Skeletal muscle VO2 kinetics from cardio-pulmonary measurements: assessing distortions through O2 transport by means of stochastic work-rate signals and circulatory modelling.

During non-steady-state exercise, dynamic changes in pulmonary oxygen uptake (VO2pulm) are dissociated from skeletal muscle VO2 (VO2musc) by changes in lung and venous O2 concentrations (CvO2), and the dynamics and distribution of cardiac output (CO) between active muscle and remaining tissues (Qrem). Algorithms can compensate for fluctuations in lung O2 stores, but the influences of CO and CvO2 kinetics complicate estimation of VO2musc from cardio-pulmonary measurements. We developed an algorithm to estimate VO2musc kinetics from VO2pulm and heart rate (HR) during exercise. 17 healthy volunteers (28 ± 7 years; 71 ± 12 kg; 7 females) performed incremental exercise using recumbent cycle ergometry (VO2peak 52 ± 8 ml min(-1) kg(-1)). Participants completed a pseudo-random binary sequence (PRBS) test between 30 and 80 W. VO2pulm and HR were measured, and CO was estimated from HR changes and steady-state stroke volume. VO2musc was derived from a circulatory model and time series analyses, by solving for the unique combination of venous volume and the perfusion of non-exercising tissues that provided close to mono-exponential VO2musc kinetics. Independent simulations showed that this approach recovered the VO2musc time constant (τ) to within 7% (R(2) = 0.976). Estimates during PRBS were venous volume 2.96 ± 0.54 L; Qrem 3.63 ± 1.61 L min(-1); τHR 27 ± 11 s; τVO2musc 33 ± 8 s; τVO2pulm 43 ± 14 s; VO2pulm time delay 19 ± 8 s. The combination of stochastic test signals, time series analyses, and a circulatory model permitted non-invasive estimates of VO2musc kinetics. Large kinetic dissociations exist between muscular and pulmonary VO2 during rapid exercise transients.

Performance, training and lifestyle parameters of marathon runners aged 20-80 years: results of the PACE-study.

Successful finishing of marathon requires regular endurance training and appropriate lifestyle. Thus, marathon running times and training data from large samples of physically active and fit elderly are ideal for the assessment of age-related performance. In the present study we analyzed 439 278 running times from result lists of 108 marathon competitions and data from a survey via internet questionnaire about training and behavioural factors of marathon finishers. Marathon times and 6 992 data sets from the internet questionnaire were separated into groups based on age and sex and analyzed by two-way ANOVA. Our main findings are that 1) there are virtually no relevant running time differences (p<0.01) in marathon finishers from 20 to 55 years and 2) the majority of middle-aged and elderly athletes have training histories of less than seven years of running. With the exception of marathon running times we did not encounter any significant gender related differences (p>0.01). The present findings strengthen the concept that considers aging as a biological process that can be considerably speeded up or slowed down by multiple lifestyle related factors.

Age-related changes in marathon and half-marathon performances.

We examined age-related changes in endurance performance of marathon and half-marathon finishers. A total of 405 515 running times were separated into groups based on age, sex, and distance. After exclusion of repetitive running times, 300 757 runners were analyzed by ANOVA (factors: age, sex). For each age group (six decades, 20-79 years), mean running times for all finishers, as well as top-ten performers, were assessed. As expected, age and sex had significant influence on running times. Female running times were about 10 % (marathon) and 13 % (half-marathon) above the corresponding times of their age-matched peers. The main finding is that in our sample of trained subjects significant age-related losses in endurance performance did not occur before the age of 50 years. Mean marathon and half-marathon times were virtually identical for the age groups from 20-49 years. Moreover, age-related performance decreases (p < 0.01) of the 50 - 69-year-old subjects were only in the range of 2.6 - 4.4 % per decade. These results suggest that the majority of older athletes are able to maintain a high degree of physical plasticity. The hypothesis that lifestyle factors have considerably stronger influences on functional capacity than the factor age is also supported by these findings from physically active and fit elderly.

