Delta Efficiency Research Articles

Leg cycling efficiency is unaltered in healthy aging regardless of sex or training status.

Muscular efficiency during exercise has been used to interrogate aspects of human muscle energetics, including mitochondrial coupling and biomechanical efficiencies. Typically, assessments of muscular efficiency have involved graded exercises. Results of previous studies have been interpreted to indicate a decline in exercise efficiency with aging owing to decreased mitochondrial function. However, discrepancies in variables such as exercise stage duration, cycling cadence, and treadmill walking mechanics may have affected interpretations of results. Furthermore, recent data from our lab examining the ATP to oxygen ratio (P:O) in mitochondrial preparations isolated from NIA mouse skeletal muscle showed no change with aging. Thus, we hypothesized that delta efficiency (Δ€) during steady-rate cycling exercise would not be altered in older healthy subjects compared with young counterparts regardless of biological sex or training status. Young (21-35 yr) and older (60-80 yr) men (n = 21) and women (n = 20) underwent continual, progressive leg cycle ergometer tests pedaling at 60 RPM for three stages (35, 60, 85 W) lasting 4 min. Δ€was calculated as: (Δ work accomplished/Δ energy expended). Overall, cycling efficiencies were not significantly different in older compared with young subjects. Similarly, trained subjects did not exhibit significantly different exercise efficiencies compared to untrained. Moreover, there were no differences between men and women. Hence, our results obtained on healthy young and older subjects are interpreted to mean that previous reports of decreased efficiency in older individuals were attributable to metabolic or biomechanical comorbidities, not aging per se.NEW & NOTEWORTHY Muscular power is reduced, but the efficiency of movement is unaltered in healthy aging.

Eccentric Exercise-Induced Muscle Damage Reduces Gross Efficiency.

The effect of eccentric exercise-induced muscle damage (EIMD) on cycling efficiency is unknown. The aim of the present study was to assess the effect of EIMD on gross and delta efficiency and the cardiopulmonary responses to cycle ergometry. Twenty-one recreational athletes performed cycling at 70%, 90%, and 110% of the gas exchange threshold (GET) under control conditions (Control) and 24 h following an eccentric damaging protocol (Damage). Knee extensor isometric maximal voluntary contraction, potentiated twitch ( Qtw,pot ), and voluntary activation were assessed before Control and Damage. Gross and delta efficiency were assessed using indirect calorimetry, and cardiopulmonary responses were measured at each power output. Electromyography root-mean-square (EMG RMS ) during cycling was also determined. Maximal voluntary contraction was 25% ± 18% lower for Damage than Control ( P < 0.001). Gross efficiency was lower for Damage than Control ( P < 0.001) by 0.55% ± 0.79%, 0.59% ± 0.73%, and 0.60% ± 0.87% for 70%, 90%, and 110% GET, respectively. Delta efficiency was unchanged between conditions ( P = 0.513). Concurrently, cycling EMG RMS was higher for Damage than Control ( P = 0.004). An intensity-dependent increase in breath frequency and V̇ E /V̇CO 2 was found, which were higher for Damage only at 110% GET ( P ≤ 0.019). Thus, gross efficiency is reduced following EIMD. The concurrently higher EMG RMS suggests that increases in muscle activation in the presence of EIMD might have contributed to reduced gross efficiency. The lack of change in delta efficiency might relate to its poor reliability hindering the ability to detect change. The findings also show that EIMD-associated hyperventilation is dependent on exercise intensity, which might relate to increases in central command with EIMD.

Body mass and V'O2 at rest affect gross efficiency during moderate-intensity cycling in untrained young healthy men: correlations with V'O2MAX.

