Rate Of Velocity Development Research Articles

Influence of stimulation frequency on early and late phase rate of torque and velocity development.

The early (≤50 ms) rate of torque development (RTD) is dependent upon the speed of neuromuscular activation; however, few studies have evaluated the determinants of rate of velocity development (RVD), which may be load-dependent. The purpose here was to explore the relationship between stimulation frequency with the early and late (≥100 ms) phase isometric RTD and isotonic RVD. The knee extensors of 16 (five female) young recreationally active participants were stimulated using 14 frequencies from 1 to 100 Hz during isometric and isotonic ("unloaded" and 7.5% of the isometric maximal voluntary contraction [MVC]) contractions. Isometric RTD and isotonic RVD were evaluated for the early (0-50 ms) and late (0-100 ms) phases from torque and velocity onset, respectively. Sigmoid functions were fit and bilinear regressions were used to examine the slopes of the steep portion of the curve and the plateau frequency. RTD- and RVD-frequency relationships were well described by a sigmoid function (all r2 > 0.96). Compared with the late phase, early isometric RTD, and unloaded RVD displayed lower slopes (all P ≤ 0.001) and higher plateau frequencies (all P < 0.001). In contrast, early and late RVD of a moderately loaded isotonic contraction did not display different slopes (P = 0.055) or plateau frequencies (P = 0.690). Early isometric RTD and unloaded isotonic RVD are more dependent on changes in stimulation frequency compared with late phases. However, RVD for a moderately loaded isotonic contraction displayed similar responses for the early and late phases. Therefore, a high frequency of activation is critical for early torque and velocity generation but dependent upon the load for isotonic contractions.NEW & NOTEWORTHY We show that during an "unloaded" isotonic contraction, the early phase rate of velocity development is more dependent upon a high electrical activation frequency compared with the late phase, similar to isometric torque. However, early and late phase rates of velocity development of moderately loaded isotonic contractions display similar responses. These results indicate that the determinants of isotonic shortening function are dependent on the externally applied load, highlighting the importance of task-specificity of contraction.

Effects of High-Velocity Versus Low-Velocity Resistance Training on Muscle Echo Intensity in Healthy Young Women: A Randomized Controlled Trial.

Improving muscle quality to prevent and treat muscle dysfunction is critical. However, effective measures to improve muscle quality remain poorly understood. We investigated the effects of high- and low-velocity resistance training (RT) on muscle quality, mass, and function before and after an 8-week intervention. High-velocity RT would improve muscle quality more effectively than low-velocity RT. Randomized controlled trial. Level 1. A total of 33 healthy young women (23.1 ± 2.2 years) were assigned randomly to high-velocity (n = 16) or low-velocity (n = 17) groups. Both groups underwent concentric knee extension RT with a 60% 1-repetition maximum (1RM) load, performing 10 repetitions of 4 sets, 3 times per week for 8 weeks. The high-velocity group was instructed to complete each repetition as quickly as possible (mean repetition duration of 0.5 seconds), while the low-velocity group was required to execute each repetition in 3 seconds. Before and after the 8-week intervention, quadriceps femoris echo intensity (EI), muscle thickness (MT), isokinetic peak torque (60 and 300 deg/s), rate of velocity development (RVD) at 300 deg/s, and 1RM were assessed. Split-plot factorial design analysis of variance was used to compare the group × time interaction. A group×time interaction was observed for EI (P < 0.01). Only the high-velocity group showed a significant reduction in EI after the intervention. MT revealed a main effect of time (P < 0.01), with both groups significantly increasing MT. RVD showed a group × time interaction (P < 0.05), with significant increase only in the high-velocity group. Isokinetic peak torque and 1RM showed main effects of time (P < 0.01), with significant increases in both groups. High-velocity RT may be superior to low-velocity RT in enhancing muscle quality and RVD. These results emphasize the importance of RT velocity for muscle quality improvement.

