Comparison of oxygen uptake during and after the execution of resistance exercises and exercises performed on ergometers, matched for intensity.

The aim of this study was to compare the values of oxygen uptake (VO2) during and after strength training exercises (STe) and ergometer exercises (Ee), matched for intensity and exercise time. Eight men (24 ± 2.33 years) performed upper and lower body cycling Ee at the individual's ventilatory threshold (VE/VCO2). The STe session included half squats and the bench press which were performed with a load at the individual blood lactate concentration of 4 mmol/l. Both sessions lasted 30 minutes, alternating 50 seconds of effort with a 10 second transition time between upper and lower body work. The averaged overall VO2 between sessions was significantly higher for Ee (24.96 ± 3.6 ml·kg·min-1) compared to STe (21.66 ± 1.77 ml·kg·min-1) (p = 0.035), but this difference was only seen for the first 20 minutes of exercise. Absolute VO2 values between sessions did not reveal differences. There were more statistically greater values in Ee compared to STe, regarding VO2 of lower limbs (25.44 ± 3.84 ml·kg·min-1 versus 21.83 ± 2·24 ml·kg·min-1; p = 0.038) and upper limbs (24.49 ± 3.84 ml·kg·min-1 versus 21.54 ± 1.77 ml·kg·min-1; p = 0.047). There were further significant differences regarding the moment effect (p<0.0001) of both STe and Ee sessions. With respect to the moment × session effect, only VO2 5 minutes into recovery showed significant differences (p = 0.017). In conclusion, although significant increases in VO2 were seen following Ee compared to STe, it appears that the load/intensity, and not the material/equipment used for the execution of an exercise, are variables that best influence oxygen uptake.

Combustion, respiration and intermittent exercise: a theoretical perspective on oxygen uptake and energy expenditure.

While no doubt thought about for thousands of years, it was Antoine Lavoisier in the late 18th century who is largely credited with the first "modern" investigations of biological energy exchanges. From Lavoisier's work with combustion and respiration a scientific trend emerges that extends to the present day: the world gains a credible working hypothesis but validity goes missing, often for some time, until later confirmed using proper measures. This theme is applied to glucose/glycogen metabolism where energy exchanges are depicted as conversion from one form to another and, transfer from one place to another made by both the anaerobic and aerobic biochemical pathways within working skeletal muscle, and the hypothetical quantification of these components as part of an oxygen (O2) uptake measurement. The anaerobic and aerobic energy exchange components of metabolism are represented by two different interpretations of O2 uptake: one that contains a glycolytic component (1 L O2 = 21.1 kJ) and one that does not (1 L O2 = 19.6 kJ). When energy exchange transfer and oxygen-related expenditures are applied separately to exercise and recovery periods, an increased energy cost for intermittent as compared to continuous exercise is hypothesized to be a direct result.

Estimating the energy costs of intermittent exercise.

To date, steady state models represent the only acceptable methodology for the estimation of exercise energy costs. Conversely, comparisons made between continuous and intermittent exercise generally reveal major physiological discrepancies, leading to speculation as to why steady state energy expenditure models should be applied to intermittent exercise. Under intermittent conditions, skeletal muscle invokes varying aerobic and anaerobic metabolic responses, each with the potential to make significant contributions to overall energy costs. We hypothesize that if the aerobic-only energetic profile of steady state exercise can be used to estimate the energetics of non-steady state and intermittent exercise, then the converse also must be true. In fact, reasonable estimates of energy costs to work volumes or work rates can be demonstrated under steady state, non-steady state and intermittent conditions; the problem with the latter two is metabolic variability. Using resistance training as a model, estimates of both aerobic and anaerobic energy cost components, as opposed to one or the other, have reduced the overall energetic variability that appears inherent to brief, intense, intermittent exercise models.

