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Department of Human Nutrition, Foods, and Exercise (J.W.R., L.P.G., M.J.P., S.M.N.-R., C.P.E.), Virginia Tech, Blacksburg, Virginia
Department of Dairy Sciences (F.C.G.), Virginia Tech, Blacksburg, Virginia
Address reprint requests to: Janet Walberg Rankin, Ph.D., Department of Human Nutrition, Foods, and Exercise, Virginia Tech, Blacksburg VA 24061-0430. E-mail: jrankin{at}vt.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS & METHODSRESULTSCONCLUSIONACKNOWLEDGMENTSREFERENCES |
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Methods: Nineteen, untrained men (18–25 years) consumed either a milk (MILK) or a carbohydrate-electrolyte (CHO) drink immediately following each workout during a 10 week resistance training program. Muscle strength (1RM for seven exercises), body composition (DXA scan), fasted, resting concentrations of serum total and free testosterone, cortisol, IGF-1, and resting energy expenditure (REE) were measured prior to and at the end of training.
Results: Resistance training caused an increase (44 ± 4%, p < 0.001) in muscular strength for all subjects. The training program reduced percent body fat (8%, p < 0.05, –0.9 ± 0.5 kg) and increased fat-free soft tissue (FFST) mass (2%, 1.2 ± 0.3 kg, p < 0.01). MILK tended to increase body weight and FFST mass (p=0.10 and p=0.13, respectively) compared to CHO. Resting total and free testosterone concentrations decreased from baseline values in all subjects (16.7%, 11%, respectively, p < 0.05). Significant changes in fasting IGF-1, cortisol, and REE across training were not observed for either group.
Conclusion: Post-resistance exercise consumption of MILK and CHO caused similar adaptations to resistance training. It is possible that a more prolonged training with supplementation period would expand the trend for greater FFST gains in MILK.
Key words: body composition, nutrition for strength athletes, weight training, testosterone, hypertrophy
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSCONCLUSIONACKNOWLEDGMENTSREFERENCES |
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Several studies report a benefit of regular ingestion of dietary supplements on magnitude of muscle hypertrophy and strength during resistance training. Gater et al. [11] and Meredith et al. [12] demonstrated superior lean gain or muscle hypertrophy, respectively, in men in response to resistance training of 10 to 12 weeks with a daily dietary supplement of about 400–500 kcal/d compared to control group. However, it is not possible to determine from these studies whether the benefit was due to the increase in total calories or the specific macronutrients provided. Thus, it is important to compare dietary supplements with the same energy but differing macronutrient content during resistance training.
It is possible that timing of food ingestion relative to the resistance bout is critical for enhancing hypertrophy. One study using older subjects reported that muscle hypertrophy occurred with a resistance training program only when a mixed macronutrient supplement was consumed immediately after the resistance workout and not if consumption was delayed two hours [13]. Studies of protein balance after an acute resistance training bout show that consumption of food just before or just after exercise stimulates muscle protein synthesis [6, 8–10].
Adaptations in anabolic hormones may contribute to the differential effects of diet on muscle hypertrophy. For example, Volek et al. [14] reported that resting concentration of testosterone in men undergoing resistance training was correlated to protein and fat intake. Thus, chronic dietary change may induce hormonal changes that influence muscle growth or strength adaptations.
A potential benefit of milk consumption, a natural product containing both carbohydrate and protein, on acute muscle recovery following exercise compared to a carbohydrate or placebo beverage was first suggested by Cade et al. [15] following strenuous swimming and later by Wojcik et al. [16] following a single strenuous eccentric, resistance exercise bout. This complements the research suggesting a benefit of food containing protein proximal to the resistance bout for protein balance. However, more work is necessary to determine whether these acute changes continue during training and translate to great lean tissue gain or muscle function. The purpose of this investigation was to determine whether the adaptive responses to resistance training would vary when the post-exercise supplement was a carbohydrate sports beverage or an isoenergetic, flavored-milk beverage containing all macronutrients.
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MATERIALS & METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSCONCLUSIONACKNOWLEDGMENTSREFERENCES |
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Experimental Design
Before baseline testing, subjects completed a dairy food frequency form to determine usual intake. The subjects were asked to indicate frequency (choices were daily, weekly or monthly servings) of consumption of common dairy foods (choices included milk, cheese, cottage cheese, pudding/custard, ice cream, yogurt, macaroni and cheese, and pizza). Total servings consumed per week were calculated for each subject and used to rank subjects from highest to lowest in dairy consumption. Subjects were assigned sequentially to alternate groups based on their dairy intake in order to avoid bias on results of initial dairy intake.
