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Effect of Training Status on Oxygen Consumption in Women After Resistance Exercise

Benton, Melissa J.; Waggener, Green T.; Swan, Pamela D.

The Journal of Strength & Conditioning Research: March 2016 - Volume 30 - Issue 3 - p 800–806
doi: 10.1519/JSC.0000000000001146
Original Research

Benton, MJ, Waggener, GT, and Swan, PD. Effect of training status on oxygen consumption in women after resistance exercise. J Strength Cond Res 30(3): 800–806, 2016—This study compared acute postexercise oxygen consumption in 11 trained women (age, 46.5 ± 1.6 years; body mass index [BMI], 28.4 ± 1.7 kg·m−2) and 11 untrained women (age, 46.5 ± 1.5 years; BMI, 27.5 ± 1.5 kg·m−2) after resistance exercise (RE). Resistance exercise consisted of 3 sets of 8 exercises (8–12 repetitions at 50–80% 1 repetition maximum). Oxygen consumption (V[Combining Dot Above]O2 ml·min−1) was measured before and after (0, 20, 40, 60, 90, and 120 minutes) RE. Immediately after cessation of RE (time 0), oxygen consumption increased in both trained and untrained women and remained significantly above baseline through 60 minutes after exercise (p < 0.01). Total oxygen consumption during recovery was 31.3 L in trained women and 27.4 L in untrained women (p = 0.07). In trained women, total oxygen consumption was strongly related to absolute (kg) lean mass (r = 0.88; p < 0.001), relative (kilogram per square meter) lean mass (r = 0.91; p < 0.001), and duration of exercise (r = 0.68; p ≤ 0.05), but in untrained women, only training volume–load was related to total oxygen consumption (r = 0.67; p ≤ 0.05). In trained women, 86% of the variance in oxygen consumption was explained by lean mass and exercise duration, whereas volume–load explained 45% in untrained women. Our findings suggest that, in women, resistance training increases metabolic activity of lean tissue. Postexercise energy costs of RE are determined by the duration of stimulation provided by RE rather than absolute work (volume–load) performed. This phenomenon may be related to type II muscle fibers and increased protein synthesis.

1Department of Nursing, Helen and Arthur E. Johnson Beth-El College of Nursing and Health Sciences, University of Colorado, Colorado Springs, Colorado;

2Department of Exercise Science and Community Health, University of West Florida, Pensacola, Florida; and

3Exercise Science and Health Promotion Program, School of Nutrition and Health Promotion, Arizona State University, Phoenix, Arizona

Address correspondence to Melissa J. Benton, mbenton@uccs.edu.

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Introduction

Resistance exercise (RE) is most often recognized for its effect on muscular strength and lean mass (17). However, RE also evokes transient but significant increases in energy expenditure (4,31,32,34,37,44). Although often underappreciated, RE has been shown to elicit increases in metabolism marked by excess postexercise oxygen consumption that equals or exceeds the effect of endurance exercises such as running or cycling (7,10,13,18,24).

Although it is well established that RE exerts a significant effect on energy expenditure during recovery, the magnitude of effect can be influenced by exercise intensity. Higher intensities evoke greater energy expenditure during recovery than lower intensities (14,42). Gender also influences energy expenditure after RE. Although both males and females demonstrate significant increases in recovery energy expenditure, the magnitude seems to be greater in males than that in females, partially because of greater lean mass (33). These influences are consistent with what has been observed during recovery after endurance exercise (3,25,35,40).

Recovery energy expenditure after RE may also be influenced by training status. In a review of the literature, Borsheim and Bahr (6) concluded that trained adults demonstrate a more rapid return to pre-exercise resting energy expenditure than untrained adults. This metabolic adaptation results in greater efficiency and diminished energy costs but potentially diminishes the contribution of regular exercise to 24-hour energy expenditure. However, their conclusion was founded specifically on the outcomes of endurance training (15,39). It is likely that resistance training experience results in a similar adaptation, yet research regarding training status and energy expenditure after RE has been sparse and limited to young men (11,19). Previous research by Dolezal et al. (11) and Hackney et al. (19) evaluated the protective effect of training experience on muscle damage caused by a single bout of RE, using postexercise energy expenditure as an outcome measure. However, results were inconsistent, and in one study (11), untrained males demonstrated significantly greater recovery energy expenditure, whereas in the other (19), they did not. Therefore, the objective of this study was twofold: (a) to compare energy expenditure after a single bout of RE in trained and untrained women and (b) to identify influences on recovery energy expenditure based on training status. Our hypothesis was that trained women would demonstrate a more efficient recovery with decreased energy expenditure compared to untrained women, and that total energy expenditure would be related to lean mass.

