Net Energy Expenditure Research Articles

Energy replacement diminishes the effect of exercise on postprandial lipemia in boys

PurposeAcute bouts of exercise reduce postprandial triacylglycerol concentrations ([TAG]) in healthy boys and girls; however, it is not known whether this effect is mediated by the energy deficit. This study examined whether the exercise-induced reduction in postprandial [TAG] persists after immediate dietary replacement of the exercise energy expenditure (EE). MethodsEighteen healthy 11- to 13-year-old boys (mean (SD): body mass 41.3 (8.4)kg; peak oxygen uptake (V̇O2) 55 (5)mL·kg−1·min−1) completed three, 2-day conditions in a within-measures, crossover design separated by 14days. On day 1, participants rested (CON), exercised at 60% peak V̇O2 inducing a net EE of 32kJ·kg−1 body mass (EX-DEF) or completed the same exercise with the net EE replaced immediately (EX-REP). On day 2, capillary blood samples were taken in the fasted state and at pre-determined intervals throughout the 6.5h postprandial period. A standardised breakfast and lunch meal were consumed immediately and 4h, respectively, after the fasting sample. ResultsBased on ratios of the geometric means (95% confidence intervals (CI) for ratios), EX-DEF fasting [TAG] was 19% and 15% lower than CON (−32 to −4%, ES=1.15, P=0.02) and EX-REP (−29 to 0%, ES=0.91, P=0.05) respectively; CON and EX-REP were similar (−4%; P=0.59). The EX-DEF total area under the [TAG] versus time curve was 15% and 16% lower than CON (−27 to 0%, ES=0.55, P=0.05) and EX-REP (−29 to −2%, ES=0.62, P=0.03) respectively; CON and EX-REP were not different (2%; −13 to 20%, P=0.80). ConclusionImmediate replacement of the exercise-induced energy deficit negates the reduction in postprandial [TAG] in boys; this highlights the importance of maintaining a negative energy balance immediately post-exercise to maximise the metabolic health benefits of exercise.

Effects of implantable peroneal nerve stimulation on gait quality, energy expenditure, participation and user satisfaction in patients with post-stroke drop foot using an ankle-foot orthosis.

To investigate whether an implantable functional electrical stimulation (FES) system of the common peroneal nerve (ActiGait®) improves relevant aspects of gait in chronic stroke patients with a drop foot typically using an ankle-foot orthosis (AFO). Ten community-dwelling patients participated, of whom eight patients could be analysed. Gait quality (kinematic, kinetic, and spatiotemporal characteristics) during a 10-meter comfortable walk test, normalised net energy expenditure during a 6-minute walk test, participation (physical activity and stroke impact) and user satisfaction were tested before implantation and at various moments after FES-system activation up to 26 weeks. Walking with FES yielded increased maximum paretic ankle plantarflexion (FES: -0.12; AFO: -4.79°, p < 0.01), higher paretic peak ankle power (FES: 1.46; AFO: 0.98 W/kg, p < 0.05) and better step length symmetry (FES: 14.90; AFO: 21.45% , p < 0.05). User satisfaction was higher for FES, but was unrelated to objective gait improvements. Energy expenditure and participation did not change. Implantable FES improved the use of residual ankle plantarflexion motion, ankle power of the paretic leg and step length symmetry compared to using an AFO, however, not resulting in decreased energy expenditure or improved participation. User satisfaction was highest with FES, but this was not related to the observed gait improvements.

