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Weston ME, Armstrong N, Bond B, Tomlinson OW, Williams CA, Barker AR. The Influence of Acute Hypoxia on Oxygen Uptake and Muscle Oxygenation Kinetics During Cycling Exercise in Prepubertal Boys. Pediatr Exerc Sci 2024:1-8. [PMID: 38925533 DOI: 10.1123/pes.2023-0089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Revised: 04/30/2024] [Accepted: 05/05/2024] [Indexed: 06/28/2024]
Abstract
PURPOSE To examine the effect of normobaric hypoxia on pulmonary oxygen uptake (V˙O2) and muscle oxygenation kinetics during incremental and moderate-intensity exercise in children. METHODS Eight prepubertal boys (9-11 y) performed incremental cycle tests to exhaustion in both normoxia and hypoxia (fraction of inspired O2 of 15%) followed by repeat 6-minute transitions of moderate-intensity exercise in each condition over subsequent visits. RESULTS Maximal oxygen uptake (V˙O2max) was reduced in hypoxia compared with normoxia (1.69 [0.20] vs 1.87 [0.26] L·min-1, P = .028), although the gas exchange threshold was not altered in absolute terms (P = .33) or relative to V˙O2max (P = .78). During moderate-intensity exercise, the phase II V˙O2 time constant (τ) was increased in hypoxia (18 [9] vs 24 [8] s, P = .025), with deoxyhemoglobin τ unchanged (17 [8] vs 16 [6], P ≥ .28). CONCLUSIONS In prepubertal boys, hypoxia reduced V˙O2max and slowed V˙O2 phase II kinetics during moderate-intensity exercise, despite unchanged deoxyhemoglobin kinetics. These data suggest an oxygen delivery dependence of V˙O2max and moderate-intensity V˙O2 kinetics under conditions of reduced oxygen availability in prepubertal boys.
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Affiliation(s)
- Max E Weston
- Children's Health and Exercise Research Center, Public Health and Sports Sciences, Faculty of Health and Life Sciences, University of Exeter, Exeter,United Kingdom
- Department of Physiology, School of Medicine, Trinity College Dublin, Dublin,Ireland
| | - Neil Armstrong
- Children's Health and Exercise Research Center, Public Health and Sports Sciences, Faculty of Health and Life Sciences, University of Exeter, Exeter,United Kingdom
| | - Bert Bond
- Children's Health and Exercise Research Center, Public Health and Sports Sciences, Faculty of Health and Life Sciences, University of Exeter, Exeter,United Kingdom
| | - Owen W Tomlinson
- Children's Health and Exercise Research Center, Public Health and Sports Sciences, Faculty of Health and Life Sciences, University of Exeter, Exeter,United Kingdom
| | - Craig A Williams
- Children's Health and Exercise Research Center, Public Health and Sports Sciences, Faculty of Health and Life Sciences, University of Exeter, Exeter,United Kingdom
| | - Alan R Barker
- Children's Health and Exercise Research Center, Public Health and Sports Sciences, Faculty of Health and Life Sciences, University of Exeter, Exeter,United Kingdom
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Hovorka M, Prinz B, Simon D, Zöger M, Rumpl C, Nimmerichter A. Long-Term Alterations in Pulmonary V˙O2 and Muscle Deoxygenation On-Kinetics During Heavy-Intensity Exercise in Competitive Youth Cyclists: A Cohort Study. Pediatr Exerc Sci 2024:1-7. [PMID: 38714302 DOI: 10.1123/pes.2023-0110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Revised: 02/20/2024] [Accepted: 03/12/2024] [Indexed: 05/09/2024]
Abstract
PURPOSE The aim of this investigation was to assess alterations of pulmonary oxygen uptake (V˙O2) and muscle deoxygenation on-kinetics during heavy-intensity cycling in youth cyclists over a period of 15 months. METHODS Eleven cyclists (initial age, 14.3 [1.6] y; peak V˙O2, 62.2 [4.5] mL·min-1·kg-1) visited the laboratory twice on 3 occasions within 15 months. Participants performed an incremental ramp exercise test and a constant workrate test within the heavy-intensity domain during the first visit and second visit, respectively. Subsequently, parameter estimates of the V˙O2 and muscle deoxygenation on-kinetics were determined with mono-exponential models. RESULTS The V˙O2 phase II time constant decreased from occasion 1 (34 [4] s) to occasion 2 (30 [4] s, P = .005) and 3 (28 [4] s, P = .010). However, no significant alteration was observed between occasions 2 and 3 (P = .565). The V˙O2 slow component amplitude either expressed in absolute values (ie, L·min-1) or relative to end exercise V˙O2 (ie, %) showed no significant changes throughout the study (P = .972 and .996). Furthermore, the muscle deoxygenation on-kinetic mean response time showed no significant changes throughout the study (18 [8], 18 [3], and 16 [5] s for occasions 1, 2, and 3, respectively; P = .279). CONCLUSION These results indicate proportional enhancements of local muscle oxygen distribution and utilization, which both contributed to the speeding of the V˙O2 on-kinetics herein.