Seventeen young healthy physically active males (age 23 ±3 years; body mass (BM) 72.5 ±7.9 kg; height 178 ±4 cm, (mean ±SD)), not specifically trained in cycling, participated in this study. The subjects performed two cycling incremental tests at the pedalling rate of 60 rev x min-1. The first test, with the power output (PO) increases of 30 W every 3 min, was to determine the maximal oxygen uptake (V'O2max) and the power output (PO) at V'O2max, while the second test (series of 6 minutes bouts of increasing intensity) was to determine energy expenditure (EE (V'O2)), gross efficiency (GE (V'O2/PO)) and delta efficiency (DE(ΔV'O2/DPO)) during sub-lactate threshold (LT) PO. V'O2max was 3.79 ±0.40 L x min-1 and the PO at V'O2max was 288 ±27 W. In order to calculate GE and DE the V'O2 was expressed in W, by standard calculations. GE measured at 30 W, 60 W, 90 W and 120 W was 11.6 ±1.4%, 17.0 ±1.4%, 19.6 ±1.2% and 21.4 ±1.1%, respectively. DE was 29.8 ±1.9%. The subjects' BM (range 59-87 kg) was positively correlated with V'O2 at rest (p<0.01) and with the intercept of the linear V'O2 vs. PO relationship (p<0.01), whereas no correlation was found between BM and the slope of V'O2 vs. PO. No correlation was found between BM and DE, whereas GE was negatively correlated with BM (p<0.01). GE was also negatively correlated with V'O2max and the PO at V'O2max (p<0.01). We conclude that: V'O2 at rest affects GE during moderate-intensity cycling and GE negatively corelates with V'O2max and the PO at V'O2max in young healthy men.

Impairments in muscle shape changes affect metabolic demands during in-vivo contractions.

The uncoupling behaviour between muscle belly and fascicle shortening velocity (i.e. belly gearing), affects mechanical output by allowing the muscle to circumvent the limits imposed by the fascicles' force-velocity relationship. However, little is known about the 'metabolic effect' of a decrease/increase in belly gearing. In this study, we manipulated the plantar flexor muscles' capacity to change in shape (and hence belly gearing) by using compressive multidirectional loads. Metabolic, kinetic, electromyography activity and ultrasound data (in soleus and gastrocnemius medialis) were recorded during cyclic fixed-end contractions of the plantar flexor muscles in three different conditions: no load, +5 kg and +10 kg of compression. No differences were observed in mechanical power and electrophysiological variables as a function of compression intensity, whereas metabolic power increased as a function of it. At each compression intensity, differences in efficiency were observed when calculated based on fascicle or muscle behaviour and significant positive correlations (R2 range: 0.7-0.8 and p > 0.001) were observed between delta efficiency (ΔEff: Effmus-Efffas) and belly gearing (Vmus/Vfas) or ΔV (Vmus-Vfas). Thus, changes in the muscles' capacity to change in shape (e.g. in muscle stiffness or owing to compressive garments) affect the metabolic demands and the efficiency of muscle contraction.

Efficiency of cycling exercise: Quantification, mechanisms, and misunderstandings.

The energetics of cycling represents a well-studied area of exercise science, yet there are still many questions that remain. Efficiency, broadly defined as the ratio of energy output to energy input, is one key metric that, despite its importance from both a scientific as well as performance perspective, is commonly misunderstood. There are many factors that may affect cycling efficiency, both intrinsic (e.g., muscle fiber type composition) and extrinsic (e.g., cycling cadence, prior exercise, and training), creating a complex interplay of many components. Due to its relative simplicity, the measurement of oxygen uptake continues to be the most common means of measuring the energy cost of exercise (and thus efficiency); however, it is limited to only a small proportion of the range of outputs humans are capable of, further limiting our understanding of the energetics of high-intensity exercise and any mechanistic bases therein. This review presents evidence that delta efficiency does not represent muscular efficiency and challenges the notion that the slow component of oxygen uptake represents decreasing efficiency. It is noted that gross efficiency increases as intensity of exercise increases in spite of the fact that fast-twitch fibers are recruited to achieve this high power output. Understanding the energetics of high-intensity exercise will require critical evaluation of the available data.

Severe loss of mechanical efficiency in COVID‐19 patients

BackgroundThere is limited information about the impact of coronavirus disease (COVID‐19) on the muscular dysfunction, despite the generalized weakness and fatigue that patients report after overcoming the acute phase of the infection. This study aimed to detect impaired muscle efficiency by evaluating delta efficiency (DE) in patients with COVID‐19 compared with subjects with chronic obstructive pulmonary disease (COPD), ischaemic heart disease (IHD), and control group (CG).MethodsA total of 60 participants were assigned to four experimental groups: COVID‐19, COPD, IHD, and CG (n = 15 each group). Incremental exercise tests in a cycle ergometer were performed to obtain peak oxygen uptake (VO2peak). DE was obtained from the end of the first workload to the power output where the respiratory exchange ratio was 1.ResultsA lower DE was detected in patients with COVID‐19 and COPD compared with those in CG (P ≤ 0.033). However, no significant differences were observed among the experimental groups with diseases (P > 0.05). Lower VO2peak, peak ventilation, peak power output, and total exercise time were observed in the groups with diseases than in the CG (P < 0.05). A higher VO2, ventilation, and power output were detected in the CG compared with those in the groups with diseases at the first and second ventilatory threshold (P < 0.05). A higher power output was detected in the IHD group compared with those in the COVID‐19 and COPD groups (P < 0.05) at the first and second ventilatory thresholds and when the respiratory exchange ratio was 1. A significant correlation (P < 0.001) was found between the VO2peak and DE and between the peak power output and DE (P < 0.001).ConclusionsPatients with COVID‐19 showed marked mechanical inefficiency similar to that observed in COPD and IHD patients. Patients with COVID‐19 and COPD showed a significant decrease in power output compared to IHD during pedalling despite having similar response in VO2 at each intensity. Resistance training should be considered during the early phase of rehabilitation.

