Moderate Intensity Domain Research Articles

Heavy-intensity priming exercise extends the V̇o2max plateau and increases peak-power output during ramp-incremental exercise.

This study investigated whether a heavy-intensity priming exercise precisely prescribed within the heavy-intensity domain would lead to a greater peak-power output (POpeak) and a longer maximal oxygen uptake (V̇o2max) plateau. Twelve recreationally active adults participated in this study. Two visits were required: 1) a step-ramp-step test [ramp-incremental (RI) control], and 2) an RI test preceded by a priming exercise within the heavy-intensity domain (RI primed). A piecewise equation was used to quantify the V̇o2 plateau duration (V̇o2plateau-time). The mean response time (MRT) was computed during the RI control condition. The delta (Δ) V̇o2 slope (S; mL·min-1·W-1) and V̇o2-Y intercept (Y; mL·min-1) within the moderate-intensity domain between conditions (RI primed minus RI control) were also assessed using a novel graphical analysis. V̇o2plateau-time (P = 0.001; d = 1.27) and POpeak (P = 0.003; d = 1.08) were all greater in the RI primed. MRT (P < 0.001; d = 2.45) was shorter in the RI primed compared with the RI control. A larger ΔV̇o2plateau-time was correlated with a larger ΔMRT between conditions (r = -0.79; P = 0.002). This study demonstrated that heavy-intensity priming exercise lengthened the V̇o2plateau-time and increased POpeak. The overall faster RI-V̇o2 responses seem to be responsible for the longer V̇o2plateau-time. Specifically, a shorter MRT, but not changes in RI-V̇o2-slopes, was associated with a longer V̇o2plateau-time following priming exercise.NEW & NOTEWORTHY It remains unclear whether priming exercise extends the maximal oxygen uptake (V̇o2max) plateau and increases peak-power output (POpeak) during ramp-incremental (RI) tests. This study demonstrates that a priming exercise, precisely prescribed within the heavy-intensity domain, extends the plateau at V̇o2max and leads to a greater POpeak. Specifically, the extended V̇o2max plateau was associated with accelerated RI-V̇o2 responses.

Wearable near-infrared spectroscopy: reliability and sensitivity among different endurance cycling exercise intensities.

The present study investigated the reliability and sensitivity of a wearable near-infrared spectroscopy (wNIRS) device in moderate and heavy exercise intensity domains. On three separate days, eleven males performed an incremental test to exhaustion, and in the following visits, four submaximal constant-load bouts (i.e., test and retest) were performed in the moderate-intensity domain (100 and 130 W) and heavy-intensity domain (160 and 190 W). The local tissue oxygen saturation index (SmO2) and pulmonary oxygen uptake (V̇O2) were measured continuously. The absolute SmO2 and V̇O2 values and the change (Δ) from the 3rd to 6th min of exercise were calculated. There was good reliability for SmO2 measurements, as indicated by the high intraclass correlation coefficient analysis (ICC ≥0.84 for all) and low coefficient of variation between the two trials (CV ≤4.1% for all). Steady-state responses were observed for SmO2 and V̇O2 from the 3rd to the 6th min in the two moderate-intensity bouts (P>0.05), whereas SmO2 decreased and V̇O2 increased from the 3rd to the 6th min in the two heavy-intensity bouts (P<0.05). Together, these findings suggested that the SmO2 measured with a wNIRS device is reliable and sensitive to track local metabolic changes provoked by slight increments in exercise intensity.

Coupling of [Formula: see text] and [Formula: see text] kinetics: insights from multiple exercise transitions below the estimated lactate threshold.

