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A combined method for estimating ventilatory threshold.

BACKGROUND: The aims of this study were to compare two new methods (Dmax and CUSUM) for determination of the ventilatory threshold and to examine the consequences of estimation by application of these methods in combination. METHODS EXPERIMENTAL DESIGN: a comparative design was used. SETTING: the study was performed in the Exercise Physiology Laboratory in the Faculty of Medicine, Selçuk University. PARTICIPANTS: thirty-two untrained males (20.6 +/- 1.2 yrs) performed an incremental exercise test on a cycle ergometer. INTERVENTIONS: there is no intervention. MEASURES: ventilatory and gas exchange variables were measured breath-by-breath. The ventilatory thresholds were detected by conventional linear regression, CUSUM, Dmax and combined CUSUM-Dmax methods. RESULTS: The ventilatory thresholds determined by Dmax method gave the highest r-values compared to the criterion method. There was no statistical difference between thresholds determined by all methods or by the same method using different variables. Ventilatory thresholds could not be determined by the conventional linear regression method in three subjects but were determined in all subjects by the other three methods. CONCLUSIONS: Although all methods presented in this study can be used in the determination of ventilatory threshold, the Dmax method was found to be the most valid one. When using the CUSUM method, combining it with the Dmax method increases the validity of the measurement.

Adult↗

Normal values in adults during exercise testing.

The cardiopulmonary response to 1-minute incremental cycle exercise in a population of 77 sedentary middle-aged men provides an opportunity to develop typical values that may prove useful in assessing impairment and disease. Maximal oxygen uptake can be predicted from age and height, using standard predicting formulas. Patterns of change in ventilation, anaerobic threshold, heart rate, oxygen pulse, and arterial blood gases during exercise are similar to those previously reported, although the magnitude of changes may be different.

Body Weight↗

Overshoot in VO2 following the onset of moderate-intensity cycle exercise in trained cyclists.

We have previously observed that following the onset of moderate intensity cycle ergometry, the pulmonary O2 uptake (VO2) in trained cyclists often does not increase towards its steady-state value with the typical mono-exponential characteristics; rather, there is a transient "overshoot". The purpose of this study was to systematically examine this phenomenon by comparing the VO2 responses to two moderate-intensity work rates and one high-intensity work rate in trained and untrained subjects. Following a ramp exercise test to the limit of tolerance for the determination of the gas exchange threshold (GET) and VO2(peak), seven trained cyclists [mean (SD); VO2(peak) 66.6 (2.5) ml x kg(-1) x min(-1)] and eight sedentary subjects [VO2(peak) 42.9 (5.1) ml x kg(-1) x min(-1)] completed six step transitions from baseline cycling to work rates requiring 60% and 80% GET and three step transitions from baseline cycling to a work rate requiring 50% of the difference between GET and VO2(peak) (50%delta). VO2 was measured breath-by-breath and modelled using standard techniques. The sedentary subjects did not overshoot the steady-state VO2 at any intensity. At 60% GET, six of the seven cyclists overshot the steady-state VO2 [by an integral volume of 164 (44) ml between approximately 45 and 125 s]. At 80% GET, four of the seven cyclists overshot the steady-state VO2 [by an integral volume of 185 (92) ml between approximately 55 and 140 s]. None of the cyclists showed an overshoot at 50%delta. These results indicate that trained cyclists evidence an overshoot in VO2 before steady-state is reached in the transition to moderate-intensity exercise. The mechanism(s) responsible for this effect remains to be elucidated, as does whether the overshoot confers any functional or performance benefit to the trained cyclist.

Adult↗

Exercise in chronic pulmonary disease: aerobic exercise prescription.

