Exercise Intensity Domains Research Articles

A New Mechanomyographic Amplitude-Based Fatigue Threshold Test for Cycling

PURPOSE: The purposes of this study were to: a) apply the Dmax method previously used to determine the gas exchange threshold (GET) to the amplitude content of the mechanomyographic (MMG) signal to estimate the Dmax-MMG threshold; and b) compare the mean VO2 values from the Dmax-MMG, GET, and respiratory compensation point (RCP) during incremental cycle ergometry. METHODS: Ten males (mean ± SD age = 23.3 ± 3.7 yrs) performed an incremental cycle ergometer test to exhaustion. MMG signals from the vastus lateralis and VO2 were recorded. The contraction period for each pedal thrust (descending phase of the pedaling cycle) was determined from the MMG bursts. The GET and RCP values were determined by non-invasive gas exchange measurements using the V-slope method and defined as the VO2 value corresponding to the intersection of two linear regression lines derived separately from the data points below and above the breakpoints for the VCO2 vs. VO2, and VE vs. VCO2 relationships, respectively. The MMG amplitude (rms expressed in m·s2) values were calculated by averaging the last three complete pedal thrusts of each power output. The Dmax-MMG (i.e., MMG vs.VO2) was determined as the point on the third order polynomial regression curve that yielded the maximal perpendicular distance to the straight line formed by the first and the last data points. A one-way repeated measures ANOVA and Tukey post-hoc comparisons were used for mean comparison among thresholds. Pearson product moment correlations were used to determine the relationships among the three fatigue thresholds. RESULTS: The results of the present study indicated that the mean VO2 for the RCP (3.22 ± 0.22 L·min-1) was significantly greater (p < 0.05) than the GET (2.43 ± 0.26 L·min-1) and Dmax-MMG (2.63 ± 0.48 L·min-1). There was no significant difference, however, between the mean VO2 for the GET and Dmax-MMG. Furthermore, there were no significant correlations for the Dmax-MMG vs. GET (r = -0.29), Dmax-MMG vs. RCP (r = -0.04), or GET vs. RCP (r = 0.49). CONCLUSIONS: The non-significant mean difference between the GET and Dmax-MMG suggested that these thresholds may reflect a similar dimension of metabolic and neuromuscular fatigue. It is possible that like the GET, the Dmax-MMG demarcates the moderate from heavy exercise intensity domains.

Application of Critical Power in Sport

The critical power (CP) is mathematically defined as the power-asymptote of the hyperbolic relationship between power output and time-to-exhaustion. Physiologically, the CP represents the boundary between the steady-state and nonsteady state exercise intensity domains and therefore may provide a more meaningful index of performance than other well-known landmarks of aerobic fitness such as the lactate threshold and the maximal O2 uptake. Despite the potential importance to sports performance, the CP is often misinterpreted as a purely mathematical construct which lacks physiological meaning and only in recent years has this concept begun to emerge as valid and useful technique for monitoring endurance fitness. This commentary defines the basic principles of the CP concept, outlines its importance to high-intensity exercise performance, and provides an overview of the current methods available for its assessment. Interventions including training, pacing and prior exercise can be used to alter the parameters of the power-time relationship. A future challenge lies in optimizing such interventions in order to positively affect the parameters of the power-time relationship and thereby enhance sports performance in specific events.

A Test for Determining Critical Heart Rate Using the Critical Power Model

The purposes of this study were to (a) determine if the mathematical model that has previously been used to estimate the critical power (CP) was applicable to heart rate (HR) to estimate the critical heart rate (CHR), and (b) compare the CHR to the HR values at the CP (CP(HR)), ventilatory threshold (VT(HR)), and respiratory compensation point (RCP(HR)). Fifteen women (mean age ± SD = 21.7 ± 2.1 years) performed an incremental test to exhaustion to determine VO₂peak, VT(HR), and RCP(HR). The subjects also performed 4 exhaustive workbouts at different power outputs for the determination of CP and CHR. For each power output, the total number of heart beats (HB(lim)) was calculated as the product of the average 5-second HR (bpm) and total time to exhaustion (T(lim) in minutes). The HB(lim) and total work (W(lim) in kilograms-meters) were plotted as a function of the T(lim) at each power output, and the slope coefficients of the regression lines between HB(lim) or W(lim) and T(lim) were defined as the CHR and CP, respectively. A 1-way repeated-measures analysis of variance (ANOVA) indicated that CHR (172 ± 11 bpm, 92.9 ± 2.7%HRmax) was similar to RCP(HR) (172 ± 9 bpm, 92.9 ± 2.2%HRmax) but was higher (p < 0.05) than CP(HR) (154 ± 10 bpm, 83.2 ± 4.0%HRmax) and VT(HR) (152 ± 12 bpm, 82.1 ± 4.3%HRmax). The relationship between HR and T(lim) from the CHR test can be described by the CP model. The CHR test may be a practical method for estimating RCP without the need to measure expired gas samples. Furthermore, like the RCP, the CHR test may be used to demarcate the heavy from severe exercise intensity domains, predict endurance exercise performance, and prescribe a training intensity for competitive cyclists.