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Affiliation(s)
- Matthias Hovorka
- Training and Sports Sciences, University of Applied Sciences Wiener Neustadt, Wiener Neustadt,Austria
- Centre for Sport Science and University Sports, University of Vienna, Vienna,Austria
- Doctoral School of Pharmaceutical, Nutritional and Sport Sciences, University of Vienna, Vienna,Austria
| | - Bernhard Prinz
- Training and Sports Sciences, University of Applied Sciences Wiener Neustadt, Wiener Neustadt,Austria
| | - Dieter Simon
- Training and Sports Sciences, University of Applied Sciences Wiener Neustadt, Wiener Neustadt,Austria
| | - Manfred Zöger
- Training and Sports Sciences, University of Applied Sciences Wiener Neustadt, Wiener Neustadt,Austria
| | - Clemens Rumpl
- Training and Sports Sciences, University of Applied Sciences Wiener Neustadt, Wiener Neustadt,Austria
| | - Alfred Nimmerichter
- Training and Sports Sciences, University of Applied Sciences Wiener Neustadt, Wiener Neustadt,Austria
- Centre for Sport Science and University Sports, University of Vienna, Vienna,Austria
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Hovorka M, Prinz B, Simon D, Zöger M, Rumpl C, Nimmerichter A. Longitudinal alterations of pulmonary V.O2 on-kinetics during moderate-intensity exercise in competitive youth cyclists are related to alterations in the balance between microvascular O2 distribution and muscular O2 utilization. Front Sports Act Living 2022; 4:982548. [DOI: 10.3389/fspor.2022.982548] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 10/31/2022] [Indexed: 11/17/2022] Open
Abstract
PurposeThe main purpose of the current study was to investigate the dynamic adjustment of pulmonary oxygen uptake (V.O2) in response to moderate-intensity cycling on three occasions within 15 months in competitive youth cyclists. Furthermore, the muscle Δdeoxy[heme] on-kinetics and the Δdeoxy[heme]-to-V.O2 ratio were modeled to examine possible mechanistic basis regulating pulmonary V.O2 on-kinetics.MethodsEleven cyclists (initial age, 14.3 ± 1.6 y; peak V.O2, 62.2 ± 4.5 mL.min−1.kg−1) with a training history of 2–5 years and a training volume of ~10 h per week participated in this investigation. V.O2 and Δdeoxy[heme] responses during workrate-transitions to moderate-intensity cycling were measured with breath-by-breath spirometry and near-infrared spectroscopy, respectively, and subsequently modeled with mono-exponential models to derive parameter estimates. Additionally, a normalized Δdeoxy[heme]-to-V.O2 ratio was calculated for each participant. One-way repeated-measures ANOVA was used to assess effects of time on the dependent variables of the responses.ResultsThe V.O2 time constant remained unchanged between the first (~24 s) and second visit (~22 s, P > 0.05), whereas it was significantly improved through the third visit (~13 s, P = 0.006–0.013). No significant effects of time were revealed for the parameter estimates of the Δdeoxy[heme] response (P > 0.05). A significant Δdeoxy[heme]-to-V.O2 ratio “overshoot” was evident on the first (1.09 ± 0.10, P = 0.006) and second (1.05 ± 0.09, P = 0.047), though not the third (0.97 ± 0.10, P > 0.05), occasion. These “overshoots” showed strong positive relationships with the V.O2 time constant during the first (r = 0.66, P = 0.028) and second visit (r = 0.76, P = 0.007). Further, strong positive relationships have been observed between the individual changes of the fundamental phase τp and the Δdeoxy[heme]-to-V.O2 ratio “overshoot” from occasion one to two (r = 0.70, P = 0.017), and two to three (r = 0.74, P = 0.009).ConclusionThis suggests that improvements in muscle oxygen provision and utilization capacity both occurred, and each may have contributed to enhancing the dynamic adjustment of the oxidative “machinery” in competitive youth cyclists. Furthermore, it indicates a strong link between an oxygen maldistribution within the tissue of interrogation and the V.O2 time constant.
