A 45-minute Vigorous Exercise Bout Increases Metabolic Rate for 14 Hours

Amy M. Knab; R. Andrew Shanely; Karen D. Corbin; Fuxia Jin; Wei Sha; David C. Nieman

Disclosures

Med Sci Sports Exerc. 2011;43(9):1643-1648. 

In This Article

Methods

Subjects

Ten healthy male subjects (age range = 22–33 yr) were recruited via mass advertisement. Inclusion criteria included the following: subjects had to be nonsmokers, in good physical condition and capable of cycling vigorously for 45 min, and with no adverse medical issues including anxiety within closed spaces. Written informed consent was obtained from each subject, and the experimental procedures were approved by the institutional review board of Appalachian State University.

Baseline Testing

Two weeks before the study, subjects came to the North Carolina Research Campus Human Performance Laboratory for baseline testing that included body composition and V̇O2max testing and a full orientation regarding study requirements. Body composition was measured via dual-energy x-ray absorptiometry (GE Lunar iDXA; Milwaukee, WI). RMR was calculated using a fat-free mass-based equation (418 + (20.3 fat-free mass)).[2] This estimated RMR was used for calculating total dietary energy intake while in the metabolic chamber (1.4RMR) and then adjusted using measured data (see below). V̇O2max was measured using the COSMED Quark CPET metabolic cart (Rome, Italy) with the Lode cycle ergometer (Lode Excalibur Sport; Lode B.V., Groningen, The Netherlands) and a graded protocol with a 15-W·min−1 increase to exhaustion.[28] Several criteria were used to determine V̇O2max including an RER of 1.15 and higher, a plateau of oxygen consumption, and a maximal HR within 12 beats of the predicted maximum.

Study Design

Ten subjects completed two sessions in the chamber on nonconsecutive days (Monday and Wednesday or Tuesday and Thursday of the same week). During the first session, subjects remained in a rested state and engaged in no exercise while following the schedule of events depicted on the x axis in Figure 1. During the second session, the same schedule was followed except that subjects completed 45 min of exercise on a cycle ergometer at 57% Wmax. This order was followed to avoid the potential influence of the exercise session on energy expenditure during the subsequent session in the metabolic chamber. The duration of 45 min corresponds to the middle of the range suggested by the physical activity guidelines for Americans (30–60 min). Fifty-seven percent Wmax corresponds to a vigorous intensity of approximately 70% V̇O2max. Subjects were instructed to avoid exercise on the days before entering the chamber and to consume foods from a specific food list that has been used in prior studies to achieve a CHO intake of approximately 55% total energy.[20] Subjects were also instructed to avoid any supplements, including caffeine, for the duration of the study.

Figure 1.

Average 24-h energy expenditure on rest and exercise days. Forty-five minutes of cycling resulted in 519 ± 60.9 kcal of energy expended above rest day (P < 0.001), whereas 190 ± 71.4 kcal was expended above levels on the rest day for 14.2 h after exercise (P < 0.001). Net energy expenditure difference from the start of sleep to 18 h after exercise was 32.0 ± 39.3 kcal (P = 0.030).

At approximately 7:30 a.m., subjects reported to the metabolic chamber in an overnight fasted state (no food or beverage other than water from 11:00 p.m.). At 8:00 a.m., subjects were sealed in the chamber and were asked to stay in a seated position unless they needed to use the restroom or perform other necessary daily activities (e.g., washing hands, brushing teeth). Breakfast was served through an air lock passage at 9:00 a.m. On rest days, subjects remained in a seated position from breakfast to 12:30 p.m. when they were asked to get up and stretch for 2 min. On both rest and exercise days starting at 12:30 p.m., subjects were asked to get up and stretch for 2 min every hour until 6:30 p.m.

Lunch was served at 1:30 p.m., and dinner was served at 7:00 p.m. Subjects were asked to remain in the seated position until 8:00 p.m., at which point they were able to relax and lie down but not go to sleep. Bed time was at 10:30 p.m., and subjects were asked to lie down even if they were not sleeping. Subjects were woken at 6:30 a.m. and were allowed to move about the chamber and gather their belongings. At 7:15 a.m., subjects exited the chamber.

On arrival on the exercise day, subjects were oriented to the cycle ergometer and were instructed how to adjust wattage and report HR from the HR monitor (Polar HR Monitor; Kempele, Finland) during the test. The cycle ergometer was adjusted to fit the leg length of the subject. At 10:40 a.m., subjects prepared for exercise (e.g., stretch, change clothes, arrange room with towels and music). Subjects mounted the cycle ergometer and started pedaling at 11:00 a.m. The cycling protocol consisted of 2 min at 50% of the workload (57% W max), 2 min at 75% of the workload, 41 min at 100% of the workload, and another 2 min at 50% of the workload. Oxygen consumption and energy expenditure were measured continuously during the exercise bout, with HR recorded every 5 min. Immediately after exercise, subjects sat down for 40 min until 12:30 p.m. At 12:30 p.m., subjects were allowed to clean themselves and change clothes and then stayed in the seated position until lunch at 1:30 p.m.

Description of Metabolic Chamber

Studies were conducted in the newly constructed metabolic chamber located at the University of North Carolina at Chapel Hill Nutrition Research Institute, Kannapolis, NC. The chamber was modeled after the chambers at the National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD.[7] The University of North Carolina at Chapel Hill Nutrition Research Institute metabolic chamber is an open-circuit pull-type whole-room indirect calorimeter built with walk-in cooler panels. The metabolic chamber has a floor space of 10 feet 11 inches × 8 feet 0.5 inches, a height of 7 feet 10 inches, and an air volume of 18,346 L when fully furnished. The room is equipped with a twin bed, bedside table, chair, toilet, mirror, sink, multimedia laptop, telephone, intercom, nurse call button, specimen refrigerator, iris ports for blood draws, and two air locks that serve as food and specimen passes. There is sufficient space to include a bike or treadmill inside the chamber. The metabolic chamber has three windows, two looking outside and one looking into the observation room.