Osteocartilaginous metabolic markers change over a 3-week stage race in pro-cyclists

Evidence suggests that endurance and even recreational cycling may stimulate bone resorption; however, little is known about cartilage response to endurance cycling exercise. We investigated effort-dependent changes in bone turnover and cartilage biomarkers in blood and urine samples from elite cyclists during a 3-week stage race. Whole blood and urine samples were collected the day before the start of the race, at mid and end-race for serum and urinary CTx-I, NTx-I, PINP, COMP (only in serum), and CTx-II analysis by enzyme-linked immunosorbent assay. The values were corrected for plasma volume or creatinine excretion, respectively, and correlated with power output (corrected for body weight) and net energy expenditure. Bone marker concentrations in both serum and urine were slightly but significantly decreased. Among the cartilage degradation markers, only CTx-II was decreased, while COMP remained unchanged. The changes in bone and cartilage turnover indexes were correlated with the indexes of physical effort and energy consumption.Strenuous physical effort, in the absence of mechanical loading, slows bone metabolism and only minimally affects cartilage turnover. Since changes in plasma and urine volume, which normally occur in exercising athletes, can mask these effects, biomarker concentrations need to be corrected for shifts in plasma volume and urinary creatinine for correct interpretation of the data.

Index of mechanical efficiency in competitive and recreational long distance runners

The purpose of this investigation was to compare external work and net energy expenditure during a bout of repetitive stretch-shortening cycles between competitive and recreational long-distance runners. Participants were divided into either competitive or recreational runners based on their maximal oxygen consumption and self-reported 1600 m times. The stretch-shortening cycle involved a repetitive hopping protocol on a force plate while measuring oxygen consumption and lactate accumulation for a total of 10 min. External work and net energy expenditure were calculated for 3 min after steady state was achieved and the ratio between these variables was utilised as an index of mechanical efficiency. Lower extremity stiffness was calculated during this interval as well. Net energy expenditure was significantly lower in competitive runners (152.6 ± 33.3 kJ) in comparison to recreational runners (200.6 ± 41.4 kJ) (P = 0.02) given similar amounts of external work performed in both groups (competitive runners = 65.6 ± 20.1 kJ, recreational runners = 68.8 ± 12.1 kJ) (P = 0.67). Index of mechanical efficiency was significantly different between competitive runners (43.2 ± 9.0%) and recreational runners (34.8 ± 5.3%) (P = 0.03). No significant differences were found in lower extremity stiffness (P = 0.64). Competitive distance runners can perform similar levels of external work with lower net energy expenditure and thus a higher index of mechanical efficiency during repetitive stretch-shortening cycles in comparison to recreational runners with similar values of lower extremity stiffness. This ability could possibly be due differences in muscle–tendon length changes, muscle pre-activation, cross-bridge potentiation and short-latency reflex responses as a result of training which should be considered for future investigation.

Effect of weekly hiking on cardiovascular risk factors in the elderly

Hiking is one of the most popular activities among the elderly in Alpine regions. Due to the long-lasting, moderately intensive nature of this form of physical activity, hiking is generally considered to be beneficial to health. However, it is currently unclear whether once-weekly hiking--as commonly practiced at weekends--really does yield such positive effects in elderly persons aged 60 years and over. This study investigated the effect of a single weekly mountain hiking session on cardiovascular risk factors. A 9-month mountain hiking program was completed by 14 male (age 65.6 ± 2.7 years) and 10 female (age 66.2 ± 4.4 years) elderly participants. The program consisted of a single weekly hiking session with the goal of achieving a 500-m altitude increase within 3 h. Before and after the 9-month program, an electrocardiogram (ECG) was performed and blood pressure, glycated hemoglobin (HbA1c), high-density (HDL) and low-density lipoprotein (LDL) measurements were made. The elderly participants showed a normal cardiovascular risk profile at the start of the investigation. The estimated net energy expenditure for one hiking session was approximately 521 ± 91 kcal. Over the 9-month period, no changes were found in any of the investigated parameters for the entire group. However, participants with untreated hypertension showed a reduced systolic blood pressure. The present investigation showed that moderate-intensity activity only at weekends does not improve cardiovascular risk factors in elderly persons with a relatively normal cardiovascular risk profile. Conversely, elderly persons suffering from hypertension might profit from such a practice.

Effects of lower limb length and body proportions on the energy cost of overground walking in older persons.