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Breese BC, Saynor ZL, Barker AR, Armstrong N, Williams CA. Relationship between (non)linear phase II pulmonary oxygen uptake kinetics with skeletal muscle oxygenation and age in 11-15 year olds. Exp Physiol 2019; 104:1929-1941. [PMID: 31512297 DOI: 10.1113/ep087979] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Accepted: 09/09/2019] [Indexed: 12/28/2022]
Abstract
NEW FINDINGS What is the central question of this study? Do the phase II parameters of pulmonary oxygen uptake ( V ̇ O 2 ) kinetics display linear, first-order behaviour in association with alterations in skeletal muscle oxygenation during step cycling of different intensities or when exercise is initiated from an elevated work rate in youths. What is the main finding and its importance? Both linear and non-linear features of phase II V ̇ O 2 kinetics may be determined by alterations in the dynamic balance between microvascular O2 delivery and utilization in 11-15 year olds. The recruitment of higher-order (i.e. type II) muscle fibres during 'work-to-work' cycling might be responsible for modulating V ̇ O 2 kinetics with chronological age. ABSTRACT This study investigated in 19 male youths (mean age: 13.6 ± 1.1 years, range: 11.7-15.7 years) the relationship between pulmonary oxygen uptake ( V ̇ O 2 ) and muscle deoxygenation kinetics during moderate- and very heavy-intensity 'step' cycling initiated from unloaded pedalling (i.e. U → M and U → VH) and moderate to very heavy-intensity step cycling (i.e. M → VH). Pulmonary V ̇ O 2 was measured breath-by-breath along with the tissue oxygenation index (TOI) of the vastus lateralis using near-infrared spectroscopy. There were no significant differences in the phase II time constant ( τ V ̇ O 2 p ) between U → M and U → VH (23 ± 6 vs. 25 ± 7 s; P = 0.36); however, the τ V ̇ O 2 p was slower during M → VH (42 ± 16 s) compared to other conditions (P < 0.001). Quadriceps TOI decreased with a faster (P < 0.01) mean response time (MRT; i.e. time delay + τ) during U → VH (14 ± 2 s) compared to U → M (22 ± 4 s) and M → VH (20 ± 6 s). The difference (Δ) between the τ V ̇ O 2 p and MRT-TOI was greater during U → VH compared to U → M (12 ± 7 vs. 2 ± 7 s, P < 0.001) and during M → VH (23 ± 15 s) compared to other conditions (P < 0.02), suggesting an increased proportional speeding of fractional O2 extraction. The slowing of the τ V ̇ O 2 p during M → VH relative to U → M and U → VH correlated positively with chronological age (r = 0.68 and 0.57, respectively, P < 0.01). In youths, 'work-to-work' transitions slowed microvascular O2 delivery-to-O2 utilization with alterations in phase II V ̇ O 2 dynamics accentuated between the ages of 11 and 15 years.
