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  • 1
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    Respiratory muscle endurance training reduces the O 2 cost of cycling and perceived exertion in obese adolescents
    American Physiological Society ; 2017
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 313, No. 4 ( 2017-10-01), p. R487-R495
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 313, No. 4 ( 2017-10-01), p. R487-R495
    Abstract: In obesity, the increased O 2 cost of breathing negatively affects the O 2 cost of exercise and exercise tolerance. The purpose of the study was to determine whether, in obese adolescents, the addition of respiratory muscle endurance training (RMET) (isocapnic hyperpnea) to a standard body mass reduction program decreases the O 2 cost of exercise and perceived exertion. Nine male obese adolescents [16.0 ± 1.4 yr ( x ± SD), body mass 114.4 ± 22.3 kg] underwent 3 wk of RMET (5 days/week) in addition to a standard body mass reduction program. Eight age- and sex-matched obese adolescents underwent only the standard program (CTRL). Before and after interventions, patients performed on a cycle ergometer: incremental exercise; 12-min exercises at a constant work rate (CWR) of 65% and 120% at the gas exchange threshold (GET) determined before the intervention. Breath-by-breath pulmonary ventilation (V̇e) and O 2 uptake (V̇o 2 ), heart rate (HR), and ratings of perceived exertion for dyspnea/respiratory discomfort (RPE R ) and leg effort (RPE L ) were determined. Body mass decreased (by ~3.0 kg) after both RMET ( P = 0.003) and CTRL ( P = 0.002). Peak V̇o 2 was not affected by both interventions. Peak work rate was slightly, but significantly ( P = 0.04), greater after RMET but not after CTRL. During CWR 〈 GET, no changes were observed after both interventions. During CWR 〉 GET, the O 2 cost of cycling at the end of exercise ( P = 0.02), the slope of V̇o 2 vs. time (3–12 min) ( P = 0.01), RPE R ( P = 0.01), and RPE L ( P = 0.01) decreased following RMET, but not following CTRL. HR decreased after both RMET ( P = 0.02) and CTRL ( P = 0.03), whereas V̇e did not change. In obese adolescents RMET, superimposed on a standard body mass reduction program, lowered the O 2 cost of cycling and perceived exertion during constant heavy-intensity exercise.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.00396.2016
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2017
    detail.hit.zdb_id: 1477297-8
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  • 2
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    Differential depression of myocardial function and metabolism by lactate and H +
    American Physiological Society ; 1999
    In:  American Journal of Physiology-Heart and Circulatory Physiology Vol. 276, No. 1 ( 1999-01-01), p. H3-H8
    Details
    In: American Journal of Physiology-Heart and Circulatory Physiology, American Physiological Society, Vol. 276, No. 1 ( 1999-01-01), p. H3-H8
    Abstract: The effects of both high blood H + concentration ([H + ]) and high blood lactate concentration ([lactate] ) under ischemia-reperfusion conditions are receiving attention, but little is known about their effects in nonischemic hearts. Isolated rat hearts were Langendorff perfused at constant flow with media at two pH values (7.4 and 7.0) and two [lactate] (0 and 20 mM) in various sequences ( n = 6/group). Coronary flow and arterial O 2 content were kept constant at levels that allowed hearts to function without O 2 supply limitation. We measured contractility, O 2 uptake, diastolic pressure, and at the end of the protocol, tissue [lactate] and pH. Perfusion with high [lactate] raised tissue [lactate] from 5.5 ± 0.1 to 17.5 ± 2.6 μmol/heart ( P 〈 0.0001), whereas decreasing the pH of the medium decreased tissue pH from 6.94 ± 0.02 to 6.81 ± 0.06 ( P = 0.002). Heart rate was not affected by high [lactate] but was reversibly depressed by high [H + ] ( P = 0.004). Developed pressure declined by 20% in response to high [lactate] , high [H + ], and high [lactate] + high [H + ] ( P = 0.002). After the high-[lactate] challenge was withdrawn, pressure continued to decline. In contrast, withdrawing the high [H + ] challenge allowed partial recovery. The behavior of diastolic pressure mirrored that of developed pressure. Although unaffected by high [lactate] , the O 2 uptake was reversibly depressed by high [H + ]. This suggests higher O 2 cost per contraction in the presence of high [lactate]. We conclude that for similar acute contractility depression, high [lactate] induces irreversible damage, likely at some point in the pathway of O 2 utilization. In contrast, the effect of high [H + ] appears reversible. These differential behaviors may have implications for heart function during heavy exercise and ischemia-reperfusion events.
