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.     

Comparison in men of physiological responses to exercise of increasing intensity at low and moderate ambient temperatures

Summary In six male subjects the sweating thresholds, heart rate (f _c, as well as the metabolic responses to exercise of different intensities [40%, 60% and 80% maximal oxygen uptake (VO_2max)], were compared at ambient temperatures (T _a) of 5° C (LT) and 24° C (MT). Each period of exercise was preceded by a rest period at the same temperature. In LT experiments, the subjects rested until shivering occurred and in MT experiments the rest period was made to be of exactly equivalent length. Oxygen uptake (VO₂) at the end of each rest period was higher in LT than MT (P< 0.05). During 20-min exercise at 40%VO_2max performed in the cold no sweating was recorded, while at higher exercise intensities sweating occurred at similar rectal temperatures (T _re) but at lower mean skin (T _sk) and mean body temperatures (T _b) in LT than MT experiments (P<0.001). The exercise inducedVO₂ increase was greater only at the end of the light (40%VO_2max) exercise in the cold in comparison with MT (P<0.001). Bothf _c and blood lactate concentration [la]_b were lower at the end of LT than MT for moderate (60%VO_2max) and heavy (80%VO_2max) exercises. It was concluded that the sweating threshold during exercise in the cold environment had shifted towards lower (T _b) andT _sk. It was also found that subjects exposed to cold possessed a potentially greater ability to exercise at moderate and high intensities than those at 24° C since the increases inT _re,f _c and [la]_b were lower at the lowerT _a.     

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.     

Central and peripheral cardiovascular adaptations to exercise in endurance‐trained children

Stroke volume (SV) response to exercise depends on changes in cardiac filling, intrinsic myocardial contractility and left ventricular afterload. The aim of the present study was to identify whether these variables are influenced by endurance training in pre‐pubertal children during a maximal cycle test. SV, cardiac output (Doppler echocardiography), left ventricular dimensions (time–movement echocardiography) as well as arterial pressure and systemic vascular resistances were assessed in 10 child cyclists (VO_2max: 58.5 ± 4.4 mL min^?1 kg^?1) and 13 untrained children (UTC) (VO_2max: 45.9 ± 6.7 mL min^?1 kg^?1). All variables were measured at the end of the resting period, during the final minute of each workload and during the last minute of the progressive maximal aerobic test. At rest and during exercise, stroke index was significantly higher in the child cyclists than in UTC. However, the SV patterns were strictly similar for both groups. Moreover, the patterns of diastolic and systolic left ventricular dimensions, and the pattern of systemic vascular resistance of the child cyclists mimicked those of the UTC. SV patterns, as well as their underlying mechanisms, were not altered by endurance training in children. This result implied that the higher maximal SV obtained in child cyclists depended on factors influencing resting SV, such as cardiac hypertrophy, augmented myocardium relaxation properties or expanded blood volume.     

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.     

Exercise stimulus increases ventilation from maximal to supramaximal intensity

This study investigated the influence of an exercise stimulus on pulmonary ventilation (V _E) during severe levels of exercise in a group of ten athletes. The altered ventilation was assessed in relation to its effect on blood gas status, in particular to the incidence and severity of exercise induced hypoxaemia. Direct measurements of arterial blood were made at rest and during the last 15 s of two intense periods of cycling; once at an intensity found to elicit maximal oxygen uptake (VO_2max; MAX) and once at an intensity established to require 115% ofVO_2max (SMAX). Oxygen uptake (VO₂) and ventilatory markers were continually recorded during the exercise and respiratory flow-volume loops were measured at rest and during the final 30 s of each minute for both exercise intensities. When compared to MAX exercise, the subjects had higher ventilation and partial pressure of arterial oxygen (P _aO₂) during the SMAX intensity. Regression analysis for both conditions indicated the levels ofP _aO₂ and oxygen saturation of arterial blood (S _aO₂) were positively correlated with relative levels of ventilation during exercise. It was apparent that mechanical constraints to ventilate further were not present during the MAX test since the subjects were able to elevateV _E during SMAX and attenuate the level of hypoxaemia. This was also confirmed by analysis of the flow volume recordings. These data support the conclusions firstly, that overwhelming mechanical constraints onV _E were not present during the MAX exercise, secondly, the subjects exhibiting the most severe hypoxaemia had no consistent relationship with any measure of expiratory flow limitation, and thirdly, ventilatory patterns during intense exercise are strong predictors of blood gas status.     

