Power-based Resistance Training Reduced Serum Oxidized Low-Density Lipoprotein in Athletes

Power-based resistance training (PRT) allows athletes to improve athletic performance by enhancing both strength and power simultaneously. However, it is unclear whether athletes who participate in PRT can positively alter serum lipid and lipoprotein parameters. Thus, the current study investigated the effects of 6-weeks of PRT on serum lipid and lipoprotein parameters in male and female collegiate athletes. Twenty one collegiate athletes (12 female soccer players and 9 male football players) participated in PRT (4 days/week) for 6 weeks. The PRT program was composed of a variety of Olympic-style and traditional weightlifting movements along with plyometrics. Overnight fasting blood samples were collected before and after 6-weeks of power-based resistance training to analyze serum lipid and lipoprotein parameters including TG, TC, VLDL-C, LDL-C, HDL-C, Lp(a), and ox-LDL. All serum lipid and lipoprotein parameters remained unchanged, except ox-LDL which significantly (p = 0.036) decreased by 3.81% or 1.87 U·L -1 (from 49.05 ± 9.17 to 47.18 ± 9.78 U·L -1 ) following 6 weeks of power-based resistance training. The 6-weeks of PRT, designed to improve strength and power, can provide cardioprotective health benefits for male and female collegiate athletes by lowering ox-LDL.


Introduction
Card iovascular disease (CVD) has been recognized as a major leading cause of death in A merica for mo re than 10 decades, and approximately 2,200 A mericans die of CVD everyday [1]. Abnormal blood lip ids and lipoproteins known as dyslipidemia are considered one of the primary risk factors for development of CVD and characterized by elevated total cholesterol (TC), triglycerides (TG), or low-density lipoprotein cholesterol (LDL-C) and lo wered high-density lipoprotein cholesterol (HDL-C) [2]. In addition, a strong body of evidence suggests that elevated serum oxidized LDL (o x-LDL) is a key factor that accelerates the incidence of CVD by promoting the atherosclerotic progression of plaque [3].
Physical activity, as a non-pharmacological treat ment, is often reco mmended fo r sedentary ind ividuals or pat ients w ith CVD to p o s it iv e ly mo d ify b lo o d lip id s an d lipoproteins [2]. Accord ing to the meta-analysis, aerob ic exercise can decrease TC (2.0%), LDL-C (3%), and TG (5.0 -9.0%) and increase HDL-C (2.0 -3.0%) in adults [4,5]. However,the effects of anaerobic exercise such as resistance training on b lood lipids and lipoproteins are equivocal [6][7][8].
One meta-analys is has recent ly repo rted that res istance exercise may decrease TC (2.7%), LDL-C (4.6%), and TG (6.4%), but not HDL-C, in adults [6], whereas another review study has reported no strong evidence of beneficial effects of resistance exercise on modificat ion of blood lip ids and lipoproteins [7]. Moreover, only a few studies have previously examined the responses of ox-LDL to exercise training, and the results are inconsistent [9][10][11][12].
American Heart Association and American College of Sport Medicine recommend moderate intensity resistance exercise to be part of the main exercise program for sedentary or untrained indiv iduals because it helps prevent CVD and pro mote muscular strength and endurance, functional capacity, health, and fitness [7,13,14]. Unlike sedentary or untrained individuals whose main goal of resistance training is to improve their health or fitness, most trained athletes usually participate in relatively higher intensity resistance exercise to promote athletic performance rather than health or fitness. Power-based resistance training (PRT) is often reco mmended by many strength and conditioning professionals because it allows athletes to enhance athletic performance by gaining both strength and power simultaneously [15]. The reco mmended form of PRT is a co mb ination of a variety of Oly mpic-style and tradit ional weightlift ing movements and plyometrics [16]. Several studies have previously reported the positive effects of PRT on improvement in strength and performance in athletes [17][18][19][20]. However, it is unclear whether athletes participating in high intensity resistance training such as PRT can obtain cardioprotective health benefits as well. To date, no study has examined the effects of PRT on serum lip ids and lipoproteins includ ing o x-LDL in athletes. Thus, the current study investigated whether 6-weeks of PRT can provide male and female co lleg iate athletes with cardioprotective health benefits.

