Ramp Exercise Research Articles

Brain Derived Neutrophic Factor, Cerebral Activation and Memory Responses to Five Weeks of Aerobic Exercise Training

Studies have shown that the production of brain derived neutrophic factor (BDNF) in the hippocampus increases following exercise which may be the molecular link between physical activity and the improvements reported in memory and learning. PURPOSE: To determine if moderate intensity exercise training leads to an increase in plasma [BDNF] which may be associated with improvements in cognitive function, increased brain activity and/or structure. METHODS: 11 healthy males (23 ± 7 yrs (±SD)) completed a 5 week aerobic training program (92 ± 5% compliance) at an intensity of 65% maximal heart rate, 5 days/wk on a cycle ergometer. Prior to, and following training, each subject performed a ramp exercise test to fatigue for the determination of peak VO2 (VO2pk), work rate (WRpk), and estimated lactate threshold (LT). Arterialized-venous blood samples were obtained from a dorsal hand vein at rest, exhaustion and during recovery for the determination of plasma [BDNF]. Subjects underwent magnetic resonance imaging (fMRI) and a memory task before and after the training program. All exercise was performed on a cyle ergometer; pulmonary gas exchange was measured using standard techniques. RESULTS: While there was no difference in VO2pk between pre- and post-training (pre, 43.9 ± 9.2; post, 45.4 ± 8.5 ml/kg/min), the VO2 at LT was higher (p<0.05) following training (pre, 1773 ± 262; post, 2047 ± 289 ml/kg/min). Similarly, WRpk was higher (p<0.05) following training (pre, 288 ± 50; post, 313 ±56 W). Brain volume in right hippocampus and left cerebral cortex was significantly decreased following training. Compared to pre-training, fMRI showed an increase in the activation of the left hippocampus after training. There was no difference in plasma [BDNF] at rest between pre- and post-training; plasma [BDNF] increased (p<0.05) at exhaustion and was higher following training (pre, 15.4 ± 3.7; post, 17.5 ± 4.4 ng/ml: p<0.05). CONCLUSION: A moderate intensity training program resulted in small, but significant increases in exercise tolerance, brain structural and functional activation, particularly in the hippocampal region. However, there was little evidence for a relationship between changes in plasma [BDNF], brain structure and memory function.

The Relationship Between Muscle Activation and VO2 During Incremental Ramp Exercise

The Relationship Between Muscle Activation and VO2 During Incremental Ramp Exercise

(306) - LVAD Weaning Protocol Utilizing Comprehensive Cardiopulmonary Exercise Testing to Define Cardiac Reserve Capacity

The optimal protocol for determining whether adequate LV recovery has taken place to permit LVAD explantation is not well established. Peak VO2 (pVO2) is typically the only exercise parameter utilized. We developed a protocol that integrates hemodynamic, imaging, and gas exchange measures at rest, during LVAD speed reduction, and during exercise to characterize cardiac reserve capacity and guide LVAD explant decisions. A 44 year old male with LVEF 14% demonstrated no LV recovery after CABG and required insertion of a BTT Heartware LVAD on post-op day 14. After 6 months, LVAD speed reduction to 2000 rpm led to borderline-acceptable echo parameters (LVEF 49%, LVEDD 58 mm) and a pVO2 of only 14.6 ml/kg/min. We measured VO2, peripheral O2 extraction (Ca-vO2), Fick cardiac output (CO) and pulmonary wedge pressure (PCWP) each minute during an incremental ramp exercise protocol. Exercise CO increased appropriately (7.4 to 14.6 L/min) and PCWP increment was modest (+7mmHg), which prompted us to explant the LVAD. In contrast, a 61 year old patient with a BTT LVAD demonstrated a similar pVO2 (14.1 ml/kg/min). Unlike our first patient, exercise CavO2 was normal, but he was able to augment his CO to only 8.3 L/min with a 15 mmHg increase in PCWP. LVAD explant was therefore not pursued and he underwent cardiac transplantation. Nearly identical pVO2 values in our patients with divergent relative contributions of CO and CavO2 highlight the need to consider both central cardiac and peripheral O2 extraction components of pVO2. Serial measurements of PCWP in relation to CO were particularly informative based on a 2-fold PCWP-CO slope (1.5 vs. 3.1 mmHg/L/min) in the patient not explanted. Our findings suggest that reliance on LVAD explant criteria of a pVO2 > 16 mL kg/min may not adequately reflect reserve capacity and sustained recovery potential of the native heart. Enhanced phenotyping during exercise merits further investigation to refine LVAD explant criteria.

