Heart rate changes caused by varying the oxygen supply to isolated hind legs of rats

Summary In a rat with an isolated hind leg circulation perfused with varying tyrode solutions, heart rate (HR) changes were studied in dependence of in the isolated hind leg and of , [K⁺], pH and lactic acid concentration ([Lac]) measured in the venous outflow of the isolated hind leg. In experimental series I the inflow was kept constantly high (either about 65 or 72 kPa). The perfusion pressure alternated between 16 and 24 kPa leading to flow rates in isolated hind legs ( ) from 30 to 50 ml · 100 g⁻¹ · min⁻¹. The depended on the momentary (flow-limited oxygen uptake). The [K⁺] and [Lac], the pH and the remained nearly constant while the was lower at small flow rates. The HR decreases some 4 min after initial enhancement of and . Series II comprised experiments with low flow rates and a medium oxygen supply ( =2.5−17.4 ml · 100 g⁻¹ · min⁻¹), =17.5−62.7 kPa). The ranged between 0.02 and 0.2 ml · 100 g⁻¹ · min⁻¹. The [K⁺] and [Lac], the and the HR increased while the pH decreased. The [Lac] in the outflow showed a strong dependence on oxygen uptake and — at a weak oxygen supply — on the time. Cross-correlation analyses between the parameters confirmed that the HR was best temporally correlated to the [Lac] in the outflow. In series III a 17 min perfusion of normoxic solution ( =65.3 kPa) was followed by perfusion with a hypoxic tyrode solution ( =8.7 kPa). was 30 ml · 100 g⁻¹ · min⁻¹. The [Lac], the and the HR increased accompanied by a decrease in pH. However a HR increase was observed only when the actual values of [Lac], and pH exceeded their normal ranges for a resting muscle. The results support the hypothesis that heart rate is additionally influenced by metabolic muscle receptors measuring lactic acid concentration in working muscle.     

Fitness as a determinant of oxygen uptake response to constant-load exercise

Summary Exercise performed above the lactate threshold (Θ _La) produces a slowly-developing phase of oxygen uptake ( ) kinetics which elevates above that predicted from the sub-Θ _La -work rate relationship. This phenomenon has only been demonstrated, to date, in subjects who were relatively homogeneous with respect to fitness. This investigation therefore examined whether this behaviour occurred at a given absolute or whether it was a characteristic of supra-Θ _La exercise in a group of subjects with over a threefold range ofΘ _La (990–3000 ml O₂·min⁻¹) and peak (1600–5260 ml O₂·min⁻¹). Twelve healthy subjects performed: 1) exhausting incremental cycle ergometer exercise for estimation ofΘ _La ( ) and peak , and 11) a series of constant-load tests above and below for determination of the profile and efficiency of work. During all tests expired ventilation, and carbon dioxide production were monitored breath-by-breath. The efficiency of work determined during incremental exercise (28.1±0.7%, ,n=12) did not differ from that determined during sub- constant-load exercise (27.4±0.5%,p>0.05). For constant-load exercise, rose above that predicted, from the sub- -work rate relationship, for all supra- work rates. This was evident above 990 ml O₂·min⁻¹ in the least fit subject but only above 3000 ml O₂·min⁻¹ in the fittest subject. As a consequence the efficiency of work was reduced from 27.4±0.5% for sub- exercise to 22.6±0.4% (p<0.05) at the lowest supra- work rate (i.e. +20 W, on average). The efficiency of work generally decreased further at the higher supra- work rates. We conclude that the response to constant-load exercise includes an additional slow phase of the kinetics for all exercise intensities above irrespective of the fitness of the subject. Consequently, measurements of the aerobic efficiency of work during constant-load exercise must rigorously constrain the exercise intensity to the sub- domain. Supported by grants from the John D. and Catherine T. Mac-Arthur Foundation, USPHS RR 00865-15, and NIH HL 07694-01     

Effects of standing cycling and the use of toe stirrups on maximal oxygen uptake

Summary Twenty-eight subjects (6 normal men, 14 distance runners, and 8 rowers) were tested for maximal oxygen uptake ( ) and associated physiological measures during bicycle ergometer exercise with toe stirrups while standing (BEts) and during treadmill exercise (TM). Correlation between BEts and TM was high (r=0.901, p<0.05). No significant difference existed between the two values (60.3±8.9 vs. 60.5±9.7 ml · kg⁻¹ · min⁻¹; n=28). No differences were found even when three different subgroups were separately compared. It is concluded that the higher elicited during BEts as compared with normal sitting cycling may be attributed to the increased muscle blood flow and/ or involvement of a larger muscle mass, the latter being partly evidenced by the observation of greater electrornyographic activity during BEts.     

