Humans need only 200 ms to generate posture-specific muscle activation patterns for successful vertical jumps in reaction to an auditory trigger.

Introduction: It is currently unknown how the central nervous system controls ballistic whole-body movements like vertical jumps. Here we set out to study the time frame of generating muscle activation patterns for maximum-effort jumps from different initial postures.

Methods: We had ten healthy male participants make a slow countermovement from an upright position and initiate a maximal vertical jump as soon as possible following an auditory trigger.

The Force-Velocity Profile for Jumping: What It Is and What It Is Not.

Introduction: Force-velocity profiling has been proposed in the literature as a method to identify the overall mechanical characteristics of lower extremities. A force-velocity profile is obtained by plotting for jumps at different loads the effective work as a function of the average push-off velocity, fitting a straight line to the results, and extrapolating this line to find the theoretical maximum isometric force and unloaded shortening velocity. Here we investigated whether the force-velocity profile and its characteristics can be related to the intrinsic force-velocity relationship.

Limiting radial pedal forces greatly reduces maximal power output and efficiency in sprint cycling: an optimal control study.

A cyclist's performance depends critically on the generated average mechanical power output (AMPO). The instantaneous mechanical power output equals the product of crank angular velocity, crank length, and the tangential pedal force. Radial pedal forces do not contribute to mechanical power.

Motion information plays only a secondary role in sex identification of walking persons in frontal view.

Observers have a success rate above chance in identifying the sex of walking persons on the basis of movies showing only point lights. It has been claimed that observers rely heavily on motion information for their judgment. Here, we studied, for the frontal plane, the added value of motion information over just form information.

The elevated metabolic cost of walking at preferred speeds of healthy elderly on treadmills compared to overground is not related to increased self-reported anxiety.

Purpose: To investigate whether the elevation in metabolic cost of walking on treadmills compared to overground for healthy elderly is related to self-reported anxiety and if changes in self-reported anxiety are related to changes in heart rate.

Methods: We measured overground preferred walking speed, oxygen consumption rate and heart rates during rest and walking, and self-reported anxiety in 10 elderly (mean age 69.5 ± 3.

Metabolic cost in healthy fit older adults and young adults during overground and treadmill walking.

Purpose: The purpose of this study was to determine whether net metabolic cost of walking is affected by age per se.

Methods: We selected 10 healthy, active older adults (mean age 75 years) and 10 young adults (mean age 26 years), and determined their preferred overground walking speed. On the same day, in a morning and afternoon session, we had them walk at that speed overground and on a treadmill while we measured oxygen consumption rate.

3D trunk orientation measured using inertial measurement units during anatomical and dynamic sports motions.

Trunk motion is related to the performance and risk of injuries during dynamic sports motions. Optical motion capture is traditionally used to measure trunk motion during dynamic sports motions, but these systems are typically constrained to a laboratory environment. Inertial measurement units (IMUs) might provide a suitable alternative for measuring the trunk orientation during dynamic sports motions.

Effect of vasti morphology on peak sprint cycling power of a human musculoskeletal simulation model.

Fascicle length of m. vastus lateralis in cyclists has been shown to correlate positively with peak sprint cycling power normalized for lean body mass. We investigated whether vasti morphology affects sprint cycling power via force-length and force-velocity relationships.

The Metabolic Cost of Walking in healthy young and older adults - A Systematic Review and Meta Analysis.

The Metabolic Cost of Walking (MCoW) is an important variable of daily life that has been studied extensively. Several studies suggest that MCoW is higher in Older Adults (OA) than in Young Adults (YA). However, it is difficult to compare values across studies due to differences in the way MCoW was expressed, the units in which it was reported and the walking speed at which it was measured.

Effects of high loading by eccentric triceps surae training on Achilles tendon properties in humans.

Purpose: To document the magnitude and time course of human Achilles tendon adaptations (i.e. changes in tendon morphological and mechanical properties) during a 12-week high-load plantar flexion training program.

30 min of treadmill walking at self-selected speed does not increase gait variability in independent elderly.

Walking is one of the preferred exercises among elderly, but could a prolonged walking increase gait variability, a risk factor for a fall in the elderly? Here we determine whether 30 min of treadmill walking increases coefficient of variation of gait in elderly. Because gait responses to exercise depend on fitness level, we included 15 sedentary and 15 active elderly. Sedentary participants preferred a lower gait speed and made smaller steps than the actives.

Acute Effects of Walking Exercise on Stair Negotiation in Sedentary and Physically Active Older Adults.

Background: In negotiating stairs, low foot clearance increases the risk of tripping and a fall. Foot clearance may be related to physical fitness, which differs between active and sedentary participants, and be acutely affected by exercise. Impaired stair negotiation could be an acute response to exercise.