Baseline testing, performed before any supplementation or training, included body mass and height, several body circumference measures, strength assessment, resting energy expenditure (REE), body composition, blood collection and 3-day food records. After baseline testing, all subjects began the same 10 week resistance training program. Immediately following each workout, subjects consumed an isoenergetic dietary supplement of either a carbohydrate-electrolyte beverage (CHO) or low fat chocolate milk (MILK). Subjects were instructed to maintain their usual diet and activity level and not to begin other nutritional supplementation or outside exercise programs. Personal trainers supervised each workout.
Measurements
Before the start of baseline testing, subjects were instructed by a registered dietitian on procedures for recording dietary intake. Subjects completed 3 d food diaries at intervals throughout the study (0, 3, 6, 10 week) in order to assess total energy and macronutrient intake (Food Processor, version 7.60 nutrient analysis software, ESHA Research; Salem, OR).
Body weight and height before and after resistance training were measured upon arrival to the laboratory after a 12 hour fast. Weight was measured to the nearest 0.1 kg using a digital scale and height to the nearest 0.1 cm. Muscle circumference measurements were taken as the average of duplicate measurements at the mid-thigh and mid-upper arm and on the chest at the level of the fourth costosternal joints, in the horizontal plane and to the nearest 0.1 cm [17]. All anthropometric measures were completed by the same individual.
Dual-energy X-ray absorptiometry (DXA) scans were conducted to measure total body fat mass, FFST mass, and percent body fat of each participant (version 8.25a, 2000, Whole Body Analysis software, QDR4500A, Hologic Inc., Bedford, MA). Regions of interest, including the upper arms, forearms, upper legs, and lower legs, were manually examined from the total body scans for these same body composition measures. Test-retest reliability of DXA measurements within individuals resulted in coefficients of variation of 1.75%, 1.07% and 1.79% for fat mass, FFST mass, and percent body fat, respectively, in 24 young-adult men and women. One investigator conducted and analyzed all scans to ensure consistency.
Performance testing included assessment of one-repetition maximum (1RM) leg press, leg curl, leg extension, bench press, shoulder press, lateral pull down and arm curl. All strength testing was performed using Body Masters equipment (Body Masters Sports Industries; Rayne, LA). After a warm-up with a light resistance that allowed 10 repetitions, subjects were given a 1-min rest period. Resistance was then increased to allow the performance of 3–5 repetitions with a 2-minute rest period. For the final trial, resistance was adjusted so that the subject could complete only 1 repetition. Add-on weights as low as 0.45 kg were used to increase accuracy of measurements.
Fasting blood samples were taken just prior to and at the end of the 10 week training period for analysis of IGF-1, cortisol, free and total testosterone. Serum samples were analyzed for cortisol and free and total testosterone in duplicate using Coat-a-Count Radioimmunoassay (RIA) kits (Diagnostic Products Corp.; Los Angeles, CA) with intra-assay CV of 7.2%, 6.5%, 7.2%, and respectively. Serum IGF-1 was quantified by RIA according to the procedures described by Weber et al [18], with an intra-assay CV of 6.7%.
Indirect calorimetry using an open-circuit system (VMAX 29N, SensorMedics, Yorba Linda, CA) was used to measure REE after an overnight (10–12 hour) fast, before initiation and at the end of 10 week of resistance training. The final measurement was performed at least 48 hours after the last exercise workout. Instrument calibration was performed before each REE measurement, and subjects remained in a supine position throughout a 30 minute pre-measurement rest period and a subsequent 20-minute period when gas exchange was measured. REE was derived via the abbreviated Weir equation [19]: REE = [3.941 (VO2) + 1.106 (VCO2)] x 1.44; where REE=resting energy expenditure in kcal/d, VO2=oxygen consumption (mL/min), and VCO2=carbon dioxide production (mL/min). Averages were calculated for the data collected between minutes 6 and 15, as this interval had a lower coefficient of variation (5.8%) than using the full 20 min (9.5%) or minutes 6 through 20 (7.4%).