The effects of graded exercise on plasma proenkephalin peptide F and catecholamine responses at sea level

Summary The purpose of this study was to evaluate the effects of graded treadmill exercise on plasma preproenkephalin peptide F immunoreactivity and concomitant catecholamine responses at sea level (elevation, 50 m). Few data exist regarding the sea-level responses of plasma peptide F immunoreactivity to exercise. Thirty-five healthy men performed a graded exercise test on a motor-driven treadmill at the relative exercise intensities of 25, 50, 75, and 100% of maximum oxygen consumption (VO_2max). Significant (P<0.05) increases above rest were observed for plasma peptide F immunoreactivity and norepinephrine at 75 and 100% of the VO_2max and at 5 min into recovery. Significant increases in plasma epinephrine were observed at 75 and 100% of VO_2max. Whole blood lactate significantly increased above resting values at 50, 75, and 100% of the VO_2max and at 5 min into recovery. These data demonstrate that exercise stress increases plasma peptide F immunoreactivity levels at sea level. While the exercise response patterns of peptide F immunoreactivity are similar to catecholamines and blood lactate responses, no bivariate relationships were observed. These data show that sea-level response patterns to graded exercise are similar to those previously observed at moderate altitude (elevation, 2200 m).Human subjects participated in these studies after giving their free and informed voluntary consent. Investigators adhered to AR 70-25 and USAMRDC regulation 70-25 on Use of Volunteers in Research. The views, opinion, and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision, unless to designated by other official documentation.     

Heart rate overshoot at the beginning of muscle exercise

Summary A characteristic notch in the heart rate (f _c) on-response at the beginning of square-wave exercise is described in 7 very fit marathon runners and 12 sedentary young men, during cycle tests at 30% and 60% of maximal oxygen consumption (VO_2max). The (f _c) notch revealed af _c overshoot with respect to the (f _c) values predicted from exponential beat-by-beat fitted models. While at 30% of (VO_2max). all subjects showed af _c over-shoot, at 60% of (VO_2max). it occurred in the marathon runners but not in the sedentary subjects. The mean time of occurrence of thef _c overshoot from the onset of the exercise was 16.7 (SD 4.7) s and 12.2 (SD 3.2) s at 30% of (VO_2max). in the runners and the sedentary subjects respectively, and 23.8 (SD 8.8) s at 60% of (VO_2max). in the runners. The amplitude of the overshoot, with respect to rest, was 41 (SD 12) beats·min^–1and 31 (SD 4) beats·min^–1 at 30% of (VO_2max). in the runners and the sedentary subjects respectively, and 46 (SD 19) beats·min^–1 at 60% of (VO_2max). in the runners. The existence and the amplitude of thef _c overshoot may have been related to central command and muscle heart reflex mechanisms and thus may have been indicators of changes in the balance between sympathetic and parasympathetic activity occurring in fit and unfit subjects.     

Are there differences in running economy at different velocities for well-trained distance runners?

