Isometric Rate Of Force Development Research Articles

The efficacy of periodised resistance training on neuromuscular adaptation in older adults.

This study compared the effect of periodised versus non-periodised (NP) resistance training on neuromuscular adaptions in older adults. Forty-one apparently healthy untrained older adults (female=21, male=20; 70.9±5.1 years; 166.3±8.2cm; 72.9±13.4kg) were recruited and randomly stratified to an NP, block periodised (BP), or daily undulating periodised (DUP) training group. Outcome measures were assessed at baseline and following a 22-week resistance training intervention (3 day week-1), including: muscle cross-sectional area (CSA), vertical jump performance, isometric and isokinetic peak torque, isometric rate of force development (RFD), and muscle activation. Thirty-three participants satisfied all study requirements and were included in analyses (female=17, male=16; 71.3±5.4 years; 166.3±8.5cm; 72.5±13.7kg). Block periodisation, DUP, and NP resistance training induced statistically significant improvements in muscle CSA, vertical jump peak velocity, peak power and jump height, and peak isometric and isokinetic torque of the knee extensors at 60 and 180° s-1, with no between-group differences. Muscle activity and absolute RFD measures were statistically unchanged following resistance training across the entire cohort. Periodised resistance training, specifically BP and DUP, and NP resistance training are equally effective for promoting increases in muscular hypertrophy, strength, and power among untrained older adults. Consequently, periodisation strategies are not essential for optimising neuromuscular adaptations during the initial stages of resistance training in the aging population.

Sensory-motor training targeting motor dysfunction and muscle weakness in long-term care elderly combined with motivational strategies: a single blind randomized controlled study

BackgroundThis study evaluated the effects of a combined innovative training regime consisting of stochastic resonance whole-body vibration (SR-WBV) and a dance video game (DVG) on physical performance and muscle strength in long-term-care dwelling elderly.MethodsThirthy long-term-care elderly were randomly allocated to an intervention group (IG; n = 16) receiving combined SR-WBV training and DVG, or a sham group (SG; n = 14). IG performed five sets one minute of SR-WBV, with one minute rest between sets (base frequency 3 Hz up to 6 Hz, Noise 4) during the first five weeks on three days per week. From week five to eight a DVG was added to SR-WBV for IG on three days per week. SG performed a five-set SR-WBV program (1 Hz, Noise 1) lasting five times one minute, with one minute rest in between, three days a week. From week five to eight stepping exercises on a trampoline were added on three days per week. Primary outcome: Short physical performance battery (SPPB). Secondary outcome: isometric maximal voluntary contraction (IMVC), and sub phases of IMVC (Fsub), isometric rate of force development (IRFD) and sub time phases of IRFD (IRFDsub) were measured at baseline, after four and eight weeks. ANOVA with repeated measures was used for analyses of time and interaction effects and MANOVA determined between group intervention effects.ResultsBetween group effects revealed significant effects on the SPPB primary outcome after four weeks F(1, 27) = 6.17; p = 0.02) and after eight weeks F(1,27) = 11.8; p = 0.002). Secondary muscle function related outcome showed significant between group effects in IG on IRFD, Fsub 30 ms, 100 ms, 200 ms and IRFDsub 0-30 ms, 0-50 ms, 0-100 ms and 100-200 ms compared to SG (all p < 0.05).ConclusionsEight weeks SR-WBV and DVG intervention improved lower extremity physical function and muscle strength compared to a sham intervention in long-term-care elderly. SR-WBV and DVG seems to be effective as a training regime for skilling up in long-term-care elderly.Electronic supplementary materialThe online version of this article (doi:10.1186/s11556-016-0164-0) contains supplementary material, which is available to authorized users.

