The effect of heavy- vs. light-load jump squats on the development of strength, power, and speed

The purpose of this investigation was to examine the effect of an 8-week training program with heavy- vs. light-load jump squats on various physical performance measures and electromyography (EMG). Twenty-six athletic men with varying levels of resistance training experience performed sessions of jump squats with either 30% (JS30, n = 9) or 80% (JS80, n = 10) of their one repetition maximum in the squat (1RM) or served as a control (C, n = 7). An agility test, 20-m sprint, and jump squats with 30% (30J), 55% (55J), and 80% (80J) of their 1RM were performed before and after training. Peak force, peak velocity (PV), peak power (PP), jump height, and average EMG (concentric phase) were calculated for the jumps. There were significant increases in PP and PV in the 30J, 55J, and 80J for the JS30 group (p 相似文献   

Effects of elastic bands on force and power characteristics during the back squat exercise

Athletes commonly use elastic bands as a training method to increase strength and performance. The purpose of this study was to investigate the effect of elastic bands on peak force (PF), peak power (PP), and peak rate of force development (RFD) during the back-squat exercise (BSE). Ten recreationally resistance-trained subjects (4 women, 6 men, mean age 21.3 +/- 1.5 years) were tested for their 1 repetition maximum (1RM) in the BSE (mean 117.6 +/- 48.2 kg) on a Smith machine. Testing was performed on 2 separate days, with 2 sets of 3 repetitions being performed for each condition. Testing was conducted at 60% and 85% of 1RM with and without using elastic bands. In addition, 2 elastic band loading conditions were tested (B1 and B2) at each of the 2 resistances. No bands (NB) represents where all of the resistance was acquired from free-weights. B1 represents where approximately 80% of the resistance was provided by free-weights, and approximately 20% was provided by bands. B2 represents where approximately 65% of the resistance was provided by free-weights, and approximately 35% was provided from bands. The subjects completed the BSE under each condition, whereas PF, PP, and RFD was recorded using a force platform. There was a significant (p < 0.05) increase in PF between NB-85 and B2-85 of 16%. Between B1-85 and B2-85, PF was increased significantly by 5% (p < 0.05). There was a significant (p < 0.05) increase in PP between NB-85 and B2-85 of 24%. No significant differences were observed in RFD during the 85% conditions or for any of the measured variables during the 60% conditions (p < 0.05). The results suggest that the use of elastic bands in conjunction with free weights can significantly increase PF and PP during the BSE over free-weight resistance alone under certain loading conditions. The greatest differences are observed during the higher loading conditions, with the B1-85 condition appearing to be optimal for athletic performance of the ones we tested. The strength training professional could use variable resistance training (VRT) to increase PF and PP more than the traditional BSE can. VRT could also be used to train these 2 performance characteristics together, which might be especially useful in season, when weight-room training volume can sometimes be limited.     

Relationship between countermovement jump performance and multijoint isometric and dynamic tests of strength

The purpose of this investigation was to determine the relationship between countermovement vertical jump (CMJ) performance and various methods used to assess isometric and dynamic multijoint strength. Twelve NCAA Division I-AA male football and track and field athletes (age, 19.83 +/- 1.40 years; height, 179.10 +/- 4.56 cm; mass, 90.08 +/- 14.81 kg; percentage of body fat, 11.85 +/- 5.47%) participated in 2 testing sessions. The first session involved 1 repetition maximum (1RM) (kg) testing in the squat and power clean. During the second session, peak force (N), relative peak force (N x kg(-1)), peak power (W), relative peak power (W x kg(-1)), peak velocity (m x s(-1)), and jump height (meters) in a CMJ, and peak force and rate of force development (RFD) (N x s(-1)) in a maximal isometric squat (ISO squat) and maximal isometric mid-thigh pull (ISO mid-thigh) were assessed. Significant correlations (P < or = 0.05) were found when comparing relative 1RMs (1RM/body mass), in both the squat and power clean, to relative CMJ peak power, CMJ peak velocity, and CMJ height. No significant correlations existed between the 4 measures of absolute strength, which did not account for body mass (squat 1RM, power clean 1RM, ISO squat peak force, and ISO mid-thigh peak force) when compared to CMJ peak velocity and CMJ height. In conclusion, multijoint dynamic tests of strength (squat 1RM and power clean 1RM), expressed relative to body mass, are most closely correlated with CMJ performance. These results suggest that increasing maximal strength relative to body mass can improve performance in explosive lower body movements. The squat and power clean, used in a concurrent strength and power training program, are recommended for optimizing lower body power.     