Electrically Evoked Isotonic Plantar Flexion Contractions Are Impaired Less than Voluntary After a Dynamic Fatiguing Task.

Evaluating central and peripheral processes responsible for reduced power after dynamic fatiguing tasks are often limited to isometric torque, which may not accurately reflect dynamic contractile performance. Here, we compare voluntary and electrically evoked peak power (and its determinants: dynamic torque and velocity) and rate of velocity development (RVD) before and after a dynamic fatiguing task using concentric Plantar flexion contractions. Young (18-32 yr) males ( n = 11) and females ( n = 2) performed maximal-effort isotonic Plantar flexion contractions using a load of 20% isometric torque until an approximately 75% reduction in peak power. Voluntary and electrically evoked (300 Hz tibial nerve stimulation) contractions loaded to 20% and 40% isometric torque through 25° ankle joint range of motion were compared before and 0, 2.5, 5, and 10 min after task termination. At task termination, peak power and RVD of voluntary contractions at both loads were reduced more (~40% to 50% reduction) than electrically evoked (~25% to 35% reduction) contractions ( P < 0.001 and P = 0.003). Throughout the recovery period, electrically evoked peak power and RVD returned to baseline sooner (<5 min) than voluntary contractions, which were still depressed at 10 min. Reductions in peak power for the 20% load were equally due to impaired dynamic torque and velocity, whereas velocity was impaired more than dynamic torque ( P < 0.001) for the 40% load. The relative preservation of electrically evoked power and RVD compared with voluntary contractions at task termination and quicker recovery to baseline indicates that the reductions in dynamic contractile performance after task termination are due to both central and peripheral processes; however, the relative contribution of dynamic torque and velocity is load dependent.

Calcaneal tendon stiffness is not associated with dynamic time-dependent contractile output.

The ability to rapidly generate muscular torque and velocity is important in specialized activities and daily tasks of living. Tendon stiffness is one factor in the neuromuscular system that influences musculoskeletal torque transmission. Previous studies have reported weak-to-moderate correlations between tendon stiffness and rate of torque development (RTD). However, these correlations have been reported only for isometric contractions, which may not be relevant to contractions involving joint rotation (i.e., dynamic). The purpose was to investigate the effect of calcaneal tendon stiffness on the dynamic RTD and rate of velocity development (RVD) in plantar flexor muscles. Young adult males (n=13) and females (n=2) performed prone isometric- and isotonic-mode maximal voluntary plantar flexion contractions (MVC). Ultrasound imaging was used to quantify tendon morphological characteristics to estimate Young's elastic modulus (YM). Maximal voluntary and electrically evoked (300 Hz) isometric- and isotonic-mode (at 10% and 40% MVC loads) contractions were evaluated for RTD and RVD through a 25° ankle joint range of motion. YM was correlated with isometric RTD, but only for evoked contractions (RTD0-50 ms: r=0.54, p=0.02, RTD0-200 ms: r=0.62, p=0.01). Conversely, YM was not correlated with dynamic RTD (voluntary: r = -0.07-0.41, p=0.06-0.40, evoked: r = -0.2-0.3, p=0.14-0.24) nor RVD (voluntary: r = -0.08-0.24, p=0.27-0.40, evoked: r=0.12-0.3, p=0.14-0.34). These correlations would indicate that calcaneal tendon stiffness is an important factor for rapid isometric torque development, but less so for isotonic contractions. The determinants of dynamic contractile rates are more complex and warrant further study.