The present study investigated whether there are differences in running economy at different velocities for well-trained distance runners, and to what extent a commonly used incremental protocol for measuring oxygen uptake (VO₂) at different velocities affects the reliability of these measurements. Fifteen well-trained distance runners (9 male and 6 female) participated in this study. Gross oxygen cost of running (C _R), heart rate (HR) and [La⁻]_b during 5-min runs at velocities ranging from 8.0 to 17 km h⁻¹, representing intensities ranging from 60 to 90% of maximal oxygen consumption (VO_2max) was measured on two different days in random order. The athletes were also tested for lactate threshold, VO_2max and time to exhaustion at MAS (_tMAS). No significant differences in C _R between the different relative velocities or the different set velocities were found up to 90% of VO_2max. The incremental protocol for measuring VO₂ at different velocities was found not to affect the reliability of these measurements. All athletes reached their VO_2max whilst running to exhaustion at MAS. The females showed significantly lower VO_2max, but significantly better C _R than the males. At velocities representing intensities between 60 and 90% of VO_2max, no differences in C _R were found. The commonly used incremental protocol for measuring oxygen uptake (VO₂) at different velocities was found not to affect the reliability of these measurements. This means that C _R measured at sub-maximal velocities are representative for C _R at race velocity for distances above 10,000 m for most runners.     

Pressure and coverage effects of sporting compression garments on cardiovascular function,thermoregulatory function,and exercise performance

Sporting compression garments (CG) are used widely during exercise despite little evidence of benefits. The purpose of this study was to investigate coverage and pressure effects of full-body CG on cardiovascular and thermoregulatory function at rest and during prolonged exercise, and on exercise performance. Twelve recreationally trained male cyclists [mean (SD) age, 26 (7) years; [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } , 53 (8) mL kg⁻¹ min⁻¹] completed three sessions (counterbalanced order), wearing either correctly-sized CG (CSG; 11–15 mmHg), over-sized CG (OSG; 8–13 mmHg), or gym shorts (CONT). Test sessions were conducted in temperate conditions [24 (1)°C, 60 (4)% relative humidity; ~2 m s⁻¹ air velocity during exercise], consisting of resting on a chair then on a cycle ergometer, before 60-min fixed-load cycling at ~65% [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } and a 6-km time trial. Wearing CG (CSG or OSG) did not mitigate cardiovascular strain during mild orthostatic stress at rest (p = 0.20–0.93 for garment effects). During exercise, cardiac output was ~5% higher in the CG conditions (p < 0.05), which appears to be accounted for via non-significant higher end-exercise heart rate (~4–7%, p = 0.30; p = 0.06 for greater heart rate drift in CSG); other cardiovascular variables, including stroke volume, were similar among conditions (p = 0.23–0.91). Covered-skin temperature was higher in CG conditions (p < 0.001) but core (oesophageal) temperature was not (p = 0.79). Time-trial performance (mean power, time taken) was similar with or without CG (p = 0.24–0.44). In conclusion, any demonstrable physiological or psychophysical effects of full-body CG were mild and seemingly reflective more of surface coverage than pressure. No benefit was evident for exercise performance.     

Muscle triacylglycerol and hormone-sensitive lipase activity in untrained and trained human muscles

During exercise, triacylglycerol (TG) is recruited in skeletal muscles. We hypothesized that both muscle hormone-sensitive lipase (HSL) activity and TG recruitment would be higher in trained than in untrained subjects in response to prolonged exercise. Healthy male subjects (26 ± 1 years, body moss index 23.3 ± 0.5 kg m⁻²), either untrained (N = 8, VO_2max 3.8 ± 0.2 l min⁻¹) or trained (N = 8, VO_2max 5.1 ± 0.1 l min⁻¹), were studied. Before and after 3-h exercise (58 ± 1% VO_2max), a biopsy was taken. Muscle citrate synthase (32 ± 2 vs. 47 ± 6 μmol g⁻¹ min⁻¹ d.w.) and β-hydroxy-acyl-CoA-dehydrogenase (38 ± 3 vs. 52 ± 5 μmol g⁻¹ min⁻¹ d.w.) activities were lower in untrained than in trained subjects (p < 0.05). Throughout the exercise, fat oxidation was higher in trained than in untrained subjects (p < 0.05). Muscle HSL activity was similar at rest (0.72 ± 0.08 and 0.74 ± 0.03 mU mg⁻¹ protein) and after exercise (0.71 ± 0.1 and 0.68 ± 0.03 mU mg⁻¹ protein) in untrained and trained subjects. At rest, the chemically determined muscle TG content (37 ± 8 and 26 ± 5 mmol g⁻¹ d.w.) was similar (p > 0.05), and after exercise it was unchanged in untrained and lower (p < 0.05) in trained subjects (41 ± 9 and 10 ± 2 mmol g⁽¹ d.w.). Determined histochemically, TG was decreased (p < 0.05) after exercise in type I and II fibres. Depletion of TG was not different between fibre types in untrained, but tended to be higher (p = 0.07) in type I compared with type II fibres in trained muscles. In conclusion, HSL activity is similar in untrained and trained skeletal muscles both before and after prolonged exercise. However, the tendency to higher muscle TG recruitment during exercise in the trained subjects suggests a difference in the regulation of HSL or other lipases during exercise in trained compared with untrained subjects.     