Excess VO2 during ramp exercise is positively correlated to intercostal muscles deoxyhemoglobin levels above the gas exchange threshold in young trained cyclists

We assessed respiratory muscles oxygenation responses during a ramp exercise to exhaustion and further explored their relationship with the non-linear increase of VO2 (VO2 excess) observed above the gas-exchange threshold. Ten male cyclists completed a ramp exercise to exhaustion on an electromagnetically braked cycle-ergometer with a rate of increment of 30Wmin−1 with continuous monitoring of expired gases (breath-by-breath) and oxygenation status of intercostal muscles. Maximal inspiratory and expiratory pressure measurements were taken at rest and at exhaustion. The VO2 excess represents the difference between VO2max observed and VO2max expected using linear equation between the VO2 and the intensity before gas-exchange threshold. The deoxyhemoglobin remained unchanged until 60% of maximal aerobic power (MAP) and thereafter increased significantly by 37±18% and 40±22% at 80% and 100% of MAP, respectively. Additionally, the amplitude of deoxyhemoglobin increase between 60 and 100% of MAP positively correlated with the VO2 excess (r=0.69, p<0.05). Compared to exercise start, the oxygen tissue saturation index decreased from 80% of MAP (−4.8±3.2%, p<0.05) onwards. At exhaustion, maximal inspiratory and expiratory pressures declined by 7.8±16% and 12.6±10% (both p<0.05), respectively. In summary, our results suggest a significant contribution of respiratory muscles to the VO2 excess phenomenon.

The temporal relationship of thresholds between muscle activity and ventilation during bicycle ramp exercise in community dwelling elderly males.

[Purpose] To compare the appearance time of the ventilatory threshold point and the electromyographic threshold in the activity of the vastus lateralis, rectus femoris, biceps femoris long head and gastrocnemius lateral head muscles during ramp cycling exercise in elderly males. [Subjects and Methods] Eleven community dwelling elderly males participated in this study. Subjects performed exercise testing with an expiratory gas analyzer and surface electromyography to evaluate the tested muscle activities during ramp exercise. [Results] The electromyographic threshold for rectus femoris was not valid because the slope after electromyographic threshold was not significant as compared to that before electromyographic threshold. The slope of the regression line for vastus lateralis was significantly decreased after electromyographic threshold while biceps femoris and gastrocnemius were increased. The electromyographic threshold appearance times for vastus lateralis and gastrocnemius were significantly earlier than ventilatory threshold point. There were no difference in electromyographic threshold appearance times among three muscles. [Conclusion] These results suggest that the increase in the slope of the regression line after electromyographic threshold for vastus lateralis was decreased, possibly indicating to postpone muscular fatigue resulting from the activation of biceps femoris and gastrocnemius as biarticular antagonists. This recruitment pattern might be an elderly-specific strategy.

Thresholds in ventilation, cerebral and muscle oxygenation, and muscle activity during incremental cycling exercise

Introduction: Cycle time-trial performance is a function of the highest sustainable power output. The first (VT-1) and second (VT-2) ventilatory thresholds are practical tools for coaches and athletes to set training zones and exercise intensity. Specifically, VT-2 is closely linked to critical power, a primary determinant of endurance performance. The cascade of physiological events in the organs responsible for power production accompanying these respiratory thresholds remains contentious and yet to be fully characterized. Electromyographic (EMG) thresholds have been identified in leg muscles during incremental exercise while near infrared spectroscopy (NIRS) has revealed thresholds in both muscle deoxygenation and cerebral oxygenation towards the end of an incremental exercise test. However, the relative timing of the different muscle and brain oxygenation and muscle electrical activity responses to each other is unclear. Purpose: The aim of the present study was to examine the thresholds of cerebral and muscle oxygenation, along with muscle electrical activity during a ramp exercise test in relation to VT-1 and VT-2. Methods: Twenty-five recreational cyclists (mean±SD: age 37±8yrs, body mass 78±13kg, height 178±8cm, VO 2 max 53±8mL/kg/min) completed a ramp exercise test to exhaustion on an electromagnetically braked cycle-ergometer with a work rate increment of 25 W/min. Throughout the test, continuous measures of expired gas (breath-by-breath), prefrontal cortex and vastus lateralis (VL) oxygenation via NIRS, and EMG Root Mean Square activity for the VL, rectus femoris (RF), and biceps femoris (BF) muscles were recorded. Thresholds were defined by a double-linear model. Results: The results are summarized in Figure 1. VT-1 and VT-2 occurred at 57 ± 6% and 81 ± 6% of the exercise, respectively. There was a threshold in both cerebral deoxyhaemoglobin and oxyhaemoglobin (56±13% and 56±8% of exercise, respectively) which were not significantly different from VT-1 ( P >0.86, cohens d 0.8). Only one threshold could be identified for muscle parameters with a threshold in muscle oxyhaemoglobin (78±9% of exercise), attenuation in muscle deoxyhaemoglobin (80±8% of exercise), and increase in EMG activity of VL, RF and BF (89±5%, 82±14% and 85±9% of exercise, respectively). The thresholds in BF and VL EMG activity occurred after VT-2 ( P 0.6). Conclusion: The threshold in cerebral oxygenation parameters occurred at both VT-1 and VT-2. Conversely, the present investigation failed to support a role for VL muscle oxygenation and electrical activity at VT-1, but did display a threshold at or after VT-2. The changes in cerebral oxygenation and in BF and VL electrical activity occurred after VT-2, suggesting that the metabolic and ventilatory events characterizing this latter cardiorespiratory threshold may affect both cerebral and muscle oxygenation levels and subsequent muscle recruitment responses. These physiological mechanisms are important factors in describing key training concepts and performance capability; for instance critical power. Any marked rise in muscle recruitment above VT-2 or critical power will result in early onset of fatigue and limit exercise performance.

