Coaches and athletes are continually searching for ways to gain a competitive "edge" by improving athletic performance through the use of a variety of ergogenic substances and nutritional supplementation (11). Recently the use of trace mineral supplementation in athletes has been popularized because of highly publicized research implicating chromium (Cr) picolinate supplementation coupled with strength training for the enhancement of body composition and improved athletic performance (12,17-19).
Chromium is an essential trace element which functions in carbohydrate, protein, and lipid metabolism and in the regulation of blood glucose homeostasis by potentiating the effects of insulin (4,9,30). According to the National Research Council, the safe and acceptable level of Cr intake is 1-4 μmol·d−1 (50-200 μg·d−1) (25). It is hypothesized that chromium's role in the enhancement of insulin activity results in increased uptake and assembly of amino acids into protein, decreased breakdown of muscle protein, and improved efficiency of the deposition of lipids in adipose tissue (12,22); however, the exact mechanisms remain unknown (9,22,30). Since the dietary intake of Cr in the United States may be suboptimal (6,30), it may be advantageous for athletes concerned with increasing or maintaining lean body mass and/or reducing body fat to maintain adequate levels of Cr intake in the diet.
Collegiate wrestlers must constantly manipulate body composition to maximize competitive performance, and therefore they tend to avoid foods high in Cr such as those high in saturated fat and sodium (6,29). Studies also indicate that repeated bouts of strenuous exercise can significantly increase the urinary output of Cr and may lead to a depletion of Cr body stores (3,8). Thus, it would seem appropriate for these athletes to supplement their diets with Cr picolinate to reduce unwanted body fat while retaining or, in some cases, increasing lean body mass.
The effect of Cr supplementation in athletes has not been adequately examined, and no conclusive data exist that implicate the relationship of chromium supplementation to performance variables such as strength, anaerobic power, and/or aerobic power. In humans, numerous studies have demonstrated the success of Cr supplementation in improving glucose tolerance in diabetics (15,23,32) and in subjects with impaired glucose tolerance (3,20), and in improving protein anabolism in malnourished individuals (1,5,32,). However, other studies have shown decreases (26) or no change (5) in body fat levels following Cr supplementation in these same specific populations. Although a few recent studies demonstrated desirable body composition alterations with the use of Cr supplementation coupled with strength training programs, important problems in research design, such as relatively short supplementation periods (6 wk), no evaluation of neuromuscular performance (13), and the exclusive use of skinfold measurements and anthropometrical prediction equations derived from normal populations (as opposed to sport-specific elite athletes) in the estimation of body composition (13,18), may have confounded these findings. On the other hand, studies that have reported no positive effects of Cr failed to use a control group in their methodological design, only supplemented for short periods of time, and used nonspecific tests of strength that failed to replicate the athletes mode of training (10). Additionally, no conclusive data exist regarding Cr supplementation in athletes for the potential enhancement of sport specific physiological performance parameters, such as neuromuscular and metabolic power, or on alterations in blood-borne metabolites related to athletic performance, such as glucose and insulin. In addition to the obvious interest in physical performance, it was also important to document the potential use of chromium supplementation on long-term weight management. Therefore, the purpose of this study was to assess the effects of a 14-wk Cr picolinate supplementation combined with a typical preseason resistance training and conditioning program on body composition and neuromuscular performance in NCAA Division I wrestlers. It was hypothesized that this dual treatment of supplementation and exercise would maintain and/or increase lean body mass, reduce body fat, and improve physiological performance beyond levels of adaptations seen with training alone.
Subjects. Twenty (20) male, NCAA Division I varsity wrestlers (aged 18-23 yr) from the University of Oklahoma participated in this study. Following questioning regarding previous and/or current use of any ergogenic aids, two individuals were excluded from the study. All participants were also subject to random drug testing throughout the study period from both the University of Oklahoma and the NCAA. No subject was removed from the study population because of a positive drug test. Approval for the use of human subjects was given by the Institutional Human Subject Review Board and informed consent was obtained from all subjects before the pretesting period.