Validity and reliability of three methods of stiffness assessment

BackgroundStiffness is commonly assessed in relation to injury and athletic performance. The purpose of this research was to compare the validity and reliability of 3 in vivo methods of stiffness assessment using 1 cohort of participants. MethodsTo determine inter-day reliability, 15 female netballers were assessed for stiffness twice within 1 week using unilateral hopping (vertical stiffness), free oscillations of the calf, and myometry of various muscles of the triceps surae. To establish convergent construct validity, stiffness was compared to static and dynamic strength measurements. ResultsTest–retest stiffness results revealed that vertical stiffness produced moderate to high reliability results and myometry presented moderate to very high reliability. In contrast, the free oscillation technique displayed low to moderate reliability. Vertical stiffness demonstrated a significant correlation with rate of force development during a squat jump, whilst myometer stiffness measurements from 3 sites in the lower limb revealed significant correlations with isometric rate of force development. Further, significant negative correlations were evident between the eccentric utilisation ratio and various myometer stiffness results. No relationships were established between the free oscillation technique and any of the performance measurements. ConclusionThese results suggest that vertical stiffness and myometry are valid and reliable methods for assessing stiffness.

Preliminary inconclusive results of a randomised double blinded cross-over pilot trial in long-term-care dwelling elderly assessing the feasibility of stochastic resonance whole-body vibration

BackgroundThis randomised double-blinded controlled cross-over pilot study examined feasibility and preliminary effects of stochastic resonance whole-body vibration training applied in long term care elderly.FindingsNine long term care elderly were recruited and randomized to group A (6 Hz, Noise 4 SR-WBV/ Sham) or B (Sham / 1 Hz, Noise 1 SR-WBV). Feasibility outcomes included recruitment rate, attrition, adherence and safety. Physical performance outcomes focused on the Expanded Timed Get Up-and-Go (ETGUG) test, the Short Physical Performance Battery (SPPB), and lower extremity muscle strength.Of 24 subjects initially approached 9 started and 5 completed the study resulting in 37.5 recruitment, 44.4 attrition and 81.7 % adherence rates. No adverse events were reported. There is more evidence of improved performance levels in the SR-WBV treatment group with significant differences in average change for isometric rate of force development (p = 0.016 left leg; p = 0.028 right leg). No statistical significance was reached for other parameters.ConclusionsThe findings of this study indicate that the used training protocol for long term care elderly is feasible, however, requires more closely monitoring of participants; e.g. needs protocol modifications that target improved compliance with the intervention in this setting. SR-WBV shows beneficial effects on physical performance for those adhering to the intervention.Trial registrationU.S. National Institutes of Health NCT01543243Electronic supplementary materialThe online version of this article (doi:10.1186/s11556-015-0150-y) contains supplementary material, which is available to authorized users.

Associated decrements in rate of force development and neural drive after maximal eccentric exercise.

The present study investigated the changes in contractile rate of force development (RFD) and the neural drive following a single bout of eccentric exercise. Twenty-four subjects performed 15 × 10 maximal isokinetic eccentric knee extensor contractions. Prior to and at 24, 48, 72, 96, and 168 h during post-exercise recovery, isometric RFD (30, 50 100, and 200 ms), normalized RFD [1/6,1/2, and 2/3 of maximal voluntary contraction (MVC)] and rate of electromyography rise (RER; 30, 50, and 75 ms) were measured. RFD decreased by 28-42% peaking at 48 h (P < 0.01-P < 0.001) and remained depressed at 168 h (P < 0.05). Normalized RFD at 2/3 of MVC decreased by 22-39% (P < 0.01), peaked at 72 h and returned to baseline at 168 h. These changes in RFD were associated with a decrease in RER at 48 h-96 h (P < 0.05-P < 0.001). Accumulated changes (area under curve) revealed a greater relative decrease in accumulated RFD at 100 ms by -2727 ± 309 (%h; P < 0.05) and 200 ms by -3035 ± 271 (%h; P < 0.001) compared with MVC, which decreased, by -1956 ± 234 (%h). In conclusion, RFD and RER are both markedly reduced following a bout of maximal eccentric exercise. This association suggests that exercise-induced decrements in RFD can, in part, be explained decrements in neural drive.

