Increasing Work Rate Research Articles

Hyperoxia enhances self-paced exercise performance to a greater extent in cool than hot conditions.

What is the central question of this study? Hyperoxia enhances endurance performance by increasing O2 availability to locomotor muscles. We investigated whether hyperoxia can also improve prolonged self-paced exercise in conditions of elevated thermal and cardiovascular strain. What is the main finding and its importance? Hyperoxia improved self-paced exercise performance in hot and cool conditions. However, the extent of the improvement (increased work rate relative to normoxia) was greater in cool conditions. This suggests that the development of thermal and cardiovascular strain during prolonged self-paced exercise under heat stress might attenuate the hyperoxia-mediated increase in O2 delivery to locomotor muscles. The aim of this study was to determine whether breathing hyperoxic gas when self-paced exercise performance is impaired under heat stress enhances power output. Nine well-trained male cyclists performed four 40min cycling time trials: two at 18°C (COOL) and two at 35°C (HOT). For the first 30min, participants breathed ambient air, and for the remaining 10min normoxic (fraction of inspired O2 0.21; NOR) or hyperoxic (fraction of inspired O2 0.45; HYPER) air. During the first 30min of the time trials, power output was lower in the HOT (∼250W) compared with COOL (∼273W) conditions (P<0.05). In the final 10min, power output was higher in HOT-HYPER (264±25W) than in HOT-NOR (244±31W; P=0.008) and in COOL-HYPER (315±28W) than in COOL-NOR (284±25W; P<0.001). The increase in absolute power output in COOL-HYPER was greater than in HOT-HYPER (∼12W; P=0.057), as was normalized power output (∼30%; P<0.001). The peripheral capillary percentage oxygen saturation increased in HOT-HYPER and COOL-HYPER (P<0.05), with COOL-HYPER being higher than HOT-HYPER (P<0.01). Heart rate was higher during the HOT compared with COOL trials (P<0.01), as were mean skin temperature (P<0.001) and peak rectal temperature (HOT, ∼39.5°C and COOL, ∼38.9°C; P<0.01). Thermal discomfort was also higher in the HOT compared with COOL (P<0.01), whereas ratings of perceived exertion were similar (P>0.05). Hyperoxia enhanced performance during the final 25% of a 40min time trial in both HOT and COOL conditions compared with normoxia. However, the attenuated increase in absolute and normalized power output noted in the HOT condition suggests that heat stress might mitigate the influence of hyperoxia.

CAN CARDIOPULMONARY EXERCISE TESTING COMBINED WITH STRESS ECHOCARDIOGRAPHY HELP TO IDENTIFY HEART FAILURE WITH PRESERVED EJECTION FRACTION IN OBESE HYPERTENSIVES?

Objective: Background:AH and obesity are the most common pathologies that with long-term course lead to HFpEF. Although exercise intolerance and dyspnea are main symptoms of HF, they may also be caused by obesity. Recent data demonstrated that combination of cardiopulmonary exercise testing (CPX) and stress echocardiography may help to identify HFpEF at earlier time point in patients with associated diseases. Objective: to assess ability of CPX combined with diastolic stress testing to identify HFpEF in patients with AH and obesity. Design and method: We investigated 56 patients with AH and obesity aged 35–60, 22 (40%) of them also had signs of HFpEF. All patients underwent CPX in combination with diastolic stress testing. We used stepwise protocol for cycle ergometer with 8 exercise periods at progressively increasing work rate (25 watts every step). Stress echocardiography was performed at 3 levels: the 2-d exercise step (50 watts), anaerobic threshold (AT) and submaximal heart rate (HR). Results: All patients had reduced exercise capacity more severe in group with HFpEF, only 8 (36%) patients with HFpEF versus 19 (56%) without it reached submaximal HR during test. The main cause for end of test in HFpEF patients was dyspnea, in obese hypertensives without HFpEF – exertion. Peak VO2 was decreased in both groups (55–65% of predicted). This parameter was significantly higher (80–85% of predicted) in patients with obesity and normal heart function compared with HFpEF patients when predicted for height. O2 pulse at AT was slightly lower in patients with obesity and HFpEF (65% versus 78% of predicted). Ve/VCO2 slope at AT was slightly increased in both groups with significant growth in HFpEF patients (30,9 versus 33,1). Peak E/e[Combining Acute Accent] average ratio measured at AT was increased (14,7 versus 9,4) due to decrease of peak e[Combining Acute Accent] velocity (6,0 versus 11,1) in HFpEF patients. Conclusions: Both obesity and HFpEF reduce aerobic capacity and cause dyspnea. Combination of CPX and stress echocardiography helps to identify influence of HFpEF on exercise tolerance of patients with AH and obesity. Peak VO2 predicted for height (not weight), Ve/VCO2 slope measured at AT can be useful parameters.