Exercise Training
Resistance training sessions consisted of periodized workouts supervised by personal trainers. Each workout included the same exercises as those used for 1RM test, 3 d/week for 10 week (Table 1). Training intensity was determined using the subjects’ initial 1RMs. Another strength assessment was completed at week five and the intensity for the remainder of the study was based on these new 1RMs. Financial incentives (announced after baseline testing) were offered for strength gain and attendance. Subject attendance at training sessions was 94.4%.
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Statistical Analysis
Statistical evaluation of most data was performed using a two-way analysis of variance (ANOVA) with repeated measures design to test for effect of group, time and group by time interaction. A t test was performed to detect differences between treatments in body weight and composition change scores. A paired t test was used to analyze REE data for the combined groups. The level of significance for all analyses was set at p 
0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSCONCLUSIONACKNOWLEDGMENTSREFERENCES |
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Regional changes in body composition (trunk, arm, and leg regions) were examined for all subjects combined. Approximately half of the total fat lost by the full subject group was in the trunk region. Arms and legs accounted for 18% and 33% of total body fat loss, respectively. In contrast, expressed relative to baseline values, body fat loss was greatest for arms (10%) compared to trunk (6%) and legs (5%).
The trunk region accounted for slightly more than half (51%) of the FFST gain for all subjects with legs and arms contributing 20% and 28% to the gain. However, expressed as percent change from initial mass, the arms had the highest proportional increase (3%) compared to trunk (2%) and legs (2%).
Muscular Strength
Muscular strength was not significantly different for any of the seven exercises between groups prior to training (Table 4). All subjects, independent of treatment, significantly increased muscular strength by 44 ± 4% at the end of the 10 week training period for the seven exercises combined (p < 0.001). Muscular strength increased for all exercises, but improvement was greatest for leg press, 82 ± 11% and lowest for lateral pull down 15 ± 2% (Table 4). None of the strength gains were different by group.
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Hormones
Serum hormone concentrations were not significantly different between treatments before the start of training (Table 5). The training program with supplementation caused a significant reduction from baseline in basal concentrations of both free testosterone and total testosterone with no difference between groups. Cortisol tended to decrease 15% for all subjects, but variation in response between subjects prevented it from meeting the criteria for significance (p=0.056). Free testosterone to cortisol ratio (FTCR) was calculated as an index of overtraining. As the concentrations of both hormones decreased in similar proportions, there was only a modest, nonsignificant change in FTCR from 0.15 to 0.17.
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DISCUSSION |
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The resistance training program was successful in significantly increasing FFST mass by 2% and reducing percent body fat by 8%. The average lean tissue gain of 1.2 kg and the 6% loss of body fat are similar to other studies using comparable resistance training protocols in young men [1, 4]. Most studies have reported only the changes in total lean and fat mass, but use of DXA in this study allowed estimation of regional change in body composition. We found that the region with the greatest magnitude of FFST mass gain and body fat mass loss was the trunk followed by the legs and arms. However, the greatest proportional change from initial values for both fat and FFST mass was in the arm region. This is consistent with the fact that the only body part showing significant change in circumference was the arms. Similar to our results, Treuth et al. [23] observed the greatest proportional gain in lean tissue in the trunk but the greatest absolute change from baseline in the arm region in older men (average age 60 years). In contrast, young women experienced most of the 1.7% lean gain consequent to resistance training in the leg region [24].
Although our subjects experienced significant gains in FFST mass, this was not reflected by an increase in REE. More studies have reported a significant increase (between 5% and 9%) in REE as a consequence of resistance training in young men [1, 25] than no change in resting [26] or sleeping metabolic rate [2]. It is difficult to determine the reason for the difference in response among studies as all of the studies also observed significant hypertrophy of lean body mass, suggesting increased metabolic need. Although it is possible that a longer training program would cause greater muscle hypertrophy and thus more increase in metabolic rate, data from the above studies do not lend support to this. Gain in lean body mass was remarkably similar in those studies, between 2.0 and 2.7 kg, in spite of duration of training ranging between 10 and 24 weeks [1, 3, 25]. The greatest gain in lean mass was actually in the study of shortest duration [1]. Campbell et al [27] suggest that lack of a control group in many of the studies investigating the effect of training on metabolic rate confounds the interpretation of their results. An early study from their laboratory [28] claimed a 15% increase in metabolic rate following 14 weeks of resistance training. However, a later study from the same laboratory, using a control group, found that both the control as well as the exercising group had an increase in metabolic rate over the study period, eliminating any effect of the training program [27].
