Introduction: Individuals with rotator cuff tears have been found to compensate in their movement patterns by using lower thoracohumeral elevation angles during certain tasks, as well as increased internal rotation of the shoulder (Vidt et al., 2016). Leading joint hypothesis suggests there is one leading joint that creates the foundation for the entire limb motion, and there are other subordinate joints which monitor the passive interaction torque and create a net torque aiding to limb motions required for the task. This experiment seeks to establish a better understanding of joint control strategies during a wide range of arm movements. Based on the leading joint hypothesis, we hypothesize that when a subject has a rotator cuff tear, their performance of planar and three-dimensional motions should be altered not only at the shoulder, which is often the leading joint, but also at other joints on the arm, such as the elbow and wrist. This paper will focus on the effect of normal aging on the control of the joints of the arm.
Methods: There were 4 groups of participants: healthy younger adults (n=14)(21.74 ± 1.97), healthy older adults (n=12)(55-75), older adults (n=4)(55-75) with a partial-thickness rotator cuff tear, and older adults (n=4)(55-75) with a full-thickness rotator cuff tear (RCT). All four groups completed strength testing, horizontal drawing and pointing tasks, and three dimensional (3D) activities of daily living. Kinematic and kinetic variables of the arm were obtained during horizontal and 3D tasks using data from 12 reflective markers placed on the arm, 8 motion capture cameras, and Cortex motion capture software (Motion Analysis Corp., Santa Rosa, CA). Strength testing tasks were measured using a dynamometer. All strength testing and 3D tasks were completed for three trials and horizontal tasks were completed for two trials.
Results: Results of the younger adult participants showed that during the forward portion of seven 3D tasks, there were four phases of different joint control mechanics seen in a majority of the movements. These phases included active rotation of both the shoulder and the elbow joint, active rotation of the shoulder with passive rotation of the elbow, passive rotation of the shoulder with active rotation of the elbow, and passive rotation of both the shoulder and the elbow. Passive rotation during movements was a result of gravitational torque on the different segments of the arm and interaction torque caused as a result of the multi-joint structure of human limbs. The number of tested participants for the minor RCT, and RCT older adults groups is not yet high enough to produce significant results and because of this their results are not reported in this article. Between the older adult control group and the young adult control group in the tasks upward reach to eye height and hair comb there were significant differences found between the groups. The differences were found in shorter overall time and distance between the two groups in the upward eye task.
Discussion: Through the available results, multiple phases were found where one or both of the joints of the arm moved passively which further supports the LJH and extends it to include 3D movements. With available data, it can be concluded that healthy older adults use movement control strategies, such as shortening distance covered, decreasing time percentage in active joint phases, and increasing time percentage in passive joint phases, to account for atrophy along with other age-related declines in performance, such as a decrease in range of motion. This article is a part of a bigger project which aims to better understand how older adults with RCTs compensate for the decreased strength, the decreased range of motion, and the pain that accompany this type of injury. It is anticipated that the results of this experiment will lead to more research toward better understanding how to treat patients with RCTs.

According to the Center for Disease Control, 1 in every 3 individuals will fall in their lifetime. Treadmill perturbation training has been a beneficial tool to increase reactive postural control and decrease the amount of falls. This study looked at the extent of the training effects on 29 healthy young adults to evaluate if stepping improvements in one direction could generalize to improvements in the quality of stepping in other directions. Outcome variables of Margin of Stability (MOS), step length, and step latency were evaluated for all 15 participants trained with forward perturbations and 14 participants trained with backward perturbations. From the paired t-tests, there were limited significant improvements in stepping with regards to motor learning and generalization. The only significant outcome was an increase in step length for the participants who trained in the backward direction (p=0.014; p<0.05). However, this significant increase in step length for this backward group did not generalize when the participants stepped in the forward direction post training. From the correlation tests, there was a significant, moderate correlation between motor learning and generalization (rho =0.527, p= 0.043; p<0.05), thus suggesting there may be a relationship between the amount of learning and the amount of generalization observed. Further evaluation of the second step and the foot motion during stepping may reveal more information and explain the changes in stepping to describe how healthy young adults were able to regain balance with each perturbation given.