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Affiliation(s)
- Brynmor C Breese
- School of Biomedical Sciences, Faculty of Medicine and Dentistry, University of Plymouth, Plymouth, UK
| | - Zoe L Saynor
- Department of Sport and Exercise Science, Faculty of Science, University of Portsmouth, Portsmouth, UK
| | - Alan R Barker
- Children's Health and Exercise Research Centre, Sport and Health Sciences, College of Life and Environmental Sciences, University of Exeter, Exeter, UK
| | - Neil Armstrong
- Children's Health and Exercise Research Centre, Sport and Health Sciences, College of Life and Environmental Sciences, University of Exeter, Exeter, UK
| | - Craig A Williams
- Children's Health and Exercise Research Centre, Sport and Health Sciences, College of Life and Environmental Sciences, University of Exeter, Exeter, UK
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Abstract
Pulmonary oxygen uptake ( V˙O2 ) kinetics, which describes the aerobic response to near instantaneous changes in metabolic demand, provides a valuable insight into the control and coordination of oxidative phosphorylation during exercise. Despite their applicability to the highly sporadic habitual physical activity and exercise patterns of children, relatively little is known regarding the influence of internal and external stimuli on the dynamic V˙O2 response. Although insufficient evidence is available during moderate-intensity exercise, an age-related slowing of the phase 2 time constant (τ) and augmentation of the V˙O2 slow component appears to manifest during heavy-intensity exercise, which may be related to changes in the muscle phosphate controllers of oxidative phosphorylation, muscle oxygen delivery and utilization, and/or muscle fiber type recruitment patterns. Similar to findings in adults, aerobic training is associated with a faster phase 2 τ and smaller V˙O2 slow component in youth, independent of age or maturity, indicative of an enhanced oxidative metabolism. However, a lack of longitudinal or intervention-based training studies limits our ability to attribute these changes to training per se. Further, methodologically rigorous studies are required to fully resolve the interaction(s) between age, sex, biological maturity, and external stimuli, such as exercise training and exercise intensity and the dynamic V˙O2 response at the onset and offset of exercise.
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Armstrong N. Top 10 Research Questions Related to Youth Aerobic Fitness. RESEARCH QUARTERLY FOR EXERCISE AND SPORT 2017; 88:130-148. [PMID: 28402178 DOI: 10.1080/02701367.2017.1303298] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Peak oxygen uptake ([Formula: see text]2) is internationally recognized as the criterion measure of youth aerobic fitness, but despite pediatric data being available for almost 80 years, its measurement and interpretation in relation to growth, maturation, and health remain controversial. The trainability of youth aerobic fitness continues to be hotly debated, and causal mechanisms of training-induced changes and their modulation by chronological age, biological maturation, and sex are still to be resolved. The daily physical activity of youth is characterized by intermittent bouts and rapid changes in intensity, but physical activity of the intensity and duration required to determine peak [Formula: see text]2 is rarely (if ever) experienced by most youth. In this context, it may therefore be the transient kinetics of pulmonary [Formula: see text]2 that best reflect youth aerobic fitness. There are remarkably few rigorous studies of youth pulmonary [Formula: see text]2 kinetics at the onset of exercise in different intensity domains, and the influence of chronological age, biological maturation, and sex during step changes in exercise intensity are not confidently documented. Understanding the trainability of the parameters of youth pulmonary [Formula: see text]2 kinetics is primarily based on a few comparative studies of athletes and nonathletes. The underlying mechanisms of changes due to training require further exploration. The aims of the present article are therefore to provide a brief overview of aerobic fitness during growth and maturation, increase awareness of current controversies in its assessment and interpretation, identify gaps in knowledge, raise 10 relevant research questions, and indicate potential areas for future research.
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McNarry MA, Harrison NK, Withers T, Chinnappa N, Lewis MJ. Pulmonary oxygen uptake and muscle deoxygenation kinetics during heavy intensity cycling exercise in patients with emphysema and idiopathic pulmonary fibrosis. BMC Pulm Med 2017; 17:26. [PMID: 28143453 PMCID: PMC5282850 DOI: 10.1186/s12890-017-0364-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Accepted: 01/10/2017] [Indexed: 05/29/2023] Open
Abstract
BACKGROUND Little is known about the mechanistic basis for the exercise intolerance characteristic of patients with respiratory disease; a lack of clearly defined, distinct patient groups limits interpretation of many studies. The purpose of this pilot study was to investigate the pulmonary oxygen uptake ([Formula: see text] O2) response, and its potential determinants, in patients with emphysema and idiopathic pulmonary fibrosis (IPF). METHODS Following a ramp incremental test for the determination of peak [Formula: see text] O2 and the gas exchange threshold, six emphysema (66 ± 7 years; FEV1, 36 ± 16%), five IPF (65 ± 12 years; FEV1, 82 ± 11%) and ten healthy control participants (63 ± 6 years) completed three repeat, heavy-intensity exercise transitions on a cycle ergometer. Throughout each transition, pulmonary gas exchange, heart rate and muscle deoxygenation ([HHb], patients only) were assessed continuously and subsequently modelled using a mono-exponential with ([Formula: see text] O2, [HHb]) or without (HR) a time delay. RESULTS The [Formula: see text] O2 phase II time-constant (τ) did not differ between IPF and emphysema, with both groups significantly slower than healthy controls (Emphysema, 65 ± 11; IPF, 69 ± 7; Control, 31 ± 7 s; P < 0.05). The HR τ was slower in emphysema relative to IPF, with both groups significantly slower than controls (Emphysema, 87 ± 19; IPF, 119 ± 20; Control, 58 ± 11 s; P < 0.05). In contrast, neither the [HHb] τ nor [HHb]:O2 ratio differed between patient groups. CONCLUSIONS The slower [Formula: see text] O2 kinetics in emphysema and IPF may reflect poorer matching of O2 delivery-to-utilisation. Our findings extend our understanding of the exercise dysfunction in patients with respiratory disease and may help to inform the development of appropriately targeted rehabilitation strategies.