Muscle quality indices separately associate with joint-level power-related measures of the knee extensors in older males

PurposeThe purpose of this study was to investigate associations of muscle quality indices with joint-level power-related measures in the knee extensors of thirty-two older males (65–88 years).MethodsMuscle quality indices included: echo intensity, ratio of intracellular- to total water content (ICW/TW), and specific muscle strength. Echo intensity was acquired from the rectus femoris (EIRF) and vastus lateralis (EIVL) by ultrasonography. ICW/TW was computed from electrical resistance of the right thigh obtained by bioelectrical impedance spectroscopy. Specific muscle strength was determined as the normalized maximal voluntary isometric knee extension (MVIC) torque to estimated knee extensor volume. Isotonic maximal effort knee extensions with a load set to 20% MVIC torque were performed to obtain the knee extension power-related measures (peak power, rate of power development [RPD], and rate of velocity development [RVD]). Power and RPD were normalized to MVIC.ResultsThere were no significant correlations between muscle quality indices except between EIRF and EIVL (|r|≤ 0.253, P ≥ 0.162). EIRF was negatively correlated with normalized RPD and RVD (r ≤ − 0.361, P ≤ 0.050). ICW/TW was positively correlated with normalized peak power (r = 0.421, P = 0.020). Specific muscle strength was positively correlated with absolute peak power and RPD (r ≥ 0.452, P ≤ 0.012).ConclusionKnee extension power-related measures were lower in participants with higher EI, lower ICW/TW, and lower specific muscle strength, but the muscle quality indices may be determined by independent physiological characteristics.

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

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). In this study, we investigated how restricting ROM influences power production while also exploring the relationship with time-dependent measures before and after isometric resistance training. Using a HUMAC NORM dynamometer, seven males (27 ± 7 yr) and six females (22 ± 3 yr) underwent 8 wk of maximal isometric dorsiflexion training 3 days/wk. 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°-30° of plantar flexion) ROM at 10% and 50% MVC; large (40°-0° of plantar flexion) ROM at 10% and 50% MVC] for both legs, pre- and posttraining. 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.NEW & NOTEWORTHY Power output was greater in the unrestricted than restricted ROM, and there were strong relationships between rate of torque development (RTD) and velocity development (RVD) with peak power. RTD and RVD had the strongest relationships with power when ROM was restricted and unrestricted, respectively. Following 8 wk of isometric training, discrepancies in power between restricted and unrestricted ROM were reduced. Increasing RTD through isometric training increased power in dynamic movements, especially when ROM was restricted.

Effect of Muscle Action on the Kinetic and Kinematic Behavior of the Barbell during Isoinertial Strength Assessment

An isoinertial strength assessment was performed to examine the kinetic and kinematic behavior of the barbell during several muscle actions. Velocity–time characteristics, force–time relationship, one repetition maximum (1RM), power output, and acceleration were compared in eccentric–concentric (EC) versus concentric only (C) sequences of the bench press (BP) and military press (MP). In two separate sessions, 28 and 29 resistance-trained athletes executed EC or C sequences in random order of the BP and MP, respectively, in an incremental load test up to their 1RM. Higher values were recorded in BP-EC than in BP-C, MP-EC, or MP-C (p &lt; 0.01) for peak acceleration, peak rate of force development, peak rate of velocity development, and power output. Significant differences were detected between exercises in terms of the portion of the concentric phase (%) at which peak acceleration was detected, or acceleration up until peak velocity was observed (p &lt; 0.05). No differences were observed between exercises in the portion of the concentric phase where acceleration up to the braking phase took place. The eccentric muscle action prior to concentric movement was a key factor to enhance the kinematic and kinetic performance in BP exercise. No such effects of the countermovement were produced in MP.

Power loss is attenuated following a second bout of high-intensity eccentric contractions due to the repeated bout effect's protection of rate of torque and velocity development.