Resistance training caused a significant reduction in resting total testosterone and free testosterone concentrations with no significant difference between supplement groups. Although some studies report an increase in concentration of free or total testosterone in subjects participating in resistance training [29], most report no change [29, 30]. One study [30] observed a trend for reduction in free testosterone over a 24 week training program. It has been suggested that intense training with large training volume (as used in our study) can cause overtraining. Although the reduction in testosterone suggests this could be the case with our subjects, cortisol, an indicator of excessive stress, tended to decrease. Thus, the ratio of free testosterone to cortisol, an index used to define an overtrained state, did not suggest overtraining. An alternative explanation for the decline in resting testosterone concentrations could be a training-induced increase in androgen turnover [30] and/or an increase in plasma volume due to training.
Effect of Type of Beverage Consumed post Exercise
Type of beverage consumed after each resistance training bout did not have a significant effect on body composition, strength, hormones or REE in young men undergoing a rigorous resistance training program for 10 weeks. Statistical trends in differences between groups existed and favored MILK for both body weight and FFST mass gain.
Several studies show that provision of a daily dietary supplement (not necessarily temporally tied to the exercise session) improves gains in lean tissue resulting from a resistance training program compared to those who do not consume any supplement [11, 12]. However, neither of these studies clarify whether it is the additional energy or a specific macronutrient mix that provides this benefit. For example, Gater et al. [11] found that supplementation with 1 to 1.5 cans of a mixed macronutrient beverage (energy not specified) led to a significant increase in lean body mass (LBM; 3.6 kg) from pretraining, while consumption of a placebo induced a lower (2.1 kg) increase in LBM. Meredith et al. [12] reported that daily consumption of a mixed macronutrient supplement in elderly men who participated in a 12 week resistance program had increased leg muscle mass (but not greater fat-free mass) concurrent with 35% higher energy intake and 28% higher protein consumption. The increase in muscle area correlated with the increase in protein intake (r = 0.63). Although this suggests that the protein in the supplement was critical, the design does not allow clear conclusions about the unique value of protein because the supplement also provided additional energy compared to those not consuming a supplement.
Other studies have attempted to tease out the effect of energy from that of macronutrients by comparing supplements with different macronutrients but the same caloric value. Lemon et al. [21] compared a 1.5 g/kg carbohydrate supplement to a 1.5 g/kg protein supplement consumed daily during an intensive 1 mo resistance training program. They found that the protein supplement boosted total protein intake and promoted a significantly more positive nitrogen balance compared to the carbohydrate supplement. However, this was not reflected in differences in improvements in muscle size and strength between the groups.
More recent studies examining the differential effects of supplemental macronutrients are conflicting. While Rozenek et al. [2] observed greater increases in fat free mass for subjects consuming either a high calorie (2010 kcal/d) supplement with carbohydrate and protein or an isocaloric carbohydrate supplement compared to subjects doing the same training without supplement ingestion, other studies did not find that those who consumed a supplement, regardless of composition, had greater lean tissue gains than those who consumed a placebo during training [22, 26]. An important difference between these studies is the extreme variation in energy content of the supplement. Subjects in the study by Rozenek et al. [2] consumed an extra 2010 kcal/d from the supplement compared to 
73 and 336 kcal/d for subjects in the studies by Antonio et al. [31] and Godard et al. [22], respectively. As the extremely high energy value of the supplement in the study by Rozenek et al. [2] is impractical for most individuals, the majority of the literature does not support the value of modest, post-exercise food ingestion for the gain in lean tissue consequent to a resistance training program in young, healthy individuals.
The general lack of benefit of dietary supplement on chronic lean gain is in contrast to the superior acute protein balance when protein is included in the food consumed just before or after exercise. Several studies from one laboratory demonstrated that as little as 6 g of amino acid or protein in the beverages consumed after a resistance exercise bout improved muscle protein balance [6, 8, 10]. None of those studies attempted to contrast the effects of energy from protein with carbohydrate to that from carbohydrate alone on protein metabolism following resistance exercise. Roy et al. [9] compared a mixed macronutrient beverage (carbohydrate, fat, and protein) to a carbohydrate only or placebo beverage after a resistance exercise bout. Both energy-containing beverages caused similar increases in whole body protein synthesis without changing protein breakdown.
