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Abstract

F-30 Free Communication/Poster - Oxygen Uptake Kinetics

Medicine & Science in Sports & Exercise: May 2013 - Volume 45 - Issue 5S - p 586-589
doi: 10.1249/01.mss.0000433748.30875.1a
  • Free

May 31, 2013, 1:00 PM - 6:00 PM

Room: Hall C

2472 Board #173 May 31, 2:00 PM - 3:30 PM

Noninvasive Quantification of Muscle Hemodynamics and Metabolism in Women with Fibromyalgia Using Diffuse Optical Spectroscopies

Guoqiang Yu, Yu Shang, Katelyn Gurley, Brock Symons, Douglas Long, Ratchakrit Srikuea, Leslie J. Crofford, Charlotte A. Peterson. University of Kentucky, Lexington, KY.

(No relationships reported)

Women with fibromyalgia (FM) have symptoms of increased muscular fatigue and reduced exercise tolerance, which may be associated with alterations in muscle microcirculation and oxygen metabolism. We have recently developed a hybrid near-infrared diffuse optical instrument for simultaneous measurement of blood flow and oxygenation in deep muscle tissue.

PURPOSE: To characterize muscle blood flow, blood oxygenation and oxygen metabolism in post-menopausal women with and without FM.

METHODS: Fourteen women with FM and twenty-three healthy controls participated in this study. Two experimental protocols for challenging muscle function were applied to the subjects, including 6 sets of 12 isometric contractions of knee extensor muscles with steadily increased strength, followed by temporary cuff occlusion on forearm for 3 minutes. Leg or arm muscle hemodynamics, including relative blood flow (rBF), oxy- and deoxy-hemoglobin concentration ([HbO2] and [Hb]), total hemoglobin concentration (THC) and blood oxygen saturation (StO2), were continuously monitored throughout protocols using a custom-built hybrid diffuse optical instrument that combined a commercial near-infrared spectroscopy (NIRS) oximeter for tissue oxygenation measurements and a custom-designed diffuse correlation spectroscopy (DCS) flowmeter for tissue blood flow measurements. Relative oxygen extraction fraction (rOEF) and oxygen consumption rate (rVO2) were calculated from the measured blood flow and oxygenation data. Post-manipulation recovery in muscle hemodynamics was characterized by the recovery half-time, i.e., a time interval from the end of manipulation (fatiguing exercise or cuff occlusion) to the time that tissue hemodynamics reached a half-maximal value.

RESULTS: Muscle rOEF during exercise in subjects with FM was significantly lower than in healthy controls (99.7 ± 2.6 vs 107.4 ± 2.0; p = 0.03), and the half-times of [HbO2] and [Hb] were significantly longer (p < 0.05) following fatiguing exercise and cuff occlusion.

CONCLUSIONS: Our results suggest an alteration of muscle oxygen utilization in the FM population. This study demonstrates the potential of using combined diffuse optical spectroscopies (i.e., NIRS/DCS) to comprehensively evaluate tissue oxygen and flow kinetics in skeletal muscle.

2473 Board #174 May 31, 2:00 PM - 3:30 PM

Near Infrared Spectroscopy (NIRS) to Assess the Onset of Increased Metabolism during Muscle Contractions

Matthew J. Rogatzki, Yi Sun, Brian Ferguson, James R. McDonald, L. Bruce Gladden, FACSM. Auburn University, Auburn, AL.

(No relationships reported)

PURPOSE: The aims of the present study were to 1) Determine whether there is a time delay (TD) in O2 at the onset of contractions; and 2) Explore the contribution of myoglobin versus hemoglobin to the NIRS signals during muscle contractions.

METHODS: Canine gastrocnemius (GS) muscles (n = 6) were isolated and pump perfused while NIRS signals were recorded continuously. The GS was electrically stimulated via the sciatic nerve (8V, 50Hz, 0.2ms pulse, 200ms duration) to elicit muscle contractions at the rate of 1 contraction/2 s. The myoglobin contribution to NIRS spectra was evaluated by comparing the NIRS signals during blood perfusion to the signals during Hb-free Krebs-Henseleit bicarbonate buffer (KHBB) perfusion. The TD was determined from the fitting of deoxy-NIRS signals (HHbMb) with a monoexponential model.