High-intensity unaccustomed eccentric contractions result in weakness and power loss because of fatigue and muscle damage. Through the repeated bout effect (RBE), adaptations occur, then damage and weakness are attenuated following a subsequent bout. However, it is unclear whether the RBE protects peak power output. We investigated the influence of the RBE on power production and estimated fatigue- and damage-induced neuromuscular impairments following repeated high-intensity eccentric contractions. Twelve healthy adult males performed 5 sets of 30 maximal eccentric elbow flexions and repeated an identical bout 4 weeks later. Recovery was tracked over 7 days following both bouts. Reduced maximum voluntary isometric contraction torque, and increased serum creatine kinase and self-reported soreness indirectly inferred muscle damage. Peak isotonic power, time-dependent measures- rate of velocity development (RVD) and rate of torque development (RTD)- and several electrophysiological indices of neuromuscular function were assessed. The RBE protected peak power, with a protective index of 66% 24 h after the second eccentric exercise bout. The protection of power also related to preserved RVD (R2 = 0.61, P < 0.01) and RTD (R2 = 0.39, P < 0.01). Furthermore, the RBE's protection against muscle damage permitted the estimation of fatigue-associated neuromuscular performance decrements following eccentric exercise. Novelty: The repeated bout effect protects peak isotonic power. Protection of peak power relates to preserved rates of torque and velocity development, but more so rate of velocity development. The repeated bout effect has little influence on indices of neuromuscular fatigue.

Age-related Differences In Rapid Neuromuscular Parameters Of The Plantar Flexors And Correlations With Physical Function

Few studies have concurrently examined multiple rapid neuromuscular characteristics of the plantar flexors (PFs) in middle-aged (MM) and older (OM) males. Further, it is important to determine the association between these measures and physical function. PURPOSE:To compare rapid neuromuscular parameters of the PFs in MM and OM, and examine correlates of physical functioning. METHODS:Twenty-nine healthy, MM (n=14; 45.3±2.6 yrs) and OM (n=15; 65.3±3.2 yrs) performed fast, isotonic (IT) contractions with a load of 0.5 Nm and slow, isokinetic (IK; 60°·s-1) concentric contractions of the PFs using a dynamometer. Participants were instructed to push with the ball of their foot “as hard and fast as possible” prior to each contraction. Peak velocity (PV), rate of velocity development (RVDIT), and rate of electromyography rise (RER) were obtained from IT trials. During the IK trials, time to peak torque (TPT) and rate of velocity development (RVDIK) were acquired. RVD was obtained from the linear slope of the velocity-time curve (Δvelocity/Δtime)as the highest rolling 20 ms value. RER of the medial gastrocnemius was derived from the linear slope of the normalized electromyography signal as the highest rolling 50 ms value. Maximal walking velocity (MWV) and time to complete 5 chair rises (5CR) were also recorded. Group comparisons were made with independent samples t-tests, while Pearson correlation coefficients were calculated to examine select relationships. RESULTS:RVDITwas lower (MM=5202.83±510.23 vs. OM=4630.29±854.23°·s-2; p=0.037), and 5CR time greater (16%; p=0.022) in OM.RER was only correlated (r=0.431; p=0.026) with RVDIT. Only PV (r=0.396; p=0.033) and RVDIT(r=0.480;p=0.008) were correlated with MWV, while only TPT was correlated with 5CR time (r=0.451; p=0.014). CONCLUSIONS:Our findings suggest that rapid neuromuscular measures may be differentially influenced by age, and only particular parameters are associated with physical function.

The Influence Of Hamstring Muscle-tendon Stiffness On Isolated And Dynamic Velocity Based Parameters

