Relative Rate Of Force Development Research Articles

Fiber Type Composition and Rate of Force Development in Endurance- and Resistance-Trained Individuals.

Methenitis, S, Spengos, K, Zaras, N, Stasinaki, A-N, Papadimas, G, Karampatsos, G, Arnaoutis, G, and Terzis, G. Fiber type composition and rate of force development in endurance- and resistance-trained individuals. J Strength Cond Res 33(9): 2388-2397, 2019-The purpose of the study was to investigate the relationship between muscle fiber composition and the rate of force development (RFD) in well-trained individuals with different training background. Thirty-eight young men with different training background participated: 9 endurance runners, 10 power-trained individuals, 9 strength-trained individuals, and 10 sedentary individuals. They performed maximal isometric leg press for the measurement of RFD. Body composition (dual x-ray absorptiometry) and vastus lateralis fiber type composition were also evaluated. When all participants were examined as a group, moderate correlations were found between the percent of type II muscle fibers and RFD between 100 and 600 milliseconds (r = 0.321-0.497; p ≤ 0.05). The correlation coefficients were higher for the cross-sectional area (CSA) and the %CSA of type II and IIx muscle fibers (r = 0.599-0.847; p < 0.001). For the power group, RFD up to 250 milliseconds highly correlated with % type IIx muscle fibers and type IIx fiber CSA (r = 0.670-0.826; p ≤ 0.05), as well as with %CSA of type IIx fibers (r = 0.714-0.975; p ≤ 0.05). Significant correlations were found between the relative RFD (·kg lower extremities lean mass) and CSA-%CSA of type II and IIx fibers for the power group (r = 0.676-0.903; p ≤ 0.05). No significant correlations were found between muscle morphology and RFD for the other groups. In conclusion, the present data suggest that there is a strong link between the type IIx muscle fibers and early RFD and relative RFD in power-trained participants. Type II fibers seem to be moderately linked with RFD in non-power-trained individuals.

MECHANICAL LOWER LIMB MUSCLE FUNCTION AND ITS ASSOCIATION WITH PERFORMANCE IN ELITE TEAM GYMNASTS

TeamGym (TG) differs from individual gymnastics as it is performed in teams including 6-12 participants competing in acrobatic performance in three disciplines: trampette jumping, tumbling track jumping, and floor exercises. The physical demands required by TG athletes largely remain unknown, and likely are dictated by the specific disciplines and equipment used. This study aimed at describing physiological capacity by investigating mechanical lower limb muscle function and its association with TG performance in 24 senior elite (12 males, 12 females) team gymnasts. Methods: Anthropometrical data as well as 25m sprint ability, repetitive jumps (RJ), countermovement jumping (CMJ), drop jumping from a height of 48cm (DJ48), maximal isometric leg press muscle strength (MVC) and rate of force development (RFD) were measured. Results: Significant sex differences (p&lt;0.05) were observed for all variables, except MVC. Total sprint times were 3.36±0.1s in males vs. 3.70±0.1s in females, CMJ height 0.51±0.05 vs. 0.41±0.03m, DJ48 rebound height 0.43±0.06 vs. 0.34±0.06m, with no difference in concentric peak power production between CMJ and DJ48. MVC was 38.3±9.9N/kg in males vs. 36.4±9.2N/kg in females. In female gymnasts, correlations (r2=0.41-0.46, p&lt;0.05) were found between trampette and tumbling performance and sprint ability. In male gymnasts, correlations (r2=0.44, p&lt;0.05) emerged between trampette performance and relative RFD (%MVC/s). Conclusions: Moderate associations were found between mechanical lower limb muscle function and functional tumbling performance in male and female TeamGym, indicating that performance in elite TeamGym also relies on factors other than isolated mechanical muscle function.

Rate of force development to evaluate the neuromuscular fatigue and recovery after an intermittent isometric handgrip task with different blood flow restriction conditions

Abstract Aim: To investigate the neuromuscular fatigue and recovery after an intermittent isometric handgrip exercise (IIHE) executed until failure with different blood flow restriction (BFR) conditions (free flow, partial and total vascular restriction). Methods: Thirteen healthy men carried out an IIHE at 45% of maximum voluntary isometric force (MVIF) until failure with total restriction (TR), partial restriction (PR) or free flow (FF). The rate of force development (RFD) was extracted from the MIVF over the time intervals of 0-30, 0-50, 0-100, and 0-200ms and normalized by MVIF [relative RFD (RFDr)]. Results: The RFDr decreased significantly (p<0.01) after the IIHE in all BFR conditions and time intervals studied, remaining lower for five minutes. The medians of the RFDr in FF condition were significantly lower (p=0.01) at 30ms (1.56 %MVIF·s-1) and 50ms (1.70 %MVIF·s-1) when compared to TR at 30ms (2.34 %MVIF·s-1) and 50ms (2.63 %MVIF·s-1) in minute 1 post failure. Conclusions: These results show that, regardless of the blood flow restriction level, there is no RFD recovery five minutes after an exhaustive IIHE. When the task was executed with FF, the reduction of the RFD was greater when compared with the TR condition.