Acute EPOC response in women to circuit training and treadmill exercise of matched oxygen consumption

The purpose of the study was to evaluate the effects of circuit training (CT) and treadmill exercise performed at matched rates of oxygen consumption and exercise duration on elevated post-exercise oxygen consumption (EPOC) in untrained women, while controlling for the menstrual cycle. Eight, untrained females (31.3±9.1 years; 2.04±0.26 l min^–1 estimated VO_2max; BMI=24.6±3.9 kg/m²) volunteered to participate in the study. Testing was performed during the early follicular phase for each subject to minimize hormonal variability between tests. Subjects performed two exercise sessions approximately 28 days apart. Resting, supine energy expenditure was measured for 30 min preceding exercise and for 1 h after completion of exercise. Respiratory gas exchange data were collected continuously during rest and exercise periods via indirect calorimetry. CT consisted of three sets of eight common resistance exercises. Pre-exercise and exercise oxygen consumption was not different between testing days (P>0.05). Thus, exercise conditions were appropriately matched. Analysis of EPOC data revealed that CT resulted in a significantly higher (p<0.05) oxygen uptake during the first 30 min of recovery (0.27±0.01 l min^–1 vs 0.23±0.01 l min^–1); though, at 60 min, treatment differences were not present. Mean VO₂ remained significantly higher (0.231±0.01 l min^–1) than pre-exercise measures (0.193±0.01 l min^–1) throughout the 60-min EPOC period (p<0.05). Heart rate, RPE, V_E and RER were all significantly greater during CT (p<0.05). When exercise VO₂ and exercise duration were matched, CT was associated with a greater metabolic disturbance and cost during the early phases of EPOC.     

Exercise and myocardial tolerance to ischaemia‐reperfusion

It is well established that both short‐term (1–5 days) and long‐term (weeks to months) high intensity exercise (i.e. 70–75%VO_2max) provides cardioprotection against ischaemia‐reperfusion injury. However, it is unclear if moderate intensity exercise will also provide cardioprotection. Aim: Therefore, these experiments compared the protective effects of moderate vs. high intensity exercise in providing defense against ischaemia‐reperfusion injury. Methods: Male Sprague–Dawley rats were randomly assigned to one of three‐experimental groups: (1) sedentary (control); (2) moderate intensity treadmill exercise (60 min day^?1 at ～55%VO_2max); or (3) high intensity treadmill exercise (60 min day^?1 at ～75%VO_2max). Hearts were exposed to 20 min of global ischaemia followed by 30 min reperfusion in an isolated working heart preparation. Results: Compared with sedentary rats, both moderate and high intensity exercised rats maintained a higher (P < 0.05) percentage of pre‐ischaemia cardiac output and cardiac work (cardiac output × systolic blood pressure) during reperfusion. No differences in the percent recovery of cardiac output and heart work existed (P > 0.05) between the two exercise groups. Conclusions: These data reveal that both moderate and high intensity exercise training provide equivalent protection against ischaemia‐reperfusion injury.     

