External Power Output Research Articles

Thermoelectric generator efficiency: An experimental and computational approach to analysing thermoelectric generator performance

TEGs are devices that convert heat directly into electricity through the Seebeck effect, offering a promising solution for waste heat recovery in various industries. In this research, COMSOL Multiphysics 6.0 was used to conduct a comprehensive 3-dimensional computational study of TEGs. Integrating thermal and electrical models in COMSOL facilitates a detailed understanding of the thermoelectric phenomenon. Applying six distinct temperature gradients, temperature and electrical distribution, power output, and efficiency of the TEG was thoroughly analysed. Experimental validation confirms strong agreement between simulation and experimental data, emphasizing accuracy. The average efficiency for the TEG at 1 Ω load is 3.12 %, increasing to 3.62 % for a 2 Ω load. The relative error between the computational model and the experimental model was 5 % for open circuit, 12.56 % for closed circuit at 1 Ω, and 12.14 % for closed circuit at 2 Ω, affirming the accuracy of the computational approach. Therefore, the computational model is validated by experimental results.Moreover, the findings highlight the relationship between external load resistance and power output, revealing that the maximum output power was achieved when the external load resistance matched the internal load resistance at 2 Ω. This work also significantly contributes to advancing the computational modelling of TEGs, validated through rigorous experimental analysis.

Research on modeling and control strategy of zero-carbon hybrid power system based on the ammonia-hydrogen engine

In the context of carbon neutrality, high efficiency, low carbon, and zero environmental impact have become an essential development direction of internal combustion engines (ICEs). Hydrogen energy has the advantage of having a high calorific value. It also has zero carbon emissions and is considered one of the significant alternative fuels for ICEs. Moreover, ammonia has a high octane number and has an anti-knock effect, which facilitates the mitigation of knock in hydrogen ICEs and potentially mitigates the negative impact of knock on engine volume power. Scholars have carried out some explorations on ammonia-hydrogen ICEs (AHICE), which have been applied in marine power systems. It is anticipated that AHICE will become one of the most significant development directions in the field of vehicle power systems in the future. However, there are still some problems with using AHICEs in passenger cars. The proposed work presented a zero-carbon hybrid power system based on an AHICE. Specifically, the external characteristics curve and power output boundary were obtained by bench experiments of the ICE under wide open throttle (WOT) conditions and diverse engine speeds and λ. Indeed, a hybrid system model consisting of an AHICE and a power battery was built where the AHICE was used to respond to the demanded power and the power battery was used to provide additional power and store the electrical energy converted from braking. Incidentally, an engine control strategy was developed to expand the knock limit and power boundary by dynamically adjusting the ammonia-hydrogen volume ratio. Finally, a hybrid power system simulation model was established based on MATLAB/Simulink. The CLTC-P and WLTC simulation results demonstrated that the zero-carbon hybrid system which comprised AHICE and power battery can work in the high efficiency area. The AHICE demonstrates lower fuel consumption while satisfying power requirements. This work provides a promising route to zero-carbon hybrid technology for the passenger car industry facing the challenge of carbon neutrality.

Overview of interpretive modelling of fusion performance in JET DTE2 discharges with TRANSP