Feasibility Study Evaluating Four Weeks Stochastic Resonance Whole-Body Vibration Training with Healthy Female Students

This study assessed the feasibility of stochastic resonance whole-body vibration (SR-WBV) training and its impact on isometric maximal voluntary contraction (IMVC), isometric rate of force development (IRFD) and a drop jump test (DJ) in healthy female students. Twelve participants were randomised to static squats during SR-WBV 6 Hz, noise level 4, over 4 weeks or to a control group (no training). Feasibility outcomes included the number of students agreeing to participate, the number of drop-outs, the adherence to the SR-WBV and the evaluation of the protocol. Secondary outcomes were IMVC, IRFD and DJ. Results: Among 35 eligible students, 12 agreed to participate and two dropped out. The adherence was 41 of 60 possible sessions. There were moderate to large, but statistically non-significant, gains in the secondary outcomes. Conclusion: These results suggest that such a study would be feasible although with some modifications such as a better familiarisation to the DJ.

Maximal strength training improves bone mineral density and neuromuscular performance in young adult women.

-Exercise guidelines highlight maximizing bone mass early in life as a strategy to prevent osteoporosis. Which intervention is most effective for this purpose remains unclear. This study investigated the musculoskeletal effects of high acceleration, maximal strength training (MST), in young adult women. Thirty healthy women (22 ± 2 years) were randomly assigned to a training group (TG) and a control group (CG). The TG completed 12 weeks of squat MST, executed at 85-90% of maximal strength 1 repetition maximum (1RM), emphasizing progressive loading and high acceleration in the concentric phase. The CG was encouraged to follow the American College of Sports Medicine's exercise guidelines for skeletal health. Measurements included bone mineral density (BMD) and body composition by dual-energy X-ray absorptiometry, dynamic and isometric rate of force development (RFD), and squat 1RM. Serum levels of type 1 collagen amino-terminal propeptide (P1NP), type 1 collagen C breakdown products (CTX), and sclerostin were analyzed by immunoassays. In the TG, lumbar spine and total hip BMD increased by 2.2 and 1.0%, whereas serum P1NP increased by 26.2%. Dynamic RFD and 1RM improved by 81.7 and 97.7%, and isometric RFD improved by 38% at 100 milliseconds. These improvements were significantly greater than those observed in the CG. Within the CG, dynamic RFD and 1RM increased by 27.2 and 12.9% while no other significant changes occurred. These findings suggest that squat MST may serve as a simple, time-efficient strategy to optimize peak bone mass in early adulthood.

Effect of stochastic resonance whole body vibration on functional performance in the frail elderly: A pilot study

The aim of this pilot study was to evaluate the feasibility and the effect size of a four-week stochastic resonance whole body vibration (SR-WBV) intervention on functional performance and strength in frail elderly individuals. Twenty-seven participants have been recruited and randomly distributed in an intervention group (IG) and a sham group (SG). Primary outcomes were feasibility objectives like recruitment, compliance and safety. Secondary outcomes were short physical performance battery (SPPB), isometric maximum voluntary contraction (IMVC) and isometric rate of force development (IRFD). The intervention was feasible and safe. Furthermore it showed significant effects (p=0.035) and medium effect size (0.43) within the IG in SPPB. SR-WBV training over four weeks with frail elderly individuals is a safe intervention method. The compliance was good and SR-WBV intervention seems to improve functional performance. Further research over a longer time frame for the strength measurements (IMVC and IRFD) is needed to detect potential intervention effects in the force measurements as well. Clinical Trial register: NTC01704976.

Feasibility Study Evaluating Four Weeks Stochastic Resonance Whole-Body Vibration Training with Healthy Female Students

This study assessed the feasibility of stochastic resonance whole-body vibration (SR-WBV) training and its impact on isometric maximal voluntary contraction (IMVC), isometric rate of force development (IRFD) and a drop jump test (DJ) in healthy female students. Twelve participants were randomised to static squats during SR-WBV 6 Hz, noise level 4, over 4 weeks or to a control group (no training). Feasibility outcomes included the number of students agreeing to participate, the number of drop-outs, the adherence to the SR-WBV and the evaluation of the protocol. Secondary outcomes were IMVC, IRFD and DJ. Results: Among 35 eligible students, 12 agreed to participate and two dropped out. The adherence was 41 of 60 possible sessions. There were moderate to large, but statistically non-significant, gains in the secondary outcomes. Conclusion: These results suggest that such a study would be feasible although with some modifications such as a better familiarization to the DJ.