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Affiliation(s)
| | - Nicholas K Harrison
- College of Medicine, Swansea University, Swansea, UK.,Respiratory Unit, Morriston Hospital, Swansea, UK
| | - Tom Withers
- A-STEM, College of Engineering, Swansea University, Swansea, UK
| | | | - Michael J Lewis
- A-STEM, College of Engineering, Swansea University, Swansea, UK
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SAYNOR ZOELOUISE, BARKER ALANROBERT, OADES PATRICKJOHN, WILLIAMS CRAIGANTHONY. Impaired Pulmonary V˙O2 Kinetics in Cystic Fibrosis Depend on Exercise Intensity. Med Sci Sports Exerc 2016; 48:2090-2099. [DOI: 10.1249/mss.0000000000001004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Wilcox SL, Broxterman RM, Barstow TJ. Constructing quasi-linear V̇O2 responses from nonlinear parameters. J Appl Physiol (1985) 2015; 120:121-9. [PMID: 26565018 DOI: 10.1152/japplphysiol.00507.2015] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Accepted: 11/08/2015] [Indexed: 11/22/2022] Open
Abstract
Oxygen uptake (V̇O2) kinetics have been shown to be governed by a nonlinear control system across a range of work rates. However, the linearity of the V̇O2 response to ramp incremental exercise would appear to be the result of a linear control system. This apparent contradiction could represent a balancing of changing V̇O2 kinetics parameter values across a range of work rates. To test this, six healthy men completed bouts of ramp incremental exercise at 15, 30, and 60 W/min (15R, 30R, 60R, respectively) and four bouts of an extended-step incremental exercise. V̇O2 parameter values were derived from the step exercise using two monoexponential models: one starting at time zero and encompassing the entire stage (MONO), and the other truncated to the first 5 min and allowing a time delay (5TD). The resulting parameter values were applied to an integrative model to estimate the ramp responses. As work rate increased, gain values increased (P < 0.001 for MONO and 5TD), as did mean response time (or time constant) values (MONO: P < 0.001; 5TD: P = 0.003). Up to maximal V̇O2 (V̇O(2 max)), the gains of the estimated ramp responses from both models were not different from the gains of the actual observed V̇O2 responses for 15R and 30R (15R: 11.3 ± 1.2, 11.7 ± 0.7, 10.9 ± 0.3; 30R: 10.5 ± 0.8, 11.0 ± 0.5, 10.7 ± 0.3 ml O2·min(-1)·W(-1), for actual, MONO, 5TD, respectively) but were significantly greater for 60R (8.7 ± 1.0, 9.9 ± 0.4, 10.3 ± 0.3 ml O2·min(-1)·W(-1) for actual, MONO, 5TD, respectively). Up to 80%V̇O(2 max) gain values were not significantly different for any ramp rate (P > 0.05 for all). We conclude that the apparent linearity of the V̇O2 response to ramp incremental exercise is consequent to a balancing of increasing time constant and gain parameter values.