In the paper we present an overview of interpretive modelling of a database of JET-ILW 2021 D-T discharges using the TRANSP code. The main aim is to assess our capability of computationally reproducing the fusion performance of various D-T plasma scenarios using different external heating and D-T mixtures, and to understand the performance driving mechanisms. We find that interpretive simulations confirm a general power-law relationship between increasing external heating power and fusion output, which is supported by absolutely calibrated neutron yield measurements. A comparison of measured and computed D-T neutron rates shows that the calculations’ discrepancy depends on the absolute neutron yield. The calculations are found to agree well with measurements for higher performing discharges with external heating power above ∼20 , while low-neutron shots display an average discrepancy of around +40% compared to measured neutron yields. A similar trend is found for the ratio between thermal and beam-target fusion, where larger discrepancies are seen in shots with dominant beam-driven performance. We compare the observations to studies of JET-ILW D discharges, to find that on average the fusion performance is well modelled over a range of heating power, although an increased unsystematic deviation for lower-performing shots is observed. The ratio between thermal and beam-induced D-T fusion is found to be increasing weakly with growing external heating power, with a maximum value of 1 achieved in a baseline scenario experiment. An evaluation of the fusion power computational uncertainty shows a strong dependence on the plasma scenario type and fusion drive characteristics, varying between ±25% and 35%. D-T fusion alpha simulations show that the ratio between volume-integrated electron and ion heating from alphas is 10 for the majority of analysed discharges. Alphas are computed to contribute between ∼15% and 40% to the total electron heating in the core of highest performing D-T discharges. An alternative workflow to TRANSP was employed to model JET D-T plasmas with the highest fusion yield and dominant non-thermal fusion component because of the use of fundamental radio-frequency heating of a large minority in the scenario, which is calculated to have provided ∼10% to the total fusion power.

Identification of novel indole-based dyes as active photo-sensitizers: Synthesis, photophysical, electrochemical and computational investigation

Novel D–π–A type indole-based compounds have been designed and synthesized as active photosensitizers for dye-sensitized solar cells (DSSCs). The molecular structures of indole-based compounds were identified and characterized using IR, NMR, and HRMS spectra data. The attributes of the indole-based compounds were evaluated in terms of their optical, electrochemical, light-harvesting efficiency (LHE), HOMO/LUMO level and redox behaviour. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were conducted to disclose the electronic and optical attributes of novel indole-based compounds. All the compounds revealed well-defined absorption with elevated absorptivity and a small band gap (2.89–3.01 eV). The HOMO to LUMO energy transfer percentage obtained from TD-DFT, for the synthesized compounds is in the range of 86%–99%. The projected light-harvesting efficiency (LHE) for the indole-based compounds is between 0.371 and 0.666. The greatest open circuit voltage (Voc) value was found in the methoxyphenyl-substituted indole-based compound, which is advantageous for DSSCs to obtain external maximum power output.

Maintenance of internal load despite a stepwise reduction in external load during moderate intensity heart rate clamped cycling with acute graded normobaric hypoxia in males

ObjectivesTo investigate the acute effects of graded hypoxia on external and internal loads during 60 min of endurance cycling at a clamped heart rate. DesignRepeated measures. MethodsOn separate visits, 16 trained males cycled for 60 min at a clamped heart rate corresponding to 80 % of their first ventilatory threshold at sea-level and 2500 m, 3000 m, 3500 m and 4000 m simulated altitudes (inspired oxygen fractions of 20.9 %, 15.4 %, 14.5 %, 13.6 % and 12.7 %, respectively). Markers of external (power output) and internal (blood lactate concentration, tissue saturation index, cardio-respiratory and perceptual responses) loads were measured every 15 min during cycling. Neuromuscular function of knee extensors was characterised pre- and post-exercise. ResultsCompared to sea-level (101 ± 22 W), there was a stepwise reduction in power output with increasing hypoxia severity (−17.9 ± 8.9 %, −27.1 ± 10.7 %, −34.2 ± 12.0 % and − 44.6 ± 15.1 % at 2500 m, 3000 m, 3500 m, and 4000 m, respectively, all p < 0.05). Blood lactate and tissue saturation index were not different across hypoxia severities, and perceptual responses were exacerbated at 4000 m only, with increased breathing difficulty. Knee extensor torque decreased post-exercise (−14.5 ± 9.0 %, p < 0.05), independent of condition. ConclusionsIncreasing hypoxia severity reduces cycling power output and arterial oxygen saturation in a stepwise fashion without affecting exercise responses between sea-level and simulated altitudes up to 3500 m despite breathing difficulty being elevated at 4000 m.

