Rapid Force Research Articles

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

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

Transient Kinetics Measured with Force Steps Discriminate between Double Stranded DNA Elongation and Melting and Define the Reaction Energetics

Double stranded DNA pulled to ∼65 pN undergoes an overstretching transition from the basic conformation (B-form) to a 1.7 times longer conformation that represents a fundamental stage in the structural transitions during DNA recombination, replication and repair. By using a dual laser optical tweezers with a fast force feedback (2 ms rise time), we recorded the length transient following force steps imposed on the λ-phage DNA with different degrees of melting and at different temperatures (10-25°C). The rate-force relations obtained from the lengthening transient under our rapid force clamp following 2-35 pN force pull to the overstretching force shows that the whole 70% extension is a two state reaction from the B-form to an S-form that precedes and is independent of melting. The shortening transient following 20-35 pN force drop from the overstretching force is made by stepwise shortenings and pauses due to S-B transitions and reannealing of the melted segments. The temperature dependence of the lengthening transient shows that the entropic contribution to the reaction at room temperature is only 1/3 of the entropy change expected from thermal melting. The structural parameters that describe the distances from the B and the S state to the transition state, do not depend on temperature. Accordingly the total elongation of a single two-state unit, and therefore q, the index of cooperativity (22bp) of the reaction, do not depend on temperature, suggesting that it arises from structural factors, such as the nucleic acid sequence. Supported by IIT-SEED (Genova) and Ente Cassa di Risparmio di Firenze.

No Differences in Kinetics between the Squat Jump, Push Press and Mid-Thigh Power Clean

The aim of this investigation was to determine the differences in kinetic data during the mid-thigh power clean, squat jump and push press. Trained individuals (n=11; age 23 ± 3.5 yrs; height 176.5 ± 5.56 cm; body mass 85.78 ± 14.29 kg) performed 1 set of 3 repetitions of the mid-thigh power cleans, squat jumps and push press, using 60% of 1 repetition maximum (1RM) power clean, in a randomized order, while standing on a force platform. Peak vertical ground reaction forces (Fz), instantaneous rate of force development (RFD) and peak power output were compared between exercises, using a one way analysis of variance. There were no significant (p>0.05) differences in peak Fz, RFD or peak power output between exercises, although the greatest Fz and RFD were observed during the mid-thigh power clean, and the highest peak power was observed in the squat jump. From the findings of this study the peak Fz, RFD and peak power during the mid-thigh power clean, squat jump and push press, performed using 60% 1RM power clean, are comparable. If the focus of training is rapid force production under high load then the exercise that permits the greatest loading should be used, which is likely to be the squat jump.

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.

Point of No Return: How Do Financial Resources Affect the Timing of Retirement After a Job Separation?

This project uses the Survey of Income and Program Participation to examine the decision to retire after job separation among the increasing number of older individuals who leave a job between 55 and 70, and how this decision varies by labor market conditions and the resources available to the unemployed. Among individuals whose jobless spells end in retirement, most do so within a year after separation. The availability of resources like Social Security retirement benefits, high net worth, and defined benefit pensions appear to encourage more rapid labor force exit and retirement, rather than supporting job seekers during a long search. Surprisingly, retirement is only modestly more likely when the unemployment rate is high, and a greater duration of unemployment insurance benefits has little effect on retirement timing. Poor health and work-limiting disabilities are also associated with more rapid labor force exit and retirement. These results suggest little tolerance for long job searches – regardless of labor market prospects – and indicate that those who can afford to retire will do so rather quickly.

Islamic Militancy and Global Insecurity: An Analysis of Boko-Haram Crisis in Northern Nigeria

The paper essentially examines the Boko-Haram insurgency in Northern Nigeria and its contribution to global insecurity. In it we have argued that the emergence of Islamic militancy the world over, particularly in Afghanistan, Pakistan, Yemen, and North Africa and in Nigeria poses a great threat to global security. The paper adopted the desk research and data derived were analyzed using content analysis. The findings from the analysis show that the Boko-Haram sect and its activities are increasingly becoming more radicalized with devastating and destructive impact in scale and momentum on the Nigerian society. The activities have led to the destruction of lives and properties and have made the Northern Nigerian environment unconducive for investment from within and outside the country; and the activities have seriously eroded or threatened the nation’s national cohesion and integration. Based on the findings, we have recommended among other measures for the government to put in place a Special Rapid Response Force, that is well trained, very mobile and well equipped to deal with these kinds of situations wherever they occur in the future and; government to seek for international collaboration with US and other European countries on counter terrorism in order to tackle global insecurity.

