Exercise-induced hypoxemia in athletes: Role of inadequate hyperventilation

Summary These experiments examined the exercise-induced changes in pulmonary gas exchange in elite endurance athletes and tested the hypothesis that an inadequate hyperventilatory response might explain the large intersubject variability in arterial partial pressure of oxygen (P _a0₂) during heavy exercise in this population. Twelve highly trained endurance cyclists [maximum oxygen consumption (VO_2max) range = 65-77 ml·kg^–1·min^–1] performed a normoxic graded exercise test on a cycle ergometer toVO_2max at sea level. During incremental exercise atVO_2max 5 of the 12 subjects had ideal alveolar to arterial P02 gradients (P _A-aO₂) of above 5 kPa (range 5-5.7) and a decline from restingP _aO₂ (P _aO₂) 2.4 kPa or above (range 2.4-2.7). In contrast, 4 subjects had a maximal exercise (P _A-aO₂) of 4.0-4.3 kPa with P _aO₂ of 0.4-1.3 kPa while the remaining 3 subjects hadP _A-aO₂ of 4.3-5 kPa with P _aO₂ between 1.7 and 2.0 kPa. The correlation between P_AO₂ andP _aO₂ atVO_2max was 0.17. Further, the correlation between the ratio of ventilation to oxygen consumption VSP _aO₂ and arterial partial pressure of carbon dioxide VSP _aO₂ atVO_2max was 0.17 and 0.34, respectively. These experiments demonstrate that heavy exercise results in significantly compromised pulmonary gas exchange in approximately 40% of the elite endurance athletes studied. These data do not support the hypothesis that the principal mechanism to explain this gas exchange failure is an inadequate hyperventilatory response.     

Ventilatory threshold and work efficiency during exercise on cycle and paddling ergometers in young female kayakists

The aim of this study was to assess the effects of increasing specific (paddling erogmeter) and non-specific (cycle ergometer) exercise on parameters relating to the ventilatory threshold (Th_vent) and work efficiency in 11 young female flat-water kayakists. When these trained subjects were tested using non-specific workloads, their oxygen uptake (VO₂) values at Th_vent, as a percentage ofVO_2max (%VO_2max), were close to those of untrained subjects [74.2 (5.6) %VO_2max, mean (SD)]. However, when we tested the same subjects using specific exercise, we recorded values typical of highly trained athletes [84.8 (4.7) %VO_2max). For the non-specific exercise on the cycle erogmeter, we recorded work efficiency values close to those of untrained subjects [22.3 (2.5) %]; however, for the specific exercise on the paddling ergometer, we recorded much lower values [13.4 (3.0) %] both at the level of Th_vent. The work efficiency at two warm-up submaximal exercise loads on the paddling ergometer was non-significantly lower than values at Th_vent [12.3 (2.8) % and 12.9 (2.9) % respectively]. Significant correlations were found between maximal-performanceVO₂ (ml · kg^–1 · min^–1) and performance at Th_vent during paddling and race performance (0.623, 0.630 and 0.648 respectively, allP<0.05). Because the results of both specific and non-specific submaximal exercise tests are different, we suggest caution in the interpretation of physiological variables that may be sensitive to training status. The evaluation of Th_vent and work efficiency as supplementary parameters during laboratory studies enables the determination of the effectiveness of the training process and the specific adaptation of the subjects.     

