr; VO2max, 66.0+/-6.4 L.min.kg), both immediately before and after each exercise bout. Cell counts were performed, and the heparinized blood was subjected to LPS-stimulation for 2 h. RESULTS: There was a significant rise in white blood cell counts after the first exercise bout (81%, P<0.001), increasing to 123% (P<0.001) after the second bout. After the first and second runs, the tissue factor activity in LPS-stimulated monocytes was enhanced by 70% (not significant) and almost 200% (P=0.012), respectively, compared with baseline values. The high monocyte responsiveness after the second bout remained undiminished 2 h later. Similarly, the interleukin (IL)-8 production had risen 70% (P=0.022) after the first run and 100% (P=0.005) after the second run, relative to baseline values. IL-6 or leukotriene B4 levels did not change significantly. The rise in LPS-induced thromboxane B2 was 80% (P=0.024) after the first run and 63% after the second run (P=0.071, not significant). VO2max correlated negatively with the concentration of granulocytes immediately after the second exercise bout (R=0.864, P=0.006). CONCLUSIONS: The results of this study are evidence that two physical exercise bouts separated by a 4-h rest are associated with an enhanced propensity of the blood cells to generate tissue factor activity and some proinflammatory products compared with one exercise bout.     

Rate and amplitude of adaptation to intermittent and continuous exercise in older men

PURPOSE: This study determined the amplitude and rate of adaptation to 10 wk of continuous (CEx) and intermittent exercise (IEx) in a group of older men when the training intensity and total amount of work completed by each exercise group were the same. METHODS: Ten healthy men were assigned to either a CEx (63 +/- 1 yr) or IEx (65 +/- 1 yr) group while a further five subjects (65 +/- 1 yr) acted as nonexercising controls (CON). The three groups (CEx, IEx, and CON) were matched for age, peak oxygen uptake (VO2peak), and cardiac output (Qpeak) before commencing training. The CEx group trained for 30 min at an intensity corresponding to 70-75% VO2peak, and the IEx group trained for a total exercise time of 30 min using intermittent exercise (60-s exercise, 60-s rest) at the same absolute intensity as the CEx group (CEx 112 +/- 5W; IEx 112 +/- 5W). The exercise groups trained three times per week and completed a similar amount of work during each training session (CEx, 199 +/- 9 kJ; IEx 195 +/- 9 kJ, P = 0.67). RESULTS: The CEx and IEx groups had similar and significant amplitude increases in peak VO2, ventilation (VEpeak), power, Q, and SV after training. Peak VO2, Qpeak, SVpeak, and peak arteriovenous O2 difference for the CON group were unchanged. The change in VO2peak, peak ventilation, and peak power for CEx and IEx groups were best described by a linear model. Moreover, the CEx and IEx groups had the same rate of change in VO2peak (CEx: 0.02 +/- 0.00 L x min(-1) x wk(-1), IEx: 0.02 +/- 0.00 L x min(-1) x wk(-1), P = 0.32), VEpeak (CEx: 2.0 +/- 0.2 L x min(-1) x wk(-1), IEx: 1.2 +/- 0.5 L x min(-1) x wk(-1), P = 0.10), and peak power (CEx: 2.6 +/- 0.4 W x wk(-1), IEx: 2.6 +/- 0.4 W x wk(-1), P = 0.92). CONCLUSION: These results suggest that the amplitude and rate of change of select adaptations in men aged 60-70 yr are independent of the mode of training (i.e., continuous or intermittent exercise) when the absolute training intensity and the total amount of work completed were similar.     

Effect of training status and relative exercise intensity on physiological responses in men

PURPOSE: This study examined the effect of training status and relative exercise intensity on physiological responses to endurance exercise in humans. METHODS: Seven endurance trained (TR: peak oxygen uptake [VO2peak] = 65.8 +/- 2.4 mL x kg(-1) min(-1)) and six untrained (UT: VO2peak = 46.2 +/- 1.9 mL x kg(-1) x min(-1)) men cycled for 60 min, either at a work rate corresponding to approximately 70% VO2peak or approximately 95% lactate threshold (LT). RESULTS: The work rate and relative exercise intensity (i.e., % VO2peak) for UT 95% LT were lower (P < 0.01) than for all of the other trials. Although the work rate for UT 70% VO2peak was lower (P < 0.001) than for TR 70% VO2peak and TR 95% LT, average heart rate (HR) for the trial was higher (P < 0.01) throughout exercise in UT 70% VO2peak compared with all of the other trials. Plasma lactate and ammonia concentrations were greater (P < 0.01) during exercise in UT 70% VO2peak compared with all of the other trials. There was a tendency (P = 0.077) for plasma hypoxanthine to be greater at 60 min in UT 70% VO2peak compared with the other trials. At no time were any of the plasma metabolite concentrations different between the UT 95% LT, TR 95% LT and TR 70% VO2peak trials. CONCLUSIONS: These data demonstrate that HR and plasma markers of metabolic stress were greater in UT compared with TR when exercise was performed at 70% VO2peak but were similar during exercise at 95% LT.     