Clinical Data Support that Psyllium Is Not Fermented in the Gut

1 Procter & Gamble, Quantitative Sciences, Mason, Ohio, USA Correspondence: Johnson McRorie, PhD, FACG, AGAF, Procter & Gamble, Quantitative Sciences, 8700 Mason-Montgomery Road, Mason, Ohio 45040, USA. E-mail: [email protected]

Comparison of Dimensions and Residual Forces of Various Orthodontic Elastomeric Ligatures

Objective: The study aimed to compare dimensions and residual forces of various commercial type orthodontic elastomeric ligatures available in Thailand. Materials and Methods: The study compared 5 types of elastomeric ligatures: MU-MTEC, UnitekTM, MorelliTM, WelovehealthTM and DentsplyTM. A digital caliper was used to measure dimensions: the inner and outer diameters and cross-sectional thickness. Then the initial extension force and residual force on days 1, 2, 3, 4, 5, 6, 7, 14 and 28 were measured according to ISO 21606: 2007. The data were analyzed with the Kruskal-Wallis test and Spearmans rank correlation. Results: No significant difference was found between the outer diameter of MU-MTEC and WelovehealthTM. However, significant mean differences were found in dimensions among the other ligature types. The lowest mean for inner diameter and cross sectional thickness was found in UnitekTM and the lowest mean for outer diameter was found in MorelliTM. The highest mean inner diameter, outer diameter and cross sectional thickness was found in Dentsply, UnitekTM, and MorelliTM, respectively. In terms of initial extension force, significant differences (p&lt;0.001) were found among all samples. The highest mean was found in DentsplyTM (2.69 N) and the lowest mean was found in WelovehealthTM (1.80 N). All samples had rapid force degradation at about 42.21-56.23% after 24 hours, with a slow degradation rate until Week 1 and a constantly stable rate from Weeks 1-4. The greatest force decay on the first day was found in MorelliTM (56.23%). At 28 days, the residual force for all types of elastomeric ligature was about 31.97-46.84%. Conclusion: All 5 brands of commercial elastomeric ligatures had different dimensions, initial extension forces and residual forces. The correlation between brand and dimension, initial extension force and residual force showed different patterns. All elastomeric ligatures had greater force decay on the first day (residual force 43.77 57.79%), then slightly decreased over 28 days.

Effects of dopamine replacement therapy on lower extremity kinetics and kinematics during a rapid force production task in persons with Parkinson disease

Postural instability appears to be a dopamine resistance motor deficit in persons with Parkinson disease (PD); however, little is known about the effects of dopamine replacement on the relative biomechanical contributions of individual lower extremity joints during postural control tasks. To gain insight, we examined persons with PD using both clinical and laboratory measures. For a clinical measure of motor severity we utilized the Unified Parkinson Disease Rating Scale motor subsection during both OFF and ON medication conditions. For the laboratory measure we utilized data gathered during a rapid lower extremity force production task. Kinematic and kinetic variables at the hip, knee, and ankle were gathered during a counter movement jump during both OFF and ON medication conditions. Sixteen persons with PD with a median Hoehn and Yahr severity of 2.5 completed the study. Medication resulted in significant improvements of angular displacement for the hip, knee, and ankle. Furthermore, significant improvements were revealed only at the hip for peak net moments and average angular velocity compared to the OFF medication condition. These results suggest that dopamine replacement medication result in decreased clinical motor disease severity and have a greater influence on kinetics and kinematics proximally. This proximally focused improvement may be due to active recruitment of muscle force and reductions in passive restraint during lower extremity rapid force production.

