Kinematic and electromyographic analysis of wheelchair propulsion on ramps of different slopes for young men with paraplegia.

Objective: To gain insight into the biomechanics of upslope wheelchair stroking by examining the changes in kinematic and electromyographic characteristics of wheelchair propulsion over ramps of different slopes.

Design: Repeated-measures design. Each subject pushed up a wooden ramp (7.

Perception-action coupling and anticipatory performance in baseball batting.

The authors examined 10 expert and 10 novice baseball batters' ability to distinguish between a fastball and a change-up in a virtual environment. They used 2 different response modes: (a) an uncoupled response in which the batters verbally predicted the type of pitch and (b) a coupled response in which the batters swung a baseball bat to try and hit the virtual ball. The authors manipulated visual information from the pitcher and ball in 6 visual conditions.

The use of anticipatory visual cues by highly skilled tennis players.

The authors examined 13 skilled and 12 novice tennis performers' ability to use visual information of an opponent's movement pattern to anticipate and respond. In Experiment 1, skilled and novice players anticipated the type of stroke and the direction in which the ball was hit in a highly coupled perception-action environment. Both groups of players correctly anticipated at greater than chance levels.

Anticipatory postural adjustments for altering direction during walking.

The authors examined how individuals adapt their gait and regulate their body configuration before altering direction during walking. Eight young adults were asked to change direction during walking with different turning angles (0 degree, 45 degree, 90 degree), pivot foot (left, right), and walking speeds (normal and fast). The authors used video and force platform systems to determine participants' whole-body center of mass and the center of pressure during the step before they changed direction.

Estimation of lifted weight and produced effort through perception of point-light display.

It has been shown that human observers can estimate the weight of a box from the observation of a point-light display of a lifting motion. We asked observers to report the weight of the box and the effort produced by five lifters ranging in size and strength to determine if observers can perceive lifter size. In experiment 1, five or six weights from each of five lifters were shown to fourteen observers in a random order.

Force control is greater in the upper compared with the lower extremity.

The authors investigated whether force control is similar between the upper and lower limbs and between contractions that involve 1 or 2 joints. Six volunteers (27.5 +/- 11.

Comparing the pre- and post-impact ball and racquet kinematics of elite tennis players' first and second serves: a preliminary study.

The aim of this study was to compare the pre- and post-impact three-dimensional kinematics of the ball and racquet during first and second serves performed by elite tennis players. Data were collected from four male and four female right-handed professional players during competition using two high-speed cameras (200 Hz). For each player, one first serve and one second serve from the 'deuce' or right service court that landed within the specified target area were analysed.

Motor output is more variable during eccentric compared with concentric contractions.

Purpose: This study examined the ability of 10 young (25.3 +/- 2.8 yr) healthy individuals to control knee-extension force during several discrete concentric and eccentric contractions.

Age and contraction type influence motor output variability in rapid discrete tasks.

The purpose of this study was to examine the ability to control knee-extension force during discrete isometric (IC), concentric (CC), and eccentric contractions (EC) in 24 young (mean age +/- SD = 25.3 +/- 2.8 yr) and 24 old (mean age +/- SD = 73.

Modeling variability of force during isometric contractions of the quadriceps femoris.

The authors modeled variability of force during continuous isometric contractions of the quadriceps femoris. Twenty adults (aged 25 +/- 6 years old) performed isometric leg extensions. Target forces were 11 percentages of maximum voluntary contraction (%MVC), ranging from 2 to 95%, and 5 absolute levels, from 25 to 225 N.

Impulse and Movement Space-Time Variability.

In 3 experiments, the authors examined movement space-time variability as a function of the force-time properties of the initial impulse in a movement timing task. In the range of motion and movement time task conditions, peak force, initial rate of force, and force duration were manipulated either independently or in combination across a range of parameter values. The findings showed that (a) impulse variability is predicted well by the elaboration of the isometric force variability scaling functions of L.