Defining Intensity Domains from the End Power of a 3-min All-out Cycling Test

The purpose of this study was to develop a modified version of a 3-min all-out cycling test (3MT) using equipment readily available to cyclists and to identify exercise intensity domains using the average power output over the last 30 s of the 3MT (end-test power (EP)). Sixteen competitive cyclists (V(O2peak) = 60.3 +/- 8.3 mL.kg.min) completed three laboratory visits using their own bicycles and a power-measuring rear wheel. In visit 1, subjects performed an incremental load test to volitional termination on an electronically braked trainer (100 + 25 W every 4 min). Power output at lactate threshold was determined by absolute 4 mmol.L (OBLA-PO) and 1 mmol.L over exercise baseline (LT-PO). Power output at ventilatory threshold (VT-PO) was computed on the basis of the V-slope method. Power output at V(O2peak) (V(O2peak)-PO) was the mean power observed during the stage at which peak O2 consumption was recorded. In visits 2 and 3, subjects performed the 3MT using a progressive resistance trainer with Visit 2 as a familiarization trial. During Visit 3, EP was recorded. EP (273 +/- 52 W) was significantly greater than VT-PO, OBLA-PO, and LT-PO (232 +/- 64, 235 +/- 54, and 208 +/- 45 W, respectively) but significantly less than V(O2peak)-PO (288 +/- 56 W). EP was correlated with V(O2peak)-PO (r = 0.97), VT-PO (r = 0.87), OBLA-PO (r = 0.85), and LT-PO (r = 0.79) with regression estimates through the origin made using 105%, 86%, 86%, and 76% of EP, respectively. Demarcations for moderate- to heavy-intensity (LT-PO at 76% EP) and heavy- to severe-intensity (100% EP) domains may be estimated. The 3MT can be used to define exercise intensity in competitive cyclists using readily available equipment.

Pathophysiology, diagnosis and management of exercise-induced anaphylaxis

The aim of this review is to challenge the current opinions of the pathophysiological mechanisms that give rise to food dependent exercise-induced anaphylaxis (FDEIA) and to consider these mechanisms within the wider context of exercise physiology to further inform our understanding and treatment of this condition. Exercise-induced anaphylaxis (food dependent and nonfood dependent) is a clinical syndrome in which anaphylaxis occurs in conjunction with exercise. Given the rarity of the condition, our current understanding relies on the many case studies and reviews of the topic. The pathophysiology of FDEIA remains to be fully elucidated with well constructed trials but current working hypotheses to date involve alterations in plasma osmolaltiy and pH, tissue enzyme activity, blood flow redistribution, altered gastrointestinal permeability and facilitated epitope recognition/allergen binding. Implications for future research are the physiological changes that occur during exercise need deeper consideration to ensure that proposed mechanisms are realistic and actually occur within the time frame and exercise-intensity domain during which the reported FDEIA occurred. These theories must be tested rigorously with sufficiently powered studies if progress is to be made in determining the perplexing pathophysiology of FDEIA.