Chromium supplementation. The design of this study involved a double blind, placebo-controlled randomized control trial. Wrestlers were initially grouped according to weight classification (± 3 kg) and then randomly assigned to a treatment (Cr+3; chromium supplement), placebo (P; sodium diphosphate), or control group (C; no supplement) using a stratified random sampling technique. This allowed for each member of the treatment group one cohort in each of the other two groups matched on competitive weight classifications. The experimental group received 200 μg Cr in the form of a Cr picolinate gelcap once a day, 7 d·wk−1, for the duration of the 14-wk supplementation period. This level of supplementation did not exceed the safe and acceptable level of 1-4 μmol·d−1 (50-200 μg·d−1) (25). The group randomly assigned to the placebo group (P) received a placebo gelcap containing sodium diphosphate that appeared identical to the treatment gelcap. Supplements and placebos were prepared by the College of Pharmacy, having met all requirements for preparation of supplements for use by human subjects. Both the Cr picolinate supplement and the placebo gelcaps were distributed every day of the week following afternoon workout sessions. Weekend packets (two pills) were distributed every Friday, and subjects were instructed on the importance of ingesting one gelcap per day both Saturday and Sunday. A subject was also instructed to consume two pills following any missed days during the weekend. Subject compliance for both supplementation and training during the week was monitored on a daily basis by the research team.
Preseason training program. All subjects were involved in a progressive resistance training program and metabolic conditioning regimen for the entire 14-wk study. This training program was designed as a 4-d·wk−1 split routine and developed specifically to coincide with the study pre- and post-testing timetable. The resistance program was designed using the concept of periodization and followed a basic 14-wk macrocycle of repetitions and load assignments indicated for the development of strength, power, and increased lean body mass. This particular training cycle was divided into three 4-wk microcycles, each designed to elicit specific physiological adaptations through the manipulation of training volume by adjusting workout loads and repetitions. This program also allowed for two 1-wk testing periods before and at the end of the study. Workouts for each athlete were identical in type, progression, and order of exercises included for each day and differed only in the load assignments based on the subject's pretest 1RM values and body weight. On any given day, workouts consisted of approximately 10 upper or lower body lifts which included large muscle mass, multi-joint exercises such as the leg press, bench press, and power clean, as well as supplemental single-joint movements such as bicep curls, hamstring curls, and quadricep extensions. Subjects were required to attend all lifting sessions to remain in the subject pool. Workout compliance was monitored on a daily basis by the strength and conditioning staff and research team, and those individuals missing more than three workouts during the course of the study were eliminated from the subject pool. Metabolic conditioning was conducted separately from the resistance program 3 d·wk−1. This training included long-distance runs (2 miles) designed for increased cardiovascular endurance, middle-distance interval sprint training and timed sparring designed to stress the anaerobic lactic system, and short-duration (4-10 s) explosive wrestling-specific drills designed to stress the anaerobic alactic systems.
Testing schedule. Initial testing was conducted within a 10-d period before the beginning of the supplementation period; however, before the pretesting began, subjects underwent 3 wk of training. This period of training was used to help control for the possible improvements in neuromuscular and/or body composition variables that resulted from motor learning or reconditioning of the athletes returning from various summer training schedules. All testing was completed without any subjects experiencing acute weight loss typically encountered by wrestlers when preparing for competition.
Dietary records. Daily dietary intakes were estimated during the 14-wk treatment period using 3-d dietary records before each data collection period. Instruction on how to properly record information was given to each subject individually by a registered dietitian. Estimating serving sizes and providing adequate detail were emphasized during this instruction. Food records were analyzed for nutrient and mineral content using Nutritionist IV software. Dietary consumption for the supplementation period was also monitored by a registered dietitian overseeing daily varsity athletic training table meals, and any significant dietary deviations for any of the subjects during the course of the study was documented.
Strength and endurance testing. This portion of the testing was completed at the University of Oklahoma Strength and Conditioning Complex under the direct supervision of the principle investigator and the OU conditioning staff. The areas assessed included absolute upper body endurance (maximal repetitions of seated low-pulls using a constant load for all subjects), absolute lower body endurance (maximal repetitions of leg press performed with constant load for all subjects), global muscular power (Olympic power clean), and maximal upper body strength (1RM bench press). These measures of muscular performance were selected since they were considered to be sport-specific movements that mimic, as close as could be expected, both energy systems and physical movements used in competitive wrestling. All strength and endurance testing followed the same progression (power clean, bench press, leg press, low pull) for both the pre- and post-testing sessions and each test was separated by an adequate recovery period of no shorter than 5 min. All lifts followed standardized procedures that each athlete used and was monitored by the staff.