Physiological and Perceptual Responses to Step-Wise and Ramp Graded Exercise Tests in Children

Step-wise graded exercise tests are common protocols to measure aerobic fitness in children but have limitations due to the nature of the increments. Modifying these tests to a ramp protocol could overcome some of these limitations. PURPOSE: To examine physiological and perceptual responses to step-wise and ramped graded exercise tests in children (n = 8; age = 13.3 ± 2.2 yrs.). METHODS: The standardized James protocol (STEP) and a modified-ramp James protocol (RAMP) were performed on a cycle ergometer on separate days. Protocol order was counterbalanced. STEP commenced with three 3-min stages, followed by 1-min stages. Work rate increases were based on body surface area. For RAMP, work rate was ramped to match the 3-min and 1-min stages of STEP. Work rate was increased until volitional exhaustion for both tests. Oxygen consumption (VO2), heart rate (HR), respiratory exchange ratio (RER) and OMNI ratings of perceived exertion for chest (RPE-chest), legs (RPE-legs) and overall (RPE-overall) were recorded at the end of each 3-minute stage and peak exercise. Physiological and perceptual responses between tests were compared using two-way repeated-measure ANOVAs and test time (TT) and peak power (PP) were compared using repeated measure t-tests. Significance was established at p<0.05. RESULTS: The physiological and RPE responses were similar between tests at the end of each 3-min submaximal stage (p>0.05). At peak exercise, absolute and relative VO2 for STEP were 2.17 ± 0.67 L∙min-1 and 42.5± 5.9 ml∙kg-1 ∙min-1. For RAMP, absolute and relative VO2peak were 2.33± 0.89 L∙min-1 and 45.3 ± 8.9 ml∙kg-1 ∙min-1. The differences were not significant. There were no differences between STEP and RAMP for peak HR (196.3 ± 9.8 bpm vs. 196.1 ± 9.7 bpm) and peak RER (1.24 ± 0.11 vs. 1.21 ± 0.06). At peak exercise, RPE-chest, RPE-leg and RPE-overall were similar between STEP (4.8 ± 4.0, 8.4 ± 2.1 and 7.6 ± 3.0, respectively) and RAMP (5.6 ± 3.4, 8.5± 2.3 and 8.0± 1.8, respectively) (p>0.05). TT and PP for STEP were 11.3± 2.5 min and 196.8 ± 70.7 W and 12.4 ± 2.4 min and 210.3 ± 65.5 W for RAMP (p=0.11 and p=0.12, respectively) CONCLUSION: Although limitations in step-wise protocols exist, submaximal and peak physiological and perceptual responses were similar to a ramp protocol. Both protocols may be appropriate in children to measure aerobic fitness.

Heat dissipation rate constrains reproductive investment in a wild bird

Abstract The “heat dissipation limit” theory (HDL) posits that animals with higher capacity to dissipate metabolic heat can increase reproductive investment. This theory remains untested in the wild. We recently showed that increased workload in a small bird causally relates to maximum body temperature. Here, we have expanded this approach by experimentally facilitating sensible heat transfer rate in nestling‐feeding blue tits—a small bird with high resting‐ and work‐induced body temperatures—through removal of ventral plumage. Feather‐clipped parents did not increase work rate but sired larger, and sometimes heavier, nestlings while maintaining lower body temperature and losing less body mass than controls. Thus, when relieved of the demands to dissipate metabolic heat, parents could invest more into both current (nestling condition) and future (self‐maintenance) reproduction. In accordance with the HDL theory, we conclude that constraints on heat dissipation rate could be a potent mediator of life‐history trade‐offs in wild animals. A plain language summary is available for this article.