During a step-change in exercise power output (PO), ventilation ([Formula: see text]) increases with a similar time course to the rate of carbon dioxide delivery to the lungs ([Formula: see text]). To test the strength of this coupling, we compared [Formula: see text] and [Formula: see text] kinetics from ten independent exercise transitions performed within the moderate-intensity domain. Thirteen males completed 3-5 repetitions of ∆40W step transitions initiated from 20, 40, 60, 80, 100, and 120W on a cycle ergometer. Preceding the ∆40W step transitions from 60, 80, 100, and 120W was a 6min bout of 20W cycling from which the transitions of variable ∆PO were examined. Gas exchange ([Formula: see text] and oxygen uptake, [Formula: see text]) and [Formula: see text] were measured by mass spectrometry and volume turbine. The kinetics of the responses were characterized by the time constant (τ) and amplitude (Δ[Formula: see text]/Δ[Formula: see text]). Overall, [Formula: see text] kinetics were consistently slower than [Formula: see text] kinetics (by ~ 45%) and τ[Formula: see text] rose progressively with increasing baseline PO and with heightened ∆PO from a common baseline. Compared to τ[Formula: see text], τ[Formula: see text] was on average slightly greater (by ~ 4s). Repeated-measures analysis of variance revealed that there was no interaction between τ[Formula: see text] and τ[Formula: see text] in either the variable baseline (p = 0.49) and constant baseline (p = 0.56) conditions indicating that each changed in unison. Additionally, for Δ[Formula: see text]/Δ[Formula: see text], there was no effect of either variable baseline PO (p = 0.05) or increasing ΔPO (p = 0.16). These data provide further evidence that, within the moderate-intensity domain, both the temporal- and amplitude-based characteristics of V̇E kinetics are inextricably linked to those of [Formula: see text].

Moderate Intensity Arm Cycling As A Viable Exercise Alternative For Overfat And Obese Individuals

The prescription of aerobic exercise engaging the arms may extend the reach of physical activity and improve cardiorespiratory fitness in individuals with obesity. PURPOSE: This study compared the acute cardiopulmonary responses obtained during isocaloric arm and leg cycling trials performed at different intensities among individual’s with and without excess body fat. METHODS: Participants were 37 young adults divided into two groups based on their fat mass index, lean and average (LA) and overfat and obese (OFO). They were tested for mode-specific work rate at the ventilatory threshold (VT) and volitional fatigue (VF) during two randomized ramp tests. The main experiments consisted of four randomized constant work rate isocaloric trials for arm and leg cycling performed at moderate (i.e., work rate equivalent to 80% of VT obtained during the ramp tests) and heavy (i.e., work rate equivalent to 30% of the difference between VT and VF obtained during the ramp tests). The time to expend 100 kcal (Tkcal100) was recorded, and oxygen uptake (V̇O2) was averaged for the duration of the tests. A two-way mixed factorial ANCOVA with physical activity level as a covariate determined work rate at VT, and V̇O2 peak responses to the ramp tests. A three-way mixed factorial ANCOVA with the mode-specific fitness difference and physical activity level as covariates were run for Tkcal100 and V̇O2 obtained during isocaloric trials. Cohen’s d were calculated and interpreted with magnitude thresholds and significance level was set at p ≤ 0.05. RESULTS: Significantly lower work rates at VT and V̇O2 peak were shown for the OFO during ramp tests (LA: 43.4 ± 1.9%, OFO: 37.6 ± 1.9%). Tkcal100 was significantly longer for OFO (25 ± 2 min) in comparison to LA (21 ± 1 min) during isocaloric trials (d = 0.36). The V̇O2 responses were significantly greater in leg cycling (20.4 ± 1.3 mL/min/kg) than arm cycling (15.5 ± 1.3 mL/min/kg), while effect sizes were larger during heavy exercise (d = 1.45) compared to moderate (d = 1.13). CONCLUSION: Arm cycling performed at moderate intensity could be an alternative for young adults with excess body fat and poor cardiorespiratory fitness since this exercise modality elicited a sufficient metabolic response above three metabolic equivalents, which is within the moderate intensity domain suggested by current guidelines.

Evaluating the Accuracy of Using Fixed Ranges of METs to Categorize Exertional Intensity in a Heterogeneous Group of Healthy Individuals: Implications for Cardiorespiratory Fitness and Health Outcomes.