Anaerobic Threshold by Mathematical Model in Healthy and Post-Myocardial Infarction Men.

The aim of this study was to determine the anaerobic threshold (AT) in a population of healthy and post-myocardial infarction men by applying Hinkley's mathematical method and comparing its performance to the ventilatory visual method. This mathematical model, in lieu of observer-dependent visual determination, can produce more reliable results due to the uniformity of the procedure. 17 middle-aged men (55±3 years) were studied in 2 groups: 9 healthy men (54±2 years); and 8 men with previous myocardial infarction (57±3 years). All subjects underwent an incremental ramp exercise test until physical exhaustion. Breath-by-breath ventilatory variables, heart rate (HR), and vastus lateralis surface electromyography (sEMG) signal were collected throughout the test. Carbon dioxide output (V˙CO2), HR, and sEMG were studied, and the AT determination methods were compared using correlation coefficients and Bland-Altman plots. Parametric statistical tests were applied with significance level set at 5%. No significant differences were found in the HR, sEMG, and ventilatory variables at AT between the different methods, such as the intensity of effort relative to AT. Moreover, important concordance and significant correlations were observed between the methods. We concluded that the mathematical model was suitable for detecting the AT in both healthy and myocardial infarction subjects.

The interrelationship between muscle oxygenation, muscle activation, and pulmonary oxygen uptake to incremental ramp exercise: influence of aerobic fitness.

We investigated whether muscle and ventilatory responses to incremental ramp exercise would be influenced by aerobic fitness status by means of a cross-sectional study with a large subject population. Sixty-four male students (age: 21.2 ± 3.2 years) with a heterogeneous peak oxygen uptake (51.9 ± 6.3 mL·min(-1)·kg(-1), range 39.7-66.2 mL·min(-1)·kg(-1)) performed an incremental ramp cycle test (20-35 W·min(-1)) to exhaustion. Breath-by-breath gas exchange was recorded, and muscle activation and oxygenation were measured with surface electromyography and near-infrared spectroscopy, respectively. The integrated electromyography (iEMG), mean power frequency (MPF), deoxygenated [hemoglobin and myoglobin] (deoxy[Hb+Mb]), and total[Hb+Mb] responses were set out as functions of work rate and fitted with a double linear function. The respiratory compensation point (RCP) was compared and correlated with the breakpoints (BPs) (as percentage of peak oxygen uptake) in muscle activation and oxygenation. The BP in total[Hb+Mb] (83.2% ± 3.0% peak oxygen uptake) preceded (P < 0.001) the BP in iEMG (86.7% ± 4.0% peak oxygen uptake) and MPF (86.3% ± 4.1% peak oxygen uptake), which in turn preceded (P < 0.01) the BP in deoxy[Hb+Mb] (88.2% ± 4.5% peak oxygen uptake) and RCP (87.4% ± 4.5% peak oxygen uptake). Furthermore, the peak oxygen uptake was significantly (P < 0.001) positively correlated to the BPs and RCP, indicating that the BPs in total[Hb+Mb] (r = 0.66; P < 0.001), deoxy[Hb+Mb] (r = 0.76; P < 0.001), iEMG (r = 0.61; P < 0.001), MPF (r = 0.63; P < 0.001), and RCP (r = 0.75; P < 0.001) occurred at a higher percentage of peak oxygen uptake in subjects with a higher peak oxygen uptake. In this study a close relationship between muscle oxygenation, activation, and pulmonary oxygen uptake was found, occurring in a cascade of events. In subjects with a higher aerobic fitness level this cascade occurred at a higher relative intensity.