Endurance exercise training (EXT) is singly the most important aspect of rehabilitation for patients with chronic pulmonary disease. When effective, this modality of physical reconditioning leads to improved functional exercise capacity and reduced breathlessness. Early implementation is desirable to obtain more meaningful responses (e.g., when FEV1 falls below 50% of the predicted value in patients with chronic obstructive disease). Preparation for effective EXT requires optimization of respiratory system mechanics (e.g., using bronchodilator therapy), prevention of gas exchange failure (i.e., using supplemental oxygen), nutritional guidance, and psychological support (e.g., to overcome stigmata of disability, fear, and inclination to panic). EXT should be applied using a rigorous, scientifically based aerobic exercise prescription (AXRx) that recognizes basic principles of the human response to exercise prescription while considering individual pathophysiological limitations and identifying safety thresholds for exercise participation. The mode of aerobic exercise should use large muscle groups of the legs (e.g., treadmill or cycle ergometer). The recommended duration is an accumulation of 30 min of exercise per session at the target intensity, achieved by continuous or interval training. EXT should be supervised with a recommended frequency of at least three times per week for 6--8 wk. Target exercise intensity can be monitored by oxygen uptake, work rate, heart rate, or perceived exertion. Target intensity can be determined initially on the basis of 40% of a reference value for maximum oxygen uptake and linked to other variables through predictable interrelationships. All aspects of the AXRx must be reviewed with regard to progression during training. Pulmonary rehabilitation must recognize the importance of achieving clinically meaningful responses (e.g., increased 6-min walking distance of 54 m) as well as the need for maintenance exercise program to sustain the benefits.

Exercise↗

Effects of estrus cycle on thermoregulatory responses during exercise in rats.

In female rats, rectal temperature (Tre), tail vasomotor response, oxygen uptake (VO2), and carbon dioxide production (VCO2) were measured in proestrus and estrus stages during treadmill running at two different speeds at an ambient temperature (Ta) of 24 degrees C. Experiments were performed at 2.00-6.00 a.m., when the difference in Tre was greatest between the two stages; Tre at rest in the estrus stage was 0.54 degrees C higher than in the proestrus stage. In a mild warm environment, threshold Tre for a rise in tail skin temperature (Ttail) was also higher in the estrus stage than in the proestrus stage. In contrast, no difference was seen in the threshold Tre and steady state Tre at the end of exercise between proestrus and estrus stages. These values were higher at the higher work intensity. VO2 was also similar between the two stages, except in the second 5 min after the beginning of exercise, when VO2 was greater and Tre rose more steeply in the proestrus stage. These data indicate that deep body temperature during exercise is regulated at a certain level depending on the work intensity and is not influenced by the estrus cycle.

Animals↗

Oxygen uptake and heart rate kinetics during heavy exercise: a comparison between arm cranking and leg cycling.

This study examined the oxygen uptake (VO(2)) and heart rate (HR) kinetics during arm cranking and leg cycling at work rates above the anaerobic threshold (AT). Ten untrained male subjects [21.6 (1.3) years] completed two 7 min 15 s constant-load arm cranking and two leg cycling tests at a power output halfway between the mode-specific AT and peak VO(2). The time constants for phase II VO(2) (tau) and HR (tau) kinetics were determined by fitting a monoexponential curve from the end of phase I until 3 min of exercise. VO(2) tau and HR tau values were significantly (P < 0.001) slower in arm cranking [VO(2) tau = 66.4 (3.0) s; HR tau = 74.7 (4.4) s] than in leg cycling [VO(2) tau = 42.0 (1.9) s; HR tau = 55.6 (3.5) s]. The VO(2) slow component (VO(2SC)) accounted for a significantly (P < 0.001) greater percentage of the total exercise response during arm cranking [23.8 (1.6)%] than during leg cycling [14.2 (1.5)%]. The greater relative VO(2SC) and the slower VO(2) tau with arm exercise are consistent with a greater recruitment of metabolically inefficient type II muscle fibres during arm cranking than during leg cycling.

Adult↗

Training improves muscle oxidative capacity and oxygenation recovery kinetics in patients with chronic obstructive pulmonary disease.