Background. Although walking has been extensively investigated in its biomechanical and physiological aspects, little is known on whether lower limb length and body proportions affect the energy cost of overground walking in older persons. Methods. We enrolled 50 men and 12 women aged 65 years and over, mean 69.1 ± SD 5.4, who at the end of their cardiac rehabilitation program performed the six-minute walk test while wearing a portable device for direct calorimetry and who walked a distance comparable to that of nondisabled community-dwelling older persons. Results. In the multivariable regression model (F = 12.75, P < 0.001, adjusted R2 = 0.278) the energy cost of overground walking, expressed as the net energy expenditure, in kg−1 sec−1, needed to provide own body mass with 1 joule kinetic energy, was inversely related to lower limb length and directly related to lower limb length to height ratio (β ± SE(β) = −3.72∗10−3 ± 0.74∗10−3, P < 0.001, and 6.61∗10−3 ± 2.14∗10−3, P = 0.003, resp.). Ancillary analyses also showed that, altogether, 1 cm increase in lower limb length reduced the energy cost of overground walking by 2.57% (95%CI 2.35–2.79). Conclusions. Lower limb length and body proportions actually affect the energy cost of overground walking in older persons.

Prediction Equations of Energy Expenditure in Chinese Youth Based on Step Frequency During Walking and Running

Purpose: This study set out to examine the relationship between step frequency and velocity to develop a step frequency-based equation to predict Chinese youth's energy expenditure (EE) during walking and running. Method: A total of 173 boys and girls aged 11 to 18 years old participated in this study. The participants walked and ran on a treadmill at speeds of 3 km/hr, 4 km/hr, 5 km/hr, 6 km/hr, 7 km/hr, and 8 km/hr. EE was measured using indirect calorimetry of open circuit spirometry (Cosmed K4b2 metabolic analyzer). Using multiple regression analysis, the relationship between step frequency and velocity was first examined, and the prediction equation of EE based on step frequency, age, and gender was derived. Results: The hypothesized relationship between step frequency and velocity was confirmed and an accurate (R 2 = .78) EE prediction equation was derived: Net EE = − 13.7744+1.8004 (step frequency) – 5.5715 (age) – 11.5244 (gender). Conclusion: A step frequency-, age-, and gender-based equation was derived to predict the EE of youth during walking and running. The equation can be used to develop a simple device to estimate EE during walking and running in this population.

Acute energy intake restriction, moderate intensity exercise and postprandial plasma triacylglycerol concentration in girls

This study compared the effect of an isoenergetic energy deficit, induced by mild energy-intake restriction or acute exercise, on postprandial triacylglycerol concentrations ([TAG]) in girls. Eleven healthy girls (mean(SD): age 12.1(0.6) years; body mass 42.1(5.8) kg; peak oxygen uptake ( V ̇ O 2 peak ) 47(6) mL kg −1 min −1 ) completed three, two-day conditions in a counterbalanced, crossover design. On day 1, participants rested (CON), restricted food energy intake by 1.47(0.18) MJ (ER) or walked at 60% V ̇ O 2 peak (EX; net energy expenditure 1.46(0.01) MJ). On day 2, capillary blood samples were taken in the fasted state and at pre-determined intervals throughout the 6.5 h postprandial period. A standardised breakfast was consumed immediately after the fasting sample and a standardised lunch at 4 h. Compared with CON, fasting [TAG] was lower after ER (95% confidence interval (95% CI) −0.22 to −0.01, effect size (ES) = 0.42) and EX (95% CI −0.38 to −0.19, ES = 1.33); EX was lower than ER (95% CI −0.30 to −0.03, ES = 0.66). Differences in postprandial [TAG] over time between conditions were moderate (ES = 0.50). The total area under the [TAG] versus time curve was lower after EX than CON (95% CI −2.89 to −0.86, ES = 0.80), with a small difference between ER and CON (95% CI −1.85 to 0.16, ES = 0.27) and EX and ER (95% CI −2.48 to 0.42, ES = 0.40). An exercise-induced energy deficit elicits a greater reduction in fasting and postprandial [TAG] in girls than an isoenergetic diet-induced energy deficit.