Ventilatory anaerobic threshold in healthy children

Summary The ventilatory anaerobic threshold (VAT) during graded exercise was defined as the oxygen uptake ( ) immediately below the exercise intensity at which pulmonary ventilation increased disproportionally relative to . Since VAT is considered to be a sensitive and noninvasive measure for evaluating cardiorespiratoy endurance performance, the purpose of the present study was to determine normal values in children. We examined 257 healthy children (140 boys and 117 girls) varying in age from 5.7 to 18.5 years, during treadmill exercise. The data were analyzed in relation to sex and age. In boys the lowest (ml · min⁻¹ · kg⁻¹) was found in the youngest age group (5–6 year). In girls, on the other hand, no significant increase occurred with age. For VAT, expressed as ml O₂ · min⁻¹ · kg⁻¹ or as a percent of a significant decrease was found in boys and girls with age. This suggests an increase in lactacid anaerobic capacity during growth. In contrast to observations in adults, only low correlations were found between and VAT (r=0.28 in boys and r=0.52 in girls), which suggests that the development of the underlying physiological mechanism does not occur at the same rate in growing children. These data provide normal values for VAT that can be used for clinical exercise testing in the pediatric age group.     

Longitudinal associations between anaerobic threshold and distance running performance

Summary Longitudinal alterations in anaerobic threshold (AT) and distance running performance were assessed three times within a 4-month period of intensive training, using 20 male, trained middle-distance runners (19–23 yr). A major effect of the high intensity regular intensive training together with 60- to 90-min AT level running training (2d ·wk ⁻¹) was a significant increase in the amount of O₂ uptake corresponding to AT ( AT; ml O₂ · min⁻¹ · kg⁻¹) and in maximal oxygen uptake ( ; ml O₂ · min⁻¹ · kg⁻¹). Both AT and showed significant correlations (r=−0.69 to −0.92 andr=−0.60 to −0.85, respectively) with the 10,000 m run time in every test. However, further analyses of the data indicate that increasing AT (r=−0.63,P<0.05) rather than (r=−0.15) could result in improving the 10,000 m race performance to a larger extent, and that the absolute amount of change (δ) in the 10,000 m run time is best accounted for by a combination of δ AT and δ5,000 m run time. Our data suggest that, among runners not previously trained over long distances, training-induced alterations in AT in response to regular intensive training together with AT level running training may contribute significantly to the enhancement of AT and endurance running performance, probably together with an increase in muscle respiratory capacity. This study was supported by Grant 59780141 from the Scientific Research Fund of the Ministry of Education, Science, and Culture, Japan     

Oxygen consumption and metabolic strain in rowing ergometer exercise

Summary Oxygen consumption ( ) when rowing was determined on a mechanically braked rowing ergometer (RE) with an electronic measuring device. was measured by an open spirometric system. The pneumotachograph valve was fixed to the sliding seat, thus reducing movement artefacts. A multi-stage test was performed, beginning with a work load of 150 W and increasing by 50 W every 2 minutes up to exhaustion. Serum lactate concentrations were determined in a 30 s break between the work stages. 61 examinations of oarsmen performing at maximum power of 5 W · kg⁻¹ or more were analysed. and heart rate (HR) for each working stage were measured and the regression line of on the work load (P) and an estimation error (s_xy) were calculated: (ml · min⁻¹) (S_xy = ± 337 ml,r = 0.98) Good reproducibility was found in repeated examinations. Similar spiroergometry was carried out on a bicycle ergometer (BE) with 10 well trained rowers and 6 trained cyclists. of rowing was about 600 ml · min⁻¹ higher than for bicycling in the submaximal stages for both groups. The of RE exercise was 2.6% higher than for oarsmen on BE, and the cyclists reached a greater on BE than the oarsmen. No differences were found between RE and BE exercise heart rate. The net work efficiency when rowing was 19% for both groups, experienced and inexperienced: when cycling it was 25% for cyclists and 23% for oarsmen.     