We studied 21 patients with chronic obstructive pulmonary disease aged [mean (SD)] 63 (10) years, with a mean forced expiratory volume in 1 s of 40 (6)% and a peak oxygen uptake of 67 (11)% of predicted values. Patients trained for 6 weeks on a cycle ergometer at high work-rates (WR). Near-infrared spectroscopy was used to obtain the time-constant of the deoxygenation recovery signal (tauHbO(2)) during three constant WR exercise tests, one below and two above the lactic acidosis threshold (theta(L)). Glycolytic and oxidative enzymes and lactate concentrations were assessed in muscle biopsies. The tauHbO(2) decreased significantly in all three constant WR tests: -18 (24)s, -20 (23) s and -13 (22) s, respectively. Endurance time increased in the higher WR tests, by 5.7 (4.8) min and 3.6 (2.7) min, respectively. The activity of citrate-synthase (CS) and creatine-kinase changed significantly from 20 (10) to 30 (13) micro mol x min(-1) x g(-1)and from 3.825 (950) to 3.402 (526) micro mol x min(-1) x g(-1), respectively. Training also improved significantly the mean response time of the on-transient of oxygen uptake (tau'VO(2)) of the below-theta(L) test. We found significant correlations between changes in CS and changes in tauHbO(2), tau'VO(2) and endurance time. We conclude that leg training accelerates the speed of re-oxygenation of the vastus lateralis muscle after exercise. This improvement is correlated to changes in the oxidative enzymes.

Adaptation, Physiological↗

Performance predicting factors in prolonged exhausting exercise of varying intensity.

Several endurance sports, e.g. road cycling, have a varying intensity profile during competition. At present, few laboratory tests take this intensity profile into consideration. Thus, the purpose of this study was to examine the prognostic value of heart rate (HR), lactate (La(-1)), potassium (K(+)), and respiratory exchange ratio (RER) performance at an exhausting cycling exercise with varying intensity. Eight national level cyclists performed two cycle tests each on a cycle ergometer: (1) a incremental test to establish VO(2max), maximum power (W (max)), and lactate threshold (VO(2LT)), and (2) a variable intensity protocol (VIP). Exercise intensity for the VIP was based upon the VO(2max) obtained during the incremental test. The VIP consisted of six high intense (HI) workloads at 90% of VO(2max) for 3 min each, interspersed by five middle intense (MI) workloads at 70% of VO(2max )for 6 min each. VO(2 )and HR were continuously measured throughout the tests. Venous blood samples were taken before, during, and after the test. Increases in HR, La(-), K(+), and RER were observed when workload changed from MI to HI workload (P < 0.05). Potassium and RER decreased after transition from HI to MI workloads (P < 0.05). There was a negative correlation between time to exhaustion and decrease in La(-) concentration during the first MI (r = -0.714; P = 0.047). Furthermore, time to exhaustion correlated with VO(2LT )calculated from the ramp test (r = 0.738; P = 0.037). Our results suggest that the magnitude of decrease of La(-1) between the first HI workload and the consecutive MI workload could predict performance during prolonged exercise with variable intensity.

Adult↗

Effect of moderate inspiratory hypoxia on exercise performance in sickle cell trait.

In previous work (Weisman IM, Zeballos RJ, Johnson BD: Cardiopulmonary and gas exchange responses to acute strenuous exercise at 1,270 meters in sickle cell trait. Am J Med 1988; 84: 377-383), no significant differences in cardiopulmonary and gas exchange responses to acute, strenuous exercise were observed between volunteers with sickle cell trait (SCT) and control subjects at an altitude of 1,270 meters. The current study was designed to evaluate the effect of a greater hypoxic stimulus on the response of healthy, black male basic recruits, 11 with SCT (HbAS) and 11 control subjects, to acute strenuous exercise. Simulated 2,300-meter and simulated sea-level conditions were achieved by adjustment of the fraction of inspired oxygen (simulated condition of 2,300 meters equal to 18 percent; simulated sea-level condition equal to 24 percent) at the same barometric pressure (656 mm Hg). For each simulated condition, the subjects performed an incremental exercise test to exhaustion on a cycle ergometer. One steady-state exercise test with radial arterial access for arterial blood gases was performed under each condition on Day 2. Peak incremental exercise values for oxygen consumption (2.9 versus 2.81 liters/minute), heart rate (189 versus 187 beats/minute), oxygen pulse (15.4 versus 15.1 ml/beat), and anaerobic threshold (1.59 versus 1.62 liters/minute), at the simulated 2,300-meter height revealed no significant differences between men with SCT and control subjects, respectively. A 5 to 9 percent decrement in exercise performance at the simulated 2,300-meter level compared with exercise performance at the simulated sea-level condition was noted for both groups. Steady-state exercise values for arterial oxygen tension (64 versus 65 mm Hg), arterial oxygen saturation (90 versus 90 percent), alveolar-arterial oxygen pressure difference (22 versus 21 mm Hg), and physiologic dead space to tidal volume ratio (12 versus 11) at the simulated condition of 2,300 meters were similar for the SCT and control groups, respectively. It is concluded that in a moderate hypoxic environment, the cardiopulmonary and gas exchange responses of persons with SCT during brief episodes of exhaustive exercise were comparable to those of control subjects.

