Peak Isometric Force Research Articles

Recovery Patterns in Electroencephalographic Global Field Power During Maximal Isometric Force Production

In previous work, cortical activity decreased with fatigue following novel movements or small muscle group actions. These muscle actions, however, do not appear related to the cortical activity seen with biologically relevant and highly trained movement patterns (i.e., ingrained patterns). The cortical recovery response to ingrained patterns-and how it differs with altered load, speed, or volume - is unknown. The purpose of this balanced, within-group study was to investigate differences in cortical activity 24 hours after physically distinct variations of a highly trained squat exercise (n = 7, minimum 4 years resistance training experience). Four resistance protocols were chosen: rate of force development (PWR, 6 × 3 squat jumps at 30% of 1 repetition maximum [1RM]); magnitude of force development (FOR, 6 × 3 squat at 95% of 1RM); volume of force development (VOL, 6 × 10 squat at 80% of their 1RM); and control (CTRL, 6 sets unracking an empty bar). Twenty-four hours later, subjects performed a peak isometric squat while electroencephalographic and biochemical markers of exertion and fatigue were obtained. Global field power detected the quantity of activity superficial to motor regions. Waveforms of activity throughout the isometric squats were obtained and grand averages calculated to produce quantitative depictions of cortical activity. Significance was P ≤ 0.05. Peak isometric squat force was not statistically different 24 hours postexercise (Force [N]: PWR: 2828.79 ± 461.17; FOR: 2887.64 ± 453.09; VOL: 2910.17 ± 625.81; CTRL 2768.53 ± 374.85). Subjects produced similar and characteristic cortical activity patterns during isometric squats despite varying indices of fatigue. Differences were observed based upon the use or nonuse of aerobic endurance exercise in their training program. Patterns of activity in data seem to have emerged based on differences in training preference. Global Field Power (uV) during the isometric squat for PWR was 26.98 ± 14.64; FOR 24.06 ± 19.05; VOL 23.05 ± 13.37; and CTRL 15.78 ± 8.11. Previous research suggests that cortical activity decreases with physical activity; however, despite substantial endocrine, perceptual, and biomechanical differences between protocols, cortical activity was not decreased below control during the performance of a maximal isometric squat 24 hours after various exercise protocols.

A mass–length scaling law for modeling muscle strength in the lower limb

Musculoskeletal computer models are often used to study muscle function in children with and without impaired mobility. Calculations of muscle forces depend in part on the assumed strength of each muscle, represented by the peak isometric force parameter, which is usually based on measurements obtained from cadavers of adult donors. The aim of the present study was twofold: first, to develop a method for scaling lower-limb peak isometric muscle forces in typically-developing children; and second, to determine the effect of this scaling method on model calculations of muscle forces obtained for normal gait. Muscle volumes were determined from magnetic resonance (MR) images obtained from ten children aged from 7 to 13 yr. A new mass–length scaling law was developed based on the assumption that muscle volume and body mass are linearly related, which was confirmed by the obtained volume and body mass data. Two musculoskeletal models were developed for each subject: one in which peak isometric muscle forces were estimated using the mass–length scaling law; and another in which these parameters were determined directly from the MR-derived muscle volumes. Musculoskeletal modeling and quantitative gait analysis were then used to calculate lower-limb muscle forces in normal walking. The patterns of muscle forces predicted by the model with scaled peak isometric force values were similar to those predicted by the MR-based model, implying that assessments of muscle function obtained from these two methods are practically equivalent. These results support the use of mass–length scaling in the development of subject-specific musculoskeletal models of children.

Low Vitamin D Impairs Strength Recovery After Anterior Cruciate Ligament Surgery

The purpose of this study was to identify strength gains after an anterior cruciate ligament injury and surgery and during inflammatory challenge in participants with disparate vitamin D levels. Plasma samples were obtained from those who had not previously experienced an anterior cruciate ligament injury and from injured patients 2 weeks before and 3 months after anterior cruciate ligament surgery. Plasma 25-hydroxyvitamin D and cytokine concentrations were measured in each blood sample. Single-leg peak isometric forces were measured 2 weeks presurgery and 3 months postsurgery. Compared with noninjured participants, inflammatory cytokines were elevated prior to and following anterior cruciate ligament reconstruction. During this inflammatory challenge, the peak isometric force increases after surgery were significantly lower in those with plasma 25-hydroxyvitamin D concentrations <30 ng/mL compared with those with concentrations ≥30 ng/mL. The authors conclude that low vitamin D appears to hinder strength recovery after anterior cruciate ligament surgery and during inflammatory insult.