Metabolic and endocrine responses to graded exercise under acute hypoxia

Summary Eight male subjects (24±1 years old) performed graded ergocycle exercises in normoxic (N) and acute hypoxic (H) conditions (14.5% O₂). decreased from 55.5±1.3 to 45.8±1.4 ml · kg⁻¹ · min⁻¹ in H condition. Plasma glucose and free fatty acid concentrations remained unchanged throughout exercise in both conditions. Increase in blood lactate concentration was associated with relative workload in both conditions. At lactate concentrations were similar in the two conditions, plasma insulin, glucagon, and LH concentrations did not significantly change in either. Plasma δ4-androstenedione and testosterone increased in a similar manner in both conditions. Finally plasma norepinephrine concentration reached at was significantly lower in hypoxia. These results suggest that acute moderate hypoxia does not affect metabolic and hormonal responses to short exercise performed at similar relative workloads, i.e. when the reduction of due to hypoxia is taken into consideration. The lower catecholamine response to maximal exercise under acute hypoxia might suggest that the sympathetic response could be related to relative as well as absolute workloads. Supported by grants from FCAC and FRSQ, Québec and NSERC, Canada     

Transfer effects in endurance exercise

Summary The effects of 8 weeks of bicycle endurance training (5 x /week for 30 min) on maximal oxygen uptake capacity ( ) during arm and leg ergometry, and on the ultrastructure of an untrained arm muscle (m. deltoideus), and a trained leg muscle (m. vastus lateralis) were studied. With the training, leg- for bicycling increased by +13%, while the capillary per fiber ratio and the volume density of mitochondria in m. vastus lateralis increased by +15% and +40%, respectively. In contrast, the untrained m. deltoideus showed an unchanged capillary per fiber ratio and a decreased mitochondrial volume density (−17%). Despite this decrease of mitochondrial volume arm- increased by +9%. It seems unlikely that the observed discrepancy can be explained by cardiovascular adaptations, since arm cranking did not fully tax the cardiovascular system (arm- /leg- : 0.74 and 0.71 before and after training, respectively). Thus neither cardiovascular adaptations nor local structural changes in the untrained muscles could explain the increased arm- . However, the enhanced capacity for lactate clearance after endurance training could be sufficient to account for the larger during arm cranking. We propose that an increased net oxidation of lactate might be responsible for the increased arm- found after bicycle endurance training. This work was supported by grant 3.128.81 from the Swiss National Science Foundation, and by Cilo S.A., Bicycles, Romanel/Switzerland     

Hypoxic ventilatory response during rest and exercise after a Himalayan expedition

Hypoxic ventilatory response (HVR) was examined before and after acclimatization to high altitude. Transient hyperoxic switches according to Dejours's technique were used to examine the contribution of HVR to the hyperpnoea of increasing exercise intensities. Ten mountaineers were exposed to hypoxia (oxygen fraction in inspired gas,F ₁O₂ = 0.11, 79 mmHg) before the expedition and after return from altitude (56 days, 30 days at 4900 m or higher). After 25-min breathing hypoxic gas, the subjects performed a maximal cycle ergometer test (increments 50 W per 5 min). Respired gases and ventilation were analysed breath-by-breath, partial pressure of oxygen (PO₂) and oxygen saturation (SO₂) were measured in capillary blood. The HVR was tested by switching two breaths to anF ₁O₂ of 1.0. The nadir of after the switch was measured (decrease in ventilation, D ). The HVR was expressed as the D at a PO₂ of 40 mmHg (D ) and the D versus decrease ofSO₂ (D /[100 −SO₂]). The HVR estimated by D increased from 19.9 to 28.01 · min⁻¹ (median,P = 0.013). The HVR expressed as D /(100 −SO₂) at rest was no different before and after acclimatization (0.89 and 0.86 l · min⁻¹ · %⁻¹, respectively) and during exercise it did not change before the expedition (0.831 · min⁻¹ %⁻¹). However, D /(100 −SO₂) increased significantly with exercise intensity after the expedition (1.61 l · min⁻¹ · %⁻¹ at 200 W). The changes of D versusSO₂ as well as of D versus were steeper after the expedition than before. In summary, after return from 30 day at high altitude, an increased HVR was observed. The augmentation of HVR was evident at higher exercise intensities and we suggest that this reflects a change in sensitivity of the peripheral chemoreflex loop.     