The optimal back squat load for potential osteogenesis

The osteogenic potential of exercise is reported to be partially a function of the magnitude of training loads. This study evaluated the ground reaction force (GRF) and rate of force development (RFD) of the eccentric and concentric phases of the back squat at 3 different loads. Twelve subjects performed the back squat on a force platform with loading conditions of 80, 100, and 120% of their 1 repetition maximum (RM). Back squats performed at 120% of the 1RM produced the highest GRF in both the eccentric and concentric conditions. No significant differences were found between RFD for any of the loading conditions. Performing the back squat at loads of 120% of the estimated 1RM, accomplished with reduced range of motion, results in higher GRF than the back squat performed at 80 or 100% of the 1RM. Thus, supermaximal back squat loads in excess of the 1RM, with decreased range of motion, may be a useful part of a resistance training program designed to maximize osteogenic potential.     

The effects of amino acid supplementation on muscular performance during resistance training overreaching

The purpose of this study was to examine the effects of amino acid supplementation on muscular strength, power, and high-intensity endurance during short-term resistance training overreaching. Seventeen resistance-trained men were randomly assigned to either an amino acid (AA) or placebo (P) group and underwent 4 weeks of total-body resistance training consisting of two 2-week phases of overreaching (phase 1: 3 x 8-12 repetitions maximum [RM], 8 exercises; phase 2: 5 x 3-5 RM, 5 exercises). Muscle strength, power, and high-intensity endurance were determined before (T1) and at the end of each training week (T2-T5). One repetition maximum squat and bench press decreased at T2 in P (5.2 and 3.4 kg, respectively) but not in AA, and significant increases in 1 RM squat and bench press were observed at T3-T5 in both groups. A decrease in the ballistic bench press peak power was observed at T3 in P but not AA. The fatigue index during the 20-repetition jump squat assessment did not change in the P group at T3 and T5 (fatigue index = 18.6 and 18.3%, respectively) whereas a trend for reduction was observed in the AA group (p = 0.06) at T3 (12.8%) but not T5 (15.2%; p = 0.12). These results indicate that the initial impact of high-volume resistance training overreaching reduces muscle strength and power, and it appears that these reductions are attenuated with amino acid supplementation. In addition, an initial high-volume, moderate-intensity phase of overreaching followed by a higher intensity, moderate-volume phase appears to be very effective for enhancing muscle strength in resistance-trained men.     

Throwing performance after resistance training and detraining

The purpose of the present study was to investigate the effect of short-term resistance training and detraining on shot put throwing performance. Eleven young healthy subjects with basic shot put skills participated in 14 weeks of resistance training, which was followed by 4 weeks of detraining. Shot put performance in four field tests was measured before (T1) and after (T2) resistance training and after detraining (T3). At the same time points, one repetition maximum (1RM) was measured in squat, bench press, and leg press. Fat-free mass (FFM) was determined with dual x-ray absorptiometry and muscle biopsies obtained from vastus lateralis for the determination of fiber type composition and cross-sectional area (CSA). 1RM strength increased 22-34% (p < 0.01) at T2 and decreased 4-5% (not significantly different) at T3. Shot put performance increased 6-12% (p < 0.05) after training and remained unaltered after detraining. FFM increased at T2 (p < 0.05) but remained unchanged between T2 and T3. Muscle fiber CSA increased 12-18% (p < 0.05) at T2. Type I muscle fiber CSA was not altered after detraining, but type IIa and IIx fiber CSA was reduced 10-12% (p < 0.05). The percentage of type IIx muscle fibers was reduced after training (T1 = 18.7 +/- 4, T2 = 10.4 +/- 1; p < 0.05), and it was increased at T3 compared with T2 (T3 = 13.7 +/- 1; p < 0.05). These results suggest that shot put performance remains unaltered after 4 weeks of complete detraining in moderately resistance-trained subjects. This might be linked to the concomitant reduction of muscle fiber CSA and increase in the percentage of type IIx muscle fibers.     