    Type of Medium: Online Resource
    ISSN: 0363-6135 , 1522-1539
    URL: Article
    DOI: 10.1152/ajpheart.1999.276.1.H3
    RVK:
    WA 15000
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1999
    detail.hit.zdb_id: 1477308-9
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  • 3
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    Progressive recruitment of muscle fibers is not necessary for the slow component of V̇ o 2 kinetics
    American Physiological Society ; 2008
    In:  Journal of Applied Physiology Vol. 105, No. 2 ( 2008-08), p. 575-580
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 105, No. 2 ( 2008-08), p. 575-580
    Abstract: The “slow component” of O 2 uptake (V̇o 2 ) kinetics during constant-load heavy-intensity exercise is traditionally thought to derive from a progressive recruitment of muscle fibers. In this study, which represents a reanalysis of data taken from a previous study by our group (Grassi B, Hogan MC, Greenhaff PL, Hamann JJ, Kelley KM, Aschenbach WG, Constantin-Teodosiu D, Gladden LB. J Physiol 538: 195–207, 2002) we evaluated the presence of a slow component-like response in the isolated dog gastrocnemius in situ ( n = 6) during 4 min of contractions at ∼60–70% of peak V̇o 2 . In this preparation all muscle fibers are maximally activated by electrical stimulation from the beginning of the contraction period, and no progressive recruitment of fibers is possible. Muscle V̇o 2 was calculated as blood flow multiplied by arteriovenous O 2 content difference. The muscle fatigued (force decreased by ∼20–25%) during contractions. Kinetics of adjustment were evaluated for 1) V̇o 2 , uncorrected for force development; 2) V̇o 2 normalized for peak force; 3) V̇o 2 normalized for force-time integral. A slow component-like response, described in only one muscle out of six when uncorrected V̇o 2 was considered, was observed in all muscles when V̇o 2 /peak force and V̇o 2 /force-time were considered. The amplitude of the slow component-like response, expressed as a fraction of the total response, was higher for V̇o 2 /peak force (0.18 ± 0.06, means ± SE) and for V̇o 2 /force-time (0.22 ± 0.05) compared with uncorrected V̇o 2 (0.04 ± 0.04). A progressive recruitment of muscle fibers may not be necessary for the development of the slow component of V̇o 2 kinetics, which may be caused by the metabolic factors that induce muscle fatigue and, as a consequence, reduce the efficiency of muscle contractions.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.01129.2007
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2008
    detail.hit.zdb_id: 1404365-8
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  • 4
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    Reply to Borrani, Malatesta, and Candau
    American Physiological Society ; 2009
    In:  Journal of Applied Physiology Vol. 106, No. 2 ( 2009-02), p. 747-747
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 106, No. 2 ( 2009-02), p. 747-747
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.91400.2008
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2009
    detail.hit.zdb_id: 1404365-8
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  • 5
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    A simple method for assessing the energy cost of running during incremental tests
    American Physiological Society ; 2009
    In:  Journal of Applied Physiology Vol. 107, No. 4 ( 2009-10), p. 1068-1075
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 107, No. 4 ( 2009-10), p. 1068-1075
    Abstract: The energy cost of running (Cr) is classically determined from steady-state oxygen consumption (V̇o 2 ) at constant speed, divided by running speed. In the present study, Cr was determined during incremental treadmill tests in the course of the assessment of V̇o 2max and related parameters as follows. Assume that the running speed is increased by a constant amount (Δv) at regular short intervals (T) and that, during each intensity transient below the gas exchange threshold, V̇o 2 increases exponentially, without time delay, toward the steady state. If V̇o 2 is averaged over homologous times within each speed step, neglecting the initial 10 s, the V̇o 2 difference between corresponding time values becomes constant and equal to the difference between the appropriate steady states. Thus Cr was obtained from the ratio of the difference between the V̇o 2 averages for any two homologous times, within subsequent periods, to the corresponding speed difference. Since in aerobic conditions, Cr on the treadmill is independent of the speed, and since Δv and T were constant, the relationship between V̇o 2 and speed is described by straight lines, where the slope yields Cr above resting. This was indeed experimentally observed, the slopes of the linear regressions ( R 2 range: 0.78 to 0.97 n = 9 to 16) within the three time windows being essentially equal. In six subjects, the grand-average of Cr amounted to 0.177 ± 0.011 ml O 2 /(kg·m) [3.70 ± 0.23 J/(kg·m)]. This value is essentially equal to that obtained for the same subjects by applying the “classical” procedure [0.177 ± 0.015 ml O 2 /(kg·m); 3.70 ± 0.31 J/(kg·m)], so confirming the validity of the incremental approach for assessing the energy cost of treadmill running.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00063.2009