Changes in ventilation at the start and end of moderate and heavy exercise of short and long duration

Summary These experiments examined the effect of exercise intensity and duration on the magnitude of the abrupt change in ventilation at the start ( ) and end ( ) of exercise. Five subjects performed constant load treadmill exercise at 50% and 80% of their maximum oxygen consumption ( ) for 6 and 10 min while inspiring atmospheric air. The subjects also completed additional exercise tests at 80% for 10 min while inspiring an oxygen-enriched gas mixture. During each exercise trial ventilation was measured breath-by-breath. The and were determined by using non-linear curve-fitting techniques. The results showed that was greater at the start of the 80-% exercise tests compared to the 50-% tests and that at each level of exercise was greater than . The results also demonstrated that was inversely related to the intensity and duration of exercise. Furthermore, the was not altered subsequent to the inspiration of oxygen-enriched air. These findings have led us to postulate that the stimulus responsible for is reduced during exercise and that the degree of reduction is related to the intensity and duration of exercise. In addition, it was concluded that these changes might occur independently of peripheral chemoreceptor activity.     

Ventilation studied with circulatory occlusion during two intensities of exercise

Summary Our purpose was to study the possible role of a pulmonary chemoreceptor in the control of ventilation during exercise. Respiratory gas exchange was measured breath-by-breath at two intensities of exercise with circulatory occlusion of the legs. Eight male subjects exercised on a cycle ergometer at 49 and 98 W for 12 min; circulation to the legs was occluded by thigh cuffs (26.7 kPa) for two min after six min of unoccluded exercise. PETCO₂ and decreased and PETO₂ increased significantly during occlusion at both workloads. Occlusion elicited marked hyperventilation, as evidenced by sharp increases in , and . A sudden sharp increase in PETCO₂ was seen 12.3±0.5 and 6.5±1.2 s after cuff release in all subjects during exercise at 49 and 98 W, respectively. At 49 W a post-occlusion inflection in was seen in 7 subjects 21.1±5.8 s after the PETCO₂ inflection. Three subjects showed an inflection in at 98 W 23.3±7.5 s after the PETCO₂ inflection. There were significant increases in PETCO₂, and after cuff release. mirrored better than , post occlusion. On the basis of a significant lag time between inflections in PETCO₂ and following cuff release, it is concluded that the influences of a pulmonary CO₂ receptor were not seen.     

Differences in oxygen consumption and external power between male and female speed skaters during supramaximal cycling

Summary Differences in performance levels between elite male and female endurance athletes are often explained by differences found in max even when expressed in max per kilogram lean body mass ( /LBM). Such an explanation is only a matter of course when less or no difference exists in mechanical efficiency, anaerobic power and technical variables like friction constants between males and females, particularly during supramaximal exercises. In this study five elite male speed skaters were compared with five elite female speed skaters with respect to oxygen consumption and external power during a 3 min supramaximal bicycle ergometer test. The training background and training history of both groups were comparable. Although the elite males showed a 20% higher /BW and 8% higher /LBM (71.0 versus 65.0 1·min⁻¹·kg⁻¹) than the females, the female group showed the same mean external power P_c per kilogram bodyweight, and a surprising 12% higher P_C/LBM than the males (6.47 versus 5.79 W·kg⁻¹). Hence the female group delivered 22% more external power per liter of oxygen consumption. With the help of additional data from 14 male and 11 female sub-elite skaters it is shown that the differences between the elite groups are mainly due to sex differences. In the light of differences between men and women reported in other studies, it seems likely that the differences found in this study are due to a difference in mechanical efficiency which particularly occurs in supramaximal tasks. With respect to skating performance, it is concluded that the difference in performance level between elite male and female skaters will mainly be determined by differences in skating technique and in frictional losses, and not by differences in work capacity.     