Acute Hormonal and Force Responses to Combined Strength and Endurance Loadings in Men and Women: The “Order Effect”

PurposeTo examine acute responses and recovery of serum hormones and muscle force following combined strength (S) and endurance (E) loading sessions in which the order of exercises is reversed (ES vs. SE).MethodsThis cross-over study design included recreationally endurance trained men and women (age 21–45 years, n = 12 men n = 10 women) who performed both loadings. Maximal bilateral isometric strength (MVC), isometric rate of force development (RFD) and serum concentrations of testosterone (T), cortisol (C), growth hormone (GH), insulin-like growth factor 1 (IGF-1), binding protein 3 (IGFBP3) and sex hormone binding globulin (SHBG) were measured during and after both loadings.ResultsBoth of the present combined (ES and SE) loadings led to a greater acute decrease in MVC in men than in women, while RFD was slightly affected only in men. Recovery of MVC and RFD to baseline was complete at 24 h regardless of the order of exercises. In men, neuromuscular fatigue was accompanied by increased C concentrations observed post SE. This was followed by decreased concentrations of T at 24 h and 48 h that were significantly lower than those observed following ES. GH response in men also differed significantly post loadings. In women, only a significant difference in T between ES and SE loadings was observed at post.ConclusionThese observed differences in hormonal responses despite similarities in neuromuscular fatigue in men indicate the presence of an order effect as the body was not fully recovered at 48 h following SE. These findings may be applicable in training prescription in order to optimize specific training adaptations.

Maximal strength training improves work economy, rate of force development and maximal strength more than conventional strength training

This study compared maximal strength training (MST) with equal training volume (kg × sets × repetitions) of conventional strength training (CON) primarily with regard to work economy, and second one repetition maximum (1RM) and rate of force development (RFD) of single leg knee extension. In an intra-individual design, one leg was randomized to knee-extension MST (4 or 5RM) and the other leg to CON (3 × 10RM) three times per week for 8 weeks. MST was performed with maximal concentric mobilization of force while CON was performed with moderate velocity. Eight untrained or moderately trained men (26 ± 1 years) completed the study. The improvement in gross work economy was -0.10 ± 0.08 L min(-1) larger after MST (P = 0.011, between groups). From pre- to post-test the MST and CON improved net work economy with 31 % (P < 0.001) and 18 % (P = 0.01), respectively. Compared with CON, the improvement in 1RM and dynamic RFD was 13.7 ± 8.4 kg (P = 0.002) and 587 ± 679 N s(-1) (P = 0.044) larger after MST, whereas isometric RFD was of borderline significance 3,028 ± 3,674 N s(-1) (P = 0.053). From pre- to post-test, MST improved 1RM and isometric RFD with 50 % (P < 0.001) and 155 % (P < 0.001), respectively whereas CON improved 1RM and isometric RFD with 35 % (P < 0.001) and 83 % (P = 0.028), respectively. Anthropometric measures of quadriceps femoris muscle mass and peak oxygen uptake did not change. In conclusion, 8 weeks of MST was more effective than CON for improving work economy, 1RM and RFD in untrained and moderately trained men. The advantageous effect of MST to improve work economy could be due to larger improvements in 1RM and RFD.

Orthovanadate and Orthophosphate Inhibit Muscle Force via Two Different Pathways of the Myosin ATPase Cycle

Measurements of the half-sarcomere stiffness during activation of skinned fibers from rabbit psoas (sarcomere length 2.5 μm, temperature 12°C) indicate that addition of 0.1 mM orthovanadate (Vi) to the solution produces a drop to ∼1/2 in number of force-generating myosin motors, proportional to the drop in steady isometric force (T0), an effect similar to that produced by the addition of 10 mM phosphate (Pi). However, in contrast to Pi, Vi does not change the rate of isometric force development. The depression of T0 in a series of activations in presence of Vi is consistent with an apparent second-order rate constant of ∼1 × 103 M−1 s−1. The rate constant of T0 recovery in a series of activations after removal of Vi is 3.5 × 10−2 s−1. These results, together with the finding in the literature that the ATPase rate is reduced by Vi in proportion to isometric force, are reproduced with a kinetic model of the acto-myosin cross-bridge cycle where binding of Vi to the force-generating actomyosin-ADP state induces detachment from actin to form a stable myosin-ADP-Vi complex that is not able to complete the hydrolysis cycle and reenters the cycle only via reattachment to actin upon activation in Vi-free solution.

