Strength Training Experience Research Articles

The effects of eccentric hamstring strength training on dynamic jumping performance and isokinetic strength parameters: a pilot study on the implications for the prevention of hamstring injuries

Objectives Although previous research shows that the hamstring length–tension relationship during eccentric contractions plays a role in hamstring injury, training methods to promote beneficial adaptations are still unclear. The purpose of this pilot study was to determine whether an eccentric hamstring specific training programme results in favourable adaptations. Design Eccentric training consisting of the Nordic hamstring exercise performed twice a week for four weeks. Pre- and post-training concentric/concentric isokinetic testing of peak torque (PT) and position of peak torque (POS) was performed for both the quadriceps and hamstrings of both legs at 60° s −1. Vertical jump height was also assessed. Participants Nine athletic, male subjects with no previous strength training experience. Results There was a significant increase in vertical jump height (pre=51.0±4.8 cm, post=54.4±6.3 cm, p=0.04), a significant reduction in quadriceps PT (pre=204.6±21.9 N.m., post=181.5±19.9 N.m., p=0.01), a significant decrease in hamstring POS from full knee extension (pre=32.5±7.4°, post=26.2±8.6°, p=0.01) and a significant hamstring POS difference between limbs (dominant=33.8±9.5°, non-dominant=24.9±6.5°, p=0.01). Conclusion Nordic hamstring exercise training may produce favourable neuromuscular adaptations for the possible prevention of hamstring injuries while enhancing performance in athletic, untrained males.

“Psyching-Up” Enhances Force Production During the Bench Press Exercise

We investigated the effect of "psyching-up" on force production during the bench press. Twelve men (mean age +/- SD: 27.4 +/- 11.2 years) and 8 women (20.9 +/- 2.5 years) with strength-training experience performed 5 bench press repetitions on a modified Biodex isokinetic dynamometer during 3 interventions. The interventions were counterbalanced and included a free-choice psych-up, a cognitive distraction, and an attention-placebo. Peak force recorded after psyching-up (mean +/- SD: 764 +/- 269 N.m) was significantly different from both distraction (703 +/- 282 N.m, p = 0.003) and attention-placebo (708 +/- 248 N.m, p = 0.01). The mean percentage increase in peak force from distraction to psyching-up was 11.8% (6 to 18%, 95% confidence interval [CI]) and 8.1% from placebo to psyching-up (3 to 13%, 95% CI). The results of the present study indicate that psyching-up may increase force production during the bench press exercise in participants with at least 1 year strength-training experience.

Echocardiographic Evaluation of Stress Test for Determining Safety of Participation in Strength Training

Suitability for safe participation in aerobic exercise is typically determined by a cardiopulmonary exercise test, using a treadmill or cycle. With increased participation in strength training by healthy clients as well as rehabilitation patients, there is a need to develop a test for determining suitability for safe participation in strength training. This investigation describes a strength stress test that may be used for determining safety of participation in strength training. Ten healthy subjects (28.3 +/- 5.9 years and 75.3 +/- 14.4 kg) with strength training experience participated. Following a resting echocardiogram, subjects performed 3 sets of leg presses at an 8 repetition maximum. Resting and exercise end-diastolic and end-systolic volumes were obtained during the last repetition of each set and were indexed for body surface area (ESV(I), EDV(I)). Ejection fraction, cardiac output, and stroke volume were calculated. Cardiac output increased significantly (p < 0.05) for each set in comparison to rest and also during the third set in comparison to sets 1 and 2. Ejection fraction increased, whereas ESV(I) and EDV(I) decreased significantly for each set compared to rest, and also during sets 2 and 3 when compared to set 1. Responses to sets 2 and 3 indicate increased cardiac stress with increasing sets to exhaustion analogous to changes observed during tests designed to assess anaerobic and aerobic power. Thus, this protocol may be used as a test for evaluating the ability to participate in modest strength training consistent with exercise prescriptions developed for participants of health clubs and rehabilitation facilities. Strength testing protocol described may be adapted and modified for evaluating other lifts such as arm work and job-related tasks.

