Peak force and rate of force development during isometric and dynamic mid-thigh clean pulls performed at various intensities

Eight male collegiate weightlifters (age: 21.2 +/- 0.9 years; height: 177.6 +/- 2.3 cm; and body mass: 85.1 +/- 3.3 kg) participated in this study to compare isometric to dynamic force-time dependent variables. Subjects performed the isometric and dynamic mid-thigh clean pulls at 30-120% of their one repetition maximum (1RM) power clean (118.4 +/- 5.5 kg) on a 61 x 121.9-cm AMTI forceplate. Variables such as peak force (PF) and peak rate of force development (PRFD) were calculated and were compared between isometric and dynamic conditions. The relationships between force-time dependent variables and vertical jump performances also were examined. The data indicate that the isometric PF had no significant correlations with the dynamic PF against light loads. On the one hand, there was a general trend toward stronger relationships between the isometric and dynamic PF as the external load increased for dynamic muscle actions. On the other hand, the isometric and dynamic PRFD had no significant correlations regardless of the external load used for dynamic testing. In addition, the isometric PF and dynamic PRFD were shown to be strongly correlated with vertical jump performances, whereas the isometric PRFD and dynamic PF had no significant correlations with vertical jump performances. In conclusion, it appears that the isometric and dynamic measures of force-time curve characteristics represent relatively specific qualities, especially when dynamic testing involves small external loads. Additionally, the results suggest that athletes who possess greater isometric maximum strength and dynamic explosive strength tend to be able to jump higher.     

Short-term in-season ballistic training improves power,muscle volume and throwing velocity in junior handball players. A randomized control trial

This study investigated the effects of a ballistic training programme using an arm/shoulder specific strength device (ASSSD) on the upper body peak power (PP), muscle volume (MV) of the dominant arm and throwing velocity in junior handball players. Twenty-six players were randomly assigned to an experimental (EG = 15, age 17.6 ± 0.51 years) and control (CG = 11, age 17.36 ± 0.50 years) group. Over an 8-week in-season period, the EG performed a ballistic training programme (2 sessions/week) immediately before their normal team handball training. Both groups underwent tests on the ASSSD, which operates in consecutive accelerative and decelerative actions, for throwing characteristics determination. Peak power (PP), peak force (PF), peak velocity (PV), peak rate of power development (PRPD), muscle volume (MV), throwing velocity with runup, standing throw, and jump throw were also assessed before/after the training programme. The EG group showed significant post-training improvements in PP (52.50% – p < 0.001), PF (26.45% – p < 0.01) and PRPD (78.47% – p < 0.001) better than the CG (1.81, 0.67 and 1.64%, p > 0.05, respectively). There was also a post-training improvement in the velocity at PP (22.82% – p < 0.001) and PF (42.45% – p < 0.001) in the EG compared to the CG (4.18 and 8.53%, p > 0.05 respectively). There was a significant increase in acceleration at PP (51.50% – p < 0.01) and PF (69.67% – p < 0.001). MV increased (19.11% – p < 0.001) in the EG, with no significant change (3.34% – p = 0.84) in the CG. Finally, significant increases were obtained in the three throw types (3.1–6.21%, p < 0.05- < 0.001) in the EG compared to the CG. The additional ASSSD training protocol was able to improve muscle strength/volume and ball throwing velocity in junior handball players.     

Eight weeks of ballistic exercise improves power independently of changes in strength and muscle fiber type expression

This study investigated the effects of ballistic resistance training and strength training on muscle fiber composition, peak force (PF), maximal strength, and peak power (PP). Fourteen males (age = 21.3 +/- 2.9, body mass = 77.8 +/- 10.1 kg) with 3 months of resistance training experience completed the study. Subjects were tested pre and post for their squat one-repetition maximum (1RM) and PP in the jump squat (JS). Peak force and rate of force development (RFD) were tested during an isometric midthigh pull. Muscle biopsies were obtained from the vastus lateralis for analysis of muscle fiber type expression. Subjects were matched for strength and then randomly selected into either training (T) or control (C) groups. Group T performed 8 weeks of JS training using a periodized program with loading between 26 and 48% of 1RM, 3 days per week. Group T showed significant improvement in PP from 4088.9 +/- 520.6 to 5737.6 +/- 651.8 W. Rate of force development improved significantly in group T from 12687.5 +/- 4644.0 to 25343.8 +/- 12614.4 N x s(-1). PV improved significantly from 1.59 +/- 0.41 to 2.11 +/- 0.75 m x s(-1). No changes occurred in PF, 1RM, or muscle fiber type expression for group T. No changes occurred in any variables in group C. The results of this study indicate that using ballistic resistance exercise is an effective method for increasing PP and RFD independently of changes in maximum strength (1RM, PF), and those increases are a result of factors other than changes in muscle fiber type expression.     

