You will burn more fat during the cardio session if you perform it at 60 % max..
As you increase the intensity, the substrate utilization shifts to plasma glucose instead of fat.
It's also true that if the duration of cardio sessions is the same, you will burn slightly more calories during HIIT, but more of those calories will be glucose.
It's true that HIIT might increase your resting metabolic rate more than low & moderate intensity cardio, but I don't know if the difference would be as significant in someone who already performs resistance training, since resistance training by itself can increase resting fat oxidation & oxygen consumption (check the last three studies)...
Conclusion of study 3, for example, was "We found no evidence that the high-intensity physical training was more effective than the moderate-intensity physical training in enhancing body composition"...
Try both, or cycle between moderate & high intensity.
(1) Substrate metabolism during different exercise intensities in endurance-trained women.
Romijn JA, Coyle EF, Sidossis LS, Rosenblatt J, Wolfe RR.
Department of Endocrinology and Metabolism, Leiden University Medical Center, 2300 RC Leiden, The Netherlands.
jaromijn@endo.azl.nl
We have studied eight endurance-trained women at rest and during exercise at 25, 65, and 85% of maximal oxygen uptake. The rate of appearance (R(a)) of free fatty acids (FFA) was determined by infusion of [(2)H(2)]palmitate, and fat oxidation rates were determined by indirect calorimetry. Glucose kinetics were assessed with [6,6-(2)H(2)]glucose. Glucose R(a) increased in relation to exercise intensity. In contrast, whereas FFA R(a) was significantly increased to the same extent in low- and moderate-intensity exercise, during high-intensity exercise, FFA R(a) was reduced compared with the other exercise values.
Carbohydrate oxidation increased progressively with exercise intensity, whereas the highest rate of fat oxidation was during exercise at 65% of maximal oxygen uptake. After correction for differences in lean body mass, there were no differences between these results and previously reported data in endurance-trained men studied under the same conditions, except for slight differences in glucose metabolism during low-intensity exercise (Romijn JA, Coyle EF, Sidossis LS, Gastaldelli A, Horowitz JF, Endert E, and Wolfe RR. Am J Physiol Endocrinol Metab 265: E380-E391, 1993). We conclude that the patterns of changes in substrate kinetics during moderate- and high-intensity exercise are similar in trained men and women.
(2)The effects of increasing exercise intensity on muscle fuel utilisation in humans.
van Loon LJ, Greenhaff PL, Constantin-Teodosiu D, Saris WH, Wagenmakers AJ.
Nutrition and Toxicology Research Institute NUTRIM, Department of Human Biology, Maastricht University, Maastricht, The Netherlands.
l.vanloon@hb.unimaas.nl
1. Contemporary stable isotope methodology was applied in combination with muscle biopsy sampling to accurately quantify substrate utilisation and study the regulation of muscle fuel selection during exercise. 2. Eight cyclists were studied at rest and during three consecutive 30 min stages of exercise at intensities of 40, 55 and 75 % maximal workload (W(max)). A continuous infusion of [U-(13)C]palmitate and [6,6-(2)H(2)]glucose was administered to determine plasma free fatty acid (FFA) oxidation and estimate plasma glucose oxidation, respectively. Biopsy samples were collected before and after each exercise stage. 3. Muscle glycogen and plasma glucose oxidation rates increased with every increment in exercise intensity.
Whole-body fat oxidation increased to 32 +/- 2 kJ min(-1) at 55 % W(max), but declined at 75 % W(max) (19 +/- 2 kJ min(-1)). This decline involved a decrease in the oxidation rate of both plasma FFA and triacylglycerol fat sources (sum of intramuscular plus lipoprotein-derived triacylglycerol), and was accompanied by increases in muscle pyruvate dehydrogenase complex activation and acetylation of the carnitine pool, resulting in a decline in muscle free carnitine concentration. 4. We conclude that the most likely mechanism for the reduction in fat oxidation during high-intensity exercise is a downregulation of carnitine palmitoyltransferase I, either by this marked decline in free carnitine availability or by a decrease in intracellular pH.
Am J Clin Nutr 2002 May;75(5):818-26 Related Articles, Links
(3)Effects of exercise intensity on cardiovascular fitness, total body composition, and visceral adiposity of obese adolescents.
Gutin B, Barbeau P, Owens S, Lemmon CR, Bauman M, Allison J, Kang HS, Litaker MS.
Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, GA 30912, USA.
bgutin@mail.mcg.edu
BACKGROUND: Little is known about how the intensity of exercise influences cardiovascular fitness and body composition, especially in obese adolescents. OBJECTIVE: Our goal was to determine the effects of physical training intensity on the cardiovascular fitness, percentage of body fat (%BF), and visceral adipose tissue (VAT) of obese adolescents. DESIGN: Obese 13-16-y-olds (n = 80) were assigned to 1) biweekly lifestyle education (LSE), 2) LSE + moderate-intensity physical training, or 3) LSE + high-intensity physical training. The intervention lasted 8 mo. Physical training was offered 5 d/wk, and the target energy expenditure for all subjects in physical training groups was 1047 kJ (250 kcal)/session. Cardiovascular fitness was measured with a multistage treadmill test, %BF with dual-energy X-ray absorptiometry, and VAT with magnetic resonance imaging. RESULTS: The increase in cardiovascular fitness in the high-intensity physical training group, but not in the moderate-intensity group, was significantly greater than that in the LSE alone group (P = 0.009); no other comparisons of the 3 groups were significant. Compared with the LSE alone group, a group composed of subjects in both physical training groups combined who attended training sessions >or=2 d/wk showed favorable changes in cardiovascular fitness (P < 0.001), %BF (P = 0.001), and VAT (P = 0.029).