Participants
Twenty one collegiate athletes (12 female soccer players and 9 male football players), between 18 and 23 years of age, participated in the study during the off-season. All participants were physically active (defined as a regular physical activ ity perfo rmed mo re than 4 days a week), free of any self-reported in jury and cardiovascular or metabolic diseases, and not taking any medications known to alter blood lip ids and lipoproteins. The participants provided written informed consent and the medical history forms prior to performing any study protocols. All study procedures were reviewed and approved by the Institutional Review Board. The participants were encouraged to maintain a normal dietary reg imen, and refrained fro m any types of strenuous exercises other than PRT throughout the study period. In addition, no co mpetitive football or soccer games were scheduled during the study period.

Procedures
The participants were tested for one-repetition maximu m (1-RM ) in clean, incline press, and Olymp ic-style back squat (angle of knee < 90°) on a separate day to determine the lower and upper body strength. The initial weight for the 1-RM test was determined by the participant's training history. Once the participants successfully lifted the first weight, additional resistance (2.5 -5.0 kg) was added until the participants were not able to successfully comp lete a lift. The participants rested for 3 minutes between each 1-RM attempt to recover fro m the previous attempt, and the last successful lift was recorded as 1-RM.
The 1-RM for other upper and lo wer body movements was estimated by pre-determined 1-RM of clean, incline press, or squat. For instance, the 1-RM fo r the fo llowing Oly mpicstyle weightlifting movements was estimated by the clean 1-RM; snatch -60% of clean 1-RM, clean pull -120% of clean 1-RM, hand clean and Ro man ian deadlift (RDL)-90% of clean 1-RM, jerk variations -90% o f clean 1-RM, snatch pull -72 % of clean 1-RM (equivalent to 120% o f snatch 1-RM), and hang snatch -54% of clean 1-RM (equivalent to 90% of snatch 1-RM ). The 1-RM for the tradit ional horizontal bench press was estimated to be 120% of incline press 1-RM . The Oly mpic -style back squat 1-RM was used to estimate the 1-RM for the front squat (80% of squat 1-RM) and lunge variations (25% of squat 1-RM). The PRT program consisted of a comb ination of various Oly mp ic-style and traditional weightlifting movements along with plyometrics as shown in Table 1. The participants performed PRT for 4 days per week (Monday, Tuesday, Thursday, and Friday) for 6 weeks. After performing a series of selected warm-up activ ities for 15 minutes, the participants performed each PRT session around 60 minutes. In the current study, following weekly undulating periodization was used; week 1 -70% 1-RM, week 2 -80% 1-RM, week 3 -75% 1-RM, week 4 -90% 1-RM, week 5 -80% 1-RM, and week 6 -95% 1-RM. For a cool-down, a variety of proprioceptive neuromuscular facilitation stretches targeting upper (chest, rotator cuff,deltoids, and upper back) or lower (hamstrings, hips/glutes, lower back, and quadriceps) body muscle groups were performed for 10 minutes after each workout. All PRT sessions were supervised and led by a certified strength and conditioning professional to ensure maximu m co mpliance.

Anal yses of TC, TG, and Ox-LDL
The participants reported to the laboratory for blood draw between 07:00 and 08:00 AM after 10 -12 hours of overnight fasting. Blood samples were collected at pre-(week 0) and post-PRT (week 7). After 15 minutes of resting in a chair, venous blood was drawn fro m the antecubital vein. Immediately after blood draw, blood samples remained at room temperature for 20 minutes to be clotted, and then were centrifuged at 1,800g for 15 minutes to separate serum. Seru m samples were then immediately fro zen at -80 °C for the further analysis of seru m lipid and lipoprotein parameters.
Seru m samples in duplicate were assayed for TC (Kit# 85430, Cliniqa, San Marcos, CA) and TG (Kit# 85460, Clin iqa, San Marcos, CA) by an enzy mat ic co lorimetric method, and ox-LDL was analyzed by an enzy me-linked immu mosorbent assay (Cat# 10-1143-01, Mercodia, Uppsala, Sweden). Optical density was measured by the Spectra Max Plus 384 microplate spectrophotometer (Molecular Devices, Sunnyvale, CA ). Each assay was performed as instructed by the manufacture's assay procedure. To min imize inter-and intra-assay variability, all serum samp les for each assay were analy zed at one time in a single plate.