Adult↗

The effects of contrast and length of gratings on the visual evoked potential.

Visual evoked potentials (VEP's) were obtained to grating stimuli modulated in phase at 8 Hz. The amplitude of the VEP was linearly related to the length of a centrally-fixated grating up to a critical length value equivalent to 9-16 grating cycles, for a range of spatial frequencies; thereafter amplitude first decreased then increased with increasing length. VEP amplitude was proportional to log. contrast as well as to length, and the intercept of the regression line with the contrast axis coincided with the psychophysical threshold for gratings of different lengths. More sensitive measurements with low-contrast stimuli around threshold indicated that in this range VEP amplitude is linearly related to contrast, and there is no threshold nonlinearity. The effects of visual field location and adaptation on the VEP to gratings of different lengths and spatial frequencies were also studied. The relationship of these findings to psychophysical, single-cell and transient VEP data is discussed.

Adaptation, Ocular↗

The simplified V-slope method of detecting the gas exchange threshold.

A simplified V-slope method was used to visually determine the first point of departure from linearity of carbon dioxide output (VCO2) plotted against oxygen uptake (VO2). The point at which VCO2 departed from a line with a slope equal to 1.00 was visually selected as the gas exchange threshold during incremental exercise. The simplified method of threshold detection was compared with a computerized V-slope method. Both methods were used to determine the gas exchange threshold during incremental cycling (10 W.min-1) in 17 untrained female subjects. The thresholds occurred at 41.1% and 45.1% of VO2max using the computerized and simplified V-slope methods, respectively. The correlation between the oxygen uptake measured at the threshold using the two methods was 0.95. Power output, VO2, and heart rate values determined at the gas exchange threshold using the simplified V-slope method were significantly higher than the corresponding values obtained using the computerized V-slope method. The simplified V-slope method consistently placed the gas exchange threshold at the work rate that was about 10 W above the power output determined by the computerized method. Although the two methods were highly correlated, the simplified V-slope method tended to overestimate threshold values determined from a computerized gas exchange method.

Adaptation, Physiological↗

Muscle energetics in short-term training during hypoxia in elite combination skiers.

Four well-trained combination skiers were studied through pre- and post-training for the effects of short-term intermittent training during hypoxia on muscle energetics during submaximal exercise as measured by Phosphorus-31 nuclear magnetic resonance and maximal aerobic power (VO2max). The hypoxia and training in the cold was conducted in a hypobaric chamber and comprised 60-min aerobic exercise (at an intensity equivalent to the blood lactate threshold), using a cycle ergometer or a treadmill twice a day for 4, consecutive days at 5 degrees C, in conditions equivalent to an altitude of 2000 m (593 mm Hg). No change in VO2max was observed over the training period, while in the muscle energetics during submaximal exercise, the values of phosphocreatine/(phosphocreatine+inorganic phosphate) and intracellular pH were found to be significantly increased by training during hypoxia. During recovery, the time constant of phosphocreatine was found to have been significantly reduced [pre, 27.9 (SD 6.7) s; post, 22.5 (SD 4.7) s, P < 0.01]. The observed inhibition of phosphocreatine as well as that of intracellular pH changes after training during hypoxia and quicker recovery of phosphocreatine in submaximal exercise tests, may indicate improved oxidative capacity (i.e. a high adenosine 5'-triphosphate formation rate) despite the short-term hypoxia training.

Adult↗

Cardiorespiratory response of heart transplantation recipients to exercise in the early postoperative period.