The Efficacy of Chlorella Supplementation on Multiple Indices of Cycling Performance

This study investigated the effects of chlorella supplementation on submaximal endurance, time trial performance, lactate threshold, and power indices during a repeated sprint performance test by fourteen male trained cyclists. Participants ingested 6 g/day of chlorella or placebo for 21-days in a double-blinded randomized counter-balanced cross-over design, with a fourteen-day washout period between trials. Each completed a 2-day testing period comprising a 1-hour submaximal endurance test at 55% external power output max and a 16.1 km time trial (Day-1), followed by a lactate threshold (Dmax) and repeated sprint performance tests (3 X 20 s sprints interspersed by 4-mins) (Day-2). Heart rate (b.min−1), RER, V̇O2 (ml·kg−1·min−1), lactate and glucose (mmol/L), time (secs), power output (W/kg), and hemoglobin (g/L) were compared across conditions. Following chlorella supplementation (chlorella vs. placebo for each measurement) average lactate and heart rate were significantly lower (p < 0.05) during submaximal endurance tests (1.68 ± 0.50 mmol/L vs. 1.91 ± 0.65 mmol/L & 138 ± 11b.min−1 vs. 144 ± 10b.min−1), average power and peak power (W/kg) were significantly higher during repeated sprint bouts (9.5 ± 0.7 W/kg vs. 9.0 ± 0.7 W/kg & 12.0 ± 1.2 W/kg vs. 11.4 ± 1.4 W/kg), hemoglobin significantly increased (149.1 ± 10.3 g/L) in comparison to placebo (143.4 ± 8.7 g/L) (p = 0.05). No differences existed between conditions for all oxygen consumption values, 16.1 km time trial measures and lactate threshold tests (p > 0.05). In conclusion, chlorella may pose as an additional supplement for cyclists to consider, particularly for those cyclists who want to improve their sprinting.

Effects of exercise-induced metabolic and mechanical loading on skeletal muscle mitochondrial function in male rats.

Over the past decades, a growing interest in eccentric (ECC) exercise has emerged, but mitochondrial adaptations to ECC training remain poorly documented. Using an approach for manipulating mechanical and metabolic exercise power, we positioned that for the same metabolic power, training using concentric (CON) or ECC contractions would induce similar skeletal muscle mitochondrial adaptations. Sixty adult rats were randomly assigned to a control (CTRL) or three treadmill training groups running at 15 m·min-1 for 45 min, 5 days weekly for 8 wk at targeted upward or downward slopes. Animals from the CON (+15%) and ECC30 (-30%) groups were trained at iso-metabolic power, whereas CON and ECC15 (-15%) exercised at iso-mechanical power. Assessments were made of vastus intermedius mitochondrial respiration (oxygraphy), enzymatic activities (spectrophotometry), and real-time qPCR for mRNA transcripts. Maximal rates of mitochondrial respiration were 14%-15% higher in CON and ECC30 compared with CTRL and ECC15. Apparent Km for ADP for trained groups was 40%-66% higher than CTRL, with statistical significance reached for CON and ECC30. Complex I and citrate synthase activities were 1.6 (ECC15) to 1.8 (ECC30 and CON) times values of CTRL. Complex IV activity was higher than CTRL (P < 0.05) only for CON and ECC30. mRNA transcripts analyses showed higher TFAM, SLC25A4, CKMT2, and PPID in the ECC30 compared with CTRL. Findings confirm that training-induced skeletal muscle mitochondrial function adaptations are governed by the extent of metabolic overload irrespective of exercise modality. The distinctive ECC30 mRNA transcript pattern may reflect a cytoskeleton damage-repair or ECC adaptive cycle that differs from that of biogenesis.NEW & NOTEWORTHY Anticipating outcomes of eccentric versus concentric training is confounded by differences in mechanical efficiency. Our observations in groups of rats submitted to uphill and downhill running regimens inducing similar levels of metabolic demands or same external power outputs reaffirm that independent of modality, oxygen requirements and not external work governs skeletal muscle mitochondrial function adaptations.