A mathematical model of force transmission from intrafascicularly terminating muscle fibers

Many long skeletal muscles are comprised of fibers that terminate intrafascicularly. Force from terminating fibers can be transmitted through shear within the endomysium that surrounds fibers or through tension within the endomysium that extends from fibers to the tendon; however, it is unclear which pathway dominates in force transmission from terminating fibers. The purpose of this work was to develop mathematical models to (i) compare the efficacy of lateral (through shear) and longitudinal (through tension) force transmission in intrafascicularly terminating fibers, and (ii) determine how force transmission is affected by variations in the structure and properties of fibers and the endomysium. The models demonstrated that even though the amount of force that can be transmitted from an intrafascicularly terminating fiber is dependent on fiber resting length (the unstretched length at which passive stress is zero), endomysium shear modulus, and fiber volume fraction (the fraction of the muscle cross-sectional area that is occupied by fibers), fibers that have values of resting length, shear modulus, and volume fraction within physiologic ranges can transmit nearly all of their peak isometric force laterally through shearing of the endomysium. By contrast, the models predicted only limited force transmission ability through tension within the endomysium that extends from the fiber to the tendon. Moreover, when fiber volume fraction decreases to unhealthy ranges (less than 50%), the force-transmitting potential of terminating fibers through shearing of the endomysium decreases significantly. The models presented here support the hypothesis that lateral force transmission through shearing of the endomysium is an effective mode of force transmission in terminating fibers.

Isometric Peak Force of Shoulder Rotators in Cricketers with and without History of Shoulder Pain

Isometric Peak Force of Shoulder Rotators in Cricketers with and without History of Shoulder Pain

Changes in Relationship Between Static Jump Height, Strength Characteristics, and Body Composition with Training

The ability to jump is an important characteristic in volleyball. The relationship between factors associated with vertical jump height and how they change as an athlete develops from generally untrained (incoming freshman) to trained as part of a periodized conditioning program is not well known. PURPOSE: To analyze how the relationship of body composition, maximum strength, and strength characteristics with static weighted (20kg) and un-weighted vertical jumps changes as an athlete increases explosive strength (as measured by vertical jump height). METHODS: Data from seventeen female NCAA DI volleyball players collected from 2007-2010 as part of an ongoing athlete monitoring program was analyzed. Body composition was measured via air displacement plethsmography. Maximum strength (isometric peak force - IPF) and strength characteristics (peak force [email protected] 50ms, 90ms, and 250ms; rate of force development, 0-200ms -RFD) were measured with isometric mid-thigh pulls on a force plate, and static jumps with 0 and 20kg. Jump height was determined through flight time using a force plate. Allometric scaling of the different force values (IPFa, [email protected], [email protected], [email protected]) was used to normalize differences in the body mass of the athletes (absolute force/ (body mass (kg0.67)). Correlations (Pearson) were used to determine the strength of relationships and paired t-tests were used to determine differences in explosive strength over time. RESULTS: Over three years, there was a significant increase (p≤0.01) in un-weighted jump height (23.5±2.8 to 27.1±4.5), jump height with 20kg (15.7±2.8cm to 19.9±4.5cm, IPF (2584±425N to 2941±578N), and IPFa (152±21N /kg0.67 to 172±3021N /kg0.67). Correlations increased in magnitude between: un-weighted vertical jump height and IPF (-0.26 to 0.34), IPFa (-0.14 to 0.41), [email protected] (0.02 to 0.53), [email protected](0.11 to 0.54) and RFD (0.10 to 0.51); and vertical jump height with 20kg and IPF (0.05 to 0.48), IPFa (0.14 to 0.57). Correlations decreased in magnitude between both vertical jump conditions (0kg and 20kg) and % body fat (0kg: -0.73 to -0.61, 20kg -0.61 to -0.54). CONCLUSIONS: As strength increases throughout the athletes' collegiate career their relationship to jumping ability becomes stronger. The relationship between % body fat and jump height decreases with no change in % body fat.