Influence of acute passive stretching on the oxygen uptake vs work rate slope during an incremental cycle test.

The aim of the study was to investigate the effects of acute passive stretching on O2 uptake (VO2) vs work rate slope during a continuous incremental ramp exercise. On two different occasions, eight participants (age 23 ± 3 years; stature 1.71 ± 0.10 m; body mass 68 ± 8 kg; mean ± SD) performed two maximum incremental ramp tests on a cycle ergometer (25 W/min), with and without pre-exercise stretching. During tests, we measured VO2 and other metabolic and cardiorespiratory parameters on a breath-by-breath basis. The VO2 vs work rate slopes were calculated below (S 1) and above (S 2) the first ventilatory threshold (VET1). With stretching: (1) peak VO2 did not change, while peak work rate decreased (P < 0.05, ES = -0.41; CI -1.40/-0.58); (2) in spite of a similar S 1, S 2 was steeper by about 11 % (P < 0.05; ES = 0.62; CI -0.38/-1.62). Stretching reduced peak work rate and altered the [Formula: see text] vs work rate relationship above VET1 (S 2), without affecting peak VO2. The present findings have practical implications, questioning the use of stretching manoeuvres especially when peak work rate plays a key role in exercise performance.

Aerobic Function and Muscle Deoxygenation Dynamics during Ramp Exercise in Children.

This study aimed to characterize changes in deoxyhemoglobin ([HHb]) response dynamics in boys and girls during ramp incremental exercise to investigate whether the reduced peak oxygen uptake (peak V˙O2) in girls is associated with poorer matching of muscle O2 delivery to muscle O2 utilization, as evidenced by a more rapid increase in [HHb]. Fifty-two children (31 boys, 9.9 ± 0.6 yr, 1.38 ± 0.07 m, 31.70 ± 5.78 kg) completed ramp incremental exercise on a cycle ergometer during which pulmonary gas exchange and muscle oxygenation parameters were measured. When muscle [HHb] was expressed against absolute work rate and V˙O2, girls had an earlier change in [HHb], as evidenced by the lower c/d parameter (girls, 54 ± 20 W, vs boys, 67 ± 19 W, P = 0.023; girls, 0.82 ± 0.28 L·min(-1), vs boys, 0.95 ± 0.19 L·min(-1), P = 0.055) and plateau (girls, 85 ± 12 W, vs boys, 99 ± 18 W, P = 0.031; girls, 1.02 ± 0.25 L·min(-1), vs boys, 1.22 ± 0.28 L·min(-1), P = 0.014). However, when expressed against relative work rate or V˙O2, there were no sex differences in ([HHb]) response dynamics (all P > 0.20). Significant correlations were observed between absolute and fat-free mass normalized peak V˙O2 and the HHb c/d and plateau parameters when expressed against absolute work rate or V˙O2. Furthermore, when entered into a multiple regression model, the [HHb] plateau against absolute V˙O2 contributed 12% of the variance in peak V˙O2 after adjusting for fat-free mass, gas exchange threshold, and body fatness (model R2 = 0.81, P < 0.001). The sex difference in peak V˙O2 in 9- to 10-yr-old children is, in part, related to sex-specific changes in muscle O2 extraction dynamics during incremental exercise.

Beneficial effects of training at the anaerobic threshold in addition to pharmacotherapy on weight loss, body composition, and exercise performance in women with obesity.

ObjectiveThe aim of this study was to determine and compare the effects of weight loss achieved through orlistat therapy alone or a combination of orlistat and an aerobic exercise training program on aerobic fitness and body composition in obese females.MethodsTwenty-eight obese patients were randomly assigned to receive 12-week treatment with hypocaloric diet–orlistat or diet–orlistat–exercise. Each participant performed an incremental ramp exercise test every 4 weeks to measure aerobic fitness. Fourteen participants performed continuous exercise (approximately 45 minutes per session) at a work rate corresponding to the anaerobic threshold three times per week.ResultsA decrease in the fat mass to body weight ratio of 3.8% (P=0.006) was observed at the end of the 12 weeks in the orlistat group, while a decrease of 9.5% (P=0.001) was seen in the orlistat–exercise group. Maximal exercise capacity increased by 46.5% in the orlistat–exercise group and by 19.5% in the orlistat group.ConclusionWhile orlistat therapy resulted in an improvement in body composition and aerobic fitness at the end of the 12-week period, its combination with exercise training provided improvements in the same parameters within the first 4 weeks of the study. These additional beneficial effects of combining aerobic exercise with orlistat therapy are important with regards to obesity-associated risk factors.

