Reduced neuromuscular activity and force generation during prolonged cycling

2001 ◽  
Vol 281 (1) ◽  
pp. R187-R196 ◽  
Author(s):  
A. St Clair Gibson ◽  
E. J. Schabort ◽  
T. D. Noakes
Keyword(s):  
Power Output ◽  
High Intensity ◽  
Voluntary Contraction ◽  
Active Muscle ◽  
Mean Power ◽  
Variable Intensity ◽  
Neuromuscular Activity ◽  
Integrated Emg ◽  
The Mean ◽  
Mean Power Output

We examined neuromuscular activity during stochastic (variable intensity) 100-km cycling time trials (TT) and the effect of dietary carbohydrate manipulation. Seven endurance-trained cyclists performed two 100-km TT that included five 1-km and four 4-km high-intensity epochs (HIE) during which power output, electromyogram (EMG), and muscle glycogen data were analyzed. The mean power output of the 4-km HIE decreased significantly throughout the trial from 319 ± 48 W for the first 4-km HIE to 278 ± 39 W for the last 4-km HIE ( P < 0.01). The mean integrated EMG (IEMG) activity during the first 4-km HIE was 16.4 ± 9.8% of the value attained during the pretrial maximal voluntary contraction (MVC). IEMG decreased significantly throughout the trial, reaching 11.1 ± 5.6% during the last 4-km HIE ( P < 0.01). The study establishes that neuromuscular activity in peripheral skeletal muscle falls parallel with reduction in power output during bouts of high-intensity exercise. These changes occurred when <20% of available muscle was recruited and suggest the presence of a central neural governor that reduces the active muscle recruited during prolonged exercise.

scholarly journals An Analysis of Variability in Power Output During Indoor and Outdoor Cycling Time Trials

2019 ◽  
Vol 14 (9) ◽  
pp. 1273-1279 ◽  
Author(s):  
Owen Jeffries ◽  
Mark Waldron ◽  
Stephen D. Patterson ◽  
Brook Galna
Keyword(s):  
Power Output ◽  
Time Trial ◽  
Mean Power ◽  
Portable Power ◽  
Output Variability ◽  
Competitive Cyclists ◽  
The Mean ◽  
Mean Power Output ◽  
Testing Protocols ◽  
Indoor And Outdoor

Purpose: Regulation of power output during cycling encompasses the integration of internal and external demands to maximize performance. However, relatively little is known about variation in power output in response to the external demands of outdoor cycling. The authors compared the mean power output and the magnitude of power-output variability and structure during a 20-min time trial performed indoors and outdoors. Methods: Twenty male competitive cyclists ( 60.4 [7.1] mL·kg−1·min−1) performed 2 randomized maximal 20-min time-trial tests: outdoors at a cycle-specific racing circuit and indoors on a laboratory-based electromagnetically braked training ergometer, 7 d apart. Power output was sampled at 1 Hz and collected on the same bike equipped with a portable power meter in both tests. Results: Twenty-minute time-trial performance indoor (280 [44] W) was not different from outdoor (284 [41] W) (P = .256), showing a strong correlation (r = .94; P < .001). Within-persons SD was greater outdoors (69 [21] W) than indoors (33 [10] W) (P < .001). Increased variability was observed across all frequencies in data from outdoor cycling compared with indoors (P < .001) except for the very slowest frequency bin (<0.0033 Hz, P = .930). Conclusions: The findings indicate a greater magnitude of variability in power output during cycling outdoors. This suggests that constraints imposed by the external environment lead to moderate- and high-frequency fluctuations in power output. Therefore, indoor testing protocols should be designed to reflect the external demands of cycling outdoors.

Variability in Power Output During Cycling in International Olympic-Distance Triathlon

2014 ◽  
Vol 9 (4) ◽  
pp. 732-734 ◽  
Author(s):  
Naroa Etxebarria ◽  
Shaun D’Auria ◽  
Judith M. Anson ◽  
David B. Pyne ◽  
Richard A. Ferguson
Keyword(s):  
Body Mass ◽  
Power Output ◽  
Coefficient Of Variation ◽  
Aerobic Power ◽  
Maximal Aerobic Power ◽  
Mean Power ◽  
Large Power ◽  
Elite Level ◽  
The Mean ◽  
Mean Power Output