A Mechanomyographic Fatigue Threshold Test for Cycling

The purposes of this study were twofold: 1) to derive the mechanomyographic mean power frequency fatigue threshold (MMG MPFFT) for submaximal cycle ergometry; and 2) to compare the power outputs associated to the MMG MPFFT to other neuromuscular and gas exchange fatigue thresholds. 9 adults (5 men and 4 women; mean+/-SD age=23.7+/-3.7 years; body weight=66.3+/-8.2 kg) performed an incremental cycle ergometry test to exhaustion while expired gas samples, electromyographic (EMG), and MMG signals were measured from the vastus lateralis muscle. The non-significant correlations (r=0.17 to 0.66; p>0.05) among the physical working capacity at the fatigue threshold (PWCFT), MMG MPFFT, and gas exchange threshold (GET) suggested that different physiological mechanisms may underlie these 3 fatigue thresholds. A significant correlation (r=0.83) for the MPFFT vs. respiratory compensation point (RCP) suggested that these fatigue thresholds may be mediated by a common physiological mechanism. In addition, the significantly lower mean values found for the PWCFT (mean+/-SD=163+/-43 W), MMG MPFFT (132+/-33 W), and GET (144+/-28 W) than MPFFT (196+/-53 W) and RCP (202+/-41 W) suggested that these gas exchange and neuromuscular fatigue thresholds may demarcate different exercise intensity domains.

A Comparison of Fatigue Thresholds Derived from the Amplitude and Frequency Domains of the Electromyographic Signal

PURPOSE: The physical work capacity at the fatigue threshold (PWCFT) is determined from fatigue-induced increases in the amplitude of the surface electromyographic (EMG) signal, while the mean power frequency fatigue threshold (MPFFT) is estimated from the compression of the power density spectrum of the signal. The purpose of this study was to compare the mean power outputs from the PWCFT and MPFFT during incremental cycle ergometry. METHODS: Ten subjects (mean ± SD age = 23.3 ± 3.7 yrs) performed an incremental cycle ergometer test to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis muscle. During each 2 min power output of the incremental test, six, 10 s EMG samples were recorded. The EMG amplitude and EMG MPF values were calculated for each of the 10 s epochs and separately plotted across time for each power output of the test. The PWCFT was determined by averaging the highest power output that resulted in a non-significant (p > 0.05; single-tailed t-test) slope coefficient for the EMG amplitude versus time relationship and the lowest power output that resulted in a significant (p < 0.05) positive slope coefficient. The MPFFT was determined by averaging the highest power output that resulted in a non-significant (p > 0.05; single-tailed t-test) slope coefficient for the EMG MPF versus time relationship and the lowest power output that resulted in a significant (p < 0.05) negative slope coefficient. RESULTS: The results of a paired t-test indicated that the mean power output for the MPFFT (177.5 ± 64.8 W) was significantly greater (p < 0.05) than that of the PWCFT (152.5 ± 48.9 W). CONCLUSIONS: The significantly greater mean power output for the fatigue threshold based on the frequency (MPFFT) of the surface EMG signal than for the amplitude (PWCFT) suggested that the MPFFT and PWCFT reflect different dimensions of neuromuscular fatigue. It is possible that the PWCFT demarcates the moderate from heavy exercise intensity domains, while the MPFFT may demarcate the heavy from severe intensity domains.

Aerobic exercise training intensity in patients with chronic heart failure: principles of assessment and prescription

Chronic heart failure (CHF) is a significant cause of worldwide mortality and morbidity, whose clinical picture is characterized by exercise intolerance and impaired quality of life. Aerobic exercise training is a well-established nonpharmacological tool improving the CHF’s pathophysiological, clinical, and prognostic picture, and prescription of an adequate training intensity is crucial to obtain both exercise-induced benefits and a reasonable control of exercise-related risk. However, clarity is still lacking regarding the definition of exercise intensity domains and the lower and upper intensity limits of prescriptible aerobic exercise in CHF patients. The purpose of this review is to provide an update of the methods for the exercise intensity assessment and continuous aerobic training intensity prescription in the CHF population, furnishing indications useful for implementation of physical rehabilitation programs in these patients.

