Body position affects the power spectrum of heart rate variability during dynamic exercise

Summary The power spectrum analysis of R-R interval variability (RRV) has been estimated by means of an autoregressive method in six men in supine (S) and sitting (C) postures at rest and during steady-state cycle exercise at about 14010, 28%, 45%, 67% of the maximal oxygen consumption (% VO_2max). The total power of RRV decreased exponentially as a function of exercise intensity in a similar way in both postures. Three components were recognized in the power spectra: firstly, a high frequency peak (HF), an expression of respiratory arrhythmia, the central frequency (f _central) of which increased in both S and C from a resting value of about 0.26 Hz to 0.42 Hz at 67% VO_2max; secondly, a low frequency peak (LF) related to arterial pressure control, the f _central of which remained constant at 0.1 Hz in C, whereas in S above 28% VO_2max decreased to 0.07 Hz; and thirdly, a very low frequency component (VLF; less than 0.05 Hz, no f _central). The power of the three components (as a percentage of the total power) depended on the body posture and the metabolic demand. HF% at rest was 30.3 (SEM 6.6) % in S and 5.0 (SEM 0.8) % in C. During exercise HF% decreased by about 30% in S and increased to 19.7 (SEM 5.5) % at 28% VO_2max in C. LF% was lower in S than in C at rest [31.6 (SEM 5.7) % vs 44.9 (SEM 6.4) %; P<0.05], remaining constant up to 28% VO_2max. At the highest intenstities it increased to 54.0 (SEM 15.6) % in S whereas in C it decreased to 8.5 (SEM 1.6) %. VLF represented the remaining power and the change was in the opposite direction to LF. The changes in power spectrum distribution of RRV during exercise depended on the intensity and the body posture. In particular, the LF peak showed opposite trends in S and C tasks, thus suggesting a different readjustment of arterial pressure control mechanisms in relation to the blood distribution and peripheral resistances.     

Heart rate variability in exercising humans: effect of water immersion

Power spectrum analysis of heart-rate variability was made in seven men [mean age 22 (SEM 1) years] in head-out water immersion (W) and in air (A, control) at rest and during steady-state cycling to maximal intensity (maximum oxygen uptake, V˙O_2max). At rest W resulted in a trebled increase in the total power (P?V˙O_2max, thereafter decreasing towards nil in both conditions. The HF% decreased in similar ways in W and A to about half at 55%–60% V˙O_2max and then increased to reach 1.5 times the resting values at V˙O_2max. The central frequency of HF increased linearly with oxygen uptake, showing a tendency to be higher in W than in A at medium to high intensities. The VLF% remained unchanged. The lack of differences in the LF peak between W and A during exercise would suggest that blood distribution had no effect on the readjustments in control mechanisms of arterial pressure. On the other hand, the findings of similar HF powers and the very similar values for ventilation in W and A confirmed the direct effect of the respiratory activity in heart rate modulation during exercise.     

Heart rate variability during dynamic exercise in elderly males and females

It has been proposed that cardiac control is altered in the elderly. Power spectral analysis of heart rate variability (HRV) was performed on 12 male and 11 female elderly subjects (mean age 74 years) while at rest in supine and sitting positions, and at steady states during 5 min of exercise (35–95% peak oxygen consumption, V˙O_2peak). There were no differences in power, measured as a percentage of the total of the high frequency peak (HF, centred at about 0.25 Hz; 13% in males vs 12% in females), low frequency peak (LF, centred at 0.09 Hz; 25% in males and 22% in females), and very low frequency component (VLF, at 0.03 Hz; 66% in males and 69% in females) between body positions at rest. There was no difference in spectral power between male and female subjects. Total power decreased as a function of oxygen consumption during exercise, LF% did not change up to about 14 ml · kg⁻¹ · min⁻¹ (40% and 80% V˙O_2peak in males and females, respectively), then decreased towards minimal values in both genders. HF% power and central frequency increased linearly with metabolic demand, reaching higher values in male subjects than in female subjects at V˙O_2peak, while VLF% remained unchanged. Thus, the power spectra components of HRV did not reflect the changes in autonomic activity that occur at increasing exercise intensities, confirming previous findings in young subjects, and indicated similar responses in both genders. Accepted: 30 November 1999     