Heart rate and performance parameters in elite cyclists: a longitudinal study

PURPOSE: This study was designed to evaluate the stability of target heart rate (HR) values corresponding to performance markers such as lactate threshold (LT) and the first and second ventilatory thresholds (VT1, VT2) in a group of 13 professional road cyclists (VO2max, approximately 75.0 mL x kg(-1) x min(-1)) during the course of a complete sports season. METHODS: Each subject performed a progressive exercise test on a bicycle ergometer (ramp protocol with workload increases of 25 W x min(-1)) three times during the season corresponding to the "active" rest (fall: November), precompetition (winter: January), and competition periods (spring: May) to determine HR values at LT, VT1 and VT2. RESULTS: Despite a significant improvement in performance throughout the training season (i.e., increases in the power output eliciting LT, VT1, or VT2), target HR values were overall stable (HR at LT: 154 +/- 3, 152 +/- 3, and 154 +/- 2 beats x min(-1); HR at VT1: 155 +/- 3, 156 +/- 3, and 159 +/- 3 beats x min(-1); and at VT2: 178 +/- 2, 173 +/- 3, and 176 +/- 2 beats x min(-1) during rest, precompetition, and competition periods, respectively). CONCLUSION: A single laboratory testing session at the beginning of the season might be sufficient to adequately prescribe training loads based on HR data in elite endurance athletes such as professional cyclists. This would simplify the testing schedule generally used for this type of athlete.     

Influence of continuous and interval training on oxygen uptake on-kinetics

PURPOSE: To examine the relative effectiveness of moderate-intensity continuous training and high-intensity interval training on pulmonary O2 uptake (VO2) kinetics at the onset of moderate- and severe-intensity cycle exercise in previously sedentary subjects. METHODS: Twenty-three healthy subjects (11 males; mean +/- SD age 24 +/- 5 yr; VO2peak 34.3 +/- 5.5 mL x kg(-1) x min(-1)) were assigned to one of three groups: a continuous training group that completed three to four sessions per week of 30-min duration at 60% VO2peak (LO); an interval training group that completed three to four sessions per week involving 20 x 1-min exercise bouts at 90% VO2peak separated by 1-min rest periods (HI); or a control group (CON). Before and after the 6-wk intervention period, all subjects completed a series of step exercise tests to moderate and severe work rates during which pulmonary VO2 was measured breath-by-breath. RESULTS: ANOVA revealed that continuous and interval training were similarly effective in reducing the phase II VO2 time constant during moderate (LO: from 31 +/- 8 to 23 +/- 5 s; HI: from 32 +/- 9 to 21 +/- 4 s; both P < 0.05; CON: from 30 +/- 6 to 29 +/- 7 s; NSD) and severe exercise (LO: from 35 +/- 6 to 24 +/- 7 s; HI: from 32 +/- 11 to 24 +/- 7 s; both P < 0.05; CON: from 27 +/- 7 to 25 +/- 5 s; NSD) and in reducing the amplitude of the VO2 slow component (LO: from 0.38 +/- 0.10 to 0.29 +/- 0.09 L x min(-1); HI: from 0.41 +/- 0.28 to 0.30 +/- 0.28 L x min(-1); both P < 0.05; CON: from 0.54 +/- 0.22 to 0.66 +/- 0.38 L.min; NSD). CONCLUSIONS: Six weeks of low-intensity continuous training and high-intensity interval training were similarly effective in enhancing VO2 on-kinetics following step transitions to moderate and severe exercise in previously untrained subjects.     

Acceleration with exercise during head-down bed rest preserves upright exercise responses

INTRODUCTION: This study was designed to elucidate the effect of short-arm centrifuge-induced artificial gravity with exercise training during ground-based simulated spaceflight, i.e., prolonged head-down bed rest (HDBR), on respiratory and cardiovascular responses to upright exercise. METHODS: There were 10 healthy men who underwent 20 d of -6 degrees HDBR, and were assigned to either a countermeasure (CM) group (n = 5) or a no countermeasure (No-CM) group (n = 5). The subjects in the CM group performed two sessions (20 min each session, 40 min total) of short-arm centrifuge-induced artificial gravity with exercise training in a supine position on alternate days (10 d total) during HDBR. The first session was set at 0.8-1.4 G load at heart level with a constant exercise intensity (60 W), and the second session began with a 0.3 G load at heart level with an interval exercise protocol (40-80% peak oxygen uptake; VO2peak). The measurements of respiratory and cardiovascular responses to incremental exercise were performed pre- and post-HDBR. RESULTS: The 20 d of HDBR increased minute expired ventilation, heart rate, and respiratory exchange ratio and decreased stroke volume during submaximal exercise in the No-CM group, whereas these parameters were unchanged in the CM group. In the No-CM group, VO2peak decreased significantly (47.0 +/- 8.6 to 34.8 +/- 6.8 ml x kg(-1) x min(-1), p < 0.05), whereas VO2peak in the CM group did not show a significant decrease following 20 d of HDBR (47.7 +/- 10.0 to 43.9 +/- 8.9 ml x kg(-1) x min(-1)). These results suggest that short-arm centrifuge-induced artificial gravity with exercise training is effective in maintaining respiratory and cardiovascular responses to upright exercise.     