Appropriate quantification of exertional intensity remains elusive. To compare, in a large and heterogeneous cohort of healthy females and males, the commonly used intensity classification system (i.e., light, moderate, vigorous, near-maximal) based on fixed ranges of metabolic equivalents (METs) to an individualized schema based on the exercise intensity domains (i.e., moderate, heavy, severe). A heterogenous sample of 565 individuals (females 165; males 400; age range 18-83years old) were included in the study. Individuals performed a ramp-incremental exercise test from which gas exchange threshold (GET), respiratory compensation point (RCP) and maximum oxygen uptake (VO2max) were determined to build the exercise intensity domain schema (moderate = METs ≤ GET; heavy = METs > GET but ≤ RCP; severe = METs > RCP) for each individual. Pearson's chi-square tests over contingency tables were used to evaluate frequency distribution within intensity domains at each MET value. A multi-level regression model was performed to identify predictors of the amplitude of the exercise intensity domains. A critical discrepancy existed between the confines of the exercise intensity domains and the commonly used fixed MET classification system. Overall, the upper limit of the moderate-intensity domain ranged between 2 and 13 METs and of the heavy-intensity domain between 3 and 18 METs, whereas the severe-intensity domain included METs from 4 onward. Findings show that the common practice of assigning fixed values of METs to relative categories of intensity risks misclassifications of the physiological stress imposed by exercise and physical activity. These misclassifications can lead to erroneous interpretations of the dose-response relationship of exercise and physical activity.

Individual cardiovascular responsiveness to work-matched exercise within the moderate- and severe-intensity domains

PurposeWe investigated the cardiovascular individual response to 6 weeks (3×/week) of work-matched within the severe-intensity domain (high-intensity interval training, HIIT) or moderate-intensity domain (moderate-intensity continuous training, MICT). In addition, we analyzed the cardiovascular factors at baseline underlying the response variability.Methods42 healthy sedentary participants were randomly assigned to HIIT or MICT. We applied the region of practical equivalence-method for identifying the levels of responders to the maximal oxygen uptake (V̇O2max) response. For investigating the influence of cardiovascular markers, we trained a Bayesian machine learning model on cardiovascular markers.ResultsDespite that HIIT and MICT induced significant increases in V̇O2max, HIIT had greater improvements than MICT (p < 0.001). Greater variability was observed in MICT, with approximately 50% classified as “non-responder” and “undecided”. 20 “responders”, one “undecided” and no “non-responders” were observed in HIIT. The variability in the ∆V̇O2max was associated with initial cardiorespiratory fitness, arterial stiffness, and left-ventricular (LV) mass and LV end-diastolic diameter in HIIT; whereas, microvascular responsiveness and right-ventricular (RV) excursion velocity showed a significant association in MICT.ConclusionOur findings highlight the critical influence of exercise-intensity domains and biological variability on the individual V̇O2max response. The incidence of “non-responders” in MICT was one third of the group; whereas, no “non-responders” were observed in HIIT. The incidence of “responders” was 11 out of 21 participants in MICT, and 20 out of 21 participants in HIIT. The response in HIIT showed associations with baseline fitness, arterial stiffness, and LV-morphology; whereas, it was associated with RV systolic function in MICT.

W' Reconstitution Accelerates More with Decreasing Intensity in the Heavy- versus the Moderate-Intensity Domain.

The purpose of this study was to investigate the effect of the recovery intensity domain on W' reconstitution. We used the W'BAL model as a framework and tested its predictive capabilities (W'PRED) across the different intensity domains. Twelve young men (51.7 ± 5.9 mL·kg-1·min-1) completed a ramp incremental test, three to five constant power output (PO) tests to determine critical power (CP) and W', and minimally two trials to verify the maximal lactate (La-) steady state. During four experimental trials, subjects performed two work bouts (WB1 and WB2) at P6 (i.e., PO that predicts exhaustion within 6 min) separated by a recovery interval at CP-10 W, Δgas exchange threshold (GET)-CP, GET, and 50% GET, respectively. WB1 was designed to deplete 75% W', and the recovery time varied to replenish 50% W'. WB2 was performed to exhaustion (W'ACT). W'PRED was compared with W'ACT to evaluate the accuracy of the W'BAL model. Excess postexercise oxygen consumption was calculated as the difference between the measured and the predicted oxygen uptake during recovery. W'ACT averaged 49% ± 24%, 69% ± 24%, 81% ± 28%, and 93% ± 21% for CP-10 W, ΔGET-CP, GET, and 50% GET, respectively (P = 0.002). W'PRED overestimated W'ACT in CP-10 W (34% ± 32%, P = 0.004) and underestimated W'ACT in 50% GET (24% ± 28%, P = 0.013). Excess postexercise oxygen consumption was lowest in CP-10 W (P < 0.01) and higher in GET compared with ΔGET-CP (P = 0.01). We demonstrated that W'PRED overestimated and underestimated W'ACT in the heavy- and moderate-intensity domain, respectively. Therefore, the practical applicability of a single recovery time constant, which only relies on the difference between the recovery PO and the CP, is questionable.