Acoustic tweezing cytometry for live-cell subcellular modulation of intracellular cytoskeleton contractility

Mechanical forces are critical to modulate cell spreading, contractility, gene expression, and even stem cell differentiation. Yet, existing tools that can apply controllable subcellular forces to a large number of single cells simultaneously are still limited. Here we report a novel ultrasound tweezing cytometry utilizing ultrasound pulses to actuate functionalized lipid microbubbles covalently attached to single live cells to exert mechanical forces in the pN - nN range. Ultrasonic excitation of microbubbles could elicit a rapid and sustained reactive intracellular cytoskeleton contractile force increase in different adherent mechanosensitive cells. Further, ultrasound-mediated intracellular cytoskeleton contractility enhancement was dose-dependent and required an intact actin cytoskeleton as well as RhoA/ROCK signaling. Our results demonstrated the great potential of ultrasound tweezing cytometry technique using functionalized microbubbles as an actuatable, biocompatible, and multifunctional agent for biomechanical stimulations of cells.

Effect of brief daily resistance training on rapid force development in painful neck and shoulder muscles: randomized controlled trial

Objective: To determine the effect of small daily amounts of progressive resistance training on rapid force development of painful neck/shoulder muscles.Methods: 198 generally healthy adults with frequent neck/shoulder muscle pain (mean: age 43·1 years, computer use 93% of work time, 88% women, duration of pain 186 day during the previous year) were randomly allocated to 2- or 12 min of daily progressive resistance training with elastic tubing or to a control group receiving weekly information on general health. A blinded assessor took measures at baseline and at 10-week follow-up; participants performed maximal voluntary contractions at a static 90-degree shoulder joint angle. Rapid force development was determined as the rate of torque development and maximal muscle strength was determined as the peak torque.Results: Compared with the control group, rate of torque development increased 31·0 Nm s−1 [95% confidence interval: (1·33–11·80)] in the 2-min group and 33·2 Nm s−1 (1·66–12·33) in the 12-min group from baseline to 10-week follow-up, corresponding to an increase of 16·0% and 18·2% for the two groups, respectively. The increase was significantly different compared to controls (P<0·05) for both training groups. Maximal muscle strength increased only ∼5–6% [mean and 95% confidence interval for 2- and 12-min groups to control, respectively: 2·5 Nm (0·05–0·73) and 2·2 Nm (0·01–0·70)]. No significant differences between the 2- and 12-min groups were evident. A weak but significant relationship existed between changes in rapid force development and pain (r = 0·27, P<0·01), but not between changes in maximal muscle strength and pain.Conclusion: Small daily amounts of progressive resistance training in adults with frequent neck/shoulder pain increases rapid force development and, to a less extent, maximal force capacity.

Congolese Elections 2011: Mostly a Problem of Global Governance and Negative 'Soft Power', not Resources

When Congolese President Joseph Kabila was inaugurated for a second term on 20 December 2011 the fallout from the 28 November elections in the Democratic Republic of the Congo (DRC) was 'situation normal: continued instability'. After Kabila's main opponent, Etienne Tshisekedi, 'swore himself in' on 23 December (Tshisekedi website), there were two men claiming to be president and several other candidates demanding a new ballot. The 2006 elections, the DRC's first since the Global and Inclusive Agreement (Dialogue Inter-Congolais 2002), were shambolic, but clearly legitimate (UN 2007, Carter Center 2006a, b, c). This was partly due to the fact that the United Nations Organization Mission in the Democratic Republic of the Congo (Monuc) had a stronger presence than its successor, the United Nations Organization Stabilization Mission in the Democratic Republic of the Congo (Monusco). There was also more international attention in 2006, including an EU rapid reaction force. However, many of the issues in the 2011 election - violence, logistical problems and irregularities - were present in the previous one (see, eg, UN 2006; Carter Center 2006a, b, c). There was possibly as much international financial and logistical support as there had been in 2006. There were fewer international observers but more local ones. The main differences relate to context, the structure of international assistance and the lack of a second presidential round. The crisis had been years in the making. More important than diminished engagement in the mechanics of the election was the international community's sham attention to governance in sub-Saharan Africa and the culture of impunity it has encouraged. The West, unlike China, has failed to appreciate the strategic importance of the DRC. By encouraging regional dictators instead of enthusiastically supporting the rule of law early and often, it tacitly encouraged bad behaviour.