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Methods

Experimental Approach to the Problem

Twenty-two trained (n = 11) and untrained (n = 11) women completed one session of anthropometric measurement followed by 3 strength testing sessions to determine their maximal strength (1 repetition maximum [1RM]) in 8 exercises. They then completed an acute bout of RE with metabolic measurement before (resting) and for 120 minutes after (recovery) to determine oxygen consumption (V[Combining Dot Above]O2 ml·min−1) as a surrogate for energy expenditure. Oxygen consumption was compared before and after RE for each training group, and relationships to anthropometric and training characteristics were evaluated.

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Subjects

Trained women were recruited after completion of an 8-week resistance training program that has been previously described (1). Eleven trained women (age, 46.5 ± 1.6 years; body mass index [BMI], 22.4 ± 1.6 kg·m−2) were then pair matched by age and BMI to 11 untrained women (age, 46.5 ± 1.5 years; BMI, 27.5 ± 1.5 kg·m−2) who reported no previous resistance training experience (2). Each subject came to the laboratory to complete body composition testing, 3 separate trials to determine maximal strength, and a single RE bout followed by 2 hours of metabolic testing. All were nonsmokers. The same investigator completed all testing for both cohorts of women. The study was approved by the University Institutional Review Board, and all subjects completed an informed consent before participation.

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Anthropometric Measurements

All subjects reported to the test center for measurements in the morning immediately after waking. Subjects were instructed not to eat or drink anything but water for 12 hours or to exercise for 24 hours before this session. Body composition (lean and fat mass) was calculated using air displacement plethysmography (BodPod; Cosmed USA, Concord, CA, USA). Subjects removed all jewelry and wore only tight-fitting exercise clothing and a Lycra swim cap (TYR Sport, Inc., Huntington Beach, CA, USA). Lung volumes were predicted using the manufacturer's equation.

Fat-free mass index (FFMI) was calculated as a measure of relative lean mass using the formula described by Schutz et al. (38): fat-free mass (kilogram) divided by height2 (square meter).

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Strength Measurements

All subjects completed a series of 3 strength measurements to determine the maximum amount of weight that could be lifted in one repetition (1RM). The same exercises and equipment (Cybex, Medway, MA, USA) with which they were tested were used for the RE bout. At least 24 hours rest was provided between sessions. Subjects were tested at each session for the same 8 exercises (chest press, latissimus pulldown, leg press, shoulder press, seated row, leg extension, triceps pushdown, and biceps curl). The warm-up for each exercise consisted of 10 repetitions at a light weight that could be easily achieved, followed by 5 and 3 repetitions at slightly heavier loads. A 2-minute rest was provided between warm-up sets and each single attempt. The goal for each exercise was to identify the maximum weight within 5 attempts. The maximum weight successfully lifted with good form during the 3 sessions was determined to be the 1RM for each exercise.

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Metabolic Testing

Resting metabolic testing was performed before and after a single bout of RE. Consistent with the recommendation of Compher et al. (9), subjects were instructed not to consume any alcoholic beverage or engage in any physical activity for 24 hours before this session. Participants were instructed to consume a light breakfast between 5:00 and 8:00 AM on the morning they were scheduled for metabolic testing. Participants arrived at the testing center and commenced pre-exercise metabolic testing exactly 4 hours after prandial. Analysis of the pre-exercise meal was completed using Food Processor software (ESHA Research, Salem, OR). All subjects reporting regular menses were scheduled 3–5 days after the beginning of menstruation (22).

Subjects were positioned in a reclining chair with their feet elevated and habituated to the open-circuit spirometry metabolic analysis system (True One 2400; Parvo Medics, Sandy, UT, USA) for 20 minutes in a semidarkened, quiet, temperature-controlled (22–24° C) room. A mask with a nonrebreathing respiratory valve (Hans Rudolph, Inc., Shawnee, KS, USA) was placed over the nose and mouth, and a tight seal was verified to prevent air leakage. The manufacturer's calibration procedures were followed before all measurement sessions. Subjects were prompted to remain awake and not move or talk once the mask was in place. After the 20-minute habituation period, oxygen consumption (V[Combining Dot Above]O2 ml·min−1) was measured, and energy expenditure (kilocalorie per minute) was estimated from a mean of 10 minutes of continuous gas sampling through indirect calorimetry using the Weir formula (43).