The Effect of Blood Ketone Concentration and Exercise Intensity on Exogenous Ketone Oxidation Rates in Athletes.

Exogenous ketones potentially provide an alternative, energetically advantageous fuel to power exercising skeletal muscle. However, there is limited evidence regarding their relative contribution to energy expenditure during exercise. Furthermore, the effect of blood ketone concentration and exercise intensity on exogenous ketone oxidation rates is unknown. Six athletes completed cycling ergometer exercise on three occasions within a single-blind, random-order controlled, crossover design study. Exercise duration was 60 min, consisting of 20-min intervals at 25%, 50%, and 75% maximal power output (WMax). Participants consumed (i) bitter flavored water (control), (ii) a low-dose β-hydroxybutyrate (βHB) ketone monoester (KME; 252 mg·kg BW-1, "low ketosis"), or (iii) a high-dose βHB KME (752 mg·kg BW-1, "high ketosis"). The KME contained a 13C isotope label, allowing for the determination of whole-body exogenous βHB oxidation rates through sampled respiratory gases. Despite an approximate doubling of blood βHB concentrations between low- and high-ketosis conditions (~2 mM vs ~4.4 mM), exogenous βHB oxidation rates were similar at rest and throughout exercise. The contribution of exogenous βHB oxidation to energy expenditure peaked during the 25% WMax exercise intensity but was relatively low (4.46% ± 2.71%). Delta efficiency during cycling exercise was significantly greater in the low-ketosis (25.9% ± 2.1%) versus control condition (24.1% ± 1.9%; P = 0.027). Regardless of exercise intensity, exogenous βHB oxidation contributes minimally to energy expenditure and is not increased by elevating circulating concentrations greater than ~2 mM. Despite low exogenous βHB oxidation rates, exercise efficiency was significantly improved when blood βHB concentration was raised to ~2 mM.

Gross and delta efficiencies during uphill running and cycling among elite triathletes

PurposeTo investigate the gross efficiency (GE) and delta efficiency (DE) during cycling and running in elite triathletes.MethodsFive male and five female elite triathletes completed two incremental treadmill tests with an inclination of 2.5° to determine their GE and DE during cycling and running. The speed increments between the 5-min stages were 2.4 and 0.6 km h−1 during the cycling and running tests, respectively. For each test, GE was calculated as the ratio between the mechanical work rate (MWR) and the metabolic rate (MR) at an intensity corresponding to a net increase in blood-lactate concentration of 1 mmol l−1. DE was calculated by dividing the delta increase in MWR by the delta increase in MR for each test. Pearson correlations and paired-sample t tests were used to investigate the relationships and differences, respectively.ResultsThere was a correlation between GEcycle and GErun (r = 0.66; P = 0.038; R2 = 0.44), but the correlation between DEcycle and DErun was not statistically significant (r = − 0.045; P = 0.90; R2 = 0.0020). There were differences between GEcycle and GErun (t = 80.8; P < 0.001) as well as between DEcycle and DErun (t = 27.8; P < 0.001).ConclusionsElite triathletes with high GE during running also have high GE during cycling, when exercising at a treadmill inclination of 2.5°. For a moderate uphill incline, elite triathletes are more energy efficient during cycling than during running, independent of work rate.