RESULTS: TD from the fitting of HHbMb was not significantly different for 1 contraction/2 s between blood perfusion (8.4 ± 1.4 s) and KHBB perfusion (8.9 ± 2.6 s). However, the TD of HHbMb during KHBB perfusion could be partially explained by dissolved O2, and O2 from the dynamic KHBB supply (perfusion) (sufficient for 7.3 ± 2.4 s). The Mb contribution to NIRS signals averaged 57 ± 18% but a large inter-individual variability was observed (39 - 83%).

CONCLUSIONS: A TD for HHbMb was still observed during KHBB perfusion as well as blood perfusion when assessed with a monoexponential model; this could be mostly explained by O2 storage in the KHBB trial. Additionally, the Mb contribution to the overall NIRS signals is on the order of 50+% during muscle contractions; albeit measurement of this contribution was highly variable.

2474 Board #175 May 31, 2:00 PM - 3:30 PM

Pulmonary Oxygen Uptake Off-Kinetics and Fitness in Obese Adolescents

Mary K. Bowen1, R. Lee Franco1, Ross Arena, FACSM2, Heather L. Caslin1, Ronald K. Evans1, Edmond P. Wickham1. 1Virginia Commonwealth University, Richmond, VA. 2The University of New Mexico, Albuquerque, NM.

(No relationships reported)

In adolescents, the pulmonary oxygen (O2) uptake off-kinetic response during recovery from exercise has received little attention in comparison to O2 on-kinetics during the transition to steady-state exercise. Although studies have reported equivocal findings in comparing O2 on-kinetics between obese and lean adolescents, no relationship has been shown between peak oxygen consumption (VO2) and the O2 on-kinetics response to moderate intensity exercise. The evaluation of pulmonary O2 off-kinetics in adolescents has only occurred in lean subjects and training status did not have an impact on O2 uptake during recovery.

PURPOSE: To determine the relationship between peak VO2 and pulmonary O2 off-kinetics in obese adolescents.

METHODS: Twenty-five obese adolescents (13.81±1.65 yrs, 36.15±4.65 kg/m2) volunteered to participate and completed a graded exercise test to exhaustion on a treadmill. Breath by breath data from the first 4-min of treadmill walking (2.5 mph, 0% grade) at moderate intensity (<60% of peak VO2) and during the immediate 4-min passive recovery was averaged into 10s intervals and fit with a monoexponential equation to determine the pulmonary oxygen on- and off-kinetic time constant, respectively.

RESULTS: A significant inverse relationship (r = -0.585, P = 0.002) was found between the time constant for pulmonary O2 off-kinetics during exercise recovery (36.80±9.07 s) and peak VO2 (45.72±5.4 mLO2·leankg-1·min-1). Similar to previous studies, oxygen on-kinetics during the transition to moderate intensity exercise was not related to peak VO2 (r = -0.294, P = 0.154).

CONCLUSIONS: These results suggest that the greater an obese adolescents cardiorespiratory fitness, the faster their pulmonary O2 off-kinetics during recovery from exercise. A longer O2 off-kinetic time constant displayed with lower cardiorespiratory fitness may reflect the effects of elevated pulmonary ventilation, cardiac work, deep body temperature, lactate clearance, and gluconeogenesis during recovery from exercise.

Support: Virginia Premier Inc; NIH (K23-HD053742:EPW; UL1RR031990:VCU)

2475 Board #176 May 31, 2:00 PM - 3:30 PM

True Maximal Muscle Deoxygenation Attainment During Intense Cycling Is Site-specific

Matthew D. Spencer1, Tatsuro Amano2, Mikio Miwa2, Narihiko Kondo2, John M. Kowalchuk3, Donald H. Paterson, FACSM3, Shunsaku Koga1. 1Kobe Design University, Kobe, Japan. 2Kobe University, Kobe, Japan. 3The University of Western Ontario, London, ON, Canada.