Resistance exercise commenced after completion of pre-exercise metabolic testing. Participants completed 3 sets of the same 8 exercises used for maximal strength testing. One minute of rest was given between each set of each exercise (5,27,36). The first set was a warm-up set of 10 repetitions at 50% 1RM, and the second and third sets consisted of 8–12 repetitions at 80% 1RM. For efficiency, exercises were paired and alternated by muscle group (e.g., chest press-latissimus pulldown, leg press-shoulder press, seated row-leg extension, and triceps pushdown-biceps curl). After completing 3 sets of each pair of exercises, participants moved on to the next pair. A total of 24 sets were completed during the RE session.

Postexercise metabolic testing commenced after completion of RE under the same conditions as pre-exercise metabolic testing, except that subjects were allowed to watch an informational travel or historical video to assist them to remain awake for the 120-minute postexercise testing period. Oxygen consumption was measured initially (time 0) and at 20, 40, 60, 90, and 120 minutes of recovery.

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Statistical Analyses

Data were analyzed using SPSS Statistics 21 (IBM, Somers, NY, USA). An alpha level of p ≤ 0.05 was used to determine significance, and mean and SE were reported for all values. Descriptive statistics were used to analyze participant characteristics, and analysis of variance (ANOVA) was used to identify significant differences between trained and untrained women. Repeated-measures ANOVA with a Bonferroni correction was used to evaluate oxygen consumption before and after exercise and identify differences over time and between groups. Effect size was calculated as eta-squared (η2) with cut points of 0.01, 0.06, and 0.14 for small, medium, and large effects, respectively (16). Pearson product-moment correlations were used to analyze relationships between anthropometrics, exercise variables, and metabolic measurements. To determine the contribution of subject characteristics to total energy expenditure, linear regression analysis was conducted for independent variables based on Pearson coefficients.

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Results

There were no significant differences in age, body composition, exercise duration, volume–load, or pre-exercise macronutrient energy intake between trained and untrained women (Table 1). Upper body strength was 61% greater (p ≤ 0.05, η2 = 0.36) in trained women, although lower body strength was equal between groups. Trained women completed RE in slightly less time and achieved a slightly greater volume–load, although this did not achieve significance. Before RE, there was no difference in resting energy expenditure between groups (V[Combining Dot Above]O2 trained = 235 ± 15 ml·min−l; V[Combining Dot Above]O2 untrained = 207 ± 12 ml·min−l). However, a significant time × group difference was observed during recovery (Figure 1). Whereas oxygen consumption (V[Combining Dot Above]O2 ml·min−l) immediately after RE was significantly increased in both groups compared to pre-exercise baseline (p < 0.001; η2 = 0.89), V[Combining Dot Above]O2 was significantly greater (p < 0.001; η2 = 0.48) in trained women (421 ± 20 ml·min−l) compared with untrained women (315 ± 15 ml·min−l). Oxygen consumption remained significantly above pre-exercise levels through 60 minutes of the recovery period (p < 0.01; η2 = 0.41) for both trained and untrained women, although there were no further between-group differences at any measurement time point (Figure 1). A trend was observed for total oxygen consumption during recovery in favor of trained women who consumed 14% more oxygen than untrained women (31.3 ± 1.7 vs. 27.4 ± 1.3 L, respectively), although this did not achieve significance (p = 0.07; η2 = 0.15).

Table 1

Table 1

Figure 1

Figure 1

Correlation analysis identified distinct influences on oxygen consumption after RE based on training status. In trained women, absolute (kilogram) lean mass (r = 0.88; p < 0.001), relative (FFMI: kilogram per square meter) lean mass (r = 0.91; p < 0.001), and duration (minutes) of RE (r = 0.68; p ≤ 0.05) were found to be strongly related to total oxygen consumed during recovery, but these variables were not significant in untrained women. In untrained women, postexercise oxygen consumption was solely related to volume–load (kilogram) achieved during RE (r = 0.67; p ≤ 0.05), but there was no significant relationship between volume–load and oxygen consumption in trained women. Pre-exercise dietary intake (energy, protein, carbohydrate, or fat) was not related to oxygen consumption before RE or during the recovery period in either trained or untrained women.

Regression analysis demonstrated that in trained women, lean mass (absolute and relative) and exercise duration explained 86% of the variance in post-RE oxygen consumption (Table 2). The model was not improved by including volume–load. By comparison, in untrained women, training volume–load explained 45% of the variance, and including lean mass and exercise duration did not significantly improve the model (Table 3).

