Alsabih, Ahmed O.N.
Effects of prior resistance or endurance exercise on metabolism during and after moderate intensity exercise.
MSc(R) thesis, University of Glasgow.
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Loss of body fat requires a negative energy balance, thus, interventions that increase fat oxidation are likely have beneficial effects in the prevention and management of obesity. Recent studies have indicated that prior resistance exercise increases fat oxidation during subsequent moderate intensity exercise. However, it is not clear from the data presented in these studies whether any prior exercise would increase subsequent fat oxidation, or whether this enhanced fat oxidation continues in the post-exercise period. Therefore, the purpose of this study was to compare the effects of prior resistance and prior endurance exercise (moderate- and high-intensity exercise) on metabolic responses and fat oxidation both during and after a subsequent bout of moderate intensity exercise.
With institutional ethics approval, nine healthy men (mean ± SD: Age 26.3 ± 5.7 years; body mass index (BMI) 26.0 ± 3.0 kg.m-2, body mass 76.9 ± 7.7 kg, fat free mass (FFM) 62.0 ± 6.1 kg, maximal oxygen uptake VO2 max 47 ± 5.6 ml kg-1 min-1) participated. Following preliminary tests, volunteers undertook three main experimental trials in a random order, separated by a week. For each trial volunteers attended in the fasted state; consumed a standard 600 kcal breakfast; then undertook either 30 min moderate exercise at 40% VO2 max reserve, prior moderate trial (M), 15 min high intensity exercise at 80% VO2 max reserve prior high trial (H), or 30 min resistance exercise comprising 3 x 10 reps of six exercises working the major muscle groups, prior resistance trial (R), [Ex.1]; following 30 min of rest [post-Ex.1] and a further 60 minutes of moderate-intensity exercise [Ex.2] was completed. Volunteers were then provided with a standard test lunch (800 kcal) and observations were continued during a further 4.5 hours of rest [post-Ex.2]. Mixed expired air and blood samples were taken at regular intervals throughout the trial. Data were compared using two-way repeated-measures ANOVA, with post-hoc Tukey test and are presented as mean ± SEM unless otherwise stated. Significance was accepted at p < 0.05.
Area under the curve (AUC) over the total study duration 7.5 hours (0-450 min), for oxygen uptake (VO2), carbon dioxide output (VCO2), and respiratory exchange ratio (RER) did not differ between the different interventions. However, a summary measurements of the AUC during different phases of the study showed that during Ex.1,VO2 was lower in the (R) = 42.0 ± 2.5 l/min compared with the in the (H) = 49.2 ± 2.5 l/min, (P < 0.05). Post Ex.1 VO2 was significantly higher in (H) = 21.4 ± 1.0 l/min, compared with the (M) = 15.0 ± 0.8 l/min, (P < 0.05). During the first exercise session Ex.1, RER was significantly different between trials (M vs. H vs. R: 0.88 ± 0.01 vs. 0.95 ± 0.01 vs. 1.01 ± 0.02, P < 0.01). During the second exercise session Ex2, RER was significantly lower in (R) = 0.84 ± 0.01 than (M) = 0.88 ± 0.01, (P < 0.05). Area under the curve over the total study duration 7.5 hours (0-450 min), for plasma glucose, insulin, non-esterified fatty acid (NEFA) and triglyceride (TG), were not different between the different trials. However, at the end of Ex.1 at the 60 min time point, glucose and insulin concentrations were significantly lower in (M) compared to (H) ,P < 0.05. Non-esterified fatty acid concentration was significantly lower in (R) compared to (M) at the 180 time point (P < 0.01). Triglyceride concentrations were significantly lower in (M) compared to (R) at the 75 min time point (P < 0.01), at the 180 min time point (P < 0.05), and at the end of the trial at the 390 min and 450 min time points (P < 0.01). Furthermore, TG concentrations were significantly higher in (H) than in (M) at the end of the trial at time points 390 min (P < 0.05), 450 min (P < 0.01)
These data demonstrate that the respiratory exchange ratio (RER) is lower during moderate intensity exercise when this is preceded by resistance compared to moderate and high intensity exercise. This is consistent with the previous observations. However, RER during Ex.1 was significantly higher (exceeding 1.0, which suggests a non metabolic source of CO2) during resistance exercise compared to both moderate and high intensity exercise, and RER was not different between the trials over the total study period. This indicates that, compared to prior moderate and high intensity exercise, prior resistance exercise offers no clear additional benefits for increased fat oxidation during and after subsequent moderate intensity exercise. With regards to triglyceride, the data from this thesis suggests that prior moderate intensity exercise may have a slight advantage, with lower triglyceride plasma concentration during and after subsequent moderate intensity exercise and 3-4 hours postprandial, compared to prior high and resistance exercise. In addition, this work has shown that there is no difference in fat oxidation over the course of the day, between the different interventions
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