(No relationships reported)

Time-resolved near-infrared spectroscopy (TRS NIRS) derived muscle deoxygenation ([HHb]; absolute μM) reflects the balance between O2 availability & O2 utilization. Dynamic heterogeneities exist across the quadriceps muscle complex during exercise, even after correction for differences in adipose tissue thickness (ATT). The profile of [HHb] during ramp incremental (RI) exercise is characterized by a near-plateau ([HHb]peak) at higher intensities; however, it is unknown whether this [HHb]peak represents the true maximum.

PURPOSE: To compare the ATT-corrected [HHb]peak responses at 3 quadriceps muscle sites during RI and severe-intensity (SVR) exercise, and occlusion (OCC).

METHODS: Healthy males (n=7; 25±4yr) each completed a stationary cycling RI (20 W/min) test to determine [HHb]peak (at proximal and distal vastus lateralis (VLp and VLd) and rectus femoris (RF)), VO2peak and peak work rate (WRpeak). Following this test (≥48 hours post-RI), subjects completed SVR exercise (WR corresponding to 120%VO2peak) with [HHb] and VO2p monitored continuously. Additionally, [HHb] and total hemoglobin ([Hb]tot) were monitored continuously at rest and during subsequent OCC (250 mmHg; cuff positioned proximal to NIRS probes) of sufficient duration to elicit a near-plateau in [HHb]. Site-specific ATT was assessed (B-mode ultrasound) and its relationship with resting [Hb]tot was used to correct absolute [HHb] values. ATT-corrected [HHb]peak and VO2peak were given as the highest continuous 20s average for each condition.

RESULTS: Subjects’ VO2peak and WRpeak during RI were 53±10 ml·min-1·kg-1 and 306±44W, respectively; this resulted in a SVR WR of 337±49W. For VLd and RF, [HHb]peak was higher (p<0.05) during OCC (VLd=131±44; RF=134±31μM) than RI (VLd:75±16; RF=100±24; p<0.05 between) and SVR (VLd=75±15; RF=95±21; p<0.05 between). [HHb]peak was similar (p>0.05) across conditions at the VLp (OCC=79±20; RI=81±20; SVR=74±19μM). [HHb] peaked and then decreased prior to exercise cessation during SVR at all 3 sites.

CONCLUSION: A “[HHb] reserve” exists during RI and SVR at the VLd and RF, implying either sufficient blood flow to meet oxidative demands or insufficient diffusion time for complete equilibration. In VLp this [HHb] reserve was absent suggesting that a critical PO2 is challenged during RI and SVR cycling.

2476 Board #177 May 31, 2:00 PM - 3:30 PM

Influence Of The Phosphodiesterase-5 Inhibitor Tadalafil On Oxygen Uptake Kinetics During Moderate-intensity Exercise In Humans

Cosme F. Buzzachera1, Gian P. Emerenziani2, Maria C. Gallotta2, Paolo Sgrò2, Emanuele Franciosi2, Luigi Di Luigi2, Laura Guidetti, FACSM2, Carlo Baldari, FACSM2. 1North University of Parana, Londrina, Brazil. 2University of Rome, Rome, Italy.

(No relationships reported)

Previous research has shown that nitric oxide (NO)-3’5’cyclic guanosine monophosphate (cGMP) signaling pathway play an important role both in muscle vasodilatation and in the regulation of oxidative metabolism during exercise. Tadalafil, a phosphodiesterase-5 inhibitor commonly used for therapeutic and nontherapeutic purposes, reduces cGMP hydrolysis and might, to some extent, influence muscle hemodynamic and oxidative processes, and arguably, affect oxygen uptake (VO2) kinetics during exercise.

PURPOSE: To examine whether the oral administration of Tadalafil influences pulmonary VO2 kinetics during moderate-intensity exercise in humans.

METHODS: Twelve healthy males (age 26.0 ± 3.6 yrs, VO2peak 48.7 ± 5.1 ml.kg-1.min-1) were randomly assigned to receive either two tablets of placebo or Tadalafil (20mg) in a double-blind crossover design, with a 14-days wash-out period between the two conditions. After the administration of either placebo or Tadalafil, subjects performed a 30-min. bout of moderate-intensity exercise on a cycle ergometer. Pulmonary gas exchange (breath-by-breath) and heart rate were measured continuously throughout baseline and exercise transition, and the kinetics of VO2 was modeled using non-linear regression. Blood lactate concentrations and blood pressure responses were recorded every 5-min period of the test. Data were analyzed using paired t-tests.