On the simple calculation of walking efficiency without kinematic information for its convenient use

BackgroundSince walking is a daily activity not to require the maximal effort in healthy populations, a very few universal bio-parameters and/or methods have been defined to evaluate individual walking characteristics in those populations. A concept of “economy” is a potential candidate; however, walking economy highly depends on speed, so direct comparisons of economy values are difficult between studies. We investigated whether the vertical component of net walking “efficiency” (Effvert; %) is constant across speed. In that case, direct comparisons of Effvert will be possible between studies or individuals at any voluntary speed.MethodsThirty young male participants walked at eight speeds on the level or ± 5% gradients, providing vertical speeds (vvert). Differences in energy expenditure between level and uphill or downhill gradients (ΔEE) were calculated. The metabolic rate for vertical component (MRvert) was calculated by multiplying ΔEE with body mass (BM). The mechanical power output for vertical component (Pmech) was calculated by multiplying BM, gravitational acceleration, and vvert. Effvert was obtained from the ratio of Pmech to MRvert at each vvert. Delta efficiency (Delta-E; %) was also calculated from the inverse slope of the regression line representing the relationship of Pmech to MRvert.ResultsUpward Effvert was nearly constant at around 35% and downward Effvert ranged widely (49–80%). No significant differences were observed between upward Delta-E (35.5 ± 8.8%) and Effvert at any speeds, but not between downward Delta-E (44.9 ± 12.8%) and Effvert.ConclusionsUpward ΔEE could be proportional to vvert. Upward, but not downward, Effvert should be useful not only for healthy populations but also for clinical patients to evaluate individual gait characteristics, because it requires only two metabolic measurements on the level and uphill gradients without kinematic information at any voluntary speed.Trial registrationUMIN000017690 (R000020501; registered May 26th, 2015, before the first trial) and UMIN000031456 (R000035911; registered Feb. 23rd, 2018, before the first trial).

Seven-day ischaemic preconditioning improves muscle efficiency during cycling

ABSTRACTIschaemic preconditioning (IPC) has emerged as a potential non-invasive ergogenic aid to enhance exercise performance. Repeated application of IPC has demonstrated clinical efficacy, therefore our aims were to investigate its effect on endurance cycling performance and muscle efficiency. Twenty participants undertook 7-d repeated bilateral lower limb occlusion (4 x 5-min) of IPC (220 mmHg) or sham (20 mmHg). Prior to and 72-h following the intervention, participants performed submaximal cycling at 70, 80 and 90% of ventilatory threshold (VT) followed by an incremental exercise test. IPC had no effect on O2max (P = 0.110); however, time to exhaustion increased by ~ 9% and Wmax by ~ 5 % (IPC pre 307 ± 45 to post 323 ± 51 W) relative to sham (P = 0.002). There were no changes in gross efficiency (GE) (P > 0.05); however, delta efficiency (DE) increased by 3.1% following IPC (P = 0.011). Deoxyhaemoglobin (HHb) was reduced following IPC ~ 30% (P = 0.017) with no change in total haemoglobin (tHb). Repeated IPC over 7-d enhanced muscle efficiency and extended cycling performance. The physiological effects of repeated IPC on skeletal muscle efficiency explains the notable improvements in endurance performance.

A Comparison of Methodological Approaches to Measuring Cycling Mechanical Efficiency

BackgroundMuch is known about theoretical bases of different mechanical efficiency indices and effects of physiological and biomechanical factors to them. However, there are only a few studies available about practical bases and interactions between these efficiency indices, which were the aims of the present study.MethodsFourteen physically active men (n = 12) and women (n = 2) participated in this study. From the incremental test, six different mechanical efficiency indices were calculated for cycling work: gross (GE) and net (NE) efficiencies, two work efficiencies (WE), and economy (T) at 150 W, and in addition delta efficiency (DE) using 3–5 observation points.ResultsIt was found that the efficiency indices can be divided into three groups by Spearman’s rank correlation: GE, T, and NE in group I; DE and extrapolated WE in group II; and measured WE in group III. Furthermore, group II appeared to have poor reliability due to its dependence on a work-expended energy regression line, which accuracy is poorly measured by confidence interval.ConclusionAs efficiency indices fall naturally into three classes that do not interact with each other, it means that they measure fundamentally different aspects of mechanical efficiency. Based on problems and imprecisions with other efficiency indices, GE, or group I, seems to be the best indicator for mechanical efficiency because of its consistency and unambiguity. Based on this methodological analysis, the baseline subtractions in efficiency indices are not encouraged.