Whole body vibration to attenuate reduction of explosive force in chronic kidney disease patients: a randomized controlled trial

To investigate whether whole body vibration (WBV) training increases the explosive force of the knee extensors in chronic kidney disease (CKD) patients. Fourteen CKD patients undergoing hemodialysis were randomly allocated in WBV training or Sham group. Explosive force parameters (contractile impulse [CImp] and relative rate of force development [RFDr]) obtained in early (30 and 50 msec) and late phases (100 and 200 msec) of the knee extensors force/time curve. CImp and RFDr obtained at the early phase of force/time curve reduced after the intervention period, with a smaller decline for WBV (CImp at 50 msec [~−15% and −51%, P=0.038], RFDr at 30 msec [~−22% and −52%, P=0.044] and RFDr at 50 msec [~−11% and −54%; P=0.008]). In the late phase there was a lower decline for WBV group compared to Sham group, respectively: CImp: 100 msec (~−8% and −55%, P=0.025), 200 msec (~−3% and −46%, P= 0.025); RFDr 100 msec (~0.01% and −56%, P=0.033), 200 msec (~−5% and −36%, P=0.004). Three months of WBV training may attenuate the explosive force reduction in CKD patients.

Influence of Whole Body Vibration and Specific Warm-ups on Force during an Isometric Mid-Thigh Pull

Purpose: The purpose of this study was to investigate the effects of general and specific warm-up protocols on rate of force development (RFD), relative RFD (rRFD), ground reaction force (GRF) and relative ground reaction force (rGRF) during an isometric mid-thigh pull (IMTP), after WBV exposure. Methods: Fifteen healthy recreationally trained males (age: 24.1 ± 2.3 yrs, height: 72.9 ± 7.8 cm; mass: 86.9 ± 8.3) completed five protocols: baseline, isometric vibration (iVib), isometric no vibration (iNV), dynamic vibration (dVib) and dynamic no vibration (dNV). The baseline was completed without any warm-up prior to the IMTP. The intervention protocols had the same prescription of 4 sets of 30-second bouts of quarter squats (dynamic [DQS] and isometric [IQS]) on the WBV platform with or without vibration. Following a one-minute rest period after each protocol, participants completed three maximal IMTPs. Results: Repeated measures ANOVA with a Bonferroni post hoc demonstrated that RFD in dNV (7657.8 ± 2292.5 N/s) was significantly greater than iVib (7156.4 ± 2170.0 N/s). However, the other experimental trials for RFD demonstrated no significant differences (p>0.05). There were also no significant differences for rRFD, GRF or rGRF between protocols. Conclusion: These results demonstrate that a dynamic warm-up without WBV elicits greater RFD than an isometric warm-up with WBV prior to a maximal isometric exercise. Further research needs to be investigated utilizing dynamic and isometric warm-ups in conjunction with WBV and power output. Keywords: males, recreationally trained, power

Avaliação da taxa de produção de força e torque em indivíduos com espasticidade pós-avc

The aim of this study was to compare the rate of force development (RFD) and maximum torque in spastic stroke survivors and healthy individuals. Fifteen stroke survivors (57.3 ± 11.2 years) with ankle spasticity and fifteen healthy individuals (59.3 ± 6.4 years) participated in this study. An isokinetic dynamometer was used to maximum voluntary isometric contraction (MVC) and RFD assessment of plantar flexors muscles of ankle, which the individuals were instructed to produce maximum torque as fast as possible. The absolute RFD was normalized by MVC (relative RFD). In results were observed significant differences in RFD of affected limb (43.3 ± 8.5 Nm/s) and unaffected limb (98.9 ± 20.4 Nm/s) compared to healthy (186.2 ± 25.2 Nm/s), but with no differences between affected and unaffected limbs (p=0.15). In relation to relative RFD, the affected limb (9.76 ± 1.1 %MVC/s) was significant different than healthy (13.08 ± 1.5 %MVC/s). The MVC produced by affected limb (46.55 ± 7.98 Nm) was significant lower than unaffected limb (84.29 ± 8.47 Nm) and, the two limbs of stroke survivors were weakness than healthy individuals (128.02 ± 9.36 Nm). Lastly, the spasticity level present higher negative correlation in relation to RFD (R= -0.725; p= 0.002) and MVC (R= -0.717; p=0.003). The spasticity promotes alterations in capacity to produce maximum force and fast force in affected and unaffected limbs of stroke survivors compared to healthy.