RESULTS: Compared to placebo, the Tadalafil condition did not differ for heart rate (139 ± 13 vs. 142 ± 13bpm), systolic (145 ± 17 vs. 143 ± 26 mmHg) and diastolic blood pressure (58 ± 15 vs. 64 ± 13 mmHg), and blood lactate concentration (3.5 ± 0.5 vs. 3.6 ± 0.7 mmol/L, respectively for placebo and Tadalafil conditions) (P > 0.05). In addition, the time constant (49 ± 14 vs. 43 ± 13 sec), amplitude (1.25 ± 0.2 vs. 1.28 ± 0.2 L/min), and functional ‘gain’ (9.5 ± 0.8 vs. 9.7 ± 1.4 ml/min/W) of the fundamental phase of VO2 kinetics were also similar between placebo and Tadalafil conditions, respectively (P > 0.05).

CONCLUSION: Inhibition of Phospodiesterase-5 with Tadalafil does not substantially influence pulmonary VO2 kinetics during moderate-intensity exercise in humans.

2477 Board #178 May 31, 2:00 PM - 3:30 PM

The Work Of Breathing And The Slow Component Of O2 Uptake Kinetics During Strenuous Exercise

Troy J. Cross1, Caroline Winters2, Naama Constantini, FACSM3, Surendran Sabapathy1. 1Griffith University, Gold Coast, Australia. 2Vrije Universiteit, Amsterdam, Netherlands. 3Hadassah-Hebrew University Medical Centre, Jerusalem, Israel.

(No relationships reported)

The slow component of O2 uptake kinetics (VO2sc) represents a progressive decline in work efficiency during strenuous constant-load exercise. The majority of the VO2sc is explained by factors intrinsic to the working muscles (∼86%). The remainder of the VO2sc is likely due to the rising work of breathing (Wb) associated with the hyperventilatory response to strenuous activity. To date, no study has quantified the Wb (and its components) with respect to the VO2sc during strenuous exercise.

PURPOSE: The aim of this study was to quantify the Wb during strenuous constant-load exercise, and to examine the relationship between the resistive and elastic components of Wb, and the amplitude of the VO2sc.

METHODS: 11 healthy, physically active participants (24 ± 1 yr) performed two separate, 6-min bouts of heavy (HVY) and severe intensity (SEV) cycling exercise. Gas-exchange and oesophageal manometry were used to quantify the amplitude of the VO2sc and Wb parameters during exercise. The VO2sc was determined as the difference in O2 uptake between the 3rd and 6th min of constant-load exercise. The Wb parameters were quantified over the same period.

RESULTS: The amplitude of the VO2sc was significantly greater (p<0.01) during SEV (291 ± 32 ml·min-1) compared with HVY trials (148 ± 31 ml·min-1). The relative increase in total Wb over the VO2sc period was significantly greater during SEV than for HVY exercise (79 ± 14% v 13 ± 3%, p<0.01). There was no relationship between the Wb and the VO2sc for HVY trials. Conversely, the VO2sc was positively (p<0.01) correlated with the increase in inspiratory elastic Wb (R2 = 71%), inspiratory resistive Wb (R2 = 86%) and expiratory resistive Wb (R2 = 87%) between the 3rd and 6th min of SEV exercise.

CONCLUSIONS: These results suggest that the resistive and elastic Wb significantly influences the development of the VO2sc during strenuous exercise, particularly in the severe intensity domain.

2478 Board #179 May 31, 2:00 PM - 3:30 PM

Effect Of Eccentric Muscle Damage On O2 Uptake Kinetics And Muscle Deoxygenation During Moderate-intensity Cycling Exercise

Joshua P. Nederveen, Juan M. Murias, Donald H. Paterson, FACSM, John M. Kowalchuk. University of Western Ontario, London, ON, Canada.

(No relationships reported)

Eccentric exercise-induced damage is known to alter the structure and function of muscles and produce substantial microvascular dysfunction. The impact of this dysfunction on O2 delivery during exercise in the moderate-intensity domain has yet to be elucidated.