Effect of loading on enhancement of power performance over three consecutive trials

The acute effects of maximal voluntary isometric contractions (MVICs) in the squat position on subsequent measures of power output over 3 consecutive sets were investigated. Sixteen trained men experienced with back squats participated in the study. A 7-second MVIC was performed 4 minutes before the execution of 5 maximal countermovement jumps (CMJs) and was repeated for 3 consecutive sets (protocol 1). The results were compared to power output performance in a similar protocol (protocol 2) that excluded the 7-second MVICs. No significant differences occurred in any of the power output measurements between protocol 1 and protocol 2, nor did significance occur linearly across the 4 sets of CMJ, with the exception of a decrease in peak power in protocol 2 (p < or = 0.05). Using both mean and maximal values only one significant correlation between either relative strength and performance enhancement or absolute strength and performance enhancement was present at p < or = 0.01. At p < or = 0.05, significant correlations were found between absolute strength and mean peak power (PP), mean peak acceleration (PA), mean peak force (PF), max PP, max PA, max PF, and max peak velocity. These data indicate that the execution of an MVIC performed before a power exercise was inadequate to acutely enhance power output over any of 3 consecutive trials.     

The importance of isometric maximum strength and peak rate-of-force development in sprint cycling

This study was designed to investigate the relationship of whole-body maximum strength to variables potentially associated with track sprint-cycling success. These variables included body composition, power measures, coach's rank, and sprint-cycling times. The study was carried out in 2 parts. The first part (n = 30) served as a pilot for the second part (n = 20). Subjects for both parts ranged from international-caliber sprint cyclists to local-level cyclists. Maximum strength was measured using an isometric midthigh pull (IPF). Explosive strength was measured as the peak rate-of-force development (IPRFD) from the isometric force-time curve. Peak power was estimated from countermovement (CMJPP) and static vertical jumps (SJPP) and measured by modified Wingate tests. Athletes were ranked by the U.S. national cycling coach (part 1). Sprint times (from a standing start) were measured using timing gates placed at 25, 82.5, 165, 247.5, and 330 m of an outdoor velodrome (part 2). Maximum strength (both absolute and body-mass corrected) and explosive strength were shown to be strongly correlated with jump and Wingate power. Additionally, maximum strength was strongly correlated with both coach's rank (parts 1 and 2) and sprint cycling times (part 2). The results suggest that larger, stronger sprint cyclists have an advantage in producing power and are generally faster sprint cyclists.     

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.     

Effect of concurrent endurance and circuit resistance training sequence on muscular strength and power development

The purpose of this study was to examine the influence of the sequence order of high-intensity endurance training and circuit training on changes in muscular strength and anaerobic power. Forty-eight physical education students (ages, 21.4 +/- 1.3 years) were assigned to 1 of 5 groups: no training controls (C, n = 9), endurance training (E, n = 10), circuit training (S, n = 9), endurance before circuit training in the same session, (E+S, n = 10), and circuit before endurance training in the same session (S+E, n = 10). Subjects performed 2 sessions per week for 12 weeks. Resistance-type circuit training targeted strength endurance (weeks 1-6) and explosive strength and power (weeks 7-12). Endurance training sessions included 5 repetitions run at the velocity associated with Vo2max (Vo2max) for a duration equal to 50% of the time to exhaustion at Vo2max; recovery was for an equal period at 60% Vo2max. Maximal strength in the half squat, strength endurance in the 1-leg half squat and hip extension, and explosive strength and power in a 5-jump test and countermovement jump were measured pre- and post-testing. No significant differences were shown following training between the S+E and E+S groups for all exercise tests. However, both S+E and E+S groups improved less than the S group in 1 repetition maximum (p < 0.01), right and left 1-leg half squat (p < 0.02), 5-jump test (p < 0.01), peak jumping force (p < 0.05), peak jumping power (p < 0.02), and peak jumping height (p < 0.05). The intrasession sequence did not influence the adaptive response of muscular strength and explosive strength and power. Circuit training alone induced strength and power improvements that were significantly greater than when resistance and endurance training were combined, irrespective of the intrasession sequencing.     

