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Applied Sciences: Physical Fitness And Performance

Influence of exercise training on physiological and performance changes with weight loss in men

KRAEMER, WILLIAM J.; VOLEK, JEFF S.; CLARK, KRISTINE L.; GORDON, SCOTT E.; PUHL, SUSAN M.; KOZIRIS, L. PERRY; McBRIDE, JEFFREY M.; TRIPLETT-McBRIDE, N. TRAVIS; PUTUKIAN, MARGOT; NEWTON, ROBERT U.; HÄKKINEN, KEIJO; BUSH, JILL A.; SEBASTIANELLI, WAYNE J.

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Medicine & Science in Sports & Exercise: September 1999 - Volume 31 - Issue 9 - p 1320-1329
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Abstract

Weight loss occurs when energy output (i.e., RMR plus the thermic effect of activity and food) is greater than energy input (i.e., dietary intake). Reducing dietary energy intake certainly provides a simple and effective method to lose total body mass, at least temporarily. Decreases in body mass with dietary restriction can result in a loss of fat-free mass (30). However, the loss of fat-free mass (i.e., primarily skeletal muscle) can be undesirable because of the important functional and metabolic roles the muscle plays in force production and metabolic rate. It was hypothesized that concurrent dieting and heavy resistance training may spare the loss of fat-free mass, thereby leading to improvements in muscular strength, body composition, and metabolic rate over dieting alone.

There is a distinct need for a greater understanding of the combined effects of resistance training and endurance training performed simultaneously during a weight loss program. While many studies have certainly described the physiological responses to dietary-induced weight loss in men, fewer studies have examined the impact of specific (i.e., endurance or resistance exercise) training programs performed with dietary restriction in men (3,4,9). To our knowledge, no data are available in men examining the combined influence of performing both heavy resistance and endurance training as a part of an overall weight loss program (7,9).

Resistance training has resulted in skeletal muscle hypertrophy and had positive effects on body composition and muscular strength and power (15,19). These physiological adaptations are dependent upon the program design and several acute program variables (e.g., load used, number of sets and repetitions, rest periods between sets, etc.) (16). Further data are needed to gain insights into the question of whether a diet adequate in protein, fiber, and vitamins and minerals but low in total energy, can help mediate the expected chronic adaptations to heavy resistance training? Despite the fact that resistance training may result in only very small improvements in peak oxygen consumption (11), endurance oriented training has been shown to induce much greater increases in aerobic capacity, even during weight loss (23). Endurance training also has positive effects on serum lipids (36). Therefore, we hypothesized that the incorporation of both heavy resistance training and endurance training into a weight-loss dietary regimen would appear to offer several simultaneous advantages over those provided by weight loss induced by dietary restriction alone or dieting with only one form of exercise training. Therefore, the primary purpose of this investigation was to examine the effects of diet alone and diet combined with endurance training and diet combined with endurance and heavy resistance training on physiological and performance adaptations in overweight adult men.

METHODS

Subjects and experimental design. Prior approval by the Institutional Review Board for the Use of Human Subjects at the Pennsylvania State University was obtained for the investigation. Each subject had the risks of the experiment explained to them and signed an informed consent document. This study conformed with the policy statement regarding the use of human subjects as published by Medicine and Science in Sports and Exercise. All of the 35 healthy men who completed the study were screened by a physician and demonstrated no endocrine, orthopedic, or any other pathological disorders, except for being overweight (i.e., ≥ 120% of desirable weight defined as the midpoint of the range of weights for a medium frame man from the 1983 Metropolitan Height and Weight tables). Our first goal was to match the groups for age and percent body fat. Except for the control group (statistically set at N = 6), we attempted to recruit 10 to 12 men for each group. The men were then randomly placed into one of four groups. After an attrition of one to four men per group because of scheduling difficulties, the following N sizes were observed and used for all analyses in this study. However, no significant differences were observed among the groups at the beginning of the study in any of the variables. Control group (C; N = 6) which just performed the testing, maintained body weight, and normal activities; a diet group (D; N = 8) which maintained normal activities while reducing calories for weight loss; a diet group which performed an aerobic endurance training program 3 d·wk−1 (DE; N = 11); and a diet group which performed an aerobic endurance training program combined with a heavy resistance training program 3 d·wk−1 (DES; N = 10). The experimental testing took place before the program (Week 0), at the midpoint of the study (Week 6), and the end of the program (Week 12). Descriptive data for the experimental groups are presented in Table 1.