CARBOHYDRATE SUPPLEMENTATION FAILS TO REVERT THE EFFECT OF ENDURANCE EXERCISE ON SUBSEQUENT STRENGTH EXERCISE PERFORMANCE

Previous studies indicated that endurance exercise might have an adverse effect on subsequent strength exercise performance. The decrease in strength performance might be related to the changes promoted by endurance exercise in energy metabolism. PURPOSE Our aim was verify if carbohydrate (CHO) feeding can attenuate the effects of endurance exercise on strength development. METHODS Six female university students (164±2.5cm;64.9±4.4kg) with strength training experience were submitted to a VO2max test (44±1.9ml.min−1) and an 1-RM test in the leg press (186±9.8kg) followed by a maximum repetitions test (2 sets of leg press exercise performed at 70% of 1-RM value until exhaustion, 1st set 21±1.2 reps and 2nd set 11±0.9 reps) in different days. In a double-blind design, the subjects were submitted to 2 different trials, receiving placebo (P) or CHO beverages (1L of P or 6% CHO solutions), 60 min before (500ml) and during (500ml) endurance exercise bout. These bouts were performed in a treadmill at 70% of VO2max for 45 minutes. Subsequently, the subjects performed an 1-RM test followed by a maximum repetitions test. RESULTS No changes were observed in 1-RM test. There was a similar decline in maximum repetitions test (an index of muscular endurance) in both trials (P- 1st set 13±1.6 reps and 2nd set 6±0.9 reps CHO- 1st set 15±1.2 reps and 2nd set 7±0.8 reps, P < 0.05). CONCLUSIONS In the 1-RM test, the additional participation of fast-twitch fibers IIa and IIb might overcome the effect of endurance exercise, thus contributing to the lack of alteration in this parameter. Muscular endurance tasks relied in the recruitment of slow- twitch fibers, we believe that the decrease seen in maximum repetitions test was due to a reduction of muscle glycogen in these fibers induced by endurance exercise. No differences were observed in glycaemia in both trials, suggesting a greater participation of intramuscular substrates. In conclusion, CHO supplementation was inefficient to revert the deleterious effect of endurance exercise on maximum repetitions test.

Effects of long-term creatine supplementation on liver and kidney functions in American college football players.

The purpose of this study was to determine the effect of long-term Cr supplementation on blood parameters reflecting liver and kidney function. Twenty-three members of an NCAA Division II American football team (ages = 19-24 years) with at least 2 years of strength training experience were divided into a Cr monohydrate group (CrM, n = 10) in which they voluntarily and spontaneously ingested creatine, and a control group (n = 13) in which they took no supplements. Individuals in the CrM group averaged regular daily consumption of 5 to 20 g (mean SD = 13.9 5.8 g) for 0.25 to 5.6 years (2.9 1.8 years). Venous blood analysis for serum albumin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, bilirubin, urea, and creatinine produced no significant differences between groups. Creatinine clearance was estimated from serum creatinine and was not significantly different between groups. Within the CrM group, correlations between all blood parameters and either daily dosage or duration of supplementation were nonsignificant. Therefore, it appears that oral supplementation with CrM has no long-term detrimental effects on kidney or liver functions in highly trained college athletes in the absence of other nutritional supplements.

SAFETY OF UNWEIGHTED AND WEIGHTED PLYOMETRIC TRAINING IN STRENGTH TRAINED WOMEN

Plyometric (stretch-shortening cycle) exercises are traditionally performed at bodyweight to improve power. Training for optimal mechanical power output however, requires a range of resistances. Adding resistance during lower body plyometric exercise increases impact forces exerted on the athlete at landing that may cause injury or soreness. The purpose of this study was to compare the safety and muscle soreness response to plyometric vs. weighted plyometric training in strength trained women. 14 women (means: age = 25 + 4 yrs; wt = 63 + 10 kg; % bodyfat = 19 + 5) with a minimum of 1 yr of strength training experience (means: 1RM squat = 1.3 + 0.3% of bodyweight; VJ = 43.0 + 7.3 cm) were randomly assigned to either a plyometric (P, n = 7) or a weighted plyometric (WP, n = 7) training group. P performed depth jumps (4 ± 6 at 41 cm), split squats (3 ± 6), and double leg hops (3 × 5) with bodyweight 2x/wk for 4-wks. WP performed identical exercises, with bodyweight plus 20% of baseline squat 1RM (wk 1) up to 40% of baseline squat 1RM (wk 4). Resistance for WP was set using dumbbells. P and WP subjects also performed squats at 85% of 1RM (3 × 6) one day/wk after the respective P and WP workouts. Injuries and muscle soreness were monitored using a scale developed by Shaw and colleagues (1–4; 1 = no soreness, 4 = painfully sore) immediately post and 2 days post all 8 workouts. Results: No injuries or significant muscle soreness occurred over the course of the 4-wk study. No significant difference (p < 0.05) in soreness response was observed between the P and WP groups. Immediate post workout soreness averaged: (P = 1.2 + 0.4, WP = 1.5 + 0.6) and 2 days post workout soreness averaged: (P = 1.3 + 0.5, WP = 1.5 + 0.7). Conclusion: 1) Neither plyometric or weighted plyometic exercises, as performed in this study, resulted in any injuries or significant muscle soreness in strength trained women.