The effects of combined ballistic and heavy resistance training on maximal lower- and upper-body strength in recreationally trained men

The purpose of the present study was to investigate the additive effects of ballistic training to a traditional heavy resistance training program on upper- and lower-body maximal strength. Seventeen resistance-trained men were randomly assigned to 1 of 2 groups: (i) a combined ballistic and heavy resistance training group (COM; age = 21.4 +/- 1.7 years, body mass = 82.7 +/- 15.1 kg) or (ii) a heavy resistance training group (HR; age = 20.1 +/- 1.2 years, body mass = 81.0 +/- 9.2 kg) and subsequently participated in an 8-week periodized training program. Training was performed 3 days per week, that is, 6-8 exercises per workout (6-8 traditional exercises for HR; 4-6 traditional + 2 ballistic exercises in COM) for 3-8 repetitions. A significant increase in 1-repetition maximum (1RM) squat was shown in both groups (COM = 15.2%; HR = 17.3%) with no difference observed between groups. However, 1RM bench press increased to a significantly greater extent (P = 0.04) in COM than HR (11.6% vs. 7.1%, respectively). For peak power attained during the jump squat, an interaction (P = 0.02) was observed where the 5.4% increase in COM and -3.2% reduction in HR were statistically significant. Nonsignificant increases were observed in peak plyometric push-up power in COM (8.5%) and HR (3.4%). Lean body mass increased significantly in both groups, with no between-group differences observed. The results of this study support the inclusion of ballistic exercises into a heavy resistance training program for increasing 1RM bench press and enhancing lower-body power.     

Influence of contraction velocity in untrained individuals over the initial early phase of resistance training

The purpose of this study was to determine the early phase adaptations in short-term traditional (TRT) versus superslow (SST) resistance training. Sixteen apparently healthy subjects participated in this study. Subjects were pretested and posttested for their 1 repetition maximums (1RM) in the squat and bench press, peak power in a countermovement jump (CMJ) and squat jump (SJ), and body composition using dual energy x-ray absorptiometry. Subjects participated in an 8-week resistance training program in either SST (n = 9, 3 men, 6 women), using 50% of 1RM, or TRT (n = 7, 3 men, 4 women), using 80% of 1RM. Both groups trained 3 days per week. The TRT and SST groups improved in strength by 6.8 and 3.6% in the squat exercise and by 8.6 and 9.1% in the bench press, respectively. Peak power for the CMJ increased significantly in the TRT group, from 23.0 +/- 5.5 W/kg to 25.0 +/- 6.3 W/kg; no such increase was seen with respect to the SST group. Both groups' 1RM increased significantly for both the bench press and the squat. No changes in body composition were seen for either group. The results of this study suggest that TRT is more effective for improving peak power than SST.     

Effect of potentiation and stretching on maximal force, rate of force development, and range of motion

The purpose of this investigation was to compare the effects of stretching vs. potentiation on subsequent maximal force and rate of force development capabilities of subjects in an isometric squat. Ten male collegiate athletes participated as subjects in this study. Subjects were tested during 3 separate sessions that involved joint range of motion (ROM) measurements of the lower body and isometric squat trials on a force plate to determine peak force (PF) and rate of force development (RFD) values. One testing session was preceded by 10 minutes of quiet sitting (C), 1 by a 30-minute lower-body stretching protocol (S), and 1 by 3 sets of a leg press exercise using 90% of the subjects' previously determined 1 repetition maximum (P). Three repetitions were performed for each set of the leg press, with a 3-minute rest period between each set. PF during the isometric squat was not significantly different following any of the 3 conditions (C: 100.0 +/- 0.0%, S: 101.2 +/- 6.5%, P: 98.6 +/- 6.2%). However, RFD was significantly lower in P (87.5 +/- 12.8%) compared with both C (100.0 +/- 0.0%) and S (102.6 +/- 18.5%). Significant improvement in ROM occurred only following P. It appears the potentiation protocol used in the current investigation may actually have had fatiguing effects instead of potentiating effects, but it did result in significant increases in ROM.     