Muscular peak power. Upper and lower body power was also measured to document the effectiveness of the power phase of the teams training cycle. Power production for the chest and hip extensors (bench press and leg press) was assessed for each subject using a Cybex Smithpress (Owatonna, MN) bench press and an Icarion leg press (Sun Valley, CA) and the technique of accelerometry. A piezoresistive accelerometer (ICSensors, Milpitas, CA, model 3145; sensitivity = 410 mV·g−1 @ 100 Hz; Frequency = 0.32 kHz) was mounted to the bar of the Smithpress and to the footpad of the leg press. The accelerometer, in series with an A/D board, collected data at 2-ms intervals and power (W) at each interval was then determined by multiplying the integral of acceleration, velocity, by the mass lifted and its acceleration, accounting for gravity (P = ν·m·a). Bench press power was measured using a load of 60% of the subjects one repetition maximum (1RM) assessed previously, and leg press power was assessed using a load equal to twice the subject's body mass (kg).
Body composition. Body composition was assessed to document changes in lean body mass and fat mass that might be attributed to chromium supplementation. The assessment of body composition was done using hydrodensitometry and anthropometry both before and immediately following the 14-wk supplementation period. The underwater weighing procedure was chosen as one of the assessment methods since previous research only used anthropometrical data to document the efficacy of the chromium supplementation (12,17,18). Parameters of total body mass, lean body mass, fat mass, and percent fat were determined using these testing protocols. All subjects were weighed hydrostatically in the morning after fasting overnight. Each subject was asked to perform a complete exhalation while being submerged in water resting only on a body support carriage, the weight of which was accounted for and recorded as the "tare" weight before the test. The subject was given at least six trials to produce the heaviest underwater weight possible, recorded in pounds and converted to kilograms to be used in estimating body density. Vital lung capacity was measured using a Single Breath Wedge Spirometer (Vitalograph 122000, Hans Rudolph Inc., Kansas City, MO) and functional residual lung volume (RV) was estimated by using 0.24 multiplied by vital capacity (35). The largest of three separate trials was recorded for each subject. Although direct measurement of residual lung volumes is preferred, an error of only 0.003 g·cm−3 has been documented using the aforementioned estimation techniques in collegiate wrestlers (27). Percent body fat was estimated using body density (28). Skinfold thicknesses and regional body circumferences were also measured to determine possible changes in subcutaneous fat and/or limb girth. The nine sites used for skinfold measurement included abdominal, biceps, chest/pectoral, medial calf, midaxillary, subscapular, suprailium, anterior thigh, and triceps. Circumferential measurements were performed at 10 sites including abdomen, calf, forearm, hips/buttocks, upper arm, waist, thigh, shoulders, chest, and neck. Each measurement was obtained in triplicate and all anthropometric measurements were obtained by the same investigator in both pre- and post-testing sessions following ACSM standardized measurement protocols (2).
Metabolic performance. Maximal aerobic power (O2peak) was estimated on a treadmill using the Bruce protocol and the total time of the test before subject failure (14) to examine general cardiovascular fitness. Peak anaerobic power (AnP) and maximal anaerobic capacity (AnC) were also assessed using the Wingate 30-s cycle ergometer test following standardized procedures and calculations (13). These measures of anaerobic performance reflect the dominant energy system used during wrestling. Maximal aerobic power, AnP, and AnC were calculated relative to the subject's total body mass in kilograms (kg).