PLYOMETRIC TRAINING AT VARIED RESISTANCE

Plyometric (stretch-shortening cycle) exercises are traditionally performed at bodyweight to improve power. Training for optimal mechanical power output however, requires a range of resistances. The purpose of this study was to compare the effects of 4 wks of plyometric vs. weighted plyometric training on vertical jump (VJ) in strength trained women. 14 women (means: age = 25 ± 4 yrs; wt = 63 ± 10 kg; %BF = 19 ± 5) with a minimum of 1 yr of strength training experience (means: 1RM squat = 1.3 ± 0.3% of bodyweight; VJ = 43.0 ± 7.3 cm) were randomly assigned to either a plyometric (P, n = 7) or a weighted plyometric (WP, n = 7) training group. P performed depth jumps, split squats, and double leg hops with bodyweight 2x/wk for 4 wks. WP performed identical exercises, with bodyweight plus 20% of baseline squat 1 RM (wk 1) up to 40% of baseline squat 1RM (wk 4). Resistance for WP was set using dumbbells. P and WP subjects also performed squats at 85% of 1RM (3 ± 6) one day/wk after the respective P and WP workouts. VJ (cm) with counter-movement was assessed using a Vertec. Both groups significantly increased VJ (P = 4.7 ± 3.6 cm, 11.4%, p = 0.013; WP = 4.7 ± 1.4 cm, 11.0%, p = 0.000). No difference (p > 0.05) was observed between groups. Conclusion: As performed in this study, plyometric and weighted plyometric exercises both result in significant, but similar improvement in vertical jump in strength trained women.

Single- vs. Multiple-Set Strength Training in Women

The aim of this study was to compare the effects of single-set and multiple-set strength training in women. Twenty-seven women (aged 20-40 years) with basic experience in strength training were randomly allocated to either a single-set group (n = 9), a 3-set group (n = 9), or a nontraining control group (n = 9). Both training groups underwent a whole-body strengthening program, exercising 2 days a week for 6 weeks. Exercises included bilateral leg extension, bilateral leg curl, abdominal crunch, seated hip adduction/abduction, seated bench press, and lateral pull-down. The single-set group's program consisted of only 1 set of 6-9 repetitions until failure, whereas the multiple-set group trained with 3 sets of 6-9 repetitions until failure (rest interval between sets, 2 minutes). Two times before and 3 days after termination of the training program, subjects were tested for their 1 repetition maximum strength on the bilateral leg extension and the seated bench press machine. Data were analyzed using a repeated-measures analysis of variance, Scheffé tests, t-tests, and calculation of effect sizes. Both training groups made significant strength improvements in leg extension (multiple-set group, 15%; single-set group, 6%; p 0.05). However, in the seated bench press only the 3-set group showed a significant increase in maximal strength (10%). Calculation of effect sizes and percentage gains revealed higher strength gains in the multiple-set group. No significant differences were found in the control group. These findings suggest superior strength gains occurred following 3-set strength training compared with single-set strength training in women with basic experience in resistance training.

Effect of Oral Creatine Monohydrate and Creatine Phosphate Supplementation on Maximal Strength Indices, Body Composition, and Blood Pressure

The use of creatine as an ergogenic aid for athletic performance is growing in popularity, despite limited scientific support for its efficacy. The purpose of this study was to determine the effect of creatine (Cr) monohydrate (CrM) and creatine phosphate (CrP) supplementation on strength, body composition, and blood pressure over a 6-week period. Thirty-five males (age range = 19–29 years) with at least 2 years of strength training experience were tested on three separate occasions (pretest, 3 weeks, 6 weeks). Strength tests performed were the one-repetition maximum (1-RM) bench press, 1-RM leg press, and maximal repetitions on the seated preacher bar curl with a fixed amount of weight. Subjects were divided into three groups matched for strength: placebo (Pl), CrM, and CrP. All subjects were provided a standardized strength training regimen and ingested a loading dosage of 20 g per day for the first 3 days of the study, followed by a maintenance dose of 10 g per day for the remainder of the 6-week supplementation period. Significant differences were noted between the Pl group and the two Cr groups for changes in lean body mass, body weight, and 1-RM bench press. These results suggest that oral Cr supplementation will result in greater strength and fat-free mass development. In addition, CrP may be as effective as CrM in achieving these desired outcomes.