The ultimate goal of human movement control research is to understand how natural movements performed in daily reaching activities, are controlled. Natural movements require coordination of multiple degrees of freedom (DOF) of the arm. Patterns of arm joint control were studied during daily functional tasks, which were performed through the rotation of seven DOF in the arm. Analyzed movements which imitated the following 3 activities of daily living: moving an empty soda can from a table and placing it on a further position; placing the empty soda can from initial position at table to a position at shoulder level on a shelf; and placing the empty soda can from initial position at table to a position at eye level on a shelf. Kinematic and kinetic analyses were conducted for these three movements. The studied kinematic characteristics were: hand trajectory in the sagittal plane, displacements of the 7 DOF, and contribution of each DOF to hand velocity. The kinetic analysis involved computation of 3-dimensional vectors of muscle torque (MT), interaction torque (IT), gravity torque (GT), and net torque (NT) at the shoulder, elbow, and wrist. Using the relationship NT = MT + GT + IT, the role of active control and passive factors (gravitation and inter-segmental dynamics) in rotation of each joint by computing MT contribution (MTC) to NT was assessed. MTC was computed using the ratio of the signed MT projection on NT to NT magnitude. Despite a variety of joint movements available across the different tasks, 3 patterns of shoulder and elbow coordination prevailed in each movement: 1) active rotation of the shoulder and predominantly passive rotation of the elbow; 2) active rotation of the elbow and predominantly passive rotation of the shoulder; and 3) passive rotation of both joints. Analysis of wrist control suggested that MT mainly compensates for passive torque and provides adjustment of wrist motion according to requirements of each task. In conclusion, it was observed that the 3 shoulder-elbow coordination patterns (during which at least one joint moved) passively represented joint control primitives, underlying the performance of well-learned arm movements, although these patterns may be less prevalent during non-habitual movements.

The ultimate goal of human movement control research is to understand how natural movements performed in daily activities, are controlled. Natural movements require coordination of multiple degrees of freedom (DOF) of the arm. Here, patterns of arm joint control during daily functional tasks were examined, which are performed through rotation of the shoulder, elbow, and wrist with the use of seven DOF: shoulder flexion/extension, abduction/adduction, and internal/external rotation; elbow flexion/extension and pronation/supination; wrist flexion/extension and radial/ulnar deviation. Analyzed movements imitated two activities of daily living: combing the hair and turning the page in a book. Kinematic and kinetic analyses were conducted. The studied kinematic characteristics were displacements of the 7 DOF and contribution of each DOF to hand velocity. The kinetic analysis involved computation of 3-dimensional vectors of muscle torque (MT), interaction torque (IT), gravity torque (GT), and net torque (NT) at the shoulder, elbow, and wrist. Using a relationship NT = MT + GT + IT, the role of active control and the passive factors (gravitation and inter-segmental dynamics) in rotation of each joint was assessed by computing MT contribution (MTC) to NT. MTC was computed using the ratio of the signed MT projection on NT to NT magnitude. Despite the variety of joint movements required across the different tasks, 3 patterns of shoulder and elbow coordination prevailed in each movement: 1) active rotation of the shoulder and predominantly passive rotation of the elbow; 2) active rotation of the elbow and predominantly passive rotation of the shoulder; and 3) passive rotation of both joints. Analysis of wrist control suggested that MT mainly compensates for passive torque and provides adjustment of wrist motion according to requirements of both tasks. The 3 shoulder-elbow coordination patterns during which at least one joint moves largely passively represent joint control primitives underlying performance of well-learned arm movements, although these patterns may be less prevalent during non-habitual movements. The advantage of these control primitives is that they require minimal neural effort for joint coordination, and thus increase neural resources that can be used for cognitive tasks.

Introduction: Individuals with rotator cuff tears (RCT) have been found to compensate in their movement patterns by using lower thoracohumeral elevation angles during certain tasks, as well as increased internal rotation of the shoulder (Vidt et al., 2016). The leading joint hypothesis (LJH) suggests there is one leading joint that creates the foundation for the entire limb motion, and there are other subordinate joints that monitor the passive interaction torque (IT) and create a net torque (NT) aiding to limb motions required for the task. This experiment hopes to establish a better understanding of joint control strategies during a wide range of arm movements. Based off of the LJH, we hypothesize that when a subject has a rotator cuff tear, their performance of planar and three- dimensional motions should be altered not only at the shoulder, which is often the leading joint, but also at other joints on the arm such as the elbow and wrist.