Maximal manual stretcher carriage: performance and recovery of male and female ambulance workers.

The effects of a maximal duration stretcher carriage on heart rate (HR), lactate concentration, hand steadiness and hand-grip strength were studied up to 72 h post-exercise in 17 male and 15 female military ambulance personnel. Using both hands for transport, the participants walked on a treadmill ergometer at a speed of 4.5 km/h. Force measurements at the handlebars yielded mean loads of 245 N (25 kg) on each side. Each step on the treadmill induced additional force oscillations with peak forces up to 470 N corresponding to 130% (women) and 98% (men) of maximal voluntary contraction (MVC). In the males the maximal transport time was about twice the time in women (mean +/- SD: 184 +/- 51 s vs. 98 +/- 34 s). These differences had no significant effect on HR and lactate values. The same applies to hand steadiness, which showed only a transient deterioration immediately after exercise. In contrast to these parameters, substantial differences were seen in hand-grip strength recovery. Immediately after exercise, maximal hand-grip strength decreased by 150 N (25% MVC) in the males vs. 50 N (14%) in the females. Irrespective of gender, individuals with larger hand-grip strength and longer carriage durations (range 120 s-280 s) showed the slowest strength recoveries (up to 72 h) as compared to 1 h of recovery in participants with short transport durations (range 27 s-120 s). These findings suggest that the increasing number of eccentric strains during uninterrupted stretcher carriage induces cumulative muscle damages that may require some days for complete recovery.

Hand-grip strength of young men, women and highly trained female athletes.

Hand-grip strength has been identified as one limiting factor for manual lifting and carrying loads. To obtain epidemiologically relevant hand-grip strength data for pre-employment screening, we determined maximal isometric hand-grip strength in 1,654 healthy men and 533 healthy women aged 20-25 years. Moreover, to assess the potential margins for improvement in hand-grip strength of women by training, we studied 60 highly trained elite female athletes from sports known to require high hand-grip forces (judo, handball). Maximal isometric hand-grip force was recorded over 15 s using a handheld hand-grip ergometer. Biometric parameters included lean body mass (LBM) and hand dimensions. Mean maximal hand-grip strength showed the expected clear difference between men (541 N) and women (329 N). Less expected was the gender related distribution of hand-grip strength: 90% of females produced less force than 95% of males. Though female athletes were significantly stronger (444 N) than their untrained female counterparts, this value corresponded to only the 25th percentile of the male subjects. Hand-grip strength was linearly correlated with LBM. Furthermore, both relative hand-grip strength parameters (F (max)/body weight and F (max)/LBM) did not show any correlation to hand dimensions. The present findings show that the differences in hand-grip strength of men and women are larger than previously reported. An appreciable difference still remains when using lean body mass as reference. The results of female national elite athletes even indicate that the strength level attainable by extremely high training will rarely surpass the 50th percentile of untrained or not specifically trained men.

Physical performance, body weight and BMI of young adults in Germany 2000 - 2004: results of the physical-fitness-test study.

In westernized countries the sedentary lifestyle in conjunction with a hypercaloric diet has caused an increase in the number of obese adults. Moreover, recent studies suggest that the prevalence of overweight in children increased during the last decade. However, the literature has to be interpreted with some caution since the majority of epidemiological studies examining health, fitness, and obesity rely on self-reported data rather than measurements. A further limitation is that most studies examine either physical activity or nutrition, only few deal with both aspects simultaneously. In the present study we analyzed both aspects in more than 58,000 persons aged between 17 and 26 years. All of them were applicants for the German Bundeswehr, which accepts only volunteers with school leaving certificates and a body mass index (BMI) below 30 kg . m (-2). The admitted subjects performed a Physical-Fitness-Test (PFT) consisting of 5 simple sport tests (shuttle run, sit-ups, push-ups, standing jump, Cooper test). For 23 000 subjects additional measurements of body height and body weight as well as information about their education level were available. These data were combined with the PFT results. We found large deficits in the physical fitness of young adults: More than 37 % of the participants failed to pass the PFT, with failure rates of the male volunteers increasing significantly since 2001. While the female volunteers showed virtually constant body weight and BMI, the corresponding values of men increased monotonously between the age of 17 and 26 years. Physical fitness was positively, BMI negatively correlated with education level. The present findings suggest that body weight increases and fitness decreases in non-obese young adults in Germany. Despite the correlations between BMI and physical fitness the terms "overweight" and "physically unfit" should not be regarded as synonyms.