Reductions In Cerebral Saturation Measured By Tr-nirs During Incremental And Interval Exercise In Children

PURPOSE: Time resolved near-infrared spectroscopy (TR-NIRS) can accurately and non-invasively measure cerebral O2 saturation (stO2). While several studies report this measurement during incremental exercise, little is known about responses to interval-type exercise, which more closely represent real-life exercise engagement. Further, the potential role of cerebral hemodynamics/oxygenation in regulating exercise performance in children is unknown, and stO2 patterns in the pre-frontal cortex (PFC) at high intensities may reflect early perception/onset of fatigue. Here, we compared the measured reductions in stO2 during incremental exercise with oscillations in stO2 during interval exercise in children. METHODS: 9 children (6 F) completed 2 cycle ergometry tests: 1. A maximal test to exhaustion, with pedaling resistance increased continuously over 10-12 min (ramp test); 2. A series of 10 2-minute bouts at ∼ 80% of peak VO2, punctuated by 1-minute rests (10x2). For all testing, a TR-NIRS probe (TRS-20, Hamamatsu) was placed on the forehead to record continuously PFC stO2. For ramp tests, the drop in stO2 was calculated between maximum value (2-5 min after start), and stO2 value at 80% peak VO2, as well as the difference between maximum and lowest stO2, typically recorded at peak VO2. In 10x2 tests, the magnitude of stO2 oscillations (max to min) for each bout was calculated, and values compared. RESULTS: On average, during ramp tests at 80% of peak stO2 dropped by 3.3 ± 1.2 % points below the maximum value, and at peak exertion by 7.4 ± 1.7 % points. During interval exercise, the lowest drop was measured during the 3rd bout (3.3 ± 1.0 % points), then gradually increased and stabilized during the last 4 bouts, when it ranged from 4.5±.8 to 4.8±1.0 % points. The average maximum individual drop was 5.6 ± .8 %. CONCLUSIONS: Both ramp and 10x2 exercise are associated with drops in PFC stO2, reflecting changes in cerebral oxygenation. During ramp exercise the magnitude of the stO2 drop appears proportional to work intensity. During interval exercise, the stO2 drop is initially similar to that observed at comparable work rates during the ramp test, and then gradually increases without however reaching the maximal drop recorded at peak exertion. These finding may have implications in determining the cognitive component of exercise participation/performance in different subject groups. Support: NIH Grants NICHD P01HD048721 & UL1 TR000153

Exercise And Repeated Testing Improves The Accuracy Of Laser Doppler Assessment Of Endothelial Function

Assessment of post-occlusive reactive hyperemia (PORH) via Laser Doppler flowmetry allows to estimate endothelial function; while broadly used due to low cost and noninvasiveness, this technique is prone to issues of low accuracy and inter-measurement variability To determine if PORH accuracy could be enhanced by performing tests in the dilated post-exercise state, or by averaging results of two consecutive resting tests. METHODS:6 healthy subjects (23±1yrs, 4F) underwent 78 PORH tests; following a 1-min blood flow occlusion induced via a BP cuff inflated at 150mmHG, arteriolar compensatory dilation was recorded with a laser Doppler probe (Perimed, Sweden) placed at the base of the middle finger. Measurements were performed at rest and following a 10 min ramped cycling exercise test to exhaustion (repeat visits were >48h apart), and included: time to peak perfusion (Pkt), peak perfusion, velocity to peak perfusion, and ratio of max perfusion/pre-occlusive perfusion (Max/Pre). Results from each test were compared to each participant’s average of all pre- and post exercise measurements. RESULTS: Pkt and Max/Pre were the most stable variables; yet on average any given resting measurement was off, as compared to each participant’s mean of all measurements, by 26±3% (Pkt), and by 27±4% (Max/Pre); the discrepancy decreased significantly post-exercise (Pkt 18±3%, p<.05; Max/Pre 14±2%, p<.02), by averaging results from two resting studies (Pkt 19±3%, p<.001; Max/Pre 18±3%, p<.02), or from two post-exercise studies (Pkt 12±2%, p<.001; Max/Pre 9±2%, p<.001). CONCLUSIONS: PORH was confirmed as a valuable tool to assess endothelial function; two relatively simple interventions, post-exercise testing or averaging results from two studies, significantly increased measurement accuracy. Support: NIH Grants NICHD P01HD048721 & UL1 TR000153

The Effect of Dietary Nitrate on the Physiological Responses to 3-Weeks Sprint Interval Training.