The use of pupillometry in the assessment of cardiac autonomic function in elite different type trained athletes

The aim of the present study was to evaluate cardiac autonomic function by pupillometry in male athletes. Fifteen elite endurance- (END) and eleven power-trained (POWER) athletes and fifteen sedentary individuals (CONTROL) were studied. All subjects underwent three pupillometric measurements: at rest, peak exercise testing and recovery phase. The pupillometric indices studied were: baseline pupil radius (R1), minimum pupil radius (R2), maximum constriction velocity (VC_max), maximum constriction acceleration (AC_max), amplitude (AMP, R1–R2), constriction ratio (AMP%). During exercise, RR intervals were obtained for each subject with a Polar S810i for time and frequency domain heart rate variability (HRV) analysis. The following parameters of HRV were measured: standard deviation of all NN intervals (SDNN), the mean square successive differences (rMSSD), percent of NN intervals differing >50 ms from the preceding NN (pNN50), low (LF)- and high (HF)- frequency components of the autoregressive power spectrum of the NN intervals and their ratio (LF/HF). At rest and recovery, END showed significantly increased VC_max and AC_max compared to POWER and CONTROL. AMP% was significantly greater in END at rest, peak exercise and recovery compared to POWER and CONTROL. END and POWER had significantly greater AMP at rest and recovery compared to CONTROL. Moreover, all HRV indices were significantly increased in END compared to POWER and CONTROL. However, POWER showed significantly increased rMSSD and LF compared to CONTROL. HRV parameters were significantly correlated with pupillometric parameters during exercise. Our results indicated that any kind of exercise training and mainly endurance one affects autonomic regulation of pupillary light reflex.     

Effects of high altitude acclimatization on heart rate variability in resting humans

The sympatho-vagal nerve interaction at the heart was studied by means of power spectrum analysis of heart rate variability in seven Caucasians (aged 27–35 years) in resting supine and sitting positions before and during 35 days of a sojourn at 5050 m above sea level (asl) and in six Sherpas (aged 22–30 years) at high altitude only. A high frequency peak (HF)-central frequency between 0.20 and 0.33 Hz, a low frequency peak (LF)-central frequency between 0.08 and 0.14 Hz, and a very low frequency component ( < 0.05 Hz), no peak observed, were found in the power spectrum in both positions and independent of altitude. The peak powers, as a percentage of the total power, were affected by both body position and altitude. At sea level the change from a supine to a sitting position yielded a decrease in percentage HF from 25 (SEM 1.9)% to 6.2 (SEM 1.5) % (P < 0.05) and a significant increase in the ratio between LF and HF powers (LF : HF) from 1.7 (SEM 0.4) to 6.9 (SEM 1.6). At altitude compared to sea level in the supine position, percentage HF decreased from 25% to 10.9 (SEM 1.0)% (P < 0.05) and the LF:HF ratio increased from 1.7 to 4.8 (SEM 0.7) (P < 0.05). No changes occurred at altitude in the sitting position either in the peak powers or in the LF:HF ratio, but the central frequency of HF peak increased significantly from 0.25 (SEM 0.02) Hz to 0.32 (SEM 0.01) Hz. In the Sherpas comparable results to the Caucasians were found in both body positions. The high LF:HF ratios observed at altitude in both body positions and groups would suggest that hypoxia caused a shift of sympatho-vagal nerve interaction at rest toward a dominance of the sympathetic system, which was found at sea level only in the sitting position. An acclimatization period of 10 days higher than 2850 m asl and 1 month at 5050 m asl did not modify the interactions of the autonomic systems.     

