Shinsuke Yoshioka

Computation of the kinematics and the minimum peak joint moments of sit-to-stand movements

BackgroundA sit-to-stand (STS) movement requires muscle strength higher than that of other daily activities. There are many elderly people, who experience difficulty when standing up from a chair. The muscle strength required (or the load on the joints) during a STS task is determined by the kinematics (movement pattern). The purpose of this study was to evaluate the kinematics and resultant joint moments of people standing up from a chair in order to determine the minimum peak joint moments required for a STS task.MethodsThis study consisted of three steps. In the first step, kinematic data of lower extremity joint angles (hip, knee and ankle) during STS movements were experimentally collected from human subjects. Eighty-five sets of STS kinematic data were obtained. In the second step, the experimentally collected kinematic data and a link segment model of the human body were used to generate more than 5,000,000 computed STS movements. In the third step, using inverse dynamics method, joint moments of the lower extremity were calculated for all movements obtained through the preceding steps. From the outputs of the third step, the optimal kinematics (movement pattern) in terms of minimized peak joint moment for the hip, knee and ankle was determined.ResultsThe peak hip joint moment ranged from 0.24 to 1.92 N.m/kg. The peak knee joint moment ranged from 0.51 to 1.97 N.m/kg, and the peak ankle joint moment ranged from -0.11 to 1.32 N.m/kg. The optimal movement patterns differed depending on which minimized joint moment index was selected (hip, knee or ankle). However, the sum of the peak hip joint moment and peak knee joint moment was always approximately 1.53 N.m/kg regardless of which minimized joint moment index was selected.ConclusionThe most important finding of this study was that the relation between the peak joint moments at the hip and knee joints was complementary and the sum of those moments needed to be greater than 1.53 N.m/kg in order to perform a successful STS. A combined hip-knee value of 1.5 N.m/kg or lower may indicate the need for physical rehabilitation and/or exercise to increase muscular force.

Biomechanical analysis of the relation between movement time and joint moment development during a sit-to-stand task.

BackgroundSlowness of movement is a factor that may cause a decrease of quality of daily life. Mobility in the elderly and people with movement impairments may be improved by increasing the quickness of fundamental locomotor tasks. Because it has not been revealed how much muscle strength is required to improve quickness, the purpose of this study was to reveal the relation between movement time and the required muscle strength in a sit to stand (STS) task. Previous research found that the sum of the peak hip and knee joint moments was relatively invariant throughout a range of movement patterns (Yoshioka et al., 2007, Biomedical Engineering Online 6:26). The sum of the peak hip and knee joint moment is an appropriate index to evaluate the muscle strength required for an STS task, since the effect of the movement pattern variation can be reduced, that is, the results can be evaluated purely from the viewpoint of the movement times. Therefore, the sum of the peak hip and knee joint moment was used as the index to indicate the required muscle strength.MethodsExperimental kinematics data were collected from 11 subjects. The time at which the vertical position of the right shoulder fell outside three standard deviations of the vertical positions during the static initial posture was regarded as the start time. The time at which the vertical position fell within three standard deviations of the vertical positions during static upright standing posture was regarded as the finish time. Each movement time of the experimental movements was linearly lengthened and shortened through post-processing. Combining the experimental procedure and the post-processing, movements having various movement patterns and a wide range of movement times were obtained. The joint moment and the static and inertial components of the joint moment were calculated with an inverse dynamics method. The static component reflects the gravitational and/or external forces, while the inertial component reflects the acceleration of the body.ResultsThe quantitative relation between the movement time and the sum of the peak hip and knee joint moments were obtained. As the STS movement time increased, the joint moments decreased exponentially and converged to the static component (1.51 ~ 1.54 N.m/kg). When the movement time was the longest (movement time: 7.0 seconds), the joint moments (1.57 N.m/kg) closely corresponded to the minimum of 1.53 N.m/kg as reported by Yoshioka et al..ConclusionThe key findings of this study are as follows. (1) The minimum required joint moment for an STS task is essentially equivalent to the static component of the joint moment. (2) For fast and moderate speed movements (less than 2.5 seconds), joint moments increased exponentially as the movement speed increased. (3) For slow movements greater than 2.5 seconds, the joint moments were relatively constant. The results of this STS research has practical applications, especially in rehabilitations and exercise prescription where improved movement time is an intended target, since the required muscle strength can be quantitatively estimated.