TABLE 1
TABLE 1:
Descriptive data of the experimental groups (mean ± SD).

Training protocols. Unique to this study was that all exercise programs were individually supervised by our laboratory's trained team of certified "personal trainers." The cardiovascular conditioning programs followed the American College of Sports Medicine guidelines for intensity, frequency, and duration of exercise (14). Subjects in the DE and DES groups participated in a program of whole body aerobic endurance exercise individually designed to elicit a target heart rate of 70-80% of the functional capacity as determined by treadmill testing. During the first week, each session lasted ∼30 min (not including warm-up and cool-down) and this was gradually increased to 50 min over the subsequent weeks. Intensity and duration of exercise were individually increased for each subject as improvement and toleration occurred. For variety, endurance activities included a cross-training mix of treadmill walking/jogging, stationary cycling, seated rowing, and stationary stair climbing.

In contrast to the DE group, the DES group also performed a strength training workout after their aerobic training session. The strength training program consisted of a squat exercise performed on a Tru-Squat machine (Southern Xercise Inc., Cleveland, TN) and additional Nautilus machine (Nautilus Intl. Huntersville, NC) exercises for each of the major muscle groups consisting of the following exercises: military press, bench press, lat pull down, seated rows, sit-ups, lower back, leg press, hamstring curls, calf raises, and arm curls. The programs followed typical repetition maximum (RM) resistance training principles for progression in the resistance and volume of exercise in a program (18). The resistance training protocol also used a nonlinear periodization model, meaning that the loads were changed within the week with subjects varying their resistance loads for the exercises on different days alternating between heavy day (5-7 RM) and moderate day (8-10 RM) loads. Target RM zones were maintained for the load intensity, but subjects did not always go to complete failure to limit joint stress. Subjects progressed from 1-3 sets over the first 2-3 wk with short rest between sets and exercises when using moderate loads (i.e., 1 min) and longer rest periods (2-3 min) when using the heavier loads. This program variation reduced boredom and has been shown to enhance short-term resistance training adaptations when compared with constant loading programs (16). Throughout the 12 wk subjects were highly encouraged to increase the amount of weight lifted within each designated repetition range.

Experimental tests. All experimental dependent variables demonstrated very good test-retest reliability as intraclass correlation coefficients were determined for all tests; they ranged from R = 0.95 to R = 0.98. All subjects were completely familiarized with all testing procedures before the experiment to reduce the influence of any learning effects caused solely by the mechanics of performing the test protocol.

Body mass was measured on a balance scale to the nearest 100 g and body density was determined via hydrodensitometry. A description of the equipment used for underwater weighing is provided by Akers and Buskirk (1). Underwater weight of the subject was determined by a scale utilizing four electronic force cubes (load cells) attached to a chart recorder. Following a maximal exhalation subjects were weighed underwater and residual volume measurements were performed while subjects were still in the tank using an open-circuit nitrogen washout technique. Percent body fat was calculated from body density using the Siri equation (31). Fat mass was determined by multiplying percent fat times body mass, and fat-free mass was determined by subtracting fat mass from body mass.

Maximal force production (1-RM) in the upper body was determined via a Nautilus straight bar bench press and in the lower body via the Tru-Squat machine. The 1 RM test protocols were performed using methods previously described and used extensively in our laboratory (17). These tests are specific to the exercise training protocol and provided the best representation of maximal muscular strength of the upper and lower body musculature.

Maximal oxygen consumption was determined using a graded exercise test on a Quinton (Seattle, WA) motor driven treadmill using a modified Bruce protocol (31). During each stage of the test, heart rate was monitored continuously via a 12-lead EKG (Marquette, Model Case-15, Milwaukee, WI), and ratings of perceived exertion (RPE) were recorded each minute. Blood pressure was obtained every 2 min via brachial auscultation. Expired gases were analyzed during the last 6 min of the test using an automated metabolic system. The gas analyzers consisted of a Beckman LB-2 CO2 analyzer (Beckman Instruments, Schiller Park, IL) and S3A O2 Analyzer (Applied Electrochemistry, AEI Technologies, Pittsburgh, PA) and were calibrated before each test with standard gases. Standard gas tanks were calibrated via Scholander methodology. Flow was measured by a Hans Rudolph model 4813 pneumotach and transduced to volume by a Fitco Micro-Flow model FLO-1 instrument. These signals were integrated in a software package by Fitco (Farmingdale, NY).