Purpose:The patterns of power output in the ~1-h cycle section of Olympic-distance triathlon races are not well documented. Here the authors establish a typical cycling-race profile derived from several International Triathlon Union elite-level draftinglegal triathlon races.Methods:The authors collated 12 different race power profiles from elite male triathletes (N = 5, age 25 ± 5 y, body mass 65.5 ± 5.6 kg; mean ± SD) during 7 international races. Power output was recorded using SRM cranks and analyzed with proprietary software.Results:The mean power output was 252 ± 33 W, or 3.9 ± 0.5 W/kg in relative terms, with a coefficient of variation of 71% ± 13%. Normalized power (power output an athlete could sustain if intensity were maintained constant without any variability) for the entire cycle section was 291 ± 29 W, or 40 ± 13 W higher than the actual mean power output. There were 34 ± 14 peaks of power output above 600 W and ~18% time spent at >100% of maximal aerobic power.Conclusion:Cycling during Olympic-distance triathlon, characterized by frequent and large power variations including repeat supramaximal efforts, equates to a higher workload than cycling at constant power.

scholarly journals The Effect of Beetroot Ingestion on High-Intensity Interval Training: A Systematic Review and Meta-Analysis

Nutrients ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 3674
Author(s):  
Tak Hiong Wong ◽  
Alexiaa Sim ◽  
Stephen F. Burns
Keyword(s):  
Systematic Review ◽  
Power Output ◽  
High Intensity ◽  
Meta Analysis ◽  
Interval Training ◽  
High Intensity Interval Training ◽  
Mean Power ◽  
Nitrate Supplementation ◽  
High Intensity Interval ◽  
Mean Power Output

Dietary nitrate supplementation has shown promising ergogenic effects on endurance exercise. However, at present there is no systematic analysis evaluating the effects of acute or chronic nitrate supplementation on performance measures during high-intensity interval training (HIIT) and sprint interval training (SIT). The main aim of this systematic review and meta-analysis was to evaluate the evidence for supplementation of dietary beetroot—a common source of nitrate—to improve peak and mean power output during HIIT and SIT. A systematic literature search was carried out following PRISMA guidelines and the PICOS framework within the following databases: PubMed, ProQuest, ScienceDirect, and SPORTDiscus. Search terms used were: ((nitrate OR nitrite OR beetroot) AND (HIIT or high intensity or sprint interval or SIT) AND (performance)). A total of 17 studies were included and reviewed independently. Seven studies applied an acute supplementation strategy and ten studies applied chronic supplementation. The standardised mean difference for mean power output showed an overall trivial, non-significant effect in favour of placebo (Hedges’ g = −0.05, 95% CI −0.32 to 0.21, Z = 0.39, p = 0.69). The standardised mean difference for peak power output showed a trivial, non-significant effect in favour of the beetroot juice intervention (Hedges’ g = 0.08, 95% CI -0.14 to 0.30, Z = 0.72, p = 0.47). The present meta-analysis showed trivial statistical heterogeneity in power output, but the variation in the exercise protocols, nitrate dosage, type of beetroot products, supplementation strategy, and duration among studies restricted a firm conclusion of the effect of beetroot supplementation on HIIT performance. Our findings suggest that beetroot supplementation offers no significant improvement to peak or mean power output during HIIT or SIT. Future research could further examine the ergogenic potential by optimising the beetroot supplementation strategy in terms of dosage, timing, and type of beetroot product. The potential combined effect of other ingredients in the beetroot products should not be undermined. Finally, a chronic supplementation protocol with a higher beetroot dosage (>12.9 mmol/day for 6 days) is recommended for future HIIT and SIT study.

Measuring the Effect of Vegetated Roofs on the Performance of Photovoltaic Panels in a Combined System

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Hamid Ogaili ◽  
David J. Sailor
Keyword(s):  
Power Output ◽  
Green Roof ◽  
Transfer Coefficients ◽  
Combined System ◽  
Mean Power ◽  
Black And White ◽  
Heat Transfer Coefficients ◽  
Vegetated Roofs ◽  
The Mean ◽  
Mean Power Output

Experiments were conducted in summer using two identical photovoltaic (PV) panels at two heights using three roofing types: white, black, and green (vegetated). For experiments at an 18 cm height, the mean power output of the PV-green roof system was 1.2% and 0.8% higher than the PV-black and PV-white roofs, respectively. At a 24 cm height, the benefit of the green roof was slightly diminished with power output for the PV above a green roof being 1.0% and 0.7% higher than the black and white roof experiments, respectively. These results were consistent with measured variations in mean panel surface temperatures; the green roof systems were generally cooler by 1.5–3 °C. A unique aspect of this research is the investigation into the effect of vegetation on the convective cooling of the PV panels. Panel heat transfer coefficients for the PV-green roof were 10–20% higher than for the white and black roof configurations, suggesting a mixing benefit associated with the roughness of the plant canopy. While the best PV performance was obtained by locating PV above a green roof, the relative benefits diminish with distance between the PV and the roof.

scholarly journals Eccentric-concentric Ratio: A Key Factor for Defining Strength Training in Soccer