Increased Perceived Effort during Low-Intensity Exercise Linked to Type 2 Diabetes

Exercise is a cornerstone of type 2 diabetes (T2D) treatment, but most people with T2D are sedentary. We identified a novel behavioral barrier to exercise in women with T2D compared to nondiabetic women — greater effort during low intensity exercise. We hypothesized that the presence of T2D would confer greater effort for adults across a range of exercise intensities, even when controlling for fitness. As T2D decreases fitness more in women than men, we also hypothesized sex would modify this association. We analyzed secondary data from past sedentary, overweight research participants with and without T2D who were free of cardiopulmonary comorbidities. During graded exercise tests to assess fitness (VO2peak), we repeatedly measured objective effort (heart rate (HR)) and subjective effort (Borg Rating of Perceived Exertion (RPE)). We plotted the rise of RPE and HR, respectively, against increases in relative work rate (%VO2peak: VO2 at work rate divided by VO2peak) at lower intensities below anaerobic threshold (AT) and higher intensities above AT. Adults with T2D (n=57) had similar age and adiposity as those without T2D (n=55), but had lower VO2peak: 20.7± 4.5 vs. 24.5 ± 6.6 ml/kg/min (p&amp;lt;0.05). Below AT, people with T2D had a steeper rise in RPE for each unit increase in %VO2peak than those without T2D (p=0.0029), and this finding was more pronounced in men than women (p=0.004). T2D status did not influence the association of %VO2peak and RPE above AT, or the association of HR and %VO2peak either below or above AT. People with T2D have significantly greater RPE during lower intensity exercise below AT as compared to people without T2D. This finding was not explained by fitness differences and, counter to our hypothesis, was more significant in men. We found no group differences in RPE at higher intensity exercise where physiological inputs tend to dominate behavioral predictors of effort. Future work should further characterize sex-specific mechanisms of exercise effort for people with T2D. Disclosure A.G. Huebschmann: Research Support; Self; Merck &amp; Co., Inc.. M. Wahl: None. R.L. Scalzo: None. D. Rafferty: None. J.G. Regensteiner: None.

Second-order modeling for the pulmonary oxygen uptake on-kinetics: a comprehensive solution for overshooting and nonovershooting responses to exercise.

The human oxygen uptake (V̇o2) response to step-like increases in work rate is currently modeled by a First Order System Multi-Exponential (FOME) arrangement. Because of their first-order nature, none of FOME model's exponentials is able to model an overshoot in the oxygen uptake kinetics (OV̇o2K). Nevertheless, OV̇o2K phenomena are observed in the fundamental component of trained individuals' step responses. We hypothesized that a Mixed Multi-Exponential (MiME) model, where the fundamental component is modeled with a second- instead of a first-order system, would present a better overall performance than that of the traditional FOME model in fitting V̇o2 on-kinetics at all work rates, either presenting or not OV̇o2K. Fourteen well-trained male cyclists performed three step on-transitions at each of three work rates below their individual lactate thresholds' work rate (WRLT), and two step on-transitions at each of two exercise intensities above WRLT. Averaged responses for each work rate were fitted with MiME and FOME models. Root mean standard errors were used for comparisons between fitting performances. Additionally, a methodology for detecting and quantifying OV̇o2K phenomena is proposed. Second order solutions performed better (P < 0.000) than the first-order exponential when the OV̇o2K was present, and did not differ statistically (P = 0.973) in its absence. OV̇o2K occurrences were observed below and, for the first time, above WRLT (88 and 7%, respectively). We concluded that the MiME model is more adequate and comprehensive than the FOME model in explaining V̇o2 step on-transient responses, considering cases with or without OV̇o2K altogether.NEW & NOTEWORTHY To our knowledge, this is the first study applying second-order system equations to model V̇o2 on-kinetics, which is useful for both mathematical representation and physiological understanding of the overshoot phenomenon manifesting in the fundamental components of some step responses. Moreover, an objective methodology for detecting and quantifying this overshoot that considers data from the whole response is proposed. Finally, this is the first work detecting overshoot occurrences outside the moderate domain of exercise.