Autonomic nervous control of heart rate during blood-flow restricted exercise in man

Summary Power spectra of instantaneous heart rate (f _c) allows the estimation of the contribution of sympathetic and parasympathetic control of f _c during steady-state conditions. The present study was designed to examine autonomic control of f _c as influenced by normal dynamic leg exercise and by ischemic leg exercise. Eight subjects performed supine cycle ergometry at 30% of their control peak work rate, with and without blood-flow restriction. Blood-flow restriction was induced by exposing the exercising legs to a supra-atmospheric pressure of 6.7 kPa (leg positive pressure; LPP). The exercise responses of arterial pressure and f _c increased (P<0.05) by LPP exposure. The exaggerated pressor response may be attributed to a chemoreflex drive originating in the ischemic muscles. Exposure to LPP during exercise also produced a significant decrease in parasympathetically mediated high frequency (HF; 0.15-1.00 Hz) fluctuation of f _c, as indicated by a decrease (P<0.05) in percent HF power compared to the control exercise level. During LPP exercise, the sympathetically mediated very low frequency (VLF; 0–0.05 Hz) fluctuation of f _c increased, as indicated by an increase (P<0.05) in percent VLF power above control exercise levels. Both LPP and control exercise conditions decreased (P<0.05) power in all frequency ranges of interest compared to their respective resting conditions. The results suggest that the increase in f _c associated with normal dynamic exercise was mediated predominantly by parasympathetic withdrawal, whereas the exaggerated f _c response during ischemic exercise resulted from a combination of cardiac sympathetic drive and parasympathetic withdrawal. The increase in sympathetic activity is attributable to a muscle chemoreflex drive, which also may have attenuated parasympathetic activity by reciprocal inhibition. Alternatively, augmented central command mediated parasympathetic withdrawal during ischemic exercise.     

Enhanced systolic myocardial function in elite endurance athletes during combined arm-and-leg exercise

The aim here was to employ color tissue velocity imaging (TVI), to test the hypothesis that highly trained endurance athletes exhibit enhanced systolic function of the left ventricular (LV) myocardium both at rest and during combined arm-and-leg exercise in comparison with untrained subjects. For each of the ten elite male (EG) and ten matched control participants (CG), LV dimensions and systolic function were assessed at rest using echocardiography. Subsequently, these subjects exercised continuously on a combined arm-and-leg cycle ergometer for 3 min each at 50, 60, 70, 80, 90 and 100% of VO_2max. Oxygen uptake, heart rate, systolic blood pressure (SBP) and peak contraction systolic velocities of the LV myocardium (PSV) were recorded in the end of each level. At rest, the trained and untrained groups differed with respect to LV dimensions, but not systolic function. At 60–100% VO_2max, the EG group demonstrated both higher PSV and SBP. The observation that the EG athletes had higher PSV than CG during exercise at 60–100% VO_2max, but not at rest or at 50% of VO_2max, suggested an enhanced systolic capacity. This improvement is likely to be due to an enhanced inotropic contractility, which only becomes apparent during 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.     

Estimation of maximal heart rate using the relationship between heart rate variability and exercise intensity in 40–67 years old men

Large interindividual variation in maximal heart rate (HR_max) may not be accounted for by age alone. In order to evaluate a novel method in the prediction of HR_max, this study examined the profile of HR variability (HRV) during exercise in 40–67 years old men (n = 74). R–R intervals were recorded during supine rest and during a graded exercise test by cycle ergometry until exhaustion. A third-degree polynomial function was fitted to the HRV data recorded during exercise to represent the HRV profile of each subject. The instantaneous beat-to-beat R–R interval variability (SD1), high (HF) and low frequency power decreased between all consecutive exercise intensities (P < 0.033). The relationship between HR_max and a variable illustrating the declining rate of HF (HR_HF50%) was stronger (r = 0.50, P < 0.001) than between HR_max and age (r = −0.36, P < 0.01). The regression analysis showed that a more accurate estimation of HR_max was attained when HRV was used in the equation in addition to age: HR_max = 160.633–0.603(age) + 0.441(HR_HF50%) (SEE = 9.8 bpm vs. 11.6 bpm in the equation based on age alone). The decline of HRV during incremental exercise seems to be useful for accurate estimation of maximal heart rate.     

Effect of low-dose endurance training on heart rate variability at rest and during an incremental maximal exercise test

We evaluated the effects of low-dose endurance training on autonomic HR control. We assessed the heart rate variability (HRV) of 11 untrained male subjects (36.8 +/- 7.2 years) at rest and during an incremental maximal aerobic exercise test prior to a 7-week preparatory period and prior to and following a 14-week endurance training period, including a low to high intensity exercise session twice a week. Total (0.04-1.2 Hz), low (0.04-0.15 Hz) and high (0.15-1.2 Hz) frequency power of HRV were computed by short-time Fourier transform. The preparatory period induced no change in aerobic power or HRV. The endurance training period increased peak aerobic power by 12% (P < 0.001), decreased the HR (P < 0.01) and increased all HRV indices (P < 0.05-0.01) at absolute submaximal exercise intensities, but not at rest. In conclusion, low-dose endurance training enhanced vagal control during exercise, but did not alter resting vagal HR control.     