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Affiliation(s)
- Samuel L Wilcox
- Department of Kinesiology, Kansas State University, Manhattan, Kansas; and
| | - Ryan M Broxterman
- Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas
| | - Thomas J Barstow
- Department of Kinesiology, Kansas State University, Manhattan, Kansas; and
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Armstrong N, Barker AR, McManus AM. Muscle metabolism changes with age and maturation: How do they relate to youth sport performance? Br J Sports Med 2015; 49:860-4. [PMID: 25940635 DOI: 10.1136/bjsports-2014-094491] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/30/2015] [Indexed: 11/04/2022]
Abstract
AIM To provide an evidence-based review of muscle metabolism changes with sex-, age- and maturation with reference to the development of youth sport performance. METHODS A narrative review of data from both invasive and non-invasive studies, from 1970 to 2015, founded on personal databases supported with computer searches of PubMed and Google Scholar. RESULTS Youth sport performance is underpinned by sex-, age- and maturation-related changes in muscle metabolism. Investigations of muscle size, structure and metabolism; substrate utilisation; pulmonary oxygen uptake kinetics; muscle phosphocreatine kinetics; peak anaerobic and aerobic performance; and fatigue resistance; determined using a range of conventional and emerging techniques present a consistent picture. Age-related changes have been consistently documented but specific and independent maturation-related effects on muscle metabolism during exercise have proved elusive to establish. Children are better equipped for exercise supported primarily by oxidative metabolism than by anaerobic metabolism. Sexual dimorphism is apparent in several physiological variables underpinning youth sport performance. As young people mature there is a progressive but asynchronous transition into an adult metabolic profile. CONCLUSIONS The application of recent developments in technology to the laboratory study of the exercising child and adolescent has both supplemented existing knowledge and provided novel insights into developmental exercise physiology. A sound foundation of laboratory-based knowledge has been established but the lack of rigorously designed child-specific and sport-specific testing environments has clouded the interpretation of the data in real life situations. The primary challenge remains the translation of laboratory research into the optimisation of youth sports participation and performance.
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Affiliation(s)
- Neil Armstrong
- Children's Health and Exercise Research Centre, University of Exeter, Exeter, Devon, UK
| | - Alan R Barker
- Children's Health and Exercise Research Centre, University of Exeter, Exeter, Devon, UK
| | - Alison M McManus
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
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Williams CA, Saynor ZL, Tomlinson OW, Barker AR. Cystic fibrosis and physiological responses to exercise. Expert Rev Respir Med 2014; 8:751-62. [DOI: 10.1586/17476348.2014.966693] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Influence of thigh activation on the VO₂ slow component in boys and men. Eur J Appl Physiol 2014; 114:2309-19. [PMID: 25011494 DOI: 10.1007/s00421-014-2941-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Accepted: 06/16/2014] [Indexed: 10/25/2022]
Abstract
PURPOSE During constant work rate exercise above the lactate threshold (LT), the initial rapid phase of pulmonary oxygen uptake (VO₂) kinetics is supplemented by an additional VO₂ slow component (VO₂Sc) which reduces the efficiency of muscular work. The VO₂Sc amplitude has been shown to increase with maturation but the mechanisms are poorly understood. We utilized the transverse relaxation time (T₂) of muscle protons from magnetic resonance imaging (MRI) to test the hypothesis that a lower VO₂ slow component (VO₂Sc) amplitude in children would be associated with a reduced muscle recruitment compared to adults. METHODS Eight boys (mean age 11.4 ± 0.4) and eight men (mean age 25.3 ± 3.3 years) completed repeated step transitions of unloaded-to-very heavy-intensity (U → VH) exercise on a cycle ergometer. MRI scans of the thigh region were acquired at rest and after VH exercise up to the VO₂Sc time delay (ScTD) and after 6 min. T₂ for each of eight muscles was adjusted in relation to cross-sectional area and then summed to provide the area-weighted ΣT₂ as an index of thigh recruitment. RESULTS There were no child/adult differences in the relative VO₂Sc amplitude [Boys 14 ± 7 vs. Men 18 ± 3 %, P = 0.15, effect size (ES) = 0.8] during which the change (∆) in area-weighted ΣT₂ between the ScTD and 6 min was not different between groups (Boys 1.6 ± 1.2 vs. Men 2.3 ± 1.1 ms, P = 0.27, ES = 0.6). A positive and strong correlation was found between the relative VO₂Sc amplitude and the magnitude of the area-weighted ∆ΣT₂ in men (r = 0.92, P = 0.001) but not in boys (r = 0.09, P = 0.84). CONCLUSIONS This study provides evidence to show that progressive muscle recruitment (as inferred from T₂ changes) contributes to the development of the VO₂Sc during intense submaximal exercise independent of age.