Increased VLDL-TAG turnover during and after acute moderate-intensity exercise

PURPOSE AND METHODS: Breakdown rates of very low density lipoprotein triacylglycerols (VLDL-TAG) were quantified before (3 h), during (45 min), and after (3 h) moderate physical exercise at 40% VO2 max in young sedentary subjects (four male and four female, age 29.8 +/-1.6 yr, BMI 24.1 +/- 0.9 kg x m, VO2max 37.0 +/- 1.7 mL x kg x min), using boluses of H5-glycerol (100 mu mol x kg) and H2-palmitate (6.6 mu mol x kg). The catabolic rates of VLDL-TAG were calculated from the decay in the isotopic enrichment using a single-pool model. The results were compared with those obtained during 6 h of rest in five of the same volunteers. RESULTS: VLDL-TAG concentration remained constant throughout the study with exercise (P = NS). The fractional catabolic rate was nearly doubled from rest to exercise (P < 0.05 vs rest) and increased to an even greater extent during the early phase of recovery (P < 0.001 vs rest). During the late recovery phase, the value returned to the preexercise value (P = NS vs rest). The values for the absolute catabolic rate (kabs) followed the same trend. CONCLUSION: VLDL-TAG turnover was increased during exercise and during the early phase of recovery.     

Effect of prior exercise on VO(2) slow component is not related to muscle temperature

INTRODUCTION: It has been widely reported that the VO(2) slow component is reduced in the second of two bouts of heavy exercise. It has also been shown that an increase in muscle temperature (Tm) produced by wearing hot-water-perfused pants causes a reduction in the VO(2) slow component. Therefore, the aim of this study was to investigate whether the effect of prior heavy exercise on the VO(2) slow component of subsequent heavy exercise is related to the warming-up of the exercising limbs. METHODS: Six male subjects completed an exercise protocol consisting of two constant-load exercise bouts (EX-1 and EX-2) at 90% VO(2peak), separated by 6 min of rest. The Tm of the m. vastus lateralis was measured with an indwelling thermistor. Seven days later, the subjects completed a second exercise protocol consisting of a passive warming-up of the upper legs until the same Tm was reached as after EX-1, followed by a constant-load work bout (EX-3) identical to EX-1 and EX-2. RESULTS: Tm reached comparable levels at the start of EX-2 and EX-3 (37.3 +/- 0.6 degrees C and 37.2 +/- 0.3 degrees C, respectively). The VO(2) slow component (measured as deltaVO(2)(6-2 min)) was reduced by 57% after prior heavy exercise ( < 0.05), whereas no significant reduction was observed after prior passive warming-up. CONCLUSIONS: The results of this study indicate that the reduction in VO(2) slow component observed after prior heavy exercise cannot be explained by an increase in muscle temperature of the upper legs.     

Ventilatory and gas exchange responses during heavy constant work-rate exercise.

PURPOSE: At constant work-rates below the gas exchange threshold (VO(2 theta)), VO(2) normally achieves steady-state values within 3 min, whereas at heavier work-rates, VO(2) may continue to rise. The VO(2) response to heavy exercise can be described by a three-exponential model with the slow phase usually commencing 2-3 min after the onset of exercise. The aim of our study was to estimate precisely the VO(2), VCO(2), VE and f(C) required for above-VO(2 theta) exercise from the relationship of the specific variable to work-rate below VO(2 theta) and to compare this with the actual value achieved. METHODS: Nine cyclists performed five constant work-rates of 8 min duration, four below VO(2 theta) (40, 80, 120, 160 W) and one midway between VO(2 theta) and VO(2max) (295 +/- 34 W). The VO(2), VCO(2), VE and f(C) were averaged for the final 2 min of each below-VO(2 theta) test and were found to be linear with respect to work-rate (average r2 >0.95). Variables for the above-VO(2 theta) work-rate were predicted by extrapolation and compared with the actual measured values at the end of the exercise bout. RESULTS: VO(2) exceeded the predicted value by 0.48 +/- 0.21 L x min(-1) (12.4 +/- 5.1%), VCO(2) by 0.78 +/- 0.26 L x min(-1) (23.2 +/- 7.2%), VE by 40.3 +/- 16.3 L x min(-1) (51.0 +/- 23.1%), and f(C) by 12.2 +/- 12.5 beats x min(-1) (8.8 +/- 9.3%), all P < 0.0001 except f(C) P < 0.02, paired t-test. The point at which VO(2) during above-VO(2 theta) exercise exceeded the predicted value (145.7 +/- 64.9 s) agreed with the point at which the slow component of VO(2) began, as determined by nonlinear regression analysis (131.5 +/- 44.3 s, P = NS, ANOVA). CONCLUSION: There is an excessive metabolic response to heavy exercise over and above that predicted by extrapolation from light-moderate exercise and this excess VO(2) approximates on average to the slow phase of a three-compartment exponential model.