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2009
    detail.hit.zdb_id: 1404365-8
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  • 6
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    A validated model of oxygen uptake and circulatory dynamic interactions at exercise onset in humans
    American Physiological Society ; 2013
    In:  Journal of Applied Physiology Vol. 115, No. 5 ( 2013-09-01), p. 743-755
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 115, No. 5 ( 2013-09-01), p. 743-755
    Abstract: At the onset of muscular exercise, the kinetics of pulmonary O 2 uptake (V̇o 2P ) reflect the integrated dynamic responses of the ventilatory, circulatory, and neuromuscular systems for O 2 transport and utilization. Muscle O 2 uptake (V̇o 2m ) kinetics, however, are dissociated from V̇o 2P kinetics by intervening O 2 capacitances and the dynamics of the circulation and ventilation. We developed a multicompartment computational model (MCM) to investigate these dynamic interactions and optimized and validated the MCM using previously published, simultaneously measured V̇o 2m , alveolar O 2 uptake (V̇o 2A ), and muscle blood flow (Q̇ m ) in healthy young men during cycle ergometry. The model was used to show that 1) the kinetics of V̇o 2A during exercise transients are very sensitive to preexercise blood flow distribution and the absolute value of Q̇ m , 2) a low preexercise Q̇ m exaggerates the magnitude of the transient fall in venous O 2 concentration for any given V̇o 2m kinetics, necessitating a tighter coupling of Q̇ m /V̇o 2m (or a reduction in the available work rate range) during the exercise transient to avoid limits to O 2 extraction, and 3) information regarding exercise-related alterations in O 2 uptake and blood flow in nonexercising tissues and their effects on mixed venous O 2 concentration is required to accurately predict V̇o 2A kinetics from knowledge of V̇o 2m and Q̇ m dynamics. Importantly, these data clearly demonstrate that V̇o 2A kinetics are nonexponential, nonlinear distortions of V̇o 2m kinetics that can be explained in a MCM by interactions among circulatory and cellular respiratory control processes before and during exercise.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00184.2013
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2013
    detail.hit.zdb_id: 1404365-8
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  • 7
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    Role of convective O 2 delivery in determiningV˙ o 2 on-kinetics in canine muscle contracting at peak V˙ o 2
    American Physiological Society ; 2000
    In:  Journal of Applied Physiology Vol. 89, No. 4 ( 2000-10-01), p. 1293-1301
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 89, No. 4 ( 2000-10-01), p. 1293-1301
    Abstract: A previous study (Grassi B, Gladden LB, Samaja M, Stary CM, and Hogan MC, J Appl Physiol 85: 1394–1403, 1998) showed that convective O 2 delivery to muscle did not limit O 2 uptake (V˙o 2 ) on-kinetics during transitions from rest to contractions at ∼60% of peakV˙o 2 . The present study aimed to determine whether this finding is also true for transitions involving contractions of higher metabolic intensities.V˙o 2 on-kinetics were determined in isolated canine gastrocnemius muscles in situ ( n = 5) during transitions from rest to 4 min of electrically stimulated isometric tetanic contractions corresponding to the muscle peakV˙o 2 . Two conditions were compared: 1) spontaneous adjustment of muscle blood flow (Q˙) (Control) and 2) pump-perfused Q˙, adjusted ∼15–30 s before contractions at a constant level corresponding to the steady-state value during contractions in Control (Fast O 2 Delivery). In Fast O 2 Delivery, adenosine was infused intra-arterially. Q˙ was measured continuously in the popliteal vein; arterial and popliteal venous O 2 contents were measured at rest and at 5- to 7-s intervals during the transition. Muscle V˙o 2 was determined as Q˙times the arteriovenous blood O 2 content difference. The time to reach 63% of the V˙o 2 difference between resting baseline and steady-state values during contractions was 24.9 ± 1.6 (SE) s in Control and 18.5 ± 1.8 s in Fast O 2 Delivery ( P 〈 0.05). FasterV˙o 2 on-kinetics in Fast O 2 Delivery was associated with an ∼30% reduction in the calculated O 2 deficit and with less muscle fatigue. During transitions involving contractions at peak V˙o 2 , convective O 2 delivery to muscle, together with an inertia of oxidative metabolism, contributes in determining theV˙o 2 on-kinetics.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.2000.89.4.1293
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2000
    detail.hit.zdb_id: 1404365-8
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  • 8
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    Muscle oxygenation and pulmonary gas exchange kinetics during cycling exercise on-transitions in humans