Table 2

Table 2

Table 3

Table 3

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Discussion

To our knowledge, this is the first study to evaluate the effect of training status on recovery energy expenditure in women after RE. Our initial hypothesis was that training experience would result in greater efficiency that would be manifested by decreased energy expenditure during recovery. However, our findings do not support our hypothesis and, indeed, trained women were found to have not only greater energy expenditure immediately after exercise but also slightly greater total energy expenditure during the recovery period. This was unexpected based on previous research by Dolezal et al. (11) and Hackney et al. (19) who evaluated the effect of training status on energy expenditure after RE in young men. These previous studies reported greater oxygen consumption in untrained compared to trained men, although the difference was reported as statistically significant only by Dolezal et al. (11).

The reasons for the difference in our findings are unclear although study design may have an influence. Our study evaluated only the 2-hour period immediately after cessation of exercise, but Dolezal et al. (11) and Hackney et al. (19) did not. Instead, they waited to commence measurement of recovery energy expenditure until 24 hours after RE and then repeated a series of 30-minute measurements at 24-hour intervals for a total of 72 hours of recovery. Furthermore, both previous studies used exercise protocols emphasizing eccentric contractions that are known to result in greater and more prolonged muscle damage than concentric contractions (8,26,29,30). By comparison, the exercise protocol used in our study did not overly emphasize the eccentric phase of contractions and so may not have resulted in as much muscle damage in our subjects.

Our results also differ from previous research regarding training status and recovery after endurance exercise (15,39). Muscle fiber types may offer a possible explanation for this difference. Endurance training increases the percentage of type I muscle fibers (23), whereas resistance training increases type II fibers, especially in women (20). It is possible that the cellular level adaptations that promote aerobic efficiency during recovery are more specific to type I fibers that proliferate in endurance-trained individuals than to type II fibers that are stimulated during RE. Unquestionably, evidence indicates that there are specific and separate metabolic adaptations to resistance training (12) compared to endurance training (21). As a result, muscle protein synthesis may play a role. An acute bout of RE stimulates increased muscle protein synthesis for at least 2 hours after exercise (28), and in recreationally trained subjects, such as the trained women in our study, phosphorylation as a marker of muscle protein synthesis is greater after RE in type II fibers than in type I fibers (41). Thus, the greater energy expenditure after RE in trained women may represent a specific type II muscle fiber response for hypertrophy (45) that would not be expected to occur after endurance exercise.

The secondary purpose of our study was to evaluate influences on recovery energy expenditure based on training status. Our hypothesis was that lean mass would exert the strongest influence, yet we observed this to be true only in trained women. Nonetheless, in trained women, both absolute and relative lean mass influenced energy expenditure after RE and when combined with exercise duration explained almost 90% of the variation in energy expenditure during the first 2 hours after RE. By comparison, in untrained women, only the work performed during RE (i.e., training volume–load) influenced postexercise energy expenditure. Although it explained less than half of the variance, it was the only characteristic found to be related to recovery energy expenditure in untrained women. Mechanistically, we would suggest that the difference in these influences represents the adaptive response of skeletal muscle fibers to resistance training, and that the shift to type II muscle fibers that occurs with training experience likely results in a greater influence of lean mass on recovery energy expenditure. As a result, energy costs of RE are determined by exercise duration (length of stimulus) rather than absolute work (volume–load) performed.

Our small sample size is an undoubted limitation to our findings. However, our sample was actually larger or equivalent in size to those of previous researchers (11,15,19,39), and our effect sizes were consistently large. Furthermore, a novel characteristic of our study is the use of FFMI as a measure of relative lean mass and evaluation of its effect on energy expenditure. We believe that we are the first to report this relationship. Although we would certainly not characterize our results as conclusive, we would describe them as suggestive. Further research using a longitudinal training design may provide more conclusive results.

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Practical Applications

For women participating in RE for recreational and health benefits, energy expenditure may be as important as hypertrophy and strength increases. Our findings suggest that a regular resistance training program may have a significant impact on 24-hour energy expenditure and that training experience seems to augment rather than blunt this impact. The trained women in our study did not perform significantly more work, nor did they exercise for a significantly longer period. In fact, they performed relatively the same work in a slightly shorter period, yet they were observed to consume more oxygen and hence expend more energy during recovery. Exercise professionals can use our findings to educate women who may believe that progressively longer training sessions and heavier loads are required to promote increased energy expenditure during recovery. Although minimal recommendations for RE are 2–3 days per week, the American College of Sports Medicine recommends frequencies of 4–6 days per week for more experienced lifters (36). Based on our current findings, such regular and frequent training may not only promote hypertrophy but also increases 24-hour energy expenditure resulting in potentially enhanced fat loss and an overall healthier body composition.

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Acknowledgments

This study was supported in part by a faculty research grant from Valdosta State University. There are no conflicts of interest for any of the authors.

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Keywords:

energy expenditure; lean mass; FFMI; exercise duration; volume–load

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