Potential Utility of a Loaded Treadmill Protocol for Tactical Athletes.

Swearingen, JT, Weiss, LW, Smith, WA, Stephenson, MD, and Schilling, BK. Potential utility of a loaded treadmill protocol for tactical athletes. J Strength Cond Res 32(3): 610-616, 2018-Aerobic capacity is an important variable for tactical athletes, with V[Combining Dot Above]O2max being the most direct way of estimating it in a laboratory setting. A mode-specific protocol involving fixed-weight, torso-borne loads was assessed in the current study. On 4 separate days, 15 men (age 22.1 ± 2.7 years, mass 85.1 ± 10.6 kg, height 179.0 ± 7.7 cm) performed a weighted treadmill walking protocol (2 trials) and a nonweighted treadmill running protocol (2 trials). Both the weighted and nonweighted protocols were reliable, with intraclass correlation coefficient values of 0.79 and 0.87, respectively. V[Combining Dot Above]O2peak values from both protocols were highly correlated (r = 0.90, p < 0.01). However, V[Combining Dot Above]O2peak was higher during the nonweighted protocol (t = 7.547, d = 2.47, p < 0.01). Work rate was calculated for both the last completed stage and stage during which participants reached fatigue. Work rates for both protocols on the last completed stage were similar (t = 1.44, d = 0.83, p = 0.17), although the work rate for the final attempted stage was greater for the weighted-walking protocol (t = 5.85, d = 3.60, p < 0.01). These data suggest a weighted-walking V[Combining Dot Above]O2peak that is highly associated with a running V[Combining Dot Above]O2peak. This test may be applied to those who routinely perform torso-borne load carriage, such as tactical athletes. Future weighted-walking protocols should seek achieve higher resolution, especially near the end stage of the test where subjects reach volitional fatigue. Large increases in work rate may not be feasible at the end stages of the test.

A Simplified Approach to Select Exercise Endurance Intensity for Interventional Studies in COPD

ABSTRACTTime to exercise limitation (Tlim) in response to constant work rate (CWR) is sensitive to interventions in chronic obstructive pulmonary disease (COPD). This is particularly true when the pre-intervention test lasts between 3 and 8 min (Tlim3′–8′). There is, however, no simple method to select a work rate which is consistently associated with Tlim3′–8′ across the spectrum of COPD severity.We assessed 59 GOLD stages II–IV patients who initially cycled to Tlim at 75% peak. In case of short (<3 min, low-endurance) or long (>8 min, high-endurance) tests, patients exercised after 60 min at 50% or 90%, respectively (CWR50%⇐75%⇒90%).Critical mechanical constraints and limiting dyspnea at 75% were reached within the desired timeframe in 27 “mid-endurance” patients (46%). Increasing work rate intensity to 90% hastened the mechanical-ventilatory responses leading to Tlim3′–8′ in 23/26 (88%) “high-endurance” patients; conversely, decreasing exercise intensity to 50% slowed those responses leading to Tlim3′–8′ in 5/6 (83%) “high-endurance” patients. Repeating the tests at higher (60%) or lower (80%) intensities fail to consistently produce Tlim3′–8′ in “low-” and “high-endurance”, respectively (p > 0.05). Compared to a fixed work rate at 75%, CWR50%⇐75%⇒90% significantly decreased Tlim's coefficient of variation; consequently, the required N to detect 100 s or 33% improvement in Tlim decreased from 82 to 26 and 41 to 14, respectively.This simplified approach to individualized work rate adjustment (CWR50%⇐75%⇒90%) might allow greater sensitivity in evaluating interventional efficacy in improving respiratory mechanics and exercise tolerance while simultaneously reducing sample size requirements in patients with COPD.

Cardio respiratory response: Validation of new modifications of Bruce protocol for exercise testing and training in elite Saudi triathlon and soccer players.