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.     

Dependence of lactate removal on muscle metabolism in man

Summary If lactate is primarily oxidized in skeletal muscle in man, it is expected that lactate uptake would increase linearly with increasing muscle metabolism (VO₂). Therefore, lactate removal was investigated (N=9) after 6 min exercise bouts (90% VO₂ max), at rest, and during 30 min of recovery exercise, when the relative intensities were constant to equate lactate production while permitting exercise metabolism (VO₂) to vary. Recovery exercises were therefore conducted at 26.8% VO₂ max for arm exercise, 26.8% VO₂ max for leg exercise, and 29% VO₂ max for combined arm and leg exercise. These exercise intensities were calculated from VO₂ max values established separately for each of the three modes of exercise. Lactate removal was slowest at rest (p<0.05). Removal during leg recovery was faster than during the arm condition (p<0.05), but the leg removal was not different from the combined arm and leg condition (p>0.05). The VO₂ cost of the arm (0.73±0.04 l/min), leg (1.04±0.05 l/min) and combined arm and leg exercise (1.23±0.10 l/min) were distinctly different from each other (p<0.05). There was a high correlation (r=0.92) between VO₂ cost, and the lactate removal rates of the corresponding recovery conditions. These findings indicate that lactate increases proportionately with the metabolically active muscle mass, providing exercise remains aerobic. Thus in man, it appears that lactate removal from the blood during recovery exercise occurs primarily in skeletal muscle.     

The role of central command in ventilatory control during static exercise

The role of central command in the respiratory response to 15 min of rhythmic-static (isometric) exercise was studied in humans. Voluntary exercise (VE) was compared with electrically induced exercise (EE) at three different work intensities, i.e. 5%, 15% and 25% of maximal voluntary contraction. A group of 12 volunteers participated in the study and each of them performed six sessions. A session consisted of at least 5 min rest, 15 min rhythmic-static single leg exercise (4 s contraction/12 s relaxation) and at least 5 min recovery. Force, minute ventilation (V _E) and oxygen uptake (VO₂) were measured. In EE, both V _E and VO₂ increased continuously during the entire exercise period after an initial rapid increase at all three work intensities. Correlation between VE and VO₂ was highly significant during EE. During all three work intensities of VE, VE and VO₂ achieved a steady-state after the initial increase. During VE, VE did not correlate as closely with VO₂ as during EE. All these findings indicate that central command was not imperative for an adequate ventilatory response to exercise within all three work intensities investigated. Without the influence of central command, correlation between VE and VO₂ was even better than during VE.     

Influence of intensive cycling training on heart rate variability during rest and exercise.

The current study examined whether changes in heart rate variability (HRV) following intensive cycling training contribute to the mechanism of training-induced bradycardia. Thirteen healthy untrained subjects, ages 18-27 years, underwent recordings of heart rate (HR) and VO2max before and after 8 weeks of cycling, 25-60 min/day, 5 days/week at > 80% maximum HR (HRmax). Heart rate recordings were obtained during supine rest and submaximal exercise and were analysed for the following components of HRV: low frequency (LF, 0.041-0.15 Hz); high frequency (HF, 0.15-0.40 Hz); LF/HF ratio and total power (TP, 0-0.40 Hz). At posttraining, VO2max was significantly increased while HR was significantly reduced at rest and all absolute exercise work rates. Training-induced lower HR was accompanied by significantly greater HF and TP during rest as well as LF, HF, and TP during all absolute exercise work rates. Posttraining HR and the majority of HRV measures were similar to pretraining values at the same relative exercise intensity (% HRmax). These results indicated that 8 weeks of intensive cycling training increased HRV and cardiac vagal modulation during rest and absolute exercise work rates but had little effect during relative exercise work rates. Increased vagal modulation resulting from intensive exercise training may contribute to the mechanism of training-induced bradycardia.     

