Peak power is reduced following lengthening contractions despite a maintenance of shortening velocity

2013 ◽  
Vol 38 (12) ◽  
pp. 1196-1205 ◽  
Author(s):  
Geoffrey A. Power ◽  
Brian H. Dalton ◽  
Charles L. Rice ◽  
Anthony A. Vandervoort
Keyword(s):  
Peak Power ◽  
Recovery Period ◽  
Shortening Velocity ◽  
Lengthening Contractions ◽  
Maximum Voluntary Isometric Contraction ◽  
Relative Contribution ◽  
Rate Of Torque Development ◽  
Isometric Torque ◽  
Torque Development ◽  
Shortening Contractions

Following repetitive lengthening contractions, power (the product of torque and velocity) is impaired during shortening contractions. However, the relative contribution of each component to power loss and the underlying factors are unclear. We investigated neuromuscular properties of the dorsiflexors in 8 males (27 ± 3 years) and 8 females (26 ± 4 years) for a potential sex-related difference before, during, and after 150 unaccustomed maximal lengthening actions. Velocity-dependent power was determined from shortening contractions at 8 levels (1 N·m to 70% of maximum voluntary isometric contraction (MVC)) before, after, and throughout recovery assessed at 0–30 min, 24 h, and 48 h. Immediately following task termination, both sexes displayed similar impairments of 30%, 4%, and 10% in MVC torque, shortening velocity, and overall peak power, respectively (P < 0.05). Peak rate of isometric torque development (RTD) was reduced by 10% in males, but females exhibited a 35% reduction (P < 0.05). Rate of torque development for the MVC remained depressed in both sexes throughout the 30 min recovery period; however, the RTD returned to normal by 24 h in males but did not recover by 48 h in females. Power was reduced preferentially at higher loads (i.e., 60% MVC), with a greater loss in females (65%) than males (45%). For lower loads (<20% MVC), power was impaired minimally (4%–8%; P < 0.05) and recovered within 30 min in both groups. The reduction in maximal angular velocity persisted until 30 min of recovery, and peak power did not recover until 24 h for both sexes. Unaccustomed lengthening contractions decreased power preferentially at higher loads, whereas peak power was reduced minimally owing to maintenance of maximal shortening velocity.

Reproducibility of velocity-dependent power: before and after lengthening contractions

2011 ◽  
Vol 36 (5) ◽  
pp. 626-633 ◽  
Author(s):  
Geoffrey A. Power ◽  
Brian H. Dalton ◽  
Charles L. Rice ◽  
Anthony A. Vandervoort
Keyword(s):  
Peak Power ◽  
High Reliability ◽  
Similar Amount ◽  
Shortening Velocity ◽  
Lengthening Contractions ◽  
Isokinetic Testing ◽  
Typical Error ◽  
Before And After ◽  
Absolute Reliability ◽  
Ankle Dorsiflexors

The determination of power using isokinetic testing has been shown to be highly reliable. However, isotonic and isokinetic testing involve specific mechanical constraints that likely necessitate different neuromuscular strategies. Therefore, the purpose here was to establish test–retest intrarater reliability (separated by 7 days) of loaded maximal shortening velocity and velocity-dependent power of the ankle dorsiflexors using the isotonic mode of the Biodex dynamometer (i) at baseline and (ii) throughout recovery following 150 high-intensity lengthening contractions. Intraclass correlation coefficients (ICC)2,1 with 95% CIs were used to determine relative reliability, whereas absolute reliability included typical error (TEM) and typical error expressed as a coefficient of variation (TEMCV). Twenty-four young men and women volunteered for the study. Maximal shortening velocity and power were determined with a fixed resistance set at 20% of maximal voluntary isometric contraction across 2 testing sessions separated by 7 days. ICCs were 0.93 and 0.98 for maximal shortening velocity and peak power, respectively. Following the lengthening contractions, ICCs indicated high reliability for maximal shortening velocity and peak power, 0.86 and 0.94, respectively, suggesting that a similar amount of fatigue was incurred on both days. Measures of absolute reliability for maximal shortening velocity and peak power also yielded high reliability. The isotonic mode is highly reliable when testing velocity-dependent power of the ankle dorsiflexors at baseline and following fatiguing lengthening contractions. The high reliability of this measure is encouraging and suggests that the isotonic mode can be used in various settings to track group changes before and after training and following fatigue and lengthening contractions.

scholarly journals Elbow Extensors and Volar Flexors Strength Capacity and Its Relation to Shooting Performance in Basketball Players—A Pilot Study