MVIC运动不能提高大学生篮球运动员的激活后增强效应

本研究旨在探讨激活后增强效应(post-activation potentiation, PAP)对大学生篮球运动员上肢力量表现和肌肉损伤指标的影响,以及不同最大自主等长收缩(maximal voluntary isometric contraction, MVIC)时间诱发激活后增强效应后,对卧推(bench press throw, BPT)表现的影响。本研究招募30名大学生男性篮球运动员进行重复交叉实验。所有受试者均接受3组3 s卧推MVICs (3 MVICs)、3组5 s卧推MVICs (5 MVICs)、对照控制(CON)共3次干预,记录推掷高度与杠铃腾空时间,并分析推掷高度、力量与功率的峰值。研究表明:3 MVICs、5 MVICs、CON处理后,卧推高度在后测各时间点皆显著低于前测平均值,功率峰值在第4分钟、第8分钟及后测平均值上,皆显著低于前测平均值。但是,力量峰值在后测各时间点与前测平均值均无显著性差异。本研究初步认为给予较长的组间恢复时间,3 MVICs、5 MVICs产生肌肉疲劳的程度可能高于诱发PAP的程度,进而无法提升训练良好运动员的上肢爆发力表现。     

Tendon Achilles lengthening for the treatment of neuropathic ulcers causes a temporary reduction in forefoot pressure associated with changes in plantar flexor power rather than ankle motion during gait

The purposes of this study were to determine the effects of tendon Achilles lengthening (TAL) on ambulatory plantar pressures and ankle range of motion, moment, and power, and to determine whether changes in forefoot pressure after treatment of a neuropathic ulcer are related to changes in ankle dorsiflexion range of motion (DFROM) or plantar flexor (PF) power during gait. Pressure and gait tests were performed before treatment, and at 3 weeks and 8 months after treatment in two randomly assigned groups of subjects with diabetes, equinus deformity, and a neuropathic forefoot ulcer treated with TAL and total contact casting (TAL group, n=14), or total contact casting alone (TCC group, n=14). The TAL group had an initial decrease in forefoot peak pressure (PP) (27%), forefoot pressure-time integral (PTI) (42%), PF moment (53%), and PF power (65%), along with an initial increase in rear foot PP (34%), rear foot PTI (48%), and DFROM (74%). Post-surgical changes in rear foot pressure and DFROM were maintained up to 8 months after treatment with TAL, whereas forefoot pressure and PF moment and power increased significantly. Changes in forefoot pressure after treatment in either group were correlated with changes in PF power (r=0.45-0.60), but not with changes in DFROM during gait (r=-0.02-0.08). Results suggest TAL causes a temporary reduction in forefoot pressure primarily by reducing PF power during gait. The initial decrease in forefoot pressure, followed by progressive reloading of forefoot tissues as PF muscles regain strength after TAL, may help reduce the risk of ulcer recurrence in patients with diabetes.     

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.     

A comparison of high-speed power training and traditional slow-speed resistance training in older men and women

Muscle power, the product of force × velocity, is a critical determinant of function in older adults. Resistance training (RT) at high speed has been shown to improve peak muscle power in this population; however, different functional tasks may benefit from the improvement of power at values other than "peak" values, for example, tasks that require a greater velocity component or a greater force component. This study compared the effect of high-speed RT on muscle performance (peak power [PP] and its components [PP force and PP velocity] and overall peak velocity [VEL]) across a broad range of external resistances. Thirty-eight older men and women were randomized to high-speed power training at 40% of the 1-repetition maximum (1RM) (n = 13 [74.1 ± 6.4 years]); traditional RT at 80% 1RM (n = 13 [70.1 ± 7.0 years]); or control (n = 12 [72.8 ± 4.1 years]). Measures of muscle performance were obtained at baseline and after the 12-week training intervention. Muscle power and 1RM strength improved similarly with both high-speed and traditional slow-speed RT. However, speed-related muscle performance characteristics, PP velocity and overall VEL, were most positively impacted by high-speed power training, especially at lower external resistances. Because gains in speed-related measures with high-speed training compared to traditional RT do not come at the expense of other muscle performance outcomes, we recommend using an RT protocol in older adults that emphasizes high-speed movements at low external resistances.     