The Effect of External Power Output and Its Reliability on Propulsion Technique Variables in Wheelchair Users With Spinal Cord Injury.

The purpose of this study was to assess 1) how treadmill slope variance affected external power output (PO) and propulsion technique reliability; and 2) how PO is associated with propulsion technique. Eighteen individuals with spinal cord injury performed two wheelchair treadmill exercise blocks (0% and 1% treadmill slope, standardized velocity) twice on two separate days. PO, velocity, and 14 propulsion technique variables were measured. In a follow-up study, N = 29 performed wheelchair treadmill drag tests. Target and actual slope were documented and PO, intraclass correlation coefficients (ICC) and smallest detectable differences (SDD) were calculated. Within and between visits, the reliability study ICCs were perfect for velocity (1.0), weak for PO (0.33-0.46), and acceptable (>0.70) for five (0% slope) and 10 (1% slope) propulsion technique variables, resulting in SDDs of 35-196%. Measured PO explained 56-90% of the variance in key propulsion technique variables. In the follow-up, PO ICCs were weak (0.43) and SDDs high. Bias between target and actual slope appeared random. In conclusion, PO variability accounts for 50-90% of the variability in propulsion technique variables when speed and wheelchair set-up are held constant. Therefore, small differences in PO between interventions could mask the effect of the interventions on propulsion technique.

Validity and Reliability of Hydraulic-Analogy Bioenergetic Models in Sprint Roller Skiing.

Purpose: To develop a method for individual parameter estimation of four hydraulic-analogy bioenergetic models and to assess the validity and reliability of these models’ prediction of aerobic and anaerobic metabolic utilization during sprint roller-skiing.Methods: Eleven elite cross-country skiers performed two treadmill roller-skiing time trials on a course consisting of three flat sections interspersed by two uphill sections. Aerobic and anaerobic metabolic rate contributions, external power output, and gross efficiency were determined. Two versions each (fixed or free maximal aerobic metabolic rate) of a two-tank hydraulic-analogy bioenergetic model (2TM-fixed and 2TM-free) and a more complex three-tank model (3TM-fixed and 3TM-free) were programmed into MATLAB. The aerobic metabolic rate (MRae) and the accumulated anaerobic energy expenditure (Ean,acc) from the first time trial (STT1) together with a gray-box model in MATLAB, were used to estimate the bioenergetic model parameters. Validity was assessed by simulation of each bioenergetic model using the estimated parameters from STT1 and the total metabolic rate (MRtot) in the second time trial (STT2).Results: The validity and reliability of the parameter estimation method based on STT1 revealed valid and reliable overall results for all the four models vs. measurement data with the 2TM-free model being the most valid. Mean differences in model-vs.-measured MRae ranged between -0.005 and 0.016 kW with typical errors between 0.002 and 0.009 kW. Mean differences in Ean,acc at STT termination ranged between −4.3 and 0.5 kJ and typical errors were between 0.6 and 2.1 kJ. The root mean square error (RMSE) for 2TM-free on the instantaneous STT1 data was 0.05 kW for MRae and 0.61 kJ for Ean,acc, which was lower than the other three models (all P < 0.05). Compared to the results in STT1, the validity and reliability of each individually adapted bioenergetic model was worse during STT2 with models underpredicting MRae and overpredicting Ean,acc vs. measurement data (all P < 0.05). Moreover, the 2TM-free had the lowest RMSEs during STT2.Conclusion: The 2TM-free provided the highest validity and reliability in MRae and Ean,acc for both the parameter estimation in STT1 and the model validity and reliability evaluation in the succeeding STT2.

Twenty-one days of spirulina supplementation lowers heart rate during submaximal cycling and augments power output during repeated sprints in trained cyclists.