Natriuretic peptides and fat metabolism

The regulation of adipose tissue metabolism has for many years been the domain of insulin action to promote glucose uptake and lipogenesis, and the catecholamines of the sympathetic nervous system working through β-adrenergic receptors (βARs) and PKA to stimulate lipolysis and the release of these stored fatty acids. Catecholamines can also increase the machinery for uncoupled respiration in brown adipocytes - including the “browning” of cells in white adipose depots - together resulting in net energy expenditure. However we now know that this is not the whole story. Several years ago the receptors for the cardiac natriuretic peptides ANP and BNP were found to be expressed in adipose tissue. It was then noted that ANP could increase lipolysis via PKG phosphorylation of the same targets as PKA. Using cultured adipocytes, as well as mice with targeted deletions of GC-A/NPRA and NPRC, we have found that ANP/BNP can stimulate “browning” of adipocytes similar to that elicited by catecholamines. In earlier work, we established that βARs drive the transcription of brown adipocyte genes and respiratory uncoupling through a signaling cascade from PKA to p38 MAP kinase. The natriuretic peptides and PKG also utilize this novel p38 MAPK pathway such that the βARs and NPRA work together, additively increasing expression of brown adipocyte marker genes, as well as reflexively controlling each other’s components. These findings shed new light on the control of body fat and energy expenditure, with important implications for understanding obesity as well as cardiovascular disease such as hypertension and heart failure. Since obesity in humans as well as rodents is accompanied by increased levels of NPRC in adipose tissue, thus impairing signaling, and obese individuals often exhibit high blood pressure, therapeutic approaches that target the NP receptors may have the potential to increase energy expenditure, promote weight loss and reduce blood pressure.

Reciprocal regulation of calcium‐/phosphate‐regulating hormones in cyclists during the Giro d'Italia 3‐week stage race

Calcium and phosphate are essential for cell functions, and their serum concentrations result from the balance between intestinal absorption, bony storage, and urinary excretion. Fibroblast growth factor 23 (FGF23), expressed by osteocytes and osteoblasts, acts in the kidney, leading to hypophosphatemia and low 1,25-dihydroxycholecalciferol synthesis, but suppresses parathyroid function. The aim of this study was to explore the effects of a high-energy demanding cycling race on this bone-kidney-parathyroid axis. We studied nine cyclists during the 2011 Giro d'Italia stage race. Pre-analytical and analytical phases followed academic and anti-doping recommendations. Serum parathyroid hormone (PTH), 25(OH)D, total calcium, inorganic phosphorus, and plasma FGF23 were measured on days -1, 12, and 22 and corrected for changes in plasma volume. Dietary calcium and phosphorus, anthropometric parameters (height, weight, and body mass index) and indexes of metabolic effort (net energy expenditure, power output) were recorded. Dietary calcium and phosphorus intakes were kept at the same levels throughout the race. Twenty-five (OH)D, PTH, and calcium concentrations remained stable. FGF23 increased 50% with a positive correlation with the indexes of metabolic effort and, consequently, phosphorous decreased, although only in the first half. The strong metabolic effort acts on the bone-kidney-parathyroid system, and the rise in FGF23 plasma concentration might be aimed at maintaining calcium and phosphorus homeostasis.

