Introduction
The prevalence of overweight in African American (AA) women has increased over the past 20 years. As of 2006, 50+% of non-Hispanic black women, aged 20-39 years, were classified as obese, with the percentage even higher (60+%) in older age groups (13 23 3 39 41 33
Previous research has shown that an excess post-exercise oxygen consumption (EPOC) response is evoked with intermittent compared with continuous exercise (5 10,12,19 15,34 32 38
There appears to be minimal research investigating the influence of resistance training on EE in AA women. Also, AA women have a high incidence of overweight. Using typical routines and equipment commonly used by the general public, the resistance exercise intensity that will invoke the greatest overall effect on EE in this population needs to be determined to make recommendations and develop resistance exercise programs that promote the greatest impact on caloric expenditure and health. If a high-intensity exercise regimen is found to produce a greater EE than a low-intensity regimen, high-intensity programs can be recommended to individuals.
Therefore, the purpose of this study was to compare the post-exercise EE from bouts of low-intensity resistance exercise and high-intensity resistance exercise that were equated for work volumes in AA overweight women. The primary research questions were as follows: (a) For AA overweight women, will an acute bout of high-intensity resistance exercise, compared with low-intensity resistance exercise of equal work volume, stimulate a greater EPOC? and (b) Will variables that help explain EPOC-ventilatory volume (VE ), blood lactate concentration ([Lac]b ), heart rate (HR), and respiratory exchange ratio (RER)-be augmented 30 minutes post exercise? These variables are known to explain EPOC and were feasible for measurement in this study. A secondary research question was Will high-intensity resistance exercise compared with low-intensity resistance exercise of equal work volume produce similar responses for V̇o2 , VE , HR, RER, and rating of perceived exertion (RPE) during exercise? The RPE is a subjective measure of exercise difficulty (8
Methods
Experimental Approach to the Problem
A within-subject experimental design was used. Ten healthy, overweight, AA women visited the Human Performance Laboratory 4 times, completing a pretesting session and 3 data collection sessions (control, low intensity, or high intensity). During the first visit, body composition and cardiorespiratory fitness level were determined for descriptive measures and muscular strength was determined for calculating weight loads for the treatment sessions. The next 3 visits involved 1 no-exercise control (CN) session and 2 treatment sessions: low-intensity resistance exercise (LO) at 45% of their 8-repetition maximum (RM) or high-intensity resistance exercise (HI) at 85% of their 8-RM. Although the time of day tested varied from subject to subject, these 3 sessions were completed at the same time of day for each individual subject. Due to scheduling difficulties for subjects, the CN session was completed first so that the exercise sessions could easily be completed within the specified period of the menstrual cycle. One treatment session was completed the following day, and the second treatment session was completed 3-7 days later. To control for potential menstrual cycle influence on EPOC (26 10
A testing schematic for variables measured during the treatment sessions is presented in Figure 1 . Heart rate and oxygen consumption were measured from 15 minutes before, during, and for 30 minutes after each session. The RPE was determined after completing the third set of each of the 9 exercises for each session. Blood samples for lactate determination were collected just prior to beginning exercise, immediately post exercise, 15 and 30 minutes post exercise. The exercise duration for each session was 21 minutes for HI and 24 minutes for LO. Caloric expenditure was calculated using oxygen consumption values obtained during and post exercise. Excess post-exercise oxygen consumption was determined by comparing oxygen baseline values obtained during the CN session with post-exercise values.
Figure 1: Testing schematic.
Subjects
Ten apparently healthy, eumenorrheic, overweight (body mass index, 25-29.9 kg·m−2 ), college aged, AA female students volunteered for the study. Participants were considered sedentary. They had not taken part in a regular resistance training program (more than 2 d·wk−1 ) during the 6 months prior to the study; however, they were familiar with the resistance training exercises and equipment used in this study from experience prior to the last 6 months. Participants taking oral or injectable birth control were included. Exclusion criteria were pregnancy, cigarette smoking, the presence of glandular disorders or hormone therapy, or consumption of medications that could affect metabolism (i.e., thyroid medication, insulin, and steroids).