Previous research has demonstrated sex differences in active hamstring muscle-tendon stiffness as well as associations between stiffness and landing biomechanics and architectural tissue properties. Little is known whether active stiffness relates to other measures of muscle function (i.e., maximum voluntary isometric contraction [MVIC], isotonic dynamometry) and performance (i.e., sprinting). PURPOSE: To conduct a pilot study examining the relationship between active hamstring muscle-tendon stiffness and isometric torque production, isotonic velocity development, and sprint velocity. A secondary research interest was to examine the relationship between the isotonic velocity parameters and sprint performance. METHODS: Nine recreationally active and healthy subjects (7 males, 2 females) (24 ± 3 years) completed an MVIC for the hamstrings (30° knee flexion) followed by three 40m sprint trials using an infrared timing gate system (Brower, Draper, UT). At least 48 hours later, subjects completed a measure of hamstring muscle-tendon stiffness (damped oscillatory technique) and an isotonic knee flexion test on a fixed dynamometer (Biodex, Shirley, NY). The isotonic test began at 90° of knee flexion and was eccentric/concentric through a 90° arc of motion with subjects lying prone. Eccentric velocity was set at 180°/s and concentric torque was set at 25% of MVIC. Bivariate correlations were conducted between stiffness, MVIC (normalized to body mass), sprint times, time to peak velocity, rate of velocity development (RVD, 0-100ms), and rebound time (-50°/s to +50°/s). RESULTS: Stiffness (24.3 ± 11.7 Nm/kg) was only significantly related (r= .681, P= .043) to MVIC (1.48 ± 0.23 Nm/kg). Stiffness was not significantly related to rebound time (0.076 ± 0.026s) (r= -.354, P= .350), time to peak velocity (0.214 ± 0.034s) (r= -.285, P= .457), RVD0-100 (1314.64 ± 222.30°/s2) (r= -.336, P= .377), or sprint velocities (5.90 ± 0.56 m/s) (r= .248, P= .521). Rebound time (r= -.535, P= .138) and RVD0-100 (r= -.436, P= .241) were not significantly related to sprint times. CONCLUSIONS: Although only the association between stiffness and normalized MVIC reached statistical significance, the magnitude of the other observed relationships provides impetus for further study with a larger sample size.

Leg Extension Strength, Explosive Strength, Muscle Activation, and Growth as Predictors of Vertical Jump Performance in Youth Athletes

The purpose of this study was to examine the relationships among leg extension strength, explosive strength, muscle activation, and measurements of growth to predictions of vertical jump performance in youth athletes. Height, body mass, skinfolds, and quadriceps femoris muscle cross-sectional area were measured in 39 sports active children (20 females, 19 males, age = 12.52 ± 0.62 years old). Peak torque (PT), rate of torque development (RTD), rate of velocity development (RVD), and rate of electromyographic amplitude rise (RER) were measured during isometric and isokinetic leg extensions. PT, RTD, and RVD were expressed in absolute terms and normalized to body mass. Estimated jump height (JH) and peak power (PP) were assessed during static (SJ), counter-movement (CMJ), and drop (DJ) jumps. JH exhibited greater correlations with PT normalized to body mass (r = 0.387–0.758) than absolute PT (r = 0.338–0.417), whereas PP exhibited greater correlations with absolute PT (r = 0.368–0.837). Only negligible to moderate relationships existed between JH and PP across all jumps (r = 0.053–0.605). Over 50% of the variability in PP was predicted in 24 of 30 regression models with absolute muscle strength, muscle activation, and measurements of growth, while only 6 of 30 models predicted more than 50% of the variability in JH. Overall, absolute static and dynamic muscle strength, muscle activation, and growth better explained PP measured during vertical jumps than estimated JH.

Comparison of age-specific leg extensor muscle function torque-time and rapid velocity attributes across the adult lifespan: A relative deficiency investigation.