Sex differences in performance-matched marathon runners

Summary Six male and six female runners were chosen on the basis of age (20–30 years) and their performance over the marathon distance (mean time = 199.4, SEM 2.3 min for men and 201.8, SEM 1.8 min for women). The purpose was to find possible sex differences in maximal aerobic power (VO_2max), anaerobic threshold, running economy, degree and utilization of VO_2max (when running a marathon) and amount of training. The results showed that performance-matched male and female marathon runners had approximately the same VO_2max (about 60 ml·kg^–1·min^–1). For both sexes the anaerobic threshold was reached at an exercise intensity of about 83% of VO_2max, or 88%–90% of maximal heart rate. The females' running economy was poorer, i.e. their oxygen uptake during running at a standard submaximal speed was higher (P<0.05). The heart rate, respiratory exchange ratio and blood lactate concentration also confirmed that a given running speed resulted in higher physiological. strain for the females. The percentage utilization of VO_2max at the average marathon running speed was somewhat higher for the females, but the difference was not significant. For both sexes the oxygen uptake at average speed was 93%–94% of the oxygen uptake corresponding to the anaerobic threshold. Answers to a questionnaire showed that the females' training programme over the last 2 months prior to running the actual marathon comprised almost twice as many kilometres of running per week compared to the males (60 and 33 km, respectively). The better state of training of the females was also confirmed by a 10% higher VO_2max, in relation to lean body mass than that of the male runners. Apart from the well-known variation in height and differences in the percentage of fat, the difference between performance-matched male and female marathon runners seemed primarily to be found in running economy and amount of training.     

Impact of menstrual cycle phase on the exercise status of young,sedentary women

The purpose of the present study was to compare exercise status during the follicular (FP) and luteal (LP) phases of the menstrual cycle of a single group of young, sedentary women, where the marked differential in the blood concentrations of 17-oestradiol ([E₂]) and progesterone ([P₄]) has the potential to alter the metabolic response to exercise. Fourteen females [21.8 (4.0) years, peak oxygen uptake (V̇O_2peak) <45 ml·kg ^–1·min^–1] performed both incremental exercise to exhaustion and steady-state submaximal cycle ergometer exercise while measurements were made of several metabolic and hormonal variables. With the incremental exercise test, time to exhaustion, maximal power output and total work done were not different between the two phases, nor were the absolute values for V̇O_2peak or the corresponding values for ventilation (V̇E), respiratory frequency (f_R) and heart rate (HR). Resting, end-exercise and peak (post-exercise) plasma lactate concentrations and the lactate threshold were not different between the two phases either. However, as the workloads increased during the incremental protocol, plasma lactate concentration, carbon dioxide output (CO₂) and the respiratory exchange ratio (RER) all were lower during LP, while oxygen uptake (V̇O₂) was higher. With steady-state submaximal exercise, at workloads corresponding to 25% and 75% of menstrual cycle phase-specific O_2peak, V̇O₂ and the oxygen pulse (V̇O₂/HR) were higher and RER and plasma lactate concentration lower during LP. Regardless of phase, [E₂] increased with both incremental and steady-state submaximal exercise, while [P₄] was unchanged. It is concluded that while exercise capacity, as defined by O_2peak and the lactate threshold, is unaffected by cycle phase in young, sedentary women, the metabolic responses in the LP during both incremental and steady-state submaximal exercise suggest a greater dependence on fat as an energy source.     

Respiratory muscle function in trained and untrained adolescents during short-term high intensity exercise

Summary The breathing pattern and respiratory muscle function were investigated in ten trained and ten untrained adolescents (aged 15–16 years) while undergoing an incremental intensity exercise test on a cycle ergometer up to 80% maximal oxygen consumption ( O_2max), maintained to exhaustion. Before and after exercise, maximal inspiratory (P _{I max}) and expiratory (P _{E max}) pressures were measured at residual volume and total lung capacity, respectively. During exercise, the breathing pattern [tidal volume (V _T), respiratory frequency (f _R), ventilation] and the relative contribution of ribcage and abdomen to V _T were assessed using inductance plethysmography. Electromyographic activities of transversus abdominis (EMG_tr) and diaphragm (EMG_di) muscles were recorded and analysed during exercise. There was a difference in the change in the pattern of breathing between the trained and the untrained group; f _R increased significantly (P < 0.05) at 40% O_2maxfor the untrained group. Before exercise there was no difference in the maximal respiratory pressures. Up to 60% and 80% O_2max, transversus abdominis and diaphragm muscle activity increased significantly in the trained adolescents. However in this group, no evidence of respiratory muscle fatigue appeared: P _{I max}, P _{E max} and the frequency spectrum of EMG_tr and EMG_di were not altered by exercise up to exhaustion. In the untrained group, who had high ventilatory responses, expiratory muscle function was unchanged at the end of the exercise, but signs of inspiratory muscle fatigue appeared in that P _{I max} was significantly decreased after exercise.     