Participant demographics are presented in Table 1 . The homogeneous study sample was composed of young women of similar height and body mass, with a lower than average cardiorespiratory fitness and a higher than average percent body fat for their age group (2 2
Table 1: Subject characteristics (n = 10).*
Procedures
Body Composition
Body volume was estimated using air displacement densitometry plethysmography (Bod Pod Life Measurement Instruments, Concord, CA, USA). Methods for the Bod Pod have been previously described and have demonstrated reliability and validity across populations (27
V̇o2 max
Using the standard Bruce protocol (11 b 2 portable metabolic measurement system (Cosmed USA Inc., Chicago, IL, USA). Prior to data collection, the Cosmed portable metabolic system was sent for manufacturer recalibration and performance evaluation. The Cosmed was returned recalibrated and in good working order as designated by the manufacturer. This metabolic system has been validated across various ranges and intensities of physical activity and was calibrated before each test according to the manufacturer's specifications. A face mask that covered the mouth and nose of the participant was connected to a bidirectional digital turbine flow meter with an optoelectrical reader, and the apparatus was then attached to the participant using a mesh head cap. A disposable Ultimate Seal gel accessory (Hans Rudolph, Shawnee, KS) was positioned between the inside of the face mask and the participant to ensure an airtight seal. The Cosmed was placed in a harness that secured it to the upper torso of the participant. The RPE was recorded during the last 15 seconds of each stage using Borg 6- to 20-point scale (8 −1 ·min−1 ) with an increase in exercise intensity, (b) attainment of an RER of 1.10 or greater, (c) plateau of HR within ±10 b·min−1 of age-predicted maximum HR, and (d) exhaustion or an RPE of 18+ (24
Muscular Strength
Each participant performed an 8-RM strength test for 9 exercises on Universal Power resistance exercise machines (Universal, Cedar Rapids, IA). Exercises were performed in the following order: chest fly, triceps extension, deltoid lift, leg press, incline chest press, latissimus pull-down, leg curl, leg extension, and biceps curl. Participants were given detailed instructions and practiced each exercise several times at very low load to familiarize them with the technique for warm-up. After the warm-up, each participant performed each exercise with an estimated 60% of her perceived 8-RM for 8-repetitions (reps). Incremental increases of 2.5, 5, or 10 kg, depending on the exercise, were completed until their 8-RM was reached (38 16
Resistance Exercise Training Sessions
On arrival for testing, height and body weight were measured. The metabolic system was calibrated according to the manufacturer's specifications prior to each participant's resistance training session. The HR monitor and metabolic measurement device were strapped and secured to the subject as described earlier and remained in position throughout testing. Subjects sat quietly for 30 minutes prior to exercise, but data collection did not begin until the last 15 minutes of this period to establish baseline. Expired gas was measured continuously from 15 minutes prior to exercise, throughout the resistance exercise training sessions, and for 30 minutes post exercise. Breath-by-breath samples were averaged over 60-second intervals. Test data were downloaded to a laptop using Windows XP (Microsoft, Redmond, WA) and Cosmed Version 7.0 software, 2003 (Cosmed USA Inc.).
After a supervised stretching routine, subjects performed the 9 resistance training exercises. Intensity level was calculated as a percentage of the subjects' 8-RM. To equate workload, the HI session involved performing 3 sets of 8 reps at 85% 8-RM, while the LO session involved performing 3 sets of 15 reps at 45% 8-RM or the next closest lower weight on the machine. Each set required 47-63 seconds to complete and was followed by a 60-second rest period. The time for each resistance training session was approximately 21 minutes for HI and 24 minutes for LO at each session. The same investigator ensured that correct form was maintained and provided verbal encouragement during exercise. At the end of third set of each of the 9 exercises, RPE was recorded. Following the resistance training session, participants sat quietly in a chair for 30 minutes. A blood sample was collected just prior to beginning exercise, immediately after exercise ended, and 15 and 30 minutes post exercise. Blood lactate concentration was determined using a capillary blood sample obtained from the fingertip. Approximately 32 μl of blood was collected into a heparinized capillary tube. Blood lactate concentration was determined using a calibrated Accutrend portable lactate analyzer (Boehringer, Mannheim, Germany). The Accutrend lactate analyzer has been shown to produce valid and reliable results (7
Excess Post-Exercise Oxygen Consumption Measurement
V̇o2 measurements were collected for only 30 minutes post exercise to reduce discomfort for subjects and to avoid fidgeting that could falsely elevate EPOC levels (29 38 2 determined from the CN session. The oxygen consumption was plotted against time, and the area under the curve was determined using the trapezoidal rule. Because EPOC could not be calculated for the rest periods during exercise, only the 0-30 minutes after all exercise ended was calculated for comparison. Because strenuous exercise greatly influences blood pH, the Weir equation (25 21,33 2 and bicarbonate buffering that assist in normalizing acid-base balance (21 2 was used to calculate calories expended during exercise. Because a mix of carbohydrate and fat substrate use was expected, 4.8 kcal/LO2 was used to calculate calories expended during the post-exercise period (33
A no-exercise CN was conducted to account for diurnal variations and to avoid the possibility of false elevations of metabolism due to pre-exercise arousal (9
Dietary Journal
To account for unexpected fluctuations of nutrient intake, each subject kept a dietary journal of foods consumed 24 hours before the testing days for the control and treatment sessions. On these days, subjects were asked to eat comparable foods in like amounts at similar times to avoid fluctuations that could affect substrate metabolism and metabolic rate. Each dietary record was analyzed for daily caloric intake (kiloJoule) and the percentage of macronutrients using a nutritional software program (Healthkeeper Performance Diet Pro Version 4.0.3; Healthkeeper Inc., Aspen, CO, USA). Daily energy intake was considered essentially equal if the total for each day measured was within ±200 kJ.