Resolving the determinants of high‐intensity exercise performance

Resolving the determinants of high‐intensity exercise performance

Critical power in adolescent boys and girls — an exploratory study

The purpose of the study was to identify critical power (CP) in boys and girls and to examine the physiological responses to exercise at and 10% above CP (CP+10%) in a sub-group of boys. Nine boys and 9 girls (mean age 12.3 (0.5) y performed 3 constant-load tests to derive CP. Eight of the boys then exercised, in random order, at CP and CP+10% until volitional exhaustion. CP was 123 (28) and 91 (26) W for boys and girls, respectively (p < 0.02), which was equivalent to 75 (6) and 72 (10) % of peak oxygen uptake, respectively (p > 0.47). Boys' time to exhaustion at CP was 18 min 37 s (4 min 13 s), which was significantly longer (p < 0.007) than that at CP+10% (9 min 42 s (2 min 31 s)). End-exercise values for blood lactate concentration (B[La]) and maximal oxygen uptake were higher in the CP+10% trial (5.0 (2.4) mmol.L-1 and 2.15 (0.4) L.min-1, respectively) than in the CP trial, (B[La], 4.7 (2.1) mmol.L-1; maximal oxygen uptake, 2.05 (0.35) L.min-1; p > 0.13). Peak oxygen uptake (expressed as a percentage of the peak value) was not attained at the end of the trials (94 (12) and 98 (14) % for CP and CP+10%, respectively). These results provide information about the boundary between the heavy and severe exercise intensity domains in children, and have demonstrated that CP in a group of boys does not represent a sustainable steady-state intensity of exercise.

Carbohydrate and fat metabolism related to blood lactate in boys and male adolescents

The half maximal constant (k (el)) of the relative rate of carbohydrate oxidation (relCHO) was individually approximated (relCHO = 100/(1 + k (el)/BLC(2)) as a function of the blood lactate concentration (BLC) in 11 pre-pubertal boys and 11 male adolescents (age: 11.6 +/- 0.1 vs. 16.4 +/- 0.2 years, height: 151.6 +/- 1.7 vs. 182.4 +/- 2.3 cm, body mass: 38.2 +/- 1.1 vs. 68.7 +/- 2.3 kg, all P < 0.001) during incremental cycle ergometry. k (el) explained 89.0 +/- 2.2 and 91.9 +/- 2.2% of the variance of the reliance on CHO in boys and adolescents respectively (both P < 0.001). No difference in k (el) [1.34 +/- 0.40 vs. 1.48 +/- 0.30 (mmol l(-1))(2)] was found between boys and adolescents. The BLC was lower (P < 0.05) in boys when relCHO was higher than 91.2 +/- 2.1 and 92.1 +/- 1.3% in boys and adolescents respectively. This seems to explain why the reliance on CHO and the BLC are independent of maturation in the moderate and heavy exercise intensity domain and the BLC but not the relCHO which is higher under severe and maximal exercise conditions in more mature subjects.

Determination of the intensity of a power jump session by means of heart rate monitoring

A Power Jump (PJ) session is considered to be a safe and easy class that also involves intermittent exercises that prolong the time to exhaustion. However, there is not enough information about this subject in the literature. The purpose of this study was to determine the intensity of a PJ session by means of heart rate (HR) monitoring. Eleven physically active females participated in the study (age: 21.7 ± 1.9 years; body mass: 59.3 ± 4.8 kg; height: 162.6 ± 5.6 cm; percentage body fat: 22.6 ± 3.2 %). Participants were asked to perform an incremental test (IT), in order to obtain values for oxygen uptake (VO2), maximal heart rate (HRmax), heart rate deflection point (HRDP) and energy expenditure (EE). The HR of the subjects was monitored during a special type of Power Jump session called “mix nine” on two different occasions. According to the HRDP values, physiological domains could be divided into three exercise intensity classes: moderate, heavy and severe. Descriptive statistics were adopted (mean ± SD). Student’s t test was used to compare HR and EE between PJ1 and PJ2. For comparisons between domains, two-way ANOVA and the Scheffe test were used. The level of significance was set at p<0.05. Mean HRmax obtained during the IT was 195±10bpm. The velocities, HR and %HRmax corresponding to HRDP and 80% of HRDP were 10.1±0.95km.h-1, 178±7bpm and 91.7±4.0%; and 8.1±0.76km.h-1, 143±5bpm and 73.4±3.2%, respectively. Values for HRmean and EE were significantly different when PJ1 (161±11bpm, 386±58.2kcal) and PJ2 (156±10bpm, 355.1±53.8kcal) were compared. The times spent in each exercise intensity domain were: heavy 51±14.5%; severe 27±19.7% and moderate 23±8.7%. These results show that the subjects spent most of the time in the heavy exercise domain which, in turn, appears to be the most indicated for improving aerobic capacity.