Efeitos agudos de diferentes métodos de treinamento com pesos sobre o gasto energético em homens treinados / Acute effects of different weight training methods on energy expenditure in trained men

INTRODUÇÃO: O treinamento com pesos vem sendo amplamente utilizado como estratégia de controle e redução ponderal, assim o gasto energético (GE) contribui de forma significativa para este processo. OBJETIVO: Comparar os efeitos agudos do método circuito (MC) com o método tradicional (MT) sobre o GE. MÉTODOS: Trata-se de uma pesquisa com delineamento crossover e aleatorizado, a amostra foi composta por 10 homens adultos treinados com idade entre 18 e 29 anos. Foram realizadas duas sessões experimentais com wash out de sete dias: no MC os exercícios foram realizados alternados por segmento em forma de estações, durante o MT os exercícios foram realizados em séries consecutivas. Ambos os métodos seguiram a mesma sequência de oito exercícios com o mesmo trabalho total: 60% de 1RM, 24 séries/estações e 10 repetições. O lactato sanguíneo foi coletado em repouso e a cada três séries/estações. O ar expirado foi coletado por 30 minutos antes e ~31 minutos durante todas as sessões de treinamento. O GE aeróbio de exercício (GEAE, kj) e do intervalo de recuperação (GEAIR, kj) foram estimados pela calorimetria indireta através da medida do consumo de oxigênio e o GE anaeróbio (GEA, kj) pela concentração de lactato sanguíneo ([La]). O GE total (GET, kj) foi registrado pelo somatório do GEA, GEAE e GEAIR. RESULTADOS: Os dados demonstraram que o GEA foi maior no MT do que o MC, no entanto, o GEAE, GEAIR e o GET não foram diferentes significativamente entre os métodos. O MT apresentou maior [La] do que o MC. CONCLUSÃO: Conclui-se que o MC e o MT produzem similar GET, contudo, percebe-se que o MT utiliza mais a via anaeróbia do que o MC.

INTRODUCTION: The weight training has been widely used as strategy of reduction and weight control, so the energy expenditure (EE) contributes significantly to this process. OBJECTIVE: Compare the acute effects of the circuit method (CM) with the traditional method (TM) on the EE. METHODS: This is a research with randomized crossover design; the sample consisted of ten adult men recreationally trained aged between 18 to 29 years. There were two experimental sessions with seven-day wash out: in CM the exercises were performed by alternating segment in form of stations, during TM the exercises were performed in consecutive sets. Both training methods followed the same sequence of eight exercises with the same total work: 60% of 1RM, 24 sets/stations and ten repetitions. The collection of blood lactate was performed at rest and the every three sets/stations. The expired air was collected per 30 minutes before and ~31 minutes during all the training sessions. The aerobic exercise (AEEE, kj) and of rest interval (RIEE, kj) EEs were estimated by indirect calorimetry by measuring oxygen consumption and the anaerobic EE (AEE, kj) by blood lactate concentration ([La]). The total EE (TEE, kj) was recorded by the sum of AEE, RIEE and AEE. RESULTS: Data showed that the AEE was greater in TM than the CM; however, the AEEE, RIEE and the TEE were not significantly different between the methods. The TM presented higher [La] than the CM. CONCLUSION: We conclude that the CM and TM produces similar EE during and post-workout, however, one realizes that the TM uses more anaerobic system than the MC.

Glucose and fat oxidation: bomb calorimeter be damned.

For both respiration and combustion, the energy loss difference between glucose and fat oxidation often is referenced to the efficiency of the fuel. Yet, the addition of anaerobic metabolism with ATP resynthesis to complete respiratory glucose oxidation further contributes to energy loss in the form of entropy changes that are not measured or quantified by calorimetry; combustion and respiratory fat/lactate oxidation lack this anaerobic component. Indeed, the presence or absence of an anaerobic energy expenditure component needs to be applied to the estimation of energy costs in regard to glucose, lactate, and fuel oxidation, especially when the measurement of oxygen uptake alone may incorrectly define energy expenditure.

The effect of time-under-tension and weight lifting cadence on aerobic, anaerobic, and recovery energy expenditures: 3 submaximal sets.