The purposes of this study were to examine the age-related differences in absolute and normalized torque-time parameters in five distinct groups across the adult lifespan, and the relationship between rapid strength and limb acceleration capacities across the lifespan. One-hundred and thirty-six healthy men were categorized as young athletes (n=27; age=20.7yrs), young controls (n=32; 21.9yrs), middle young (n=32; 49.8yrs), middle old (n=15; 58.9yrs), and old (n=30; 71.3yrs) cohorts. Participants performed maximal voluntary contractions (MVCs) of the leg extensors under isometric and isokinetic (240deg.·s-1) conditions. Outcome measures included peak torque (PT), absolute and MVC normalized (norm) rate of torque development (RTD) at 50 and 200ms, RTD50/PT ratio, and rate of velocity development (RVD). The PT and absolute RTD at 200ms declined from young to old age (P<.05). The middle age groups exhibited an overall preservation of early RTD, and a potential enhancement of early normalized RTD (P=.06 for middle young vs. controls, for RTDnorm50). The RTD50/PT ratio was higher in the middle young (P<.05) compared to both the young groups. Generally, the RVD declined more linearly and exhibited worse preservation at mid-life than the early absolute or normalized RTD variables. All absolute torque-time variables were correlated (r=0.43-0.73, P<.001) to the RVD for all groups combined. These findings showed distinct age-related declines occurred for different muscle function parameters unique to specific stages of the lifespan. Normalized RTD variables may reveal plausible mechanisms of age-related neuromuscular changes and the RTD50/PT ratio may be a useful tool for determining relative deficiencies, such that mid-life adults (45-64yrs) should address their relative limitation of PT by enhancing strength at mid-life, whereas older adults (65+ yrs) may need more emphasis on RTD improvements. In addition, both mid-life and older men should seek to improve rapid limb velocity capacities due to the susceptibility of RVD to decline more incrementally across the lifespan. Such information may help to improve anti-aging strategies by countering age-specific muscle function deficiencies and may improve mid-life adults' ability to transition better functionally into old age.

Rate of Muscle Contraction Is Associated With Cognition in Women, Not in Men.

In older persons, lower hand grip strength is associated with poorer cognition. Little is known about how the rate of muscle contraction relates to cognition and upper extremity motor function, and sex differences are understudied. Linear regression, adjusting for age, race, education, body mass index, appendicular lean mass, and knee pain, assessed sex-specific cross-sectional associations of peak torque, rate of torque development (RTD), and rate of velocity development (RVD) with cognition and upper extremity motor function. In men (n = 447), higher rate-adjusted peak torque and a greater RVD were associated with faster simple finger tapping speed, and a greater RVD was associated with higher nondominant pegboard performance. In women (n = 447), higher peak torque was not associated with any measures, but a greater RTD was associated with faster simple tapping speed and higher language performance, and a greater RVD was associated with higher executive function, attention, memory, and nondominant pegboard performance. In women with low isokinetic peak torque, RVD was associated with attention and memory. RVD capacity may reflect neural health, especially in women with low muscle strength.

The rate of velocity development associates with muscle echo intensity, but not muscle cross-sectional area in older men.

The examination of mechanisms contributing to the age-related reductions in rapid velocity development is limited. The purpose of this study was to examine the influence of muscle cross-sectional area (CSA) and echo intensity (EI) on plantarflexor rate of velocity development (RVD) in older adults. Twenty-two men (mean ± SD age = 69 ± 3years) performed three maximal plantarflexion voluntary isokinetic muscle actions at a velocity of 2.09rad·s-1. Peak RVD was determined as the peak derivative of the velocity-time curve from the onset of velocity development to the onset of the load range. B-mode ultrasound was used to examine CSA and EI from the lateral and medial gastrocnemius. Plantarflexor RVD was related to EI (r=-0.491, P = 0.020), but not CSA (r=-0.003, P = 0.989). The findings of the present investigation suggest that alterations in muscle tissue composition (i.e., increase in intramuscular fat and/or fibrous tissue) may influence the ability of older adults to rapidly accelerate their limb.

Time-dependent neuromuscular parameters in the plantar flexors support greater fatigability of old compared with younger males