PURPOSE: To determine the impact of unaccustomed eccentric exercise-induced muscle damage on the rate of adjustment in muscle deoxygenation and pulmonary O2 uptake (VO2p) kinetics during cycling exercise performed in the moderate domain.

METHODS: Nine untrained healthy young men (25±3 yr; mean±SD) completed a ramp incremental cycling test (25 W·min-1) to volitional exhaustion in order to determine maximal VO2p (VO2max, 50.4±6.0 mL·kg-1·min-1) and gas exchange threshold (GET). Participants then completed a minimum of three step-transitions to 90% GET before (PRE), 24 h (Post1) and 48 h after (Post2) eccentric exercise (100 eccentric leg press repetitions with a load corresponding to 110% of the subject’s concentric 1RM). The adjustment of VO2p was monitored breath-by-breath using a volume turbine and a mass spectrometer and changes in near-infrared spectroscopy (NIRS)-derived muscle deoxygenation (Δ[HHb]) were measured during each transition. Phase II VO2 responses were modeled using a mono-exponential equation by non-linear regression.

RESULTS: The phase II VO2p time constant (τVO2p) was similar amongst time points (τVO2p: Pre, 26±3 s; Post1, 26±4 s; Post2, 28±4 s). There were no differences in the Δ[HHb] time constant (τΔ[HHb]) (τΔ[HHb]: Pre, 15±2 s; Post1, 12±1 s; Post2, 16±2) or Δ[HHb] mean response time (MRT: Pre, 22±4 s; Post1, 21±2 s; Post2, 25±7 s ) following eccentric exercise

CONCLUSION: We propose that the unchanged VO2p kinetics coupled with similar deoxygenation kinetics suggest matching of local muscle O2 delivery to O2 utilization despite possible microvascular dysfunction associated with eccentric muscle damage. The convective blood flow and diffusive properties of muscle O2 transport appears to be unperturbed in the moderate-intensity domain following eccentric muscle damage. Supported NSERC Canada.

2479 Board #180 May 31, 2:00 PM - 3:30 PM

Oxygen Uptake Kinetics At Extreme Swimming Intensity

Ricardo J. Fernandes1, João Ribeiro1, Ana Sousa1, Joaquim Monteiro2, Laura Guidetti, FACSM3, Carlo Baldari, FACSM3, Vilas-Boas Paulo João1. 1CIFI2D, Faculty of Sport and Porto Biomechanics Laboratory, University of Porto, Porto, Portugal. 2REQUIMTE/FARMA, Faculty of Pharmacy, University of Porto, Porto, Portugal. 3University of Rome “Foro Itálico”, Rome, Italy.

(No relationships reported)

Oxygen consumption (VO2) kinetics in swimming was rarely conducted at the extreme intensity domain, i.e., at paces above VO2max, being an unexplored and challenging task.

PURPOSE: To characterize the VO2 kinetics on the shortest swimming competitive event: the 50 m freestyle.

METHODS: Six trained swimmers (24.8±8.0 yrs, 170.3±5.3 cm, 63.3±5.4 kg) performed 50 m maximal front crawl, and the VO2 was measured by a K4b2 portable gas analyser connected to the new AquaTrainer snorkel (Cosmed, Italy). VO2 data was fitted using the following mono-exponential model: VO2=VO2Basal*exp(time/time constant).

RESULTS: The duration of the effort was 31.27±3.96 s, and an instantaneous and sudden increase in the VO2 occurred from the beginning of the effort (Fig. 1), with 47.37±9.10 ml/kg/min for VO2peak and 23.53±6.30 s of time constant.

CONCLUSION: Despite the short duration of the 50 m front crawl event, swimmers were able to attain high values of VO2peak. Complementarily, the high time constant values reflect the extreme intensity in which the effort occurred, not allowing a VO2 stabilization, as reported for moderate and heavy exercise. Future analysis should focus on the assessment of the aerobic vs anaerobic energy system contribution in this swimming event.

ACKNOWLEDGMENTS: SFRH/BD/81337/2011 and PTDC/DES/101224/2008 grants.