Thus, although several studies of the acute effect of post-exercise food consumption suggest a benefit of protein containing supplements relative to carbohydrate, some of the acute studies and all of the chronic training studies, support the concept that additional energy rather than macronutrient mix is critical for FFST mass or strength gain. We did not observe any significant benefit of inclusion of protein in the post-exercise beverage on body composition. However, due to the statistical trend for greater FFST mass gains for the mixed macronutrient group in our study and evidence from some of the other studies discussed previously [2], it would be worthwhile performing additional studies with longer training periods. As the measured modification of protein balance in the acute studies is modest, it would require a prolonged study in order to detect a difference in body composition. Tipton and Wolfe [32] estimate that it would take up to a year of training to detect an effect of a post-exercise supplement on lean tissue gains.
It is possible that consumption of the supplements at a different time relative to the resistance workout would have magnified the effects on lean tissue gains. Other studies examining the effect of a bolus ingestion of a supplement proximal to a resistance exercise bout have had subjects consume it before [10], 1 h after (8, 13), 2 h after (13), 3 h after (8), or immediately after and 1 h after the exercise session (7, 9). One experiment that compared different ingestion timing within the same study observed that consumption before exercise was superior to immediately after for overall muscle protein balance (10). However, another reported that long-term muscle hypertrophy over 12 weeks was greater for older subjects (average 74 years) who consumed a supplement just after compared to 2 h after the resistance exercise bout [13]. Rasmussen et al. [8] found no difference in the acute anabolic effect of consuming a supplement 1 h versus 3 h after the exercise. More research needs to be done to compare additional timing schedules within the same study but the current data suggests that consumption before (if tolerated) or shortly after the bout would be preferable to delayed consumption.
An interaction between daily protein intake and the effect of a protein-containing supplement consumed proximal to a resistance exercise bout could explain a lack of benefit of a protein containing supplement in our subjects who consumed more than the RDA for protein. It is possible that there is a ceiling effect such that supplementation is ineffective if the daily protein is above a threshold. Other studies provide evidence against this theory. The study showing a unique benefit of an immediate post-exercise supplement on muscle hypertrophy [13] used subjects consuming an amount of protein similar to that of a study that found no benefit of a post-exercise supplement (average intake between 1.0 and 1.2 g/kg) [22]. Also, the acute anabolic effect of a post-exercise supplement was observed in male subjects whose diet contained a high amount of protein (136 g/d or 1.7 g/kg if average weight is assumed to be 80 kg) [9].
Our study did not find that type of supplement ingested had an influence on changes in any hormones. Several studies suggest that diet influences resting concentrations of some hormones. Volek et al. [14] found a negative association between resting testosterone and dietary protein, but a positive association with dietary fat. In another study, when subjects consumed a daily mixed nutrient supplement concurrent with resistance training, their resting IGF-1 concentrations fell, while those who underwent training without supplementation had an increase in resting levels of this hormone [11]. A study by Kraemer [33] contradicts this in that resting IGF-1 concentration increased, while resting testosterone fell over several days of resistance training when subjects were given a protein-carbohydrate supplement before and after resistance exercise compared to a group that exercised but did not consume the supplement. Thus, there does not appear to be a clear consensus concerning the influence of dietary change or supplementation during resistance training on concentration of resting hormones.
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CONCLUSION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSCONCLUSIONACKNOWLEDGMENTSREFERENCES |
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ACKNOWLEDGMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSCONCLUSIONACKNOWLEDGMENTSREFERENCES |
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Received September 30, 2003. Accepted March 3, 2004.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSCONCLUSIONACKNOWLEDGMENTSREFERENCES |
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This article has been cited by other articles:
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  J. W Hartman, J. E Tang, S. B Wilkinson, M. A Tarnopolsky, R. L Lawrence, A. V Fullerton, and S. M Phillips Consumption of fat-free fluid milk after resistance exercise promotes greater lean mass accretion than does consumption of soy or carbohydrate in young, novice, male weightlifters Am. J. Clinical Nutrition, August 1, 2007; 86(2): 373 - 381. [Abstract] [Full Text] [PDF]
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