12 results on '"Jenkins, David G."'
Search Results
2. Relationship between plasma lactate parameters and muscle characteristics in female cyclists
- Author
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Bishop, David, Jenkins, David G., McEniery, Michael, and Carey, Michael F.
- Subjects
Lactates -- Physiological aspects ,Cyclists -- Physiological aspects ,Muscles -- Physiological aspects ,Exercise -- Physiological aspects ,Health ,Sports and fitness - Abstract
This study investigates the relationship between plasma lactate levels, muscle fiber characteristics, and endurance performance in female cyclists. Results indicate that a type of muscle fiber that impairs performance may result from increased production or decreased removal of lactate in larger, glycolytic muscle fibers.
- Published
- 2000
3. The effects of strength training on endurance performance and muscle characteristics
- Author
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Bishop, David, Jenkins, David G., MacKinnon, Laurel T., McEniery, Michael, and Carey, Michael F.
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Women's fitness -- Physiological aspects ,Muscles -- Physiological aspects ,Cyclists -- Physiological aspects ,Health ,Sports and fitness - Abstract
Research remains inconclusive regarding benefits of strength training for female elite cyclists. Cyclists who underwent resistance training for the lower body and legs demonstrated improved repetition maximums for squatting exercises, but no significant benefits were noted for their average power output, peak oxygen consumption, lactate threshold or muscle fiber characteristics.
- Published
- 1999
4. Velocity-specific fatigue: quantifying fatigue during variable velocity cycling
- Author
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Gardner, A. Scott, Martin, David T., Jenkins, David G., Dyer, Iain, Van Eiden, Jan, Barras, Martin, and Martin, James C.
- Subjects
Fatigue -- Diagnosis ,Cyclists -- Health aspects ,Health ,Sports and fitness - Abstract
The net fatigue index and work deficit precisely quantify fatigue during variable velocity cycling. The measurement of fatigue may improve evaluation of training status, gear ratio selection, and fatigue resistance.
- Published
- 2009
5. Oxidative stress in half and full Ironman triathletes
- Author
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Knez, Wade L., Jenkins, David G., and Coombes, Jeff S.
- Subjects
Triathlon -- Health aspects ,Oxidative stress -- Health aspects ,Exercise -- Risk factors ,Exercise -- Health aspects ,Health ,Sports and fitness - Abstract
A study was conducted to examine the dose-response relationship of erythrocyte antioxidant enzyme activity and plasma oxidative stress in ultraendurance athletes training for and competing in half and full Ironman triathlons. The findings show that high-volume ultraendurance activity produces a significant decrease in resting malondialdehyde (MDA) concentration with athletes involved in full Ironman triathon training.
- Published
- 2007
6. Interval training program optimization in highly trained endurance cyclists
- Author
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Laursen, Paul B., Shing, Cecilia M., Peake, Jonathan M., Coombes, Jeff S., and Jenkins, David G.
- Subjects
Exercise -- Health aspects ,Exercise -- Research ,Cyclists -- Health aspects ,Cyclists -- Research ,Endurance sports -- Health aspects ,Endurance sports -- Research ,Health ,Sports and fitness - Abstract
The influence of three different high-intensity training (HIT) regimens on endurance performance in highly trained endurance athletes is examined. The results show that HIT performed at intensities of Pmax and durations of 60% of Tmax is an effective means for enhancing 40-km time trial performance, peak power output in highly trained cyclists.