Specificity effects of run versus cycle training on ventilatory threshold

Summary This study compared the effects of 9 weeks of run (RT) versus cycle (CT) training on ventilatory threshold (Th_v) determined during treadmill (TM) and cycle ergometer (CE) graded exercise testing. Sixteen college age men were assigned to a RT or CT group and performed a TM and a CE test before and after training. Both training groups performed similar training protocols which initially consisted of continuous exercise 4 days·week^–1 at 75–80% maximum heart rate (fc,_max) for 45 min. Training intensity was later increased to 80–85% fc _max and interval training (90–95% fc,_max) was incorporated 2 days·week^–1 into the continuous training. Both groups showed significantly improved maximal oxygen consumption ( O_2max) on both TM and CE tests (P<0.01) with no significant differences between the groups. Significant Th_v increases (P<0.05) were found on TM tests for RT (n=8) and CT (n=8) groups [mean (SD); 443 (438) and 373 (568) ml O₂·min^–1, respectively] with no difference between the groups. Results from the CE tests revealed a significant Th_v increase (P<0.01) for the CT group [566 (663) ml O₂·min^–1] with no change for the RT group. The Th_v improvement noted for the RT group was significantly different (P< 0.05) comparing CE with TM tests but not for the CT group. The results indicate that CT and RT improvement in Th_v for runners is dependent upon mode of training and testing, and there is an apparent dissociation of O_2maxand Th_v specific to training.     

A new approach to rowing ergometry: establishing exercise intensity relative to maximum force output

Summary The present experiment evaluated a new approach to establish exercise intensity during hydraulic rowing ergometry. In contrast to the traditional approach where exercise intensity is augmented by systematically increasing workload, the new procedure increments the intensity of exercise while maintaining a constant percentage of maximum force output. Ten college females exercised on a hydraulic rower that allowed for control of rowing speed and resistance. The new method to establish work intensity was to row at a cadence of 30 c·min^–1 at a force output equal to 50% of maximum rowing force at each setting determined dynamically prior to testing. Two protocols were used for the maximum tests on the hydraulic rower. Row 1 was a 17-min, six-stage, incremental continuous row test performed at increasingly difficult settings from easy (setting 1; 603 N) to difficult (setting 6; 893 N). Row 2 was identical to row 1 until 15 min when resistance was reduced to setting 2 (658 N) for allout effort during the last 2 min. During this time, cadence declined from 30 c·min^–1 to 19.4 c·min^–1 at dial setting 6 and increased to 35.4 c·min^–1 at dial setting 2. Both rowing protocols were compared to maximal physiological responses during treadmill running (TM). Compared to TM, both rowing protocols elicited. significantly lower maximum oxygen uptake (VO_2max;P<0.05; row 1=29.0% and row 2=12.9%) and maximum heart rate (HR_max;P<0.05; row 1=12.9% and row 2=6.7%). Maximum ventilation (V _Emax) during row 1 was also lower by 30.4% than TM (P<0.05). In addition, row 1 was significantly lower (P<0.05) than row 2 forVO_2max (2.23 vs 2.60 l·min^–1), HR_max (165.5 vs 177.3 beats·min^–1), andV _Emax (62.7 vs 86.3 1·min^–1). These results demonstrate thatVO_2max, HR_max, andV _Emax are depressed when rowing exercise is performed at a high intensity relative to maximum strength. We conclude that the new approach to establish exercise intensity relative to maximum force production is more effective for eliciting near maximum values ofVO₂, HR, andV _E than the conventional method that increases the workload by set increments without consideration of maximal strength.     