2019 ◽  
Vol 40 (12) ◽  
pp. 796-802 ◽  
Author(s):  
F. Javier Nuñez ◽  
Moisés de Hoyo ◽  
Alejandro Muñoz López ◽  
Borja Sañudo ◽  
Carlos Otero-Esquina ◽  
...  
Keyword(s):  
Strength Training ◽  
Power Output ◽  
Soccer Players ◽  
Control Group ◽  
Mean Power ◽  
Key Factor ◽  
The Mean ◽  
And Performance ◽  
Mean Power Output ◽  
Experimental Group

AbstractThe aims of this study were to analyse the effect of chronic strength training over concentric power (CON), eccentric power (ECC), ECC/CON ratio, and 20 m linear sprint performance in elite young soccer players. Twenty young elite Spanish soccer players were assigned to an experimental group (CPG) which performed a front-step exercise using a conical pulley, 2–3 sets of 6 repetitions each leg, during 9 weeks (CPG, n=10) in addition to its usual strength training, or to a control group (CG, n=10). The improvements in the ECC mean power (36%, ES=1.61), and ECC / CON ratio (17%, ES=1.77) were substantially greater in the CPG than in the CG while the CON mean power (16%, ES=0.83) was substantially greater in the CG than in the CPG. The sprinting time for 10 m (2.8%, ES=0.78) and the 10 m flying time between 10–20 m (1.72%, ES=0.41) were substantially enhanced in CPG and CG respectively. To be efficient when defining a functional strength training and performance increments using an inertial device, the mean power output need to be measured during the CON and ECC phases and an analysis of the ECC / CON ratio should be included.

No Improvement of Repeated-Sprint Performance With Dietary Nitrate

2014 ◽  
Vol 9 (5) ◽  
pp. 845-850 ◽  
Author(s):  
Kristy Martin ◽  
Disa Smee ◽  
Kevin G. Thompson ◽  
Ben Rattray
Keyword(s):  
Power Output ◽  
High Intensity ◽  
Cycle Ergometer ◽  
Sprint Performance ◽  
Mean Power ◽  
Double Blind ◽  
Dietary Nitrate ◽  
Repeated Sprint ◽  
Nitrate Supplementation ◽  
Mean Power Output

Purpose:Nitrate supplementation improves endurance exercise and single bouts of high-intensity activity, but its effect on repeated sprints is unclear. This study is the first to investigate the effects of acute dietary nitrate supplementation during a high-intensity intermittent-sprint test to exhaustion.Methods:Team-sport athletes (9 male, age 22.3 ± 2.1 y, VO2max 57.4 ± 8.5 mL · kg−1 · min−1; 7 female, age 20.7 ± 1.3 y, VO2max 47.2 ± 8.5 mL · kg−1 · min−1) were assigned to a double-blind, randomized, crossover design. Participants consumed 70 mL of concentrated beetroot juice containing a minimum of 0.3 g of nitrate (NT) or 70 mL of placebo (PL) 2 h before a repeated-sprint protocol involving repeated 8-s sprints with 30-s recovery on a cycle ergometer to exhaustion.Results:Fewer sprints (NT = 13 ± 5 vs PL = 15 ± 6, P = .005, d = 0.41) and less total work (NT = 49.2 ± 24.2 kJ vs PL = 57.8 ± 34.0 kJ, P = .027, d = 0.3) were completed in NT relative to PL. However there was no difference in overall mean power output or the mean power output for each individual 8-s sprint.Conclusions:These findings suggest that dietary nitrate is not beneficial for improving repeated-sprint performance, at least when such sprints are near-maximal and frequent in nature. The lack of an effect of nitrate at near-maximal oxygen uptake supports the suggestion that at greater exercise intensities nitrate does not have an ergogenic effect.

scholarly journals Functional Threshold Power in Cyclists: Validity of the Concept and Physiological Responses

2018 ◽  
Vol 39 (10) ◽  
pp. 737-742 ◽  
Author(s):  
Fernando Borszcz ◽  
Artur Tramontin ◽  
Arthur Bossi ◽  
Lorival Carminatti ◽  
Vitor Costa
Keyword(s):  
Power Output ◽  
Time Trial ◽  
Threshold Power ◽  
Time To Exhaustion ◽  
Mean Power ◽  
Incremental Test ◽  
Individual Anaerobic Threshold ◽  
The Mean ◽  
The Individual ◽  
Mean Power Output

AbstractFunctional threshold power is defined as the highest power output a cyclist can maintain in a quasi-steady state for approximately 60 min (FTP60). In order to improve practicality for regular evaluations, FTP60 could theoretically be determined as 95% of the mean power output in a 20-min time trial (FTP20). This study tested this assumption and the validity of FTP20 and FTP60 against the individual anaerobic threshold (IAT). Twenty-three trained male cyclists performed an incremental test to exhaustion, 20- and 60-min time trials, and a time to exhaustion at FTP20. Power output, heart rate and oxygen uptake representing FTP20, FTP60 and IAT were not different (p>0.05), and large to very large correlations were found (r=0.61 to 0.88). Bland-Altman plots between FTP20, FTP60 and IAT showed small bias (–1 to –5 W), but large limits of agreement ([–40 to 32 W] to [–62 to 60 W]). Time to exhaustion at FTP20 was 50.9±15.7 min. In conclusion, FTP20 and FTP60 should not be used interchangeably on an individual basis and their validity against IAT should be interpreted with caution.