Recovery of hand grip strength and hand steadiness after exhausting manual stretcher carriage.

Rescue activities frequently require not only substantial and sustained hand-grip forces but also a subtle coordination of hand and finger muscles, e.g. when manipulating injection syringes after manual stretcher carriage. We investigated the recovery kinetics of manual coordination and muscle strength after exhausting stretcher carriage (4.5 km/h, load at each handle bar: 25 kg). Hand steadiness (frequency and duration of wall contacts when holding a metal pin into a small bore) and parameters of hand-grip strength were determined in 15 male volunteers before and immediately after the stretcher carriage. Measurements were repeated after 0.5, 1, 4 and 24 h of recovery. Mean carrying time was 215+/-87 s (SD), mean transport distance amounted to 264+/-104 m. During the carriage test, forces at the stretcher handles oscillated in the order of +/-50 N within each gait cycle. Immediately after exhaustion, hand steadiness was significantly deteriorated (threefold increase in frequency and duration of wall contacts), maximum and mean hand-grip force over 15 s were reduced by almost 20%. While the recovery of hand steadiness was complete by minute 30 after stretcher carriage, a significant reduction in maximum and mean hand-grip force by 12% could still be observed after 24 h. The present findings demonstrate that hand steadiness recovers much faster than maximum hand-grip strength after exhaustive manual stretcher carriage (less than 30 min vs. more than 24 h). Probably, muscle damage induced in particular by the eccentric components during stretcher transport seems to affect only the generation of large forces. By contrast, the generation and coordination of the much lower forces required for hand-steadiness appears to be impaired only during the short transient of metabolic recovery.

Cardiovascular responses to apnea during dynamic exercise.

Breath holding maneuvers induce hypoxia, hypercapnia, and various cardiovascular responses typically including increases in total peripheral resistance, mean arterial pressure (MAP) and decreases in heart rate (HR). During dynamic exercise these responses may have a generally negative impact on performance. Moreover, they deserve particular attention in cardiovascular risk subjects. In 26 healthy sport students we studied the HR and MAP effects induced by the combination of dynamic exercise (cycle ergometry, 30 W and 250 W) with 20 s of either respiratory arrest (mouth piece pressure held constant at 20 mm Hg), free breathing, or rebreathing, i. e. periods of unimpeded breathing leading to similar levels of hypercapnia and hypoxia as the respiratory arrest. The measurements yielded no major differences between the conditions of rebreathing and free breathing. In contrast, 20 s of apnea led to a marked increase in MAP and a HR depression at both levels of exercise intensity. Additionally, there was a delayed MAP recovery after this stimulus. The present findings show that breath holding has marked effects on MAP and HR during dynamic exercise, which are essentially independent of the resulting hypoxia and of increases in intrathoracic pressure. The key factor seems to be an increase in total peripheral resistance, probably including a vasoconstriction in the exercising muscles.

Reduction of blood pressure response during strength training through intermittent muscle relaxations.