Redefining Physiologic Predictors of Endurance Performance with Measures of Skeletal Muscle Oxygenation: E pluribus unum

PURPOSE: To scrutinize the ability of classic measures of endurance performance vs. NIRS-derived measures of skeletal muscle oxygenation to predict 25 km cycling time trial performance. METHODS: 14 participants (4 f / 10 m) underwent 3 sequential exercise bouts on a cycle ergometer while fitted with NIRS devices over each vastus lateralis: 1) A warmup consisting of 2 sequential 7.5-min bouts of 50 and 100 W at 80 rpm to determine gross efficiency (GE), exercise economy (EC), and delta efficiency (DE) across the same absolute workloads followed by an incremental max test to volitional fatigue (VF) used to discern 3 separate measures of ventilatory threshold (VT), maximal rates of whole-body oxygen consumption (VO2max) and maximal aerobic power (Wmax); 2) A warmup consisting of 2 sequential 7.5-min bouts at 80 rpm corresponding to 15% and 30% Wmax for GE, EC, and DE across the same relative workloads followed by a 60 sec ramp to a sustained 110% Wmax until VF to verify VO2max; and 3) A 25 km TT. Ventilatory measures were sampled throughout bouts 1 and 2. RESULTS: Stepwise and multiple linear regression analyses revealed that from the classic variables only mean VTVO2 (2.59 ± 0.53 l O2·min-1, p = 0.019) and EC at 15% Wmax (47 ± 10 W, p = 0.030) explained (adj R2 = 0.463; p = 0.013) 25 km TT performance (46:40 ± 04:36 min:sec) variance whereas the change in skeletal muscle oxygenation (ΔSmO2; -6.9 ± 6.1%; p = 0.001) from 50 to 100 W and the deoxygenated hemoglobin and myoglobin index (HHb) at Wmax (9.57 ± 1.56; p = 0.044) were the best NIRS-derived variables to describe TT performance (adj R2 = 0.751; p < 0.001). When combining all variables, skeletal muscle measures provided a superior physiologic explanation of 25 km TT performance versus those classically used to describe endurance performance (VTVO2, EC @ 15% Wmax, HHbmax, and ΔSmO2 at p = 0.083, 0.056, 0.008, and 0.005, respectively). CONCLUSION: These results demonstrate that measures reflecting the balance of skeletal muscle O2 delivery and utilization during exercise are superior to classic measures of whole-body aerobic capacity, ventilatory threshold, and/or the efficiency of exercise at predicting 25 km time trial (TT) cycling performance.

Effect of acute ingestion of β-hydroxybutyrate salts on the response to graded exercise in trained cyclists

Acute ingestion of ketone salts induces nutritional ketosis by elevating β-hydroxybutyrate (βHB), but few studies have examined the metabolic effects of ingestion prior to exercise. Nineteen trained cyclists (12 male, 7 female) undertook graded exercise (8 min each at ∼30%, 40%, 50%, 60%, 70%, and 80% VO2peak) on a cycle ergometer on two occasions separated by either 7 or 14 days. Trials included ingestion of boluses of either (i) plain water (3.8 mL kg body mass−1) (CON) or (ii) βHB salts (0.38 g kg body mass−1) in plain water (3.8 mL kg body mass−1) (KET), at both 60 min and 15 min prior to exercise. During KET, plasma [βHB] increased to 0.33 ± 0.16 mM prior to exercise and 0.44 ± 0.15 mM at the end of exercise (both p < .05). Plasma glucose was 0.44 ± 0.27 mM lower (p < .01) 30 min after ingestion of KET and remained ∼0.2 mM lower throughout exercise compared to CON (p < .001). Respiratory exchange ratio (RER) was higher during KET compared to CON (p < .001) and 0.03–0.04 higher from 30%VO2peak to 60%VO2peak (all p < .05). No differences in plasma lactate, rate of perceived exertion, or gross or delta efficiency were observed between trials. Gastrointestinal symptoms were reported in 13 out of 19 participants during KET. Acute ingestion of βHB salts induces nutritional ketosis and alters the metabolic response to exercise in trained cyclists. Elevated RER during KET may be indicative of increased ketone body oxidation during exercise, but at the plasma βHB concentrations achieved, ingestion of βHB salts does not affect lactate appearance, perceived exertion, or muscular efficiency.

No change in energy efficiency in lactation: Insights from a longitudinal study.