The Bruce protocol is the traditional method used to assess maximal fitness level, although it may have limitations, such as its short duration and large work rate increases, with very high levels of exertion that consist of speed/incline combinations. Modifications have been added to elicit similar maximal fitness achievements. The authors of this experimental trial have proposed a new treadmill protocol that allows optimal test duration in conjunction with peak oxygen consumption ‘VO2max’, and with appropriate patient comfort and safety during both exercise testing and training.SubjectsTwenty-two elite Saudi players, comprising eleven Saudi triathlon athletes, and eleven Saudi elite soccer players, BMI, body fat mass percentage, body fat free mass percentage. cardiovascular parameter; including, absolute and relative “VO2max” as well as maximal heart rate “HR max”, were assessed during a graded treadmill running modified protocol, using a Quark Cardio Pulmonary Exercise Testing Unit (CPET).ResultsDescriptive statistics were used to obtain the anthropometric characteristics, including comparisons between the means, independent sample T-test and a regression analysis, to test the association of the protocol duration and the corresponding, dependent variables.Conclusions, clinical relevanceIt is often difficult to achieve a high cardiorespiratory response, VO2max, without an association to high values of HR max, and peak perceived exertion. This may lead to cardiovascular risk. Our new modifications can provide a practical, valid alternative protocol to be used comfortably both during exercise testing and training, rather than performance testing only, to achieve high VO2max with minimal cardiovascular stress.

An integrated view on the oxygenation responses to incremental exercise at the brain, the locomotor and respiratory muscles.

In the past two decades oxygenation responses to incremental ramp exercise, measured non-invasively by means of near-infrared spectroscopy at different locations in the body, have advanced the insights on the underpinning mechanisms of the whole-body pulmonary oxygen uptake ([Formula: see text]) response. In healthy subjects the complex oxygenation responses at the level of locomotor and respiratory muscles, and brain were simplified and quantified by the detection of breakpoints as a deviation in the ongoing response pattern as work rate increases. These breakpoints were located in a narrow intensity range between 75 and 90% of the maximal [Formula: see text] and were closely related to traditionally determined thresholds in pulmonary gas exchange (respiratory compensation point), blood lactate measurements (maximal lactate steady state), and critical power. Therefore, it has been assumed that these breakpoints in the oxygenation patterns at different sites in the body might be equivalent and could, therefore, be used interchangeably. In the present review the typical oxygenation responses (at locomotor and respiratory muscle level, and cerebral level) are described and a possible framework is provided showing the physiological events that might link the breakpoints at different body sites with the thresholds determined from pulmonary gas exchange and blood lactate measurements. However, despite a possible physiological association, several arguments prevent the current practical application of these breakpoints measured at a single site as markers of exercise intensity making it highly questionable whether measurements of the oxygenation response at one single site can be used as a reflection of whole-body responses to different exercise intensities.

Supplemental Oxygen During High-Intensity Exercise Training in Nonhypoxemic Chronic Obstructive Pulmonary Disease

BackgroundPhysical exercise training is an evidence-based treatment in chronic obstructive pulmonary disease, and patients' peak work rate is associated with reduced chronic obstructive pulmonary disease mortality. We assessed whether supplemental oxygen during exercise training in nonhypoxemic patients with chronic obstructive pulmonary disease might lead to superior training outcomes, including improved peak work rate. MethodsThis was a randomized, double-blind, controlled, crossover trial. Twenty-nine patients with chronic obstructive pulmonary disease (aged 63.5 ± 5.9 years; forced expiratory volume in 1 second percent predicted, 46.4 ± 8.6) completed 2 consecutive 6-week periods of endurance and strength training with progressive intensity, which was performed 3 times per week with supplemental oxygen or compressed medical air (flow via nasal cannula: 10 L/min). Each session of electrocardiography-controlled interval cycling lasted 31 minutes and consisted of a warm-up, 7 cycles of 1-minute intervals at 70% to 80% of peak work rate alternating with 2 minutes of active recovery, and final cooldown. Thereafter, patients completed 8 strength-training exercises of 1 set each with 8 to 15 repetitions to failure. Change in peak work rate was the primary study end point. ResultsThe increase in peak work rate was more than twice as high when patients exercised with supplemental oxygen compared with medical air (0.16 ± 0.02 W/kg vs 0.07 ± 0.02 W/kg; P < .001), which was consistent with all other secondary study end points related to exercise capacity. The impact of oxygen on peak work rate was 39.1% of the overall training effect, whereas it had no influence on strength gain (P > .1 for all exercises). ConclusionsWe report that supplemental oxygen in nonhypoxemic chronic obstructive pulmonary disease doubled the effect of endurance training but had no effect on strength gain.