    American Physiological Society ; 2003
    In:  Journal of Applied Physiology Vol. 95, No. 1 ( 2003-07), p. 149-158
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 95, No. 1 ( 2003-07), p. 149-158
    Abstract: Near-infrared spectroscopy (NIRS) was utilized to gain insights into the kinetics of oxidative metabolism during exercise transitions. Ten untrained young men were tested on a cycle ergometer during transitions from unloaded pedaling to 5 min of constant-load exercise below ( 〈 VT) or above ( 〉 VT) the ventilatory threshold. Vastus lateralis oxygenation was determined by NIRS, and pulmonary O 2 uptake ( V̇o 2 ) was determined breath-by-breath. Changes in deoxygenated hemoglobin + myoglobin concentration {Δ[deoxy(Hb + Mb)]} were taken as a muscle oxygenation index. At the transition, Δ[deoxy(Hb + Mb)] was unmodified [time delay (TD)] for 8.9 ± 0.5 s at 〈 VT or 6.4 ± 0.9 s at 〉 VT (both significantly different from 0) and then increased, following a monoexponential function [time constant (τ) = 8.5 ± 0.9 s for 〈 VT and 7.2 ± 0.7 s for 〉 VT]. For 〉 VT a slow component of Δ[deoxy(Hb + Mb)] on-kinetics was observed in 9 of 10 subjects after 75.0 ± 14.0 s of exercise. A significant correlation was described between the mean response time (MRT = TD + τ) of the primary component of Δ[deoxy(Hb + Mb)] on-kinetics and the τ of the primary component of the pulmonary V̇o 2 on-kinetics. The constant muscle oxygenation during the initial phase of the on-transition indicates a tight coupling between increases in O 2 delivery and O 2 utilization. The lack of a drop in muscle oxygenation at the transition suggests adequacy of O 2 availability in relation to needs.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00695.2002
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2003
    detail.hit.zdb_id: 1404365-8
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  • 9
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    Separate and combined effects of a 10-d exposure to hypoxia and inactivity on oxidative function in vivo and mitochondrial respiration ex vivo in humans
    American Physiological Society ; 2016
    In:  Journal of Applied Physiology Vol. 121, No. 1 ( 2016-07-01), p. 154-163
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 121, No. 1 ( 2016-07-01), p. 154-163
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.00832.2015
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2016
    detail.hit.zdb_id: 1404365-8
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  • 10
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    Lack of functional effects of neuromuscular electrical stimulation on skeletal muscle oxidative metabolism in healthy humans
    American Physiological Society ; 2012
    In:  Journal of Applied Physiology Vol. 113, No. 7 ( 2012-10-01), p. 1101-1109
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 113, No. 7 ( 2012-10-01), p. 1101-1109
    Abstract: A recent study has demonstrated that neuromuscular electrical stimulation (NMES) determines, in vitro, a fast-to-slow shift in the metabolic profile of muscle fibers. The aim of the present study was to evaluate if, in the same subjects, these changes would translate, in vivo, into an enhanced skeletal muscle oxidative metabolism. Seven young men were tested (cycle ergometer) during incremental exercises up to voluntary exhaustion and moderate and heavy constant-load exercises (CLE). Measurements were carried out before and after an 8-wk training program by isometric bilateral NMES (quadriceps muscles), which induced an ∼25% increase in maximal isometric force. Breath-by-breath pulmonary O 2 uptake (V̇o 2 ) and vastus lateralis oxygenation indexes (by near-infrared spectroscopy) were determined. Skeletal muscle fractional O 2 extraction was estimated by near-infrared spectroscopy on the basis of changes in concentration of deoxygenated hemoglobin + myoglobin. Values obtained at exhaustion were considered “peak” values. The following functional evaluation variables were unaffected by NMES: peak V̇o 2 ; gas exchange threshold; the V̇o 2 vs. work rate relationship (O 2 cost of cycling); changes in concentration of deoxygenated hemoglobin + myoglobin vs. work rate relationship (related to the matching between O 2 delivery and V̇o 2 ); peak fractional O 2 extraction; V̇o 2 kinetics (during moderate and heavy CLE) and the amplitude of its slow component (during heavy CLE). Thus NMES did not affect several variables of functional evaluation of skeletal muscle oxidative metabolism. Muscle hypertrophy induced by NMES could impair peripheral O 2 diffusion, possibly counterbalancing, in vivo, the fast-to-slow phenotypic changes that were observed in vitro, in a previous work, in the same subjects of the present study.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/japplphysiol.01627.2011
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 2012
    detail.hit.zdb_id: 1404365-8
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    SSG: 31
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