Exercise modality and metabolic efficiency in children

Current exercise prescription guidelines for children recommend at least 60 min of moderate-to-vigorous physical activity every day. However, little is known about the efficacy of different cardiorespiratory exercise modalities prescribed to the pediatric cohort. Sixteen healthy children (8-12 years) completed 5-min trials of treadmill walking, cycling, and elliptical training in a randomized order. The treadmill walking speed was determined from measurements collected during a self-selected walking trial. The workloads for treadmill walking, cycling, and elliptical training were matched (40.3 W). Mechanical efficiency (ME%), perceived exertion (RPE), oxygen uptake, metabolic equivalents, and net energy expenditure were measured. ME% in walking was significantly higher than in cycling (P = 0.001) and elliptical training (P < 0.001), and cycling was significantly higher than elliptical training (P = 0.003). RPE in walking was significantly lower than in elliptical training (P = 0.006) but not from cycling (P = 0.314), and cycling resulted in significantly lower RPE than elliptical training (P = 0.021). Treadmill walking appears to be the most efficacious exercise prescription for otherwise healthy children; however, longitudinal studies need to be implemented to investigate the long-term benefits of each exercise modality.

Appetite, energy intake, and PYY3–36 responses to energy-matched continuous exercise and submaximal high-intensity exercise

High-intensity intermittent exercise induces physiological adaptations similar to energy-matched continuous exercise, but the comparative appetite and energy balance responses are unknown. Twelve healthy males (mean ± SD: age, 22 ± 3 years; body mass index, 23.7 ± 3.0 kg·m(-2); maximum oxygen uptake, 52.4 ± 7.1 mL·kg(-1)·min(-1)) completed three 8 h trials (control, steady-state exercise (SSE), high-intensity intermittent exercise (HIIE)) separated by 1 week. Trials commenced upon completion of a standardized breakfast. Exercise was performed from hour 2 to hour 3. In SSE, 60 min of cycling at 59.5% ± 1.6% of maximum oxygen uptake was performed. In HIIE, ten 4-min cycling intervals were completed at 85.8% ± 4.0% of maximum oxygen uptake, with a 2-min rest between each interval. A standardized lunch and an ad libitum afternoon meal were provided at hours 3.75 and 7, respectively. Appetite ratings and peptide YY3-36 concentrations were measured throughout each trial. Appetite was acutely suppressed during exercise, but more so during HIIE (p < 0.05). Peptide YY3-36 concentrations increased significantly upon cessation of exercise in SSE (p = 0.002), but were highest in the hours after exercise in HIIE (p = 0.05). Exercise energy expenditure was not different between HIIE and SSE (p = 0.649), but perceived exertion was higher in HIIE (p < 0.0005). Ad libitum energy intake did not differ between trials (p = 0.833). Therefore, relative energy intake (energy intake minus the net energy expenditure of exercise) was lower in the SSE and HIIE trials than in the control trial (control, 4759 ± 1268 kJ; SSE, 2362 ± 1224 kJ; HIIE, 2523 ± 1402 kJ; p < 0.0005). An acute bout of energy-matched continuous exercise and HIIE were equally effective at inducing an energy deficit without stimulating compensatory increases in appetite.

Acute effects of exercise and calorie restriction on triglyceride metabolism in women.

The mechanisms by which exercise reduces fasting plasma triglyceride (TG) concentrations in women and the effect of negative energy balance independent of muscular contraction are not known.The aim of this study was to evaluate the effects of equivalent energy deficits induced by exercise or calorie restriction on basal VLDL-TG metabolism in women. Eleven healthy women (age = 23.5 ± 2.7 yr, body mass index = 21.6 ± 1.4 kg·m-2; mean ± SD) underwent a stable isotopically labeled tracer infusion study to determine basal VLDL-TG kinetics after performing, in random order, three experimental trials on the previous day: (i) a single exercise bout (brisk walking at 60% of peak oxygen consumption for 123 ± 18 min, with a net energy expenditure of 2.06 ± 0.39 MJ, ∼500 kcal), (ii) dietary energy restriction of 2.10 ± 0.41 MJ, and (iii) a control day of isocaloric feeding and rest (zero energy balance). Fasting plasma VLDL-TG concentration was approximately 30% lower after the exercise trial compared with the control trial (P < 0.001), whereas no significant change was detected after the calorie restriction trial (P = 0.297 vs control). Relative to the control condition, exercise increased the plasma clearance rate of VLDL-TG by 22% (P = 0.001) and reduced hepatic VLDL-TG secretion rate by approximately 17% (P = 0.042), whereas hypocaloric diet had no effect on VLDL-TG kinetics (P > 0.2). (i) Exercise-induced hypotriglyceridemia in women manifests through a different mechanism (increased clearance and decreased secretion of VLDL-TG) than that previously described in men (increased clearance of VLDL-TG only), and (ii) exercise affects TG homeostasis by eliciting changes in VLDL-TG kinetics that cannot be reproduced by an equivalent diet-induced energy deficit, indicating that these changes are independent of the exercise-induced negative energy balance but instead are specific to muscular contraction.