Older adults are more fatigable than young during dynamic tasks, especially those that involve moderate to fast unconstrained velocity shortening contractions. Rate of torque development (RTD), rate of velocity development (RVD) and rate of neuromuscular activation are time-dependent neuromuscular parameters which have not been explored in relation to age-related differences in fatigability. The purpose was to determine whether these time-dependent measures affect the greater age-related fatigability in peak power during moderately fast and maximal effort shortening plantar flexions. Neuromuscular properties were recorded from 10 old (~78years) and 10 young (~24years) men during 50 maximal-effort unconstrained velocity shortening plantar flexions against a resistance equivalent to 20% maximal voluntary isometric contraction torque. At task termination, peak power, and angular velocity, and torque at peak power were decreased by 30, 18, and 16%, respectively, for the young (p<0.05), and 46, 28, 30% for the old (p<0.05) compared to pre-fatigue values with the old exhibiting greater reductions across all measures (p<0.05). Voluntary RVD and RTD decreased, respectively, by 24 and 26% in the young and by 47 and 40% in the old at task termination, with greater decrements in the old (p<0.05). Rate of neuromuscular activation of the soleus decreased over time for both age groups (~47%; p<0.05), but for the medial gastrocnemius (MG) only the old experienced significant decrements (46%) by task termination. All parameters were correlated strongly with the fatigue-related reduction in peak power (r=0.81–0.94, p<0.05), except for MG and soleus rates of neuromuscular activation (r=0.25–0.30, p>0.10). Fatigue-related declines in voluntary RTD and RVD were both moderately correlated with MG rate of neuromuscular activation (r=0.51–0.52, p<0.05), but exhibited a trend with soleus (r=0.39–0.41, p=0.07–0.09). Thus, time-dependent factors, RVD and RTD, are likely important indicators of intrinsic muscle properties leading to the greater age-related decline in peak power when performing a repetitive dynamic fatigue task, which may be due to greater fatigue-related central impairments for the older men than young.

Relative differences in strength and power from slow to fast isokinetic velocities may reflect dynapenia.

We compared absolute and normalized values for peak torque (PT), mean power (MP), rate of velocity development, and electromyography (EMG) amplitude during maximal isometric and concentric isokinetic leg extension muscle actions, as well as the %decrease in PT and %increase in MP from 1.05 to 3.14 rad·s(-1) in younger versus older men. Measurements were performed twice for reliability. Isokinetic measurements were normalized to the isometric muscle actions. Absolute isometric PT, isokinetic PT and MP, and EMG amplitudes at 1.05 and 3.14 rad·s(-1) were greater in the younger men, although normalizing to isometric PT eliminated the age differences. The older men exhibited greater %decrease in PT (37.2% vs. 31.3%) and lower %increase in MP (87.6% vs. 126.4%) regardless of normalization. Normalization eliminated absolute differences in isokinetic strength and power, but the relative differences from slow to fast velocities may reflect dynapenia characterized by age-related decreases in fast-twitch fiber function.

Greater Fatigability In Older Than Younger Men Is Related To The Rate Of Velocity Development

Greater Fatigability In Older Than Younger Men Is Related To The Rate Of Velocity Development

Comparisons of voluntary and evoked rate of torque development and rate of velocity development during isokinetic muscle actions

BACKGROUND: The rate of torque development (RTD) and the rate of velocity development (RVD) have previously been described as related; however, a direct comparison has not been performed. OBJECTIVE: The purposes of this study were to compare voluntary and evoked RVD and RTD during the same maximal isokinetic leg extensions muscle actions and to indirectly explore the influence of motor unit discharge frequency on these variables. METHODS: Sixteen men completed three maximal voluntary and three maximal evoked isokinetic leg extension muscle actions at 60 ◦ ·s −1 . Peak RVD, general RVD, peak RTD, and electromechanical delay (EMD) were calculated from the voluntary and evoked muscle actions. Voluntary and evoked RTD and RVD were also calculated for each 10 ms epoch up to 200 ms of the muscle actions. RESULTS:There was no interaction between voluntary and evoked RVD across time (p = 0.12), but there was an interaction for RTD ( p< 0.01). However, peak RTD occurred prior to the isokinetic load range. Peak RTD ( p< 0.001), peak RVD ( p< 0.01), general RVD ( p< 0.01), isokinetic load range ( p< 0.001), EMD ( p< 0.001), and PT ( p< 0.001) were greater for voluntary than evoked muscle actions, which was expected due to the influence of voluntary motor unit firing rates. CONCLUSIONS: Overall, these results suggested that the calculation of RTD during the acceleration phase of an isokinetic muscle action may not be valid due to the unknown load and increasing velocity. Furthermore, the RVD may be influenced by motor unit firing rate, but to a lesser extent than RTD.