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.     

Response of left ventricular diastolic filling to graded exercise relative to the lactate threshold

Summary During incremental exercise, the left ventricular ejection fraction increases up to the intensity of the anaerobic threshold and tends to level off at higher exercise intensities. Since there is a correlation between the response of peak filling rate and ejection fraction to exercise, this study was conducted to determine whether the response of left ventricular diastolic function is similar to the response of systolic function relative to lactate threshold. Twelve healthy men performed two exercise tests on a cycle ergometer. In the first test, lactate threshold and maximal power output were determined. In the second exercise test, gated radionuclide ventriculography was performed at rest, at the lactate threshold intensity, and at peak exercise to measure ejection fraction and peak filling rate. Ejection fraction increased significantly from rest [mean (SD): 62 (5)%] to lactate threshold [76 (7) %] and did not change significantly from lactate threshold to peak exercise [77 (7)%]. Likewise, peak filling rate (normalized for stroke counts) increased from resting [6.1 (0.9)V _s · s^–1] to lactate threshold [9.4 (1.8)V _s · s^–1] and did not change significantly from lactate threshold to peak exercise [9.6 (2.9)V _s · s^–1]. There was no correlation between the change in peak filling rate and the change in ejection fraction from rest to lactate threshold. Thus, during incremental exercise, left ventricular diastolic function responds qualitatively similar to systolic function.     

Effectiveness of low-frequency vibration recovery method on blood lactate removal,muscle contractile properties and on time to exhaustion during cycling at <Emphasis Type="Italic">V</Emphasis>O<Subscript>2max</Subscript> power output

The aim of the study was to determine the effectiveness of low-frequency vibration recovery (LFV-rec) on blood lactate removal, muscle contractile properties, and on time to exhaustion during cycling at maximal oxygen uptake power output (pVO_2max). Twelve active males carried out three experimental sessions. In session 1, participant’s maximal oxygen uptake (VO_2max) and pVO_2max were determined, and in sessions 2 and 3, the participants performed a fatiguing exercise (2 min of cycling at pVO_2max) and then a 15 min recovery period using one of two different methods: LFV-rec which consisted on sitting with feet on the vibratory platform (20 Hz; 4 mm) and passive recovery (P-rec), sitting without vibration stimulus. After that, participants performed an all-out exercise test on cycle ergometer at pVO_2max. In the recovery period, variables such as heart rate (HR), blood lactate concentration [Lac], and tensiomyographic parameters (D _m: maximal radial displacement; T _s: time of contraction maintenance, and T _r: relaxation time) were measured. In an all-out exercise test, mean time to exhaustion (TTE), total distance covered (TD), mean cycling velocity (V _m), and maximal HR (HR_max) were also assessed. The results showed no effect of recovery strategy on any of the assessed variables; nevertheless, higher values, although not significant, were observed in TTE, TD, and V _m after LFV-rec intervention. In conclusion, LFV-rec strategy applied during 15 min after short and intense exercise does not seem to be effective on blood lactate removal, muscle contractile properties, and on time to exhaustion during cycling at pVO_2max.     

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.     

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.     

Impact of the exercise mode on heart rate recovery after maximal exercise

Heart rate recovery 1 min after exercise termination (HRR-1) is a prognostic predictor. However, the influence of the exercise mode on HRR-1 is incompletely characterised. Twenty-nine young and healthy subjects and 16 elderly patients with chronic heart failure underwent cardiopulmonary exercise testing using cycle ergometer and treadmill ramp protocols in random order. HRR-1 and heart rate recovery 2 and 3 min after exercise (HRR-2, HRR-3) during active recovery and peak oxygen consumption (peak VO₂) were measured. In both healthy subjects (32 ± 14 vs. 27 ± 10 bpm) and HF patients (19 ± 8 vs. 14 ± 9 bpm), HRR-1 was faster after cycle exercise (p = 0.029; p for between group difference 0.94). In contrast, HRR-2 and HRR-3 were similar after both tests in both groups. Peak VO₂ was lower during cycle as compared to treadmill exercise in both groups. In conclusion, in both healthy subjects and HF patients, HRR-1 depends on the mode of exercise as peak VO₂ does.