Effect of an iron supplement on body iron status and aerobic capacity of young training women

Summary Serum iron deficiency has a high incidence in female athletes. We investigated the effects of a daily oral iron supplement, (160 mg) administered during an intensive 7-week physical training programme, on body iron status, and the maximal aerobic capacity (VO_2max) of 13 women (group A) compared to 15 who took a placebo (group B). The subjects were 19 years old. Blood samples were obtained before training began and on days 1, 7, 21 and 42 of training. They were analysed for packed cell volume (PVC) and for haemoglobin (Hb), 2,3-diphosphoglycerate (2,3-DPG), haptoglobin, iron and ferritin concentrations. TheVO_2max was measured on days 0, 21 and 42 of training. Following 21 days of training Hb, PCV and ferritin were significantly higher (P0.01) in group A compared to group B. Over the training period Hb rose by 9.3% and 2.4% in groups A and B, respectively. At the end of training 66% of group B exhibited ferritin concentrations below 10 ng·ml^–1, while none of group A had such low values. MeanVO_2max of group A had increased by 7.5% following 21 days of training (P0.01) and by 15.3% after 42 days. No appreciable increase inVO_2max had occurred in group B by day 21 (significantly lower thanVO_2max of group A;P0.05), however by day 42 it had increased by 14.3% (P0.05). In both groups 2,3-DPG·g Hb^–1 had increased significantly (P0.005) by day 7 (22%) and remained at that level for an additional 35 days. We concluded that a daily oral iron supplement given to young women during intensive training improved several haematological variables and their body iron status. This improvement was associated with an increasedVO_2max only during the early stages of their training (day 21) compared with the placebo group.     

Cardiac output during exercise in paraplegic subjects

Summary The purpose of this study was to measure the cardiac output using the CO₂ rebreathing method during submaximal and maximal arm cranking exercise in six male paraplegic subjects with a high level of spinal cord injury (HP). They were compared with eight able bodied subjects (AB) who were not trained in arm exercise. Maximal O₂ consumption ( O_2max) was lower in HP (1.1 1·min^–1, SD 0.1; 17.5 ml·min^–·kg, SD 4) than in AB (2.5 1·min^–1, SD 0.6; 36.7 ml·min^–1·kg, SD 10.7). Maximal cardiac output was similar in the groups (HP, 141·min^–1 SD 2.6; AB, 16.81·min^–1 SD 4). The same result was obtained for maximal heart rate (f _c,max (HP, 175 beats·min^–1, SD 18; AB, 187 beats·min^–, SD 16) and the maximal stroke volume (HP, 82 ml, SD 13; AB, 91 ml, SD 27). The slopes of the relationshipf _c/ O₂ were higher in HP than AB (P<0.025) but when expressed as a % O_2max there were no differences. The results suggests a major alteration of oxygen transport capacity to active muscle mass in paraplegics due to changes in vasomotor regulation below the level of the lesion.     

Effects of supramaximal exercise on blood glucose levels during a subsequent exercise

Summary The purpose of the present investigation was to examine the effects of hyperglycoemia induced by supramaximal exercise on blood glucose homeostasis during submaximal exercise following immediately after. Six men were subjected to three experimental situations; in two of these situations, 3 min of high-intensity exercise (corresponding to 112, SD 1%VO_{2 max}) was immediately followed by either a 60-min period of submaximal exercise (68, SD 2%VO_{2 max}) or a 60-min resting period. In the third situation, subjects performed a 63-min period of submaximal exercise only. There were no significant differences between the heurt rates, oxygen uptakes, and respiratory exchange ratios during the two submaximal exercise bouts (> 15 min) whether or not preceded by supramaximal exercise. The supramaximal exercise was associated within 10 min of the start increases (P<0.05) in blood glucose, insulin, and lactate concentrations. This hyperglycemia was more pronounced when subjects continued to exercise submaximally than when they rested (at 7.5 min;P<0.05). There was a more rapid return to normal exercise blood glucose and insulin values during submaximal exercise compared with rest. The data show that the hyperinsulinemia following supramaximal exercise is corrected in between 10–30 min during submaximal exercise following immediately, suggesting that this exercise combination does not lead to premature hypoglycemia.     