Strength changes during an in-season resistance-training program for football

The purpose of this study was to examine the effects of both intensity and volume of training during a 2 d.wk(-1) in-season resistance-training program (RTP) for American football players. Fifty-three National Collegiate Athletic Association Division III football players were tested in the 1 repetition maximum (1RM) bench press and 1RM squat on the first day of summer training camp (PRE) and during the final week of the regular season (POST). Subjects were required to perform 3 sets of 6-8 repetitions per exercise. Significant strength improvements in squat were observed from PRE (155.0 +/- 31.8 kg) to POST (163.3 +/- 30.0 kg), whereas no PRE to POST changes in bench press were seen (124.7 +/- 21.0 kg vs.123.9 +/- 18.6 kg, respectively). Training volume and training compliance were not related to strength improvement. Further analysis showed that athletes training at >or=80% of their PRE 1RM had significantly greater strength improvements than athletes training at <80% of their PRE 1RM, for both bench press and squat. Strength improvements can be seen in American football players, during an in-season RTP, as long as exercise intensity is >or=80% of the 1RM.     

Effects of whole-body low-intensity resistance training with slow movement and tonic force generation on muscular size and strength in young men

Our previous study showed that relatively low-intensity (approximately 50% one-repetition maximum [1RM]) resistance training (knee extension) with slow movement and tonic force generation (LST) caused as significant an increase in muscular size and strength as high-intensity (approximately 80% 1RM) resistance training with normal speed (HN). However, that study examined only local effects of one type of exercise (knee extension) on knee extensor muscles. The present study was performed to examine whether a whole-body LST resistance training regimen is as effective on muscular hypertrophy and strength gain as HN resistance training. Thirty-six healthy young men without experience of regular resistance training were assigned into three groups (each n = 12) and performed whole-body resistance training regimens comprising five types of exercise (vertical squat, chest press, latissimus dorsi pull-down, abdominal bend, and back extension: three sets each) with LST (approximately 55-60% 1RM, 3 seconds for eccentric and concentric actions, and no relaxing phase); HN (approximately 80-90% 1RM, 1 second for concentric and eccentric actions, 1 second for relaxing); and a sedentary control group (CON). The mean repetition maximum was eight-repetition maximum in LST and HN. The training session was performed twice a week for 13 weeks. The LST training caused significant (p < 0.05) increases in whole-body muscle thickness (6.8 +/- 3.4% in a sum of six sites) and 1RM strength (33.0 +/- 8.8% in a sum of five exercises) comparable with those induced by HN training (9.1 +/- 4.2%, 41.2 +/- 7.6% in each measurement item). There were no such changes in the CON group. The results suggest that a whole-body LST resistance training regimen is as effective for muscular hypertrophy and strength gain as HN resistance training.     

Role of concentric force in limiting improvement in muscular strength

We hypothesized that resistance training with combined eccentric and concentric actions, and concentric action only, should yield similar changes in muscular strength. Subjects in a free weight group trained three times a week for 12 wk with eccentric and concentric actions (FW, n = 16), a second group trained with concentric-only contractions using hydraulic resistance (HY; n = 12), and a control group did not train (n = 11). Training for FW and HY included five sets of supine bench press and upright squat at an intensity of 1-6 repetition maximum (RM) plus five supplementary exercises at 5-10 RM for a total of 20 sets per session for approximately 50 min. Testing at pre-, mid-, and posttraining included 1) 1 RM bench press and squat with and 2) without prestretch using free weights; 3)isokinetic peak force and power for bench press and squat at 5 degrees/s, and isotonic peak velocity and power for bench press with 20-kg load and squat with 70-kg load; 4) hydraulic peak bench press force and power, and peak knee extension torque and power at fast and slow speeds; and 5) surface anthropometry (fatfolds and girths to estimate upper arm and thigh volume and muscle area). Changes in overall fatness, muscularity, and muscle + bone cross-sectional area of the limbs did not differ between groups (P greater than 0.05). Improvements in free weight bench press and squat were similar (P greater than 0.05) in FW (approximately 24%) and HY (approximately 22%, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased rate of force development and neural drive of human skeletal muscle following resistance training.