In this study, we evaluated the cardiorespiratory function of orthotopic heart transplantation (OHT) recipients during exercise. Seventeen male OHT recipients, ranging in age from 22 to 60 years, participated in this study 47 +/- 21 days after surgery. The control group consisted of 17 sedentary healthy men. Breath-by-breath measurement of cardiorespiratory function was obtained during the incremental exercise of leg cycling. At peak exercise, the oxygen (O2) uptake (16.5 +/- 3.3 vs 33.9 +/- 8.2 mL.kg-1.min-1), work rate (82 +/- 19 vs 169 +/- 42 watts), heart rate (HR), O2 pulse, and blood lactate level of the OHT recipients were significantly lower than the respective values of the control group. At the ventilatory threshold, the OHT group also showed a significantly lower O2 uptake (10.7 +/- 1.6 vs 18.3 +/- 5.1 mL.kg-1.min-1), work rate (39 +/- 12 vs 89 +/- 33 watts), HR, O2 pulse, ventilatory equivalent for O2, and ventilatory equivalent for carbon dioxide. The OHT recipients showed a high resting HR (97 +/- 7 beats/min) and a low peak HR (123 +/- 14 beats/min) during exercise, and their HR continued to increase for 1 to 3 minutes after cessation of exercise. Our data revealed a low level of cardiorespiratory endurance in OHT recipients during the early postoperative stage. A multidisciplinary cardiac rehabilitation program should be considered to enhance physical functional capacity and quality of life, and promote return to work.

Adult↗

[The sensitivity to apoptosis is enhanced in U937-ASPI-3K cells which stably express antisense ATM/PI-3K].

OBJECTIVE: To analyse the characteristics of apoptosis sensitivity in U937-ASPI-3K cells which is stably expressing anti-sense ATM/PI-3K. METHOD: Annexin V-PI apoptosis detection kid and flow cytometry were used to determine apoptosis rate, Western blot to the expression level of cytochrome C protein and Bcl-2 protein. RESULTS: U937-ASPI-3K cells had a lowered threshold for triggering apoptosis in response to low dose irradiation. Cell apoptosis rate was 28% and (53.0 +/- 5.4)%, respectively, at 8 and 48 hours after 1.5 Gy (137)Cs irradiation, while in U937-pZEOSV2 (+) control group it was 4.2% and (11.0 +/- 3.3)%, respectively. Cytosolic cytochrome C protein band was gradually intensified in U937-ASPI-3K in 4 - 8 h after irradiation, but was not detected in control group. Bcl-2 protein gradually decreased in U937-ASPI-3K in 4 - 8 h after irradiation, but didn't change obviously in control group. CONCLUSION: Cell line U937-ASPI-3K acquired a phenotype with a lowered threshold for triggering apoptosis. It demonstrated that selective inactivation of ATM gene might be of considerable value in tumor treatment.

Apoptosis↗

[Incremental stress test: comparison between protocols and cardiorespiratory reference values in healthy workers].

The aim of this study was double: to compare two different incremental stress protocols and to obtain reference values for a standardised exercise test in healthy workers. Firstly, eighty healthy male workers, 40 coal miners and 40 hospital workers, aged 19-54, performed in 2 different days 2 cycle ergometer tests up to exhaustion, increasing the work load respectively by 30 watts every 3 minutes (protocol A) and by 30 watts each minute (protocol B). Ventilatory and gas exchange measurements were done by a breath-by-breath apparatus equipped with a turbine and fast gas analysers for O2 and CO2. For each test the ventilatory anaerobic threshold (VAT) was blindly determined as oxygen uptake (V'O2 VAT) using standardised gas exchange and ventilatory indices (V'CO2, V'E, V'E/V'O2) that were found giving comparable results with those derived from the blood lactacte curve. Significant differences were observed between the two protocols only concerning the average work load at exhaustion and at the VAT: the highest being with the protocol B. Conversely, either the maximal oxygen uptake (V'O2 max) and the V'O2 VAT were comparable between protocols, as well as the other cardio-respiratory parameters were at these exercise levels. Oxygen uptake and heart rate increased in average linearly with the work load with very similar slopes in both protocols. Comparable results between protocols were found also as what concerns the slopes of the other physiological variables (V'E, V'CO2) analysed against the V'O2, particularly for exercise levels lower or equal to the individual VAT. Thus, these results suggest a very good comparability between the two protocols, concerning both the levels of maximal and sub-maximal aerobic capacity (V'O2 max, V'O2 VAT) and the cardio-respiratory pattern related to the oxygen uptake. Reference values for the 30 watts/3 minutes cycle ergometer stress test were achieved in other 320 healthy Sardinian workers concerning both the maximal (V'O2 max) and sub-maximal (V'O2 VAT) aerobic capacity and the range of normality for the cardio-respiratory pattern during the test, particularly for completely aerobic work loads, namely work loads not above the V'O2 VAT. These prediction equations can be useful for the evaluation of working capacity of workers employed in manual jobs characterised by moderate-to-high dynamic energy expenditure.