Neuromuscular responses to impact and collision during elite rugby league match play

The purpose of this study was to investigate the relationship between the prematch and short-term postmatch neuromuscular responses to the intensity, number, and distribution of impacts associated with collisions during elite Rugby League match play. Twenty-two elite male Rugby League players were monitored during 8 regular season competition matches using portable global positioning system (GPS) technology. The intensity, number, and distribution of impact forces experienced by players during match play were recorded using integrated accelerometry. Peak rate of force development (PRFD), peak power (PP), and peak force (PF) were measured during a countermovement jump on a force plate 24 hours prematch, 30 minutes prematch, 30 minutes postmatch and then at 24-hour intervals for a period of 5 days postmatch. The change in the dependent variables at each sample collection time was compared with that at 24 hours prematch and 30-minute prematch measures. There were significant (p < 0.05) decreases in PRFD and PP up to 24 hours postmatch with PF significantly (p < 0.05) being decreased 30 minutes postmatch. Significant (p < 0.05) correlations were found between the total number of impacts and PRFD and PP 30 minutes postmatch. Impact zones 4 (7.1-8.0 G), 5 (>8.1-10.0 G), and 6 (>10.1 G) were significantly (p < 0.05) correlated to PRFD and PP 30 minutes postmatch with the number of zone 5 and 6 impacts significantly (p < 0.05) correlated to PRFD and PP 24 hours postmatch. Elite Rugby League match play resulted in significant neuromuscular fatigue and was highly dependent on the number of heavy collisions >7.1G. Results demonstrate that neuromuscular function is compromised for up to 48 hours postmatch indicating that at least 2 days of modified activity is required to achieve full neuromuscular recovery after elite Rugby League match play. Position-specific demands on energy systems and the influence of repeated blunt force trauma during collisions during elite Rugby League match play should be considered when planning postmatch recovery protocols and training activities to optimize subsequent performance.     

Closed-kinetic chain upper-body training improves throwing performance of NCAA Division I softball players

Closed-kinetic chain resistance training (CKCRT) of the lower body is superior to open-kinetic chain resistance training (OKCRT) to improve performance parameters (e.g., vertical jump), but the effects of upper-body CKCRT on throwing performance remain unknown. This study compared shoulder strength, power, and throwing velocity changes in athletes training the upper body exclusively with either CKCRT (using a system of ropes and slings) or OKCRT. Fourteen female National Collegiate Athletic Association Division I softball player volunteers were blocked and randomly placed into two groups: CKCRT and OKCRT. Blocking ensured the same number of veteran players and rookies in each training group. Training occurred three times weekly for 12 weeks during the team's supervised off-season program. Olympic, lower-body, core training, and upper-body intensity and volume in OKCRT and CKCRT were equalized between groups. Criterion variables pre- and posttraining included throwing velocity, bench press one-repetition maximum (1RM), dynamic single-leg balance, and isokinetic peak torque and power (PWR) (at 180 degrees x s(-1)) for shoulder flexion, extension, internal rotation, and external rotation (ER). The CKCRT group significantly improved throwing velocity by 2.0 mph (3.4%, p < 0.05), and the OKCRT group improved 0.3 mph (0.5%, NS). A significant interaction was observed (p < 0.05). The CKCRT group improved its 1RM bench press to the same degree (1.9 kg) as the OKCRT group (p < 0.05 within each group). The CKCRT group improved all measures of shoulder strength and power, whereas OKCRT conferred little change in shoulder torque and power scores. Although throwing is an open-chain movement, adaptations from CKCRT may confer benefits to subsequent performance. Strength coaches can incorporate upper-body CKCRT without sacrificing gains in maximal strength or performance criteria associated with an athletic open-chain movement such as throwing.     