- Published
- 2002
7. Immunomodulatory Function of Interleukin-15 and Its Role in Exercise, Immunotherapy, and Cancer Outcomes.
- Author
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Farley MJ, Bartlett DB, Skinner TL, Schaumberg MA, and Jenkins DG
- Subjects
- Humans, Exercise physiology, Muscle, Skeletal physiology, Immunotherapy, Immunomodulation, Interleukin-15 physiology, Neoplasms therapy
- Abstract
Exercise has been shown to improve physical and psychosocial outcomes for people across the cancer care continuum. A proposed mechanism underpinning the relationship between exercise and cancer outcomes is exercise-induced immunomodulation via secretion of anti-inflammatory myokines from skeletal muscle tissue. Myokines have the potential to impair cancer growth through modulation of natural killer (NK) cells and CD8+ T cells while improving the effectiveness of cancer therapies. Interleukin-15 (IL-15), one of the most abundant myokines found in skeletal muscle, has a key immunoregulatory role in supporting the proliferation and maturation of T cells and NK cells, which have a key role in the host's immune response to cancer. Furthermore, IL-15 is being explored clinically as an immunotherapy agent with doses similar to the IL-15 concentrations released by skeletal muscle during exercise. Here we review the role of IL-15 within the immune system, examine how IL-15 is produced as a myokine during exercise, and how it may improve outcomes for people with cancer, specifically as an adjuvant or neoadjuvant to immunotherapy. We summarize the available evidence showing changes in IL-15 in response to both acute exercise and training, and the results are inconsistent; higher quality research is needed to advance the understanding of how exercise-mediated increases in IL-15 potentially benefit those who are being treated for, or who have had, cancer., (Copyright © 2022 by the American College of Sports Medicine.)
- Published
- 2023
- Full Text
- View/download PDF
8. Oral Contraceptive Use Dampens Physiological Adaptations to Sprint Interval Training.
- Author
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Schaumberg MA, Jenkins DG, Janse DE Jonge XA, Emmerton LM, and Skinner TL
- Subjects
- Adult, Cardiac Output physiology, Female, Humans, Menstruation physiology, Oxygen Consumption physiology, Perception, Physical Exertion physiology, Respiration, Stroke Volume physiology, Young Adult, Adaptation, Physiological, Athletic Performance physiology, Contraceptives, Oral administration & dosage, High-Intensity Interval Training
- Abstract
Purpose: Oral contraceptive (OC) use reduces peak aerobic capacity (V˙O2peak); however, whether it also influences adaptations to training has yet to be determined. This study aimed to examine the influence of OC use on peak performance (peak power output [PPO]) and physiological adaptations (V˙O2peak and peak cardiac output [Q˙peak]) after sprint interval training (SIT) in recreationally active women., Methods: Women taking an OC (n = 25) or experiencing natural regular menstrual cycles (MC; n = 16) completed an incremental exercise test to assess V˙O2peak, PPO, and Q˙peak before, immediately after, and 4 wk after 12 sessions of SIT. The SIT consisted ten 1-min efforts at 100% to 120% PPO in a 1:2 work-rest ratio., Results: Though V˙O2peak increased in both groups after SIT (both P < 0.001), the MC group showed greater improvement (OC, +8.5%; MC, +13.0%; P = 0.010). Similarly, Q˙peak increased in both groups, with greater improvement in the MC group (OC, +4.0%; MC, +16.1%; P = 0.013). PPO increased in both groups (OC, +13.1%; MC, +13.8%; NS). All parameters decreased 4 wk after SIT cessation, but remained elevated from pretraining levels; the OC group showed more sustained training effects in V˙O2peak (OC, -4.0%; MC, -7.7%; P = 0.010)., Conclusion: SIT improved peak exercise responses in recreationally active women. However, OC use dampened V˙O2peak and Q˙peak adaptation. A follow-up period indicated that OC users had spared V˙O2peak adaptations, suggesting that OC use may influence the time course of physiological training adaptations. Therefore, OC use should be verified, controlled for, and considered when interpreting physiological adaptations to exercise training in women.