UNLABELLED: The increase in blood pressure during training is a disadvantage of strength training in the elderly. To reduce this effect it is generally recommended to apply lower levels of relative muscle strength with longer contraction durations or higher number of repetitions (continuous mode (CM), e. g. 50% of maximal strength, 10 to 15 repetitions without pauses). Alternatively, higher contraction forces could be combined with frequent periods of muscle relaxation and fewer repetitions (intermittent mode (IM), e. g. 80% of maximal strength, 8 repetitions consisting of 1.5 s concentric contraction, 1.5 s eccentric contraction and 3 s pause). We compared the blood pressure effects of both approaches during leg press exercise in two age groups (10 subjects aged 22 to 42 y, 9 subjects aged 60 to 72 y). Blood pressure was measured continuously by a non-invasive method (FINAPRES, Ohmeda 2300, Englewood USA). RESULTS: 1. The age of the subjects had no significant influence on the slopes of blood pressure increase during the different exercise modes. 2. The frequent insertion of short (3 s) periods of muscle relaxation (IM) decreased the blood pressure response more effectively than a reduction in contraction strength alone (CM). Short muscle relaxations have an immediate, mechanical effect on blood pressure and they allow a metabolic recovery which attenuates the trend of blood pressure increase.

Cardiac output, leg blood flow and oxygen uptake during foot plantar flexions.

When studying the adjustment of muscle perfusion during exercise, the influence of central factors (e.g. blood volume, central blood pressure and venous return) can be reduced by choosing small muscle groups. In the present study parallel determinations of cardiac output (CO), leg blood flow (LBF) and pulmonary oxygen (VO2) uptake were performed in 9 healthy male subjects at the onset and cessation of dynamic foot plantar flexions. The volunteers exercised with both feet for 5 minutes at 3 different resistances corresponding to 6%, 18% and 30% of the mean maximal voluntary contraction. Doppler measurements at the aortic root and in the femoral artery were utilized to estimate CO and LBF. Oxygen uptake was analyzed breath-by-breath as the difference between inspired and expired oxygen volumes. Within the first 10 s of exercise LBF increased from 400 ml x min(-1) to about 1,000 ml x min(-1) at all exercises intensities. During the subsequent 5 minutes of exercise, LBF decreased to about 800 ml x min(-1) at the lowest intensity. By contrast, it increased to about 1,900 ml x min(-1) at the highest intensity. The changes in CO during exercise were quantitatively identical with the changes in LBF. The present results suggest that the fine adjustment of muscle blood flow and muscle metabolism starts only after a fast and uniform circulatory on response. The second component may lead to leg perfusion values above, at or below the initial peak perfusion levels. The off-transients of LBF displayed no comparable fast responses. They were slower than the recovery kinetics of any cardiovascular parameter measured in the present study.

Origin of back pain during bedrest: A new hypothesis.

Back pain during bed rest has frequently been reported. Until recently, studies concentrated mainly on length changes of the spine. Functional aspects such as reduced movements of the back, although anecdotally reported, could neither be quantified nor were they taken into account as a potential cause of back pain. In the present study the geometry of the spinal columns of eight healthy men was continuously recorded over 24 h before, during, and after a seven-day 6 degree head-down tilt period (Series 1). The approach is based on the measurement of skin distances between four pairs of miniaturized ultrasound transmitters and receivers fixed on the back in parallel to the thoracic and lumbar spine. After a four-week break, the entire study was repeated with the same subjects (Series 2). The major findings are: 1. The length increase of the spine segments investigated was virtually identical in both series. 2. During the bedrest period significantly greater pain occurred in Series 1 as compared to Series 2. Pain was generally confined to the lumbar region about 10 cm lateral of the spinous processes. 3. Pain was most prominent when trunk motions were minimal, while movements over the maximal range of the spine transiently reduced the pain remarkably. 4. During bed rest, the amplitude of voluntary movements of the lumbar segment was reduced in particular during Series 1. It is concluded that back pain during bed rest is induced by reduced amplitudes of spine movements rather than by increases in the spine length. It is suggested that isometric muscle contractions of low intensity are a primary course of back pain. Regular, slow, large-amplitude movements of the spine are recommended as a countermeasure.

Comparison between the physiological response to roller skiing and in-line skating in biathletes.