We examined the aerobic and anaerobic energy expenditures of weight lifting (bench press); submaximal work was kept constant among protocols. Ten male subjects (age, 23.2 ± 3.1 years; height, 177.3 ± 5.3 cm; weight, 82.1 ± 11.5 kg) were randomly assigned to 3 lifting sessions of 3 sets of 5 repetitions at 70% 1 repetition maximum (1RM) using 3 lifting cadences: 1.5 s down and 1.5 s up (15 s per set), 4 s down and 1 s up (25 s per set), and 1 s down and 4 s up (25 s per set). No differences were found among the aerobic exercise energy expenditures for each lifting cadence. However, anaerobic energy expenditure was significantly different among protocols: 1.5 down-1.5 up, 16.5 ± 8.1 kJ; 4 down-1 up, 21.6 ± 8.1 kJ; and 1 down-4 up, 26.7 ± 7.2 kJ (p = 0.001). Excess postexercise oxygen consumption (EPOC; after each set) was lower for 1.5 down-1.5 up, 38.6 ± 17.8 kJ; versus 4 down-1 up, 50.2 ± 23.5 kJ; and 1 down-4 up, 50.0 ± 22.6 kJ (p = 0.002). Total energy expenditure also was significantly less for 1.5 up-1.5 down, 60.2 ± 23.8 kJ; versus 4 down-1 up, 80.0 ± 27.7 kJ; and 1 down-4 up, 84.2 ± 28.3 kJ (p = 0.001). Differences in EPOC and total energy expenditure with submaximal lifting were based not on the amount of work performed or with a particular eccentric-concentric cadence, but on the time to completion of the weight lifting exercise - time-under-tension; longer submaximal lifting times had greater energy expenditure.

Energy expenditure characteristics of weight lifting: 2 sets to fatigue.

We investigated the work performed and energy expenditure characteristics within and among 2 sets of the bench press at 70%, 80%, and 90% of 1 repetition maximum (1RM). For both sets fatigue was the end point. We asked: do multiple sets affect subsequent work output along with aerobic, anaerobic, and excess postexercise oxygen consumption (EPOC) contributions? Ten males participated. Work was significantly less for the 2nd set within the 70% and 80% protocols, but not the 90% protocol. Anaerobic (glycolytic) energy expenditure was less for the 2nd set within all protocols. However, within all protocols, the work / energy expenditure ratio was not different between sets. Overall work was significantly different among protocols, becoming less as the weight lifted was increased: 70%, 637.1 ± 122.4 J; 80%, 512.4 ± 93.4 J; 90%, 324.7 ± 92.6 J (p < 0.001). EPOC was not different among protocols after the 1st set, 2nd set, or combined overall. Moreover, the overall EPOC did not correlate with overall work performed (r = 0.31, p = 0.11). EPOC overall did correlate with aerobic (r = 0.68, p < 0.001) and anaerobic (r = 0.65, p < 0.001) energy expenditures. In terms of a work / energy expenditure ratio, the least amount of completed work at 90% 1RM required greater energy expenditure as compared with 70% and 80% because of an EPOC that is similar for all. As more work is completed (i.e., lower weight, more repetitions), aerobic and anaerobic exercise energy expenditures appear to increase accordingly, yet absolute EPOC remains essentially unchanged, contributing less to the overall energy expenditure.

Quantifying the immediate recovery energy expenditure of resistance training.