Transfer effects of endurance training to exercise with untrained limbs

Summary There has been a controversy over whether the increases in maximal oxygen uptake ( O_{2 max}) and reductions in heart rate at a given submaximal workload after endurance training are limited to exercise with trained limbs or also may be observed during exercise with untrained limbs. In the present study five initially very sedentary young men trained by leg cycling (LT) and five by arm cranking (AT) 30 min per day on 4 days a week for 11 weeks at an intensity 75–80% O_{2 max}. Before and after training the subjects performed submaximal and maximal arm cranking and leg cycling tests. Leg cycling and arm cranking O_{2 max} increased 15% and 9% after LT and 12% and 35% after AT, respectively. Heart rate at a given submaximal workload was lower (p<0.05) during trained and untrained limb exercise following LT and AT. However, subjective ratings of perceived exertion (RPE) at a given submaximal workload were lower (p<0.01) only during exercise with trained limbs after LT and AT. In light of previous findings, the present increases in O_{2 max} and reductions in submaximal exercise heart rate with untrained limbs suggest that the initial fitness of the subjects as well as the intensity, frequency, and duration of training may be important factors in determining the extent to which transfer effects of endurance training can be observed. Although the present data suggest that reductions in RPE after endurance training may be the result of local changes in trained muscles, the possible contribution of central nervous adaptations cannot be excluded.Supported in part by Grant HL 18907 from The National Heart, Lung, and Blood Institute     

Uniqueness of interval and continuous training at the same maintained exercise intensity

Summary The present study sought to evaluate the inconsistencies previously observed regarding the predominance of continuous or interval training for improving fitness. The experimental design initially equated and subsequently maintained the same relative exercise intensity by both groups throughout the program. Twelve subjects were equally divided into continuous (CT, exercise at 50% maximal work) or interval (IT, 30 s work, 30 s rest at 100% maximal work) training groups that cycled 30 min day^–1, 3 days week^–1, for 8 weeks. Following training, aerobic power (VO_2max), exercising work rates, and peak power output were all higher (9–16%) after IT than after CT (5–7%). Vastus lateralis muscle citrate synthase activity increased 25% after CT but not after IT. A consistent increase in adenylate kinase activity (25%) was observed only after IT. During continuous cycling testing the CT group had reduced blood lactate (1a_b) levels and respiratory quotient at both the same absolute and relative (70% VO_2max) work rates after training, while the IT group displayed similar changes only at the same absolute work rates. By contrast, both groups responded similarly during intermittent cycling testing with lower 1a_b concentrations seen only at absolute work rates. These results show that, of the two types of training programs currently employed, IT produces higher increases in VO_2max and in maximal exercise capacity. Nevertheless, CT is more effective at increasing muscle oxidative capacity and delaying the accumulation of 1a_b during continuous exercise.     

Attenuated relationship between cardiac output and oxygen uptake during high-intensity exercise

Aim: Recent findings have challenged the belief that the cardiac output (CO) and oxygen consumption (VO₂) relationship is linear from rest to maximal exercise. The purpose of this study was to determine the CO and stroke volume (SV) response to a range of exercise intensities, 40–100% of VO_2max, during cycling. Methods: Ten well‐trained cyclists performed a series of discontinuous exercise bouts to determine the CO and SV vs. VO₂ responses. Results: The rate of increase in CO, relative to VO₂, during exercise from 40 to 70% of VO_2max was 4.4 ± 1.4 L L^?1. During exercise at 70–100% of VO_2max, the rate of increase in CO was reduced to 2.1 ± 0.9 L L^?1 (P = 0.01). Stroke volume during exercise at 80–100% of VO_2max was reduced by 7% when compared to exercise at 50–70% of VO_2max (134 ± 5 vs. 143 ± 5 mL per beat, P = 0.02). Whole body arterial‐venous O₂ difference increased significantly as intensity increased. Conclusion: The observation that the rate of increase in CO is reduced as exercise intensity increases suggests that cardiovascular performance displays signs of compromised function before maximal VO₂ is reached.     

Repetitive static muscle contractions in humans —a trigger of metabolic and oxidative stress?