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Wüst RCI, McDonald JR, Sun Y, Ferguson BS, Rogatzki MJ, Spires J, Kowalchuk JM, Gladden LB, Rossiter HB. Slowed muscle oxygen uptake kinetics with raised metabolism are not dependent on blood flow or recruitment dynamics. J Physiol 2014; 592:1857-71. [PMID: 24469073 DOI: 10.1113/jphysiol.2013.267476] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Oxygen uptake kinetics (τVO2) are slowed when exercise is initiated from a raised metabolic rate. Whether this reflects the recruitment of muscle fibres differing in oxidative capacity, or slowed blood flow (Q) kinetics is unclear. This study determined τVO2 in canine muscle in situ, with experimental control over muscle activation and Q during contractions initiated from rest and a raised metabolic rate. The gastrocnemius complex of nine anaesthetised, ventilated dogs was isolated and attached to a force transducer. Isometric tetanic contractions (50 Hz; 200 ms duration) via supramaximal sciatic nerve stimulation were used to manipulate metabolic rate: 3 min stimulation at 0.33 Hz (S1), followed by 3 min at 0.67 Hz (S2). Circulation was initially intact (SPON), and subsequently isolated for pump-perfusion (PUMP) above the greatest value in SPON. Muscle VO2 was determined contraction-by-contraction using an ultrasonic flowmeter and venous oximeter, and normalised to tension-time integral (TTI). τVO2/TTI and τQ were less in S1SPON (mean ± s.d.: 13 ± 3 s and 12 ± 4 s, respectively) than in S2SPON (29 ± 19 s and 31 ± 13 s, respectively; P < 0.05). τVO2/TTI was unchanged by pump-perfusion (S1PUMP, 12 ± 4 s; S2PUMP, 24 ± 6 s; P < 0.001) despite increased O2 delivery; at S2 onset, venous O2 saturation was 21 ± 4% and 65 ± 5% in SPON and PUMP, respectively. VO2 kinetics remained slowed when contractions were initiated from a raised metabolic rate despite uniform muscle stimulation and increased O2 delivery. The intracellular mechanism may relate to a falling energy state, approaching saturating ADP concentration, and/or slowed mitochondrial activation; but further study is required. These data add to the evidence that muscle VO2 control is more complex than previously suggested.
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Affiliation(s)
- Rob C I Wüst
- Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W. Carson Street, CDCRC Building, Torrance, CA 90502, USA.
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Influence of prior exercise on VO2 kinetics subsequent exhaustive rowing performance. PLoS One 2014; 9:e84208. [PMID: 24404156 PMCID: PMC3880282 DOI: 10.1371/journal.pone.0084208] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Accepted: 11/12/2013] [Indexed: 11/19/2022] Open
Abstract
Prior exercise has the potential to enhance subsequent performance by accelerating the oxygen uptake (VO2) kinetics. The present study investigated the effects of two different intensities of prior exercise on pulmonary VO2 kinetics and exercise time during subsequent exhaustive rowing exercise. It was hypothesized that in prior heavy, but not prior moderate exercise condition, overall VO2 kinetics would be faster and the VO2 primary amplitude would be higher, leading to longer exercise time at VO2max. Six subjects (mean ± SD; age: 22.9±4.5 yr; height: 181.2±7.1 cm and body mass: 75.5±3.4 kg) completed square-wave transitions to 100% of VO2max from three different conditions: without prior exercise, with prior moderate and heavy exercise. VO2 was measured using a telemetric portable gas analyser (K4b2, Cosmed, Rome, Italy) and the data were modelled using either mono or double exponential fittings. The use of prior moderate exercise resulted in a faster VO2 pulmonary kinetics response (τ1 = 13.41±3.96 s), an improved performance in the time to exhaustion (238.8±50.2 s) and similar blood lactate concentrations ([La−]) values (11.8±1.7 mmol.L−1) compared to the condition without prior exercise (16.0±5.56 s, 215.3±60.1 s and 10.7±1.2 mmol.L−1, for τ1, time sustained at VO2max and [La−], respectively). Performance of prior heavy exercise, although useful in accelerating the VO2 pulmonary kinetics response during a subsequent time to exhaustion exercise (τ1 = 9.18±1.60 s), resulted in a shorter time sustained at VO2max (155.5±46.0 s), while [La−] was similar (13.5±1.7 mmol.L−1) compared to the other two conditions. Although both prior moderate and heavy exercise resulted in a faster pulmonary VO2 kinetics response, only prior moderate exercise lead to improved rowing performance.