Lactation is the most energy-demanding phase of reproduction for human females, but it is still unclear how women in different environments are able to meet this additional energy demand. Previous studies have investigated whether changes in metabolism could have an energy-sparing effect in lactation, with conflicting results. Here, we asked whether increased energy efficiency in physical activity serves as an energy-sparing mechanism in lactation. We used a longitudinal design with a control group. Participants were 33 well-nourished, exclusively breastfeeding women and 29 non-pregnant, non-lactating (NPNL) controls aged 32 ± 4 years. Lactating women were measured at peak- and post-lactation. NPNL controls completed a baseline measurement and a follow-up visit. Energy efficiency in physical activity was assessed using a graded submaximal exercise test and calculated as delta efficiency (change in work accomplished over change in energy expended) and gross efficiency (work accomplished over energy expended). There was no significant change in either delta efficiency or gross efficiency from peak to post lactation in lactating women, and no significant difference in delta efficiency between lactating women and NPNL controls at any time period. However, lactating women showed greater between-visit variation in delta efficiency than the NPNL controls. Additionally, 79% of lactating participants lost weight between visits (mean weight loss -3.6 ± 2.3kg), consistent with a mobilization of body tissues to support lactation. We found no support for the idea that lactating women undergo an increase in energy efficiency to support the energy costs of lactation.

Optimal Operating Parameters of 100MW Delta IV Ughelli Gas Turbine Power Plant Unit

The possibility of improving the overall efficiency of 100MW Delta IV Ughelli gas turbine power plant unit is presented. The study used Non-Dominated Sorting Genetic Algorithm (NSGA) to minimize the exergy destruction by optimally adjusting the operating parameters (decision variables). The adjusted operating variables were compressor pressure ratio rp, compressor isentropic efficiency ηic, turbine isentropic efficiency ηit, turbine inlet temperature T3, inlet flow rate of air ṁa and mass flow rate of fuel ṁf. The ambient temperature and pressure were held constant at 303K and 1.013 bar respectively because of location limitations. The optimization code was written in MATLAB programming language. The decision variables (constraints) were obtained randomly within the admissible range. The optimal values of the decision variables were obtained by minimizing the objective function (total exergy destruction). The choice of 300 generations was to enable the full utilization of the search space without putting strain on the computation time and complexity. The determined optimum values of the operating variables were rp= 12.41, ηic = 86.40%, ηit =89.12%, T3=1,486.36K ṁa =355.82kg/s and ṁf =8.62kg/s. The obtained optimal values of rp, ηic, ηit and T3 were higher than their base values while that for ṁa and ṁf were less. Increased rp brings about higher thermal efficiency while increased ηic guarantees less exergy destruction in the compressor. Increased ηic and T3 are crucial in decreasing the exergy destruction in the combustion chamber and in reducing the cycle fuel consumption. Reduced ṁa and ṁf play vital roles in the reduction of the total exergy destruction. They reduction also result in less emissions from the plant thereby decreasing the gas turbine’s negative impacts on the environment. Suggested coatings of compressor blades will lead to increased compressor efficiency whereas thermal barrier coatings of the hot sections of the plant will increase the lifespan of the parts at the designed firing temperature. Thermal barrier coatings also allow increased firing temperature while still maintaining the original designed lifespan.

Enhanced Endurance Performance by Periodization of Carbohydrate Intake: "Sleep Low" Strategy.

We investigated the effect of a chronic dietary periodization strategy on endurance performance in trained athletes. Twenty-one triathletes (V˙O2max: 58.7 ± 5.7 mL·min(-1)·kg(-1)) were divided into two groups: a "sleep-low" (SL) (n = 11) and a control (CON) group (n = 10) consumed the same daily carbohydrate (CHO) intake (6 g·kg(-1)·d(-1)) but with different timing over the day to manipulate CHO availability before and after training sessions. The SL strategy consisted of a 3-wk training-diet intervention comprising three blocks of diet-exercise manipulations: 1) "train-high" interval training sessions in the evening with high-CHO availability, 2) overnight CHO restriction ("sleeping-low"), and 3) "train-low" sessions with low endogenous and exogenous CHO availability. The CON group followed the same training program but with high CHO availability throughout training sessions (no CHO restriction overnight, training sessions with exogenous CHO provision). There was a significant improvement in delta efficiency during submaximal cycling for SL versus CON (CON, +1.4% ± 9.3%; SL, +11% ± 15%, P < 0.05). SL also improved supramaximal cycling to exhaustion at 150% of peak aerobic power (CON, +1.63% ± 12.4%; SL, +12.5% ± 19.0%; P = 0.06) and 10-km running performance (CON, -0.10% ± 2.03%; SL, -2.9% ± 2.15%; P < 0.05). Fat mass was decreased in SL (CON, -2.6 ± 7.4; SL, -8.5% ± 7.4% before; P < 0.01), but not lean mass (CON, -0.22 ± 1.0; SL, -0.16% ± 1.7% PRE). Short-term periodization of dietary CHO availability around selected training sessions promoted significant improvements in submaximal cycling economy, as well as supramaximal cycling capacity and 10-km running time in trained endurance athletes.