Searching for strategies to reduce the mechanical demands of the sit-to-stand task with a muscle-actuated optimal control model.

Background: The sit-to-stand task, which involves rising unassisted from sitting on a chair to standing, is important in daily life. Many people with muscle weakness, reduced range of motion or loading-related pain in a particular joint have difficulty performing the task. How should a person suffering from such impairment best perform the sit-to-stand task and, in the case of pain in a particular joint, with reduced loading of that joint?

Methods: We developed a musculoskeletal model with reference parameter values based on properties of healthy strong subjects.

Optimizing the Distribution of Leg Muscles for Vertical Jumping.

A goal of biomechanics and motor control is to understand the design of the human musculoskeletal system. Here we investigated human functional morphology by making predictions about the muscle volume distribution that is optimal for a specific motor task. We examined a well-studied and relatively simple human movement, vertical jumping.

The Relationship between Pedal Force and Crank Angular Velocity in Sprint Cycling.

Purpose: Relationships between tangential pedal force and crank angular velocity in sprint cycling tend to be linear. We set out to understand why they are not hyperbolic, like the intrinsic force-velocity relationship of muscles.

Methods: We simulated isokinetic sprint cycling at crank angular velocities ranging from 30 to 150 rpm with a forward dynamic model of the human musculoskeletal system actuated by eight lower extremity muscle groups.

How do elite ski jumpers handle the dynamic conditions in imitation jumps?

We examined the effect of boundary conditions in imitation ski jumping on movement dynamics and coordination. We compared imitation ski jumps with--and without--the possibility to generate shear propulsion forces. Six elite ski jumpers performed imitation jumps by jumping from a fixed surface and from a rolling platform.

Muscle contractile properties as an explanation of the higher mean power output in marmosets than humans during jumping.

The muscle mass-specific mean power output (PMMS,mean) during push-off in jumping in marmosets (Callithrix jacchus) is more than twice that in humans. In the present study it was tested whether this is attributable to differences in muscle contractile properties. In biopsies of marmoset m.

The structural and mechanical properties of the Achilles tendon 2 years after surgical repair.

Background: Acute ruptures of the Achilles tendon affect the tendon's structural and mechanical properties. The long-term effects of surgical repair on these properties remain unclear.

Purpose: To evaluate effects of early mobilization versus traditional immobilization rehabilitation programs 2 years after surgical Achilles tendon repair, by comparing force-elongation and stress-strain relationships of the injured tendon to those of the uninjured tendon.

Effect of unloading and loading on power in simulated countermovement and squat jumps.

Purpose: In the literature, substantial decreases in power output in jumping have been described for both unloading and loading, and these have been attributed to the intrinsic force-velocity-power relationship of muscle. The purpose of this study was to gain a solid understanding of how and why unloading and loading affect power output during jumping.

Methods: Vertical jumps were simulated with a model of the musculoskeletal system, consisting of four rigid segments actuated by six muscles.

Mechanical output in jumps of marmosets (Callithrix jacchus).

In this study we determined the mechanical output of common marmosets (Callithrix jacchus) during jumping. Vertical ground reaction forces were measured in 18 animals while they jumped from an instrumented crossbar to a crossbar located 70 cm higher. From the vertical force time histories, we calculated the rate of change of mechanical energy of the centre of mass (dE/dt).

Effects of isometric scaling on vertical jumping performance.

Jump height, defined as vertical displacement in the airborne phase, depends on vertical takeoff velocity. For centuries, researchers have speculated on how jump height is affected by body size and many have adhered to what has come to be known as Borelli's law, which states that jump height does not depend on body size per se. The underlying assumption is that the amount of work produced per kg body mass during the push-off is independent of size.

Humans make near-optimal adjustments of control to initial body configuration in vertical squat jumping.

We investigated adjustments of control to initial posture in squat jumping. Eleven male subjects jumped from three initial postures: preferred initial posture (PP), a posture in which the trunk was rotated 18° more backward (BP) and a posture in which it was rotated 15° more forward (FP) than in PP. Kinematics, ground reaction forces and electromyograms (EMG) were collected.

Measurement of pelvic motion is a prerequisite for accurate estimation of hip joint work in maximum height squat jumping.

In experiments investigating vertical squat jumping, the HAT segment is typically defined as a line drawn from the hip to some point proximally on the upper body (eg, the neck, the acromion), and the hip joint as the angle between this line and the upper legs (θUL-HAT). In reality, the hip joint is the angle between the pelvis and the upper legs (θUL-pelvis). This study aimed to estimate to what extent hip joint definition affects hip joint work in maximal squat jumping.