Motor unit rate coding is severely impaired during forceful and fast muscular contractions in individuals post stroke

Information regarding how motor units are controlled to produce forces in individuals with stroke and the mechanisms behind muscle weakness and movement slowness can potentially inform rehabilitation strategies. The purpose of this study was to describe the rate coding mechanism in individuals poststroke during both constant (n = 8) and rapid (n = 4) force production tasks. Isometric ankle dorsiflexion force, motor unit action potentials, and surface electromyography were recorded from the paretic and nonparetic tibialis anterior. In the paretic limb, strength was 38% less and the rate of force development was 63% slower. Linear regression was used to describe and compare the relationships between motor unit and electromyogram (EMG) measures and force. During constant force contractions up to 80% maximal voluntary contraction (MVC), rate coding was compressed and discharge rates were lower in the paretic limb. During rapid muscle contractions up to 90% MVC, the first interspike interval was prolonged and the rate of EMG rise was less in the paretic limb. Future rehabilitation strategies for individuals with stroke could focus on regaining these specific aspects of motor unit rate coding and neuromuscular activation.

Rapid Force Production in Children and Adults

Children demonstrate lower force production capacities compared with adults, which has often been attributed to "neuromuscular immaturity." However, tendon stiffness, which influences both the electromechanical delay (EMD) and rate of force development (RFD) in adults, is lower in children and may influence rapid force production. The aims of this study were 1) to document EMD and RFD variation as a function of age, 2) to determine the relationships between tendon stiffness and parameters relating to rapid force production in children and adults, and 3) to estimate the relative neural and mechanical contributions to age-related changes in force production by examining the effects of tendon stiffness and muscle activation rate (rate of EMG increase [REI]) on RFD. Achilles tendon stiffness, EMD, RFD, and REI were measured during plantarflexion contractions in 47 prepubertal children (5-12 yr) and 19 adults. Relationships were determined between 1) stiffness and EMD, 2) stiffness and RFD, and 3) REI and RFD. The relative contributions of age, stiffness, and REI on RFD were determined using a multiple regression analysis. Age-related differences in tendon stiffness, EMD, RFD, and REI were also examined according to chronological age (5-6, 7-8, and 9-10 yr) and compared with adults. Increases in tendon stiffness with age were correlated with decreases in EMD (r < -0.83). Stiffness and REI could account for up to 35% and 30% of RFD variability in children, respectively, which increased to 58% when these variables were combined. Both neural and mechanical factors influence rapid force production in prepubertal children. Children's longer EMD and slower RFD indicate a less effective development and transfer of muscular forces, which may have implications for complex movement performance.

Rapid Divergent Evolution of Male Genitalia Among Populations of Drosophila buzzatii

Fil: Soto, Ignacio Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Ecologia, Genetica y Evolucion de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecologia, Genetica y Evolucion de Buenos Aires; Argentina

Differences in Climbing-Specific Strength Between Boulder and Lead Rock Climbers

The purpose of this study was to compare maximal muscle strength and rapid force capacity of finger flexors between boulder and lead climbers of national-international level. Ten boulder (mean ± SD, age 27 ± 8 years) and 10 lead climbers (age 27 ± 6 years) volunteered for the study. Ten nonclimbers (age 25 ± 4 years) were also tested. Isometric maximal voluntary contraction (MVC) force and rate of force development (RFD) produced in "crimp" and "open-crimp" hand positions were evaluated on an instrumented hold. Climbers were stronger than nonclimbers. More interestingly, MVC force and RFD were significantly greater in boulder compared with lead climbers (p < 0.05), in both crimp and open-crimp positions. The RFD was the most discriminatory outcome, as the largest difference between boulder and lead climbers (34-38%) was observed for this variable. The RFD may reflect the specific requirements of bouldering and seems to be more appropriate than pure maximal strength for investigating muscle function in rock climbers.

Acute Neuromuscular and Endocrine Responses and Recovery to Single-Session Combined Endurance and Strength Loadings