Oxygen consumption in the severe exercise intensity domain during incremental and square-wave test modes

Incremental tests are commonly used to predict metabolic responses during square-wave mode exercises. However, in some cases the predicted and observed results may be not similar. Main objective: To verify the hypothesis that, at certain intensities in the severe domain, VO2 determined during the incremental test is lower than that observed at these workloads using the square-wave test. Methodological proceedings: Eight physically active males (21.5 ± 4 years, 73.7 ± 5.3 kg and 180.8 ± 4.1 cm) performed: 1) an incremental test on cycle ergometer to determine the VO2 of the intensities (VO2INC); 2) a square-wave test at three severe intensities (Light (L), Medium (M) and Heavy (H)) to determine the critical power (CP) and to compare the VO2 (VO2RET) observed with the VO2INC; 3) a square-wave test at CP intensity to compare the time response of VO2 with P, M and L, at four different sample times. Results: The VO2INC at L intensity underestimated the VO2RET (3.2 ± 0.5 vs. 3.8 ± 0.6 l.min-1). No differences were observed at the other intensities (M: 3.5 ± 0.5 vs. 3.6 ± 0.5 l.min-1; H: 3.7 ± 0.5 vs. 3.4 ± 0.6 l.min-1; CP: 2.7 ± 0.5 vs. 3.0 ± 0.6 l.min-1). The VO2 at CP was lower at all times, exhibited a steady state and did not achieve VO2max. Initially, at L intensity, the VO2 was smaller than its pairs. However, at the last sample time, it achieved VO2max and became equal to the other severe intensities. Conclusion: The incremental test underestimates the VO2 observed at lighter intensities within the severe domain.

Commentaries on Viewpoint: Fatigue mechanisms determining exercise performance: Integrative physiology is systems physiology

Commentaries on Viewpoint: Fatigue mechanisms determining exercise performance: Integrative physiology is systems physiology

Aerobic Potential, Stroke Parameters, and Coordination in Swimming Front-Crawl Performance

The purposes of this review were (1) to review the recent studies conducted in swimming on the assessment of aerobic potential and establishment of exercise-intensity domains (it is important that exercise-intensity domains be accurately defined and their physiological underpinnings well understood to optimize and evaluate training programs); (2) to analyze changes in traditionally measured stroke rate and stroke length during exhaustive swims, particularly in relation to the predetermined intensity domains (introduction of an "optimal swimming technique speed"); and (3) to introduce the latest swimming research on arm coordination that might help us better understand the technical adaptations of swimmers under physical stress.

‘overshoot’ during moderate-intensity exercise in endurance-trained athletes: The influence of exercise modality

The purpose of this study was to investigate the influence of exercise modality on the 'overshoot' in V(O2) that has been reported following the onset of moderate-intensity (below the gas exchange threshold, GET) exercise in endurance athletes. Seven trained endurance cyclists and seven trained endurance runners completed six square-wave transitions to a work-rate or running speed requiring 80% of mode-specific GET during both cycle and treadmill running exercise. The kinetics of V(O2) was assessed using non-linear regression and any overshoot in V(O2) was quantified as the integrated volume (IV) of O(2) consumed above the steady-state requirement. During cycling, an overshoot in V(O2) was evident in all seven cyclists (IV = 136 +/- 41 ml) and in four runners (IV = 81 +/- 94 ml). During running, an overshoot in V(O2) was evident in four runners (IV = 72 +/- 61 ml) but no cyclists. These data challenge the notion that V(O2) always rises towards a steady-state with near-exponential kinetics in this exercise intensity domain. The greater incidence of the V(O2) overshoot during cycling (11/14 subjects) compared to running (4/14 subjects) indicates that the overshoot phenomenon is related to an interaction between high levels of aerobic fitness and exercise modality. We speculate that a transient loss in muscle efficiency as a consequence of a non-constant ATP requirement following the onset of constant-work-rate exercise or an initially excessive recruitment of motor units (relative to the work-rate) might contribute to the overshoot phenomenon.