2020 ◽  
Vol 10 (22) ◽  
pp. 8206
Author(s):  
Darjan Smajla ◽  
Žiga Kozinc ◽  
Nejc Šarabon
Keyword(s):  
Scaling Factor ◽  
Long Distance ◽  
Basketball Players ◽  
Rate Of Torque Development ◽  
Strength Capacity ◽  
Isometric Torque ◽  
Muscle Groups ◽  
Sufficient Strength ◽  
Torque Development ◽  
Basketball Shooting

Rate of force/torque development scaling factor (RFD-SF/RTD-SF) has been used as a tool for assessing neuromuscular quickness. The aim was to investigate strength capacities of two major shooting muscle groups and their relationship to basketball shooting performance, and to compare the RFD-SF as well as shooting performance between junior and senior basketball players, and finally to examine the differences in RTD-SF between elbow extensors and volar flexors. In 23 male basketball players (13 juniors and 10 seniors) we assessed maximal isometric torque (TMVC), maximal rate of torque development and RTD-SF slope (kRTD-SF) for elbow extensors and volar flexors. The subjects performed 10 throws at 2.3 m (short) and 8.9 m (long) from the basket. Our results showed similar kRTD-SF and TMVC in both groups. Better shooting performance from short distance was observed in senior players. Significant associations between kRTD-SF, TMVC and shooting performance were found only in juniors. Elbow extensors TMVC was found to have a significant positive large association with shooting performance from long distance. It seems that muscle capacity has an important role in shooting performance in junior compared to players. Sufficient strength capacity of major shooting muscles is important for juniors’ shooting performance from a long distance.

Voluntary activation level and muscle fiber recruitment of human quadriceps during lengthening contractions

2004 ◽  
Vol 97 (2) ◽  
pp. 619-626 ◽  
Author(s):  
J. G. M. Beltman ◽  
A. J. Sargeant ◽  
W. van Mechelen ◽  
A. de Haan
Keyword(s):  
Fiber Type ◽  
Femoral Nerve ◽  
Voluntary Activation ◽  
Type I ◽  
Lengthening Contractions ◽  
Activation Level ◽  
Voluntary Activation Level ◽  
Isometric Torque ◽  
Type I Fibers ◽  
Shortening Contractions

Voluntary activation levels during lengthening, isometric, and shortening contractions (angular velocity 60°/s) were investigated by using electrical stimulation of the femoral nerve (triplet, 300 Hz) superimposed on maximal efforts. Recruitment of fiber populations was investigated by using the phosphocreatine-to-creatine ratio (PCr/Cr) of single characterized muscle fibers obtained from needle biopsies at rest and immediately after a series of 10 lengthening, isometric, and shortening contractions (1 s on/1 s off). Maximal voluntary torque was significantly higher during lengthening (270 ± 55 N·m) compared with shortening contractions (199 ± 47 N·m, P < 0.05) but was not different from isometric contractions (252 ± 47 N·m). Isometric torque was higher than torque during shortening ( P < 0.05). Voluntary activation level during maximal attempted lengthening contractions (79 ± 8%) was significantly lower compared with isometric (93 ± 5%) and shortening contractions (92 ± 3%, P < 0.05). Mean PCr/Cr values of all fibers from all subjects at rest were 2.5 ± 0.6, 2.0 ± 0.7, and 2.0 ± 0.7, respectively, for type I, IIa, and IIax fibers. After 10 contractions, the mean PCr/Cr values for grouped fiber populations (regardless of fiber type) were all significantly different from rest (1.3 ± 0.2, 0.7 ± 0.3, and 0.8 ± 0.6 for lengthening, isometric, and shortening contractions, respectively; P < 0.05). The cumulative distributions of individual fiber populations after either contraction mode were significantly different from rest ( P < 0.05). Curves after lengthening contractions were less shifted compared with curves from isometric and shortening contractions ( P < 0.05), with a smaller shift for the type IIax compared with type I fibers in the lengthening contractions. The results indicate a reduced voluntary drive during lengthening contractions. PCr/Cr values of single fibers indicated a hierarchical order of recruitment of all fiber populations during maximal attempted lengthening contractions.