Summary Repetitive static exercise (RSE) is a repetitive condition of partial ischaemia/reperfusion and may therefore be connected to the formation of oxygen-derived free radicals and tissue damage. Seven subjects performed two-legged intermittent knee extension exercise repeating at 10 s on and 10 s off at a target force corresponding to about 30% of the maximal voluntary contraction force. The RSE was continued for 80 min (n=4) or to fatigue (n=3). Four of the subjects also performed submaximal dynamic exercise (DE) at. an intensity of about 60% maximal oxygen uptake (VO_2max) for the same period. Whole body oxygen uptake (VO₂) increased gradually with time during RSE (P<0.05), indicating a decreased mechanical efficiency. This was further supported by a slow increase in leg blood flow (P<0.05) and leg oxygen utilization (n.s.) during RSE. In contrast, prolonged RSE had no effect onVO₂ during submaximal cycling. Maximal force (measured in six additional subjects) declined gradually during RSE and was not completely restored after 60 min of recovery. After 20 and 80 min (or at fatigue) RSE phosphocreatine (PC) dropped to 74% and 60% of the initial value, respectively. A similar decrease in PC occurred during DE. Muscle and arterial lactate concentrations remained low during both RSE and DE. The three subjects who were unable to continue RSE for 80 min showed no signs of a more severe energy imbalance than the other subjects. A continuous release of K⁺ occurred during both RSE and DE. The total muscle loss of K⁺ was about 3% and 6% of the total muscle K⁺ content during RSE and DE, respectively. Muscle glutathione, glutathione disulphide, ubiquinone and -tocopherol are involved in the cellular defence system against free radicals. During RSE and DE these parameters were unchanged and plasma malondialdehyde (a product of free radical induced lipid peroxidation) remained below the detection limit. In conclusion, prolonged RSE resulted in a gradual decrease in PC, mechanical efficiency and maximal force. There were no signs of an enhanced rate of free radical formation.     

Stroke volume response to progressive exercise in athletes engaged in different types of training

Summary Using the impedance cardiography method, heart rate ( _c) matched changes on indexed stroke volume (SI) and cardiac output (CI) were compared in subjects engaged in different types of training. The subjects consisted of untrained controls (C), volleyball players (VB) who spent about half of their training time (360 min · week^–1) doing anaerobic conditioning exercises and who had a maximal oxygen uptake ( ) 41% higher than the controls, and distance runners (D) who spent all their training time (366 min·week^–1) doing aerobic conditioning exercises and who had a 26% higher than VB. The subjects performed progressive submaximal cycle ergometer exercise (10 W·min^–1) up to _c of 150 beats·min^–1. In group C, SI had increased significantly (P<0.05) at _c of 90 beats·min^–1 ( + 32%) and maintained this difference up to 110 beats·min^–1, only to return to resting values on reaching 130 beats·min^–1 with no further changes. In group VB, SI peaked (+ 54%) at _c of 110 beats·min^–1, reaching a value significantly higher than that of group C, but decreased progressively to 22010 of the resting value on reaching 150 beats·min^–1. In group D, SI peaked at _c of 130 beats·min^–1 (+ 54%), reaching a value significantly higher than that of group VB, and showed no significant reduction with respect to this peak value on reaching 150 beats·min^–1. As a consequence, the mean CI increase per _c unit was progressively higher in VB than in C (+46%) and in D than in VB (+ 105%). It was concluded that thef _c value at which SI ceased to increase during incremental exercise was closely related to the endurance component in the training programme.     