Dietary nitrate (NIT) supplementation has been shown to increase nitric oxide (NO) metabolites and enhance exercise performance. Sprint interval training (SIT) has been shown to improve aerobic fitness following 2-4 weeks of training. Considering NIT has been shown to enhance intermittent high intensity exercise the addition of NIT prior to SIT may enhance the physiological changes in aerobic fitness. PURPOSE: To investigate whether dietary nitrate ingested prior to SIT can enhance the physiological adaptations to SIT. METHODS: 27 participants completed an initial incremental ramp exercise test to exhaustion (IXT) for determination of VO2max, HRmax and WRmax. Participants were subsequently randomly assigned to a control group (CONT; n=8), SIT + placebo (PLA) group (n=10) or a SIT + NIT group (n=9) and were matched based on VO2max. Participants in each of the SIT groups then underwent 3-weeks of SIT consisting of 4-6 repeated 15 s all out sprints on a cycle ergometer, interspersed with 4 min active recovery. Participants consumed either a NIT or PLA dose 2.5 h prior to each training session. The dose consisted of 2 x 60 ml nitrate gels (∼8.1 mmol nitrate) or NIT-depleted PLA. In the control group participants were asked to maintain their normal lifestyle throughout the 3 week training period. Upon completion of the SIT protocol or CONT condition all participants repeated the initial IXT 48 h following the final training session. Differences between groups, time points and their interaction were established by mixed methods repeated measures ANOVA. RESULTS: There were no differences in VO2max prior to training (CONT: 44.8 ± 8.1, SIT + PLA: 40.6 ± 7.3, SIT + NIT: 42.3 ± 6.6 ml•kg•min-1, P=0.494) but VO2max improved pre - post training (P=0.019). Post-hoc analysis revealed changes in VO2max occurred in the SIT + NIT group (45.1 ± 9.3 ml•kg•min-1, 6.7 %, P=0.026) but not the SIT + PLA (42.5 ± 5 ml•kg•min-1, 4.7 %, P=0.097) or CONT groups (45.2 ± 7.8 ml•kg•min-1, 1 %, P=0.738). WRmax improved from pre - post training in both SIT groups (PLA: 274 ± 42 - 287 ± 42 W, P=0.006, NIT: 286 ± 47 - 314 ± 55 W, P<0.001) however no changes were seen in the CONT group (291 ± 60 - 287 ± 63 W, P=0.352). CONCLUSIONS: Results from the current study suggest that NIT may enhance the aerobic adaptations to SIT however the mechanism underpinning this response is currently unknown.

Alterations in endothelial function and fractional O2 extraction in long‐term cancer survivors treated with chemotherapy and radiation

Chemotherapy and radiation cancer therapeutics increase arterial stiffness and decrease aerobic exercise capacity. During exercise, the profile of microvascular fractional O2 extraction measured via near‐infrared spectroscopy (NIRS) derived muscle deoxygenation (Δdeoxy‐[Hb+Mb]) provides information on the dynamic matching of O2 delivery‐to‐O2 utilization. We tested the hypothesis that cancer survivors would have an altered profile of Δdeoxy‐[Hb+Mb] during exercise that would be related to decreases in endothelial function. To date, 2 cancer survivors (CS) and 1 healthy control (HC) completed a brachial artery flow‐mediated dilation test (FMD) and ramp exercise test on a cycle ergometer. During exercise Δdeoxy‐[Hb+Mb] of the vastus lateralis and rectus femoris was measured, normalized from baseline (0%) to the gas exchange threshold (GET) (100%). The power output at GET (POGET) was lower in CS compared to HC. CS had a smaller shear rate normalized FMD compared to HC (1.07 × 10‐5 vs. 3.54 × 10‐5 %Δ/s‐1 s, respectively). Both groups displayed a linear increase in %Δdeoxy‐[Hb+Mb]. The %Δdeoxy‐[Hb+Mb] slope of the vastus lateralis was greater in CS compared to HC when plotted as a function of POGET (2.04 vs. 0.80 % W‐1, respectively) and %POGET (1.84 vs. 1.17 % %W‐1, respectively). A greater %Δdeoxy‐[Hb+Mb] slope of the rectus femoris was also observed in CS compared to HC (1.29 vs. 0.74 % W‐1 and 1.17 vs. 1.09 % %W‐1, respectively). In conclusion, the greater reliance on fractional O2 extraction in CS during exercise suggests an impaired matching of O2 delivery‐to‐O2 utilization relationship during exercise compared to HC, which may be the result of decreased endothelial function.