Mechanical efficiency of high versus moderate intensity aerobic exercise in coronary heart disease patients: A randomized clinical trial.

Mechanical efficiency (ME) refers to the ability of an individual to transfer energy consumed by external work. A decreased ME, could represent an increased energy cost during exercise and may, therefore, be limited in terms of physical activity. This study aimed to compare the influence of two different exercise protocols: moderate continuous training (MCT) versus high intensity interval training (HIIT), as part of a cardiac rehabilitation program on ME values among coronary patients. One hundred and ten coronary patients were assigned to either HIIT or MCT groups for 8 weeks. Incremental exercise tests in a cycle ergometer were performed to obtain VO2peak. Net energy expenditure (EE) and ME were obtained at intensities corresponding to the first (VT1) and second (VT2) ventilatory thresholds, and at VO2peak. Both exercise programs significantly increase VO2peak with a higher increase in the HIIT group (2.96 ± 2.33 mL/kg/min vs. 3.88 ± 2.40 mL/kg/min, for patients of the MCT and HIIT groups, respectively, p < 0.001). The ME at VO2peak and VT2 only significantly increased in the HIIT group. At VT1, ME significantly increased in both groups, with a greater increase in the HIIT group (2.20 ± ± 6.25% vs. 5.52 ± 5.53%, for patients of the MCT and HIIT groups, respectively, p < 0.001). The application of HIIT to patients with chronic ischemic heart disease of low risk re- sulted in a greater improvement in VO2peak and in ME at VT1, than when MCT was applied. Moreover, only the application of HIIT brought about a significant increase in ME at VT2 and at VO2peak.

Biomechanics and energetics of walking on uneven terrain

Walking on uneven terrain is more energetically costly than walking on smooth ground, but the biomechanical factors that contribute to this increase are unknown. To identify possible factors, we constructed an uneven terrain treadmill that allowed us to record biomechanical, electromyographic and metabolic energetics data from human subjects. We hypothesized that walking on uneven terrain would increase step width and length variability, joint mechanical work and muscle co-activation compared with walking on smooth terrain. We tested healthy subjects (N=11) walking at 1.0 m s(-1), and found that, when walking on uneven terrain with up to 2.5 cm variation, subjects decreased their step length by 4% and did not significantly change their step width, while both step length and width variability increased significantly (22 and 36%, respectively; P<0.05). Uneven terrain walking caused a 28 and 62% increase in positive knee and hip work, respectively, and a 26% greater magnitude of negative knee work (0.0106, 0.1078 and 0.0425 J kg(-1), respectively; P<0.05). Mean muscle activity increased in seven muscles in the lower leg and thigh (P<0.05). These changes caused overall net metabolic energy expenditure to increase by 0.73 W kg(-1) (28%; P<0.0001). Much of that increase could be explained by the increased mechanical work observed at the knee and hip. Greater muscle co-activation could also contribute to increased energetic cost but to unknown degree. The findings provide insight into how lower limb muscles are used differently for natural terrain compared with laboratory conditions.