Treadmill running using an RPE-clamp model: mediators of perception and implications for exercise prescription.

The mediators of the perception of effort during exercise are still unclear. The aim of the present study was to examine physiological responses during runs using a rating of perceived exertion (RPE)-clamp model at the RPE corresponding to the gas exchange threshold (RPEGET) and 15% above GET (RPEGET+15%) to identify potential mediators and performance applications for RPE during treadmill running. Twenty-one runners ([Formula: see text]max = 51.7 ± 8.3ml kg-1 min-1) performed a graded exercise test to determine maximal oxygen consumption and the RPE associated with GET and GET + 15% followed by randomized 60min RPE-clamp runs at RPEGET and RPEGET+15%. Mean differences for [Formula: see text], heart rate (HR), minute ventilation ([Formula: see text]), respiratory frequency ([Formula: see text], respiratory exchange ratio (RER), and velocity were compared across each run. After minute 14, [Formula: see text], RER and velocity did not differ across conditions, but decreased across time (p < 0.05). There was a significant (p < 0.05) condition × time interaction for [Formula: see text], where values were significantly higher during RPE-clamp runs at RPEGET+15% and decreased across time in both conditions. There were no differences across condition or time for HR, and only small difference between conditions for [Formula: see text]. HR and [Formula: see text] may play a role in mediating the perception of effort, while [Formula: see text], RER, and [Formula: see text] may not. Although HR and [Formula: see text] may mediate the maintenance of a perceptual intensity, they may not be sensitive to differentiate perceptual intensities at GET and GET + 15%. Thus, prescribing exercise using an RPE-clamp model may only reflect a sustainable [Formula: see text] within the moderate intensity domain.

Physiological Responses to Intermittent Endurance Exercise with Blood Flow Restriction in the Moderate Intensity Domain

Blood flow restriction (BFR) endurance training may induce both endurance and strength improvements. However, there is no consensus on the ideal BFR endurance exercise prescription in order to balance the physiological and perceptual responses. PURPOSE: The purpose of this investigation was to examine the physiological responses, as well as the perceived exertion in responses to a range of BFR endurance protocols. METHODS: Participants randomly performed 7 exercise protocols: 50% of the difference between peak oxygen uptake (VO2) and ventilatory threshold (VT) (∆50%), 90%, 80%, and 70% of VT with and without BFR. Each protocol consisted of two sets of five work intervals (2 minutes work, 1 minute rest) separated by 5 minutes of recovery. Pulmonary VO2 was recorded breath-by-breath, muscle activation (vastus medialis (VM), vastus lateralis (VL)) was assessed by surface electromyography (sEMG), microvascular oxygenation (tissue oxygenation index (TOI)) was assessed by near-infrared spectroscopy (NIRS), and level of perceived exertion (RPE) was assessed using the Borg scale. The last 30 seconds of intervals 5 and 10 were used for analysis. sEMG data were normalized to baseline cycling (20 watts). TOI during each condition was analyzed compared to baseline cycling and then expressed as change from baseline (arbitrary units) to compare between conditions. RESULTS: The ∆50% protocol resulted in a higher end exercise (interval 10) VO2 compared to all other conditions, no other differences in VO2 were observed. No sEMG differences were observed between conditions (VL- p = 0.24, VM- p = 0.33) or between interval 5 and 10. All BFR conditions resulted in a decrease in TOI from baseline. TOI was greater for all BFR conditions (70%BFR = -36.4 ± 21.9, 80%BFR = -40.4 ± 6.5, 90%BFR = -44.7±7.25) compared to the non-BFR conditions (70% = +4.3 ± 20.2, 80% = +11.8 ± 5.5, 90% = +7.25). No differences in TOI between ∆50 (-36.93 ± 10.8) and any BFR conditions were observed. RPE was greater during 90%BFR (18.0 ± 0) and 80%BFR (17.1 ± 1.1) compared to 70% (11.3 ± 0.6) and 90% (13.0 ± 0). No differences were observed between 70%BFR (14.6 ± 0.6) and non-BFR conditions. CONCLUSION: This study demonstrated that cycling with the addition of BFR at an intensity equivalent to 70% of VT may provide a balance between physiological strain and perceived exertion.