Methods: There were 3 groups of participants: healthy younger adults (age 21.74 ± 1.97), healthy older adult controls (age 69.53 ± 6.85), and older adults with a RCT (age 64.33 ± 4.04). All three groups completed strength testing, horizontal drawing and pointing tasks, and three-dimensional (3D) activities of daily living (ADLs). Kinematic and kinetic variables of the arm were obtained during horizontal and 3D tasks using data from 13 reflective markers placed on the arm and trunk, 8 motion capture cameras, and Cortex motion capture software (Motion Analysis Corp., Santa Rosa, CA). During these tasks, electromyography (EMG) electrodes were placed on 12 muscles along the arm that affect shoulder, elbow, and wrist rotation. Strength testing tasks were measured using a dynamometer. All strength testing and 3D tasks were completed for three trials and horizontal tasks were completed for two trials.

Results: Results of the younger adult participants showed that during the forward portion of seven 3D tasks, there were four phases of different joint control mechanics seen in a majority of the movements. These phases included active rotation of both the shoulder and the elbow joint, active rotation of the shoulder with passive rotation of the elbow, passive rotation of the shoulder with active rotation of the elbow, and passive rotation of both the shoulder and the elbow. Passive rotation during movements was a result of gravitational torque (GT) on the different segments of the arm and IT caused as a result the multi-joint structure of human limbs. The number of tested participants for the healthy older adults and RCT older adults groups is not yet high enough to produce significant results and because of this their results are not reported in this article.

Discussion: Through the available results, multiple phases were found where one or both of the joints of the arm moved passively which further supports the LJH and extends it to include 3D movements. This article is a part of a bigger project which hopes to get a better understanding of how older adults adjust to large passive torques acting on the arm during 3D movements and how older adults with RCTs compensate for the decreased strength, the decreased range of motion (ROM), and the pain that accompany these types of tears. Hopefully the results of this experiment lead to more research toward better understanding how to treat patients with RCTs.

This study investigated the effect of a small added load on postural stability in older adults. Sixteen healthy older adults (6 male, 10 female, age=72 ± 3.2y, height=172± 9.3 cm, weight=84± 7.6 kg) performed clinical measures of postural control with different loads placed on the shoulders (0%, 1% and 3% bodyweight). The functional reach test, comprising a forward, right and left lateral reach, along with COP data measured through the use of a force plate were the postural control measures utilized in this study. COP data used were COP sway velocity and COP mean sway area, in the form of a 95% confidence ellipse. During the COP trials, visual input (eyes open and eyes closed) and surface conditions (firm and foam) were varied to evaluate the effect of the loads under different conditions. Two trials of each measurement were performed for all tests, and participants were allowed rest intervals as needed. Anticipated results show a decreased reach distance of 8% in the forward direction, and a 7% decrease in the left and right lateral directions under a 1% bodyweight load. For expected results of COP velocity, there will be a 12% increase from baseline COP sway velocity in the 1% bodyweight condition. Anticipated results for COP sway area show a 39% increase in the eyes open firm surface, under a 1% bodyweight load, and a 40% increase under the 3% load. These expected results show a significant effect on postural control with a 1% and 3% bodyweight load placed on the shoulders of older adults. This information may be valuable in combatting the epidemic of falls seen among the elderly population, as part of an exercise program for improving balance and postural stability.

Research on joint control during arm movements in adults has led to the development of the Leading Joint Hypothesis (LJH), which states that the central nervous system takes advantage of interaction torque (IT) and muscle torque (MT) to produce movements with maximum efficiency in the multi-jointed limbs of the human body. A gap in knowledge exists in determining how this mature pattern of joint control develops in children. Prior research focused on the kinematics of joint control for children below the age of three; however, not much is known about interjoint coordination with respect to MT and IT in school-aged children. In the present study, joint control at the shoulder, elbow, and wrist during drawing of five shapes was investigated. A random sample of nine typically developing children ages 6 to 12 served as subjects. The task was to trace with the index finger a template placed on a horizontal table. The template consisted of a circle, horizontal, vertical, right-diagonal, and left-diagonal line. Analysis of muscle torque contribution (MTC) revealed the individual roles of MT and IT in the shoulder, elbow, and wrist joints. During drawing of the horizontal line, which requires the most difficult joint control pattern in adults because it does not allow the use of IT for joint rotation, joint control was found to change through development. For the youngest children, the function of elbow MT modified to suppress IT, thereby producing large elbow rotation. The oldest children simplified this by using the shoulder as the principal joint of movement production and with decreased assistance from the elbow. For the other four drawing movements, differences in the pattern of joint control used by all of the subjects was unaffected by an increase in age. Overall, the results suggest that in children above 6 years of age, minor changes in joint control occur during drawing of relatively simple movements. The limited effect of age that was observed could be related to the restriction of movements to the horizontal plane. For a future study, three-dimensional movements that provide more freedom in joint control due to redundancy of degrees of freedom could be more informative about developmental changes in joint coordination.