Impaired aerobic function in patients with cystic fibrosis during ramp exercise.

This study aimed to document the matching of muscle O2 delivery to O2 use in young patients with cystic fibrosis (CF) from muscle deoxygenation (HHb) dynamics during ramp exercise. Ten patients with stable, mild-to-moderate CF (12.7 ± 2.8 yr) and 10 healthy controls (CON, 12.8 ± 2.8 yr) completed a combined ramp and supramaximal cycling test to determine maximal O2 uptake (V˙O2max). Changes in gas exchange and ventilation, HR, and m. vastus lateralis HHb (near-infrared spectroscopy) were assessed. Δ[HHb]-work rate and Δ[HHb]-V˙O2 profiles were normalized and fit using a sigmoid function. Aerobic function was impaired in CF, indicated by very likely reduced fat-free mass-normalized V˙O2max (mean difference, ±90% confidence interval: -7.9 mL·kg·min, ±6.1), very likely lower V˙O2 gain (-1.44 mL·min·W, ±1.12), and a likely slower V˙O2 mean response time (11 s, ±13). An unclear effect was found upon the absolute and relative work rate (-14 W, ±44, and -0.7% peak power output, ±12.0, respectively) and the absolute and percentage (-0.10 L·min, ±0.43, and 3.3% V˙O2max, ±6.0) V˙O2 corresponding to 50% Δ[HHb] amplitude, respectively, between groups. However, arterial oxygen saturation (SpO2) was very likely lower in CF (-1%, ±1) and demonstrated moderate-to-very large relations with parameters of aerobic function. Young patients with mild-to-moderate CF present with impaired aerobic function during ramp incremental cycling exercise. Because the rate of fractional O2 extraction during ramp cycling exercise was not altered by CF, yet SpO2 was lower, the present findings support the notion of centrally mediated oxygen delivery to principally limit the aerobic function of pediatric patients with CF during ramp incremental cycling exercise.

A systematic review of diastolic stress tests in heart failure with preserved ejection fraction, with proposals from the EU-FP7 MEDIA study group.

Cardiac function should be assessed during stress in patients with suspected heart failure with preserved ejection fraction (HFPEF), but it is unclear how to define impaired diastolic reserve. We conducted a systematic review to identify which pathophysiological changes serve as appropriate targets for diagnostic imaging. We identified 38 studies of 1111 patients with HFPEF (mean age 65 years), 744 control patients without HFPEF, and 458 healthy subjects. Qualifying EF was >45-55%; diastolic dysfunction at rest was a required criterion in 45% of studies. The initial workload during bicycle exercise (25 studies) varied from 12.5 to 30 W (mean 23.1 ± 4.6), with increments of 10-25 W (mean 19.9 ± 6) and stage duration 1-5 min (mean 2.5 ± 1); targets were submaximal (n = 8) or maximal (n = 17). Other protocols used treadmill exercise, handgrip, dobutamine, lower body negative pressure, nitroprusside, fluid challenge, leg raising, or atrial pacing. Reproducibility of echocardiographic variables during stress and validation against independent reference criteria were assessed in few studies. Change in E/e' was the most frequent measurement, but there is insufficient evidence to establish this or other tests for routine use when evaluating patients with HFPEF. To meet the clinical requirements of performing stress testing in elderly subjects, we propose a ramped exercise protocol on a semi-supine bicycle, starting at 15 W, with increments of 5 W/min to a submaximal target (heart rate 100-110 b.p.m., or symptoms). Measurements during submaximal and recovery stages should include changes from baseline in LV long-axis function and indirect echocardiographic indices of LV diastolic pressure.

Increased cardiac output elicits higher V̇O2max in response to self-paced exercise.