The minimum required muscle force for a sit-to-stand task

The purpose of this study was to reveal the minimum required muscle force for a sit-to-stand task. Combining experimental procedures and computational processing, movements of various sit-to-stand patterns were obtained. Muscle forces and activations during a movement were calculated with an inverse dynamics method and a static numerical optimization method. The required muscle force for each movement was calculated with peak muscle activation, muscle physiological cross sectional area and specific tension. The robustness of the results was quantitatively evaluated with sensitivity analyses. From the results, a distinct threshold was found for the total required muscle force of the hip and knee extensors. Specifically, two findings were revealed: (1) the total force of hip and knee extensors is appropriate as the index of minimum required muscle force for a sit-to-stand task and (2) the minimum required total force is within the range of 35.3-49.2 N/kg. A muscle is not mechanically independent from other muscles, since each muscle has some synergetic or antagonistic muscles. This means that the mechanical threshold of one muscle varies with the force exertion abilities of other muscles and cannot be evaluated independently. At the same time, some kinds of mechanical threshold necessarily exist in the sit-to-stand task, since a muscle force is an only force to drive the body and people cannot stand up from a chair without muscles. These indicate that the existence of the distinct threshold in the result of the total required muscle force is reasonable.

The effect of bilateral asymmetry of muscle strength on jumping height of the countermovement jump: A computer simulation study

Abstract The purpose of the current study was to examine the effect of bilateral asymmetry of muscle strength on performance (maximal jumping height) of the countermovement jump. In experimental studies, it is impossible to control for muscle strength asymmetry, since it varies widely among individuals. In the current study, we used computer simulation. Two three-dimensional human lower limb neuromusculoskeletal models (model-symmetry and model-asymmetry) were developed. The total muscle strength of the two models was set to be identical. Bilateral muscle strength was set equal in the model-symmetry simulation, while the model-asymmetry simulation was set with a 10% bilateral strength asymmetry. The countermovement jumps were generated successfully, producing jumping heights of 0.416 m for model-symmetry and 0.419 m for model-asymmetry. The small difference in height (0.7%) indicates that bilateral asymmetry by itself does not have a significant effect on jumping performance. With model-asymmetry, the strong leg compensated for the muscle strength deficit of the weak leg by lateral movement of the body to distribute the load proportional to the muscle strength of each leg.

Effect of Expertise on 3D Force Application During the Starting Block Phase and Subsequent Steps in Sprint Running

In sprinters with different levels of block acceleration, we investigated differences in their three-dimensional force application in terms of the magnitude, direction, and impulse of the ground reaction force (GRF) during the starting block phase and subsequent two steps. Twenty-nine participants were divided into three groups (well-trained, trained, and nontrained sprinters) based on their mean anteroposterior block acceleration and experience with a block start. The participants sprinted 10 m from a block start with maximum effort. Although the mean net resultant GRF magnitude did not differ between the well-trained and trained sprinters, the net sagittal GRF vector of the well-trained sprinters was leaned significantly further forward than that of the trained and nontrained sprinters during the starting block phase. In contrast, during the starting block phase and the subsequent steps, the transverse GRF vectors which cause the anteroposterior and mediolateral acceleration of the whole-body was directed toward the anterior direction more in the well-trained sprinters as compared with the other sprinters. Therefore, a more forward-leaning GRF vector and a greater anteroposterior GRF may particularly allow well-trained sprinters to generate a greater mean anteroposterior block acceleration than trained and nontrained sprinters.

The effect of bilateral asymmetry of muscle strength on the height of a squat jump: A computer simulation study

Abstract The aim of this study was to examine the effect of bilateral asymmetry of muscle strength on maximal height of the squat jump. A computer simulation technique was used to develop two kinds of 3D human lower limb musculoskeletal model (model-symmetry and model-asymmetry). The total muscle strength of the two models was set to be identical. Bilateral muscle strength was equal in the model-symmetry simulation, while the model-asymmetry simulation was performed with a 10% bilateral strength asymmetry. A forward dynamics approach was used to simulate squat jumps. The squat jumps were successfully generated, producing jump heights of 0.389 m for model-symmetry and 0.387 m for model-asymmetry. The small difference in height (0.5%) indicated that the effect of the 10% bilateral asymmetry of muscle strength on jump height is negligible. With model-asymmetry, the strong leg compensated for the muscle strength deficit of the weak leg. Importantly, the mono-articular and large extensor muscles of the hip and knee joint of the strong leg, including the gluteus maximus, adductor magnus, and vasti, compensated for the muscle strength deficit of the weak leg.