As opposed to steady state aerobic-type exercise involving long duration, continuous, rhythmic, large muscle group activities that consume large volumes of oxygen, a resistance training set is brief, intermittent, uses multiple and isolated muscles, and is considered anaerobic in description. Because differences are evident between aerobic- and anaerobic-type exercise, it is proposed that the methods used for estimating resistance training energy expenditure should be different as compared with walking, jogging, cycling, etc. After a single set of weight lifting, for example, oxygen uptake is greater in the recovery from lifting as opposed to during the actual exercise; likewise, the anaerobic energy expenditure contribution to lifting may exceed exercise oxygen uptake. Recovery energy expenditure also does not appear well related to the anaerobic energy expenditure of the previous exercise. Based on this evidence, it is suggested that anaerobic-type exercise should not be based on aerobic-type models. In terms of excess postexercise oxygen consumption, a hypothesis is presented in regard to how non-steady-state energy expenditure in the immediate recovery from intense exercise should be properly quantified (e.g., in-between resistance training sets). The proposed concept is based on possible substrate or fuel use differences during intense exercise and aerobic recovery and the biochemistry and bioenergetics of glucose, lactate, and fat oxidation. It is proposed that immediately after a single weight lifting bout or in-between resistance training sets, as O2 uptake plummets rapidly back toward pre-exercise levels, a separate energy expenditure conversion is required for recovery that differs from non-steady-state exercise, that is, 1 L of recovery oxygen uptake = 19.6 kJ (4.7 kcal) (not the standard exercise conversion of 1 L of oxygen uptake = 21.1 kJ) (5.0 kcal).

Aerobic, anaerobic, and excess postexercise oxygen consumption energy expenditure of muscular endurance and strength: 1-set of bench press to muscular fatigue.

We use a new approach to the estimation of energy expenditure for resistance training involving nonsteady state measures of work (weight × displacement), exercise O2 uptake, blood lactate, and recovery O2 uptake; all lifts were performed to muscular failure. Our intent was to estimate and compare absolute and relative aerobic and anaerobic exercise energy expenditure and recovery energy expenditure. Single-set bench press lifts of ∼ 37, ∼ 46, and ∼ 56% (muscular endurance-type exercise) along with 70, 80, and 90% (strength-type exercise) of a 1 repetition maximum were performed. Collectively, the muscular endurance lifts resulted in larger total energy expenditure (60.2 ± 14.5 kJ) as compared with the strength lifts (43.2 ± 12.5 kJ) (p = 0.001). Overall work also was greater for muscular endurance (462 ± 131 J) as opposed to strength (253 ± 93 J) (p = 0.001); overall work and energy expenditure were related (r = 0.87, p = 0.001). Anaerobic exercise and recovery energy expenditure were significantly larger for all strength lifts as compared with aerobic exercise energy expenditure (p < 0.001). For the muscular endurance lifts, anaerobic energy expenditure was larger than recovery energy expenditure (p < 0.001) that in turn was larger than aerobic exercise energy expenditure (p < 0.001). We conclude that for a single set of resistance training to fatigue, the anaerobic and recovery energy expenditure contributions can be significantly larger than aerobic energy expenditure during the exercise. To our surprise, recovery energy expenditure was similar both within strength and muscular-endurance protocols and between protocols; moreover, recovery energy expenditure had little to no relationship with aerobic and anaerobic exercise energy expenditure or work.

Energy expenditure before, during, and after the bench press.

We examined the reliability and validity of non-steady-state aerobic and anaerobic estimations of energy expenditure during and after bouts of the bench press exercise. A Smith machine, not free weights, was used. On different days, 8 subjects (28.4 +/- 9.0 years; 170.4 +/- 11.9 cm; 68.4 +/- 14.0 kg) were randomly assigned to 3 lifting sessions of 7, 14, and 21 reps at 50% of the 1-repetition maximum (9 total sessions). No differences were found in any of the triplicate measures within 7, 14, and 21 reps. Coefficients of variation for 7, 14, and 21 reps were, respectively, for resting blood lactate, 20.3, 24.3, and 26.7%; for anaerobic exercise energy expenditure, 47.9, 29.1, and 14.2%; for aerobic exercise energy expenditure, 47.4, 28.3, and 18.4%; for excess postexercise O2 consumption, 33.0, 26.5, and 29.2%; for total energy expenditure, 21.0, 15.4, and 15.1%; and, for work, 4.5, 5.0, and 5.4%. Anaerobic energy expenditure made a significant contribution to exercise energy expenditure for all lifts (p < 0.05). Changes (Delta) in work were related to changes in energy expenditure (Delta aerobic exercise energy expenditure, r = 0.54; Delta anaerobic exercise energy expenditure, r = 0.88; Delta total energy expenditure, r = 0.88; p < 0.001). Although variability is evident and often considerable during exercise and recovery in this heterogonous sample, we suggest that non-steady-state estimates of aerobic and anaerobic exercise energy expenditure with excess postexercise O2 consumption provide a reasonable estimate of the energy cost of a single bout of weight lifting. Our results agree with those of others, without the need for multiple steady-state measurements or for the assumption of proportional increases between work and O2 uptake.