Internal Mechanical Power During Cycling Using Non-Circular Versus Circular Chainrings

Introduction : Non-circular Rotor Q-Rings have been shown to increase tangential force during the pedalling downstroke compared to conventional circular chainrings 1 , and due to this advantage, have been proposed as a potential aid in improving short-term cycling performance such as in BMX and sprint cycling races 2 . Some evidence exists that suggests this effect on pedal force may manifest in a change in metabolic cost over repeated revolutions during submaximal, steady-state cycling bouts using Rotor Q-Rings 3 . One mechanism by which a change in total metabolic cost may occur is via a change in the power required to move the limbs segments against gravitational and inertial forces through the pedal stroke (internal mechanical power, or IP) when compared to using circular chainrings (at the same external mechanical power, EP). Strutzenberger et al. 1 reported an increase in joint muscle power of the hip when Q-Rings were used compared to circular chainrings at 70 and 90 rev · min -1 , which could cause an increased IP and result in a greater total metabolic cost. The aim of this study was to further investigate the mechanical and metabolic energetics of using Q-Rings during cycling. Their effect on IP, compared to a conventional circular chainring, was assessed using a recently-proposed, multidisciplinary model for calculating IP in cycling 4 , which accounts for the strengths and limitations of previous biomechanical and physiological approaches. Total metabolic cost was also compared between the two chainrings for cycling over a range of workloads. Method : Ten elite male road cyclists completed 5-min cycling bouts at 80 rev · min -1 at 100, 200 and 300 W using a standard circular chainring and 52-tooth Q-Ring set in two positions: ‘#1’ and ‘#5’. Oxygen consumption was converted to metabolic power. Tangential and radial crank forces and crank position were measured using Axis Cranks (SPE, Carole Park, Australia). The x-intercept of the EP-metabolic power relationship, multiplied by the slope (delta efficiency), was equal to the physiological estimate of IP. The biomechanical estimate of IP was taken as the summed muscle joint power, determined from digitised video footage and inverse dynamics analysis, in excess of that required to apply power to the pedals (Giorgi et al. 2014). Results : Preliminary analysis of data is presented in Table 1. Data are presented as mean ± SD. No significant differences were found between the chainrings for total metabolic power or the physiological estimate of IP. Discussion : Further analysis will allow the description of changes in potential and rotational kinetic energies and muscle and joint powers throughout the pedal revolution. This information will permit the calculation of the biomechanical estimate of IP and comparisons to be made between chainrings and Q-Ring positions.

Exercise efficiency relates with mitochondrial content and function in older adults.

Chronic aerobic exercise has been shown to increase exercise efficiency, thus allowing less energy expenditure for a similar amount of work. The extent to which skeletal muscle mitochondria play a role in this is not fully understood, particularly in an elderly population. The purpose of this study was to determine the relationship of exercise efficiency with mitochondrial content and function. We hypothesized that the greater the mitochondrial content and/or function, the greater would be the efficiencies. Thirty-eight sedentary (S, n = 23, 10F/13M) or athletic (A, n = 15, 6F/9M) older adults (66.8 ± 0.8 years) participated in this cross sectional study. O2peak was measured with a cycle ergometer graded exercise protocol (GXT). Gross efficiency (GE, %) and net efficiency (NE, %) were estimated during a 1-h submaximal test (55% O2peak). Delta efficiency (DE, %) was calculated from the GXT. Mitochondrial function was measured as ATPmax (mmol/L/s) during a PCr recovery protocol with 31P-MR spectroscopy. Muscle biopsies were acquired for determination of mitochondrial volume density (MitoVd, %). Efficiencies were 17% (GE), 14% (NE), and 16% (DE) higher in A than S. MitoVD was 29% higher in A and ATPmax was 24% higher in A than in S. All efficiencies positively correlated with both ATPmax and MitoVd. Chronically trained older individuals had greater mitochondrial content and function, as well as greater exercise efficiencies. GE, NE, and DE were related to both mitochondrial content and function. This suggests a possible role of mitochondria in improving exercise efficiency in elderly athletic populations and allowing conservation of energy at moderate workloads.