Physical Profile Of Flemish Youth And Olympic-class Sailors

PURPOSE: In this study, the physical characteristics of 53 Flemish youth and Olympic-class sailors was related to their class of vessel and their ranking of sailing performance (based on national rankings). METHODS: The anthropometric profile (height, weight, BMI and fat %) of 53 Flemish sailors, including 11 male optimist and 10 male Laser Radial sailors, was determined. They also performed an isokinetic test (Iso) and incremental exercise protocol (IEP). The Iso consisted of 3 exercise protocols: (1) Three alternating 5 s maximal unilateral (Max Un) isometric knee extensions and flexions were performed for both legs, with 90 s recuperation time between each contraction. All contractions were performed at 60° knee flexion and 120° hip angle. (2) Five Max Un concentric knee extension-flexions were performed for both legs at angular velocity (ω) 30°·s-1, over range of motion (ROM) 20° - 70° knee flexion. Hip angle measured 120°. (3) Five Max Un eccentric knee extension-flexions were performed for both legs at ω 30°·s-1, over ROM 20° - 70° knee flexion. Hip angle was again kept at 120°. Two IEP's were used. Athletes < 16 yr performed a ramp IEP and athletes ≥ 16 yr performed a step IEP. Spearman's rho correlation coefficient (CC) and multiple regression were conducted for statistical analysis. RESULTS: The results show for both male optimist and male Laser Radial group a significant correlation between ranking and maximal isometric Quadriceps peak force of the right leg (Isom Q R). CC were respectively -0,664 (p = 0,026) and -0,691 (p = 0,019). Also, for both groups resp. 41,9 % and 56,4 % of the variation in ranking scores was accounted by Isom Q R (equations were resp. Y = 23,918 - 0,105 X and Y = 16,569 - 0,041 X). In addition, mean conventional isometric H/Q-ratio (benchmark = 60 %) and functional H/Q-ratio (benchmark = 100 %) for all sailors were resp. 42,7 ± 7,8 % and 79,0 ± 16,8 %. CONCLUSIONS: This study shows the importance of maximal isometric Quadriceps force concerning sailing performance. However, the Hamstring muscles show a limited capacity for knee joint stabilization, which suggests sailors need to strengthen their Hamstring muscles to prevent the incidence of knee injuries. Supported by the Flemish Government, Ministry of Culture, Youth, Sport and Media. Project title: Olympic Dinghy Sailing 2009-2012

Disparate velocity and force responses at peak power following muscle damage

The velocity and force at peak power are important determinants of muscle function. The purpose of this study was to identify the influence of muscle damage on the velocity and force at peak power. To induce muscle damage, one leg from each subject (n = 8) was randomly selected to perform an intense stretch-shortening contraction (SSC) protocol on a custom horizontal plyo-press. The SSC protocol (treatment) consisted 10 sets of 10 jumps at 75% of bwt with a 20-sec rest between each set. The contra-lateral control (CON) leg did not perform the SSC protocol. Peak isometric force and power output were measured immediately before (baseline) and 5-min, 24-h, 48-h, 72-h and 168-h (7-d) after the SSC protocol on each leg separately. Compared to the corresponding CON leg values and the SSC leg at baseline, we observed immediate (5-min) and persistent (24-h to 72-h) decreases (P < 0.001, treatment x time interaction) in peak isometric forces following the SSC protocol. Forces at peak power were decreased (P < 0.001, treatment x time interaction) at 5-min and 48-h after the SSC protocol. In addition to deficits at 5-min and 48-h, velocities at peak power were decreased (P < 0.001, treatment x time interaction) at 24-h and 72-h. In conclusion, velocity and force impairments at peak power displayed disparate temporal responses during muscle damage-induced weakness. Sources of support: Deseret Foundation, UT

Inhibition of TGF‐β promotes the early recovery of force following contraction‐induced skeletal muscle injury