Regional Differences in Muscle Energy Metabolism in Human Muscle by 31P-Chemical Shift Imaging.

Previous studies have reported significant region-dependent differences in the fiber-type composition of human skeletal muscle. It is therefore hypothesized that there is a difference between the deep and superficial parts of muscle energy metabolism during exercise. We hypothesized that the inorganic phosphate (Pi)/phosphocreatine (PCr) ratio of the superficial parts would be higher, compared with the deep parts, as the work rate increases, because the muscle fiber-type composition of the fast-type may be greater in the superficial parts compared with the deep parts. This study used two-dimensional 31Phosphorus Chemical Shift Imaging (31P-CSI) to detect differences between the deep and superficial parts of the human leg muscles during dynamic knee extension exercise. Six healthy men participated in this study (age 27±1 year, height 169.4±4.1 cm, weight 65.9±8.4 kg). The experiments were carried out with a 1.5-T superconducting magnet with a 5-in. diameter circular surface coil. The subjects performed dynamic one-legged knee extension exercise in the prone position, with the transmit-receive coil placed under the right quadriceps muscles in the magnet. The subjects pulled down an elastic rubber band attached to the ankle at a frequency of 0.25, 0.5 and 1 Hz for 320 s each. The intracellular pH (pHi) was calculated from the median chemical shift of the Pi peak relative to PCr. No significant difference in Pi/PCr was observed between the deep and the superficial parts of the quadriceps muscles at rest. The Pi/PCr of the superficial parts was not significantly increased with increasing work rate. Compared with the superficial areas, the Pi/PCr of the deep parts was significantly higher (p<0.05) at 1 Hz. The pHi showed no significant difference between the two parts. These results suggest that muscle oxidative metabolism is different between deep and superficial parts of quadriceps muscles during dynamic exercise.

Scale dependence of rock friction at high work rate.

Determination of the frictional properties of rocks is crucial for an understanding of earthquake mechanics, because most earthquakes are caused by frictional sliding along faults. Prior studies using rotary shear apparatus revealed a marked decrease in frictional strength, which can cause a large stress drop and strong shaking, with increasing slip rate and increasing work rate. (The mechanical work rate per unit area equals the product of the shear stress and the slip rate.) However, those important findings were obtained in experiments using rock specimens with dimensions of only several centimetres, which are much smaller than the dimensions of a natural fault (of the order of 1,000 metres). Here we use a large-scale biaxial friction apparatus with metre-sized rock specimens to investigate scale-dependent rock friction. The experiments show that rock friction in metre-sized rock specimens starts to decrease at a work rate that is one order of magnitude smaller than that in centimetre-sized rock specimens. Mechanical, visual and material observations suggest that slip-evolved stress heterogeneity on the fault accounts for the difference. On the basis of these observations, we propose that stress-concentrated areas exist in which frictional slip produces more wear materials (gouge) than in areas outside, resulting in further stress concentrations at these areas. Shear stress on the fault is primarily sustained by stress-concentrated areas that undergo a high work rate, so those areas should weaken rapidly and cause the macroscopic frictional strength to decrease abruptly. To verify this idea, we conducted numerical simulations assuming that local friction follows the frictional properties observed on centimetre-sized rock specimens. The simulations reproduced the macroscopic frictional properties observed on the metre-sized rock specimens. Given that localized stress concentrations commonly occur naturally, our results suggest that a natural fault may lose its strength faster than would be expected from the properties estimated from centimetre-sized rock samples.