Power production capabilities in the lower body were determined using a 30-s Wingate anaerobic test performed on a computerized Monark (Varberg, Sweden) cycle ergometer against an opposing force of 0.49 N (0.05 kg)·kg−1 of body mass using a protocol described in detail by Kraemer et al. (31). Flywheel revolutions were electronically monitored during the test via computer interface (Model 55sx, IBM Personal System/2). Maximum power (highest 1 s value), mean power (average power over the time curve) and percent decline (decline from the highest to the lowest points on the curve) were calculated by associated software.

RMR was only determined before and following the 12 wk experimental protocol via indirect calorimetry. Following a 10-h fast, subjects reported to the laboratory from 0500 to 0600 h and were positioned in a semirecumbant position on a bed. After a 30-min stabilization period, oxygen consumption was determined at 1-min intervals for 30 min using the same on-line metabolic system used for maximal treadmill testing.

Nutritional protocol. Each week all intervention participants attended a 1-h group format nutrition education meeting led by a registered dietitian. The weekly sessions focused on behavior modification techniques and educating subjects as to how to implement a healthy well balanced eating plan designed to lose body mass. Our objective was to create a 6- to 9-kg weight loss in each subject by moderate caloric restriction over the 12 wk. Forms for documenting daily food intake were provided at each session and these food records were reviewed for dietary compliance at the beginning of each new week. Food record forms were analyzed for total food energy and nutrient content using Nutritionist IV, Version 4 nutrient analysis software (N-Squared Computing, First Databank Division, The Hearst Corporation, San Bruno, CA). In addition, subjects were given a 1-week supply of Matola products at each meeting. Briefly, the Matola products included prepackaged high-fiber meal replacement bars, shakes, and cereal which contained approximately 50% of the USRDA for vitamins and minerals. These products were consumed in place of certain meals in a 4-d rotational sequence. In addition to other meals ingested during the day, subjects consumed the Matola products in the following order: one product on day 1, two products on day 2, three products on day 3, and no products on day 4. Thus, a total of about 12 products were consumed each week. Protein intake was ≥ RDA and ≥ 1 g·kg−1 ideal body weight. Subjects were strongly encouraged to drink copious amounts of water throughout the day. Body mass was also recorded and charted at each meeting to ensure a steady rate of weight loss (0.5 to 1.0 kg·wk−1) over the 12 wk. It was not the goal of the study to strictly control what subjects consumed outside of their scheduled Matola products. Sample menus were provided to help subjects select a variety of foods for their non-Matola meals. If weight loss was not progressing at an appropriate rate or if subjects were having problems adhering to the dietary regimen, individual counseling was provided.

Blood collection and analyses. Blood was obtained from a forearm vein after a 10 h fast between 0500 to 0600 h. Whole blood was processed and the resultant serum samples were stored at −80°C until analyses were performed. Serum glucose, blood urea nitrogen (BUN), total cholesterol, high-density lipoprotein cholesterol (HDL), and triglyceride concentrations were determined via spectrophotometry (Novaspec II, Pharmacia LKB Biochrom Limited, Cambridge, UK) and testosterone and cortisol using standard radioimmunoassay (RIA) procedures. Serum glucose was assayed in duplicate using an enzymatic (hexokinase) technique at an absorbance of 340 nm (Sigma Diagnostics, St. Louis, MO). Total cholesterol, HDL cholesterol, triglycerides, and BUN were enzymatically determined in duplicate using commercially available kits (Sigma Diagnostics). Low-density lipoprotein cholesterol (LDL) concentrations were calculated according to the method of Friedewald et al. (8). Serum testosterone and cortisol concentrations were assayed using solid-phase 125I single antibody RIA (Diagnostic Products Corp., Los Angeles, CA) with detection limits of 0.14 and 5.5 nmol·L−1, respectively. Immumoreactivity was measured with an LKB 1272 Clinigamma automatic gamma counter with an on-line data reduction system (Pharmacia Wallac, Wallac Oy, Finland). Intra- and inter-assay variances for all assays were <5% and <10%, respectively.

