Search results for "isometric"
showing 10 items of 535 documents
Muscle strength and serum testosterone, cortisol and SHBG concentrations in middle-aged and elderly men and women.
1993
Forty healthy males (M) and females (F) divided into two different age groups i.e. M50 years (range 44–57; n= 9), F50 years (range 43–54; n= 9), M70 years (range 64–73; n= 11) and F70 years (range 63–73; n= 11) volunteered as subjects for examination of muscle cross-sectional area (CSA) and maximal voluntary isometric force production characteristics of the leg extensor muscles and serum androgen and sex hormone binding globulin (SHBG) concentrations. The CSA in the male groups was greatly larger (P < 0.01) than in the female groups and both elderly groups demonstrated slightly (n.s.) smaller values in the CSA than the two middle-aged groups. Maximal force of 2854 ± 452 N in M50 was greater…
Age-related decreases in motor unit discharge rate and force control during isometric plantar flexion.
2012
Aging is related to multiple changes in muscle physiology and function. Previous findings concerning the effects of aging on motor unit discharge rate (DR) and fluctuations in DR and force are somewhat contradictory. Eight YOUNG and nine OLD physically active males performed isometric ramp (RECR) and isotonic (ISO) plantar flexions at 10 and 20% of surface EMG at MVC. Motor unit (MU) action potentials were recorded with intramuscular fine-wire electrodes and decomposed with custom build software "Daisy". DR was lower in OLD in RECR-10% (17.9%, p0.001), RECR-20% (15.8%, p0.05), ISO-10% (17.7%, p0.01) and ISO-20% (14%, n.s.). In YOUNG force fluctuations were smaller at ISO-10% (72.1%, p0.001)…
Effects of joint angle and age on ankle dorsi- and plantar-flexor strength.
2007
This study aimed at examining the effects of joint angle and age on the maximal voluntary contraction (MVC) torque, for the agonist and antagonist muscle groups around the ankle, i.e., the dorsi- and plantar-flexors. To this aim, neural and muscular factors were investigated in two groups of healthy men: 11 young (mean age, 24 years) and 18 older (mean age, 78 years). Plantar-flexion (PF) and dorsiflexion (DF) isometric MVC torques were measured in three different ankle joint angles and surface electromyographic activities of the triceps surae and of the tibialis anterior muscles were recorded. The main findings were that the DF-to-PF MVC torque ratio varied with joint angle and age, indica…
Effects of ageing on motor unit activation patterns and reflex sensitivity in dynamic movements.
2009
Both contraction type and ageing may cause changes in H-reflex excitability. H reflex is partly affected by presynaptic inhibition that may also be an important factor in the control of MU activation. The purpose of the study was to examine age related changes in H-reflex excitability and motor unit activation patterns in dynamic and in isometric contractions. Ten younger (YOUNG) and 13 elderly (OLD) males performed isometric (ISO), concentric (CON) and eccentric (ECC) plantarflexions with submaximal activation levels (20% and 40% of maximal soleus surface EMG). Intramuscular EMG data was analyzed utilizing an intramuscular spike amplitude frequency histogram method. Average H/M ratio was a…
Serum hormones and strength development during strength training in middle-aged and elderly males and females.
1994
Effects of a 12-week progressive strength training period on serum concentrations of testosterone, cortisol and sex-hormone-binding globulin (SHBG) as well as on strength development of the leg extensor muscles were investigated in nine middle-aged males (M50; range 44-57 years) and in nine middle-aged females (F50; range 43-54 years) as well as in 10 elderly males (M70; range 64-73 years) and in 11 elderly females (F70; range 66-73 years). Substantial increases took place in maximal isometric strength during the 12-week training period both in M50 (from 2834 +/- 452 to 3941 +/- 772 N; P < 0.001) and in F50 (from 2627 +/- 725 to 3488 +/- 1017 N; P < 0.001) as well as in M70 (from 2591 +/- 7…
The role of genetics and environment in lifting force and isometric trunk extensor endurance.
2004
Background and Purpose. Our understanding of what different back performance tests are measuring is limited. The purpose of this study was to investigate the relative contributions of genetics and unique and common environmental factors for 3 tests of back muscle performance in a classic twin analysis. Subjects. The subjects were a population-based sample of 122 monozygotic and 131 dizygotic male twin pairs aged 35 to 69 years (X̄=49.9, SD=7.7). Methods. Variance component analysis was applied to estimate genetic and environmental influences on isokinetic and psychophysical lifting and isometric trunk extensor endurance test performance. The Cholesky decomposition genetic factor model was u…
Lower limb muscle weakness predicts use of a multiple- versus single-step strategy to recover from forward loss of balance in older adults.
2012
BACKGROUND: Older adults compared with young adults have reduced strength and balance recovery ability. The purpose of the present study was to investigate whether age, sex, and/or lower limb strength predicted the stepping strategy used to recover from a forward loss of balance. METHODS: Ninety-five, community-dwelling, older adults, aged 65-90 years, participated in the study. Loss of balance was induced by releasing participants from a static forward lean. Participants performed four trials at three initial lean magnitudes and were subsequently classified as using a single- or multiple-step strategy. Isometric strength of the ankle, knee, and hip joint flexors and extensors was assessed …
Changes in muscle morphology, electromyographic activity, and force production characteristics during progressive strength training in young and olde…
1998
Effects of a 10-week progressive strength training program composed of a mixture of exercises for increasing muscle mass, maximal peak force, and explosive strength (rapid force production) were examined in 8 young (YM) (29+/-5 yrs) and 10 old (OM) (61+/-4 yrs) men. Electromyographic activity, maximal bilateral isometric peak force, and maximal rate of force development (RFD) of the knee extensors, muscle cross-sectional area (CSA) of the quadriceps femoris (QF), muscle fiber proportion, and fiber areas of types I, IIa, IIb, and IIab of the vastus lateralis were evaluated. Maximal and explosive strength values remained unaltered in both groups during a 3-week control period with no training…
Changes in neuromuscular performance and muscle fiber characteristics of elite power athletes self-administering androgenic and anabolic steroids
1984
The influence of androgenic-anabolic steroid-induced changes in measures of body composition, muscle fiber characteristics and various aspects of the neuromuscular performance of the leg extensor muscles was investigated in five experimental and six control power athletes during the 24-week programmed strength training followed by the additional six week training without hormone drugs. The mean values of the dosages of self-administration during the 24-week period were 31.0 +/- 14.3 mg/day for anabolic steroids (methandienone, stanozolol, nandrolone) and 178.4 +/- 82.7 mg/week for testosterone. During the 24-week hormone period the experimental group gained in fat-free weight (p less than 0…
Muscle activation during cycling at different cadences: Effect of maximal strength capacity
2007
International audience; The purpose of this study was to examine the influence of maximal strength capacity on muscle activation, during cycling, at three selected cadences: a low cadence (50 rpm), a high cadence (110 rpm) and the freely chosen cadence (FCC). Two groups of trained cyclists were selected on the basis of the different maximal isokinetic voluntary contraction values (MVCi) of their lower extremity muscles as follow: Fmin (lower MVCi group) and Fmax (higher MVCi group). All subjects performed three 4-min cycling exercises at a power output corresponding to 80 % of the ventilatory threshold under the three cadences. Neuromuscular activity of vastus lateralis (VL), rectus femoris…