Spirulina supplementation has been reported to improve time to exhaustion and maximal oxygen consumption (V̇O2max). However, there is limited information on its influence over the multiple intensities experienced by cyclists during training and competition. Fifteen trained males (age 40± 8years, V̇O2max 51.14± 6.43mL/min/kg) ingested 6g/day of spirulina or placebo for 21 days in a double-blinded randomised crossover design, with a 14-day washout period between trials. Participants completed a 1-hour submaximal endurance test at 55% external power output max and a 16.1-km time trial (day 1), followed by a lactate threshold test and repeated sprint performance tests (RSPTs) (day 2). Heart rate (bpm), respiratory exchange ratio, oxygen consumption (mL/min/kg), lactate and glucose (mmol/L), time (seconds), power output (W), and hemoglobin (g/L) were compared across conditions. Following spirulina supplementation, lactate and heart rate were significantly lower (P< 0.05) during submaximal endurance tests (2.05± 0.80mmol/L vs 2.39± 0.89mmol/L and 139± 11bpm vs 144± 12bpm), hemoglobin was significantly higher (152.6± 9.0g/L) than placebo (143.2± 8.5g/L), and peak and average power were significantly higher during RSPTs (968± 177W vs 929± 149W and 770± 117W vs 738± 86W). No differences existed between conditions for all oxygen consumption values, 16.1-km time trial measures, and lactate threshold tests (P> 0.05). Spirulina supplementation reduces homeostatic disturbances during submaximal exercise and augments power output during RSPTs. Novelty: Spirulina supplementation lowers heart rate and blood lactate during ∼1-hour submaximal cycling. Spirulina supplementation elicits significant augmentations in hemoglobin and power outputs during RSPTs.

Efficiency and perceived exertion of manual wheelchair propulsion: a physiological comparison of push vs pull wheeling

Manual wheelchair users face a high prevalence of upper extremity pain and injuries associated with poor biomechanics and the relatively low mechanical efficiency of conventional push wheeling. Recently developed geared wheels, which permit the wheelchair user to propel forwards by pulling at the handrims using a ‘rowing’ motion, have been speculated to improve ergonomics and reduce operational energy costs. This study compared the gross mechanical efficiency (GME) and perceived exertion (RPE) of these geared wheels to standard wheelchair wheels after a motor skill-based training session was conducted to familiarise participants with using both wheels. Fourteen able-bodied males were enrolled in the study. A within-participants, repeated-measures design was used to assess oxygen uptake (VO2), respiratory exchange ratio (RER), energy expenditure (En) and RPE during 5-minute, steady-state wheeling trials. Total external power output (Pext) was obtained using a drag test protocol for comparison over En to determine GME ratio. Stroke frequency and movement pattern were assessed through video tracking and propulsion testing. Although geared wheels required fewer strokes, standard wheels resulted in significantly lower VO2, RPE and En (p ≤ 0.001). These findings suggest overall that standard wheels were more mechanically efficient, likely due to internal energy loss of the geared wheel system.

The influence of different track surfaces and bicycles on mountain biking performance

ABSTRACT This study aims to evaluate the impact induced by different track surfaces and type of bicycles on the mechanical and physiological variables in mountain biker performance. Sixteen mountain bike male athletes (70,2 ± 5,4 kg of body mass, 172,7 ± 4,0 cm of height, 9,8 ± 3,5% of body fat, 52,3 ± 3,9 mL/kg/min of VO2max) participated in this study. After the laboratory cardiorespiratory, athletes complete in random order 3 field trials of 20 minutes performed at maximum intensity. The type of bike (road and mountain bikes) and surface (ground and asphalt tracks) were changed in each trail. The trials on ground track and asphalt with MTB showed no differences in most of the variables except in the values of mechanical power output. Between the ground and asphalt trials on MTB, we observed associations in mean (r = 0,877) and maximum heart rates (r = 0,879), mean (r = 0,923) and relative (r = 0,913) power outputs. The trials performed on asphalt with different bicycles showed differences in the mean power output (p = 0,007). We conclude that the different track surfaces and bicycles influence the external power output values, without changes in the central component of the effort (heart rate).