Transforming Growth Factor-β (TGF-β) is a cytokine liked to fibrosis and other inflammatory processes in many tissues. Previous studies have shown detrimental effects of TGF-β on skeletal muscle in vivo, including fibrosis, atrophy, and decreased force. Thus, inhibition TGF-β may be beneficial to muscle function. We hypothesized that inhibition of TGF-β would promote muscle regeneration following injury. Extensor digitorum longus muscles of adult, male C57Bl/6 mice were subjected to an in situ lengthening-contraction protocol to induce injury. Intraperitoneal injections of 1D11, a murine monoclonal bio-neutralizing IgG antibody against TGF-β, or equivalent amounts of a sham murine IgG were administered immediately following injury and again every three days after injury. Peak isometric force was measured before, immediately after, and 7 days post injury. Compared with contralateral control muscles, mass of injured muscles from mice that received 1D11 were 12% lower while injured muscles from sham treated mice were 19% lower. Additionally, compared with pre-injury force values, mice receiving 1D11 showed a 30% greater recovery in force production than sham treated mice. The results indicate that the therapeutic inhibition of TGF-β following contraction-induced muscle injuries may help promote the early recovery of force production. Supported by AR-058920 and AR-055624.

Strength and neuromuscular adaptation following one, four, and eight sets of high intensity resistance exercise in trained males

The optimal volume of resistance exercise to prescribe for trained individuals is unclear. The purpose of this study was to randomly assign resistance trained individuals to 6-weeks of squat exercise, prescribed at 80% of a 1 repetition-maximum (1-RM), using either one, four, or eight sets of repetitions to failure performed twice per week. Participants then performed the same peaking program for 4-weeks. Squat 1-RM, quadriceps muscle activation, and contractile rate of force development (RFD) were measured before, during, and after the training program. 32 resistance-trained male participants completed the 10-week program. Squat 1-RM was significantly increased for all groups after 6 and 10-weeks of training (P < 0.05). The 8-set group was significantly stronger than the 1-set group after 3-weeks of training (7.9% difference, P < 0.05), and remained stronger after 6 and 10-weeks of training (P < 0.05). Peak muscle activation did not change during the study. Early (30, 50 ms) and peak RFD was significantly decreased for all groups after 6 and 10-weeks of training (P < 0.05). Peak isometric force output did not change for any group. The results of this study support resistance exercise prescription in excess of 4-sets (i.e. 8-sets) for faster and greater strength gains as compared to 1-set training. Common neuromuscular changes are attributed to high intensity squats (80% 1-RM) combined with a repetition to failure prescription. This prescription may not be useful for sports application owing to decreased early and peak RFD. Individual responsiveness to 1-set of training should be evaluated in the first 3-weeks of training.

EEG Measures of Cortical Activity Return to Baseline Within 24 Hours Despite Differential Protocols Emphasizing Force, Power, and Volume

PURPOSE: While a clearer image of the physiological process of recovery from physical exertion is emerging, research into the recovery of the central nervous system is still in its infancy. The purpose of this study was to investigate the nature of motor cortical activity and peak force production 24 hours after resistance exercise. METHODS: Four resistance training protocols were chosen based on their differential interaction with force production: high power (6 x 3 squat jumps at 30% of 1RM); high force (6 x 3 squat at 95% of 1RM); high volume (6 x 10 at 80% of their 1RM); and a control day (6 sets of unracking an empty bar). Twenty-four hours after the intervention, subjects returned to perform a peak isometric squat along with corresponding EEG, perceptual, and blood measures. To control for the rate of adaptation, only highly trained male subjects (years of training: 6+/−1 yrs; squat 1RM: 174+/−26 kg; age: 22+/−3 yrs; body mass: 84.76+/−9.86 kg; n = 7) were included in this study. Cortical activity was measured using an Ag-AgCl electrode-cap, a 40-channel monopolar digital amplifier, and an expanded International 10–20 electrode placement. Linked-ears reference, a ground scalp electrode, and eye electrodes were used to account for electrical artifacts (facial contractions). Movement artifacts were removed using a spatial filter. A 32-bit analog-to-digital converter was used to digitize signals at a sampling rate of 1000hz. High and low frequency bandpass was set at DC and 100hz respectively and signals were low-pass filtered at 50hz using an Infinite Impulse Response (IIR) recursive filter set to a roll-off of 12dB/oct. Impedance was maintained at or below 5 Kohms throughout the experimental protocol. Channels possessing gross artifacts were eliminated. DC drift was removed using a 3rd order polynomial trend correction for each channel. Epochs were set from the completion of the previous movement or the movement of the bar off the rack to the completion of the next repetition. Pearson product-moment correlation coefficients were determined for selected pair wise variables. One-way and univariate analyses of variance (ANOVA) with repeated measures and Fisher's LSD post-hocs were used to detect significant mean differences. Significance level in this study was set at a 0.05 alpha level. RESULTS: Peak isometric squat force was equated by 24 hours post-exercise. The grand average movement related cortical potential area under the curve and mean global field power amplitude were also equated between recovery protocols. Despite the differences between each protocol, we were unable to detect statistically significant differences (in either mean amplitude or area under the curve) for global field power during isometric squats at an alpha level of 0.05. Therefore, the primary finding of this investigation was that 24 hours after differing maximal exertion force production protocols, cortical activity and peak force appear to recover to baseline. CONCLUSIONS: In the present study, the cortical findings suggest that the central responses of well-trained men recover from differing domains of resistance exercise within twenty-four hours. Practical Applications: It is possible that the central nervous system recovers quickly from resistance exercise in the well-trained population. Other limitations to physiological recovery, such as performance decrement, soreness, or fatigue, may be attributable to peripheral, rather than central, causes. Primary damage, particularly with eccentric movement, cannot be ignored. In addition, our laboratory has shown that exercise-induced hypoxia results in secondary damage to muscle through a series of biochemical reactions. The role of the central nervous system in the control of physiological function cannot be underestimated, and this study should be placed appropriately within the context of this evolving area of research.