PURPOSE: Roller skiing is frequently used in Nordic disciplines during the off-season periods. Recently, in-line skating has become a potential alternative. In the present study, the responses of heart rate, oxygen uptake, respiratory exchange ratio, and lactic acid concentration to roller skiing and in-line skating were compared in competitive biathletes. METHODS: Eight male subjects performed three tests with both devices on a hilly outdoor track. They were requested to adjust their speed in such a way that the following criteria were met: intensity 1, lactate concentration about 2 mmol x L(-1); intensity 2, lactate concentration about 4 mmol x L(-1); AND intensity 3, maximal speed. RESULTS: Though the subjects were not experienced in-line skaters, all managed to adjust the required intensities. This was achieved through increased velocities during in-line skating. Independent of the exercise intensity the differences in speed ranged between 1.0 and 1.4 m x s(-1). The relationships between lactic acid concentration, oxygen uptake, respiratory exchange ratio, and heart rate were not influenced by the test device. The respiratory exchange ratio amounted to 0.88, 0.95, and 1.02 for intensities 1 to 3, respectively. CONCLUSIONS: These results show that in-line skating can be regarded as an alternative to roller skiing for off-seasonal training in Nordic disciplines. A potential advantage of in-line skating is that aerobic training intensities can be obtained at competitive velocities.

Effects of hyperoxia on oxygen uptake kinetics in cystic fibrosis patients as determined by pseudo-random binary sequence exercise.

Patients with cystic fibrosis (CF) have been shown to exhibit impaired oxygen uptake (VO2) kinetics independent of their physical fitness. This study investigated whether oxygen supplementation improves VO2 kinetics in CF as determined by cycle ergometry at submaximal exercise intensities using a pseudo-random binary sequence exercise test i.e. a simultaneous application of different frequencies of sinusoidal work. The subjects were 9 CF patients and 13 healthy controls (HC) and they exercised while breathing humidified and heated air with a fractional concentration of oxygen in inspired air (F(I)O2) of either 0.21 or 0.40. With a F(I)O2 of 0.21 the respiratory exchange ratio (R) was higher in CF than in HC both at rest (0.91 vs 0.81) and during exercise (0.97 vs 0.89). Oxygen saturation (SO2) was slightly lower in CF. but remained above 90% during exercise (92.7% vs 95.2%). Spectrum analysis revealed that in CF, the amplitude ratio (AR) between V02 and exercise intensity was lower over a wide frequency range (P < 0.05). In addition, CF showed a larger negative phase shift (PS) at lower frequencies (P < 0.005). With a F(I)O2 of 0.40, SO2 increased to about 97% in both groups; while R remained higher in CF (0.92) compared to HC (0.81). In the control group, the O2 supplement raised AR but the VO, kinetics of the CF patients were not significantly affected. In HC the enhanced AR during oxygen supplementation would suggest a cardiopulmonary limitation of VO2 at the onset of submaximal exercise. In CF patients low AR and PS would indicate an attenuated VO2 response attributable to an impaired oxygen utilization in the muscles because the oxygen supplement normalised SO2 but failed to improve R and VO2 kinetics.

Recovery of free ADP, Pi, and free energy of ATP hydrolysis in human skeletal muscle.

We measured significant undershoots of the concentrations of free ADP ([ADP]) and Pi ([Pi]) and the free energy of ATP hydrolysis (DeltaGATP) below initial resting levels during recovery from severe ischemic exercise with 31P-nuclear magnetic resonance spectroscopy in 11 healthy sports students. Undershoots of the rate of oxidative phosphorylation would be predicted if the rate of oxidative phosphorylation would depend solely on free [ADP], [Pi], or DeltaGATP. However, undershoots of the rate of oxidative phosphorylation have not been reported in the literature. Furthermore, undershoots of the rate of oxidative phosphorylation are unlikely because there is evidence that a balance between ATP production and consumption cannot be achieved if an undershoot of the rate of oxidative phosphorylation actually occurs. Therefore, oxidative phosphorylation seems to depend not only on free [ADP], [Pi], or DeltaGATP. An explanation is that acidosis-related or other factors control oxidative phosphorylation additionally, at least under some conditions.