The maximal rate of rise in muscle force [rate of force development (RFD)] has important functional consequences as it determines the force that can be generated in the early phase of muscle contraction (0-200 ms). The present study examined the effect of resistance training on contractile RFD and efferent motor outflow ("neural drive") during maximal muscle contraction. Contractile RFD (slope of force-time curve), impulse (time-integrated force), electromyography (EMG) signal amplitude (mean average voltage), and rate of EMG rise (slope of EMG-time curve) were determined (1-kHz sampling rate) during maximal isometric muscle contraction (quadriceps femoris) in 15 male subjects before and after 14 wk of heavy-resistance strength training (38 sessions). Maximal isometric muscle strength [maximal voluntary contraction (MVC)] increased from 291.1 +/- 9.8 to 339.0 +/- 10.2 N. m after training. Contractile RFD determined within time intervals of 30, 50, 100, and 200 ms relative to onset of contraction increased from 1,601 +/- 117 to 2,020 +/- 119 (P < 0.05), 1,802 +/- 121 to 2,201 +/- 106 (P < 0.01), 1,543 +/- 83 to 1,806 +/- 69 (P < 0.01), and 1,141 +/- 45 to 1,363 +/- 44 N. m. s(-1) (P < 0.01), respectively. Corresponding increases were observed in contractile impulse (P < 0.01-0.05). When normalized relative to MVC, contractile RFD increased 15% after training (at zero to one-sixth MVC; P < 0.05). Furthermore, muscle EMG increased (P < 0.01-0.05) 22-143% (mean average voltage) and 41-106% (rate of EMG rise) in the early contraction phase (0-200 ms). In conclusion, increases in explosive muscle strength (contractile RFD and impulse) were observed after heavy-resistance strength training. These findings could be explained by an enhanced neural drive, as evidenced by marked increases in EMG signal amplitude and rate of EMG rise in the early phase of muscle contraction.     

Comparison between linear and nonlinear in-season training programs in freshman football players

The purpose of this study was to compare linear (LT) with nonlinear (NL) in-season training programs in freshman football players during the course of 2 separate seasons. During the first year (n = 14, mean +/- SD = 177.3 +/- 4.8 cm, 88.0 +/- 9.7 kg), the LT program was employed 2 days per week. In the second year (n = 14, 175.0 +/- 7.1 cm, 94.2 +/- 20.5 kg), a 2 days per week LT was used. Subjects were tested for maximal strength in the squat (1 repetition maximum [1RM]) and bench press (1RM) exercises. A significant improvement in 1RM squat was seen in LT, but not in NL. No significant improvement in 1RM bench press was seen in either group. A significant difference between LT and NL was observed in Delta1RM squat (13.8 +/- 7.4 kg compared with 1.6 +/- 2.6 kg, respectively). Results of this study suggest that LT may be more effective in eliciting strength gains than NL in freshman football players during an in-season training program.     

Acute effects of elastic bands during the free-weight barbell back squat exercise on velocity, power, and force production

The use of elastic bands in resistance training has been reported to be effective in increasing performance-related parameters such as power, rate of force development (RFD), and velocity. The purpose of this study was to assess the following measures during the free-weight back squat exercise with and without elastic bands: peak and mean velocity in the eccentric and concentric phases (PV-E, PV-C, MV-E, MV-C), peak force (PF), peak power in the concentric phase, and RFD immediately before and after the zero-velocity point and in the concentric phase (RFDC). Twenty trained male volunteers (age = 26.0 ± 4.4 years) performed 3 sets of 3 repetitions of squats (at 55% one repetition maximum [1RM]) on 2 separate days: 1 day without bands and the other with bands in a randomized order. The added band force equaled 20% of the subjects' 55% 1RM. Two independent force platforms collected ground reaction force data, and a 9-camera motion capture system was used for displacement measurements. The results showed that PV-E and RFDC were significantly (p < 0.05) greater with the use of bands, whereas PV-C and MV-C were greater without bands. There were no differences in any other variables. These results indicate that there may be benefits to performing squats with elastic bands in terms of RFD. Practitioners concerned with improving RFD may want to consider incorporating this easily implemented training variation.     