CO2 pulse and acid-base status during increasing work rate exercise in health and disease

The CO2 pulse (V˙CO2/heart rate), analogous to the O2 pulse (V˙O2/heart rate), was calculated during cardiopulmonary exercise testing and evaluated in normal and diseased states. Our aim was to define its application in its release in excess of that from V˙CO2/heart rate in the presence of impaired cardiovascular and lung function. In the current study, forty-five patients were divided into six physiological states: normal, exercise-induced myocardial ischemia, chronic heart failure, pulmonary vasculopathy, chronic obstructive pulmonary disease, and interstitial lung disease. We subtracted the O2 pulse from the CO2 pulse to determine the exhaled CO2 that could be attributed to CO2 pulse of buffering of lactic acid. The difference between the CO2 pulse and O2 pulse (V˙CO2/heart rate–V˙O2/heart rate) includes CO2 generated from HCO3− buffering of lactic acid. The accumulated CO2 per body mass was found to be significantly correlated with the corresponding [HCO3−] decrease (R2=0.72; P<0.0001). In summary, the increase in CO2 pulse over the O2 pulse accounted for the anaerobically-generated excess-CO2 in each of the physiological states and correlated with the decreases in the arterial Bicarbonate concentration.

VO2 Kinetics during Different Forms of Cycling Exercise on Land and in Water

Background: It is generally assumed that the physical properties of water improve aerobic me- tabolism by O 2 utilization of the working muscle particular if a great muscle mass is recruited. This study investigated the changes in VO 2 (VO 2 -work rate relationship; ∆ VO 2 / ∆ WR) during increasing work rates in different exercise conditions in water immersed exercise and on land based exercise. Methods: In order to identify possible differences in VO 2 required for a given work rate twelve trained cyclists performed four incremental exercise tests. The tests comprised whole body work and leg work, both in water and on land and were conducted on the same, electromagneti- cally braked whole body ergometer. Results: The ∆ VO 2 / ∆ WR curves were found to be similar in the four exercise conditions reach- ing from 11.9 to 12.4 ml·W -1 during water immersed exercise and 12.6 to 12.7 ml·W -1 dur- ing land based exercise respectively. When coupling arms with leg exercise the ∆ VO 2 / ∆ WR curves shift upwards at similar work rates indicating a higher oxygen demand for an enlarged muscle mass. The extra O 2 cost ( ∆ VO 2 ) for recruited arms was lower in water immersed exercise compared to land based exercise (0.057±0.072 l ·min -1 and 0.367 1±0.057·min -1 , respectively; p=.000). Differences exist in the rate of performing physical work above ventilatory threshold two. Work load values attained on land based exercise surpass that of water immersed exercise (204.2 watts vs. 154.0 watts for whole body work and 227.1 watts vs. 150.0 watts for leg work, respectively). Conclusions: Differences in ∆ VO 2 at a given work rate are to be explained rather from a biome- chanical point of view. More likely ∆ VO 2 in water seems to be influenced by both familiarity of the task and fitness level. Exercise intensity in water need to be selected at lower levels than on land.

Heterogeneity of Muscle Blood Flow and Metabolism: Influence of Exercise, Aging, and Disease States.

The systematic increase in V˙O2 uptake and O2 extraction with increasing work rates conceals a substantial heterogeneity of O2 delivery (Q˙O2)-to- V˙O2 matching across and within muscles and other organs. We hypothesize that whether increased/decreased Q˙O2/V˙O2 heterogeneity can be judged as "good" or "bad," for example, after exercise training or in aged individuals or with disease (heart failure, diabetes) depends on the resultant effects on O2 transport and contractile performance.