Mode of frequency distribution of external work efficiency of arrhythmic beats during atrial fibrillation remains normal in canine heart

The external work (EW) efficiency of individual arrhythmic beats of the left ventricle (LV) cannot directly be obtained since LV O₂ consumption (VO₂) of each beat cannot directly be measured under beat-to-beat varying contractile and loading conditions. We, however, have recently reported that VO₂ of each arrhythmic beat can reasonably be estimated by VO₂ = aPVA + bE_max + c even under varying PVA and E_max. Here, PVA is the LV pressure–volume (P–V) area as a measure of the LV total mechanical energy, E_max is the LV end-systolic elastance as an index of the LV contractility, a is a constant O₂ cost of PVA, b is a constant O₂ cost of E_max, and c is the basal metabolic VO₂ of the beat, all on a per-beat basis. Using the above formula in this study, we calculated VO₂ of the individual arrhythmic beats from their measured PVA and E_max during electrically induced atrial fibrillation (AF) in normal canine hearts. We then calculated their LV EW efficiency by dividing their measured EW with the estimated VO₂. We found that the thus calculated EW efficiency of the arrhythmic beats had a rightward skewed distribution with a mode of 15% and a maximum of 18% around a mean of 13% on average in six hearts. This mode remained comparable to the efficiency (15%) at regular tachycardia though 22% lower than mean arrhythmic tachycardia.     

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.     

The influence of exercise intensity on the power spectrum of heart rate variability

Summary The power spectral analysis of R-R interval variability (RRV) has been estimated by means of an autoregressive method in seven sedentary males at rest, during steady-state cycle exercise at 21 percent maximal oxygen uptake. (% V _{O 2max}), SEM 2%, 49% V_{O 2max}, SEM 2% and 70% V_{O 2max}, SEM 2% and during recovery. The RRV, i.e. the absolute power of the spectrum, decreased 10, 100 and 500 times in the three exercise intensities, returning to resting value during recovery. In the RRV power spectrum three components have been identified: (1) high frequency peak (HF), central frequency about 0.24 Hz at rest and recovery, and 0.28 Hz, SEM 0.02, 0.37 Hz, SEM 0.03 and 0.48 Hz, SEM 0.06 during the three exercise intensities, respectively; (2) low frequency peak (LF), central frequency about 0.1 Hz independent of the metabolic state; (3) very low frequency component (VLF), <0.05 Hz, no peak observed. The HF peak power, as a percentage of the total power (HF%), averaged 16%, SEM 5% at rest and did not change during exercise, whereas during recovery it decreased to 5%–10%. The LF% and VLF% were about 50% and 35% at rest and during low exercise intensity, respectively. At higher intensities, LF% decreased to 16% and VLF% increased to 70%. During recovery a return to resting values occurred. The HF component may reflect the increased respiratory rate and the LF peak changes the resetting of the baroreceptor reflex with exercise. The hypothesis is made that VLF fluctuations in heart rate might be partially mediated by the sympathetic system.     

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.     

Experimental acute hypoxia in healthy subjects: evaluation of systolic and diastolic function of the left ventricle at rest and during exercise using echocardiography

To clarify whether or not systolic and diastolic function of the human left ventricle (LV) were decreased during acute hypoxia, at rest and with exercise, 14 healthy male volunteers [age 25.9 (SD 3.0) years, height 182.9 (SD 7.1) cm, body mass 75.9 (SD 6.9)kg] were examined using M-mode and 2D-mode echocardiography to determine the systolic LV function as well as Doppler-echocardiography for the assessment of diastolic LV function on 2 separate test days. In random order, the subjects breathed either air on 1 day (N) or a gas mixture with reduced oxygen content on the other (H; oxygen fraction in inspired gas 0.14). Measurements on either day were made at rest, several times during incremental cycle exercise in a supine position (6-min increments of 50 W, maximal load 150 W) and in 6th min of recovery. Corresponding measurements during N and H were compared statistically. Arterial O₂ tension (P _aO₂) was normal on N-day. All subjects showed a marked acute hypoxia at rest [P _aO₂, 54.5 (SD 4.6) mmHg], during exercise and recovery on H-day. The latter was associated with tachycardia compared to N-day. All echocardiographic measurements at rest were within the limits of normal values on both test days. Ejection time, end-systolic and end-diastolic left ventricular dimensions as well as the thickness of left posterior wall and of interventricular septum showed no statistically significant influence of H either at rest or during exercise. Stroke volume and cardiac output were always higher on H-day, which could be attributed to a slight reduction in end-systolic volume with unaffected end-diastolic volume as well as to increased heart rates. Among the indices of systolic LV function the fractions of thickening in the left ventricular posterior wall and interventricular septum showed no differences between H and N at rest or during exercise. However, fibre shortening, ejection fraction and mean circumferential fibre shortening were increased on H-day on all occasions. The mitral-valve-Doppler ratio, the index of diastolic LV function, was decreased with H at rest, showed a more pronounced reduction during exercise and was still lower in 6th min of recovery compared to N-day. It was concluded that with acute hypoxia of the severity applied in this study left ventricular systolic function in our healthy subjects showed a pronounced improvement and left ventricular diastolic function was reduced, both at rest and with exercise.     