2480 Board #181 May 31, 2:00 PM - 3:30 PM

An Algorithm To Optimise Fitting Of Phase 2 Pulmonary Oxygen Uptake Kinetics From Breath-by-Breath Measurements

Alan P. Benson1, T. Scott Bowen1, Carrie Ferguson1, Scott R. Murgatroyd1, Harry B. Rossiter, FACSM2. 1University of Leeds, Leeds, United Kingdom. 2Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA.

(No relationships reported)

Muscle O2 consumption kinetics are commonly inferred from the phase (ϕ) 2 time constant (τ) of pulmonary O2 uptake (VO2P). While repeated breath-by-breath measurements are typically averaged to reduce “noise”, the effects of different averaging methods on τ estimation are not well known and the methods for ϕ1-2 transition identification are not standardised. Accurate identification of the ϕ1-2 transition is especially complex: It is hampered by breath-by-breath fluctuations, and human error can cause wide τ variations.

PURPOSE: To develop an algorithm to optimise accuracy and precision of ϕ1-2 transition identification and data averaging for τVO2P measurement.

METHODS: Monte Carlo simulations produced 106 “experimental” VO2P datasets using a single clean 20-100 W response (known ϕ1-2 = 18.6 s, τ = 28.8 s) produced from a validated physiological model with imposed Gaussian VO2P noise (SD = 70 ml/min), and sampled at a variable breathing frequency. Each dataset had 4 “exercise” transitions, averaged before fitting by binning (breath average) or by interpolation (second-by-second), or by averaging 4 τ values from a fit of each transition. Repeated fits were performed by incrementally removing a datum from the beginning of each dataset, and the accuracy and precision to identify the known ϕ1-2 transition and τ by a range of statistical measures were recorded: Reduced χ2, adjusted R2, 95% confidence interval for τ (CIτ), corrected Akaike information criterion (AIC).

RESULTS: CIτ was the most accurate method for identifying ϕ1-2 transition, averaging -1.2 ± 1.8 breaths (mean ± SD) from the true value, and within 2 breaths of true in 80% of the 106 datasets. Other measures were less favourable: 3.8 ± 4.4 breaths (44%) for χ2, -4.2 ± 0.6 breaths (1%) for R2, and -3.1 ± 1.1 breaths (33%) for AIC. Binning (with CIτ to isolate ϕ2) was the most accurate averaging method. Binning τ estimates were 0.5 ± 2.5 s different from the true value (within 2 s of true in 62% of the 106 datasets) compared to -0.2 ± 1.8 s (74%) using the known ϕ1-2 as a control. Interpolation (1.0 ± 2.9 s; 56%), and separate fitting (-1.5 ± 2.4 s; 53%) were less favourable.

CONCLUSION: Bin-averaging combined with CIτ to identify the ϕ1-2 transition before exponential fitting provides an accurate and precise method to determine phase 2 VO2P kinetics.

Supported by BBSRC BB/I00162X/1

2481 Board #182 May 31, 2:00 PM - 3:30 PM

Analysis Of Square-wave Bouts To Verify Vo2max

Daniel T. Sedgeman1, Lance C. Dalleck2, Ida E. Clark1, Nicholas A. Jamnick1, Thomas W. Kernozek, FACSM3, Robert W. Pettitt1. 1Minnesota State University, Mankato, Mankato, MN. 2The University of Auckland, Auckland, New Zealand. 3University of Wisconsin-La Crosse, La Crosse, WI.

(No relationships reported)

Submaximal and supramaximal, square-wave bouts of exercise have been reported to consistently verify “true” VO2max. Although a direct comparison between both testing protocols exists, knowledge regarding the statistical consistency between these protocols using the same group of participants is lacking.

PURPOSE: We examined the differences between the submaximal and supramaximal verification bout performed shortly subsequent to a graded exercise test (GXT).

METHODS: On two separate occasions, six males and seven females (age: 29 ± 9 years) completed a GXT protocol and an exhaustive, square-wave bout at either end-GXT power minus two-stages or at 105% end-GXT power.

RESULTS: The submaximal protocol evoked VO2max values (ml·kg-1·min-1) of 49.5 ± 5 and 49.0 ± 7 whereas the supramaximal protocol evoked values of 50.1 ± 7 and 49.1 ± 7, for the GXT and verification bouts, respectively (p > 0.05). The standard error of measurement (ml·kg-1·min-1) for submaximal (1.09) and supramaximal (1.04) trials was similar. Likewise, similar measures of consistency were observed for the submaximal (ICC α = 0.97, CV = 2.4%) and supramaximal protocols (ICC α = 0.95, CV = 2.3%).