Relationship Between Force-Time and Velocity-Time Characteristics of Dynamic and Isometric Muscle Actions

Previous research has investigated the force-time curve characteristics of isometric and dynamic muscle actions; however, few studies have addressed their relationship to dynamic exercise velocity-time variables. The purpose of this study was to investigate relationships between velocity-time characteristics (high pull and vertical jump peak velocity and rate of velocity development [HPPV, HPRVD, VJPV, VJRVD]), force-time characteristics (isometric peak force [IsoPF], body mass adjusted isometric peak force [IsoPF/BM], isometric rate of force development at different millisecond windows [IsoRFD50-250], dynamic peak force [HPPF], body mass adjusted dynamic peak force [HPPF/BM]), and vertical jump height (VJHeight). Nineteen recreationally trained men (age 23.89 ± 2.92 yr; height 176.32 ± 7.06 cm; mass 78.76 ± 16.50 kg) completed 2 testing sessions. The first session consisted of 3 isometric mid-thigh pulls on a force plate with each repetition held for 3 seconds. On the second testing session, subjects completed 3 dynamic mid-thigh high pulls with 30% IsoPF followed by 3 vertical jumps on a force plate. The HPRVD correlated with IsoRFD50 (r = 0.52) and IsoRFD100 (r = 0.49). The HPPV correlated with IsoPF/BM (r = -0.60), IsoRFD50 (r = 0.56), and IsoRFD100 (r = 0.56). The VJHeight correlated with IsoPF/BM (r = 0.61), whereas VJPV correlated with IsoPF/BM (r = 0.62). These correlations suggest that explosive isometric force production within 50 to 100 milliseconds may influence the ability to accelerate an implement or body and attain high velocity, albeit in a moderate fashion. In addition, body mass adjusted strength may positively influence vertical jump parameters.

Influence of a Single Swim Training on the Scapular Position and Isometric Muscle Strength in Young Swimmers

The purpose of our study was to investigate the influence of one swim training on isometric scapular muscle strength and the static position of the scapula in a sample of 30 healthy adolescent swimmers who were measured on two sessions at a local aquatic center. Fatigue as result of a single swim training may influence scapular position and strength. Measures included isometric evaluation of serratus anterior and upper trapezius peak isometric force using a push and shrug procedure, serratus anterior to upper trapezius strength ratios, and a semi-dynamic evaluation of lateral scapular displacement employing the Kibler method. When tested using a repeated measures ANOVA, none of the strength parameters changed significantly as a result of the single swim training. Adolescent swimmers did employ higher values for the serratus anterior than for the upper trapezius. In the three positions of the LSST, the lateral displacement of the scapula increased significantly after the training (p = .001, p < .001, p < .001) and a minor scapular asymmetry was found. (p = .037, p = .011, p = .005). The highest LSST values were present on the dominant side, at both test moments.