Statistical Analyses
Data were summarized as session means with variance presented as standard deviations. Descriptive statistics of demographic data were evaluated to determine homogeneity of the sample. The level of significance for all tests was set at p ≤ 0.05. One-way analysis of variance (ANOVA) tests were conducted for all pre-exercise and post-exercise variables where the CN session was included with the HI and LO sessions. Also, post-exercise ANOVAs were conducted for each of the first 10-minute V̇o2 measures, for the HI, LO, and CN sessions. For each ANOVA, follow-up post hoc t -tests were conducted using a Dunnet test when the CN session was included in the analysis and a Tukey test when the CN session was not included (RPE and EPOC). Dependent t -tests were conducted to evaluate RPE, and independent t -tests were conducted to evaluate the EPOC (L·O2 ). To control for type I error, the Holm's sequential Bonferroni correction procedure was used for evaluating the ANOVA tests and the standard Bonferroni was used for the multiple t -tests. All data were analyzed using SPSS Version 11.5.
Results
Levene test for homogeneity of variance was not significant for any test, indicating equal variances. Results are presented as pre-exercise, exercise, and post-exercise periods. The period of 0-30 minutes post exercise was defined as the time beginning immediately after all exercises have ended until the end of the testing post exercise.
Pre-Exercise
Total daily energy intake 24 hours before each of the resistance training sessions and CN sessions was within ±200 kJ. This indicates that there was no dietary effect that influenced substrate utilization or metabolic rate for each of the testing days.
There was no significant difference between the HI, LO, and CN sessions for pre-exercise VE (F = 0.590; p = 0.561), RER (F = 0.257; p = 0.775), HR (F = 1.084; p = 0.354), [Lac]b (F = 0.921; p = 0.410), or V̇o2 (F = 1.167; p = 0.327), indicating similar metabolic conditions prior to each testing session.
Exercise
The total work volume for HI and LO, respectively, was 5,846.9 ± 1,052.6 kg and 5,890.2 ± 1,060.3 kg. The volume of weight lifted per unit of exercise time for HI and LO, respectively, was 280.5 ± 50.5 kg·min−1 and 243.6 ± 43.9 kg·min−1 . When comparing the HI, LO, and CN sessions, the exercise VE (F = 0.724; p = 0.495), HR (F = 29.711; p = 0.000), and V̇o2 (F = 31.478; p = 0.000) were significantly different but the RER (F = 1.851; p = 0.176) was not. Post hoc pairwise comparisons revealed that the exercise HR, VE , and V̇o2 were significantly higher for both HI and LO compared with the CN, but there was no significant difference between the exercise sessions. This result was expected because the total work volume for each resistance training session was essentially equal. The mean RPE for all 9 exercises was not significantly different between the HI and LO sessions; however, the RPE for biceps exercise approached significance (t = 2.14; p = 0.051).
Post-Exercise
The post-exercise VE (F = 1.255; p = 0.303) and RER (F = 0.499; p = 0.613) were not significantly different for the HI and LO sessions. The post-exercise HR was significant (F = 6.263; p = 0.006), and the pairwise analysis revealed that the difference was between the HI and CN. The mean for each post-exercise [Lac]b was significantly different between the CN session and resistance training sessions at 0 minutes (immediately after exercise) post exercise, at 15 minutes post exercise, but not at 30 minutes (0 minutes F = 14.644; p = 0.000; 15 minutes F = 8.572; p = 0001). There was no significant difference in [Lac]b between the HI and LO sessions at anytime post exercise.
The V̇o2 post exercise was not significantly different (F = 0.685; p = 0.513) between HI and LO. There was a significant difference in minute V̇o2 (Figure 2 ) but only for the first 5 minutes and only between HI and LO compared with CON and not between HI and LO.