We found no evidence that the high-intensity physical training was more effective than the moderate-intensity physical training in enhancing body composition. CONCLUSIONS: The cardiovascular fitness of obese adolescents was significantly improved by physical training, especially high-intensity physical training. The physical training also reduced both visceral and total-body adiposity, but there was no clear effect of the intensity of physical training.
1: Eur J Appl Physiol 2002 Mar;86(5):411-7 Related Articles, Links
Effect of an acute period of resistance exercise on excess post-exercise oxygen consumption: implications for body mass management.
Schuenke MD, Mikat RP, McBride JM.
Present address: Department of Biological Sciences, Ohio University, 128 Irvine Hall, Athens, OH 45701, USA.
mschuenke@hotmail.com
Studies have shown metabolism to remain elevated for hours following resistance exercise, but none have gone beyond 16 h, nor have they followed a whole body, high intensity exercise protocol. To examine the duration of excess post-exercise oxygen consumption (EPOC) following a period of heavy resistance exercise, seven healthy men [mean (SD) age 22 (3) years, height 177 ( cm, mass 83 (10) kg, percentage body fat 10.4 (4.2)%] engaged in a 31 min period of resistance exercise, consisting of four circuits of bench press, power cleans, and squats. Each set was performed using the subject's own predetermined ten-repetition maximum and continued until failure. Oxygen consumption ( ) measurements were obtained at consistent times (34 h pre-, 29 h pre-, 24 h pre-, 10 h pre-, 5 h pre-, immediately post-, 14 h post-, 19 h post-, 24 h post-, 38 h post-, 43 h post-, and 48 h post-exercise). Post-exercise measurements were compared to the baseline measurements made at the same time of day.
The was significantly elevated ( P<0.05) above baseline values at immediately post, 14, 19, and 38 h post-exercise. Mean daily values for both post-exercise days were also significantly elevated above the mean value for the baseline day. These results suggest that EPOC duration following resistance exercise extends well beyond the previously reported duration of 16 h. The duration and magnitude of the EPOC observed in this study indicates the importance of future research to examine a possible role for high intensity resistance training in a weight management program for various populations.
J Appl Physiol 2002 Oct 11; [epub ahead of print] Related Articles, Links
Effect of Resistance Exercise on Postprandial Lipemia.
Petitt DS, Arngrimsson SA, Cureton KJ.
Department of Exercise Science, University of Georgia, Athens, GA, USA.
The purpose of this study was to examine the effect of resistance exercise on postprandial lipemia. Fourteen young men and women participated in each of three treatments: 1) control (CON), 2) resistance exercise (RE), and 3) aerobic exercise (AE) estimated to have an energy expenditure (EE) equal that for RE. Each trial consisted of performing a treatment on Day 1 and ingesting a fat-tolerance test meal 16 hours later (Day 2). Resting metabolic rate and fat oxidation were measured at baseline and at 3 and 6 hours postprandial on Day 2. Blood was collected at baseline and at 0.5, 1, 2, 3, 4, 5, and 6 hours after meal ingestion. RE and AE were similar in EE (1.7 +/- 0.1 vs 1.6 +/- 0.1 MJ, respectively; means +/- SE), as measured using the Cosmed K4b(2). Baseline triglycerides (TG) were significantly lower after RE than after CON (19%) and AE (21%). Further, the area under the postprandial response curve (AUC) for TG, adjusted for baseline differences, was significantly lower after RE than after CON (14%) and AE (18%).
Resting fat oxidation was significantly greater after RE than after CON (21%) and AE (28%). These results indicate that resistance exercise lowers baseline and postprandial TG, and increases resting fat oxidation, 16 hours after exercise.
J Gerontol A Biol Sci Med Sci 1997 Nov;52(6):M352-5 Related Articles, Links
A single bout of concentric resistance exercise increases basal metabolic rate 48 hours after exercise in healthy 59-77-year-old men.
Williamson DL, Kirwan JP.
Noll Physiological Research Center, Pennsylvania State University, USA.
BACKGROUND: It has been shown that basal metabolic rate (BMR) decreases with age. The extent to which some of the decrease can be reversed by exercise in older men and women is unclear. Resistance exercise has been shown to significantly increase muscle mass in older individuals, and because muscle is a highly active metabolic tissue there is potential to increase BMR as a secondary outcome to the training adaptation. METHODS: Twelve healthy men aged 59-77 years performed single-leg knee extension exercise (right and left leg) and bench press lifts (16 sets, 10 reps/set with timed recovery between sets) at 75% of the individual's 3RM. Subjects only performed the concentric phase of the lift. BMR was measured on two separate occasions, once after a nonexercise control period and again 48 hrs after a bout of resistance exercise. RESULTS: BMR was significantly increased (p < .006) 48 hrs after exercise (EX) compared to control (CON) (284.0 +/- 34.0 vs 274.9 +/- 34.0 kJ/hr, respectively). Calculated over a 24-hour period, the energy expenditure corresponded to 1570 +/- 193 and 1627 +/- 193 kcal/24 hr (p < .0002) for the CON and EX measures, respectively. VO2 (L/min) was higher (p < .0002) 48 hrs after the EX bout compared to 48 hrs post-CON (0.232 +/- 0.03 vs 0.225 +/- 0.03 L/min, respectively). CONCLUSION: We conclude that in healthy 59-77-year-old men,
an acute bout of resistance exercise causes a sustained increase in BMR that persists for up to 48 hours after exercise.