Leg blood flow during slow head-down tilt with and without leg venous congestion.

The effects of slow changes in body position on leg blood flow (LBF) were studied in nine healthy male subjects. Using a tilt table, sitting volunteers were tilted about 60 degrees backwards to a supine position within 40 s. To modify the venous filling in the legs, the tilt manoeuvre was repeated with congestion of the leg veins induced by two thigh cuffs inflated to a subdiastolic pressure of 60 mmHg. Doppler measurements in the femoral artery were used to estimate LBF. Additional Doppler measurements at the aortic root in five of the subjects were taken for the determination of cardiac output. The LBF was influenced by body position. In the control experiment it increased from 500 ml x min(-1) in the upright to 780 ml x min(-1) after 15 min in the supine position. A mean maximal value of 950 ml x min(-1) was observed 20 s after the tilt. Heart rate remained almost constant during the tilt phase, whereas stroke volume increased from 90 ml to 120 ml and it remained at that level after the cessation of the tilt. Congestion of the leg veins had no significant effect on heart rate, stroke volume and mean blood pressure. However, it increased vascular resistance of the leg during and after the tilt. After 15 min in the tilted position LBF amounted to 600 ml x min(-1). The results suggest that the filling of the leg veins is inversely related to leg blood flow. The most likely mechanism underlying this observation is a local effect of venous filling on vasomotor tone.

Exercise capacity during and after spaceflight.

UNLABELLED: Our aim was to elucidate why astronaut's exercise capacity after spaceflight is reduced. Therefore, the kinetics of oxygen uptake (VO2) as a measure for muscular aerobic capacity, as well as maximal oxygen uptake (VO2peak), and anaerobic threshold (PAT) as overall measures for exercise capacity were determined. Measurements of VO2peak and AT were restricted to pre- and postflight sessions. METHODS: Four crew-members of the D-2 mission (10 d) were cycling with steady state phases at 20 W and 80 W, followed by 450s of pseudo random binary sequence (PRBS) changes between 20 W and 80 W, and an incremental exercise test (10 W every 30 s) up to subjective exhaustion. Breath-by-breath VO2, VCO2, ventilation, HR, and blood pressure were continuously recorded. Blood lactate samples were drawn only during the incremental phase. The VO2 kinetics were determined by evaluation of the relationship between the workload and the instantaneous oxygen uptake of each subject. The cross-correlation function between both variables showed two characteristic items, the maximum as a measure for the muscular aerobic capacity, and its lag representing time consuming processes. RESULTS AND DISCUSSION: Each subject showed an individual characteristic of VO2 kinetics. In flight, no significant changes were detected compared to preflight data. Decreases in lags of cross-correlation function maxima and decreases in mean blood pressure during exercise indicate lowered blood volumes 2 d after the flight. Lowered blood volumes can explain the losses in exercise capacity. The maximum of the cross-correlation function did not change significantly which indicates unchanged muscular oxidative capacity.

Influence of gravity on cardiovascular reflexes from skeletal muscle receptors.

Skeletal muscles are important reflexogenic areas of the cardiovascular system. The afferent pathways of the reflex loops involve slow-conducting group III and group IV fibers that are excited by mechanical and chemical events in the muscle. The present paper reviews a series of experiments dealing with the question of whether those afferents are also influenced by gravitational forces. The results of these studies suggest the following answers: 1) gravitational forces can modulate cardiovascular reflexes from exercising skeletal muscles. 2) This effect is primarily due to changes in the interstitial fluid volume rather than to a direct mechanical influence, venous pressure, or venous volume. 3) The amplitudes of heart rate and blood pressure responses during exercise are inversely related to the local interstitial volume. Measurements during post-exercise circulatory arrest indicate that this sensitivity is mainly mediated by muscle chemoreceptors. These receptors, which also contribute to the spinal control of movement, generally appear to be sensitized by regional fluid losses and desensitized by overhydration of their environment.