The purpose of this study was to investigate acute neuromuscular and endocrine responses and recovery to a single session of combined endurance and strength loading using 2 loading orders. Forty-two men were demographically matched to perform a single session of combined endurance + strength (E + S) or strength + endurance (S + E) loading. The strength loading was conducted on a leg press and included sets of power, maximal strength, and hypertrophic loads with an overall duration of 30 minutes. The endurance loading was conducted on a bike ergometer and performed by continuous cycling over 30 minutes at 65% of subject's individual maximal watts. Both loading conditions led to significant acute reductions in maximal force production (E + S: -27%, p < 0.001; S + E: -22%, p < 0.001), rapid force produced in 500 milliseconds (E + S: -26%, p < 0.001; S + E: -18%, p < 0.001), and countermovement jump height (E + S: -15%, p < 0.001; S + E: -12%, p < 0.001), whereas no significant differences between the 2 loadings were observed. Maximal and explosive force production recovered after 48 hours after both loading conditions. Whereas no significant acute responses were found in concentrations of serum testosterone (T) and thyroid-stimulating hormone in the 2 loading conditions, concentrations of T were significantly reduced in E + S during recovery at 24 hours (-13%, p < 0.05) and 48 hours (-11%, p = 0.068), but not in S + E, and concentrations of thyroid-stimulating hormone significantly reduced after both loading conditions (24 hours: E + S, -32%, p < 0.001; S + E, -25%, p < 0.01; 48 hours: E + S, -25%, p < 0.001; S + E, -18%, p < 0.01). The loading conditions in this study showed that neuromuscular performance recovered already within 2 days, whereas endocrine function, observed particularly by decreased concentrations in serum T after the E + S loading order, remained altered still after 48 hours of recovery. These results emphasize the different needs for recovery after 2 loading orders.

Africa's Got Work to Do: Employment Prospects in the New Century

Estimates of the current and future structure of employment in sub-Saharan Africa (2005–20) are obtained based on household survey estimates for 28 countries and an elasticity-type model that relates employment to economic growth and demographic outcomes. Agriculture still employs the majority of the labor force although workers are shifting slowly out of the sector. Sub-Saharan Africa’s projected rapid labor force growth, combined with a low baseline level of private sector wage employment, means that even if sub-Saharan Africa realizes another decade of strong growth, the share of labor force employed in private firms is not expected to rise substantially. Governments need to undertake measures to attract private enterprises that provide wage employment, but they also need to focus on improving productivity in the traditional and informal sectors as these will continue to absorb the majority of the labor force.

Africa's Got Work to Do: Employment Prospects in the New Century

Estimates of the current and future structure of employment in sub-Saharan Africa (2005–20) are obtained based on household survey estimates for 28 countries and an elasticity-type model that relates employment to economic growth and demographic outcomes. Agriculture still employs the majority of the labor force although workers are shifting slowly out of the sector. Sub-Saharan Africa’s projected rapid labor force growth, combined with a low baseline level of private sector wage employment, means that even if sub-Saharan Africa realizes another decade of strong growth, the share of labor force employed in private firms is not expected to rise substantially. Governments need to undertake measures to attract private enterprises that provide wage employment, but they also need to focus on improving productivity in the traditional and informal sectors as these will continue to absorb the majority of the labor force.

The role of hind limb tendons in gibbon locomotion: springs or strings?

Tendon properties have an important effect on the mechanical behaviour of muscles, with compliant tendons allowing near-isometric muscle contraction and facilitating elastic energy storage and recoil. Stiff tendons, in contrast, facilitate rapid force transfer and precise positional control. In humans, the long Achilles tendon contributes to the mechanical efficiency of running via elastic energy storage and recovery, and its presence has been linked to the evolution of habitual bipedalism. Gibbons also possess relatively long hind limb tendons; however, their role is as yet unknown. Based on their large dimensions, and inferring from the situation in humans, we hypothesize that the tendons in the gibbon hind limb will facilitate elastic energy storage and recoil during hind-limb-powered locomotion. To investigate this, we determined the material properties of the gibbon Achilles and patellar tendon in vitro and linked this with available kinematic and kinetic data to evaluate their role in leaping and bipedalism. Tensile tests were conducted on tendon samples using a material testing machine and the load-displacement data were used to calculate stiffness, Young's modulus and hysteresis. In addition, the average stress-in-life and energy absorption capacity of both tendons were estimated. We found a functional difference between the gibbon Achilles and patellar tendon, with the Achilles tendon being more suitable for elastic energy storage and release. The patellar tendon, in contrast, has a relatively high hysteresis, making it less suitable to act as elastic spring. This suggests that the gibbon Achilles tendon might fulfil a similar function as in humans, contributing to reducing the locomotor cost of bipedalism by acting as elastic spring, while the high stiffness of the patellar tendon might favour fast force transfer upon recoil and, possibly, enhance leaping performance.