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Original Research

Weight Loss and Exercise Training Effect on Oxygen Uptake and Heart Rate Response to Locomotion

Hunter, Gary R.1,2; Fisher, Gordon2; Bryan, David R.2; Zuckerman, Paul A.2

Author Information
Journal of Strength and Conditioning Research: May 2012 - Volume 26 - Issue 5 - p 1366-1373
doi: 10.1519/JSC.0b013e31824f236c
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Abstract

Introduction

Ease during locomotion increases with weight loss (5) even in the absence of physical training. This improved ease of activity may increase free-living physical activity after weight loss (8) and may improve the chances for weight maintenance after weight loss (19). Exercise training also increases the ease of physical activity (2,7,8,10). Despite its potential importance for improving the quality of life and affecting weight gain, little is known concerning the effects exercise training has on the ease of physical activity immediately after weight loss and long term after weight loss.

High aerobic fitness is related to lower heart rate (HR) during walking and biking, increased participation in free-living physical activity (8), and less weight regain (12). Because of its effects on aerobic fitness and its relatively high energy expenditure, endurance exercise training has been the modality that has been most studied in weight loss and weight maintenance programs. Strength is also associated with increased free-living energy expenditure (18) and reduced weight gain (19). In addition, resistance exercise training programs not only increase strength but also increase the ease of walking and bicycling and increase free-living physical activity (2,7,10,13).

Despite the fact that both aerobic and resistance training are beneficial for preventing weight regain after weight loss, the authors are aware of a few, if any, studies that have compared the effects of resistance and aerobic training on the ease of physical activity during and after diet-induced weight loss. The purpose of this study was to make those comparisons. It is hypothesized that both aerobic and resistance training during diet-induced weight loss will decrease HR while walking, stair climbing, and biking more than during diet alone. It is further hypothesized that both aerobic and resistance training will maintain reduced HRs while walking, stair climbing, and biking during the year after weight loss, whereas those subjects who do not exercise train will experience an increase in HR while walking, stair climbing, and biking.

Methods

Experimental Approach to Problem

Seventy-three overweight premenopausal subjects were evaluated 3 times: (a) at baseline in the overweight state; (b) after a diet-induced (800 kcal·d−1) diet with or without exercise designed to reduce body mass index to less than 25 kg·m−2; and (c) 1 year after the achievement of body mass index of 25 kg·m−2. Strength and aerobic fitness as well as HR, respiratory quotient (RQ), and oxygen uptake (V[Combining Dot Above]O2) during submaximal steady-state cycle ergometry, stair climbing, treadmill walk on the flat, and a 2.5% grade treadmill walk were the primary study variables. Women reported normal menses and were nonsmokers. All testing was done in the follicular phase of the menstrual cycle. Women were weight stable for 1 month before all the evaluations (3 weekly body weight measurements with adjustments in energy intake made when needed). Food was provided by the General Clinical Research Center Kitchen for the last 2 weeks of all 3 weight stable conditions and during the 800 kcal·day−1 dietary intervention. Macronutrient content of the diet was 20–22% fat, 20–22% protein, and 56–58% carbohydrate. All women were admitted to the General Clinical Research Center 2 days before evaluations so that both physical activity and food intake could be monitored at all times. Testing was done in a fasted state in the morning after spending the night in the General Clinical Research Center.

Subjects

All testing procedures and risks were fully explained, and women provided verbal and written informed consent for the protocol before the start of the study. The study was approved by the University of Alabama at Birmingham Institutional Review Board. All subjects were sedentary (no exercise training for the prior year), overweight (body mass index of 27–30 kg·ht−2), and were randomly assigned to 1 of the 3 groups: (a) Diet and aerobic training (19 subjects); (b) diet and resistance training (26 subjects); and (3) diet and no exercise training (28 subjects). Differences in sample size between the groups due to dropouts because of sickness, injury, or inability to complete weight loss program. During weight loss, women assigned to exercise trained 3 times per week, and during the 1-year follow-up, women assigned to exercise trained 2 times per week. Subject characteristics are shown in Table 1.

Table 1
Table 1:
Descriptive variables for 73 women.*

Procedures

Aerobic Training

After a warm-up of 5 minutes of walking and 3–5 minutes of stretching, aerobic training entailed continuous walking or jogging on a treadmill (Quinton, Seattle WA, USA). During the first week of training, the subjects did 20 minutes of continuous exercise at 67% maximum HR. Duration and intensity increased each week so that by the beginning of the eighth week, subjects exercised continuously at 80% of maximum HR for 40 minutes. Subjects were encouraged to increase intensity (either speed or grade) when average exercise HR was consistently below 80% of maximum HR during both weight loss and 1-year weight maintenance phases. After the exercise session, subjects cooled down for 3–5 minutes with gradually decreasing exercise intensity.