An air conditioning system mixes the air in the chamber, maintaining a preset temperature and a relative humidity of <70%. For this particular study, the average temperature maintained in the chamber was 23.1°C ± 0.30°C, and the average chamber relative humidity was 54.6% ± 1.5%. Fresh conditioned air is passively drawn into the chamber from an adjacent buffer zone. Mixed expired air is drawn out of the metabolic chamber by a small fan placed at the outlet of the chamber through a centralized sampling apparatus designed with evenly spaced sectors to ensure equal sampling throughout the chamber. The flow is set manually and kept at a constant rate, typically 60 L·min−1 (capacity is 120 L·min−1). On the rest day, the flow rate was kept at 60 L·min−1 for lean individuals and 100 L·min−1 for individuals with weights ≥130 kg. On the exercise day, the flow rate was maintained at 120 L·min−1 to account for ambient CO2 buildup during exercise. These flow rates were chosen on the basis of pilot data to assess the capacity of the chamber to handle increased CO2 loads.

Before measurements, a small sample of air was cooled to 1°C and dried, drawn by a diaphragm pump, and filtered. The CO2 and O2 analyzers are differential, and their full-scale readings were set for 0%-1%. The metabolic chamber has a passive infrared motion sensor to measure spontaneous physical activity. Oxygen consumption, CO2 production, energy expenditure, RQ, and percent activity were recorded each minute. The lag time is constant at the start and at the end of exercise. Advanced noise suppression and trend identification techniques allow for accurate measurement and time discrimination of the exercise plateau as seen by the gas analyzers. Results are then aligned with the start of the exercise time. The Weir equation for energy expenditure (EE) (kcal·min−1) = 3.941V̇O2 + 1.106V̇CO2 was used for conversion of V̇O2 (L·min−1) and V̇CO2 (L·min−1) to kilocalories.

The analyzers were calibrated weekly using standard gas mixtures (zero gas is ~21% O2, balanced nitrogen; span gas is ~20% CO2, ~1% O2, balanced nitrogen). The chamber was validated using a series of propane burn tests. Five propane burns were conducted at a flow rate of 60 L·min−1. The CO2 recovery was 97.6% ± 0.6% (mean ± SD), and the O2 recovery was 99.1% ± 0.4%. Monthly propane tests were conducted to verify the accuracy of the chamber.

Before conducting trials in the chamber, we tested the reproducibility of the 24-h EE measurement. Ten subjects (including eight from the exercise portion of the study) completed two nonconsecutive sessions in the metabolic chamber (either Monday and Wednesday or Tuesday and Thursday of the same week). Subjects were fed the same three meals during both sessions in the chamber, and urine was collected for measurement of nitrogen. The average 24-h EE difference between the two chamber sessions was 66.5 ± 74.2 kcal·d−1, corresponding to a 2.5% ± 2.3% difference between days. For the eight subjects completing four separate days in the chamber, the average coefficient of variation for the three rest days was 2.3%.

Design of Metabolic Diets

Diets during chamber days were designed to provide approximately 35% fat, 55% CHO, and 15% protein. The same foods were served at all chamber visits, with the exception of the snacks provided on the exercise day to achieve energy balance. Calories were assigned to each subject on the basis of calculated RMR × 1.4. To calculate the amount of calories to provide, we took into account that 93% of energy content is metabolizable.[27] Menus were designed and analyzed with the Esha Food Processor SQL software (Esha Research, Inc., Salem, OR). Meals were delivered at designated times and picked up 30 min later. Subjects were asked to consume all foods provided. Food intake was documented, and on the rare occasion that a subject did not eat all of the food provided, the food was weighed back, and the nutrients were removed from the final nutrient analysis. To ensure energy balance conditions, 3- and 7-h predictions of 24-h EE from the chamber software were used to modify the baseline menu. On the exercise day, snacks with the same nutrient composition as the base menu were provided to account for additional calories burned during exercise. Exercise EE was calculated, and approximately one-half of the calories needed to achieve energy balance were added to lunch. The final calories needed for energy balance were determined with the 7-h prediction. On the basis of this prediction, the balance of the needed calories was provided at dinner.

Statistical Analysis

Two energy expenditure curves, one for the exercise day and one for the rest day, were generated for each subject with the x axis representing time (min), and the y axis representing energy expenditure (kcal). To determine the total energy expenditure for each activity period (before exercise, exercise preparation, exercise, immediately after exercise, dress, from dress to sleep, sleep), the area under the energy expenditure curve for each activity period was calculated by using the trapezoid rule in the EXPAND procedure in SAS (version 9.1.3; SAS Institute, Inc., Cary, NC). A paired t-test on the log-transformed area was performed to compare the energy expenditure of each activity period in the exercise day with the corresponding period in the rest day.

The total energy expenditure for each hour was also calculated using the area-under-the-curve method as described above. A paired t-test on the log-transformed area was performed to compare energy expenditure of each hour in the exercise day with the corresponding hour in the rest day.

The Shapiro-Wilk test in the UNIVARIATE procedure in SAS was used for normality check. The Benjamini-Hochberg method for false discovery rate correction in the MULTTEST procedure in SAS was used for multiple testing corrections.

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