Effects of Self-Selected Music on Strength, Explosiveness, and Mood

There has been much investigation into the use of music as an ergogenic aid to facilitate physical performance. However, previous studies have primarily focused on predetermined music and aerobic exercise. The purpose of this study was to investigate the effects of self-selected music (SSM) vs. those of no music (NM) on the mood and performance of the athletes performing bench press and squat jump. Twenty resistance trained collegiate men completed 2 experimental conditions, one while listening to SSM and the other with NM. The subjects reported their profile of mood states (POMS) and rating of perceived exertion (RPE) before and after performing 3 sets to failure of the bench press at 75% 1 repetition maximum (1RM) and 3 reps of the squat jump at 30% 1RM. Statistical analyses revealed no differences in squat jump height or relative ground reaction force, but the takeoff velocity (SSM-2.06 ± 0.17 m·s(-1); NM-1.99 ± 0.18 m·s(-1)), rate of velocity development (SSM-5.92 ± 1.46 m·s(-2); NM-5.63 ± 1.70 m·s(-2)), and rate of force development (SSM-3175.61 ± 1792.37 N·s(-1); NM-2519.12 ± 1470.32 N·s(-1)) were greater with SSM, whereas RPE (SSM-5.71 ± 1.37; NM-6.36 ± 1.61) was greater with NM. Bench press reps to failure and RPE were not different between conditions. The POMS scores of vigor (SSM-20.15 ± 5.58; NM-17.45 ± 5.84), tension (SSM-8.40 ± 3.99; NM-6.07 ± 3.26), and fatigue (SSM-8.65 ± 4.49; NM-7.40 ± 4.38) were greater with SSM. This study demonstrated increased performance during an explosive exercise and an altered mood state when listening to SSM. Therefore, listening to SSM might be beneficial for acute power performance.

Rate Of Velocity Development Less Decreased Following The Repeated Bout Of Maximal Eccentric Exercise

It has been reported that rate of velocity development (RVD) and strength are two of important measures of athletic performance, and eccentric exercise-induced muscle damage can be impaired RVD and strength performance (Nguyen et al., 2009 JSRC). It is well-documented that a bout of eccentric exercise confers protection against muscle damage after a subsequent bout of the same exercise performed several weeks to several months later (Clarkson et al., 1992 MSSE), but no study has examined effect of repeated bout of eccentric exercise on changes in RVD. PURPOSE: This study was to test the hypothesis that a repeated bout of maximal eccentric exercise of the elbow flexors would be less decreased RVD and faster recovery in comparison with the first bout. METHODS: Ten untrained young men (21.0 ± 3 yrs) performed 2 bouts of 30 maximal eccentric exercises (MAX1 & MAX2; 30°/s) of the elbow flexors of the non-dominant arm separated by 2 weeks. Maximal isokinetic concentric strength (MVC) and RVD (300°/s), muscle soreness, and range of motion were measured before, immediately after, and for 5 consecutive days after each bout. All data was analyzed by a two-way repeated measures ANOVA. RESULTS: The first bout of maximal eccentric exercise produced significant (P<0.05) decrease in maximal concentric strength (39%), RVD (49%), range of motion, and increase in muscle soreness. The changes in all criterion measures (e.g. MVC: 30%, RVD: 44%) after the second bout of the same exercise were significantly smaller (P<0.05) than that of the first bout. CONCLUSION: These results supported that MAX1 induced significantly muscle damage and soreness would be affected RVD, and protective effect occurred following the first bout of eccentric exercise results in a smaller decrease in RVD and faster recovery when the exercise is repeated after 2 weeks.