- Published
- 2017
- Full Text
- View/download PDF
9. Lower Integrated Muscle Protein Synthesis in Masters Compared with Younger Athletes.
- Author
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Doering TM, Jenkins DG, Reaburn PR, Borges NR, Hohmann E, and Phillips SM
- Subjects
- Adult, Athletes, Exercise Test, Humans, Middle Aged, Muscle, Skeletal physiology, Recovery of Function, Age Factors, Bicycling physiology, Muscle Proteins biosynthesis, Running physiology
- Abstract
Purpose: The objective of this study is to compare the integrated muscle protein synthesis (MPS) rates of masters and younger triathletes over three consecutive days of intense endurance training. Recovery of cycling performance, after muscle-damaging running, was also compared between groups., Methods: Five masters (age, 53 ± 2 yr; V˙O2max, 55.7 ± 6.9 mL·kg·min) and six younger (age, 27 ± 2 yr; V˙O2max, 62.3 ± 1.5 mL·kg·min) trained triathletes volunteered for the study. Baseline skeletal muscle and saliva were initially sampled, after which a 150-mL bolus of deuterium oxide (70%) was consumed. Participants then completed a 30-min downhill run; three 20-km cycling time trials (TT) were completed 10, 24, and 48 h after the run. Saliva was collected each morning, and skeletal muscle was again sampled 72 h after the run; both were used for MPS analysis. Diet was controlled throughout the study., Results: Over 3 d, masters triathletes showed a significantly lower myofibrillar fractional synthetic rate (1.49% ± 0.12%·d) compared with the younger (1.70% ± 0.09%·d) triathletes (P = 0.009, d = 1.98). There was also a trend for masters triathletes to produce a slower cycle TT (-3.0%, d = 0.46) than younger triathletes (-1.4%, d = 0.29) at 10 h postrun in comparison with the baseline performance. The between-group comparison of change was moderate (d = 0.51), suggesting slower acute recovery among masters triathletes., Conclusions: The present data show lower MPS rates in well-trained masters triathletes over 3 d of training, and this likely contributes to poorer muscle protein repair and remodeling. Furthermore, acute recovery of cycle TT performance tended to be poorer in the masters triathletes.
- Published
- 2016
- Full Text
- View/download PDF
10. Energy expenditure of constant- and variable-intensity cycling: power meter estimates.
- Author
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Haakonssen EC, Martin DT, Burke LM, and Jenkins DG
- Subjects
- Adult, Calorimetry, Female, Humans, Oxygen Consumption, Pulmonary Ventilation, Young Adult, Bicycling physiology, Energy Metabolism physiology, Exercise Test instrumentation
- Abstract
Purpose: The objective of this study is to compare the effects of constant- and variable-intensity cycling on gross efficiency (GE) and to compare estimates of energy expenditure (EE) made using indirect calorimetry (CAL) with estimates derived from commercially available power meters., Methods: Nine national team female road cyclists completed a GE test (GEtest = 4 min at approximately 45%, approximately 55%, approximately 65%, and approximately 75% maximal aerobic power (MAP)) before and after 10.5 min of either constant- (CON)- or variable- (VAR)-intensity cycling averaging approximately 55% MAP. GE measured before, after, and during CON and VAR cycling was compared. Total EE (kJ) for 10.5 min of VAR cycling was estimated using indirect CAL and compared with estimates on the basis of mechanical power [Schoberer Rad Messtechnik (SRM)] using the group mean GE, each athlete's mean GE, and each athlete's power to GE regression., Results: There was no effect of VAR on GEtests (P = 0.74). GE reduced from 19.1% ± 0.4% (mean ± SE) during the pretrial GEtests to 18.7% ± 0.4% during the posttrial GEtests (P < 0.05) in both conditions. Differences in GE (mean ± SD) measured during CON (18.4% ± 1.6%) and VAR cycling (18.6% ± 1.1%) were trivial (P = 0.28). SRM-based estimates of EE were most accurate when using individual athlete's power GE regression using Pre- and Post-VAR GEtest data combined (Δ(Equation is included in full-text article.)(%) ± 90% CI, 0.3 ± 0.8; R 0.98, P <0.001). Group mean estimates were within approximately 1% of CAL, although individual errors were approximately 11%., Conclusion: Findings support the use of calibrated power meters for estimating cycling EE. For trained female road cyclists, total mechanical work (kJ) multiplied by 5.3 (GE = 19%) provides a valid estimation of total EE during variable-intensity cycling <75% MAP, although determining each athlete's GE improves accuracy greatly.