Appetite, gut hormone and energy intake responses to low volume sprint interval and traditional endurance exercise

Sprint interval exercise improves several health markers but the appetite and energy balance response is unknown. This study compared the effects of sprint interval and endurance exercise on appetite, energy intake and gut hormone responses. Twelve healthy males [mean (SD): age 23 (3) years, body mass index 24.2 (2.9) kg m(-2), maximum oxygen uptake 46.3 (10.2) mL kg(-1) min(-1)] completed three 8 h trials [control (CON), endurance exercise (END), sprint interval exercise (SIE)] separated by 1 week. Trials commenced upon completion of a standardised breakfast. Sixty minutes of cycling at 68.1 (4.3) % of maximum oxygen uptake was performed from 1.75-2.75 h in END. Six 30-s Wingate tests were performed from 2.25-2.75 h in SIE. Appetite ratings, acylated ghrelin and peptide YY (PYY) concentrations were measured throughout each trial. Food intake was monitored from buffet meals at 3.5 and 7 h and an overnight food bag. Appetite (P < 0.0005) and acylated ghrelin (P < 0.002) were suppressed during exercise but more so during SIE. Peptide YY increased during exercise but most consistently during END (P < 0.05). Acylated ghrelin was lowest in the afternoon of SIE (P = 0.018) despite elevated appetite (P = 0.052). Exercise energy expenditure was higher in END than that in SIE (P < 0.0005). Energy intake was not different between trials (P > 0.05). Therefore, relative energy intake (energy intake minus the net energy expenditure of exercise) was lower in END than that in CON (15.7 %; P = 0.006) and SIE (11.5 %; P = 0.082). An acute bout of endurance exercise resulted in lower appetite perceptions in the hours after exercise than sprint interval exercise and induced a greater 24 h energy deficit due to higher energy expenditure during exercise.

Estimation of Resistance Exercise Energy Expenditure Using Triaxial Accelerometry

Recently, it was demonstrated that a uniaxial accelerometer worn at the hip could estimate resistance exercise energy expenditure. As resistance exercise takes place in more than 1 plane, the use of a triaxial accelerometer may be more effective in estimating resistance exercise energy expenditure. The aims of this study were to estimate the energy cost of resistance exercise using triaxial accelerometry and to determine the optimal location for wearing triaxial accelerometers during resistance exercise. Thirty subjects (15 men and 15 women; age = 21.7 ± 1.0 years) performed a resistance exercise protocol consisting of 2 sets of 8 exercises (10RM loads). During the resistance exercise protocol, subjects wore triaxial accelerometers on the wrist, waist, and ankle; a heart rate monitor; and a portable metabolic system. Net energy expenditure was significantly correlated with vertical (r = 0.67, p < 0.001), horizontal (r = 0.43, p = 0.02), third axis (r = 0.36, p = 0.048), and sum of 3 axes (r = 0.50, p = 0.005) counts at the waist, and horizontal counts at the wrist (r = -0.40, p = 0.03). Regression analysis using fat-free mass, sex, and the sum of accelerometer counts at the waist as variables was used to develop an equation that explained 73% of the variance of resistance exercise energy expenditure. A triaxial accelerometer worn at the waist can be used to estimate resistance exercise energy expenditure but appears to offer no benefit over uniaxial accelerometry. The use of accelerometers in estimating resistance exercise energy expenditure may prove useful for individuals and athletes who participate in resistance training and are focused on maintaining a tightly regulated energy balance.