Recently, a self-paced protocol demonstrated higher maximal oxygen uptake versus the traditional ramp protocol. The primary aim of the current study was to further explore potential differences in maximal oxygen uptake between the ramp and self-paced protocols using simultaneous measurement of cardiac output. Active men and women of various fitness levels (N = 30, mean age = 26.0 ± 5.0 years) completed 3 graded exercise tests separated by a minimum of 48 h. Participants initially completed progressive ramp exercise to exhaustion to determine maximal oxygen uptake followed by a verification test to confirm maximal oxygen uptake attainment. Over the next 2 sessions, they performed a self-paced and an additional ramp protocol. During exercise, gas exchange data were obtained using indirect calorimetry, and thoracic impedance was utilized to estimate hemodynamic function (stroke volume and cardiac output). One-way ANOVA with repeated measures was used to determine differences in maximal oxygen uptake and cardiac output between ramp and self-paced testing. Results demonstrated lower (p < 0.001) maximal oxygen uptake via the ramp (47.2 ± 10.2 mL·kg(-1)·min(-1)) versus the self-paced (50.2 ± 9.6 mL·kg(-1)·min(-1)) protocol, with no interaction (p = 0.06) seen for fitness level. Maximal heart rate and cardiac output (p = 0.02) were higher in the self-paced protocol versus ramp exercise. In conclusion, data show that the traditional ramp protocol may underestimate maximal oxygen uptake compared with a newly developed self-paced protocol, with a greater cardiac output potentially responsible for this outcome.

Aerobic fitness influences cerebral oxygenation response to maximal exercise in healthy subjects

The study examined whether the aerobic fitness level modifies the cerebral oxygenation response to incremental ramp exercise, and more specifically the decline in cerebral oxygenation from heavy exercise up to maximal intensities. 11 untrained (V˙O2max 47.3±4.0mLmin−1kg−1) and 13 endurance-trained (V˙O2max 61.2±8.0mLmin−1kg−1) healthy men performed a maximal ramp cycle exercise. Left prefrontal cortex oxygenation (ΔHbO2) was monitored by near-infrared spectroscopy. A cerebral oxygenation threshold decline (ThCOx) during exercise was determined. ThCox occurred in all subjects but for higher V˙O2 (mLmin−1kg−1) in endurance-trained than in untrained subjects (P<0.01). At submaximal exercise intensity corresponding to ThCOx, ΔHbO2 was higher in endurance-trained than in untrained subjects (P<0.05). V˙O2 at ThCox was related to V˙O2 at respiratory compensation point (n=24, r=0.93, P<0.001) and to V˙O2max (n=24, r=0.92, P<0.001). These findings indicate that above the respiratory compensation point the prefrontal O2 demand exceeds the supply in untrained and in endurance-trained subjects. In addition, the occurrence of ThCOx was delayed to higher absolute exercise intensities in endurance-trained in relation with their higher V˙O2max than untrained men. These results demonstrated that aerobic fitness influences cerebral oxygenation during exercise.

The impact of pedal rate on muscle oxygenation, muscle activation and whole-body VO₂ during ramp exercise in healthy subjects.

The aim of this project was to study the impact of pedal rate on breakpoints in muscle oxygenation (deoxy[Hb + Mb] and total[Hb + Mb]) and activation (iEMG and MPF) at high intensities during ramp exercise. Twelve physically active students performed incremental ramp exercises at 60 rpm, starting either at 50 or 80 W (i.e., 60rpm50 and 60rpm80), and at 100 rpm, starting at 50 W (100rpm50). Pulmonary VO2, muscle activation (iEMG and MPF) and oxygenation were recorded with EMG and NIRS, respectively. IEMG, MPF, deoxy[Hb + Mb] and total[Hb + Mb] were expressed as functions of work rate (WR) and pulmonary VO2 (%VO2peak) and analyzed with double-linear models. The breakpoints (BP) of iEMG, MPF, total[Hb + Mb] and deoxy[Hb + Mb] in %VO2peak did not differ among the pedal rate conditions (P > 0.05), whereas the BPs in WR were significantly lower in 100rpm50 compared to 60rpm50 and 60rpm80 (P < 0.01). Across the pedal rate conditions the BP (in %VO2peak) of total[Hb + Mb] (82.7 ± 1.5 %VO2peak) was significantly lower (P < 0.01) compared to the BP in iEMG (84.3 ± 1.7 %VO2peak) and MPF (84.2 ± 1.6 %VO2peak), whereas the BP in deoxy[Hb + Mb] (87.4 ± 1.4 %VO2peak) and respiratory compensation point (89.9 ± 1.8 %VO2peak) were significantly higher (P < 0.01) compared to the BP in total[Hb + Mb], iEMG and MPF. Additionally, the BPs in iEMG, MPF, total[Hb + Mb] and deoxy[Hb + Mb], and the RCP were highly correlated (r > 0.90; P < 0.001). The present study showed that muscle activation and oxygenation at high intensities during incremental exercise are related to pulmonary VO2 rather than external WR, with a close interrelationship between that muscle activation, oxygenation and pulmonary VO2.