Dissociation between\dot V_{O_2 \max } and ventilatory threshold responses to endurance training

Summary The purpose of this investigation was to determine whether the ventilatory gas exchange threshold (T_vent) changes significantly during the first 1–3 weeks of endurance training. Six men were studied during 3 weeks of training, which consisted of pedaling on a cycle ergometer 6 d·wk 30 min per session at 70% of pretraining . At the end of each week, T_vent, and maximal and submaximal heart rates were determined during an incremental exercise test on the cycle ergometer. Constant-load submaximal exercise blood lactate concentrations were determined during training sessions on Monday, Wednesday, and Friday of each week of training. T_vent did not change significantly during the 3 weeks of training (+ 0.09 l·min^–1;P>0.05). In contrast, significant changes occurred in all other training indexes measured. increased by 0.36 l·min^–1 (P<0.05) after just 2 weeks of training and did not change further after 3 weeks. Significant reductions (40–45%;p<0.05) in blood lactate levels during training sessions occurred by the middle of the 2nd week of training. Decreases in maximal (~ 11 bt·min^–1) and submaximal (~ 14 bt·min^–1) exercise heart rates after 1 week of training were significant (P<0.05). The results demonstrate that changes in T_vent lag behind alterations in several other cardiovascular and metabolic parameters in response to endurance training. The dissociation between the significant improvement in and the lack of a significant increase in T_vent during the first 3 weeks of training indicates that the exercise-induced changes in these two parameters are regulated by different mechanisms.     

Endurance training slows down the kinetics of heart rate increase in the transition from moderate to heavier submaximal exercise intensities

Summary To find out whether endurance training influences the kinetics of the increases in heart rate (f _c) during exercise driven by the sympathetic nervous system, the changes in the rate off _c adjustment to step increments in exercise intensities from 100 to 150 W were followed in seven healthy, previously sedentary men, subjected to 10-week training. The training programme consisted of 30-min cycle exercise at 50%–70% of maximal oxygen uptake ( O_2max) three times a week. Every week during the first 5 weeks of training, and then after the 10th week the subjects underwent the submaximal three-stage exercise test (50, 100 and 150 W) with continuousf _c recording. At the completion of the training programme, the subjects' O_2max had increased significantly(39.2 ml·min^–1·kg^–1, SD 4.7 vs 46 ml·min^–1·kg^–1, SD 5.6) and the steady-statef _c at rest and at all submaximal intensities were significantly reduced. The greatest decrease in steady-statef _c was found at 150 W (146 beats·min^–1, SD 10 vs 169 beats·min^–1, SD 9) but the difference between the steady-statef _c at 150 W and that at 100 W (f _c) did not decrease significantly (26 beats·min^–1, SD 7 vs 32 beats·min^–1, SD 6). The time constant () of thef _c increase from the steady-state at 100 W to steady-state at 150 W increased during training from 99.4 s, SD 6.6 to 123.7 s, SD 22.7 (P<0.01) and the acceleration index (A=0.63·f _c·^–1) decreased from 0.20 beats·min^–1·s^–1, SD 0.05 to 0.14 beats·min^–1·s^–1, SD 0.04 (P<0.02). The major part of the changes in and A occurred during the first 4 weeks of training. It was concluded that heart acceleration following incremental exercise intensities slowed down in the early phase of endurance training, most probably due to diminished sympathetic activation.     

The effects of intensity of exercise on excess postexercise oxygen consumption and energy expenditure in moderately trained men and women

Summary This experiment investigated the effects of intensity of exercise on excess postexercise oxygen consumption (EPOC) in eight trained men and eight women. Three exercise intensities were employed 40%, 50%, and 70% of the predetermined maximal oxygen consumption (VO_2max). All ventilation measured was undertaken with a standard, calibrated, open circuit spirometry system. No differences in the 40%, 50% and 70% VO_2max trials were observed among resting levels of oxygen consumption (V0₂) for either the men or the women. The men had significantly higher resting VO₂ values being 0.31 (SEM 0.01) 1·min^–1 than did the women, 0.26 (SEM 0.01) 1·min^–1 (P < 0.05). The results indicated that there were highly significant EPOC for both the men and the women during the 3-h postexercise period when compared with resting levels and that these were dependent upon the exercise intensity employed. The duration of EPOC differed between the men and the women but increased with exercise intensity: for the men 40% – 31.2 min; 50% – 42.1 min; and 70% – 47.6 min and for the women, 40% – 26.9 min; 50% – 35.6 min; and 70% – 39.1 min. The highest EPOC, in terms of both time and energy utilised was at 70% VO_2max. The regression equation for the men, where y=O₂ in litres, and x=exercise intensity as a percentage of maximum was y=0.380x + 1.9 (r ²=0.968) and for the women is y=0.374x–0.857 (r ²=0.825). These findings would indicate that the men and the women had to exercise at the same percentage of their VO_2max to achieve the maximal benefits in terms of energy expenditure and hence body mass loss. However, it was shown that a significant EPOC can be achieved at moderate to low exercise intensities but without the same body mass loss and energy expenditure.     