Dynamic Adjustment Of Beat-by-beat Cardiac Output And Vo2 Kinetics During Moderate Intensity Exercise Transitions

The kinetic adjustment of oxygen utilization (VO2) to exercise transitions of higher metabolic demands is proposed to be affected by central and peripheral alterations within the O2 transport system and/or intracellular mechanisms of control. Although limitations in O2 availability within the microcirculation but not at the conduit artery level have been proposed, knowledge is limited in relation to the contribution of the dynamic adjustment of cardiac output (Q) to the VO2 kinetics response, and how training status might modify this response. PURPOSE: This study aimed to compare the adjustment of muscle VO2 (i.e., Phase II VO2) to that of central O2 delivery as examined by the adjustment of Q during step transitions to moderate intensity exercise. METHODS: Sixteen young healthy male participants (35 ± 6 yrs) performed 3 step transitions from 20W to moderate-intensity cycling on a cycle ergometer to determine the breath-by-breath VO2 and the beat-by-beat Q responses. Participants were separated into two groups: trained (n= 9, VO2max 4.54 ± 0.40 L/min) and untrained (n= 7, VO2max 3.49 ± 0.68 L/min). Phase II VO2 and Q were modeled with a monoexponential model. Paired and unpaired t-tests and Pearson product moment correlations were used to compare the time constants of VO2 (τVO2) and Q (τQ). Statistical significance was set at P<0.05. RESULTS: Mean τVO2 was faster in the trained (13.9 ± 2.7s) compared to untrained (24.4 ± 6.4 s). τQ was slower than τVO2 in the trained (18.5 ± 6.0 s) but not untrained (20.2 ± 9.2 s). No difference was found between τQ between groups. Overall mean data showed no difference between τVO2 (18.5 ± 7.1 s) and τQ (19.3 ± 7.3 s). No significant correlations were found between τVO2 and τQ in trained (r=0.34), untrained (r=0.47), or when considering the two conditions together (r=0.37). CONCLUSION: This study demonstrated the dynamic adjustment of Q to exercise transition within the moderate intensity domain does not differ amongst trained and untrained individuals, even in the presence of training induced speeding of the VO2 kinetics. These data support the notion that mechanisms other than central delivery of O2, such as improved blood flow redistribution within the active tissues and/or intracellular components are responsible for controlling the rate of adjustment of VO2.

Magnetized plasma implosion in a snail target driven by a moderate-intensity laser pulse

Optical generation of compact magnetized plasma structures is studied in the moderate intensity domain. A sub-ns laser beam irradiated snail-shaped targets with the intensity of about 1016 W/cm2. With a neat optical diagnostics, a sub-megagauss magnetized plasmoid is traced inside the target. On the observed hydrodynamic time scale, the hot plasma formation achieves a theta-pinch-like density and magnetic field distribution, which implodes into the target interior. This simple and elegant plasma magnetization scheme in the moderate-intensity domain is of particular interest for fundamental astrophysical-related studies and for development of future technologies.

Duty Cycle Impairs Functional Sympatholysis During Moderate Intensity Hand‐grip Exercise