Statistical analyses. Comparisons between values obtained at baseline, week 6, and week 12 within each group and between groups at each time point were made using a two-way analysis of variance (ANOVA). In the presence of a significant F value post-hoc comparisons of means were provided by Fisher's LSD test. Statistical power calculations demonstrated power in this investigation ranged from 0.79 to 0.80. The relationship between changes in selected variables were made using simple regression. The level of significance was P ≤ 0.05.

RESULTS

Estimated dietary intake for the three experimental groups is shown in Table 2. There were no significant differences between groups in any of the examined nutritional variables. The changes in body mass, percent fat, fat mass, and fat-free mass following the 12-wk experimental period in all four groups are presented in Table 3 and Figure 1. No significant changes in body mass or body composition were observed in the C group. Body mass was significantly decreased for all dietary intervention groups at week 6 and continued to decline, although at a slower rate, from week 6 to week 12. Percent body fat and fat mass were also significantly reduced at week 12 for all dietary groups. The DES achieved a significantly greater loss in percent body fat (−8.42%) at week 12 compared with the DE group (−4.70%) and the D group (−3.62%). The diet-only group also demonstrated a significant reduction in fat-free mass at week 6 and week 12. At week 12, the percent of body mass loss attributed to fat for the D, DE, and DES groups was 69, 78, and 97%, respectively.

TABLE 2
TABLE 2:
Estimated daily nutrient intake for the three experimental groups (mean ± SD).
TABLE 3
TABLE 3:
Body composition data (mean ± SD).
Figure 1-Ab
Figure 1-Ab:
solute changes (x ± SD) in body mass, fat mass, and fat-free mass (FFM) after 12 wk in the control (C), diet-only (D), diet + endurance training (DE), and diet + endurance + strength training (DES) groups. * =P ≤ 0.05 from corresponding change in the C group.

Maximum strength, as determined by 1-RM testing in the bench press and squat exercise, was not significantly different at week 12 for C, D, or DE. However, DES significantly increased the amount of weight lifted at week 12 for both the bench press (+19.6%) and squat exercise (+32.6%) (Table 4). Maximum oxygen consumption expressed in relative terms (mL·kg−1·min−1) was significantly increased at week 12 for D (+28.4%), DE (+39.2%), and DES (+27.4%). However, peak oxygen consumption expressed in absolute terms (L·min−1) was significantly elevated only in the DE (+24.8%) and DES (+15.4%) groups (Table 5). Control data for maximum oxygen consumption was discarded because of a problem with the metabolic system and test retest reliabilities determined on a separate group showed an intra-class R = 0.96. There were no differences in peak power, mean power, or percent fatigue during the Wingate test at week 12 for the DE and DES groups. The diet-only group demonstrated a significant decline in peak and mean power output at week 6 which remained lower at week 12 (Table 6). RMR was lower after 12 wk for the D, DE, and DES groups (−80, −122, and −136 kcal·d−1, respectively). The only significant reduction in RMR (kcal·d−1) was for the DE group. However, RMR normalized to body mass or fat-free mass was not significantly altered after weight loss (Table 7). Since it has been suggested that dividing RMR by fat-free mass is inappropriate because the intercept of the relationship does not intersect zero (28), Figure 2 illustrates the relationship of RMR and fat-free mass at baseline and week 12.

TABLE 4
TABLE 4:
One repetition maximum (1-RM) strength in the bench press and squat exercise (mean ± SD).
TABLE 5
TABLE 5:
Maximum oxygen consumption (mean ± SD).
TABLE 6
TABLE 6:
Maximum power, mean power, and percent fatigue during a 30-s Wingate test (mean ± SD).
TABLE 7
TABLE 7:
Resting metabolic rate determinations (mean ± SD).
Figure 2
Figure 2:
The relationship between RMR and fat-free mass at baseline (○) and week 12 (•) in the diet (A), diet + endurance (B), and diet + endurance + strength (C) groups. A: Baseline, y = 702.66 + 19.37x, r2 = 0.47; Week 12, y = 1354 + 9.73x, r2 = 0.30. B: Baseline, y = 387.21 + 23.70x, r2 = 0.44; Week 12, y = 1064.50 + 11.71x, r2 = 0.19. C: Baseline, y = 1298.4 + 9.96x, r2 = 0.11; Week 12, y = 2358.90-8.40x, r2 = 0.04.