Determining and Controlling External Power Output During Regular Handrim Wheelchair Propulsion.

The use of a manual wheelchair is critical to 1% of the world's population. Human powered wheeled mobility research has considerably matured, which has led to improved research techniques becoming available over the last decades. To increase the understanding of wheeled mobility performance, monitoring, training, skill acquisition, and optimization of the wheelchair-user interface in rehabilitation, daily life, and sports, further standardization of measurement set-ups and analyses is required. A crucial stepping-stone is the accurate measurement and standardization of external power output (measured in Watts), which is pivotal for the interpretation and comparison of experiments aiming to improve rehabilitation practice, activities of daily living, and adaptive sports. The different methodologies and advantages of accurate power output determination during overground, treadmill, and ergometer-based testing are presented and discussed in detail. Overground propulsion provides the most externally valid mode for testing, but standardization can be troublesome. Treadmill propulsion is mechanically similar to overground propulsion, but turning and accelerating is not possible. An ergometer is the most constrained and standardization is relatively easy. The goal is to stimulate good practice and standardization to facilitate the further development of theory and its application among research facilities and applied clinical and sports sciences around the world.

Determining and Controlling External Power Output During Regular Handrim Wheelchair Propulsion

Determining and Controlling External Power Output During Regular Handrim Wheelchair Propulsion

Motor learning outcomes of handrim wheelchair propulsion during active spinal cord injury rehabilitation in comparison with experienced wheelchair users

Purpose To investigate changes in wheelchair propulsion technique and mechanical efficiency across first five weeks of active inpatient spinal cord injury rehabilitation and to compare the outcomes at discharge with experienced wheelchair users with spinal cord injury. Methods Eight individuals with recent spinal cord injury performed six weekly submaximal exercise tests. The first and last measurement additionally contained a wheelchair circuit and peak graded exercise test. Fifteen experienced individuals performed all above-mentioned tests on one occasion. Results Mechanical efficiency and propulsion technique did not change during the five weeks of inpatient rehabilitation. Peak power output during peak graded test and performance time on the wheelchair circuit improved between the first and the last week. No difference in propulsion technique, peak power output, and performance time was found between the persons with a recent injury and the experienced group. Mechanical efficiency was higher after the correction for the difference in relative power output in the experienced group. Conclusion The group with a recent injury did not improve mechanical efficiency and propulsion technique over the period of active rehabilitation, despite significant improvements on the wheelchair circuit and in work capacity. The only significant difference between the groups was found in mechanical efficiency. Implications for rehabilitation The lack of time-dependent changes in mechanical efficiency and propulsion technique in the group with a recent spinal cord injury, combined with the lack of differences in technique, work capacity and on the wheelchair circuit between the groups, suggest that important adaptations of motor learning may happen even earlier in rehabilitation and emphasize that the group in active rehabilitation was relatively skilled. Standardized observational analyses of handrim wheelchair propulsion abilities during early spinal cord injury rehabilitation provide detailed understanding of wheelchair technique, skill as well as wheelchair propulsion capacity. Measurement of external power output is critical to interpretation of gross efficiency, propulsion technique, and capacity. Wheelchair quality and body weight – next to wheelchair fitness and skill – require careful consideration both in early rehabilitation as well as in the chronic phase of spinal cord injury.

Increase in muscle power is associated with myofibrillar ATPase adaptations during resistance training.