Functional sympatholysis is a well‐known mechanism that blunts the sympathetic vasoconstrictor signal in working muscle, enabling blood flow to be maintained during exercise in the moderate intensity domain. Recent work has demonstrated that exercise intensity and contraction frequency effects functional sympatholysis via changes in metabolic rate. However, less is known about the effects duty cycle (DC) on functional sympatholysis, which alters the time that intramuscular pressure is developed throughout a contraction cycle independent of changes in frequency and intensity. Given that a higher duty cycle (i.e., 50% DC) attenuates muscle blood flow to the working limb, potentially leading to a greater metabolite buildup, we hypothesized that a 20% DC would show greater percent change in forearm vascular conductance (%Δ FVC) and forearm blood flow (%Δ FBF) when compared to 50% duty cycle.METHODSEight healthy male subjects (age: 25 ± 1 yrs; height: 176.8 ± 1.5 cm; weight: 84 ± 5 kg) agreed to participate in the current investigation. Subjects began with a four‐minute resting protocol, two‐minutes of supine blood pressure and blood flow and two‐minutes utilizing lower‐body negative pressure (LBNP; ‐30 mmHg) to increase sympathetic outflow. Subjects then underwent two exercise conditions in a randomized order consisting of 20% and 50% DC (20%:50% or 50%:20%) with ~10 min between trials to allow blood pressure and blood flow to return to baseline. All hand‐grip exercise was performed at 20 contractions per minute at a workload of 20% of subject's maximal voluntary contraction.RESULTSAbsolute FVC during the 20% duty cycle condition was significantly higher than the 50% duty cycle (20%: 398 ± 34; 50%: 327 ± 37 ml min−1 mmHg−1; P &lt; 0.01). FBF was also significantly higher in the 20% duty cycle condition (20%: 392 ± 21; 50%: 330 ± 29 ml min−1; P &lt; 0.01). During steady state hand‐grip exercise coupled with LBNP, %Δ FVC, an indicator of sympathetically‐mediated vasoconstriction, showed a larger percent reduction during 20% duty cycle (20%: −12.6 ± 1.5%; 50%: 1.4 ± 3.9%; P &lt; 0.01).CONCLUSIONThe results of the current investigation suggest that the 20% DC had a greater sympathetically‐mediated vasoconstrictor response compared to the 50% duty cycle.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect of the Muscle Metaboreflex on Heart Rate Kinetics during the Exercise Transient Spanning the Entire Moderate Intensity Domain

Effect of the Muscle Metaboreflex on Heart Rate Kinetics during the Exercise Transient Spanning the Entire Moderate Intensity Domain

The influence of metabolic and circulatory heterogeneity on the expression of pulmonary oxygen uptake kinetics in humans.

We examined the relationship amongst baseline work rate (WR), phase II pulmonary oxygen uptake (V̇(O2p)) time constant (τV̇(O2p)) and functional gain (G(P)=ΔV̇(O2p)/ΔWR) during moderate-intensity exercise. Transitions were initiated from a constant or variable baseline WR. A validated circulatory model was used to examine the role of heterogeneity in muscle metabolism (V̇(O2m)) and blood flow (Q̇(m)) in determining V̇(O2p) kinetics. We hypothesized that τV̇(O2p) and G(P) would be invariant in the constant baseline condition but would increase linearly with increased baseline WR. Fourteen men completed three to five repetitions of ∆40 W step transitions initiated from 20, 40, 60, 80, 100 and 120 W on a cycle ergometer. The ∆40 W step transitions from 60, 80, 100 and 120 W were preceded by 6 min of 20 W cycling, from which the progressive ΔWR transitions (constant baseline condition) were examined. The V̇(O2p) was measured breath by breath using mass spectrometry and a volume turbine. For a given ΔWR, both τV̇(O2p) (22-35 s) and G(P) (8.7-10.5 ml min(-1) W(-1)) increased (P < 0.05) linearly as a function of baseline WR (20-120 W). The τV̇(O2p) was invariant (P < 0.05) in transitions initiated from 20 W, but G(P) increased with ΔWR (P < 0.05). Modelling the summed influence of multiple muscle compartments revealed that τV̇(O2p) could appear fast (24 s), and similar to in vivo measurements (22 ± 6 s), despite being derived from τV̇(O2p) values with a range of 15-40 s and τQ̇(m) with a range of 20-45 s, suggesting that within the moderate-intensity domain phase II V̇(O2p) kinetics are slowed dependent on the pretransition WR and are strongly influenced by muscle metabolic and circulatory heterogeneity.

Physiological Responses during Cycle Ergometry at a Constant Perception of Effort.

13 subjects performed an incremental test to exhaustion, 4, 8-min submaximal rides, and a 1-h ride at the rating of perceived exertion (RPE) that corresponded to the physical working capacity at the OMNI threshold (PWC(OMNI)) to examine: 1) the oxygen consumption (V̇O2), heart rate (HR), minute ventilation (+V̇(E)), respiratory frequency (FR), and power output responses during 1-h work bouts at a constant RPE that corresponded to the PWC(OMNI); and 2) the ability of current models to explain the responses for physiological and perceptual parameters during the 1-h work bouts. The RPE that corresponded to the PWC(OMNI) represented a sustainable exercise intensity (56±5% (V̇O(2Peak)) within the moderate-intensity domain. The mean, normalized slope coefficients for the V̇O2, +V̇(E), and power output vs. time relationships during the 1-h rides were significantly less than zero. The mean, normalized slope coefficient for the FR vs. time relationship during the 1-h rides, however, was not significantly different from zero. Thus, RPE most clearly tracked FR responses during the 1-h rides. It was hypothesized that afferent feedback from respiratory muscles may have mediated the perception of effort during cycle ergometry at a constant RPE in the moderate-intensity domain.