Blood chemistry analysis. To examine the claim that chromium supplementation can enhance insulin sensitivity and ultimately effect glucose uptake in athletes, resting fasting serum blood glucose and insulin concentrations were determined. Blood samples were obtained by venipuncture and collected in two sodium fluoride potassium oxalate Vacutainers (Becton Dickinson, Rutherford, NJ) during both the pre- and post-testing phases of the neuromuscular testing sessions. Once obtained, each sample was stored on ice and then transported to the OU Health and Sport Sciences Biochemistry Laboratory where each sample was centrifuged for 10 min. The serum was then aliquoted and frozen at −20°C for subsequent assays to determine concentrations of insulin (μIU·dL−1) and glucose (mg·dL−1). All assays were performed in duplicate. Blood glucose concentrations were determined by a colorimetric enzymatic technique using Sigma Diagnostic kits (Sigma Chemical Co., St. Louis, MO). Insulin concentrations were determined by radioimmunoassay using Coat-A-Count solid-phase 125I diagnostic kits (Diagnostic Products Corporation, St. Louis, MO). The sensitivity of this insulin kit is 1.2 μIU·mL−1. All serum samples were measured in a single assay to eliminate interassay variation.
Statistical analysis. All data were reported as means ± SE. All statistical analysis was performed using SAS. Descriptive statistics for the dependent variables were computed using SAS Means procedure. Percent changes in mean group values were calculated as pretest mean subtracted from post-test mean, divided by the pretest mean, then multiplied by 100. Two-way repeated measures ANOVA (Group x Trial) was used to determine whether differences existed between groups, trials, and the possible existence of a group by trial interaction. The Bonferroni t statistic procedure was used to adjust the overall alpha level based on the number of multiple comparisons performed to minimize the Type I error rate. Statistical significance for all data was set at P ≤ 0.05.
Descriptive analysis.Table 1 presents the descriptive data for each group before the study. No statistically significant differences in age, height, weight, body composition, peak aerobic capacity, nutritional intake, or neuromuscular performance variables existed between the three groups at the beginning of the study.
Dietary analysis. Daily dietary Cr intakes were measured (in micrograms per day) during both the pre- and post-testing evaluation periods. Dietary chromium intakes at baseline (P = 0.619) and following the 14-wk training and supplementation period (P = 0.971) were similar for the three groups (Table 2). However, there was a significant trial effect (P = 0.003) as each group showed a decreased dietary chromium intake from pre- to post-test. The most dramatic decrease (55%) was seen in the Cr+3 group, while the other two groups experienced a 48% decrease from pretesting values. Daily dietary intake records also revealed no significant differences between groups in total caloric intake or in percent of calories from the different nutrient groups. It was interesting to note that there was a tendency for total daily caloric intakes to decrease, 18% for the placebo (P) group and 12% for the control (C) group, whereas the treatment group (Cr+3) had a 26% increase from pre- to post-test evaluations.
There were no significant differences between or within the three groups with respect to the relative changes seen in nutrient intakes as a percentage of total daily caloric intakes (Table 2); however, some interesting trends could be identified. Carbohydrate intakes (expressed as a percentage of daily calories coming from carbohydrate) tended to increase for all groups, ranging from 5% in the Cr+3 group (from 56% ± 9 to 59% ± 10) and 6% in the P group (54% ± 6 to 57% ± 6) to 12% in the C group (from 50% ± 12 to 56% ± 1). A 5% decreased protein consumption was seen in the Cr+3 group from pre- to post-test (19% ± 4 to 18% ± 4), while both the C and P groups demonstrated increased protein consumption ranging from 6% in the C group (16% ± 4 to 17% ± 2) to 19% in the P group (16% ± 2 to 19% ± 2). Percent of daily calories coming from dietary fat intakes decreased for both the Cr+3 (27% ± 5 to 24% ± 1) and P groups (28% ± 1 to 25% ± 4), representing a 11% decrease for both groups from pre- to post-testing levels, while the C group remained relatively unchanged.
Blood chemistry profiles. Resting insulin concentrations before supplementation were significantly different between groups (P = 0.014) with the Cr+3 group having a significantly higher insulin concentration (11.60 ± 2.39 vs 7.12 ± 1.33 (P) and 7.38 ± 0.72 (C)); however, no group experienced a significant change in fasting insulin concentration from the pretesting levels (P = 0.571). Additionally, there were no between group or trial differences for levels of fasting serum glucose concentrations (P = 0.492) before or after the treatment.