Aging impairs the recovery in mechanical muscle function following 4 days of disuse

As aged individuals are frequently exposed to short-term disuse caused by disease or musculoskeletal injury, it is important to understand how short-term disuse and subsequent retraining affect lower limb mechanical muscle function. The purpose of the present study was, therefore, to investigate the effect of 4days of lower limb disuse followed by 7days of active recovery on mechanical muscle function of the knee extensors in young (24.3±0.9years, n=11) and old (67.2±1.0years, n=11) recreationally active healthy males. Slow and moderate dynamic muscle strength were assessed using isokinetic dynamometry (60 and 180°s−1, respectively) along with isometric muscle strength and rapid muscle force capacity examined as contractile rate of force development (RFD), Impulse, and relative RFD (rRFD) during the initial phase of contraction (100ms time interval relative to onset of contraction). Prior to disuse, marked age-related differences (p<0.05) were observed in isometric and dynamic muscle strength (~35%) as well as in RFD and Impulse (~39%). Following disuse, young and old individuals experienced comparable decrements (p<0.05) in isometric strength (~9%), slow dynamic strength (~13%), and RFD and Impulse (~19%), whereas old individuals only experienced decrements (p<0.05) in moderate dynamic strength (12%) and rRFD (~17%). Following recovery, all measures of mechanical muscle function were restored in young individuals compared to pre-disuse values, while isometric, slow and moderate dynamic muscle strength remained suppressed (p<0.05) in old individuals (~8%) along with a tendency to suppressed RFD100 (p=0.068). In conclusion, 4days of lower limb disuse led to marked decrements in knee extensor mechanical muscle function in both young and old individuals, yet with greater decrements observed in moderate dynamic strength and rapid muscle force capacity in old individuals. While 7days of recovery – including free ambulation, one test session and a single session of strength training – was sufficient to restore mechanical muscle function in young individuals, old individuals appeared to have an impaired ability to fully recover as evidenced by suppressed values of isometric and dynamic muscle strength and rapid muscle force capacity.

Age-related changes in the rate of muscle activation and rapid force characteristics

Declines in muscle size and strength are commonly reported as a consequence of aging; however, few studies have investigated the influence of aging on the rate of muscle activation and rapid force characteristics across the lifespan. This study aims to investigate the effects of aging on the rate of muscle activation and rapid force characteristics of the plantar flexors. Plantar flexion peak force (PF), absolute (peak, 50, and 100-200ms), and relative (10%, 30%, and 50%) rate of force development (RFD), the rapid to maximal force ratio (RFD/PF), and the rate of electromyography rise (RER) were examined during an isometric maximal voluntary contraction (MVC) in young (age = 22 ± 2years), middle-aged (43 ± 2years), and old (69 ± 5years) men. The old men exhibited lower PF (30.7% and 27.6% lower, respectively) and absolute (24.4-55.1%) and relative (16.4-28.9%) RFD values compared to the young and middle-aged men (P ≤ 0.03). RER values were similar between the young and old men (P ≥ 0.30); however, RER values were greater for the middle-aged men when compared to the young and old men for the soleus (P < 0.01) and the old men for the medial gastrocnemius (P ≤ 0.02). Likewise, RFD/PF ratios were similar between young and old men (P ≥ 0.26); however, these ratios were greater for the middle-aged men at early (P ≤ 0.03), but not later (P ≥ 0.10), time intervals. The lower PF and absolute and relative RFD values for the old men may contribute to the increased functional limitations often observed in older adults. Interestingly, higher rates of muscle activation and greater early RFD/PF ratios in middle-aged men may be a reflection of physiological alterations in the neuromuscular system occurring in the fifth decade.

Are early and late rate of force development differently influenced by fast‐velocity resistance training?