On- and Off-transient Oxygen Uptake Kinetics Across Exercise Intensity Domains in Female African-America and Caucasian

The oxygen uptake (VO2) kinetic response to a step increase in work rate (WR) can be typically characterized by a mono exponential function during moderate (M) exercise and by a double exponential function during heavy (H) and very heavy (VH) exercise. During recovery from M intensity, the VO2 kinetic response decreases mono exponentially to a steady state. However, during recovery from H and VH exercise, the slow component that typically is evident during the on-transient, may or may not manifest in the off-transient. The characterization of the response to a step increase in WR has been found to provide useful indices of fitness level or degree of cardiorespiratory dysfunction. Since most studies have been conducted predominantly in male subjects, to date there is limited VO2 kinetics information in females. PURPOSE: To examine the relationship between the on- and off-transient VO2 kinetics at three distinct exercise intensities in African American (n=7; 23±3 yr) and Caucasian (n=6; 21±2 yr) females. METHODS: All subjects performed a maximal exercise test and three sets of square-wave exercise tests at M, H, and VH intensities on a cycle ergometer. RESULTS: In both groups, VO2 kinetics during M were well described by a single exponential with the on- and off-transients having similar time constants (African American: ôirc;1,on = 39±13 and 39±15 s; Caucasian: ôirc;1,off = 53±10 and41±4 s;), while H required a double exponential function (African American: & oC1,on = 47±11 and ôirc;2,on = 289±63 s and oC1, off = 46±6 and ô2,off = 259±120 s; Caucasian: oC1, on = 41±12 and ô2,on = 277± 81 s and oC1, off = 40±3 and ô2,off = 215± 133 s). The on-and off-transient VO2 kinetic response for VH, was different between groups. While both the on- and off-transients were well described by a double exponential function in Caucasians (oC1, on = 43±15 and ô2,on = 215±36 s and ô1,off = 42±7 and ô2,off = 223±64 s), the on-transient reverted to a mono-exponential profile (ôirc;1,on = 44±10 s), but the off-transient retained its two-exponential profile (ô1,off = 51±10 and ô2, off = 243±93 s) in African Americans. CONCLUSION: Caucasian and African American women have similar VO2 kinetic responses to M and H exercise. However, the on- and off- VO2 kinetic response to VH exercise remained symmetric in Caucasians but not in African Americans.

Oxygen Uptake and Heart Rate Kinetics during Moderate and Heavy Work-to-Work Transitions

The time course of phase II oxygen uptake (VO2) is slower during step transitions from an elevated exercising baseline (∼45% ventilatory threshold, VT) compared with resting or very low-level intensity baselines. The slowing in VO2 during the on-transient from an elevated exercising baseline at ∼45% VT is likely due to an attenuated heart rate (HR) response. However, the time course of VO and HR during work-to-work transitions in the moderate (between 45 and 100% VT) and heavy (above VT) exercise intensity domain is unknown. PURPOSE: The purpose of this study was to investigate VO2 and HR on-transient responses from elevated exercising baselines at moderate and heavy exercise intensities. We hypothesized 1) that the time course of phase II VO2 would not differ during work-to-work transitions from moderate and heavy intensity exercising baselines, 2) that a shift in the relative contribution of phase II and phase III responses would be observed during progressively heavier exercise, and 3) that the overall time course (mean response time, MRT) of VO2 would be directly related to the MRT of HR. METHODS: Following determination of VT and peak VO2, 13 trained male cyclists (mean± SD; age 25 ± 3.7 years; height 1.82 ± 0.07 m; weight 78.9 ± 8.0 kg; peak VO2 4.48 ± 0.46 L/min) completed work-to-work transitions representing moderate (40–50 and 50–60% VO2 reserve) and heavy (70–80 and 80–90% VO2reserve) exercise intensities. The time course and amplitude response of VO and HR was determined using a first or second-order non-linear exponential model. Comparisons were made with ANOVA and p <0.05 was considered significant. RESULTS: The time course of phase II VO2 during work-to-work transitions from 40–50(21 ± 10 s), 50–60 (22 ± 16 s), 70–80 (19 ± 4 s), and 80–90% VO2 reserve (20 ± 10 s) were not significantly different (p >0.05). As well, the time course of phase II HR during work-to-work transitions from 40–50 (23 ± 12 s), 50–60 (22 ± 12 s), 70–80 (21 ± 15 s), and 80–90% VO2 reserve (26 ± 21 s) were not significantly different (p >0.05). There was a non-significant trend (F = 2.45, p = 0.079) for a reduction in the phase II VO amplitude response during heavy work-to-work transitions, with a similar significant effect observed in HR. The MRT of HR was significantly correlated with VO2 where MRT VO2 = 0.61 (MRT HR) + 29.3 (r = 0.73, p <0.001) CONCLUSION: VO and HR respond in a linear fashion during work-to-work transitions from moderate and heavy intensity exercising baselines. The significant relationship between the MRT of HR and VO2 suggests that the time course of VO2 is HR and thus, O2 delivery dependent.