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.

Differential effects of peroxynitrite on contractile protein properties in fast- and slow-twitch skeletal muscle fibers of rat

Oxidative modification of contractile proteins is thought to be a key factor in muscle weakness observed in many pathophysiological conditions. In particular, peroxynitrite (ONOO(-)), a potent short-lived oxidant, is a likely candidate responsible for this contractile dysfunction. In this study ONOO(-) or 3-morpholinosydnonimine (Sin-1, a ONOO(-) donor) was applied to rat skinned muscle fibers to characterize the effects on contractile properties. Both ONOO(-) and Sin-1 exposure markedly reduced maximum force in slow-twitch fibers but had much less effect in fast-twitch fibers. The rate of isometric force development was also reduced without change in the number of active cross bridges. Sin-1 exposure caused a disproportionately large decrease in Ca(2+) sensitivity, evidently due to coproduction of superoxide, as it was prevented by Tempol, a superoxide dismutase mimetic. The decline in maximum force with Sin-1 and ONOO(-) treatments could be partially reversed by DTT, provided it was applied before the fiber was activated. Reversal by DTT indicates that the decrease in maximum force was due at least in part to oxidation of cysteine residues. Ascorbate caused similar reversal, further suggesting that the cysteine residues had undergone S-nitrosylation. The reduction in Ca(2+) sensitivity, however, was not reversed by either DTT or ascorbate. Western blot analysis showed cross-linking of myosin heavy chain (MHC) I, appearing as larger protein complexes after ONOO(-) exposure. The findings suggest that ONOO(-) initially decreases maximum force primarily by oxidation of cysteine residues on the myosin heads, and that the accompanying decrease in Ca(2+) sensitivity is likely due to other, less reversible actions of hydroxyl or related radicals.

Postactivation Potentiation: Upper Body Force Development Changes after Maximal Force Intervention

The neuromuscular phenomenon postactivation potentiation can possibly be used to increase the rate of force development (RFD) and maximal power (Pmax). Various intervention protocols have been examined with varying results. Maximal intervention protocols using 1 repetition maximum (1RM) have been examined in earlier studies in the lower body with positive results, but no studies have investigated maximal protocols on the upper body. Using maximal protocols would furthermore eliminate the uncertainties when expressing intensity as either numbers of RM or percentage of 1RM and hence emphasize standardization. Thus, the aim of this study was to examine the force development characteristics in the upper body after a maximal bench-press intervention. Eight strength trained male athletes performed an intervention protocol consisting of 5x 1RM in the bench press. Pre and post the intervention, a test consisting of either an isometric maximal voluntary contraction or a bench throw was completed to measure isometric RFD (iRFD) or Pmax, respectively. Statistical significance was accepted at p </= 0.05. After the intervention, a significant decrease in iRFD was observed. No difference was found in Pmax from pre to post. These results conflict with earlier results found in the lower body using the exact same intervention. It could be speculated if different activation levels in the upper body vs. the lower body could explain the conflicting results. In conclusion, to elicit postactivation potentiation in the upper body, an intervention of maximal intensity is not warranted. The practical applications of these results are that coaches and athletes should be careful to implement maximal resistance to elicit a potentiation until further studies have been conducted in this area.

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.

Effects of Adding Whole Body Vibration to Squat Training on Isometric Force/Time Characteristics