Muscle adaptations to plyometric vs. resistance training in untrained young men

The purpose of this study was to compare changes in muscle strength, power, and morphology induced by conventional strength training vs. plyometric training of equal time and effort requirements. Young, untrained men performed 12 weeks of progressive conventional resistance training (CRT, n = 8) or plyometric training (PT, n = 7). Tests before and after training included one-repetition maximum (1 RM) incline leg press, 3 RM knee extension, and 1 RM knee flexion, countermovement jumping (CMJ), and ballistic incline leg press. Also, before and after training, magnetic resonance imaging scanning was performed for the thigh, and a muscle biopsy was sampled from the vastus lateralis muscle. Muscle strength increased by approximately 20-30% (1-3 RM tests) (p < 0.001), with CRT showing 50% greater improvement in hamstring strength than PT (p < 0.01). Plyometric training increased maximum CMJ height (10%) and maximal power (Pmax; 9%) during CMJ (p < 0.01) and Pmax in ballistic leg press (17%) (p < 0.001). This was far greater than for CRT (p < 0.01), which only increased Pmax during the ballistic leg press (4%) (p < 0.05). Quadriceps, hamstring, and adductor whole-muscle cross-sectional area (CSA) increased equally (7-10%) with CRT and PT (p < 0.001). For fiber CSA analysis, some of the biopsies had to be omitted. Type I and IIa fiber CSA increased in CRT (n = 4) by 32 and 49%, respectively (p < 0.05), whereas no significant changes occurred for PT (n = 5). Myosin heavy-chain IIX content decreased from 11 to 6%, with no difference between CRT and PT. In conclusion, gross muscle size increased both by PT and CRT, whereas only CRT seemed to increase muscle fiber CSA. Gains in maximal muscle strength were essentially similar between groups, whereas muscle power increased almost exclusively with PT training.     

Influence of training background on jumping height

The aim of this study was to compare the pattern of force production and center of mass kinematics in maximal vertical jump performance between power athletes, recreational bodybuilders, and physically active subjects. Twenty-seven healthy male subjects (age: 24.5 +/- 4.3 years, height: 178.7 +/- 15.2 cm, and weight: 81.9 +/- 12.7 kg) with distinct training backgrounds were divided into 3 groups: power track athletes (PT, n = 10) with international experience, recreational bodybuilders (BB, n = 7) with at least 2 years of training experience, and physically active subjects (PA, n = 10). Subjects performed a 1 repetition maximum (1RM) leg press test and 5 countermovement jumps with no instructions regarding jumping technique. The power-trained group jumped significantly higher (p < 0.05) than the BB and PA groups (0.40 +/- 0.05, 0.31 +/- 0.04, and 0.30 +/- 0.05, respectively). The difference in jumping height was not produced by higher rates of force development (RFD) and shorter center of mass (CM) displacement. Instead, the PT group had greater CM excursion (p < 0.05) than the other groups. The PT and BB groups had a high correlation between jumping height and 1RM test (r = 0.93 and r = 0.89, p < 0.05, respectively). In conclusion, maximum strength seems to be important for jumping height, but RFD does not seem relevant to achieve maximum jumping heights. High RFD jumps should be performed during training only when sport skills have a time constraint for force application.     