Feedback control of oxygen uptake profiles during robotics‐assisted treadmill exercise

Gait rehabilitation robots have potential for cardiovascular rehabilitation of patients with neurological deficits. A novel method was developed to guide exercise intensity by feedback control of oxygen uptake rate with a focus on tracking ramps as typically applied in maximal exercise testing. This approach is important as prior observations have noted a non-linear oxygen uptake response to increasing work rate, whereas a linear progression of exercise intensity is desirable. The proposed oxygen-uptake controller has embedded within it a human-in-the-loop feedback system for control of mechanical work rate which takes its target work rate from the automatic oxygen uptake control loop. Results of step and ramp tracking of target oxygen-uptake profiles, and disturbance rejection tests, demonstrated the technical feasibility and accuracy of the approach. Comparison with open-loop tests demonstrated clearly that the feedback system linearises the oxygen-uptake response and that linear progression of exercise intensity leads to higher peak oxygen uptake values. Further work will focus on clinical feasibility and the potential for cardiovascular rehabilitation in patients with neurological deficits.

Cardiorespiratory Fitness, Oxygen Uptake Efficiency Slope And Endothelial Function In Male Adolescents

PURPOSE: VO2 max defined as the point at which oxygen uptake reaches a plateau despite further increase in work rate, is an objective measure of an individual’s cardiorespiratory fitness (CRF). Due to its effort dependency, a true plateau in VO2 during incremental exercise is seldom attained particularly in chronic disease and pediatric populations. The oxygen uptake efficiency slope (OUES) is as an objective and effort independent submaximal measure of cardiopulmonary reserve. Children with high CRF have higher OUES values than those with low CRF. Furthermore, high CRF during adolescence is associated with a healthier cardiovascular profile. The purpose of this study was to examine the relation between OUES and endothelial function (EF) in healthy male adolescents with low, moderate and high CRF. METHODS: Low fit (n=14, VO2max = 43.2±5.3, mL·kg1·min-1), moderate fit (n=16, VO2max = 53.8±3.3, mL·kg1·min-1) and high fit (n=18, VO2max = 63.7±4.0 mL·kg1·min-1) healthy asymptomatic males (mean age 15.8 ± 0.5;) participated in the study. High-resolution ultrasonography was used to assess endothelial dependent (EDD) and endothelial independent dilation (EID) in response to brachial artery flow mediated dilation and glyceryl trinitrate. VO2max was measured using open circuit spirometry during an incremental treadmill test. OUES was determined by plotting VO2 (ml·min-1) against the logarithm of VE (L·min-1) and calculating the slope of this linear relation through single regression analysis. RESULTS: EDD and VO2max were significantly lower in the low fit than the moderate and high fit group. There was no between group difference in EID. Maximal OUES was higher in the high fit than the moderate (p<0.01) and low fit (p<0.05) group. There was a significant positive relation between maximal OUES and percentage change (r=0.33, p<0.01) and absolute change in EDD (r=0.44, p<0.01). VO2 max was also significantly related to percentage change (r=0.67, p<0.001) and absolute change in EDD (r=0.73, p<0.001) CONCLUSION: VO2 max and maximal OUES are significantly related to both absolute and percent change in EDD in adolescent males.

Exercise Testing and Training Strategies for Healthy and Frail Elderly

Exercise Testing and Training Strategies for Healthy and Frail Elderly

Assessment for Exercise Prescription in Heart Failure.

Exercise training (ET) is a Guidelines Class 1A level of evidence adjunct therapy for heart failure (HF) with reduced ejection fraction treatment. As yet less certain is the role of ET for HF with preserved ejection fraction. Different ET types (endurance and resistance) and levels of intensity or domains (light, light-to-moderate and high-to-moderate) are used for ET programmes in patients with cardiac failure. Assessment of ET prescription can be performed through indirect (heart rate reserve) or direct metabolic measures (VO2 reserve, ventilatory threshold) with the most precise methodology based on the analysis of VO2 kinetics during constant work rate protocols of different workloads. The goals of assessing the effects of exercise prescription on functional capacity are traditionally represented by changes in VO2 during peak exercise by cardiopulmonary exercise testing (CPET). Nonetheless, the specific evaluation of how ET may favourably affect the abnormal patterns of VO2 linearity for work rate increase and the effects on ventilation seem important adjunctive parameters to be evaluated and monitored. Although a minority, some HF patients may not respond to ET programmes. This specific phenotype, once appropriately identified, needs a different approach and - intriguingly - should be switched to a higher ET intensity domain to yield the most comprehensive benefits from a personalised ET intervention.