Resistance Training

After a warm-up on the treadmill for 5 minutes and 3–5 minutes of stretching, subjects did the following exercises: squats (Hammerstrength V squat; Life Fitness, Schiller Park, IL, USA), leg press, elbow flexion, lateral pull-down, bench press (all Fit 5000 multistation; Paramount Fitness Line, Los Angeles, CA, USA), triceps extension (Triceps Extension, Paramount Fitness Line), military press, leg curl, knee extension (all Body Solid, Forest Park, IL, USA), lower back extension, and bent leg sit-ups. After 1 week of familiarization training with a lightweight, 1 repetition maximum (1RM) was measured. One set of 10 repetitions was performed at 65% 1RM during the first week with percent of 1RM increasing on subsequent weeks until intensity was at 80% 1RM at week 4. Starting at week 4, 2 sets of 10 repetitions were attempted at 80% 1RM for each exercise with 2-minute rest between sets. Strength was evaluated every 5 weeks, and adjustments in resistance training were made based on the most current 1RM in both weight loss and 1-year weight maintenance phases.

Resting Oxygen Uptake

Three consecutive mornings in a fasted state and after an overnight stay in the General Clinical Research Center, resting oxygen uptake was determined between 6:00 and 6:50 am. Subjects remained awake in a quiet, softly lit, well-ventilated room in which temperature was maintained between 22° and 24° C. Subjects lay supine on a comfortable bed, and oxygen uptake was measured using a ventilated hood system. After resting for 15 minutes, resting oxygen uptake was measured for 30 minutes with a computerized, open-circuit, indirect calorimetry system (Delta Trac II; Sensor Medics, Yorba, CA, USA). The last 20 minutes was used for analysis. Oxygen uptake values used in the determination of exercise net V[Combining Dot Above]O2 (i.e., exercise V[Combining Dot Above]O2 − resting V[Combining Dot Above]O2) were means of the 3 morning values. Coefficient of variation for repeat V[Combining Dot Above]O2 measures was <4% in our laboratory.

V[Combining Dot Above]O2max

A maximal modified Bruce protocol was used to determine V[Combining Dot Above]O2max (3). Heart rate was measured using a POLAR Vantage XL HR monitor (Gays Mills, WI, USA). Oxygen uptake and carbon dioxide production were measured continuously using a Sensormedics metabolic cart (Model #2900; Loma Linda, CA, USA). Gas analyzers were calibrated with certified gases of known concentrations. Standard criteria for HR, respiratory exchange ratio, and plateauing were used to ensure the achievement of V[Combining Dot Above]O2max. All subjects achieved at least 2 criteria. Coefficient of variation for repeat measures of V[Combining Dot Above]O2max was less than 3% in our laboratory.

Ease and Economy of Physical Activity

Heart rate, RQ, and oxygen uptake (V[Combining Dot Above]O2) were obtained during submaximal steady-state cycle ergometry (50 W), stair climbing (60 steps per minute up 17.8-cm steps), treadmill walk on the flat (4.8 km per hour), and a 2.5% grade treadmill walk (4.8 km per hour). The duration of each of the tasks was between 4 and 5 minutes, and steady state was obtained. Oxygen uptake and carbon dioxide production were also measured using a Sensormedics metabolic cart (Model #2900; Yoma) (See description of V[Combining Dot Above]O2max for specifics). Net oxygen uptake (work steady-state V[Combining Dot Above]O2 − resting V[Combining Dot Above]O2) is reported in milliliter O2·kg−1 per minute and is considered exercise economy for walking and stair climbing. Because work was the same for all the subjects during biking (50 W), bike oxygen uptake and economy is reported in liters per minute. Both HR and RQ increase as the intensity of exercise increases; therefore, these 2 measures are considered to give an index of exercise difficulty. Because the tasks were performed in the steady state, the RQ measure also gave an index of fuel utilization during the exercise.

Strength Measure

Using the methods previously described (7), knee extension strength was measured isometrically. Forces were measured using a universal shear beam load cell (LCC 500; Omega Engineering, Stamford, CT, USA). Knee extension maximal force was measured at knee position of 110° on the right leg at the level of the lateral malleolus. Subjects were restrained across the upper legs and hips with padded straps. After 3 warm-up trials, 3 maximal isometric contractions were recorded with 60-second rest between the trials. Test-retest reliability for this test has a coefficient of variability of <4%.

Statistical Analyses

Descriptives were examined using a 1-way (group) analysis of variance (Table 1). A 3 (group) by 3 (time) repeated measures analysis of variance was used to examine all variables of interest. Because physiological response during the 4 submaximal exercise tests was similar across the 3 time points for the 2 exercise training groups (no significant difference for deltas between aerobic and resistance trainers), T-test Bonferroni corrected post hoc tests were run comparing the pooled exercise subjects vs. the no exercise control subjects for variables in which there was a significant time by group interaction. The aerobic and resistance exercisers were combined into 1 group (exercisers) so that overweight to postoverweight and overweight to 1-year follow-up comparisons could be made. Pearson product correlations were run between the postweight loss to 1-year follow-up difference for knee extension strength and V[Combining Dot Above]O2max and locomotion HRs. All statistical assumptions were met, and significance was set at a p of ≤0.05.