High-intensity interval training speeds the adjustment of pulmonary O2uptake, but not muscle deoxygenation, during moderate-intensity exercise transitions initiated from low and elevated baseline metabolic rates

During step transitions in work rate (WR) within the moderate-intensity (MOD) exercise domain, pulmonary O2 uptake (Vo2p) kinetics are slowed, and Vo2p gain (ΔVo2p/ΔWR) is greater when exercise is initiated from an elevated metabolic rate. High-intensity interval training (HIT) has been shown to speed Vo2p kinetics when step transitions to MOD exercise are initiated from light-intensity baseline metabolic rates. The effects of HIT on step transitions initiated from elevated metabolic rates have not been established. Therefore, this study investigated the effects of HIT on Vo2p kinetics during transitions from low and elevated metabolic rates, within the MOD domain. Eight young, untrained men completed 12 sessions of HIT (spanning 4 wk). HIT consisted of 8-12 1-min intervals, cycling at a WR corresponding to 110% of pretraining maximal WR (WRmax). Pre-, mid- and posttraining, subjects completed a ramp-incremental test to determine maximum O2 uptake, WRmax, and estimated lactate threshold (θL). Participants additionally completed double-step constant-load tests, consisting of step transitions from 20 W → Δ45% θL [lower step (LS)] and Δ45 → 90% θL [upper step (US)]. HIT led to increases in maximum O2 uptake (P < 0.05) and WRmax (P < 0.01), and τVo2p of both lower and upper MOD step transitions were reduced by ∼40% (LS: 24 s → 15 s; US: 45 s → 25 s) (P < 0.01). However, the time course of adjustment of local muscle deoxygenation was unchanged in the LS and US. These results suggest that speeding of Vo2p kinetics in both the LS and US may be due, in part, to an improved matching of muscle O2 utilization to microvascular O2 delivery within the working muscle following 12 sessions of HIT, although muscle metabolic adaptations cannot be discounted.

Physiological Demands of Team-Handball Referees During Games

The objective of the present study was to examine the aerobic fitness and the physiological demands during competitive games in elite handball referees. Sixteen referees (age: 34.9 +/- 3.4 years, body mass: 77.4 +/- 10.6 kg, height: 173.5 +/- 7.5 cm, percent fat: 22.3 +/- 6.6%) of national and international levels (14 men and 2 women) were submitted to a multistage fitness test, to determine peak velocity (PV) and maximal heart rate (HR). After 48 hours, referees performed a submaximal intermittent shuttle-running test (3 minutes at 75 and 90% PV with 1-minute recovery), to determine speeds and HR at selected blood-lactate concentrations (2.0 and 4.0 mmol.L(-1)). Game intensities were arbitrarily established as follows: <HR2mmol (moderate), between HR2mmol and HR4mmol (heavy) and >HR4mmol (severe). Eight referees (2 per game) were monitored in 4 national level games. The mean VO(2)max of the referees was 48.5 +/- 6.1 ml.kg(-1).min(-1). Maximal HR, HR2mmol, and HR4mmol were 193 +/- 10, 154 +/- 13, and 167 +/- 10 b.min, respectively. The percent time spent in the moderate intensity domain was predominant (moderate 96.4%, heavy 2.3%, and severe 1.3% of total time, p < 0.05). These findings indicate that handball refereeing is of moderate intensity. In light of this study, results aerobic fitness does not seem to be a limiting factor in handball refereeing.