Contribution of systemic arterial compliance and systemic vascular resistance to effective arterial elastance changes during exercise in humans

Background: Effective arterial elastance (Ea), an index of arterial load, increases with elevations in left ventricular elastance to maximize the efficiency of left ventricular stroke work during exercise. Systemic arterial compliance (C) and vascular resistance (R) are the primary components contributing to Ea, and R plays a greater role in determining Ea at rest. We hypothesized that the contribution of C to Ea increases during exercise to maintain an optimal balance between arterial load and ventricular elastance, and that the increase in Ea is due primarily to a reduction in C. Aim: The aim of this study was to investigate the contributions of C and R to Ea during exercise. Methods: Ea (0.9 × systolic blood pressure/stroke volume), C (stroke volume/pulse pressure), R (mean blood pressure/cardiac output), and cardiac cycle length (T) were measured at rest and during exercise of 40%, 60% and 80% maximal oxygen uptake (O_2max) using Doppler echocardiography in 45 healthy men. Results: Ea did not differ between rest and 40%O_2max, but it was greater at 60% and 80%O_2max. C markedly decreased during exercise in an exercise intensity‐dependent manner. The changes in R/T during exercise were small, whereas it decreased at 40%O_2max and gradually increased at 60% and 80%O_2max. Conclusions: The present results suggest that the contribution of systemic arterial compliance to effective arterial elastance increases during exercise. Therefore, we propose that the increase in arterial load during exercise is mainly driven by a reduction in systemic arterial compliance.     

No effect of menstrual cycle phase on fuel oxidation during exercise in rowers

The aim of this investigation was to examine the effects of menstrual cycle phase on substrate oxidation and lactate concentration during exercise. Eleven eumenorrheic female rowers (18.4 ± 1.9 years; 172.0 ± 4.0 cm; 67.2 ± 8.4 kg; 27.7 ± 4.8% body fat) completed 1 h rowing ergometer exercise at 70% of maximal oxygen consumption (VO_2max) during two different phases of the menstrual cycle: the follicular phase (FP) and the luteal phase (LP). Resting and exercise measurements of the whole body energy expenditure, oxygen consumption (VO₂), respiratory exchange ratio (RER), substrate oxidation and lactate blood levels were made. Energy expenditure, VO₂ and heart rate during the 1-h exercise were not significantly different (P > 0.05) among menstrual cycle phases. Resting RER and RER during the entire 1 h exercise period were not significantly different among menstrual cycle phases. There was an increase (P < 0.05) in RER in the transition between rest and exercise and a further increase in RER occurred after the first 30 min of exercise at both menstrual cycle phases. Blood lactate concentrations significantly increased in the transition between rest and exercise and remained relatively constant during the whole 1 h of exercise in both menstrual cycle phases. No menstrual cycle phase effect (P > 0.05) was observed for blood lactate concentrations. In conclusion, our results demonstrated no effect of menstrual cycle phase on substrate oxidation and blood lactate concentration during rowing exercise at 70% of VO_2max in athletes. Normally menstruating female rowers should not be concerned about their menstrual cycle phase with regard to substrate oxidation in everyday training.