Results

There was a significant time and time by group interaction for both knee extension strength and V[Combining Dot Above]O2max (for both ml·kg−1·min−1 and mL·kg−1 fat free mass [FFM]·min−1) with post hoc analysis showing that the strength group increased strength more than the other groups and the aerobic group increased V[Combining Dot Above]O2max more than the other groups (Table 2). There was also a significant time and time by group interaction for HR during all the 4 submaximal tasks (Table 3 and Table 4). Because physiological response during the 4 submaximal exercise tests was similar across the 3 time points for the 2 exercise training groups (no significant difference for deltas between aerobic and resistance trainers), the aerobic and resistance exercisers were combined into 1 group (exercisers) so that overweight to postoverweight and overweight to 1-year follow-up comparisons could be made (Figures 1 and 2). Post hoc tests showed that exercisers significantly decreased HR in all the 4 tasks more than nonexercise control subjects between baseline and 1-year follow-up (Figure 2). Post hoc tests revealed that there were no significant differences in decrease in HR between exercisers and nonexercise controls for any exercise tasks except bike between baseline and postweight loss (Figure 1).

Table 2
Table 2:
Fitness measures for 73 women (aerobic 19, resistance 26, no exercise 28 subjects).*
Table 3
Table 3:
Submaximal stair climb and walk measures for 73 women (aerobic 19, resistance 26, and no exercise 28 subjects).*
Table 4
Table 4:
Submaximal grade walk and bike measures for 73 women (aerobic 19, resistance 26, and no exercise 28 subjects).*
Figure 1
Figure 1:
Locomotion heart rate response changes from overweight to postoverweight in 73 women. Error brackets indicateSEM and star indicates significant difference between exercisers and diet-only group (p < 0.05).
Figure 2
Figure 2:
Locomotion heart rate response changes from overweight to 1 year after weight loss in 73 women. Error brackets indicateSEM, and stars indicate significant difference between exercisers and diet-only group (p < 0.05).

There was no significant time, group, or time by group effect for the submaximal net oxygen uptakes or net energy expenditures for any of the 4 exercise tasks (Tables 3 and 4). There was no significant time effect for any of the 4 exercise tasks except stair climbing, nor was there a time by group interaction for any task (Tables 3 and 4). However, quadratic time by group interactions were significant for the submaximal walk (p < 0.02) and grade walk (p < 0.02), although post hoc tests showed a significant decrease in RQ between overweight and postoverweight state for the aerobic group submaximal walk and grade walk.

Table 5 shows correlations for changes between postoverweight and 1-year follow-up in aerobic and strength fitness and changes in locomotion HR. Changes in V[Combining Dot Above]O2max were consistently related to changes in locomotion HR, but changes in strength were not.

Table 5
Table 5:
Relationships between difference (postweight loss to 1-year follow-up) aerobic and strength fitness and difference in locomotion. (n = 73).

Discussion

Despite no change in exercise economy, diet-induced weight loss was associated with decreased HR during walking, stair climbing, and grade walking. Addition of exercise training during the diet-induced weight loss did little to further decrease in HR. However, during the year after weight loss, inclusion of either aerobic or resistance training helped to maintain the decreased HR obtained during weight loss. Individuals who did not exercise train during the year after weight loss did not maintain the lower HR during locomotion. The aerobic trainers of course had enhanced aerobic fitness, and the resistance trainers had enhanced strength. Taken together, these data suggest that exercise training during and after weight loss has a positive effect on fitness that translates into increased ease (decreased HR) during locomotion 1 year after weight loss. Based on previous research, this increased ease should translate into more free-living (separate from exercise training) physical activity (8,9), and in turn, the increased physical activity should lead to reduced weight gain (4,5,19).

Both aerobic and resistance training had an effect on maintaining the weight loss–induced decrease in HR during locomotion. A number of investigations have shown that either resistance training (2,7,10) or aerobic training (11,15,17) is accompanied by reduced HR in submaximal walking and running. To our knowledge, no studies have compared resistance and aerobic training effects on walking and stair climbing HR during and after a diet-induced weight loss. Aerobic and resistance training had only minimal additional effects on HR response to walking and stair climbing immediately after weight loss. However, the exercise training did have a positive effect on reducing the HR during cycling immediately after weight loss.