Onset of the Thermic Effect of Feeding (TEF): a randomized cross-over trial.

BACKGROUND: The purpose of this investigation was to identify the onset of the thermic effect of feeding (TEF) after ingestion of a high carbohydrate (CHO) and a high protein (PRO) 1255 kJ (300 kcal) drink. METHODS: Resting metabolic rate (RMR) and TEF were measured over 30-minute periods via indirect calorimetry using a ventilated hood technique. Eighteen subjects (7 men and 11 women) completed two randomized, double-blind trials. Data were collected in 1-minute measurement intervals. RMR was subtracted from TEF and the time of onset was obtained when two consecutive data points exceeded 5% and 10% of resting metabolic rate. RESULTS: At 5% above RMR the onset of TEF for CHO was 8.4 +/- 6.2 minutes and was not different as compared to PRO, 8.6 +/- 5.2 minutes (p = 0.77). Likewise, no differences were found with a 10% increase above RMR: CHO, 14.1 +/- 7.5 min; PRO, 16.7 +/- 6.7 min (p = 0.36). Several subjects did not show a 10% increase within 30-min. CONCLUSION: We conclude that the onset of TEF is variable among subjects but is initiated within about 5 to 20-min for most subjects after ingestion of a 1255 kJ liquid meal. No differences were found between CHO or PRO liquid meals.

Contribution of blood lactate to the energy expenditure of weight training.

Bioenergetic interpretations of energy transfer specify that rapid anaerobic, substrate-level adenosine triphosphate (ATP) turnover with lactate production is not appropriately represented by an oxygen uptake measurement. Two types of weight training, 60% of 1 repetition maximum (1RM) with repetitions to exhaustion and 80% of 1RM with limited repetitions, were compared to determine if blood lactate measurements, as an estimate of rapid substrate-level ATP turnover, provide a significant contribution to the interpretation of total energy expenditure as compared with oxygen uptake methods alone. The measurement of total energy expenditure consisted of blood lactate, exercise oxygen uptake, and a modified excess postexercise oxygen consumption (EPOC); oxygen uptake-only measurements consisted of exercise oxygen uptake and EPOC. When data from male and female subjects were pooled, total energy expenditure was significantly higher for reps to exhaustion (arm curl, +27 kJ; bench press, +27 kJ; leg press, +38 kJ; p < 0.03) and limited reps (arm curl, +12 kJ; bench press, +23 kJ; leg press, + 24 kJ; p < 0.05) when a separate measure of blood lactate was part of the interpretation. When the data from men and women were analyzed separately, blood lactate often made a significant contribution to total energy expenditure for reps to exhaustion (endurance-type training), but this trend was not always statistically evident for the limited reps (strength-type training) protocol. It is suggested that the estimation of total energy expenditure for weight training is improved with the inclusion, rather than the omission, of an estimate of rapid anaerobic substrate-level ATP turnover.

Estimating energy expenditure for brief bouts of exercise with acute recovery.