There were no changes in serum concentrations of glucose, BUN, cortisol, and testosterone for any of the groups (Table 8). Serum cholesterol and triglycerides are shown in Figure 2. Total cholesterol (Fig. 3A) and LDL cholesterol (Fig. 3C) were significantly decreased at week 6 and remained lower at week 12. There were no changes in HDL cholesterol concentrations for any group (Fig. 3B). Serum triglycerides were significantly reduced in the D and DES groups at week 6 (Fig. 3D). While triglyceride concentrations remained significantly lower at week 12 for the D group, triglycerides returned to baseline values in the DES group.

TABLE 8
TABLE 8:
Venous blood variables (mean ± SD).
Figure 3
Figure 3:
Serum concentrations (mean ± SD) of total cholesterol (A), HDL cholesterol (B), LDL cholesterol (C), and triglycerides (D). W0, Week 0; W6, Week 6; W12, Week 12; C, Control; D, Diet; DE, Diet/Endurance; DES, Diet/Endurance/Strength. * =P ≤ 0.05 from corresponding value at week 0. † = P ≤ 0.05 from corresponding value at week 6.

DISCUSSION

Dietary restriction alone does not appear to be an optimal strategy to promote weight loss for the >33% of U.S. adults currently classified as overweight (21). Whether exercise offers any physiological advantages over body fat reduction induced by dietary restriction has been debated for some time. Furthermore, the potential differential effects of various forms of exercise, including resistance training, have not been well characterized in men with regard to its influence on changes in body composition, serum lipid responses, and muscular performance during weight loss. In this investigation we provide evidence that 12 wk of moderate dietary energy restriction in conjunction with endurance training improves peak oxygen consumption; however, no advantages over diet alone are apparent in regards to total weight loss or body composition changes, serum lipoprotein profile, metabolic rate, power production capabilities, and 1-RM strength. In comparison, when heavy resistance training is added to the diet and endurance program, improvements in body composition changes and maximal strength are apparent. These data are important to help identify key program design components for development of successful weight loss programs.

As expected, all three dietary intervention groups demonstrated a significant and similar reduction in overall body mass. Thus, exercise provided no additional stimulus for greater weight loss compared with that obtained from dietary restriction alone. This finding is consistent with data from a prior study in women from our laboratory (20) as well as data from several other studies (3,4,12,26,34). The composition of weight loss, however, varied among groups. In a meta-analysis, Garrow and Summerbell (9) predict from regression analysis that for a weight loss of 10 kg by dieting alone the expected loss of fat mass is 71% and when a similar weight loss is achieved by both diet and endurance exercise the expected loss from fat mass is increased to 83%. These estimations are remarkably close to the 69 and 78% loss in fat mass observed in the diet-only and diet-plus endurance groups, respectively. Forbes (7) suggests that the two major body components, fat-free mass and fat mass, are linked and rise and fall in a predictable fashion. For exercising humans with an average percent body fat of approximately 29% (similar to that in the present study) Forbes (7) predicts that 75% of the loss in body mass to be from the fat mass component. Again, our data from the endurance trained group showing that 78% of the total loss in body mass represents fat mass is in close agreement with this estimation.

However, the proposed relationship between fat-free mass and fat mass is clearly lost when heavy resistance training is performed during dietary restriction. Our data show that inclusion of both endurance and a periodized heavy resistance exercise training three times per week resulted in nearly complete preservation of the fat-free mass component in a group of overweight men. Of the total body mass loss in the resistance training group, 97% was accounted for by fat mass. Thus, a periodized heavy resistance training program that sufficiently overloads the whole body musculature appears to provide a unique stimulus to spare catabolism of body protein and thus alter the relationship between the fat-free mass and fat mass components.