Rotator cuff tears (RCT) can affect up to 50% of the older population and this injury is typically associated with functional deficits and shoulder pain that prevent people from living a typical lifestyle. Particularly in an older population, this type of pain increases functional dependency on others and can hinder the possibility of independent living. An area of shoulder pathology that lacks research is the functional differences in symptomatic and asymptomatic tears on activities of daily living (ADL). In order to more fully understand the functional presentations associated with each of these types of tears, it is critical that we evaluate the various mechanisms that contribute to altered movement patterns. Understanding these different compensatory patterns between asymptomatic and symptomatic tears will allow for a better understanding of the presentation of this shoulder pathology and provide new insight for diagnostic and rehabilitation purposes. Therefore, the objective of this study is to quantify kinematic differences of daily upper limb movements between symptomatic and asymptomatic RCTs in an older population. To accomplish this goal, we will be using motion capture and electromyography to assess typical ADL movements and their associated muscle activation patterns during 2D and 3D tasks in older adults (≥55 years). Strength and shoulder range of motion measures will also be taken, as well as self-reported measures of function and pain. Through this project, we seek to understand the presentation of RCTs and what characteristics are associated with symptoms. Long term, outcomes from this work will be used to develop a more standardized approach to early detection and treatment of this common shoulder pathology in the older adult population.

Past research has indicated that the dominant arm produces more efficient interactive torque control during multi-joint movements. In addition, a bimanual arm movement study found that the dominant arm produced more circular trajectories during circular drawing movements, particularly during fast speed conditions. The current study serves to determine whether statistical trajectory analysis of circular drawing patterns can be used as an objective indicator of handedness. The experiment involved subjects performing unimanual circle drawing movements in both arms at two different speeds. The subjects were given handedness questionnaires to separate them into Right-Handed, Left-Handed, and Mixed-Handed categories for data analysis. The movements were tracked by optoelectronic cameras, and a paired T-test comparing the trajectories in each arm established statistical differences in performance. Right-Handed subjects had significant differences in the trajectories of each arm in which the right arm movements produced more circular trajectories. This was more pronounced in fast movements. Left-Handed subjects had no significant differences among arms in movements of either speed, likely due to a low sample size, although the trend in the fast conditions was that the left arm movements were more circular. Mixed-Handed subjects tended to produce more circular trajectories in right arm movements, which reached statistical significance in both conditions. These results indicate that this test could potentially be used as an objective measure of handedness, but more research with stronger statistical significance according to the hypotheses would need to be conducted to confirm the trends observed.

The research being proposed would develop an objective test for handedness analyzing circle-drawing movements performed with the dominant arm versus non-dominant arm. Handedness is a unique and exceptional characteristic of human beings which impacts society on an individual basis that has far-reaching influence. Its correlation and possible causation has been studied and implied in everything from mental disorders (Deep-Soboslay et al. 2010) to advanced biological processes (Driscoll, Kei, & McPherson, 2002). Despite the importance of handedness, there are many faults surrounding the widely used methods for determining and classifying handedness. The most common of these, the Edinburgh Handedness Inventory, especially suffers from reporter bias, possibly confusing categories and instructions, and underestimating ambidextrous or mixed handedness. Research done by R.L. Sainburg of Penn State and N. Dounskaia of Arizona State University points to a possible method of measuring handedness. The findings of these studies show show that the dominant arm to perform better in drawing movements than the non-dominant arm. It is proposed that an objective test could be developed for handedness using circle-drawing tasks. A participant would draw circles with both arms, these movements would be analyzed to show which arm was dominant by showing which arm made the more perfect circle. By developing an objective test, handedness could be more properly classified and assessed, helping aid research and understanding in how handedness affects humans.