Hip Abductor Rate of Torque Development as Opposed to Isometric Strength Predicts Peak Knee Valgus During Landing: Implications for Anterior Cruciate Ligament Injury

2021 ◽  
pp. 1-6
Author(s):  
Kristen M. Stearns-Reider ◽  
Rachel K. Straub ◽  
Christopher M. Powers
Keyword(s):  
Cruciate Ligament ◽  
Muscle Performance ◽  
Ligament Injury ◽  
Knee Valgus ◽  
Rate Of Torque Development ◽  
Peak Knee ◽  
Hip Abductor ◽  
Isometric Torque ◽  
Anterior Cruciate ◽  
Torque Development

Peak knee valgus has been shown to predict anterior cruciate ligament injury. The purpose of the current study was to compare peak rate of torque development (RTD) to peak isometric torque as a predictor of peak knee valgus during landing. Twenty-three healthy females participated. Hip abductor muscle performance was quantified using 2 types of isometric contractions: sustained and rapid. Peak isometric torque was calculated from the sustained isometric contraction. Peak RTD was calculated from the rapid isometric contraction (0–50 and 0–200 ms after force initiation). Kinematic data were collected during the deceleration phase of a double-leg drop jump task. Linear regression was used to assess the ability of hip abductor muscle performance variables to predict peak knee valgus. Increased peak RTD during the 0 to 50 milliseconds window after force initiation was found to significantly predict lower peak knee valgus (P = .011, R2 = .32). In contrast, neither peak RTD from 0 to 200 milliseconds after force initiation window (P = .45, R2 = .03) nor peak isometric torque (P = .49, R2 = .03) predicted peak knee valgus. The inability of the hip abductors to rapidly generate muscular force may be more indicative of “at-risk” movement behavior in females than measures of maximum strength.

scholarly journals Plyometric Exercises from a Knee Anterior Cruciate Ligament Prevention Program on the Rate of Isometric Torque Development and Vertical Jump Height

2018 ◽  
Author(s):  
Jeffrey Doeringer ◽  
Sam Johnson ◽  
Marc Norcorss ◽  
Mark Hoffman
Keyword(s):  
Anterior Cruciate Ligament ◽  
Injury Prevention ◽  
Prevention Program ◽  
Cruciate Ligament ◽  
Vertical Jump ◽  
Plyometric Training ◽  
Rate Of Torque Development ◽  
Isometric Torque ◽  
Anterior Cruciate ◽  
Torque Development

Purpose: Plyometric exercises are incorporated in anterior cruciate ligament injures of the knee (ACL) injury prevention programs that have effectively decreased risk factors for anterior cruciate ligament injures of the knee injuries, but the impact on the rate of isometric torque development of the musculature of the knee is unclear. The purpose of this study was to determine the effects of a 6-week plyometric program pulled from a commonly utilized anterior cruciate ligament injures of the knee injury prevention program on rate of isometric torque development (RTD) in healthy active females. Methods: College-aged participants were randomly split into two different groups (16-plyometric training and 15-control). Plyometric exercises included 180° jumps, bounding for distance, bounding in place, broad jump-stick, cone jumps, hop - hop stick, jump into bounding, jump - jump - jump vertical jump, mattress jumps, scissors jump, single-legged jumps for distance, squat jumps, step-jump up-down-vertical jump, tuck jumps, and wall jumps. Participants in the training group performed the exercises three times a week on alternating days, for 30-minute sessions. All participants performed a vertical jump measurement and completed maximum voluntary isometric contractions (MVICs) of ankle plantar flexion, knee extension, and knee flexion rate of torque development. Results: There was a main effect of session for plantar flexion rate of torque development time windows and vertical jump. The analysis revealed no significant differences for group by session interactions for any other rate of torque development measurement or the vertical jump. Conclusions: Plyometric exercises utilized from an anterior cruciate ligament injures of the knee injury prevention program did not change lower body isometric torque development or vertical jump height of active females. Since the plyometric training did not improve vertical jump, the training may not have been performed vigorous enough for the participants to cause a neuromuscular adaptation. Based on findings, 6-weeks of plyometric training from an isolated ACL injury prevention program should not be used to increase the vertical jump of healthy, active females.