Predicting lower body power from vertical jump prediction equations for loaded jump squats at different intensities in men and women

The purpose of this study was to determine the efficacy of estimating peak lower body power from a maximal jump squat using 3 different vertical jump prediction equations. Sixty physically active college students (30 men, 30 women) performed jump squats with a weighted bar's applied load of 20, 40, and 60% of body mass across the shoulders. Each jump squat was simultaneously monitored using a force plate and a contact mat. Peak power (PP) was calculated using vertical ground reaction force from the force plate data. Commonly used equations requiring body mass and vertical jump height to estimate PP were applied such that the system mass (mass of body + applied load) was substituted for body mass. Jump height was determined from flight time as measured with a contact mat during a maximal jump squat. Estimations of PP (PP(est)) for each load and for each prediction equation were compared with criterion PP values from a force plate (PP(FP)). The PP(est) values had high test-retest reliability and were strongly correlated to PP(FP) in both men and women at all relative loads. However, only the Harman equation accurately predicted PP(FP) at all relative loads. It can therefore be concluded that the Harman equation may be used to estimate PP of a loaded jump squat knowing the system mass and peak jump height when more precise (and expensive) measurement equipment is unavailable. Further, high reliability and correlation with criterion values suggest that serial assessment of power production across training periods could be used for relative assessment of change by either of the prediction equations used in this study.     

Difference in kinematics and kinetics between high- and low-velocity resistance loading equated by volume: implications for hypertrophy training

Although it is generally accepted that a high load is necessary for muscle hypertrophy, it is possible that a low load with a high velocity results in greater kinematics and kinetics than does a high load with a slow velocity. The purpose of this study was to determine if 2 training loads (35 and 70% 1 repetition maximum [1RM]) equated by volume, differed in terms of their session kinematic and kinetic characteristics. Twelve subjects were recruited in this acute randomized within-subject crossover design study. Two bouts of a half-squat exercise were performed 1 week apart, one with high load-low velocity (HLLV = 3 sets of 12 reps at 70% 1RM) and the other with low-load high-velocity (LLHV = 6 sets of 12 reps at 35% 1RM). Time under tension (TUT), average force, peak force (PF), average power (AP), peak power (PP), work (TW), and total impulse (TI) were calculated and compared between loads for the eccentric and concentric phases. For average eccentric and concentric single repetition values, significantly (p < 0.05) greater (～15-22%) PP outputs were associated with the LLHV loading, whereas significantly greater (～7-61%) values were associated with the HLLV condition for most other variables of interest. However, in terms of total session kinematics and kinetics, the LLHV protocol resulted in significantly greater (～16-61%) eccentric and concentric TUT, PF, AP, PP, and TW. The only variable that was significantly greater for the HLLV protocol than for the LLHV protocol was TI (～20-24%). From these results, it seems that the LLHV protocol may offer an equal if not better training stimulus for muscular adaptation than the HLLV protocol, because of the greater time under tension, power, force, and work output when the total volume of the exercise is equated.     

The optimal training load for the development of muscular power

Muscular power is considered one of the main determinants of athletic performance that require the explosive production of force such as throwing and jumping. Various training methods have been suggested to improve muscular power and dynamic athletic performance. Although various acute training valuables (e.g., sets, repetitions, rest intervals) could be manipulated, the training loads used are some of the most important factors that determine the training stimuli and the consequent training adaptations. Many research results showed that the use of different training loads elicits the different training adaptations and further indicated the load- and velocity-specific adaptations in muscular-power development. Using the optimal loads at which mechanical power output occurs has been recommended, especially to enhance maximum muscular power. Additionally, introducing periodization and combined training approach into resistance-training programs may further facilitate muscular-power development and enhance a wide variety of athletic performances.     

Kinetic and training comparisons between assisted, resisted, and free countermovement jumps

Elastic band assisted and resisted jump training may be a novel way to develop lower-body power. The purpose of this investigation was to (a) determine the kinetic differences between assisted, free, and resisted countermovement jumps and (b), investigate the effects of contrast training using either assisted, free, or resisted countermovement jump training on vertical jump performance in well-trained athletes. In part 1, 8 recreationally trained men were assessed for force output, relative peak power (PP·kg(-1)) and peak velocity during the 3 types of jump. The highest peak force was achieved in the resisted jump method, while PP·kg(-1) and peak velocity were greatest in the assisted jump. Each type of jump produced a different pattern of maximal values of the variables measured, which may have implications for developing separate components of muscular power. In part 2, 28 professional rugby players were assessed for vertical jump height before and after 4 weeks of either assisted (n = 9), resisted (n = 11), or free (n = 8) countermovement jump training. Relative to changes in the control group (1.3 ± 9.2%, mean ± SD), there were clear small improvements in jump height in the assisted (6.7 ± 9.6%) and the resisted jump training group (4.0 ± 8.8%). Elastic band assisted and resisted jump training are both effective methods for improving jump height and can be easily implemented into current training programs via contrast training methods or as a part of plyometric training sessions. Assisted and resisted jump training is recommended for athletes in whom explosive lower-body movements such as jumping and sprinting are performed as part of competition.     