Resistance training interventions aimed at increasing lower-body power and rates of force development have produced varying results. Recent studies have suggested that whole-body low-frequency vibration (WBLFV) may elicit an acute postactivation potentiation response, leading to acute improvements in power and force development. Potentially, the use of WBLFV between sets of resistance training rather than during training itself may lead to increased recruitment and synchronization of high-threshold motor units, minimize fatigue potential, and facilitate the chronic adaptation to resistance exercise. The purpose of this study was to determine the effects of applying TriPlaner, WBLFV, prior to and then intermittently between sets of Smith machine squats on short-term adaptations in explosive isometric force expression. Thirty recreationally resistance trained men aged 18-30 were randomly assigned to 1 of 3 groups: resistance training only (SQT, n = 11), resistance plus whole-body vibration (SQTV, n = 13), or active control (CON, n = 6). An isometric squat test was performed prior to and following a 6-week periodized Smith machine squat program. Whole-body low-frequency vibration was applied 180 seconds prior to the first work set (50 Hz, 2-4 mm, 30 seconds) and intermittently (50 Hz, 4-6 mm, 3 x 10 seconds, 60 seconds between exposures) within a 240-second interset rest period. Subjects were instructed to assume a quarter squat posture while positioning their feet directly under their center of mass, which was modified using a handheld goniometer to a knee angle of 135 +/- 5 degrees . Instructions were given to subjects to apply force as fast and as hard as possible for 3.5 seconds. Isometric force (N) and rates of force development (N.s(-1)) were recorded from the onset of contraction (F(0)) to time points corresponding to 30, 50, 80, 100, 150, and 250 milliseconds, as well as the peak isometric rate of force development (PISORFD), and rate of force development to initial peak in force (RFDinitial). Repeated measures analysis of variance and analysis of covariance revealed no significant group by trial interactions for isometric rate of force development (ISORFD) between 0-30, 0-50, 0-80, 0-100, 0-150, and 0-250 milliseconds and PISORFD (p > 0.05). A significant group x trial interaction was seen for RFDinitial with SQTV >CG (p = 0.04, mean difference 997.2 N.s(-1)) and SQTV >SQT (p = 0.04, mean difference 1,994.22 N.s(-1)). Significant trial by covariate interactions (week one measures for ISORFD) and main effects for trial were observed for ISORFD between 0-80, 0-100, 0-and 150 milliseconds; PISORFD; and RFDinitial (p < 0.01). A significant trial effect was seen for Finitial (%) when expressed as a relative percentage of maximal voluntary contraction (MVC) (MVC = 100%) (p = 0.015; week 1 > week 7, mean difference, 5.82%). No significant differences were seen for any other force variables from the onset of contraction to MVC between weeks 1 and 7 (p > 0.05). The data suggest that there was a significant benefit afforded by adding WBLFV to a short-term resistance training protocol with regard to "explosive" strength expression. The addition of vibration prior to and between sets of resistance exercise may be a viable alternative to vibration applied during resistance exercise when trying to improve "explosive" isometric strength.

Effects Of Six Weeks Periodized Squat Training With Or Without Whole Body Vibration Upon The Relationship Between Isometric And Dynamic Performance

Resistance training interventions aimed at increasing lower body power and rates of force development have produced varying results. Potentially, the use of WBLFV in between sets of resistance training may increase high-threshold motor unit recruitment and synchronization leading to greater adaptations in both isometric and dynamic performance. The relationship between isometric force/time characteristics and dynamic performance and their respective changes in response to resistance training is of practical importance to strength and conditioning practitioners. To determine the effects of applying whole body vibration prior to and then intermittently between sets of Smith Machine squats upon training induced changes in isometric and dynamic performance and their relationships to one another. Twenty four recreationally resistance trained men were randomly assigned to one of two groups, resistance only (SQT n = 11), or resistance plus whole body vibration (SQTV n = 13). An isometric squat test as well as Squat Jumps (SQJ) and Depth Jumps (DJ) were performed prior to, and following a six-week, periodized Smith Machine squat program. WBLFV was applied 180 s prior to the first work set (50Hz 2-4mm, 30 s) and intermittently (50Hz 4-6mm, 3 × 10 s, 60s between exposures) within a 240s inter-set rest period. Subjects were instructed to assume a quarter squat posture while positioning their feet directly under their center of mass which was modified using a hand held goniometer to a knee angle of 135 ± 5°. Measures of isometric force (N) and isometric rates of force development (N·s−1) were recorded from the onset of contraction (F0) to time points corresponding to F30ms, F80ms, F250ms, Force at initial peak (Finitial), Force at 50% of MVC (MVC50) Time Finitial (ms) as well as the Peak Isometric Force (MVCp) and Peak Isometric Rate of Force Development (PISORFD). Squat jumps were performed with a 20kg Olympic barbell with a linear position transducer attached while the DJ utilized body mass as resistance while dropping from a height of 30cm onto a switch mat. Measures recorded during jumps included jump height (cm) peak power (PMax,W), peak power per kg of body mass (PMax/kg, W/kg) and mean power (Pav,W) for both jump conditions. Correlation matrices matching isometric force/time variables and dynamic (SQJ, DJ) performance within group between weeks 1 and 7(Pre- Post training) revealed multiple significant positive, and negative correlations (p = *<.05 and**<.001, range, r = −.624 to .859). A greater total amount of positive correlations were seen for SQTV (24) compared to SQT (2). Correlation coefficients (r) calculated between percent change (%Δ) scores for similar variables revealed small to moderate r values with the only significant correlation seen for the SQTV group between F30ms and DJ height (cm) (r = −.589, R2 = −.347, p <.05). More positive correlations were seen for isometric and dynamic %Δ variables that for SQTV (9) compared to SQT (7). The addition of WBLFV to the SQTVgroup appeared to effect neuro-muscular training adaptation differently from SQT as reflected in the percent change relationship between isometric and dynamic performance measures following six weeks of exposure. WBLFV may help facilitate early phase adaptations to resistance exercise with a tendency to improve early force time components of isometric and dynamic performance.