Body composition. A repeated measures ANOVA revealed no significant differences between trials in underwater weight (3 highest trials), skinfold thickness (3 trials per site), or body circumferences (3 trials per site). Therefore, the numbers expressed as scores for each of these variables is the mean score for all three trials.
There were no significant group, trial, or group X trial effects for body weight, lean body mass, percent body fat, or fat mass. All three groups demonstrated a modest reduction (P = 0.150) in body weight from pretest values (Cr+3, 74.03 ± 3.50 to 73.46 ± 3.45; P, 71.95 ± 3.32 to 70.13 ± 2.88; and C, 69.69 ± 1.48 to 68.55 ± 1.58). Similarly, percent body fat and fat mass (kg) were not significantly different between groups (P = 0.680 and P = 0.851, respectively) or trials (P = 0.106 and P = 0.100, respectively) (Fig. 1.). Lean body mass also remained relatively unchanged for all groups and no significant differences existed between groups (P = 0.245) or from pre- to post-test values (P = 0.992) (Fig. 1.).
A statistically significant decrease from pre- to post-test was demonstrated in all three groups for both skinfold thickness (P = 0.021) and circumference measures (P = 0.007). Mean percent decrease in skinfold thickness was 13.4% and ranged from a 10.2% decrease in the P group to a 18.7% decrease in the C group. Mean percent decrease in circumference measures was 1.9% with a range of 1.8% decline in both the Cr+3 and P groups to a 2.1% decrease exhibited in the C group. Although all groups experienced significant reductions in these measures from pre- to post-testing, there were no significant differences between the three groups.
Muscular parameters.Table 3 depicts the effects of the supplementation and training protocols on neuromuscular performance variables. Repeated measures ANOVA revealed no significant trial effects for measurements of leg power (three trials) and upper body power (three trials); therefore, the average of the three trials was used for further analyses.
No significant differences existed between groups on any variables. The only significant pre- to post-test differences existed in upper body endurance (UB) (P = 0.038), expressed as total repetitions (reps) to failure on the seated low-pull exercise, and relative bench press power production (blood pressure (BP) Power) (P = 0.05) expressed as W produced per kilogram of total body weight. A significant group × trial interaction was identified for UB (P = 0.037). Paired t-tests (one-tailed) revealed that upper body endurance increased significantly from pre- to post-test in the C group (15.43 ± 1.70 reps to 21.17 ± 2.65 reps; P = 0.006). This represented an increase of 37.2%. A significant group × trial interaction also was found for BP power (P = 0.050); however, when the Bonferroni correction was applied for the post-hoc comparisons, none of the pre- to post-test changes were significant.
Metabolic performance.Table 4 shows the changes in both anaerobic (relative peak anaerobic power and peak anaerobic capacity) and aerobic (relative O2peak) performance variables resulting from the training and supplementation period. No significant differences between groups existed for any of these variables. No significant changes in peak anaerobic power (AnP) or relative anaerobic capacity (AnC) were demonstrated from pretesting values. However, relative peak aerobic power (Rel O2peak) did increase significantly from pre- to post-test in all three groups (P = 0.002). The increases ranged from 2.2% in the P group (55.83 ± 2.36 mL·kg−1·min−1 to 57.03 ± 1.57 mL·kg−1·min−1) to 7.9% in the Cr+3 group (54.88 ± 2.18 mL·kg−1·min−1 to 59.20 ± 1.56 mL·kg−1·min−1) up to as high as 9.0% in the C group (52.40 ± 2.06 mL·kg−1·min−1 to 57.11 ± 1.83 mL·kg−1·min−1). The mean increase in aerobic power across the study population was 3.41 mL·kg−1·min−1, representing an improvement of approximately 6%.
The purpose of this study was to investigate the effectiveness of chromium picolinate supplementation in a highly trained population of male athletes competing in a sport in which success is mandated by continual alterations and maintenance of body composition. The hypothesized importance of chromium supplementation could be illustrated if wrestlers were able to safely enhance gradual body fat loss during preseason conditioning while they were able concomitantly to maintain lean body mass and strength. If this were the case, then the need for severe acute weight loss immediately before competition could be significantly reduced.