CONCLUSION: For a GXT lasting ∼10 to 12 min, the submaximal or supramaximal protocols appear equally effective in determining VO2max.

2482 Board #183 May 31, 2:00 PM - 3:30 PM

The Effect Of Age And Training Status On Vo2 Kinetics

Tyler M. Grey, Matthew D. Spencer, Juan M. Murias, Glen R. Belfry, Donald H. Paterson, FACSM. University of Western Ontario, London, ON, Canada.

(No relationships reported)

Although slower oxygen uptake (VO2) kinetics is typically observed in older compared to younger adults, the VO2 kinetics responses across groups of adults of different ages has not been determined. Further, although a speeding of VO2 kinetics with endurance training is well-established it is not known if age-related slowing of VO2 kinetics occurs in a similar fashion in well-trained individuals.

PURPOSE: To determine the VO2 kinetics response across age in trained cyclists and untrained controls.

METHODS: Trained cyclists, and untrained (recreationally active) men, from three age groups were studied: young (18-39 yrs), middle-aged (40-59 yrs), and older (60-75 yrs). Subjects completed a ramp incremental cycle ergometer test (20-30 W/min) to the limit of tolerance (VO2max). Subsequently, the time course of adjustment of pulmonary VO2 (VO2p) was examined from at least three repeats of step transitions from 20W to moderate-intensity exercise. Some subjects’ data were obtained from previously conducted studies in our laboratory. VO2p was monitored breath-by-breath using a volume turbine and mass spectrometer in 6 young, 7 middle-aged, and 4 older trained men (25±7, 50±4, and 65±3 yrs, respectively) and 8 young, 9 middle-aged, and 6 older untrained males (23±4, 52±2, and 69±5 yrs, respectively). On-transient VO2p response (τVO2p) was modeled as a mono-exponential using non-linear regression. Data for VO2max versus age and τVO2p versus age were fit using a piecewise double-linear function.

RESULTS: VO2max showed little change with age for both the untrained and trained groups (49.9 and 64.9 mL·kg-1·min-1, respectively) until age ∼50 yrs; thereafter the rate of decline was 10.2 and 12.3 mL·kg-1·min-1·decade-1, respectively. τVO2p showed little change in untrained controls (26 s) until age ∼50 yrs but thereafter increased 11.6 s/decade; whereas, τVO2p in the trained group was not changed (18 s) through middle-age, then showed a modest increase of 3.4 s/decade.

CONCLUSION: Not until approximately age 50 yrs in the untrained group did both τVO2p increase and VO2max decrease substantially. In the trained group, despite the similar age-related decline in VO2max as in the untrained, the slowing of kinetics with age was appreciably less than that of the untrained.

Supported by NSERC

2483 Board #184 May 31, 2:00 PM - 3:30 PM

Incidence Of Plateau At Vo2max: Is There A Role For A Circadian Oscillator?

Dan A. Gordon1, Hannah Tilston2, Patrick Bradley2, Eleanor Walshe2, James Baker1, Marie Gernigon3, Richard Barnes2. 1Anglia Ruskin University, Cambridge, United Kingdom. 2University of Cambridge, Cambridge, United Kingdom. 3University of Angers, Angers, France.

(No relationships reported)

Incidence of plateau at O2max: Is there a role for a circadian oscillator?

Dan Gordon1, Hannah Tilston2, Eleanor Walshe2, Patrick Bradley2, James Baker2, Marie Gernigon3, Richard Barnes1

1Anglia Ruskin University, Cambridge, UK, 2University of Cambridge, Cambridge, UK, 3University of Angers, Angers, France

PURPOSE: The plateau at VO2max has been attributed to the availability of the finite anaerobic capacity. The purpose of this study was to determine if plateau incidence could be accounted for by diurnal variations, thus suggesting a circadian oscillation.

