Forty-five male resistance trained individuals volunteered to participate in this double-blind investigation. Study inclusion criteria limited research subjects to males between the ages of 18 and 35 years, who reported participation in at least two weekly resistance training sessions over the six-month period immediately prior to the start of the study. Exclusionary criteria included any reported history of significant cardiorespiratory complications or recent lower extremity musculoskeletal injury that might limit high intensity exercise efforts. Subjects provided written informed consent after verbal explanation of all study procedures, in accordance with the Institutional Medical Sciences Subcommittee for the Protection of Human Subjects.
All subjects were asked to complete three testing sessions. The first two test sessions were performed one week apart with the third trial scheduled 28 days later. The first two tests were performed 90 minutes following oral ingestion of either 4.5 grams GPLC or 4.5 grams cellulose (PL), in randomized order. The exercise testing protocol consisted of five 10-second Wingate cycle sprints separated by 1-minute active recovery periods. The findings of this acute study, presented in a previous publication, reported significantly increased power output with reduced lactate accumulations with acute GPLC supplementation (Jacobs, 2009).
The present investigation is a continuation of our acute study of GPLC in which a randomized blocks design was implemented to examine the long-term effects of varying dosages of GPLC. All of the present subjects completed acute testing with GPLC and PL in order to provide a consistent subject test exposure for the present investigation. The PL condition served as the control/baseline condition for the present study. Pilot testing had indicated that the majority of persons could correctly identify to GPLC condition compared with placebo. As it is well established that subject compliance and retention are significantly reduced when a placebo condition is identified, the present design was utilized in which the placebo condition of the first two assessments served as the baseline condition, each subject serving as their own control. Subjects were matched by body mass and then randomly assigned to one of three study groups, with one group receiving 1.5 grams per day of GPLC, one group receiving 3.0 grams GPLC per day, and the final group receiving a daily dosage of 4.5 grams of GPLC. (See Supplementation Protocol Section).
During the one month supplementation period, subjects were directed to continue with their own individual training and nutritional programs. Seven day exercise logs and three day dietary recall logs were completed by all subjects to provide verification of the consistency of training and diet. These exercise and dietary records were submitted for the weeks prior to baseline and post supplementation testing. The exercise logs provided information regarding exercise volume (sets, reps) of resistance training categorized to upper extremity, lower extremity, or structural movements. The dietary intake logs were examined using ESHA Food Processor SQL dietary analysis software (ESHA Research, Salem, OR).
All subjects were scheduled for a third cycle sprint session following the 28 days of supplementation. As with the prior assessments, subjects were asked to report for testing in the morning following 12 hr without food and to not participate in heavy exercise during the 24 hr period before testing. On test day, the subjects were provided with the same dosing as they had taken during the 28 day supplementation period. All subjects sat quietly for 90 minutes after taking the supplement before participating in the cycle sprint testing.
Subjects were matched by body mass and then randomly assigned to one of three study groups, each group receiving 28 days of GPLC supplementation in one of three dosages (1.5 g/d, 3.0 g/d, 4.5 g/d). In a double blind fashion, each subject was provided with 28 packets consisting of six capsules per day. The daily packets included six 750 mg capsules provided by Jarrow Formulas (Los Angeles, CA). The respective daily dosage was established by the appropriate combination of 750 mg GPLC capsules and 750 mg capsules of cellulose (the GPLC and cellulose capsules were visually identical). For example, the daily packets of the 1.5 g/d group were comprised of two GPLC capsules and four cellulose capsules while the 3.0 g/d group received four GPLC and two cellulose capsules and the 4.5 g/d group was provided with six GPLC capsules. Participants were directed to take their six capsule daily supplements approximately 90 minutes prior to exercise on training days and to take the six capsules with breakfast on other days. The GPLC used in this study was the USP grade nutritional product, GlycoCarn™ (Sigma Ta Health Sciences, S.p.A., Rome, Italy), a molecularly bonded form of glycine and propionyl-L-carnitine.
The testing protocol used in the present investigation is consistent with that previously described by these investigators (Jacobs, 2009). Briefly, this testing protocol included five high intensity stationary cycle sprints, each sprint 10-seconds in duration with 1-minute active recovery periods. Sprints were performed with a Monarch 894E leg ergometer (Monarch, Varberb, Sweden) with the external applied resistance equivalent to 7.5% of each subject's body mass. Ten minutes of unloaded pedalling at 60 RPM was performed as a warm-up prior to the sprint testing. The 1-minute recovery periods were active with unloaded pedalling with cadence fixed at 60 RPM.
Anaerobic power output was measured using the SMI OptoSensor 2000 (Sports Medicine Industries, Inc., St. Cloud, Minn). Power output variables included peak power (PP) which was determined as the power output established during the first 5 seconds of each ten second sprint; and mean power (MP) which was the power output measured during the full ten seconds of each sprint. The third power output variable was a power decrement (DEC) which was calculated as the difference in power output between the first 5 seconds and the second five seconds of each sprint, as expressed as a percentage of the first 5 second period.
Heart rate (HR) was determined using a Polar HR monitoring system with HR values assessed at rest, during the final five seconds of each sprint bout, as well as four and fourteen minutes after the final sprint bout.
Blood lactate levels (LAC) were assessed using the Accutrend® lactate analyzer (Sports Resource Group, Inc., Pleasantville, NY). Calibration procedures were performed prior to each testing session using standard control solutions. Blood lactate levels were determined at rest as well as four and fourteen minutes post exercise. Net lactate accumulation per unit power output was calculated as (LAC14-LACrest)·(MPave)-1 .
Thigh girth of the dominant leg was measured using a Gulick tape at 15 mm superior to the patella while in a standing position with weight shifted onto the non-dominant leg. Thigh girth measurements were taken at rest and four minutes after the final sprint bout.
A repeated measures general linear model was used to examine for differences in outcome measures between groups (1.5 g/d, 1 g/d, 4.5 g/d), conditions (pre- and post-GPLC) and across time. Measures of power output (PP, MP, DEC) were determined across time during each of the five successive sprint bouts. Values of HR were established at rest, during the final five seconds of each sprint, as well as four and fourteen minutes following the last sprint. The across time measures of LAC were taken at rest as well as four and fourteen minutes post exercise while thigh girth was assessed at rest and four minutes after the fifth sprint. In cases where significant main effects or interactions were observed, single degree of free contrasts were performed to determine specific effects without adjustment of the acceptable level of significance. Net lactate accumulation was calculated as the difference between lactate measurements 14 min post exercise and resting values divided by the average MP values of the five sprints. In all cases, p-values less than 0.05 were accepted to determine statistical significance. All analyses were performed using PASW, Version 17.