scholarly journals Effects of Acute Hypoxia on Lactate Thresholds and High-Intensity Endurance Performance—A Pilot Study

2021 ◽  
Vol 18 (14) ◽  
pp. 7573
Author(s):  
Martin Faulhaber ◽  
Katharina Gröbner ◽  
Linda Rausch ◽  
Hannes Gatterer ◽  
Verena Menz
Keyword(s):  
Power Output ◽  
High Intensity ◽  
Acute Hypoxia ◽  
Endurance Performance ◽  
Cycle Ergometer ◽  
Normobaric Hypoxia ◽  
Simulated Altitude ◽  
Mean Power ◽  
Mean Power Output ◽  
Induced Changes

The present project compared acute hypoxia-induced changes in lactate thresholds (methods according to Mader, Dickhuth and Cheng) with changes in high-intensity endurance performance. Six healthy and well-trained volunteers conducted graded cycle ergometer tests in normoxia and in acute normobaric hypoxia (simulated altitude 3000 m) to determine power output at three lactate thresholds (PMader, PDickhuth, PCheng). Subsequently, participants performed two maximal 30-min cycling time trials in normoxia (test 1 for habituation) and one in normobaric hypoxia to determine mean power output (Pmean). PMader, PDickhuth and PCheng decreased significantly from normoxia to hypoxia by 18.9 ± 9.6%, 18.4 ± 7.3%, and 11.5 ± 6.0%, whereas Pmean decreased by only 8.3 ± 1.6%. Correlation analyses revealed strong and significant correlations between Pmean and PMader (r = 0.935), PDickhuth (r = 0.931) and PCheng (r = 0.977) in normoxia and partly weaker significant correlations between Pmean and PMader (r = 0.941), PDickhuth (r = 0.869) and PCheng (r = 0.887) in hypoxia. PMader and PCheng did not significantly differ from Pmean (p = 0.867 and p = 0.784) in normoxia, whereas this was only the case for PCheng (p = 0.284) in hypoxia. Although investigated in a small and select sample, the results suggest a cautious application of lactate thresholds for exercise intensity prescription in hypoxia.

Carbohydrate Drink Use During 30 Minutes of Variable-Intensity Exercise Has No Effect on Exercise Performance in Premenarchal Girls

2021 ◽  
Vol 33 (2) ◽  
pp. 65-69
Author(s):  
C. Eric Heidorn ◽  
Brandon J. Dykstra ◽  
Cori A. Conner ◽  
Anthony D. Mahon
Keyword(s):  
Peak Power ◽  
Perceived Exertion ◽  
Rating Of Perceived Exertion ◽  
Fatigue Index ◽  
Mean Power ◽  
Variable Intensity ◽  
Performance Effects ◽  
Power Peak ◽  
The Mean ◽  
And Performance

Purpose: This study examined the physiological, perceptual, and performance effects of a 6% carbohydrate (CHO) drink during variable-intensity exercise (VIE) and a postexercise test in premenarchal girls. Methods: A total of 10 girls (10.4 [0.7] y) participated in the study. VO2peak was assessed, and the girls were familiarized with VIE and performance during the first visit. The trial order (CHO and placebo) was randomly assigned for subsequent visits. The drinks were given before VIE bouts and 1-minute performance (9 mL/kg total). Two 15-minute bouts of VIE were completed (10 repeated sequences of 20%, 55%, and 95% power at VO2peak and maximal sprints) before a 1-minute performance sprint. Results: The mean power, peak power, heart rate (HR), %HRpeak, and rating of perceived exertion during VIE did not differ between trials. However, the peak power decreased, and the rating of perceived exertion increased from the first to the second bout. During the 1-minute performance, there were no differences between the trial (CHO vs placebo) for HR (190 [9] vs 189 [9] bpm), %HRpeak (97.0% [3.2%] vs 96.6% [3.0%]), rating of perceived exertion (7.8 [2.3] vs 8.1 [1.9]), peak power (238 [70] vs 235 [60] W), fatigue index (54.7% [10.0%] vs 55.9% [12.8%]), or total work (9.4 [2.6] vs 9.4 [2.1] kJ). Conclusion: CHO supplementation did not alter physiological, perceptual, or performance responses during 30 minutes of VIE or postexercise sprint performance in premenarchal girls.

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