EIGHT WEEKS USE OF ANDROGENIC-ANABOLIC STEROIDS INCREASES FIBRINOLYTIC ACTIVITY IN BODYBUILDERS 211

The aim of this study was to investigate the effects of eight weeks self-administration of high doses androgenic-anabolic steroids (AAS) in a stacking way on fibrinolytic activity in non elite male bodybuilders. A prospective, non blinded study design was chosen. The AAS group (AAS-G, n=7) consisted of experienced AAS users who were drug free for more than 3 months at start of the study. Non using bodybuilders served as controls (CO-G, n=7). Both groups were comparable with respect to age (32.3±6.8 vs.32.1±2.9, AAS-G resp. CO-G), height (179±4 vs. 174±6 cm), weight (82.8±8.7 vs. 85.2±8.4 kg), strength training experience (8.5±2.4 and 8.4±3.8 years) and weekly training hours(9.1±3.2 resp. 8.9±3.0). At start and after eight weeks training with (AAS-G) or without (CO-G) AAS use in all subjects blood samples before and after 10 minutes venuous occlusion (VO) were taken using a Biopool Stabilyte blood collection device. In each sample euglobulin clot lysis time(ECLT) was determined. Data are presented as mean ± s.d. ANOVA for repeated measures and paired t-tests for intra-group changes were used for statistical analysis. Level of significance was set at P<0.05. At start ECLT of both groups was comparable (101.3±15.4 and 106.8±17.4 minutes, AAS-G resp. CO-G). After eight weeks AAS use, ECLT before VO in the AAS-G was significantly decreased (101.3±15.4 to 80.2±25.0 min., P<0.02), whereas ECLT after VO remained unchanged. In CO-G no significant changes were observed after eight weeks. In conclusion, eight weeks self administration of high doses AAS in a stacking way enhances fibrinolytic activity as measured by euglobulin clot lysis time in non elite bodybuilders.

Test-Retest Reliability of Selected LifeCircuit Machines

ABSTRACT This study was done to (a) determine the test-retest reliability of selected LifeCircuit strength training machines and (b) examine the accuracy of the set-up test as a percentage of 1-RM. Fifty eight subjects (28 M, 30 F) with at least 3 months strength training experience completed the study. Two testing sessions were given 3 to 7 days apart on 5 LifeCircuit weight training machines. On each day, subjects performed the set-up test (a modified version of the 1-RM test) and a standard 1-RM test on each machine. Reliability of the set-up test, done according to the manufacturer's protocol, was acceptable for men but only moderate for women. When the set-up test was converted to %1-RM, the mean values for the 5 machines ranged from 40 to 67% for men and 45 to 56% for women. While these average values suggest the machines are quite accurate in calculating %1-RM, the range of scores was very large (20–101% of 1-RM). Thus the appropriate training intensity could be markedly over- or underestimated. Given these variable results, it is recommended that instructors and trainers use caution when prescribing training programs.

The Effects of Concentric Resistance Training on Eccentric Peak Torque and Muscle Cross-sectional Area

This study was designed to investigate the effects of concentric resistance training on isokinetic concentric and eccentric peak torque and muscle cross-sectional area. Using a time-series design, 14 males with previous strength training experience were assigned to six weeks of control activity, followed by 12 weeks of high-resistance training of the knee extensors and flexors on variable resistance hydraulic equipment that allowed concentric contractions only. Angular velocities of movement about the knee and hip during training were maintained at approximately 1.05 rad.s-1. Peak concentric and eccentric torques of the knee extensors and flexors at 1.05 rad.s-1 were assessed three times before training and during the training program at six and 12 weeks. No significant changes in peak torque were observed over the control period. After six weeks of training, peak torque in all four tests were increased (p < .05) over pretraining values. After 12 weeks of training, torques were further increased (p < .05) over the values at the six-week point. Cross-sectional area (CSA) of the quadriceps femoris muscle and the hamstring muscle groups was measured by computerized tomography (CT) scanning techniques before training and during the program at six and 12 weeks. CSA was significantly (p < .05) increased for the quadriceps femoris muscle but not the hamstrings group after six weeks of training. After 12 weeks of training, the CSA of both muscle groups increased (p < .05) over the six-week measurement. The results of this study suggest that strength training effects are not completely specific to the contraction type utilized in training. J Orthop Sports Phys Ther 1991;13(3):132-137.

Relationship Between Repetitions and Selected Percentages of One Repetition Maximum

Thirty-eight male subjects with no previous muscular strength training experience were tested to determine the number of repetitions they could perform at 40, 60, and 80 percent of one repetition maximum (1 RIM)for each of seven specified weight training lifts. The results indicated that there is a significant difference (P < 0001) in the number of repetitions performed at the selected percentages of 1 RM, as well as in the number of repetitions performed at these percentages across lifts. The findings also indicate that a given number of repetitions is not always associated with the same percentages of the 1 RM when performing different lifts. The prediction of the 1 RM can not be generalized based on the number of repetitions performed.