Effect of n-3 fatty acids on free tryptophan and exercise fatigue

Free tryptophan (Trp), which is augmented by liberated free fatty acids (FFA) from adipose tissue, can induce mental fatigue via serotonin during exercise. Since an attenuation in FFA has been observed with omega-3 fatty acid (n-3fa) use, our purpose was to examine the effect of n-3fa supplementation on free Trp availability and exercise fatigue. Ten recreationally trained men (n=5) and women (n=5), with maximal oxygen consumption (O_2max)of 51.6 (3.0) and 44.3 (1.4) ml kg^–1 min^–1, respectively, were studied on two occasions following an overnight fast, before and after n-3fa supplementation (4 g day^–1 for 4 weeks). The exercise trials consisted of a 75-min treadmill run at 60% O_2max followed immediately by a high-intensity incremental bout to fatigue. Measurements included exercise monitors, plasma volume (PV), triglycerides (TG), FFA, glycerol, lactate, and glucose. Free Trp and branched-chain amino acids (BCAA) were measured and correlated with time to fatigue; all blood variables were corrected for PV. Free Trp, lactate, glucose, FFA, and glycerol were not significantly different between trials, but TG (P<0.001) and the free Trp/BCAA ratio were significantly lower after n-3fa use [1.76 (0.18)×10^-2 g ml^–1] versus before supplementation [2.17 (0.22), P=0.033]. There was a non-significant increase in time to fatigue after supplementation [10.2 (0.3) min] versus before n-3fa use [9.7 (0.2), P=0.068], and a tendency for higher BCAA levels after supplementation, P=0.068. However, neither free Trp nor the free Trp/BCAA ratio significantly predicted time to fatigue. In conclusion, n-3fa supplementation did not diminish free Trp concentrations or significantly improve endurance performance during a maximal bout of exercise.     

Changes in the susceptibility of red blood cells to oxidative and osmotic stress following submaximal exercise

Red blood cell (RBC) susceptibility to oxidative and osmotic stress in vitro was investigated in cells from trained and untrained men before and after submaximal exercise. Whilst no significant change in peroxidative haemolysis occurred immediately after 1 h of cycling at 60% of maximal aerobic capacity ( _max), a 20% increase was found 6 h later in both groups (P<0.05). The RBC osmotic fragility decreased by 15% immediately after exercise (P<0.001) and this was maintained for 6 h (Ps<0.001). There was an associated decrease in mean cell volume (P<0.05). Training decreased RBC susceptibility to peroxidative haemolysis (P<0.025) but it did not influence any other parameter. These exercise-induced changes were smaller in magnitude but qualitatively similar to those found in haemopathological states involving haem-iron incorporation into membrane lipids and the short-circuiting of antioxidant protection. To explore this similarity, a more strenuous and mechanically stressful exercise test was used. Running at 75% _max for 45 min reduced the induction time of O₂ uptake (peroxidation), consistent with reduced antioxidation capacity, and increased the maximal rate of O2 uptake in RBC challenged with cumene hydroperoxide (P<0.001). The proportion of high-density RBC increased by 10% immediately after running (P<0.001) but no change in membrane-incorporated haem-iron occurred. In contrast, treatment of RBC with oxidants (20–50 mol·l^–1 in vitro increased cell density and membrane incorporation of haem-iron substantially. These results showed that single episodes of submaximal exercise caused significant changes in RBC susceptibility to oxidative and osmotic stress. Such responses may account for the increase in RBC turnover found in athletes undertaking strenuous endurance training.