During the walk, grade walk, and stair climbing, subjects were required to do less work after weight loss because of their reduced body mass (approximately 15% less). The no exercise group thus reduced their HRs during these tasks and may have masked any changes induced by the exercise training. During biking, work did not decrease as much during weight loss, that is, the work on the bike ergometer remained at 50 W. The work done to move the legs during each pedal cycle was of course reduced after weight loss because presumably subjects would have lost some mass from the legs. However, the overall decrease in work would be minimal when compared with walking and stair climbing. Therefore, the effects of the exercise training on HR response during work is more easily detected without reduced work of moving lower-body mass confounding the analysis. Observation of the biking data supports this contention, with the no exercise group not changing HR, whereas the combined aerobic and resistance training groups decreasing HR to 9 b·min−1 after weight loss. Therefore, it can be concluded that exercise training during weight loss has a positive effect on improving the ease of exercise in an absolute task (such as cycling at 50 W). However, exercise training during weight loss has less of an effect for tasks in which the work is being done to move reduced body weight.

Increased efficiency at low cycling intensity has been reported after weight loss (14,16,18) but not at higher-intensity exercise (6). Consistent with studies that used higher-intensity steady-state exercise, the present study did not find a difference in exercise economy for any of the moderate-intensity submaximal exercise tasks after weight loss. Mechanisms for why exercise economy-efficiency increases at very low intensities (i.e., 25 W or ≤2 metabolic equivalents [METs]) but not at more moderate intensities (i.e., >3 METs) are unknown.

Consistent with the increase in biking efficiency found with low-intensity exercise, RQ has been shown to decrease during low-intensity (25 W and lower) biking (16), showing less carbohydrate metabolism. Because biking efficiency also increased requiring less energy expenditure, presumably subjects would be able to perform the biking task with less activation of inefficient fast twitch muscle fibers that would be more dependent on carbohydrate metabolism. We observed no weight loss–related decrease in RQ for our moderate-intensity exercises (including cycling), except for the stair climb. On the other hand, similar to Amati et al (1), we observed a decrease in RQ during the walk and grade walk for the aerobic exercisers but not for the resistance trainers or nonexercisers.

Although the aerobic and resistance training decreased HR during the submaximal tasks similarly, the mechanisms for the improvements are probably different. Improvements in aerobic fitness would be accompanied by increases in blood volume and increased maximal and submaximal stroke volume. Increased stroke volume would be expected to translate into reduced HR at rest and during submaximal exercise. Resistance training normally has little effect on aerobic capacity and maximal stroke volume. However, it does affect strength, and increased strength is associated with a reduction in neural activation of muscle during submaximal tasks (7,10). It could therefore be argued that stronger individuals will not have as great an activation of the sympathetic nervous system during standardized tasks such as walking or riding a stationary bicycle (i.e., a lower percent of maximal force will be needed to perform a standardized task, so less relative muscle activation and less disturbance of homeostasis). Reduced neural-hormonal disturbance would then be accompanied by changes in extrinsic control of heart rhythm so that HR is reduced. Of course, either stroke volume or arterial-venous differences would have to accompany the reduced HR if oxygen uptake remained the same as it did in this study. It is impossible to know from the present study whether submaximal stroke volume or arterial-venous differences occurred.

Practical Applications

Exercise economy was not affected by weight loss or exercise training. However, HR and thus difficulty in walking, stair climbing, and bicycling was reduced after weight loss. Although exercise training did not have an effect on exercise HR after weight loss, exercise training during the year after weight loss maintained reduced exercise HRs obtained during weight loss. Therefore, the results of this study suggest that at least some moderately intense exercise training may be helpful in improving aerobic and strength fitness and the ease of movement during and especially after weight loss. This strategy may be helpful in improving health and preventing or at least slowing weight regain because reduced HR and thus more ease in locomotion may translate into increased participation in free-living physical activity (8,9) and in turn improved body weight maintenance (4,5,19). Although not tested in this study, it is probable that combined aerobic and resistance training may have an additive effect on improving the ease of locomotion after weight loss.

Acknowledgments

This work was supported by RO1DK51684, RO1DK49779, UL 1RR025777, P60DK079626, MO1-RR-00032, P30-DK56336, and 2T32DK062710-07. Stouffer's Lean Cuisine and Weight Watchers Smart Ones kindly provided food used during the weight-maintenance periods. We acknowledge Robert Petri for technical assistance and Betty Darnell for diet development and supervision.

Sources of support: National Institutes of Health grants R01 DK 49779 and R01 DK51684, DRR General Clinical Research Center grant RR-32, Clinical Research Unit 5UL1 RR025777, Nutrition Obesity Research Center grant P30-DK56336, UAB University-wide Clinical Nutrition Research Center grant, DRTC grant P60 DK079626, and Stouffer's Lean Cuisine entrees used for control of dietary intake were kindly provided by the Nestle Food Co., Solon, OH.

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Keywords:

aerobic training; resistance training; calorie restriction

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