Oxygen Uptake Kinetics During Supra V·O2maxTreadmill Running in Humans

Accurate classification of VO2 kinetics is essential to correctly interpret its control mechanisms. The purpose of this study was to examine VO2 kinetics in severe and supra-maximal intensity running exercise using two modelling techniques. Nine subjects (mean +/- S.D: age, 27 +/- 7 years; mass, 69.8 +/- 9.0 kg; VO2max, 59.1 +/- 1.8 mL x kg x min(-1)) performed a series of "square-wave" exercise transitions to exhaustion at running speeds equivalent to 80% of the difference between the VO2 at LT and VO2max (delta), and at 100%, 110% and 120% VO2max. The VO2 response was modelled with an exponential model and with a semi-logarithmic transformation, the latter assuming a certain steady state VO2. With the exponential model there was a significant reduction in the "gain" of the primary component in supra-maximal exercise (167 +/- 5 mL x kg(-1) x km(-1) at 80% delta to 142 +/- 5 mL x kg(-1) x km(-1) at 120% VO2max, p = 0.005). The time constant of the primary component also reduced significantly with increasing intensity (17.8 +/- 1.1 s at 80% delta to 12.5 +/- 1.2 s at 120% VO2max, p < 0.05). However, in contrast, using the semi-log model, the time constant significantly increased with intensity (30.9 +/- 13.5 s at 80% delta to 72.2 +/- 23.9 s at 120% VO2max, p < 0.05). Not withstanding the need for careful interpretation of mathematically modelled data, these results demonstrate that neither the gain nor the time constant of the VO2 primary component during treadmill running are invariant across the severe and supra-maximal exercise intensity domains when fit with an exponential model. This suggests the need for a reappraisal of the VO2/work rate relationship in running exercise.

Comparação entre protocolos diretos e indiretos de avaliação da aptidão aeróbia em indivíduos fisicamente ativos

O limiar anaeróbio individual (IAT), o limiar glicêmico individual (IGT), a velocidade associada ao VO2max (Vmax), a velocidade média em corrida de 3.000m (Vm3km) e a velocidade crítica (VC) têm sido utilizados na avaliação aeróbia e prescrição de exercício para atletas-corredores. No entanto, estudos comparando estes parâmetros e sua possível aplicação para indivíduos não atletas ainda não foram realizados. Os objetivos do presente estudo foram comparar e estabelecer as relações entre IAT, IGT, Vmax, Vm3km e VC em indivíduos fisicamente ativos não atletas. Onze indivíduos fisicamente ativos e saudáveis (20,7 ± 1,8 anos; 74,2 ± 14,5kg; 48,9 ± 5,8mlO2.kg.min-1) realizaram randomicamente os seguintes testes de corrida em dias distintos: 1) determinação da Vm3km a partir do desempenho em corrida de 3.000m; 2) desempenho em corrida de 500m e 3) teste incremental em esteira ergométrica para determinação do IAT, IGT, VO2max e Vmax. A VC foi determinada por regressão linear (relação distância-tempo) a partir dos testes de 3km e 500m. Não foram verificadas diferenças entre as velocidades do IAT e IGT (184,8 ± 27,7 e 182,8 ± 27,9m.min-1; P &gt; 0,05), e entre Vmax e Vm3km (211,1 ± 30 e 213,4 ± 32,2m.min-1; P &gt; 0,05). Apesar da alta correlação entre as variáveis estudadas, a VC (199,8 ± 30,4m.min-1) superestimou o IAT e o IGT (P &lt; 0,001). Concluímos que a Vm3km pode ser utilizada como referência de Vmax e que a VC identificada em pista pode ser útil para avaliar a aptidão aeróbia e identificar domínios de intensidade de exercício para indivíduos jovens fisicamente ativos, mas não como referência de limiar anaeróbio.