In contrast to our finding that fat-free mass is essentially completely preserved with heavy resistance exercise combined with endurance training, other investigators have reported that weight training does not offer advantages in regards to body composition changes over dietary restriction alone (5,6). However, results from studies using women have reported that combined resistance training and dieting not only attenuates but maintains or increases fat-free mass (2,10,23,25,29,30). Differences in training intensity and/or incorporation of periodization (i.e., varying the program over time) into the resistance training program may help to explain these apparent discrepancies. Perhaps the uniqueness of the dietary regimen, which was comprised of moderate energy, adequate protein, vitamins and minerals, and high dietary fiber, also contributed to our findings. Heavy resistance training has been shown to increase resting concentrations of testosterone and decrease resting concentrations of cortisol in men in the early phase (first 16 workouts) of a heavy resistance training program (32); however, other studies have shown unaltered concentrations of these hormones. No significant changes in circulating testosterone and cortisol were observed in this study over the training period, indicating that an overt endocrine response reflective of the changes to the various interventions was not observed under these experimental conditions or was not observed because of a more rapid homeostatic time course of regulation (19).

Serum total cholesterol decreased at week 6 and remained lower than baseline values at week 12 for all three dietary intervention groups. At week 6 in the D, DE, and DES groups total cholesterol had declined by 16.3%, 14.6%, and 11.2%, respectively. From week 6 to week 12 total cholesterol increased in the D, DE, and DES groups by 2.6%, 1.8%, and 1.0%, respectively. Serum LDL cholesterol and triglycerides followed a similar pattern of response as total cholesterol while HDL cholesterol remained unchanged. These lipid responses are very similar to data reported in men undergoing either dietary restriction alone or diet combined with aerobic conditioning for 12 wk (12). Interestingly, Wallace et al. (35) observed a positive effect of performing resistance exercise in addition to endurance training on blood lipids (i.e., greater increase in HDL cholesterol and decrease in triglycerides) in subjects with hyperinsulinemia. Our data show no additional cholesterol lowering effect of exercise over diet alone. Thus, exercise (both endurance and resistance) did not "enhance" the positive effects of the dietary regimen in this study. Whether the weight loss, high fiber content of the diet, moderate dietary energy restriction, or a combination of these factors contributed to the serum lipid responses is unclear.

A reduction in serum cholesterol has been demonstrated to be directly linked to a reduction in coronary risk (22). It should be pointed out, however, that rapid weight loss may induce a non-steady state that has transient effects on total cholesterol and that clinical evaluation of serum lipid profiles should not be made until body mass has stabilized (27). More specifically, total cholesterol and LDL cholesterol may show an initial decline after 2 months of dieting, a moderate rise as weight loss continues (possibly because of mobilization of adipose tissue cholesterol stores), followed by a decline when body mass finally stabilizes (12,27). Since subjects in this study may still have been losing body mass at week 12, firm conclusions regarding the potential response of serum lipoproteins should be made with caution.

RMR expressed in absolute terms (kcal·d−1) declined for the D, DE, and DES groups (−3.8%, −6.4%, and −7.0%, respectively). However, RMR expressed in relative terms, either kcal·kg FFM−1·d−1 or kcal·kg BM−1·d−1, was not significantly altered in any of the dietary groups. Thus, when the changes in body mass are accounted for, all dietary intervention groups prevented the normal decline in RMR typically observed with dietary energy restriction (24). We regressed RMR across fat-free mass because of potential errors in interpreting RMR expressed as kcal·kg FFM−1·d−1(28). Interestingly, the lowest correlations between fat-free mass and RMR were observed in the DES. The change in fat-free mass was not significantly correlated with the change in RMR which is in agreement with the findings of a meta-analysis on the effects of diet and exercise on metabolic rate (33). Contrary to our hypothesis, the exercise groups demonstrated similar responses in RMR compared with the diet-only group. Geliebter et al. (10) also reported no advantage of either endurance or strength training over dieting alone on RMR in a group of subjects that lost very similar amounts of body mass to subjects in the present study. In the present study RMR in the D, DE, and DES groups declined by −80, −136, −122 kcal·d−1, respectively, compared with a decline of −88, −149, and −127 kcal·d−1 reported by Geliebter et al. (10). Thus, although strength training prevents the normal loss in FFM during dieting, the decline in RMR is not prevented. As pointed out by Heshka et al. (13), the elapsed time between weight loss and remeasurement of RMR is a critical factor in assessing the impact of a weight loss program on RMR. Since subjects may still have been losing weight at week 12, the same cautions must be taken in interpreting the RMR results as that for the serum lipid data.