This study examined the effect of fast-velocity concentric isokinetic resistance training (FV) on the rate of force development (RFD) at early (<100 ms) and late phases (>100 ms) of rising muscle force. Nine men participated in a 6-week resistance training intervention for the lower body, and nine matched subjects participated as controls (CON). During concentric isokinetic (180°s(-1)) knee extension training, subjects were instructed to do each contraction 'as fast and forcefully as possible'. Maximal muscle strength (MVC) and RFD (0-10, 0-20, …, 0-250 ms from the onset of contraction) were measured during maximal voluntary isometric contraction of the knee extensors (KE). There were no significant changes in MVC of KE in both groups after intervention (FV = 314·2 ± 101·1 versus 338·7 ± 88·0 N∙m, P>0·05; CON = 293·3 ± 94·8 versus 280·0 ± 72·2 N∙m, P>0·05). The RFD increased 39-71% at time intervals up to 90 ms from the onset of the contraction (P<0·05), whereas no change occurred at later time intervals. Similarly, relative RFD (i.e.%MVC∙s(-1)) (RFDr) increased 33-56% at time intervals up to 70 ms from the onset of the contraction (P<0·05). It can be concluded that a short period of resistance training performed with concentric fast-velocity isokinetic muscle contractions is able to enhance RFD and RFDr obtained at the early phase of rising muscle force.

Biomechanical and Nonfunctional Assessment of Physical Capacity in Male ICU Survivors*

ICU admission is associated with decreased physical function for years after discharge. The underlying mechanisms responsible for this muscle function impairment are undescribed. The aim of this study was to describe the biomechanical properties of the quadriceps muscle in ICU survivors 12 months after ICU discharge. Case-control study with consecutive inclusion of ICU survivors and age- and sex-matched controls. Patients were treated at a mixed 18-bed ICU at a tertiary care university hospital and tested at a biomechanical university laboratory. We included 16 male ICU patients (Acute Physiology and Chronic Health Evaluation II score 20 ± 7, mean ± SD), who had stayed in the ICU >72 hrs and survived to 12 months and 15 age- and sex-matched controls. None. An extensive battery of biomechanical tests, including maximum, fast, and endurance contractions, was administered during isometric knee extensions while simultaneously recording surface electromyography (quadriceps and hamstrings). Compared to controls, ICU survivors had reduced maximal voluntary torque (22%, 179 ± 64 Nm vs. 230 ± 57 Nm, p = 0.03), absolute rate of force development (50%, 868 ± 372 Nm/sec vs. 1739 ± 470 Nm/sec, p < 0.001) and relative rate of force development (32%, 512 ± 260% maximum voluntary contraction/sec vs. 754 ± 189% maximum voluntary contraction/sec, p < 0.01), and endurance time (40%, 136 ± 84 sec vs. 226 ± 111 sec, p < 0.02). Rate of force development, but not maximal voluntary torque, was significantly reduced after adjusting for muscle mass. Electromyography data indicated no impairment of motor activation strategy or central motor drive. Also, no difference in reaction time was found between patients and controls. ICU survivors had reduced rate of force development and muscular endurance 1 yr after ICU discharge. Our data indicate that the functional deficits experienced by ICU survivors originate in muscle tissue rather than the nervous system. Also, increased attention to velocity-orientated exercise during rehabilitation of ICU patients may have the potential to better physical outcome after critical illness.

Consistency of rapid muscle force characteristics: Influence of muscle contraction onset detection methodology

The purpose of this study was to investigate the consistency of commonly reported rapid force characteristics utilizing both automated and manual muscle contraction onset detection methods. Twenty-four healthy volunteers performed isometric strength testing of the plantar flexor muscle group on two nonconsecutive days. Test–retest reliability was evaluated using intraclass correlation coefficients (ICCs), standard errors of measurement (SEM), and the SEM as a percentage of the mean (SEM%) for rate of force development (RFD), relative RFD, contractile impulse, and absolute force–time values at various epoch durations using automated and manual onset detection methods. For all rapid force variables, ICC and SEM% values ranged from 0.52 to 0.96 and 7.56% to 37.56%, respectively. For the majority of these variables (20 of 23), the automated onset detection method resulted in higher ICC and lower SEM% values compared to the manual onset detection method. Regardless of onset detection methodology, the consistency of relative RFD values declined following 50% of MVC. Collectively, these findings indicated that commonly evaluated rapid muscle force variables demonstrated acceptable relative and absolute consistency values. However, these values were generally superior for the automated onset detection methodology. Additionally, the consistency of relative RFD values declines following 50% MVC and therefore should be evaluated with caution.