Reliability of a new hand-held dynamometer in measuring shoulder range of motion and strength

Acceptable reliability is a prerequisite for inclusion of physical examination tests in clinical examinations of the painful shoulder. The aim of this study was to establish the intraexaminer and interexaminer reliability of measures of shoulder range of motion (ROM) and muscle force using a new hand-held dynamometer with the ability to standardize overpressure force during passive ROM tests. Forty consecutive subjects with shoulder pain were recruited, and tests were performed by two physiotherapists. Tests included active ROM elevation, passive ROM glenohumeral abduction and external rotation and resisted abduction and external rotation. All tests demonstrated high levels of intraexaminer reliability (ICC 0.85–0.99; LOA 6–24° and 1.1–7.0 kg). Highest levels of interexaminer reliability reliability were observed for measures of active ROM flexion (ICC 0.88–0.95; LOA 14–22°). Passive ROM tests demonstrated ’moderate – substantial’ interexaminer reliability (ICC 0.45–0.62; LOA 25–34°). The ICCs for resisted tests ranged from 0.68 to 0.84, and LOA ranged from 3.2 to 8.5 kg. Active ROM flexion demonstrated high levels of both intra- and interexaminer reliability. Measures of passive ROM and peak isometric force demonstrated acceptable levels of intraexaminer reliability.

The ultrastructure and contractile properties of a fast-acting, obliquely striated, myosin-regulated muscle: the funnel retractor of squids.

We investigated the ultrastructure, contractile properties, and in vivo length changes of the fast-acting funnel retractor muscle of the long-finned squid Doryteuthis pealeii. This muscle is composed of obliquely striated, spindle-shaped fibers ~3 mum across that have an abundant sarcoplasmic reticulum, consisting primarily of membranous sacs that form 'dyads' along the surface of each cell. The contractile apparatus consists of 'myofibrils' approximately 0.25-0.5 microm wide in cross section arrayed around the periphery of each cell, surrounding a central core that contains the nucleus and large mitochondria. Thick myofilaments are approximately 25 nm in diameter and approximately 2.8 microm long. 'Dense bodies' are narrow, resembling Z lines, but are discontinuous and are not associated with the cytoskeletal fibrillar elements that are so prominent in slower obliquely striated muscles. The cells approximate each other closely with minimal intervening intercellular connective tissue. Our physiological experiments, conducted at 17 degrees C, showed that the longitudinal muscle fibers of the funnel retractor were activated rapidly (8 ms latent period following stimulation) and generated force rapidly (peak twitch force occurred within 50 ms). The longitudinal fibers had low V(max) (2.15 +/-0.26 L(0) s(-1), where L(0) was the length that generated peak isometric force) but generated relatively high isometric stress (270+/-20 mN mm(-2) physiological cross section). The fibers exhibited a moderate maximum power output (49.9 W kg(-1)), compared with vertebrate and arthropod cross striated fibers, at a V/V(max) of 0.33+/-0.044. During ventilation of the mantle cavity and locomotion, the funnel retractor muscle operated in vivo over a limited range of strains (+0.075 to -0.15 relative to resting length, L(R)) and at low strain rates (from 0.16 to 0.91 L(R) s(-1) ), corresponding to a range of V/V(max) from 0.073 to 0.42. During the exhalant phase of the jet the range of strains was even narrower: maximum range less than +/-0.04, with the muscle operating nearly isometrically during ventilation and slow, arms-first swimming. The limited length operating range of the funnel retractor muscles, especially during ventilation and slow jetting, suggests that they may act as muscular struts.