Four indirect estimations of energy expenditure were examined, (i) O(2) debt, (ii) O(2) deficit, (iii) blood lactate concentration, and (iv) excess CO(2) production during and after 6 exercise durations (2, 4, 10, 15, 30, and 75 s) performed at 3 different intensities (50%, 100%, and 200% of VO(2) max). Analysis of variance (ANOVA) was used to determine if significant differences existed among these 4 estimations of anaerobic energy expenditure and among 4 estimations of total energy expenditure (that included exercise O(2) uptake and excess post-exercise oxygen consumption, or EPOC, measurements). The data indicate that estimations of anaerobic energy expenditure often differed for brief (2, 4, and 10 s) bouts of exercise, but this did not extend to total energy expenditure. At the higher exercise intensities with the longest durations O(2) deficit, blood lactate concentration, and excess CO(2) estimates of anaerobic and total energy expenditure revealed high variability; however, they were not statistically different. Moreover, they all differed significantly from the O(2) debt interpretation (p < 0.05). It is concluded that as the contribution of rapid substrate-level ATP turnover with lactate production becomes larger, the greatest error in quantifying total energy expenditure is suggested to occur not with the method of estimation, but with the omission of a reasonable estimate of anaerobic energy expenditure.

Differences in oxygen uptake but equivalent energy expenditure between a brief bout of cycling and running.

BACKGROUND: We examined aerobic and anaerobic exercise energy expenditure and excess post-exercise oxygen consumption (EPOC) between a 250 Watt, 1-minute bout of cycling and uphill treadmill running. METHODS: Fourteen active to well-trained subjects volunteered for the investigation (VO2 max: 57.0 +/- 12.9 ml x kg x min(-1) cycle; 59.3 +/- 13.7 ml x kg x min(-1) run; p = 0.44). Anaerobic energy expenditure was estimated from Deltablood lactate. Statistical analysis was completed using a paired t-test (mean +/- SD). RESULTS: Perceived exertion did not differ between exercise bouts (14.0 +/- 2.3 cycle; 13.2 +/- 2.1 run; p = 0.29). Exercise oxygen uptake was significantly greater for running (41.4 +/- 6.9 kJ) compared to cycling (31.7 +/- 7.7 kJ) (p = 0.0001). EPOC was not different between cycling and running (p = 0.21) so that exercise oxygen uptake + EPOC was greater for running (103.0 +/- 13.5 kJ) as compared to cycling (85.4 +/- 20.2 kJ; p = 0.008). Anaerobic energy expenditure was significantly greater for cycling (32.7 +/- 8.9 kJ) versus running (22.5 +/- 11.1 kJ) (p = 0.009). Aerobic + anaerobic exercise energy expenditure (cycle 64.3 +/- 12.2 kJ; run 63.9 +/- 10.1 kJ) (p = 0.90) and total energy expenditure (including EPOC; cycle 118.0 +/- 21.8 kJ; run 125.4 +/- 19.1 kJ; p = 0.36) were similar for cycling and running. CONCLUSION: Oxygen-only measures reveal discrepancy in energy expenditure between cycling and uphill running. Measurements of exercise oxygen uptake, Deltablood lactate and a modified EPOC promote the hypothesis of a similarity in exercise and total energy expenditure between 1-minute work-equivalent bouts of cycling and uphill running.

Contribution of anaerobic energy expenditure to whole body thermogenesis.

Heat production serves as the standard measurement for the determination of energy expenditure and efficiency in animals. Estimations of metabolic heat production have traditionally focused on gas exchange (oxygen uptake and carbon dioxide production) although direct heat measurements may include an anaerobic component particularly when carbohydrate is oxidized. Stoichiometric interpretations of the ratio of carbon dioxide production to oxygen uptake suggest that both anaerobic and aerobic heat production and, by inference, all energy expenditure--can be accounted for with a measurement of oxygen uptake as 21.1 kJ per liter of oxygen. This manuscript incorporates contemporary bioenergetic interpretations of anaerobic and aerobic ATP turnover to promote the independence of these disparate types of metabolic energy transfer: each has different reactants and products, uses dissimilar enzymes, involves different types of biochemical reactions, takes place in separate cellular compartments, exploits different types of gradients and ultimately each operates with distinct efficiency. The 21.1 kJ per liter of oxygen for carbohydrate oxidation includes a small anaerobic heat component as part of anaerobic energy transfer. Faster rates of ATP turnover that exceed mitochondrial respiration and that are supported by rapid glycolytic phosphorylation with lactate production result in heat production that is independent of oxygen uptake. Simultaneous direct and indirect calorimetry has revealed that this anaerobic heat does not disappear when lactate is later oxidized and so oxygen uptake does not adequately measure anaerobic efficiency or energy expenditure (as was suggested by the "oxygen debt" hypothesis). An estimate of anaerobic energy transfer supplements the measurement of oxygen uptake and may improve the interpretation of whole-body energy expenditure.