Anal yses of Serum Li poprotein-cholesterol
Seru m lipoprotein-cholesterol including VLDL-C, LDL-C, HDL-C, and Lp(a) were analyzed by electrophoresis (Cat. # 3438 SPIFE Vis Cho lesterol, Helena Laboratory, Beau mont, TX) using the SPIFE 3000 electrophoresis system (Helena Laborato ry, Beau mont, TX). The lipoprotein -cho lesterol analysis was performed as instructed by the manufacture's assay procedures, using a co mmercially availab le control (Cat. # 3218, Helena Laboratory, Beau mont, TX). In brief, 80 μL of serum samples, in duplicate, were applied to an agarose gel follo wed by 20 minutes of electrophoresis at 16 °C with 400 volts. After applying a staining regent (Cat. # 3438, Helena Laboratory, Beau mont, TX), addit ional electrophoresis was performed at 30 °C for 15 minutes. The gel was washed and dried at 70 °C for 20 minutes, and the density of stained lipoprotein-cholesterol bands were measured in a scanning densitometer (Epson Perfection V 700, Long beach, CA) using Quick Scan 2000 software (Helena Laboratory, Beaumont, TX). To min imize inter-and intra-assay variability, all seru m samp les were analyzed at one time in a single gel.

Statistical Analyses
The sample size was calculated by G* Power 3.1.0 software [21], given an alpha level at 0.05, an effect size of 0.40, and power at 0.80. The appropriate samp le size was estimated to be 16 participants for the current study design. All statistical analyses were performed using the IBM Statistical Package fo r the Social Sciences 19.0 (IBM SPSS, Armonk, NY) and reported as mean ± standard deviation (SD) unless stated otherwise. The Shapiro-W ilk test was emp loyed to test the normality of data, and indicated that data were normally distributed. An independent-Samp les T test was used to examine the baseline differences in anthropometrical and physiological variables between males and females. A 2 (group; males and females) X 2 (t ime; preand post-PRT) repeated measures analysis of variance (ANOVA) was employed to determine the significant changes in serum lipid and lipoprotein parameters. If the main or interaction effects were significant, Bonferroni pairwise co mparisons were conducted to examine the significant mean d ifferences. A p-value < 0.05 was considered to be statistically significant.

Results
The demographic and physiological characteristics of participants at baseline are presented in Table 2. No serum lip id or lipoprotein parameters at baseline were significantly different between groups, whereas height (males: 180.90 ± 8.28 vs. females: 167.11 ± 6.44 cm) and weight (males: 102.58±18.30 vs. females: 65.00±8.21 kg) were significantly different (p=0.001).However, these anthropometric variables were not significantly altered within each group following 6-weeks of PRT.
The main effects for group and time on changes in serum lip ids and lipoproteins are presented in Table 3 and 4, respectively. There were no significant main effects for group and time o r the group X time interaction for any of the serum lip id or lipoprotein parameters, except o x-LDL which had a significant main effect fo r t ime, indicating that o x-LDL significantly (p = 0.036) decreased by 1.87 U·L -1 or 3.81% (fro m 49.05 ± 9.17 to 47.18 ± 9.78 U·L -1 ) following 6 weeks of PRT (Table 4).

