Search results for "Muscle Contraction"
showing 10 items of 569 documents
Neuromuscular responses to different resistance loading protocols using pneumatic and weight stack devices
2013
The purpose of this study was to examine single repetition characteristics and acute neuromuscular responses to typical hypertrophic (HL), maximal strength (MSL), and power (PL) loadings performed with two of the most common resistance modes; pneumatic and weight stack. Acute responses were assessed by measuring maximal voluntary contraction (MVC), corresponding quadriceps-EMG and resting and superimposed twitch torques. Activation level was calculated from the twitch torques. Decreases in MVC were greater during HL and MSL than during PL. During HL, resting twitch force decreased 8% (P < 0.05) more on the weight stack than on the pneumatic device. Furthermore, loading using the weight stac…
Prestretch potentiation of human skeletal muscle during ballistic movement
1981
The conditions associated prior to and during the transition from prestretch to shortening may have considerable influence on the final performance of muscle. In the present study male subjects of good physical condition performed vertical jumps on the force-platform with and without preliminary counter movement. In the counter movement jump (CMJ) the amplitude of the knee bending, velocity of the prestretch and the force attained at end of prestretch were the primary parameters of interest. In addition the coupling time indicating the transition from the eccentric (prestretch) phase to the concentric phase was recorded from the angular displacement and reaction force curves. In the final c…
Interaction between fascicle and tendinous tissues in short-contact stretch-shortening cycle exercise with varying eccentric intensities
2005
The interaction between fascicle and tendinous tissues (TT) in short-contact drop jumps (DJ) with three different drop heights [low (Low), optimal (OP), and high (High)] was examined with 11 subjects. The ground reaction force (F z) and ankle and knee joint angles were measured together with real-time ultrasonography (fascicle length) and electromyographic activities of the medial gastrocnemius (MG) and vastus lateralis (VL) muscles during the movement. With increasing drop height, the braking force and flight time increased from Low to OP ( P < 0.05). In High, the braking force increased but the flight time decreased compared with OP ( P < 0.05). During contact of Low and OP conditi…
Influence of stretch-shortening cycle on mechanical behaviour of triceps surae during hopping.
1992
Six subjects performed a first series of vertical plantar flexions and a second series of vertical rebounds, both involving muscle triceps surae exclusively. Vertical displacements, vertical forces and ankle angles were recorded during the entire work period of 60 seconds per series. In addition, expired gases were collected during the test and recovery for determination of the energy expenditure. Triceps surae was mechanically modelled with a contractile component and with an elastic component. Mechanical behaviour and work of the different muscle components were determined in both series. The net muscular efficiency calculated from the work performed by the centre of gravity was 17.5 +/- …
Store and recoil of elastic energy in slow and fast types of human skeletal muscles.
1982
Stretch-shortening cycle refers to the mechanical condition in which store and recoil of elastic energy occur in the skeletal muscle. This leads to a greater work output when compared to a simple shortening contraction. The subjects performed vertical jumps with and without preliminary counter-movement and with small and large knee angular displacement. The results indicated that those subjects who had more fast twitch (FT) fibers benefited more from the stretching phase performed with high speed and short angular displacement. The amounts of elastic energy stored in this phase were 30 and 26 N X kgBW-1, respectively, for FT and slow twitch (ST) type subjects. The recoil of elastic energy w…
Analyzing gastrocnemius EMG-activity and sway data from quiet and perturbed standing.
2007
In an experiment, we combined force plate measurements and surface EMG in studying quiet and perturbed standing, involving MS (Multiple sclerosis) and controls. The aim of this paper is to report the results thus obtained on the relation between filtered gastrocnemius (GA) EMG and the anterior-posterior center-of-pressure (A/P COP) coordinate. The main finding is the good correspondence between A/P COP and the filtered GA EMG in the low frequency range. The EMG envelope was calculated using a zero-lag filter. Combining this with time shifts around 250-350 ms produced a high correlation (85.5+/-8.4%) between the GA-EMG envelope and the A/P COP. This EMG-COP relation was closest when using a …
Changes in power curve shapes as an indicator of fatigue during dynamic contractions.
2010
The purpose of this study was to analyze exercise-induced leg fatigue during a dynamic fatiguing task by examining the shapes of power vs. time curves through the combined use of several statistical methods: B-spline smoothing, functional principal components and (supervised and unsupervised) classification. In addition, granulometric size distributions were also computed to allow for comparison of curves coming from different subjects. Twelve physically active men participated in one acute heavy-resistance exercise protocol which consisted of five sets of 10 repetition maximum leg press with 120 s of rest between sets. To obtain a smooth and accurate representation of the data, a basis of …
Interrelationships between electromyographic, mechanical, muscle structure and reflex time measurements in man.
1981
Reaction time (TRT) with its premotor (PMT) and motor time (MT) components, patellar reflex time (TRfT) with its latency (LAT) and motor time (RfMT) were studied together with isometric force production and relaxation time variables in one leg isometric knee extension. These variables were intercorrelated together with muscle biopsy variables taken from m. vastus lateralis. From these computations MT proved to demonstrate significant correlations to rate of isometric force development (RFD) (P less than 0.001), maximum force (P0) (P less than 0.001) and per cent distribution of ST fibers (P less than 0.001). It is speculated that these relationships are determined by the pattern of the moto…
Treadmill versus overground and barefoot versus shod comparisons of triceps surae fascicle behaviour in human walking and running
2013
Studies of human locomotion are commonly performed on a treadmill or overground, as well as with or without footwear. These testing modalities have been suggested to influence kinematics, kinetics and/or spatio-temporal variables differently. However, it is unclear whether they influence contractile behaviour at the level of the muscle fascicles. This has major relevance because results from studies performed with different combinations of the testing modalities are often compared. The present study used ultrasound to examine fascicle behaviour of the medial gastrocnemius (MG) and soleus muscles of ten young, healthy males during walking and running on a treadmill and overground, as well as…
Functional, biochemical and morphological studies on human bronchi after cryopreservation
1995
1. Human isolated bronchi have been investigated as fresh tissue or after storage (7 and 30 days) at -196 degrees C in foetal calf serum containing 1.8 M dimethyl sulphoxide. 2. After cryopreservation, the maximal contractile response to acetylcholine (3 mM) was reduced (approximately 25%) but the difference did not reach significance statistically. Maximal responses to other spasmogens tested (histamine, [Nle10]NKA(4-10), bradykinin, leukotriene D4, U46619, and KCl) did not differ between unfrozen and frozen/thawed tissues. The sensitivity of cryopreserved tissues to the constrictor agents tested was similar to that of fresh tissues. 3. The accumulation of inositol phosphates produced by a…