Direct and indirect calorimetry of lactate oxidation: implications for whole-body energy expenditure.

Whole-body energy expenditure for heavy/severe exercise is currently accounted for by either: (1) anaerobic and oxygen uptake measures during exercise where recovery energy expenditure is omitted; or (2) oxygen uptake during, and an EPOC (excess post-exercise oxygen consumption), measure following exercise where substrate level phosphorylation during exercise is considered part of EPOC. Simultaneous direct/indirect calorimetry enabled us to determine if a thermodynamic reversal (i.e. heat consumption) takes place as the highly exothermic pyruvate to lactate reaction proceeds in the opposite direction. Reversibility implies that oxygen uptake (e.g. EPOC) can indeed account for rapid glycolytic ATP production regardless if lactate is formed or not (e.g. 1.2 g glucose catabolism = 20.9 kJ x l O2(-1)). Cultured hybrid cells and mouse cardiac muscle fibres were utilized in simultaneous calorimetry and respirometry experiments where pyruvate or lactate was predominantly oxidized. The calorimetric to respiratory ratio was determined using heat flux (pW x cell(-1)) and oxygen flux (pmol x s(-1) cell(-1)) measures. Ten cell experiments gave calorimetric to respiratory ratios that showed no statistical difference (P= 0.97) whether cells respired predominantly on lactate (-516+/-53 kJ x mol O2(-1)) or pyruvate (- 517+/-89 kJ x mol O2(-1)). In three cardiac preparations, the calorimetric to respiratory ratio was -502+/-15 kJ x mol O2(-1) for lactate and -506+/-47 kJ x mol O2(-1) for pyruvate, again a non-significant difference (P= 0.91). Heat consumption did not occur during lactate oxidation. These results suggest that rapid glycolytic ATP and lactate production, and lactate oxidation, are both independently associated with heat production and thus represent separate and additive components to the measurement of total energy expenditure for exercise and recovery.

Unloading-induced remodeling in the normal and hypertrophic left ventricle.

To date, no study has assessed the degree of similarity between left ventricular (LV) reverse remodeling and atrophic remodeling. Stable LV hypertrophy was induced by creation of an arteriovenous fistula (AVF) in Lewis rats (32 days). LV unloading was induced by heterotopic transplantation of normal (NL-HT) and/or hypertrophic (AVF-HT) hearts (7 days). We compared indexes of remodeling in AVF, NL-HT, and AVF-HT groups with those of normal controls. LV unloading induced decreases in cardiomyocyte size in NL-HT and AVF-HT hearts. NL-HT and AVF-HT LV were both characterized by relative increases in collagen concentration that were largely a reflection of decreases in myocyte volume. NL-HT and AVF-HT LV were associated with similar increases in matrix metalloproteinase (MMP-2 and -9) zymographic activity, without change in the abundance of the tissue inhibitors of the MMPs. In contrast, AVF-HT, but not NL-HT, was associated with a dramatic increase in collagen cross-linking. Our findings suggest an overall similarity in the response of the normal and hypertrophic LV to surgical unloading. However, the dramatic increase in collagen cross-linking after just 1 wk of unloading suggests a potential difference in the dynamics of collagen metabolism between the two models. Further studies will be required to determine the precise molecular mechanisms responsible for these differences in extracellular matrix regulation. However, with respect to these and related issues, heterotopic transplantation of hypertrophied hearts will be a useful small animal model for defining mechanisms of myocyte-matrix interactions during decreased loading conditions.