Discussion
This study was the first to examine the effects of PRT on cardioprotective health benefits in male and female collegiate athletes. Although we do not discuss about the results of PRT-induced strength gain in this paper, our unpublished data have shown that the participants significantly imp roved upper and lower body strength up to 15.0% fo llo wing 6-weeks of PRT.
In the current study, no serum lipid or lipoprotein parameters, except ox-LDL, significantly changed following 6-weeks of PRT. Th is result was consistent with other previous studies reporting that resistant training lasting for up to 16 weeks improved upper and lower body strength, but did not significantly alter serum lipids and lipoproteins in a variety of subject groups including untrained men [22] and wo men [23], patients with type 2 d iabetes [24], obese individuals with CVD risk factors [25], or postmenopausal wo men [26]. So me studies that examined the effects of different intensities or repetitions of resistance training on serum lip ids and lipoproteins in men or wo men have also found no beneficial effects of resistance training [27][28][29]. Moreover, several studies have reported an exercise-induced increase in Lp(a) or TG following 24 weeks of low-intensity resistance training or a single session of circu it-resistance exercise [27,29].
In contrast, other studies have reported a favorable effect of resistance training on serum lip ids and lipoproteins including a decrease in TC, LDL-C, and TG and/or an increase in HDL-C [30][31][32]. For instance, sedentary wo men who participated in 3-days of non-consecutive resistant training (85% 1-RM) fo r 14 weeks decreased TC, LDL-C, and the TC to HDL-C ratio, increased HDL-C, but did not change TG [32]. Similar results have also been observed in obese women who participated in 9-weeks of resistance training; however, the TG concentration in obese women significantly increased following resistance training [30]. Another study examining the effects of high intensity resistance training (3 sets of 8 repetitions) has reported an increase in HDL-C and a decrease in TG without changing body weight or diet in healthy, active postmenopausal wo men [31].
Based on the previous studies, it is d ifficult to conclude whether resistance training can positively alter seru m lip ids and lipoproteins. One of the recent review papers has suggested that if resistance training could positively influence on serum lip ids and lipoproteins, the primary outcome would be a reduction of LDL-C for both men and wo men, with a reduction of TC being a secondary outcome for only wo men [33]. One of the possible explanations for the lack of significant changes in serum lipids and lipoproteins in the current study may be our participants' good training background. All participants in the current study were physically active (perfo rmed physical activity more than 4 days per week) and trained for many years. Most studies that have reported a significant change in serum lip ids and lipoproteins investigated in sedentary or untrained individuals. Additionally, the init ial seru m lip id and lipoprotein parameters at baseline for our participants were within the normal range.
Only a few studies have previously examined the effects of exercise train ing on o x-LDL metabolis m, and most of the studies employed aerobic exercise training as an intervention [9][10][11][12]. Fu rthermore, the results of these studies are inconsistent. The concentration of ox-LDL decreased after acute prolonged or moderate intensity aerobic exercise training in healthy [10] and obese [9] ind ividuals. However, individuals with some types of metabolic d iseases such as untreated mild hypertension with atherogenic lip id profiles [11] o r type II diabetes [12] increased ox-LDL following acute resistance exercise. The authors have speculated that one of the possible exp lanations for an increase in ox-LDL following resistance training observed in patients with metabolic diseases could be a co mpensatory mechanis m to preventing free radical tissue damage [12].
In the current study, the serum o x-LDL concentration was significantly reduced by 3.81% (or 1.87 U·L -1 ) following 6-weeks of PRT. Similar to the current study, only serum ox-LDL, but no other lipid or lipoprotein parameters, significantly decreased after high-intensity strength training in obese adults [9] that performed lo wer body strength training for 12 weeks at 90% of 1-RM along with several abdominal and back exercises consisting of 3 series of 30 repetitions [9]. According to several studies that examined the relationship between physical training status and ox-LDL levels in young female [34] and veteran endurance male [35] athletes, the trained athletes tend to have lower o x-LDL than their untrained counterparts, suggesting that atherogenic risk can be favorably influenced by participation in exercise training and affected as early as in adolescents [34].

Conclusions
Our study suggests that 6-weeks of PRT consisting of a combination of Oly mp ic-style and traditional weightlifting movements and plyometrics can provide colleg iate athletes with cardioprotective health benefits by lowering o x-LDL. Although the exact mechanis m by wh ich exercise decreases ox-LDL has not been fully understood, high-intensity resistance training such as PRT may p revent risk for atherosclerosis and CVD in indiv iduals without atherogenic risk factors.