METHOD: Following Institutional ethical approval, n= 9 well trained males (age, 23.8 ± 5.9 yrs; mass 76.9 ± 9.5 kg; height 179.6 ± 7.8 cm) agreed to participate. They completed seven VO2max trials in a randomised order at pre-determined times of the day (7am, 10am, 1pm, 4pm, 7pm and 10pm), each trial separated by 72h. All trials were completed on an electronically braked cycle ergometer at a constant cadence of 80-100 rpm with work-rate increased by 0.42 W·s-1 following a 60 s period of cycling at 100 W. Test termination: a decrease in cadence of >10 rpm or volitional exhaustion. Using a pre-calibrated metabolic cart plateau responses were determined using the criteria of ΔVO2 <50 ml·min-1 over the final two consecutive 30 s sampling periods. Prior to all trials and in the rested state blood glucose (mM), blood lactate (mM), total haemoglobin (g·dl-1), urine specific gravity (g·dl-1), core temperature (°C), blood pressure (mmHg), heart rate (b·min-1) and O2 saturation (%) were assessed.

RESULTS: There was a non-significant difference for ΔVO2 (ml·min-1) for the seven time domains, 18.1 ± 96.9 (7am), 18.9 ± 59.5 (10am), 55.7 ± 144.3 (1pm), 50.7 ± 178.2 (4pm), 88.9 ± 70.4 (7pm) and 35.3 ± 117.5 (10pm) (P= 0.901), while plateau incidences were 66% (7am), 33% (10am, 1pm), 22% (4pm, 7pm) and 55% (10pm). Additionally there was a non-significant difference across time frame for VO2max (P= 0.9999) and blood glucose (P= 0.1784).

CONCLUSIONS: The data suggests that ΔVO2 at the point of volitional exhaustion during a VO2max test is not a manifestation of a circadian oscillator. However the data projects a trend for increased response rates at both early morning and late evening contingent with previous findings assessing a circadian rhythm in anaerobic substrate metabolism.

2484 Board #185 May 31, 2:00 PM - 3:30 PM

Respiratory Muscle Training lowers the O2 Cost of Cycling and improves Exercise Tolerance in Obese Adolescents

Desy Salvadego1, Fiorenza Agosti2, Gabriella Tringali2, Alessandra Patrizi2, Andrea Gattico2, Alessandro Sartorio2, Bruno Grassi1. 1University of Udine, Udine, Italy. 2Istituto Auxologico Italiano, Milano, Italy.

(No relationships reported)

PURPOSE: In obese adolescents (OB) an increased work of breathing can negatively affect exercise tolerance. The purpose of the study was to determine whether, in OB, an endurance training program of respiratory muscles (RMT) can decrease the O2 cost of exercise and enhance exercise tolerance.

METHODS: Before and after 3 weeks of RMT (5 days/wk, isocapnic hyperpnea), ten male OB (age 15.9±1.4 [x±SD] years, body mass 112.4±21.9 kg, body mass index 38.5±7.3 kg/m2) performed, on a cycle ergometer: an incremental exercise to voluntary exhaustion; a 12-min constant work-rate exercise (CWRE) at 120% of the gas-exchange threshold determined before RMT. Pulmonary O2 uptake (V’O2) was measured breath-by-breath.

RESULTS: RMT did not significantly affect peak V’O2. During CWRE: the amplitude of the fundamental component of V’O2 kinetics was lower after (1.50±0.44 L/min) vs. before (1.65±0.39) RMT; the slow component was abolished or its amplitude was markedly reduced after RMT (4.0±5.3% of the total amplitude of the V’O2 response) vs. before RMT (8.0±5.1). As a consequence, the O2 cost of cycling was lower after (12.5±2.2 mL/min/watt) vs. before (14.5±1.8) RMT. This was associated with lower values of rate of perceived exertion for dyspnea/respiratory discomfort (3.5±2.0 vs. 5.2±2.3, in after vs. before RMT) and for “leg effort” (4.7±2.5 vs. 6.5±3.0).

CONCLUSIONS: By lowering the O2 cost of cycling, RMT can significantly enhance exercise tolerance during submaximal exercise in obese adolescents.

Supported by: Progetti di Ricerca Corrente, Italian Institute for Auxology (Milan).

© 2013 American College of Sports Medicine