Effects of aging on mechanical efficiency and muscle activation during level and uphill walking

Purpose: The metabolic cost of walking is greater in old compared to young adults. This study examines the relation between metabolic cost, muscular efficiency, and leg muscle co-activation during level and uphill walking in young and older adults. Procedures: Metabolic cost and leg muscle activation were measured in young (22.3±3.6years) and older adults (74.5±2.9years) walking on a treadmill at six different slopes (0.0–7.5% grade) and a speed of 1.3ms−1. Across the range of slopes, ‘delta mechanical efficiency’ of the muscular system and antagonist muscle co-activation were quantified. Main findings: Across all slopes, older adults walked with a 13–17% greater metabolic cost, 12% lower efficiency, and 25% more leg muscle co-activation than young adults. Among older adults, co-activation was weakly correlated to metabolic cost (r=.233) and not correlated to the lower delta efficiency. Conclusion: Lower muscular efficiency and increased leg muscle co-activation contribute to the greater metabolic cost of uphill slope walking among older adults but are unrelated to one another.

Incorporating internal mechanical power into performance models in cycling

Background: A number of models have been developed to establish the energy cost of cycling. These models have become better refined to account for the various energy demands, including air and rolling resistances. Among the established models, however, there does not appear to be sufficient consideration for changes to internal mechanical power (IP), the rate of energy to move the limbs against gravitational and inertial forces. Values up to 100 W have been reported for IP in cycling for cadences between 80 and 115 , and so the inclusion of IP in performance prediction models is arguably warranted. Quantifying IP has previously been done using either 1) a physiological approach (IP met ), in which the metabolic counterpart of the external mechanical power (power applied to the cranks) was subtracted from A– (energy expenditure) to equal the metabolic equivalent of IP met , which was then multiplied by delta efficiency (DE) to yield the IP met ; or 2) a biomechanical approach (IP mech ), which used an inverse dynamics analysis of the kinematics and kinetics of cycling. Both approaches have notable advantages and limitations, which is why quantifying a range for IP, delimited by IP met and IP mech, has been proposed by this research group.  Purpose: The aim of this study was to assess whether incorporating a range of values for IP into an established performance model would provide a better prediction of A– than when IP was not included.  Methods: Steady-state A– was measured (K4 b 2 , Cosmed, Rome, Italy) for 10 elite male cyclists who cycled for 5-6 min at 200 W at 80 and 110 on the flat duckboard of an outdoor velodrome in calm conditions. Steady-state A– was compared to A– predicted by the established model (Equation 1, see in PDF document) (di Prampero et al. 1979: Journal of Applied Physiology, 47(1), 201-106; Olds et al. Journal of Applied Physiology, 75(2), 730-737): and A– predicted by the model that includes IP (IP met and IP mech ) (Equation 2, see in PDF document): where the first term of both equations represents the cost due to air resistance and includes a coefficient of drag (C drag ), the projected frontal surface area (A frontal ), the air density (r), the velocity of the wind (v w ) and the steady-state velocity of the cyclist (v ss ). The second term represents the cost due to rolling resistance, where C rr is the coefficient of rolling resistance, S is the angle of terrain, m body and m bicycle are the masses of the participant’s body and bicycle, respectively. IP met and IP mech were determined in the laboratory for each cyclist in an identical cycling position to that adopted in the outdoor trials. Results: Mean (± s) measured at 80 was 866 W (± 78 W) and at 110 was 937 W (± 75 W). The mean difference (± 95% limits of agreement) between measured and predicted by Equation 1 was -98 W (± 214 W) at 80 and -185 W (± 191 W) at 110 . When IP met was included in the prediction (Equation 2), mean differences (± 95% limits of agreement) were 125 W (± 192 W) and 182 W (± 153 W) at 80 and 110 , respectively. The mean differences (± 95% limits of agreement) between measured and predicted by Equation 2 incorporating IP mech were -48 W (± 201 W) at 80 and -148 W (± 274 W) at 110 . Discussion: Energy expenditure () predicted using an already-established model was shown, in this study, to fall short of the measured from respiratory gas during outdoor cycling for most participants at 80 and for all at 110 . Inclusion of IP mech into the performance prediction model resulted in values closer to the measured , however they were not sufficiently large enough to account for the entire deficit from the original prediction model (Equation 1) at either cadence. When the upper limit of the IP range, IP met , was incorporated it more than compensated, in almost all cases, for the deficit from Equation 1. That is to say, the measured during outdoor cycling fell within the range of values that was predicted for when estimates of IP were considered in the model. Conclusion: Based on these results, it is recommended that future predictions of cycling performance include a cost for IP.