Oxygen Uptake Kinetics During Arm Cranking Within The Moderate Intensity Domain

Recent studies have demonstrated that on-transient oxygen uptake (VO2) kinetics are slowed when constant-load exercise is initiated from the upper compared to lower region of the moderate intensity domain (below the lactate threshold, LT). These studies, focusing exclusively on lower limb exercise, attributed this intensity-dependent slowing of VO2 kinetics during moderate-intensity exercise to different muscle fiber recruitment patterns or altered oxygen transport dynamics. PURPOSE: To determine if pulmonary VO2 and heart rate (HR) kinetics are slowed during constant-load arm exercise (arm-cranking) performed in the upper (90%LT) compared to lower (45%LT) regions of the moderate intensity domain. METHODS: Seven healthy male subjects (26 ± 3 yr) performed 4-8 repetitions of arm-cranking exercise involving: 1) a single, 6-min step transition from 9 W to 90% of the estimated LT (AC90%); two continuous, equal, 6-min step transitions from 9 W to 45% LT (AC45%), and then to 90% LT (AC45-90%); and 3) the AC90% protocol superimposed upon low-intensity leg-cycling (AC90%+LC), where baseline HR >100 beats·min-1 (range: 100-120 beats·min-1). RESULTS: The time constants (t) of the VO2 and HR responses were longer (P<0.05) during AC45-90% (tVO2: 70 ± 5 s; tHR: 59 ± 4 s) compared to AC45% (tVO2: 54 ± 6 s; tHR: 47 ± 5 s) and AC90% (tVO2: 53 ± 4 s; tHR: 46 ± 3 s). The gain (DVO2/DW) and blood lactate concentration were also significantly greater (P<0.05) for AC45-90% than AC45%. During arm-cranking superimposed upon leg-cycling (AC90%+LC), HR kinetics were significantly slowed when compared to AC90% (mean difference for tHR: 9 ± 4 s, P<0.05) and AC45% (mean difference for tHR: 9 ± 5 s, P<0.05). Similar comparisons between conditions for tVO2 yielded no significant differences. CONCLUSION: During arm exercise performed within the moderate intensity domain, VO2 and HR kinetics do not conform to a dynamically linear model. Since HR, but not VO2 kinetics were slowed during AC90%+LC, factors other than convective oxygen delivery (e.g. those intrinsic to the exercising muscle) may explain the slower VO2 response in the upper reaches of the moderate intensity domain for arm exercise.

O2 Uptake Kinetics During Knee Extension And Leg Cycling Exercise In The Moderate-intensity Domain

During the transition to the same relative intensity of exercise in the moderate-intensity domain the phase II time constant for O2 uptake (tVO2) and the VO2 gain (DVO2/DWR) tend to be greater with knee-extension (KE) than with leg cycling exercise (CE), however, the response at the same absolute work rate (WR) has not been established. PURPOSE: To examine the adaptation of pulmonary VO2 during the transition to the same relative and same absolute WRs in the moderate-intensity domain. METHODS: Four younger subjects completed an incremental exercise test to volitional fatigue during both alternate-leg KE and CE to estimate lactate threshold (θL) and peak VO2. Subjects then completed four step transitions in WR from light- to a moderate-intensity exercise corresponding to 90% θL (KErel, CErel), as well as four step transitions during CE from light-intensity to an absolute WR equal to that used during KErel (CEabs). A cadence of 50 rpm was maintained throughout all testing with KE and CE. VO2 was measured breath-by-breath using a volume turbine and mass spectrometer. The phase II VO2 response was modeled using a monoexponential function and non-linear regression techniques. RESULTS: The tVO2 was greater (p<0.05) in KErel (28 (7) s; mean (± SD)) than in CErel (15 (2) s) and in CEabs (16 (4) s) The VO2 gain was greater (p<0.05) in KErel (15.3 (2.?) ml · min-1 · W-1) than in CErel (8.5 (3.1) ml · min-1 · W-1), but not different from that found in CEabs (11.5 (6.6) ml · min-1 · W-1). CONCLUSION: The tendency for a greater tVO2 and VO2 gain during the transition to the same relative and same absolute intensity of exercise using KE compared to CE may be related to biomechanical differences or to the different muscle fibres or muscle groups recruited during the exercise transition within each modality. Supported by NSERC

Point: The kinetics of oxygen uptake during muscular exercise do manifest time-delayed phases

Modeling a physiological system's response to a stressor, such as muscular exercise, demands more than a mathematically adequate characterization of its transient response profile: adequacy and appropriateness are not synonymous. The model constituents should be reflective of the system's