Peak power, ground reaction forces, and velocity during the squat exercise performed at different loads

This study examined the changes in peak power, ground reaction force and velocity with different loads during the performance of the parallel squat movement. Twelve experienced male lifters (26.83 +/- 4.67 years of age) performed the standard parallel squat, using loads equal to 20, 30, 40, 50, 60, 70, 80, and 90% of 1 repetition maximum (1RM). Each subject performed all parallel squats with as much explosiveness as possible using his own technique. Peak power (PP), peak ground reaction force (PGRF), peak barbell velocity (PV), force at the time of PP (FPP), and velocity at the time of PP (VPP) were determined from force, velocity, and power curves calculated using barbell velocity and ground reaction force data. No significant differences were detected among loads for PP; however, the greatest PP values were associated with loads of 40 and 50% of 1RM. Higher loads produced greater PGRF and FPP values than lower loads (p < 0.05) in all cases except between loads equal to 60-50, 50-40, and 40-30% of 1RM for PGRF, and between loads equal to 70-60 and 60-50% of 1RM for FPP. Higher loads produced lower PV and VPP values than lower loads (p < 0.05) in all cases except between the 20-30, 70-80, and 80-90% of 1RM conditions. These results may be helpful in determining loads when prescribing need-specific training protocols targeting different areas of the load-velocity continuum.     

Methodological concerns for determining power output in the jump squat

The purpose of this study was to investigate the validity of power measurement techniques during the jump squat (JS) utilizing various combinations of a force plate and linear position transducer (LPT) devices. Nine men with at least 6 months of prior resistance training experience participated in this acute investigation. One repetition maximums (1RM) in the squat were determined, followed by JS testing under 2 loading conditions (30% of 1RM [JS30] and 90% of 1RM [JS90]). Three different techniques were used simultaneously in data collection: (a) 1 linear position transducer (1-LPT); (b) 1 linear position transducer and a force plate (1-LPT + FP); and (c) 2 linear position transducers and a force place (2-LPT + FP). Vertical velocity-, force-, and power-time curves were calculated for each lift using these methodologies and were compared. Peak force and peak power were overestimated by 1-LPT in both JS30 and JS90 compared with 2-LPT + FP and 1-LPT + FP (p 相似文献   

Changes in muscle architecture and performance during a competitive season in female softball players

ABSTRACT: Nimphius, S, McGuigan, MR, and Newton, RU. Changes in muscle architecture and performance during a competitive season in female softball players. J Strength Cond Res 26(10): 2655-2666, 2012-The purpose of this research was (a) to examine the performance changes that occur in elite female softball players during 20 weeks of softball training (that included 14 weeks of periodized resistance training [RT]) and (b) to examine the relationship between percent change (%change) in muscle architecture variables and %change in strength, speed, and change of direction performance. Ten female softball players (age = 18.1 ± 1.6 years, height = 166.5 ± 8.9 cm, weight = 72.4 ± 10.8 kg) from a state Australian Institute of Sport softball team were tested for maximal lower-body strength using a 3 repetition maximum for a predicted 1 repetition maximum (1RM) and peak force, peak velocity (PV), and peak power (PP) were measured during jump squats (JS) unloaded and loaded. In addition, the first base (1B) and the second base (2B) sprint performance, change of direction (505) on dominant (D) and nondominant (ND) sides, aerobic capacity, and muscle architecture characteristics of vastus lateralis (VL) including muscle thickness (MT), fascicle length (FL), and pennation angle (θp) were examined. The testing sessions occurred pre, mid, and post training (total 20 week pre- and in-season training period). Changes over time were analyzed by repeated-measures analysis of variance. The relationship between %change in muscle architecture variables and strength, speed, and change of direction variables from pre to post were assessed by Pearson product-moment correlation coefficient. Significant improvements in PV and PP occurred at all JS loads pre- to mid-testing and pre- to post-testing. Significant increases occurred pre-post in absolute 1RM, relative 1RM, 505 ND, and 2B sprint. The strongest relationships were found between %change in VL MT and 1B sprint (r = -0.80, p = 0.06), %change in VL FL and 2B sprint (r = -0.835, p = 0.02), and %change in relative 1RM and 505 D (r = -0.70, p = 0.04). In conclusion, gains in strength, power, and performance can occur during the season in elite softball players who are also engaged in a periodized RT program. Furthermore, changes in performance measures are associated with changes in muscle architecture.