- Published
- 2013
- Full Text
- View/download PDF
11. Pseudoephedrine and preexercise feeding: influence on performance.
- Author
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Pritchard-Peschek KR, Osborne MA, Slater GJ, Taaffe DR, and Jenkins DG
- Subjects
- Administration, Oral, Adult, Analysis of Variance, Athletes, Doping in Sports prevention & control, Exercise Test, Healthy Volunteers, Humans, Male, Performance-Enhancing Substances administration & dosage, Performance-Enhancing Substances blood, Performance-Enhancing Substances urine, Pseudoephedrine administration & dosage, Pseudoephedrine blood, Pseudoephedrine urine, Substance Abuse Detection standards, Time Factors, Athletic Performance, Bicycling physiology, Dietary Carbohydrates administration & dosage, Meals, Performance-Enhancing Substances pharmacokinetics, Pseudoephedrine pharmacokinetics
- Abstract
Purpose: This study examined the influence of preexercise food intake on plasma pseudoephedrine (PSE) concentrations and subsequent high-intensity exercise. In addition, urinary PSE concentrations were measured under the same conditions and compared with the present threshold of the World Anti-Doping Agency (WADA)., Methods: Ten highly trained male cyclists and triathletes (age = 30.6 ± 6.6 yr, body mass [BM] = 72.9 ± 5.1 kg, and V˙O2max = 64.8 ± 4.5 mL·kg·min; mean ± SD) undertook four cycling time trials (TT), each requiring the completion of a set amount of work (7 kJ·kg BM) in the shortest possible time. Participants were randomized into a fed or nonfed condition and orally ingested 2.8 mg·kg BM of PSE or a placebo (PLA) 90 min before exercise; in the fed trials, they consumed a meal providing 1.5 g·kg BM of CHO. Venous blood was sampled at 30, 50, and 70 min and pre-warm-up and postexercise for the analysis of plasma PSE and catecholamine concentrations, and urine was also collected for the analysis of PSE concentration., Results: Independent of the preexercise meal, 2.8 mg·kg BM of PSE did not significantly improve cycling TT performance. The fed trials resulted in lower plasma PSE concentrations at all time points compared with the nonfed trials. Both plasma epinephrine and blood lactate concentrations were higher in the PSE compared with the PLA trials, and preexercise and postexercise urinary PSE concentrations were significantly higher than the threshold (150 μg·mL) used by WADA to determine illicit PSE use., Conclusion: Irrespective of the preexercise meal, cycling TT performance of approximately 30 min was not improved after PSE supplementation. Furthermore, 2.8 mg·kg BM of PSE taken 90 min before exercise, with or without food, resulted in urinary PSE concentrations exceeding the present WADA threshold.
- Published
- 2013
- Full Text
- View/download PDF
12. Dose response of caffeine on 2000-m rowing performance.
- Author
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Skinner TL, Jenkins DG, Coombes JS, Taaffe DR, and Leveritt MD
- Subjects
- Caffeine administration & dosage, Caffeine blood, Cross-Over Studies, Dose-Response Relationship, Drug, Double-Blind Method, Humans, Male, Queensland, Ships, Young Adult, Athletic Performance, Caffeine pharmacology, Physical Exertion drug effects
- Abstract
Purpose: To determine whether a dose-response relationship exists between caffeine and 2000-m rowing performance., Methods: In this randomized, placebo-controlled, double-blind crossover study, 10 competitive male rowers (mean +/- SD: age = 20.6 +/- 1.4 yr, body mass = 87.7 +/- 10.5 kg, height = 186.8 +/- 6.8 cm, (.)VO2peak = 5.1 +/- 0.6 L x min(-1)) consumed 2, 4, or 6 mg x kg(-1) caffeine or a placebo 60 min before completing a 2000-m time trial on a rowing ergometer. The trials were preceded by a 24-h standardized diet (including a light preexercise meal of 2 g x kg(-1) CHO), and subjects were tested preexercise for hydration, caffeine abstinence, and blood glucose concentrations., Results: Time trial performance was not significantly different across the three caffeine doses or placebo (P = 0.249). After the three caffeine trials, postexercise plasma glucose and lactate concentrations were higher compared with the placebo trial (P < 0.05). Plasma caffeine concentrations after 60 min of ingestion were lower than the values reported previously by others following the same dose, and there was considerable interindividual variation in plasma caffeine concentrations in response to the various caffeine doses., Conclusions: The large interindividual response to the caffeine doses suggests that individual characteristics need to be considered when administering caffeine for performance enhancement. In addition, preexercise feeding may significantly affect plasma caffeine concentrations and the potential for caffeine to improve performance.
- Published
- 2010
- Full Text
- View/download PDF
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