Glycolytic ATP production estimated from 31P magnetic resonance spectroscopy measurements during ischemic exercise in vivo.

In an oxygen-depleted muscle, glycolytically produced ATP is inversely related to the ([ATP]+ creatine phosphate [PCr]) decrease because ATP, PCr, and glycolysis are virtually the only energy sources under these conditions. In particular, the onset of glycolysis or any appreciable increase in the rate of glycolytic ATP production will lead to a slower rate of ([ATP]+ [PCr]) breakdown at a given energy consumption. To quantify this relationship, endurance athletes performed isometric foot plantar flexion (20% of a test force [TF], n = 10; 50% TF, n = 5) during local arterial occlusion. Parameters of energy metabolism were measured with 31P magnetic resonance spectroscopy (31P-MRS). During exercise, [PCr] decreased to 80 +/- 10 (20% TF) and 11 +/- 4% (50% TF) of its resting concentration, and pH dropped from 7.04 +/- 0.01 to 6.98 +/- 0.10 (20% TF) and from 7.03 +/- 0.02 to 6.70 +/- 0.10 (50% TF). In both experiments, two phases of ([ATP]+ [PCr]) decrease were observed: an initial faster decrease was followed by a slower decline. The latter phase started at about the time when the pH began to drop. The difference between a line extrapolated from the slope of the initial phase and the measured ([ATP]+[PCr]) decrease was used as an estimate for glycolytically produced ATP. This estimate and pH were significantly correlated with r = -0.97 (20% TF) and r = -0.99 (50% TF). These results indicate that glycolytically produced ATP can be estimated from the ([ATP]+ [PCr]) decrease during exercise.

Physical responses to different modes of interval exercise in patients with chronic heart failure--application to exercise training.

METHOD: In exercise training with chronic heart failure patients, working muscles should be stressed with high intensity stimuli without causing cardiac overstraining. This is possible using interval method exercise. In this study, three interval exercise modes with different ratios of work/ recovery phases (30/60 s, 15/60 s and 10/60 s) and different work rates were compared during cycle ergometer exercise in heart failure patients. Work rate for the three interval modes was 50% (30/60 s), 70% (15/60 s) and 80% (10/60 s) of the maximum achieved during a steep ramp test (increments of 25 w/10 s) corresponding to 71, 98 and 111 watts on average. Metabolic and cardiac responses to the three interval exercises were then examined including catecholamine levels and perceived exertion. Parameters measured during interval exercise were compared with an intensity level of 75% peak VO2, determined during an ordinary ramp exercise test (increments of 12.5 W.min-1). RESULTS: (mean +/- SEM) (1) In all three interval modes, VO2, ventilation and lactate did not increase significantly during the course of exercise. Mean values during the last work phase were between 754 +/- 30 and 803 +/- 46 ml.min-1 for VO2, between 26 +/- 3 and 28 +/- 1 l.min-1 for ventilation and between 1.24 +/- 0.14 and 1.29 +/- 0.10 mmol.l-1 for lactate. (2) In mode 10/60 s, heart rate and systolic blood pressure increased significantly (82 +/- 4 --> 85 +/- 4 beats.min-1; 124 +/- 5 --> 134 +/- 5 mmHg; P < 0.05 each), while in mode 15/60 s catecholamines increased significantly (norepinephrine 0.804 +/- 0.089 --> 1.135 +/- 0.094 nmol.l-1; P < 0.008; epinephrine 0.136 +/- 0.012 --> 0.193 +/- 0.019 nmol.l-1; P < 0.005). (3) In all three modes, rating of leg fatigue and dyspnoea increased significantly during exercise but remained within the range of values considered 'very light to fairly light' on the Borg scale. (4) Compared to an intensity level of 75% peak VO2, work rate during interval work phases was between 143 and 221%, while cardiac stress (rate-pressure product) was significantly lower (83-88%). CONCLUSION: All three interval modes resulted in physical response in an acceptable range of values, and thus can be recommended.