Sustained performance by red and white muscle fibres from the dogfish Scyliorhinus canicula

The mechanical performance of red and white muscle fibres from dogfish was compared during a long series of contractions with sinusoidal movement or under isometric conditions at 12 degrees C (normal in vivo temperature). Power output was measured during sinusoidal movement at 0.75 Hz and peak-to-peak amplitude about 12% L(0). Tetanus duty cycle was 33% (0.44 s) at phase -8% (first stimulus at 0.107 s before shortening started). Initially, the red fibres produced only about one third as much power as the white fibres, 6.57+/-0.63 W kg(-1) wet mass (mean +/- s.e.m.) and 18.3+/-2.3, respectively. Red fibres were better at sustaining power output; it declined rapidly to about 60% of its initial value and then remained relatively steady for up to 450 cycles of movement. Force during shortening declined, but force during stretch did not increase: force always relaxed to a low value before stretch started. By contrast, net power output by white fibres declined rapidly to zero within about 50 cycles. Two changes contributed: decline in force during shortening and an increase in force during stretch because relaxation became progressively less complete during the series of contractions. In isometric series (0.44 s stimulation every 1.33 s, cycle frequency 0.75 Hz), red and white fibres sustained peak isometric force similarly; in the 50th cycle force was 59+/-3% and 56+/-4% of initial values. The time required for force to relax to 10% of its maximum value decreased during the series for red fibres and increased for white fibres.

Treatment of refractory anterior knee pain using botulinum toxin type A (Dysport) injection to the distal vastus lateralis muscle: a randomised placebo controlled crossover trial

ObjectivesThis randomised controlled crossover trial examined the efficacy of botulinum toxin type A (BoNT-A) injection, plus an exercise programme, to remediate chronic anterior knee pain (AKP) associated with quadriceps muscle...

Effects of 8 weeks of vibration training at different frequencies (1 or 15 Hz) in senior sportsmen on torque and force development and of 1 year of training on muscle fibers

Objective: To examine the effects of 8 weeks of vibration training at different frequencies (1 and 15 Hz) on maximal isometric torque and force development in senior sportsmen, and of 1 year of heavy-resistance and vibration trainings on muscle fibers.Methods: Seven healthy senior sportsmen (mean age: 69·0 ± 5·4 years) performed an 8 weeks of strength training of knee extensors. Vibrations were applied vertically to the axis of movement during training. One leg of each subject was trained at a frequency of 1 Hz, while the other leg was trained at 15 Hz. Measures of isometric peak torque (at knee-angles of 60, 90 and 120°) and force development were recorded before and after training. Four sportsmen continued a year-long heavy-resistance training adding every second week a session of vibration training. After training, muscle biopsies were harvested from their quadriceps muscles and used for structural analyses. Morphometry of muscle fibers was performed by light microscopy. Immunohistochemistry using anti-MHCemb and anti-N-CAM antibodies was performed to measure potential muscle damage. Data from muscle morphometry were compared to that of a series of vastus lateralis biopsies harvested from 12 young sportsmen and four healthy elderly.Results: Our results showed a significant increase in isometric peak torque at both 1 and 15 Hz vibration frequency in all three measured angles of the knee. There was no significant difference between the two frequencies, but we could find a higher increase in percentage of maximum power after the 1 Hz training. The results of force development showed a slight increase at the 1 Hz training in measured time frames from 0 to 50 and 200 ms, without statistical significance. A trend to significance was found at the 1 Hz training at the time window up to 200 ms. The 15 Hz training showed no significant changes of force development. Muscle biopsies show that the muscles of these well trained senior sportsmen contain muscle fibers which are 35% larger than those of sedentary elderly and, unexpectedly, 10% larger than those of young sportsmen. Despite 1 year of heavy resistance and vibration training, no evidence of muscle damage or denervation/reinnervation could be observed by light microscopy analyses, ATPase histochemistry and immunohistochemistry using anti-N-CAM or anti-MHC-emb antibodies.Discussion: Integration of vibration to conventional strength training in elderly sportsmen induces similar improvement of isometric peak torque and force development independently from the vibration frequency after 8 weeks of training, and long-term results in the surprising evidence of hypertrophic muscle fibers larger than those of young active sportsmen. The observation that the vibration training with low frequency is safe opens the possibility to test these rehabilitation procedures in sedentary elderly.

The Relationship Between The Eccentric Utilization Ratio, Reactive Strength, And Pre-Stretch Augmentation And Selected Dynamic And Isometric Muscle Actions.