Previous research has implicated chromium picolinate supplementation in the potentiation of insulin action in various populations, resulting in increased promotion of muscle anabolism (34) and decreased fat storage in adipose tissue (24,31), and in the expedition of facilitated diffusion of glucose from the blood, resulting in increased muscle and liver glycogen concentrations (3,15,20,21). More recently, research has been aimed at determining whether Cr supplementation can magnify the positive effects of resistance training on body composition and performance in healthy populations. In a study with a relatively short supplementation period (40 d) as compared with the one in the current investigation, Evans (12) found that Cr picolinate significantly increased lean body mass in active volunteers and in a group of college football players engaged in a strength training program. The current study found no Cr effect on body composition or neuromuscular performance. In contrast to the current study, prior research failed to address possible changes in muscular strength as a result of lean body mass increases. In addition, the changes documented by Evans (12) in body composition may have resulted from estimation error associated with use of nonvalidated skinfold prediction equations as opposed to the use of hydrodensitometry as used in the current study. Hasten (17,18) also reported significant gains in lean body mass and concomitant decreases in body fat from a similar 12-wk program of Cr supplementation and resistance training in a group of college-age students. However, these subjects did not present with expected improvements in strength as a result of increased lean body mass. Neither of these studies used a control group to address any possible influence of a placebo effect and no study has employed a longer supplementation and training period than the current investigation.
The results of the current study agree in part with the results of Clancy et al. (10) and Hallmark et al. (16) who reported that Cr picolinate supplementation coupled with strength training did not result in significant alterations in body fatness, lean body mass, or total body weight but conflict with results obtained from nonathletic populations (17). It could be assumed that reductions in anthropometric measures documented by Hasten et al. (17) were a result of a training effect which was exacerbated in these subjects because of their previously untrained state. Also, in agreement with the current study are the nonsignificant changes demonstrated in strength from pre- to post-test following supplementation seen in prior studies (10,16,17). In fact, the current study evaluated strength with the same lifts that were used during the training period in contrast to the studies that used laboratory measures of strength that differed from the training protocols (10), a phenomenon that may have prevented the detection of strength improvements.
There is no supporting literature to date that documents possible changes in aerobic and anaerobic performance as a result of enhanced insulin activity through Cr supplementation. It was thought that improvements in the cellular uptake and storage of glucose through Cr-mediated insulin potentiation could have a positive effect on metabolic performance variables involving muscle glycogen mobilization and breakdown. Although maximal aerobic power (O2peak) increased significantly for all groups (mean increase ∼ 3.41 mL·kg−1·min−1), no significant changes in metabolic performance parameters were attributable to Cr supplementation. We also believed that the possible potentiation of insulin action with Cr supplementation might improve insulin sensitivity, thus reducing the concentrations of both fasting insulin and glucose in the blood. However, no significant alterations in fasting insulin and glucose concentrations resulted from Cr picolinate supplementation, possibly because of the heightened insulin sensitivity demonstrated in this highly trained group before supplementation.
Dietary records revealed an unexpected significant reduction in dietary Cr intakes (∼ 50%) for all groups with the majority of subjects failing to meet suggested safe and adequate levels of Cr (30). However, previous studies (7,8) have shown that highly trained individuals experience a depressed Cr excretion rate which in turn might enable these individuals to increase Cr conservation from the diet (33). Interestingly, this significant dietary pattern was not explained by a significant decrease in caloric intake. It is possible that dietary values were under reported in the 3-d records, a problem that could have been avoided if all subjects had consumed a controlled daily diet. Estimates of Cr excretion such as those used in recent studies (3,6,8,16) would have been helpful in determining Cr absorption and turnover for this population.
Based on our observations with NCAA varsity wrestlers involved in preseason training, we concluded that 14-wk of Cr picolinate supplementation did not significantly enhance body composition and/or performance variables beyond the improvements experienced with resistance and metabolic training alone. However, because of the highly trained status of this particular study population, these findings should not be used to describe the possible effect of such supplementation on the general active population involved in resistance training.
In light of the recent wrestling deaths that have been linked to the dangerous techniques used to potentiate rapid and often extreme weight loss, further research is needed to determine whether there are safe levels of nutritional supplementation that could help athletes reach realistic goals relative to weight classification and body composition.
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