Control of sweating during the human menstrual cycle

Summary Thermoregulatory responses were studied in seven women during two separate experimental protocols in the follicular (F, days 4–7) phase and during the luteal (L, days 19–22) phase of the menstrual cycle. Continuous measurements of esophageal temperature (T _es), mean skin temperature ( ), oxygen uptake and forearm sweating ( ) were made during all experiments. Protocol I involved both passive heat exposure (3 h) and cycle exercise at ∼80% peak during which the environmental chamber was controlled atT _a=50.0° C, rh=14% (P _w=1.7 kPa). In protocol II subjects were tested during thirty-five minutes of exercise at ∼85% peak atT _a=35° C and rh=25% (P _w=1.4 kPa). The normal L increase in restingT _es (≈0.3° C) occurred in all seven subjects. was higher during L than F in all experiments conducted at 50° C. During exercise and passive heat exposure, theT _es threshold for sweating was higher in L, with no change in the thermosensitivity (slope) of toT _es between menstrual cycle phases. This rightward or upward shift inT _es threshold for initiation of sweating averaged 0.5° C for all experiments. The data indicate the luteal phase modulation in the control of sweating in healthy women is also apparent during severe exercise and/or heat stress.     

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

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

A prediction equation for indirect assessment of anaerobic threshold in male distance runners

Summary The predictability of anaerobic threshold (AT) from maximal aerobic power, distance running performance, chronological age, and total running distance achieved on the treadmill (TRD) was investigated in a sample of 53 male distance runners, 17–23 years of age. The dependent variable was oxygen uptake ( ) at which AT was detected (i. e., @AT). A regression analysis of the data indicated @AT could be predicted from the following four measurements with a multipleR=0.831 and a standard error of the estimate of 2.66 ml · min⁻¹ · kg⁻¹: (67.9±5.7 ml · min⁻¹ · kg⁻¹), 1,500-m running performance (254.5±14.2 s), TRD (6.82±1.13 km), and age (19.4±2.2 years). When independent variables were limited to (X ₁) and 1,500-m running performance (X ₂) for simpler assessment, a multipleR=0.806 and a standard error of the estimate of 2.76 ml · min⁻¹ · kg⁻¹ were computed. A useful prediction equation with this predictive accuracy was considered to be @AT= 0.386X₁−0.128X₂+57.11. To determine if the prediction equation developed for the 53 male distance runners could be generalized to other samples, cross-validation of the equation was tested, using 21 different distance runners, 17–22 years of age. A high correlation (R=0.927) was obtained between @AT predicted from the above equation and directly measured @AT. It is concluded that the generalized equation may be applicable to young distance runners for indirect assessment of @AT. This study was supported by grants from The Descente Foundation for the Promotion of Sports Science, awarded to K. Tanaka     

Effects of endurance training on hyperammonaemia during a 45-min constant exercise intensity

Summary Eleven laboratory-pretrained subjects (initial =54 ml·kg⁻¹·min⁻¹) took part in a study to evaluate the effect of a short endurance training programme [8–12 sessions, 1 h per session, with an intensity varying from 60% to 90% maximal oxygen consumption ] on the responses of blood ammonia (b[NH ₄ ⁺ ]) and lactate (b[la]) concentrations during progressive and constant exercise intensities. After training, during which did not increase, significant decreases in b[NH ₄ ⁺ ], b[la] and muscle proton concentration were observed at the end of the 80% constant exercise intensity, although b[NH ₄ ⁺ ] and b[la] during progressive exercise were unchanged. On the other hand, no correlations were found between muscle fibre composition and b[NH ₄ ⁺ ] in any of the exercise procedures. This study demonstrated that a constant exercise intensity was necessary to reveal the effect of training on muscle metabolic changes inducing the decrease in b[NH ₄ ⁺ ] and b[la]. At a relative power of exercise of 80% , there was no effect of muscle fibre composition on b[NH ₄ ⁺ ] accumulation.     

Factors which alter the relationship between ventilation and carbon dioxide production during exercise in normal subjects

The slope of the linear relationship between ventilation and carbon dioxide production has been thought to indicate that is one of the major stimuli to . A group of 15 normal subjects undertook different incremental treadmill exercise protocols to explore the relationship between and . An incremental protocol using 1 instead of 3-min stages of exercise resulted in an increase in the to ratio [26.84 (SEM 1.23) vs 31.08 (SEM 1.36) (P < 0.008) for the first stage, 25.24 (SEM 0.86) vs 27.83 (SEM 0.91) (P < 0.005) for the second stage and 23.90 (SEM 0.86) vs 26.34 (SEM 0.81) (P = 0.001) for the third stage]. Voluntary hyperventilation to double the control level of during exercise resulted in an increase in the to slope [from 21.3 (SEM 0.71) for the control run to 35.1 (SEM 1.2) for the hyperventilation run (P < 0.001)]. Prolonged hyperventilation (5 min) during exercise at stage 2 of the Bruce protocol resulted in a continuted elevation of and the slope. A steady state of and metabolic gas exchange can only be said to have been present after at least 3 min of exercise. Voluntary hyperventilation increased the slope of the relationship between and . End-tidal carbon dioxide fell, but remained within the normal range. These results would suggest that a non-carbon dioxide factor may have been responsible for the increase we found in during exercise, and that factors other than increased dead space ventilation can cause an increased ventilation to slope, such as that seen in some pathophysiological conditions, such as chronic heart failure.     