Figure 2: V̇o2 ml·min−1 for HI, LO, and CON. *CON significantly different than HI and LO p ≤ 0.05. No significant difference between HI and LO.
The EPOC calculated after completion of the entire resistance training bout (0-30 minutes) was not significantly different between the 2 resistance training sessions (t = −1.779; p = 0.092). Net EE for the HI, LO, and CN plus the EPOC are presented in Table 2 .
Table 2: V̇o2 (L·O2 ), EPOC, and calories for HI, LO, and CN during and post exercise.*
These findings indicate that during the post-exercise period, HI HR was significantly elevated above baseline levels throughout but LO HR was not; HI and LO V̇o2 were significantly elevated above baseline levels, but only up to 5 minutes post exercise; RERs for HI, LO, and CN were similar throughout; HI and LO [Lac]b were significantly elevated above CN immediately post exercise and 15 minutes post exercise but similar to CN at the end of the post-exercise period. These findings suggest that all variables except the HI HR had returned to near baseline levels within 30 minutes post exercise. Although most variables during exercise and post exercise were greater for the HI compared with the LO session, they were not statistically significant.
Discussion
The lack of difference in the pre-exercise variables supports similar baseline levels prior to beginning the exercise. During exercise, the HI and LO session variables HR, VE , and V̇o2 were greater than CN as expected due to the physiologic stress of exercise. These variables were similar for the HI and LO exercise sessions as anticipated due to the similar work volume. The RER was similar for HI, LO, and CN, but this variable is more difficult to interpret due to lactate buffering and oxidative metabolism. The post-exercise V̇o2 was very similar for HI and LO. The RPE surprisingly was similar for both exercise sessions. It was anticipated that the RPE would be greater for HI than the LO. The EPOC for the exercise sessions was similar and quite small.
Overall, studies, comparing various protocols and intensities of exercise, have shown that long-duration, high-intensity, split sessions or higher work volumes will produce the greatest magnitude and volume of EPOC (1,6,9,15,19,30,31,40 4,20 10,12
Braun et al. (10 2 remained elevated above baseline for 60 minutes. The 60-minute V̇o2 was 0.23 L·min−1 compared with baseline of 0.19 L·min−1 , which was reported to be statistically significant. The total EPOC was 2.27 for the first 30 minutes post exercise. The results of this study contradict the findings of the present study as both the HI and LO resistance exercise V̇o2 returned to near baseline within 30 minutes, and the EPOC was 1.26 L·O2 for HI and 0.87 L·O2 for LO. Braun et al. (10 −1 V̇o2 for 3 sets, however, was similar in the study of Braun et al. (10 −1 at 65% 1-RM for 15 reps) compared with the present study findings (276.9 ml·min−1 at 85% 8-RM for 8 reps and 240.4 ml·min−1 at 45% 8-RM for 15 reps). Braun et al. (10
Thornton and Potteiger (38 38
Individuals with a lower fitness level typically expend more energy for the same amount of work compared with individuals with a higher fitness level (35 36,17 14 37 18
Several other variables may have impacted the difference in the results of the Thornton and Potteiger's study and the present study. A greater EPOC response has been observed for subjects with a lower body fat mass (22 32
McGarvey et al. (28
Methodological issues identified by Borsheim and Bahr (9 2 is limited during resistance exercise. This limitation is due to the mechanical inability of the metabolic measurement system to make a distinction between work and recovery V̇o2 . In this study, however, the total exercise V̇o2 consumed and the total work completed in both sessions were not significantly different. Another limitation may be the participant's ability to achieve a true 8-RM. If the study were replicated determining an RM of greater precision, the results may have been different.
In summary, when comparing a high-intensity (85% 8-RM) session with a low-intensity (45% 8-RM) session of resistance training with equal work volume, the results of this investigation suggest that there is a similar exercise energy expenditure but the EPOC and other post-exercise metabolic variables, except HR, were not significantly different in overweight AA women. These findings may be a result of the participant's inability to reach a true 8-RM. The EPOC magnitude and volume were greatest within the first 8 minutes following resistance training and were quite small, therefore; the calorie expenditure from EPOC would not contribute substantively toward weight loss in the short term.
Practical Applications
Based on the results of this study, resistance exercise of the level used in this study will have a small impact directly through calories used during the program. Additionally, if continued over time, the calories will contribute to weight maintenance and/or weight loss. Because both were well tolerated, either of these protocols could be used for beginning a resistance training regimen for sedentary persons. Based on the results of this study, resistance training programs could be used initially in sedentary populations without a preconditioning program.
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