As expected the DES group experienced the greatest increases in 1-RM strength in the bench press and squat exercise. The highest gains were made in the first 6 wk with continued improvement by 12 wk of training. The lack of continued increases in 1-RM strength may have been a result of the lack of muscle mass gains over the training program (15). Since there was little change in fat-free mass in the DES group, it may be speculated that 1-RM strength improvements were mediated via changes in neural mechanisms and/or changes in the quality of protein in the muscle fiber (32). For example, fiber type conversions in the fast-twitch subpopulations from Type IIB to Type IIA increased anaerobic energy sources and enzymes, enhanced muscle tissue activation of the agonists, and/or decreased inhibition of the antagonists, and changes in neuromuscular junction are all physiological adaptations that have been shown to occur from heavy resistance training (15,19,32). The reason that some studies have reported small or no strength increases may be related to the resistance training program design. (i.e., most resistance exercise training programs have not used the higher intensities of exercise nor have they periodized heavy and light training days over the training period) (16). These data demonstrate that with proper exercise prescription and a sound weight-loss program, despite the dramatic reduction in body mass, positive adaptational responses most likely caused by neural mechanisms can be achieved with resistance training on strength performance.

Maximum oxygen consumption expressed in absolute terms (L·min−1) was increased for both groups who performed endurance training (DE and DES). When peak oxygen consumption was expressed relative to body mass (mL·kg−1·min−1) increases were observed in all dietary groups. Thus, the improvement in relative peak oxygen consumption observed in the diet-only group most likely reflects the decrease in body mass at week 12 (12). In contrast, the increase in peak oxygen consumption for the DE and DES groups reflect a true functional improvement in the muscle's oxidative ability and the body's cardiorespiratory capacity. Interestingly, the improvements in peak oxygen consumption were not detectable at week 6, indicating that training adaptations resulting in improved oxygen capacity may not be evident during the initial weeks of a training program during weight loss. This finding agrees with data reported by Phinney et al. (26) showing no improvement in peak oxygen consumption after 40 d of a very low calorie diet and regular endurance exercise. There were also no differences in the increase in maximum oxygen consumption between the DE and DES groups, indicating that even under conditions of weight loss, the concurrent resistance training and endurance training can be performed without comprising the expected cardiovascular improvements as previously demonstrated without weight loss (19). Nevertheless, whether simultaneous resistance and endurance training compromised the physical performance gains derived from weight training alone remains unknown because of the experimental design used in this investigation. One might speculate that the rate of strength gains may have been attenuated by the combination of strength and endurance training, particularly in the lower body as both forms of exercise involved the leg musculature (19).

No statistically significant changes were observed over the 12-wk training program in the Wingate anaerobic cycle power test performance except for a decline in peak and mean power output by the diet-only group and a trend for lower values in the DE group. These declines in power production capabilities most likely reflect the loss in fat-free mass observed in these groups. The resistance trained DES group did maintain their fat-free mas and their anaerobic power performance despite a significant reduction in total body mass. The mechanisms responsible for enhancing fast-velocity strength changes have been shown to be different than those which mediate slow-velocity strength changes (16). Thus, the lack of improvement in the power component of performance is most likely attributable to the fact that neither the weight training nor the cycle exercise used in the endurance training were specifically designed with power development in mind. These data demonstrate that strength increases do not necessarily contribute to changes in power as the use of controlled movements in training do not promote improvements in the rate of force development nor can such stack plate equipment be used for explosive lifting because of deceleration requirements over the range of motion to protect joints involved.

In summary, these data indicate that endurance exercise, when added to a dietary weight loss program, increase maximum oxygen consumption. However, no additional benefits are detectable over dieting alone in regards to changes in total body mass, body composition, RMR, serum lipid profile, and muscular strength in men. However, diet in conjunction with heavy resistance and endurance exercise training not only improves peak oxygen consumption but also has the largest impact on improving body composition, maximal strength, and maintaining power production capabilities. Thus, heavy resistance exercise is an important component for weight management programs in men as it offers several distinct advantages over weight loss accomplished by dieting alone.

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Keywords:

DIET; STRENGTH TRAINING; LIPOPROTEINS; TESTOSTERONE; CORTISOL; ENDURANCE TRAINING

© 1999 Lippincott Williams & Wilkins, Inc.