Intraerythrocyte and plasma lactate concentrations during exercise in humans

Summary The purpose of this study was to examine plasma and intraerythrocyte lactate concentrations during graded exercise in humans. Seven adult volunteers performed a maximum O₂ uptake ( ) test on a cycle ergometer. Plasma and intraerythrocyte lactate concentrations (mmol · L⁻¹ of plasma or cell water) were determined at rest, during exercise, and at 15-min post-exercise. The results show that plasma and intraerythrocyte lactate concentrations were not significantly different from each other at rest or moderate (⩽50% ) exercise. However, the plasma concentrations were significantly increased over the intraerythrocyte levels at 75% and 100% . The plasma to red cell lactate gradient reached a mean (±SE) 1.7±0.4 mmol · L⁻¹ of H₂O at exhaustion, and was linearly (r=0.84) related to the plasma lactate concentration during exercise. Interestingly, at 15-min post-exercise the direction of the lactate gradient was reversed, with the mean intraerythrocyte concentration now being significantly increased over that found in the plasma. These results suggest that the erythrocyte membrane provides a barrier to the flux of lactate between plasma and red cells during rapidly changing blood lactate levels. Furthermore, these data add to the growing body of research that indicates that lactate is not evenly distributed in the various water compartments of the body during non-steady state exercise.     

Peak oxygen consumption and lactate threshold in full mask versus mouth mask conditions during incremental exercise

Respirator masks vary in inhalation and exhalation resistance, and in dead volume. It is believed that these factors may contribute significantly to an early anaerobic threshold in mask wearers during maximal exercise. Very little is known concerning the effect of respirator masks on maximal oxygen consumption and the lactate threshold (LT). The purpose of the present study was to assess peak LT and the ventilatory threshold (VT) of 14 experienced cyclists performing two maximal cycle exercise protocols while wearing a full respirator mask (FM) (M17 type) and a mouth mask (MM). was 10% lower under FM conditions. Peak values for ventilation , respiratory rate (f _bpeak) and tidal volume (V _Tpeak) were all significantly lower under with FM versus MM conditions. Performance time and maximal heart rate (f _cpeak) were not different between mask conditions. The LT and VT when expressed in % and the lactate concentration (mmol · l⁻¹ at LT and VT were not significantly different across mask conditions. Bland-Altman plots demonstrated longer inhalation times, decreasedf _r values and greater oxygen extraction under FM conditions. Thus, perhaps due to the increased inhalation resistance of the FM condition, subjects were unable to attain their “normal” despite similar performance times and maximalf _c. Furthermore, despite a diminished with FM, LT and VT appeared to be the same as with a MM.     

Hormonal and metabolic response to three types of exercise of equal duration and external work output

Summary Five normal men, aged 20–30 years, participated in three types of exercise (I, II, III) of equal duration (20 min) and total external work output (120–180 kJ) separated by ten days of rest. Exercises consisted of seven sets of squats with barbells on the shoulders (I; Maximal Power Output _max=600−900 W), continuous cycling at 50 rev · min⁻¹ (II; _max=100−150 W) and seven bouts of intermittent cycling at 70 rev · min⁻¹ (III; _max=300−450 W). Plasma cortisol, glucagon and lactate increased significantly (P<0.05) during the exercise and recovery periods of the anaerobic, intermittent exercise (I and III) but not in the continuous, aerobic exercise (II). No consistent significant changes were found in plasma glucose. Plasma insulin levels decreased only during exercise II. The highest increase in cortisol and glucagon was not associated with the highest , , _max or HR; however it was associated with the anaerobic component of exercise (lactic acid). It is suggested that in exercises of equal duration and total external work output, the continuous, aerobic exercise (II) led to lowest levels of glucogenic hormones.