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Francescato MP, Cettolo V, Bellio R. Confidence intervals for the parameters estimated from simulated O2 uptake kinetics: effects of different data treatments. Exp Physiol 2013; 99:187-95. [PMID: 24121286 DOI: 10.1113/expphysiol.2013.076208] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The behaviour of pulmonary O2 uptake following a moderate-intensity step exercise increment is usually described by a first brief increase, followed by a second exponential time course reaching the new steady state (phase II). The parameters describing the phase II kinetics are investigated by applying different data treatments to the acquired O2 uptake data to reduce the effects of their noise before running a non-linear regression procedure. The effects of different data treatments (nothing, resampling at various time intervals or averaging of more repetitions) on the precision and/or accuracy of the kinetics parameters estimated by non-linear regression with a simple mono-exponential model were investigated by artificially generating 10(5) simulated responses with average breath duration of 3.5 s. The simulations showed that, whatever the explored data treatment, the average estimated parameters were close to the theoretical ones. Nevertheless, in all the explored conditions, the non-linear regression provided narrower asymptotic confidence intervals than the real ones. In particular, when the responses were resampled at 1 s time intervals, the width of the asymptotic confidence interval for the time constant was 50% of the real one, even after the averaging of more repetitions. The reasons for this discrepancy were investigated further, allowing us to identify some methods to obtain the correct confidence interval of the O2 uptake kinetics parameters. The simplest method to obtain an asymptotic confidence interval close to the real one is to average more responses resampled to a time interval slightly longer than the average breath duration.
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Affiliation(s)
- M P Francescato
- M. P. Francescato: Department of Medical and Biological Sciences, University of Udine, P.le Kolbe 4, 33100 - Udine, Italy.
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Barker AR, Trebilcock E, Breese B, Jones AM, Armstrong N. The effect of priming exercise on O2 uptake kinetics, muscle O2 delivery and utilization, muscle activity, and exercise tolerance in boys. Appl Physiol Nutr Metab 2013; 39:308-17. [PMID: 24552371 DOI: 10.1139/apnm-2013-0174] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study used priming exercise in young boys to investigate (i) how muscle oxygen delivery and oxygen utilization, and muscle activity modulate oxygen uptake kinetics during exercise; and (ii) whether the accelerated oxygen uptake kinetics following priming exercise can improve exercise tolerance. Seven boys that were aged 11.3 ± 1.6 years completed either a single bout (bout 1) or repeated bouts with 6 min of recovery (bout 2) of very heavy-intensity cycling exercise. During the tests oxygen uptake, muscle oxygenation, muscle electrical activity and exercise tolerance were measured. Priming exercise most likely shortened the oxygen uptake mean response time (change, ±90% confidence limits; -8.0 s, ±3.0), possibly increased the phase II oxygen uptake amplitude (0.11 L·min(-1), ±0.09) and very likely reduced the oxygen uptake slow component amplitude (-0.08 L·min(-1), ±0.07). Priming resulted in a likely reduction in integrated electromyography (-24% baseline, ±21% and -25% baseline, ±19) and a very likely reduction in Δ deoxyhaemoglobin/Δoxygen uptake (-0.16, ±0.11 and -0.09, ±0.05) over the phase II and slow component portions of the oxygen uptake response, respectively. A correlation was present between the change in tissue oxygenation index during bout 2 and the change in the phase II (r = -0.72, likely negative) and slow component (r = 0.72, likely positive) oxygen uptake amplitudes following priming exercise, but not for muscle activity. Exercise tolerance was likely reduced (change -177 s, ±180) following priming exercise. The altered phase II and slow component oxygen uptake amplitudes in boys following priming exercise are linked to an improved localised matching of muscle oxygen delivery to oxygen uptake and not muscle electrical activity. Despite more rapid oxygen uptake kinetics following priming exercise, exercise tolerance was not enhanced.
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Affiliation(s)
- Alan R Barker
- Children's Health and Exercise Research Centre, Sport and Health Sciences, University of Exeter, Exeter EX1 2LU, UK
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