Force-velocity Characteristics Of Muscle Research Articles

Lower extremity muscle strength across the adult lifespan in multiple sclerosis: Implications for walking and stair climbing capacity.

Persons with multiple sclerosis (pwMS) accumulate impairments in muscle strength and limitations in physical function as the disease progresses. The same symptoms are seen in the biological process of aging (years of age>60years). Nonetheless, no previous studies have examined the combined effects of aging and multiple sclerosis (MS) in regards to lower extremity muscle strength concomitant with physical function (e.g. walking capacity). The aim of this cross-sectional study was to examine potential differences in pwMS vs. healthy controls (HC) across the adult lifespan in these outcomes. A total of n=53 pwMS and n=48 age-matched HC were enrolled, and divided into groups of young (≤ 44years), middle-aged (45-59years), and old (≥ 60years). Assessment of knee extensor (KE) and plantar flexor (PF) muscle force-velocity characteristics (isometric and dynamic concentric force at contraction velocities of 0-300deg.s-1) alongside assessment of timed 25ft walk tests (T25FWT), two minute walk tests (2MWT), and 9-step stair ascend (9SSA) were carried out. Overall, substantial impairments in KE and PF isometric (ranging from -18 to -23%) and dynamic muscle strength (ranging from -26 to -38%) alongside limitations in T25FWT, 2MWT, and 9SSA (ranging from -24 to -33%) were observed in pwMS vs. HC (p<0.05). With advanced age (young → middle-aged → old), more pronounced impairments in PF (but not KE) isometric and dynamic muscle strength, alongside limitations in T25FWT, 2MWT, and 9SSA, were observed in pwMS vs. HC (p<0.05). In pwMS, associations were observed between physical function and isometric KE+PF muscle strength (r2=0.21-0.45) as well as dynamic KE+PF muscle strength (r2=0.36-0.61) (p<0.05). Substantial impairments of KE and PF muscle strength occur in pwMS across the adult lifespan accompanied by/associated with limitations in walking and stair climbing capacity, with PF muscle strength being preferentially affected in pwMS vs. HC.

Muscle mass and muscle function over the adult life span: A cross-sectional study in Flemish adults

BackgroundAging is accompanied with a progressive deterioration of skeletal muscle mass (SMM) and muscle function, also termed sarcopenia. MethodsThe aim was to describe SMM (based on bioelectrical impedance) and muscle function of the leg extensors over the adult age span in 819 men and 578 women, aged 18–78 years. The distribution of skeletal muscle index (SMI; SMM/height2) groups was described and muscle force–velocity characteristics were examined between SMI-groups over the adult life span. Subjects were divided into age categories and SMI groups to compare their muscle strength characteristics. Isometric and isokinetic strength, ballistic movement speed and muscular endurance of the knee extensors were evaluated on a Biodex dynamometer. ResultsAge by gender interaction effects were found significant (P<0.01) for all strength tests. In general, the overall drop in slow and faster knee extension strength was larger than the isometric component, with women showing larger losses by the age of 60–70 years compared to men. Regression analysis revealed significant (P<0.01) age-related reductions, with the largest explained variance for the muscular endurance parameter (24%). No age by SMI-group interaction effect was observed for muscle function, but main effects of age and SMI were significant (P<0.01). ConclusionThe age-related decline in muscle function was stronger in women. Furthermore, a low SMI results in a weaker muscle function compared to a normal SMI in each age-category, pointing out that its relationship with physical disability should therefore be further examined over the adult life-span.

Effects of series compliance on twitches superimposed on voluntary contractions.

The activation of skeletal muscle during voluntary isometric contraction has been assessed by measuring the increase in force caused by a superimposed maximal shock to the motor nerve (the twitch-interpolation technique). When the muscle is held isometric, the increase in force with stimulation (superimposed twitch force) decreases with increasing voluntary force, and a line fit through the data can be extrapolated to maximal voluntary force at the zero twitch force axis. In a previous paper we questioned the applicability of this technique in situations where a high series compliance allows the muscle to shorten during the superimposed twitch. To explore effects of series compliance, we measured force of the adductor pollicis during voluntary isometric contractions with noncompliant and compliant loading devices. With the compliant loading device, superimposed twitch force was systematically less than with the noncompliant device, and the plot of superimposed twitch force vs. voluntary force was often concave upward, preventing easy extrapolation to maximal voluntary force. These findings are consistent with force-velocity characteristics of muscle and suggest that twitch-interpolation data must be interpreted with caution when the muscle is not held isometric during the superimposed twitch.

Influence of training on the force-velocity relationship of the arm flexors of active sportsmen.

The aim of this study was to investigate the influence of specific types of muscle training, performed by previously well-trained competitive athletes, on the force-velocity relationship of the arm flexors. Four rowers, five athletes competing in tug-of-war, and six middle- and long-distance runners were measured at different stages of their training program during the period of 1 training year. The runners performed no special arm training and were included for comparative purposes. A record was made of the type and intensity of training. The force-velocity curve (FVC) was established by measuring the torques (M) and corresponding angular velocities (omega) of maximal arm flexions against different constant torques. Using Hill's equation: (M + a) (omega + b) = constant, a best fitting curve was calculated through the points of measurement. Two-way analysis of variance revealed only few statistically significant (P less than 0.05) changes in the parameters describing the course of the FVC. The results suggest that the force-velocity characteristics of muscle of previously well-trained sportsmen can hardly be influenced.