Neuromuscular performance of paretic versus non-paretic plantar flexors after stroke

The objective of this study was to compare the neuromuscular function of the paretic and non-paretic plantar flexors (i.e. soleus, gastrocnemius medialis, lateralis) in chronic stroke patients. It was hypothesized that the contractile rate of force development (RFD) and neural activation, assessed by electromyogram (EMG) and V-waves normalized to the M-wave, and voluntary activation (twitch interpolation) would be reduced during plantar flexor maximum voluntary isometric contraction and that the evoked muscle twitch properties would be reduced in the paretic limb. Ten chronic stroke survivors completed the study. The main findings were that the paretic side showed deteriorated function compared to the non-paretic leg in terms of (1) RFD in all analyzed time windows from force onset to 250 ms, although relative RFD (i.e. normalized to maximum voluntary force) was similar; (2) fast neural activation (for most analyzed time windows), assessed by EMG activity in time windows from EMG onset to 250 ms; (3) V-wave responses (except for gastrocnemius medialis); (4) voluntary activation; (5) the evoked peak twitch force, although there was no evidence of intrinsic muscle slowing; (6) EMG activity obtained at maximal voluntary force. In conclusion, this study demonstrates considerable neuromuscular asymmetry of the plantar flexors in chronic stroke survivors. Effective rehabilitation regimes should be investigated.

Effects of Different Levels of Assisted Jumping on Peak Velocity, Takeoff Velocity and Relative Rate of Force Development

Effects of Different Levels of Assisted Jumping on Peak Velocity, Takeoff Velocity and Relative Rate of Force Development

Muscle function and postural balance in lifelong trained male footballers compared with sedentary elderly men and youngsters

The present study investigated whether elderly subjects exposed to lifelong football training have better rapid muscle force characteristics, body composition and postural stability in comparison with untrained elderly. Ten elderly men exposed to lifelong football training (FTE; 69.6 +/- 1.4 years) and eight age-matched untrained elderly men (UE; 70.5 +/- 1.0 years) were studied and 49 untrained young men (UY; 32.4 +/- 0.9 years) served as a reference group. FTE showed an elevated rate of force development (RFD) and impulse at 0-30, 100 and 200 ms (relative RFD at 1/6 MVC: 567 +/- 39 vs 353 +/- 42% MVC/s), higher total lean body mass (56.9 +/- 0.8 vs 52.7 +/- 2.2 kg) and better postural stability (Flamingo test: 15 +/- 1 vs 33 +/- 2 falls) compared with UE (P<0.05), with no difference between FTE and UY. The proportion of type IIA fibers was higher and the area percentage of type IIX fibers was lower in FTE than in UE (P<0.05). Rapid muscle force characteristics and postural stability were consistently higher in elderly subjects exposed to lifelong football training, providing an enhanced ability to counteract unexpected perturbations in postural balance. The superior RFD and balance in elderly footballers were of such a magnitude that no deficit could be observed when compared with young untrained individuals.

Early and late rate of force development: differential adaptive responses to resistance training?

The objective of this study is to investigate the potentially opposing influence of qualitative and quantitative muscular adaptations in response to high-intensity resistance training on contractile rate of force development (RFD) in the early (<100 ms) and later phases (>200 ms) of rising muscle force. Fifteen healthy young males participated in a 14-week resistance training intervention for the lower body and 10 matched subjects participated as controls. Maximal muscle strength (MVC) and RFD were measured during maximal voluntary isometric contraction of the quadriceps femoris muscle. Muscle biopsies were obtained from the vastus lateralis. The main findings were that RFD in the late phase of rising muscle force increased in response to resistance training whereas early RFD remained unchanged and early relative RFD (i.e., RFD/MVC) decreased. Quantitatively, muscle fiber cross-sectional area and MVC increased whereas, qualitatively, the relative proportion of type IIX muscle fibers decreased. Multiple regression analysis showed that while increased MVC positively influenced both early and late RFD, decreased-type IIX negatively influenced early RFD only. In conclusion, early and late RFD responded differently to high-intensity resistance training due to differential influences of qualitative and quantitative muscular adaptations on early and later phases of rising muscle force.

Intermuscle differences in activation.

The objective of this study was to investigate differences within individual subjects in the ability to activate the quadriceps, plantar flexors (PF), dorsiflexors (DF), and elbow flexors (EF) during isometric contractions. Twelve male subjects performed submaximal and maximal voluntary isometric contractions, and maximal tetanic contractions were also induced by electrical stimulation. The interpolated twitch technique was used to gauge the extent of muscle inactivation or inability to produce maximum force. Measurements included torque output, absolute and relative rate of force development (RFD), and percentage of muscle inactivation. The quadriceps exceeded all other muscle groups in voluntary and tetanic torque output, voluntary absolute RFD, and absolute and relative tetanic RFD. The quadriceps also exceeded the PF and DF in voluntary relative RFD and had greater muscle inactivation (15.5%) than the EF (5.0%), PF (5.0%), and DF (1.3%). Although the higher RFD may suggest a higher percentage of type II fibers in the quadriceps, their higher threshold of recruitment leads to greater difficulty in fully activating the quadriceps.