Net Energy Expenditure of Gravity-Independent High-Speed Resistive Exercise Done by Women

Elevated metabolism is common to spaceflight while exercise in microgravity exacerbates energy costs. Thus in-flight exercise countermeasures must be devised that minimize energy costs as they are performed on hardware operable in microgravity. Female subjects (N = 28), subdivided into athletic and sedentary groups, each performed two workouts on a resistive exercise device (Impulse Training Systems; Newnan, GA). Comprised exclusively of either tonic or phasic repetitions, each exercise bout entailed two 1 -min sets interspersed by a 90-s rest from which the work volume was determined. Oxygen consumption was measured before, during, and after workouts until gas uptake returned to pre-exercise levels. Net oxygen consumption was converted to net energy expenditures via indirect calorimetry. Mean net energy expenditure and work volume values were each compared with 2 (athletes, sedentaries) x 2 (tonic, phasic) ANOVAs, with repeated measures for workout. In addition, multivariate regression employed three predictor (body mass, body fat percentage, work volume) variables to account for the net energy expenditure variance. Workouts yielded a metabolic cost of approximately 14 kcal, yet the data produced no significant intergroup or workout differences. However, work volume analysis yielded a significant (tonic > phasic) effect. The multivariate analysis explained small yet significant amounts of net energy expenditure variance. Current results: 1) are partly attributable to higher series elastic element activity seen with Impulse repetitions; and 2) offer new information with respect to in-flight exercise protocols for female astronauts.

Variation in Cell Wall Composition and Accessibility in Relation to Biofuel Potential of Short Rotation Coppice Willows

Short rotation coppice (SRC) willow is currently emerging as an important dedicated lignocellulosic energy crop in the UK. However, investigation into the variation between species and genotypes in their suitability for liquid transport biofuel processing has been limited. To address this, four traits relevant to biofuel processing (composition, enzymatic saccharification, response to pretreatment and projected ethanol yields) were studied in 35 genotypes of willow including Europe’s leading SRC willow cultivars. Large, genotype-specific variation was observed for all four traits. Significant positive correlations were identified between the accessibility of glucan to enzymatic saccharification before and after pretreatment as well as glucose release and xylose release via acid hydrolysis during pretreatment. Of particular interest is that the lignin content of the biomass did not correlate with accessibility of glucan to enzymatic saccharification. The genotype-specific variations identified have implications for SRC willow breeding and for potential reductions in both the net energy expenditure and environmental impact of the lignocellulosic biofuel process chain. The large range of projected ethanol yields demonstrate the importance of feedstock selection based on an ideotype encompassing the performance of both field biomass growth and ease of conversion.

Cardiac indexes, cardiac damage biomarkers and energy expenditure in professional cyclists during the Giro d’Italia 3-weeks stage race

The study of cardiac response to strenuous and continuous exercise is crucial to understanding the physiology of endurance. N-terminal proB-type natriuretic peptide (NT-proBNP) is a potential marker for monitoring myocardial wall stress, and troponins (TnT and TnI) are widely used in the diagnosis of cardiac ischemia and infarction. Strenuous exercise may generate transitory ischemia, myocardial stress, and diastolic left ventricular dysfunction, inducing the increased production of both these biomarkers. We measured changes in NT-proBNP and TnT in elite cyclists during a 3-week stage race, a model of strenuous exercise. The study population was 9 professional cyclists participating in the 2011 Giro d'Italia. Pre-analytical and analytical phases scrupulously followed official recommendations. Anthropometric data, net energy expenditure and cardiac indexes (rate, diastolic and systolic blood pressure) were recorded. Blood samples were drawn pre-race (day - 1) and at days 12 and 22; NT-proBNP and highly sensitive-troponin (Hs-TnT) concentrations were assayed and corrected for plasma volume changes. Body-mass index decreased and energy expenditure increased by 52% during the race. NT-proBNP concentrations increased [day -1:23.52 ng/L (9.67-34.33); day 12:63.46 ng/L (22.15-93.31); P = 0.039; day 22:89.26 ng/L (34.66-129.78) vs.day -1; P < 0.001] and correlated with heart rate (r = -0.51; P = 0.006), systolic pressure (r = 0.39; P = 0.046) and energy expenditure (r = 0.70; P < 0.001). TnT concentrations did not vary, but a widened TnT amplitude distribution was observed. Increases in NT-proBNP correlated with higher energy expenditure over a 3-week cycling stage race, possibly indicating myocardial stress.