Postactivation potentiation in a human muscle: effect on the rate of torque development of tetanic and voluntary isometric contractions

2007 ◽  
Vol 102 (4) ◽  
pp. 1394-1401 ◽  
Author(s):  
Stéphane Baudry ◽  
Jacques Duchateau
Keyword(s):  
Muscle Activation ◽  
Muscle Performance ◽  
Similar Degree ◽  
Postactivation Potentiation ◽  
Muscle Twitch ◽  
Rate Of Torque Development ◽  
Adductor Muscles ◽  
Isometric Torque ◽  
Voluntary Contractions ◽  
Torque Development

Postactivation potentiation (PAP), a mechanism by which the torque of a muscle twitch is increased following a conditioning contraction, is well documented in muscular physiology, but little is known about its effect on the maximal rate of torque development and functional significance during voluntary movements. The objective of this study was to investigate the PAP effect on the rate of isometric torque development of electrically induced and voluntary contractions. To that purpose, the electromechanical responses of the thumb adductor muscles to a single electrical stimulus (twitch), a train of 15 pulses at 250 Hz (HFT250), and during ballistic (i.e., rapid torque development) voluntary contractions at torque levels ranging from 10 to 75% of maximal voluntary contraction (MVC) were recorded before and after a conditioning 6-s MVC. The results showed that the rate of torque development was significantly ( P < 0.001) increased after the conditioning MVC, but the effect was greater for the twitch (∼200%) compared with the HFT250 (∼17%) or ballistic contractions (range: 9–24%). Although twitch potentiation was maximal immediately after the conditioning MVC, maximal potentiation for HFT250 and ballistic contractions was delayed to 1 min after the 6-s MVC. Furthermore, the similar degree of potentiation for the rate of isometric torque development between tetanic and voluntary ballistic contractions indicates that PAP is not related to the modality of muscle activation. These observations suggest that PAP may be considered as a mechanism that can influence our contractions during daily tasks and can be utilized to improve muscle performance in explosive sports.

Power attenuation from restricting range of motion is minimized in subjects with fast RTD and following isometric training

2022 ◽  
Author(s):  
Brooke Davidson ◽  
Avery Hinks ◽  
Brian H. Dalton ◽  
Ryota Akagi ◽  
Geoffrey A. Power
Keyword(s):  
Peak Power ◽  
Plantar Flexion ◽  
Time Dependent ◽  
Isometric Contractions ◽  
Fast Time ◽  
Neuromuscular Activation ◽  
Rate Of Torque Development ◽  
Isotonic Contractions ◽  
Torque Development ◽  
Strong Relationships

Time-dependent measures consisting of rate of torque development (RTD), rate of velocity development (RVD), and rate of neuromuscular activation can be used to evaluate explosive muscular performance, which becomes critical when performing movements throughout limited ranges of motion (ROM). Using a HUMAC NORM dynamometer, seven males (27 ± 7 years) and six females (22 ± 3 years) underwent 8 weeks of maximal isometric dorsiflexion training 3 days/week. One leg was trained at 0° (short-muscle tendon unit (MTU) length) and the other at 40° of plantar flexion (long-MTU length). RTD and rate of neuromuscular activation were evaluated during 'fast' maximal isometric contractions. Power, RVD, and rate of neuromuscular activation were assessed during maximal isotonic contractions in four conditions (small (40° to 30° of plantar flexion) ROM at 10 and 50% MVC; large (40° to 0° of plantar flexion) ROM at 10 and 50% MVC) for both legs, pre- and post-training. Despite no change in rate of neuromuscular activation following training, peak power, RTD, and RVD increased at both MTU lengths (p < 0.05). Strong relationships (R2=0.73) were observed between RTD and peak power in the small ROM, indicating that fast time-dependent measures are critical for optimal performance when ROM is constrained. Meanwhile, strong relationships (R2=0.90) between RVD and power were observed at the 50% load, indicating that RVD is critical when limited by load and ROM is not confined. Maximal isometric dorsiflexion training can be used to improve time-dependent measures (RTD, RVD) to minimize power attenuation when ROM is restricted.

scholarly journals Influence of sex on performance fatigability of the plantar flexors following repeated maximal dynamic shortening contractions

2017 ◽  
Vol 42 (10) ◽  
pp. 1118-1121 ◽  
Author(s):  
Amelia C. Lanning ◽  
Geoffrey A. Power ◽  
Anita D. Christie ◽  
Brian H. Dalton
Keyword(s):  
Sex Differences ◽  
Development Rate ◽  
Time Dependent ◽  
Plantar Flexors ◽  
Neuromuscular Activation ◽  
Rate Of Torque Development ◽  
Torque Development ◽  
Shortening Contractions

The purpose was to determine sex differences in fatigability during maximal, unconstrained velocity, shortening plantar flexions. The role of time-dependent measures (i.e., rate of torque development, rate of velocity development, and rate of neuromuscular activation) in such sex-related differences was also examined. By task termination, females exhibited smaller reductions in power and similar changes in rate of neuromuscular activation than males, indicating females were less fatigable than males.

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