What is the central question of this study? The aim of this study was to examine the effects of resistance training on gains in the external mechanical power output developed during climbing and myofibrillar ATPase activity in rats. What is the main finding and its importance? Using rapid flow quench experiments, we show that resistance training increases both the power output and the myofibrillar ATPase activity in the flexor digitorum profundus, biceps and deltoid muscles. Data fitting reveals that these functional ameliorations are explained by an increase in the rate constant of liberation of ATP hydrolysis products and contribute to performance gains. Skeletal muscle shows a remarkable plasticity that permits functional adaptations in response to different stimulations. To date, modifications of the proportions of myosin heavy chain (MHC) isoforms and increases in fibre size are considered to be the main factors providing sarcomeric plasticity in response to exercise training. In this study, we investigated the effects of a resistance training protocol on the myofibrillar ATPase (m-ATPase) cycle, muscle performance (power output) and MHC gene expression. For this purpose, 8-week-old Wistar Han rats were subjected to 4weeks of resistance training, with five sessions per week. Muscle samples of flexor digitorum profundus (FDP), biceps and deltoid were collected and subjected to RT-qPCR analyses and assessment of m-ATPase activity with rapid flow quench apparatus. Training led to a significant increase in muscle mass, except for the biceps, and in total mechanical power output (+135.7%, P<0.001). A shift towards an intermediate fibre type (i.e. MHC2x-to-MHC2a isoform transition) was also observed in biceps and FDP but not in the deltoid muscle. Importantly, rapid flow quench experiments revealed an enhancement of the m-ATPase activity during contraction at maximal velocity (kF ) in the three muscles, with a more marked effect in FDP (+242%, P<0.001). Data fitting revealed that the rate constant of liberation of ATP hydrolysis products (k3 ) appears to be the main factor influencing the increase in m-ATPase activity. In conclusion, the data showed that, in addition to classically observed changes in MHC isoform content and fibre hypertrophy, m-ATPase activity is enhanced during resistance training and might contribute significantly to performance gains.

When Jump Height is not a Good Indicator of Lower Limb Maximal Power Output: Theoretical Demonstration, Experimental Evidence and Practical Solutions.

Lower limb external maximal power output capacity is a key physical component of performance in many sports. During squat jump and countermovement jump tests, athletes produce high amounts of mechanical work over a short duration to displace their body mass (i.e. the dimension of mechanical power). Thus, jump height has been frequently used by the sports science and medicine communities as an indicator of the power output produced during the jump and by extension, of maximal power output capacity. However, in this article, we contend that squat jump and countermovement jump height are not systematically good indicators of power output produced during the jump and maximal power output capacity. To support our opinion, we first detail why, theoretically, jump height and maximal power output capacity are not fully related. Specifically, we demonstrate that individual body mass, push-off distance, optimal loading and the force-velocity profile confound the jump height-power relationship. We also discuss the relationship between squat jump or countermovement jump height and maximal power output capacity measured with a force plate based on data reported in the literature, which added to our own experimental evidence. Finally, we discuss the limitations of existing practical solutions (regression-based estimation equations and allometric scaling), and advocate using a valid, reliable and simple field-based procedure to compute individual power output produced during the jump and maximal power output capacity directly from jump height, body mass and push-off distance. The latter may allow researchers and practitioners to reduce bias in their assessment of lower limb mechanical power output by using jump height as an input with a simple yet accurate computation method, and not as the first/only variable of interest.

Mechanical energetics and dynamics of uphill double-poling on roller-skis at different incline-speed combinations.

ObjectivesThe purpose of this study was to investigate the effect of different incline-speed combinations, at equal external power outputs, on the mechanics and energetics of the double-poling (DP) technique in cross-country skiing.MethodsFourteen elite male cross-country skiers performed treadmill DP on roller-skis at low, moderate, and high mean external power outputs (Pmean) up a shallow incline (5%, INC5), at which DP is preferred, and up a steep incline (12%, INC12), at which DP is not preferred. Speed was set to produce equal Pmean at both inclines. From recorded kinematics and dynamics, arm power (Parm) and trunk+leg power (PT+L) were derived, as were pole propulsion power (Ppole) and body mechanical energy perpendicular to the treadmill surface (Ebody⊥).ResultsOver a locomotion cycle, the arms contributed 63% to Pmean at INC5 but surprisingly only 54% at INC12 (P<0.001), with no effect of Pmean (P = 0.312). Thus, the trunk and legs contributed substantially to Pmean both at INC5 (37%) and INC12 (46%). At both inclines, PT+L generation during the swing phase increased approximately linearly with Pmean, which increased Ebody⊥. Within the poling phase, ~30–35% of the body energy which was developed during the preceding swing phase was transferred into propulsive pole power on both inclines. At INC5, the amount of negative PT+L during the poling phase was larger than at INC12, and this difference increased with Pmean.ConclusionsThe considerable larger amount of negative PT+L during poling at INC5 than at INC12 indicate that the legs and trunk generate more power than ‘necessary’ during the swing phase and thus must absorb more energy during the poling phase. This larger surplus of PT+L at INC5 seems necessary for positioning the body and poles so that high Parm generation can occur in a short time. At INC12, less Parm is generated, probably due to less advantageous working conditions for the arms, related to body and pole positioning. These incline differences seem linked to shorter swing and longer poling times during steep uphill DP, which are due to the increased influence of gravity and slower speed at steep inclines.