The impact of velocity of movement on performance factors in resistance exercise

The purpose of this study was to determine the impact of a very slow (VS) velocity and a self-selected volitional (VOL) velocity at varying intensities on repetition number, peak force, peak power, and total volume in the squat and shoulder press exercises. On separate testing days, 9 resistance trained men (age: 23.9 +/- 2.5 years; height: 174.8 +/- 6.5 cm; body mass: 80.1 +/- 12.4 kg) performed a squat (SQ) and shoulder press (SP) exercise at 60 or 80% of 1 repetition maximum (1RM) at either VOL or VS (10-second eccentric and 10-second concentric actions) velocity for as many repetitions as possible. Force, power, and volume (repetitions x kg) were also determined. Subjects performed significantly fewer repetitions (p < or = 0.05) in the VS exercises (60% VS SQ 5 +/- 1 vs. VOL SQ 24 +/- 2; 80% VS SQ 2 +/- 0 vs. VOL SQ 12 +/- 1; 60% VS SP 4 +/- 1 vs. VOL SP 14 +/- 2; 80% VS SP 1 +/- 0 vs. VOL SP 6 +/- 1). Peak force and power were significantly higher at the VOL speed (peak force [in newtons]: 60% VS SQ 564.4 +/- 77.3 vs. VOL SQ 1229.0 +/- 134.9 N; 80% VS SQ 457.3 +/- 27.9 vs. VOL SQ 1059.3 +/- 104.7 N; 60% VS SP 321.6 +/- 37.8 vs. VOL SP 940.7 +/- 144.8 N; 80% VS SP 296.5 +/- 24.7 vs. VOL SP 702.5 +/- 57.7 N; and peak power [in watts]: 60% VS SQ 271.2 +/- 40.1 vs. VOL SQ 783.2 +/- 129.1 W; 80% VS SQ 229.3 +/- 49.5 vs. VOL SQ 520.2 +/- 85.8 W; 60% VS SP 91.3 +/- 21.9 vs. VOL SP 706.6 +/- 151.4 W; 80% VS SP 78.1 +/- 19.8 vs. VOL SP 277.6 +/- 46.4 W). VOL speed elicited higher total volume than the VS velocity. The results of this study indicate that a VS velocity may not elicit appropriate levels of force, power, or volume to optimize strength and athletic performance.     

Mechanisms underlying the reduced performance measures from using equipment with a counterbalance weight system

Bench press throws are commonly used in the assessment of upper-body power and are often performed on a Smith machine that uses a counterbalance weight to reduce the net load on the barbell. The use of a counterbalanced Smith machine was recently shown to reduce performance measures, but the mechanisms for this reduction have not been established. The purpose of this study was to determine the underlying physiological and biomechanical causes of the reduced performance measures found when using a counterbalanced Smith machine. Twenty-four men (mean ± SE: age, 23 ± 1 years; weight, 91.0 ± 3.5 kg; height, 178.9 ± 1.2 cm) performed Smith machine bench press throws at 30% of 1-repetition maximum under 4 conditions: (a) rebound movement and counterbalance, (b) rebound movement and no counterbalance, (c) concentric-only movement and counterbalance, and (d) concentric-only movement and no counterbalance. Peak power, peak force, and peak concentric and eccentric velocities were measured using a linear accelerometer, and peak ground reaction force was measured using a force plate. The counterbalance condition produced significantly (p < 0.05) lower peak accelerometer-based force (-21.2 and -17.0% for rebound and concentric-only bench press throws, respectively) but increased peak ground reaction force (5.3 and 3.2%). The discrepancy between changes in peak accelerometer-based force and peak ground reaction force suggests that an increase in net external load occurred during the movement. For performance testing of explosive movements, the use of a counterbalance system results in an underestimation of performance capability, likely because of an increase in the net external load during the concentric phase. Therefore, a counterbalance system should not be used for explosive movement performance testing.