Interaction between elastic energy utilization and active state development within the work enhancing mechanism during countermovement

The purpose of this study was to investigate the interaction between elastic energy utilization and the time available for active state development during countermovement, and to determine the contributions of these factors in enhancing work output from a quantitative standpoint. Especially, we focused on the effect of length variation of the series elastic element (SEE) and the speed of active state development. A Hill-type model of the muscle tendon complex (MTC) was constructed. A range of SEE lengths (between 0.625 and 10 times the optimal length of the contractile element) and a range of active state development rates were investigated. Forward dynamics simulations were performed to evaluate the causal factors for the gain in height during concentric (CO) and countermovement (CM) conditions. Simulated outputs suggested that the contribution of the time available for active state development was larger than the contribution of elastic energy utilization for a shorter SEE muscle. On the other hand, the contribution of the elastic energy utilization was larger for a longer SEE muscle. Additionally, the work output of the SEE in CM was considerably augmented due to increasing the speed of active state development. As results, two main findings were obtained. First, a quantitative discussion was developed regarding how the elastic energy utilization and the time available for active state development are contributing within the work enhancing mechanism. Second, it was found that elastic energy utilization and the time available for active state development have a synergistic effect during countermovement.

Unweighted state as a sidestep preparation improve the initiation and reaching performance for basketball players

The preparatory motion of a defensive motion in contact sport such as basketball should be small and involve landing on both feet for strict time and motion constraints. We thus proposed the movement creating a unweighted state. Ten basketball players performed a choice reaction sidestepping task with and without the voluntary, continuous vertical fluctuation movement. The results indicated that the preparatory movement shortened the time of their sidestep initiation (301 vs. 314 ms, p = 0.011) and reaching performance (883 vs. 910 ms, p = 0.018) but did not increase their peak ground reaction force or movement velocity. The mechanism of the improvement was estimated to be the following: in the preparation phase, the vertical body fluctuation created the force fluctuation; after the direction signal, the unweighted state can shorten the time required to initiate the sidestepping (unweighted: 279 ms; weighted: 322 ms, p = 0.002); around the initiation phase, the dropping down of the body and weighted state can contribute to the reaching performance. We conducted additional experiment investigating muscle-tendon-complex dynamics and muscle activity using ultrasound device and electromyography. The result suggests that the building up of active state of muscle might explain the improvement of sidestepping performance.

The preparatory state of ground reaction forces in defending against a dribbler in a basketball 1-on-1 dribble subphase

We previously demonstrated the relationship between sidestepping performance and the preparatory state of ground reaction forces (GRFs). The present study investigated the effect of the preparatory state of GRFs on defensive performance in 1-on-1 subphase of basketball. Ten basketball players participated in 1-on-1 dribble game of basketball. The outcomes (penetrating and guarding) and the preparatory state of GRFs (non-weighted and weighted states, i.e. vertical GRFs below and above 120% of body weight, respectively) were assessed by separating the phases. In the non-weighted state and the weighted state to determine the outcome, the probability of successful guarding was 78.8% and 29.6%, respectively. The non-weighted state prevented delay of the defensive step in the determination phase. Both the non-weighted and weighted states, immediately before the determination phase, were likely to change to the weighted state in the determination phase; during this time, the defenders preparatory state would be destabilised, presumably by the dribblers movement. These results revealed that the preparatory GRFs before the defensive step help to explain the outcome of the 1-on-1 subphase, and suggest a better way to prevent delaying initiation of the defensive step and thereby to guard more effectively against a dribbler.

The three-dimensional kinetic behaviour of the pelvic rotation in maximal sprint running

Abstract The purpose of this study was to investigate the effect of lumbosacral kinetics on sprinting. Twelve male sprinters performed 50 m sprints at maximal effort. Kinematic and ground reaction force data were recorded at approximately 40 m from sprint commencement. A whole-body inverse dynamics approach was applied to calculate joint forces and torques at the hip and lumbosacral joints. The contribution of the hips and lumbosacral joint torques to pelvic rotation was subsequently calculated, with joint force powers indicating the rate of mechanical energy transfer between segments across joint centres calculated for both hip joints. The kinetic analysis indicated that the lumbosacral torsional torque contributed significantly to pelvic rotation. Additionally, the pelvic rotation exerted anterior–posterior joint forces on the hips, contributing to the large positive joint force power at the hip of the stance leg. These hip joint force powers assisted in motion recovery during sprinting. In conclusion, the lumbosacral torsional torque might contribute to the recovery motion in sprinting through application of the anterior–posterior joint forces at the hip joints via pelvic rotation.