The ability to use the stretch shortening cycle (SSC) is essential for many sporting activities. There are several approaches by which to assess the SSC. These include the eccentric utilization ratio (EUR), the reactive strength calculation (RSC), and the percent pre-stretch augmentation (PPA). These measures are typically quantified for vertical jump displacements and power outputs. The assessment of the SSC activity via jumping activities may yield valuable information of the athletes training status and potential training interventions to improve SSC performance. To determine if EUR, RSC and PPA are related to dynamic and isometric muscle actions. Twenty seven college track athletes (age = 19.6 ± 1.0 y; body mass = 83.0 ± 25.2 kg; height = 176.9 ± 8.8 cm) performed three types of countermovement vertical jumps (CMJ) and static vertical jumps (SJ) on a force plate. Both CMJ and SJ were performed in unloaded and loaded (11 kg and 20 kg) conditions. All jump data were analyzed for vertical displacement, peak force (PF), and rate of force development (RFD). The EUR (CMJ/SJ), RSC (CMJ-SJ), and PPA ((CMJ-SJ)/SJ) × 100) were calculated for jump height, peak power, and peak force Additionally, subjects performed 2 isometric mid-thigh pull with previously established methods. The isometric mid-thigh pulls were analyzed for PF and RFD. Finally, each subject performed a one repetition maximum back squat test (1-RM) and a maximal ball throw test. There were no significant correlations between the EUR (jump height, PP, PF) for loaded or unloaded jumps and back squat, ball throw, isometric PF, and RFD. All EUR values were above 1, which is indicative of well trained athletes. Significant inverse relationships were found between the PPA calculation for PF during the unloaded condition and squat 1-RM (r = −0.85), ball throw distance (r = −0.74), and isometric PF (r = −0.55). Additionally, during the loaded conditions (11 and 20 kg) the PPA calculation for PF was significantly correlated with the back squat 1-RM (11 kg: r = −0.89; 20kg: r = −0.81), ball throw distance (11 kg: r = −0.824; 20kg: r = −0.65), isometric PF (11kg:r = −0.60; 20kg: r = −0.56), and the isometric RFD (11kg: r = −0.43; 20kg:r = −0.36). The PPA calculation for peak power during the loaded conditions was significantly correlated with the 1-RM back squat (11kg; r = −0.89; 20kg: r = −0.62), ball throw (11kg: r = −0.72; 20kg: r = −0.56), isometric PF (11kg: r = −0.47; 20kg:r = −0.40), isometric RFD (11kg: r = −0.43; 20kg: r = −0.42). The isometric RFD can be estimated by the equation: RFD = −58168.7 (PPA for PP 11kg) + 10866.415 or RFD = −142636.9 (PPA for PP 20 kg) + 10340.226. This study suggests that unloaded or loaded PPA has a relationship with an athlete's 1-RM in the back squat, the ball throw distance, and isometric PF generating capacity. Additionally, under loaded conditions the PPA appears to be related to the isometric RFD. The utilization of CMJ and SJ testing is common place in strength and conditioning and the data calculated from these measures may yield valuable information about performance capacity. The significant relationship between the 1-RM back squat and PPA suggests that strength is an underlying mechanism in the ability to utilize the SSC. Additionally, the PPA assessment may be useful in predicting the isometric RFD.

Vitamin D Status Is Not Associated with Outcomes of Experimentally-Induced Muscle Weakness and Pain in Young, Healthy Volunteers

Vitamin D receptors have been identified in skeletal muscle; and symptoms of vitamin D deficiency include muscle weakness and pain. Moreover, increased serum 25-hydroxyvitamin D (25(OH)D) concentrations have been associated with improved muscle function. To further clarify the importance of vitamin D to muscle, we examined the association between vitamin D status and exercise-induced muscle pain and weakness in healthy people. Muscle damage to the elbow flexors was induced with eccentric exercise (EE) in 48 individuals (22.5 ± 3.2 yrs). Muscle pain ratings following unloaded movement and peak isometric force (IF) were collected before EE and for 4 days post-EE. Linear regression was used to determine if serum 25(OH)D was a predictor of any outcome. In males, R 2-values from 0.48 to 1.00. R 2 for IF ranged from 0 to 0.02 and P-values from 0.48 to 1.00. In females, R 2 for pain ratings ranged from 0.01 to 0.11 and P-values from 0.14 to 0.59. R 2 for IF ranged from 0 to 0.04 and P-values from 0.41 to 0.90. In conclusion, vitamin D status did not predict muscle pain or strength after EE-induced muscle damage in young healthy men and women.