Causes of fatigue in slow-twitch rat skeletal muscle during dynamic activity

Skeletal muscle fatigue is most often studied in vitro at room temperature and is classically defined as a decline in maximum force production or power output, exclusively linked to repeated isometric contractions. However, most muscles shorten during normal use, and we propose that both the functional correlate of fatigue, as well as the fatigue mechanism, will be different during dynamic contractions compared with static contractions. Under isoflurane anesthesia, fatigue was induced in rat soleus muscles in situ by isotonic shortening contractions at 37 degrees C. Muscles were stimulated repeatedly for 1 s at 30 Hz every 2 s for a total of 15 min. The muscles were allowed to shorten isotonically against a load corresponding to one-third of maximal isometric force. Maximal unloaded shortening velocity (V(0)), maximum force production (F(max)), and isometric relaxation rate (-dF/dt) was reduced after 100 s but returned to almost initial values at the end of the stimulation protocol. Likewise, ATP and creatine phosphate (CrP) were reduced after 100 s, but the level of CrP was partially restored to initial values after 15 min. The rate of isometric force development, the velocity of shortening, and isotonic shortening were also reduced at 100 s, but in striking contrast, did not recover during the remainder of the stimulation protocol. The regulatory myosin light chain (MLC2s) was dephosphorylated after 100 s and did not recover. Although metabolic changes may account for the changes of F(max), -dF/dt, and V(0), dephosphorylation of MLC2s may be involved in the fatigue seen as sustained slower contraction velocities and decreased muscle shortening.

Isometric rate of force development, maximum voluntary contraction, and balance in women with and without joint hypermobility

To determine differences between hypermobile subjects and controls in terms of maximum strength, rate of force development, and balance. We recruited 13 subjects with hypermobility and 18 controls. Rate of force development and maximal voluntary contraction (MVC) during single leg knee extension of the right knee were measured isometrically for each subject. Balance was tested twice on a force plate with 15-second single-leg stands on the right leg. Rate of force development (N/second) and MVC (N) were extracted from the force-time curve as maximal rate of force development (= limit Deltaforce/Deltatime) and the absolute maximal value, respectively. The hypermobile subjects showed a significantly higher value for rate of force development (15.2% higher; P = 0.038, P = 0.453, epsilon = 0.693) and rate of force development related to body weight (16.4% higher; P = 0.018, P = 0.601, epsilon = 0.834) than the controls. The groups did not differ significantly in MVC (P = 0.767, P = 0.136, epsilon = 0.065), and MVC related to body weight varied randomly between the groups (P = 0.921, P = 0.050, epsilon = 0.000). In balance testing, the mediolateral sway of the hypermobile subjects showed significantly higher values (11.6% higher; P = 0.034, P = 0.050, epsilon = 0.000) than that of controls, but there was no significant difference (4.9% difference; P = 0.953, P = 0.050, epsilon = 0.000) in anteroposterior sway between the 2 groups. Hypermobile women without acute symptoms or limitations in activities of daily life have a higher rate of force development in the knee extensors and a higher mediolateral sway than controls with normal joint mobility.