Adult↗

Electromyographic fatigue thresholds of the superficial muscles of the quadriceps femoris.

The purpose of this investigation was to compare the thresholds of neuromuscular fatigue determined simultaneously from the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles using the electromyographic fatigue threshold (EMGFT) test. Eight adult volunteers [mean (SD) age, 33 (10) years] served as subjects for this investigation. The results of a one-way repeated measured ANOVA indicated that there was a significant (P < 0.05) difference among the mean EMGFT values for the VL [248(31)W], VM [223(43)W] and RF [220(30)W] muscles. Tukey post-hoc comparisons indicated that the EMGFT for the RF was significantly (P < 0.05) lower than that of the VL. These findings suggested that during cycle ergometry there is a dissociation in neuromuscular fatigue characteristics of the superficial muscles of the quadriceps femoris group.

Adult↗

Hormone-dependent fluctuations of pressure pain threshold and tactile threshold of the temporalis and masseter muscle.

In order to better objectify reported pain and disturbed sensation, psychophysical parameters as pressure pain threshold (PPT) and tactile threshold (TT) have been introduced in pain research. The present study evaluated fluctuations of these parameters, obtained using an algometer (PPT) and von Frey hairs (TT), in relation to fluctuations in female reproductive hormones. Ten students not using oral contraceptives and eight students using oral contraceptives participated in the study. In addition, seven male students served as a control group. During two menstrual cycles, the PPT and TT of the masseter and temporalis muscles, as well as from the hand, were obtained twice per week. At the end of the study the values were evaluated in relation to the different phases of the menstrual cycle, by means of a linear mixed model. The TT appeared very reproducible within subjects and did not fluctuate over time. Scores on the left temporalis muscle appeared significantly higher than that on the right side. In all subjects the PPT tended to be higher on the left side, while in students using oral contraceptives, the PPT values of the temporalis muscle were significantly higher in the menstrual phase, and lower in the follicular phase. A significant correlation between the PPT of the temporalis muscle and the TT of the overlying skin was observed.

Adult↗

Blood lactate disappearance dynamics in boys and men following exercise of similar and dissimilar peak-lactate concentrations.

Characteristically, children recover faster than adults from various types of exercise. The purpose of the present study was to explain the children's faster recovery, in part, by addressing lactate (La) removal and comparing La disappearance dynamics in the two age groups following exercise of both similar and dissimilar peak blood-lactate concentration values ([La]pk). The subjects were 14 prepubertal boys and 12 men of similar peak oxygen consumption, normalized for body mass. All subjects performed 30 s supra-maximal cycling (Wingate anaerobic test [WAnT]). [La]pk was 10.7 +/- 1.9 and 14.7 +/- 1.7 mmol x l(-1) for the boys and men, respectively (p < 0.001). The men were later retested in shortened versions of the WAnT so as to attain [La]pk values (10.5 +/- 0.7 mmol x l(-1)) comparable to those achieved by the boys. [La]pk lag time following the boys' standard WAnT was similar to that found in the men following the shortened WAnT (5.0 +/- 2.6 vs 5.7 +/- 1.3 min, respectively), but considerably shorter than that following the men's 30s-WAnT (7.6 +/- 2.1 min; p < 0.05). The La disappearance dynamics were closely matched between groups following the matched [La]pk WAnTs. [La] half-life was similar under all conditions (ca. 20 min). It is concluded that prepubertal boys are characterized by a lower [La]pk and a shorter time lag before reaching it, following 30-s supra-maximal cycling exercise. However, boys' La disappearance dynamics are not different from that of men.

Adolescent↗