Functional Electrical Stimulation Changes Muscle Oxygenation in Patients with Chronic Obstructive Pulmonary Disease During Moderate-Intensity Exercise: A Secondary Analysis

We previously showed that functional electrical stimulation during cycle ergometry (FES-cycling) increased oxygen consumption (VO2), indicating that metabolism during exercise was increased. However, the effects on muscle oxygenation have never been studied. The aim of this secondary analysis was to analyse changes in muscle oxygenation during an FES-cycling session. Eight patients with chronic obstructive pulmonary disease who were participating in a pulmonary rehabilitation programme were enrolled. Each participant carried out 30 minutes of cycle ergometry with a constant load at 50% of peak oxygen uptake, either (i) with FES or (ii) without (Placebo-FES). Oxygenation of the vastus lateralis (VL) muscle over time was measured using near-infrared spectroscopy (NIRS) during both sessions. External power output on the cycle ergometer was the same in both conditions. There were no differences in dyspnoea between the groups, although the concentrations of deoxygenated haemoglobin and myoglobin (deoxy(Hb + Mb)) in the VL were significantly greater during Placebo-FES than FES-Cycling (respectively +212 ± 65% vs. +84 ± 29%; p < 0.001), as was the decrease in muscle oxygen saturation (StO2) (p < 0.001). When adjusted for VO2, there was a greater increase over time in the deoxy(Hb + Mb)/VO2 ratio during Placebo-FES than FES-cycling (p < 0.0001). FES-cycling could be a useful strategy to decrease muscular deoxy(Hb + Mb) and limit decreases in muscle StO2, however this should be confirmed in larger studies.

Exercise-induced trunk fatigue decreases double poling performance in well-trained cross-country skiers.

To examine the effects of exercise-induced trunk fatigue on double poling performance, physiological responses and trunk strength in cross-country skiers. Sixteen well-trained male cross-country skiers completed two identical pre- and post-performance tests, separated by either a 25-min trunk fatiguing exercise sequence or rest period in a randomized, controlled cross-over design. Performance tests consisted of a maximal trunk flexion and extension test, followed by a 3-min double poling (DP) test on a ski ergometer. Peak torque during isometric trunk flexion (- 66%, p < .001) and extension (- 7.4%, p = .03) decreased in the fatigue relative to the control condition. Mean external power output during DP decreased by 14% (p < .001) and could be attributed both to reduced work per cycle (- 9%, p = .019) and a reduced cycle rate (- 6%, p = .06). Coinciding physiological changes in peak oxygen uptake (- 6%, p < .001) and peak ventilation (- 7%, p < .001) could be observed. Skiers chose a more even-pacing strategy when fatigued, with the performance difference between fatigue and control condition being most prominent during the first 2min of the post-test. In well-trained cross-country skiers, exercise-induced trunk fatigue led to a substantial decrease in DP performance, caused by both decreased work per cycle and cycle rate and accompanied by reduced aerobic power. Hence, improved fatigue resistance of the trunk may therefore be of importance for high-intensity DP in cross-country skiing.